SimPowerSystems
®
For Use with Simulink
Hydro-Québec
TransÉnergie Technologies
User’s Guide
Version 3
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SimPowerSystems User’s Guide
 COPYRIGHT 1998-2003 TransÉnergie Technologies Inc., under sublicense from
Hydro-Québec, and The MathWorks, Inc.
The software described in this document is furnished under a license agreement. The software may be used
or copied only under the terms of the license agreement. No part of this manual may be photocopied or reproduced in any form without prior written consent from The MathWorks, Inc.
FEDERAL ACQUISITION: This provision applies to all acquisitions of the Program and Documentation by
or for the federal government of the United States. By accepting delivery of the Program, the government
hereby agrees that this software qualifies as "commercial" computer software within the meaning of FAR
Part 12.212, DFARS Part 227.7202-1, DFARS Part 227.7202-3, DFARS Part 252.227-7013, and DFARS Part
252.227-7014. The terms and conditions of The MathWorks, Inc. Software License Agreement shall pertain
to the government’s use and disclosure of the Program and Documentation, and shall supersede any
conflicting contractual terms or conditions. If this license fails to meet the government’s minimum needs or
is inconsistent in any respect with federal procurement law, the government agrees to return the Program
and Documentation, unused, to MathWorks.
MATLAB, Simulink, Stateflow, Handle Graphics, and Real-Time Workshop are registered trademarks, and
TargetBox is a trademark of The MathWorks, Inc.
Other product or brand names are trademarks or registered trademarks of their respective holders.
Printing History: January 1998
First printing
September 2000 Second printing
June 2001
Online only
July 2002
Online only
September 2003 3rd printing
Version 1 (Release 10)
Revised for Version 2.1 (Release 12)
Revised for Version 2.2 (Release 12.1)
Revised for Version 2.3 (Release 13)
(Renamed from Power System Blockset
User’s Guide)
Revised for Version 3 (Release 13SP1)
Contents
About This Guide
SimPowerSystems and Physical Modeling . . . . . . . . . . . . . . viii
About the Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
Related Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x
Requirements for SimPowerSystems . . . . . . . . . . . . . . . . . . . . . . . x
Other Related Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x
Using This Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii
Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
Typographical Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . xix
Modeling Simple Systems
1
Simulating a Simple Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . .
Building the Electrical Circuit with powerlib Library . . . . . . .
Interfacing the Electrical Circuit with Simulink . . . . . . . . . . . .
Simulating Your Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1-2
1-2
1-6
1-8
Analyzing a Simple Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9
Steady-State Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9
Frequency Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11
Simulating Transients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-19
Continuous, Variable Time Step Integration Algorithms . . . . 1-21
Discretizing the Electrical System . . . . . . . . . . . . . . . . . . . . . . 1-22
i
Introducing the Phasor Simulation Method . . . . . . . . . . . . 1-26
When to Use the Phasor Solution . . . . . . . . . . . . . . . . . . . . . . . 1-26
Phasor Simulation of a Circuit Transient . . . . . . . . . . . . . . . . 1-27
Advanced Components and Techniques
2
Introducing Power Electronics . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
Simulating Motor Drives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Building and Simulating the PWM Motor Drive . . . . . . . . . . .
Using the Multimeter Block . . . . . . . . . . . . . . . . . . . . . . . . . . .
Discretizing the PWM Motor Drive . . . . . . . . . . . . . . . . . . . . . .
Performing Harmonic Analysis Using the FFT Tool . . . . . . . .
2-11
2-12
2-19
2-21
2-21
Three-Phase Systems and Machines . . . . . . . . . . . . . . . . . . .
Three-Phase Network with Electrical Machines . . . . . . . . . . .
Load Flow and Machine Initialization . . . . . . . . . . . . . . . . . . .
Using the Phasor Solution Method for Stability Studies . . . . .
2-24
2-24
2-28
2-36
Building and Customizing Nonlinear Models . . . . . . . . . . .
Modeling a Nonlinear Inductance . . . . . . . . . . . . . . . . . . . . . . .
Customizing Your Nonlinear Model . . . . . . . . . . . . . . . . . . . . .
Modeling a Nonlinear Resistance . . . . . . . . . . . . . . . . . . . . . . .
Creating Your Own Library . . . . . . . . . . . . . . . . . . . . . . . . . . .
Connecting Your Model with Other Nonlinear Blocks . . . . . .
2-40
2-40
2-45
2-51
2-56
2-56
Case Studies
3
Series-Compensated Transmission Network . . . . . . . . . . . . .
Description of the Transmission Network . . . . . . . . . . . . . . . . .
Setting the Initial Load Flow and Obtaining Steady State . . . .
Transient Performance for a Line Fault . . . . . . . . . . . . . . . . . . .
ii
Contents
3-2
3-2
3-8
3-9
Frequency Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13
Transient Performance for a Fault at Bus B2 . . . . . . . . . . . . . 3-17
Chopper-Fed DC Motor Drive . . . . . . . . . . . . . . . . . . . . . . . . .
Description of the Drive System . . . . . . . . . . . . . . . . . . . . . . . .
Modeling the DC Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Simulation of the DC Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Starting the Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Steady-State Voltage and Current Waveforms . . . . . . . . . . . .
Speed Regulation Dynamic Performance . . . . . . . . . . . . . . . . .
Simulating with a Discretized System . . . . . . . . . . . . . . . . . . .
3-21
3-21
3-24
3-28
3-28
3-29
3-30
3-31
Variable-Frequency Induction Motor Drive . . . . . . . . . . . .
Description of the Induction Motor Drive . . . . . . . . . . . . . . . . .
A Field-Oriented Variable-Speed Induction Motor Drive . . . .
Modeling the Induction Motor Drive . . . . . . . . . . . . . . . . . . . .
Simulating the Induction Motor Drive . . . . . . . . . . . . . . . . . . .
Starting the Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Steady-State Voltage and Current Waveforms . . . . . . . . . . . .
Speed Regulation Dynamic Performance . . . . . . . . . . . . . . . . .
3-33
3-33
3-35
3-38
3-42
3-42
3-43
3-44
HVDC System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Description of the HVDC Transmission System . . . . . . . . . . .
Frequency Response of the AC and DC Systems . . . . . . . . . . .
Description of the Control System . . . . . . . . . . . . . . . . . . . . . .
System Startup and Steady State . . . . . . . . . . . . . . . . . . . . . . .
Response to a Step of Reference Current . . . . . . . . . . . . . . . . .
DC Line Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
AC Line-to-Ground Fault at the Rectifier . . . . . . . . . . . . . . . .
3-46
3-46
3-48
3-50
3-54
3-60
3-61
3-63
Improving Simulation Performance
4
How SimPowerSystems Works . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
iii
Choosing an Integration Method . . . . . . . . . . . . . . . . . . . . . . . 4-5
Continuous versus Discrete Solution . . . . . . . . . . . . . . . . . . . . . 4-5
Phasor Solution Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5
Simulating with Continuous Integration Algorithms . . . . . 4-7
Choosing an Integration Algorithm . . . . . . . . . . . . . . . . . . . . . . 4-7
Simulating Switches and Power Electronic Devices . . . . . . . . . 4-7
Simulating Discretized Electrical Systems . . . . . . . . . . . . . 4-11
Limitations of Discretization with Nonlinear Models . . . . . . . 4-11
Increasing Simulation Speed . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14
Using Accelerator Mode and Real-Time Workshop . . . . . . . . . 4-14
The Nonlinear Model Library . . . . . . . . . . . . . . . . . . . . . . . . .
The Continuous Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Discrete Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Phasors Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Switch Current Source Library . . . . . . . . . . . . . . . . . . . . .
Limitations of the Nonlinear Models . . . . . . . . . . . . . . . . . . . .
Modifying the Nonlinear Models of
the powerlib_models Library . . . . . . . . . . . . . . . . . . . . . . . .
4-16
4-16
4-18
4-18
4-18
4-19
4-19
Creating Your Own Library of Models . . . . . . . . . . . . . . . . . 4-20
Changing Your Circuit Parameters . . . . . . . . . . . . . . . . . . . . 4-21
Example of MATLAB Script Performing a Parametric Study 4-21
SimPowerSystems Block Reference
5
Blocks – By Category . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Creating Electrical Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Creating Circuit Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Modeling with Phasor Elements . . . . . . . . . . . . . . . . . . . . . . . .
Modeling Power Electronics Components . . . . . . . . . . . . . . . . .
Modeling Electrical Machines . . . . . . . . . . . . . . . . . . . . . . . . . .
iv
Contents
5-2
5-4
5-4
5-6
5-6
5-6
Measuring Electrical Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7
Analyzing Electrical Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7
Additional Useful Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7
Blocks – Alphabetical List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9
SimPowerSystems Command Reference
6
v
vi
Contents
About This Guide
SimPowerSystems and Physical
Modeling (p. viii)
An overview of product features and capabilities
About the Authors (p. ix)
Blockset and documentation authors from Hydro-Québec
and other institutions
Related Products (p. x)
Products you might want to use with SimPowerSystems
Using This Guide (p. xii)
How to find help in this user’s guide
Units (p. xiii)
Physical units used in SimPowerSystems
Typographical Conventions (p. xix)
Summary of special fonts and notations
About This Guide
SimPowerSystems and Physical Modeling
Starting with MathWorks Release 13, SimPowerSystems and SimMechanics of
the Physical Modeling product family work together with Simulink® to model
electrical, mechanical, and control systems.
Electrical power systems are combinations of electrical circuits and
electromechanical devices like motors and generators. Engineers working in
this discipline are constantly improving the performance of the systems.
Requirements for drastically increased efficiency have forced power system
designers to use power electronic devices and sophisticated control system
concepts that tax traditional analysis tools and techniques. Further
complicating the analyst’s role is the fact that the system is often so nonlinear
that the only way to understand it is through simulation.
Land-based power generation from hydroelectric, steam, or other devices is not
the only use of power systems. A common attribute of these systems is their use
of power electronics and control systems to achieve their performance
objectives.
SimPowerSystems was designed to provide a modern design tool that allows
scientists and engineers to rapidly and easily build models that simulate power
systems. SimPowerSystems uses the Simulink environment, allowing you to
build a model using simple click and drag procedures. Not only can you draw
the circuit topology rapidly, but your analysis of the circuit can include its
interactions with mechanical, thermal, control, and other disciplines. This is
possible because all the electrical parts of the simulation interact with the
extensive Simulink modeling library. Since Simulink uses MATLAB® as its
computational engine, designers can also use MATLAB toolboxes and
Simulink blocksets. SimPowerSystems and SimMechanics share a special
Physical Modeling block and connection line interface.
Users can rapidly put SimPowerSystems to work. The libraries contain models
of typical power equipment such as transformers, lines, machines, and power
electronics. These models are proven ones coming from textbooks, and their
validity is based on the experience of the Power Systems Testing and
Simulation Laboratory of Hydro-Québec, a large North American utility
located in Canada. The capabilities of SimPowerSystems for modeling a typical
electrical grid are illustrated in demonstration files. And for users who want to
refresh their knowledge of power system theory, there are also self-learning
case studies.
viii
About the Authors
About the Authors
SimPowerSystems Version 3 was developed by the following people and
organizations.
Gilbert Sybille
Hydro-Québec Research Institute (IREQ), Varennes, Québec. Original author
of SimPowerSystems, technical coordinator, author of phasor simulation,
discretization techniques, and documentation.
Patrice Brunelle
TransÉnergie Technologies Inc., Montréal, Québec. Main software engineer.
Author of graphical user interfaces, model integration into Simulink and
Physical Modeling, and documentation.
Pierre Giroux, Silvano Casoria, Richard Gagnon, Innocent Kamwa, Raymond
Roussel
Hydro-Québec Research Institute (IREQ), Varennes, Québec. Key beta testers
and developers of several SPS blocks, demos, and documentation.
Roger Champagne, Louis Dessaint
École de Technologie Supérieure (ETS), Montréal, Québec. Authors of machine
models, revised state space formulation, and documentation.
Hoang Lehuy
Université Laval, Québec City. Validation tests and author of several functions
and documentation.
Acknowledgments
The authors acknowledge the contributions of the following people involved in
Versions 1 and 2.
Pierre Mercier, iOMEGAt. Project manager for Versions 1 and 2.
Also: Kamal Al-Haddad, Mohamed Tou, Christian Dufour, Momcilo
Gavrilovic, Christian Larose, David McCallum, and Bahram Khodabakhchian.
ix
About This Guide
Related Products
The MathWorks provides several products that are especially relevant to the
kinds of tasks you can perform with SimPowerSystems.
Requirements for SimPowerSystems
You must have the following products installed to use SimPowerSystems.
• MATLAB 6.5
• Simulink 5.0
Other Related Products
The toolboxes listed in the following table include functions that extend the
capabilities of MATLAB. The blocksets include blocks that extend the
capabilities of Simulink. These products enhance your use of
SimPowerSystems in various applications.
The Physical Modeling Product Family
In addition to SimPowerSystems, the Physical Modeling product family
includes SimMechanics, for modeling and simulating mechanical systems. Use
these products together to model physical systems in Simulink.
For more information about any of these products, see either
• The online documentation for that product, if it is installed or if you are
reading the documentation from the CD
• The MathWorks Web site at http://www.mathworks.com; see the “Products”
section
x
Product
Description
Control System Toolbox
Design and analyze feedback control systems
µ-Analysis and Synthesis
Toolbox
Design multivariable feedback controllers for
systems with model uncertainty
Optimization Toolbox
Solve standard and large-scale optimization
problems
Related Products
Product
Description
Real-Time Workshop®
Generate C code from Simulink models
Robust Control Toolbox
Design robust multivariable feedback control
systems
SimMechanics
Model and simulate mechanical systems
Stateflow®
Design and simulate event-driven systems
System Identification
Toolbox
Create linear dynamic models from measured
input-output data
xPC Target
Perform real-time rapid prototyping using PC
hardware
xi
About This Guide
Using This Guide
If you are a new user, begin with the first two chapters to learn
• How to build and simulate electrical circuits using the powerlib library
• How to interface an electrical circuit with Simulink blocks
• How to analyze the steady-state and frequency response of an electrical
circuit
• How to discretize your model in order to increase simulation speed,
especially for power electronic circuits and large power systems
• How to use the phasor simulation method
• How to build your own nonlinear models
If you are an experienced blockset user, see these chapters:
• The Release Notes for details on the latest release
• “Modeling Simple Systems” to learn how to simulate discretized electrical
circuits
• “Advanced Components and Techniques” to learn how to apply the phasor
simulation to transient stability study of multimachine systems
• “Case Studies” for an overview of some applications of SimPowerSystems
presented as case studies
• “Improving Simulation Performance” to learn how to increase simulation
speed
All blockset users should use the “SimPowerSystems Block Reference” for
reference information on blocks, simple demos, and GUI-based tools. For
commands, refer to “SimPowerSystems Command Reference” for a synopsis of
the command’s syntax, as well as a complete explanation of options and
operation.
xii
Units
Units
This manual uses the International System of Units (SI).
Quantity
Unit
Symbol
Time
second
s
Length
meter
m
Mass
kilogram
kg
Energy
joule
J
Current
ampere
A
Voltage
volt
V
Active power
watt
W
Apparent power
volt-ampere
VA
Reactive power
var
var
Impedance
ohm
Ω
Resistance
ohm
Ω
Inductance
henry
H
Capacitance
farad
F
Flux linkage
volt-second
V. s
Rotation speed
radians per second
revolutions per minute
rad/s
rpm
Torque
newton-meter
N.m
Inertia
kilogram-meter2
kg.m2
Friction factor
newton-meter-second
N.m.s
The manual also uses the per unit (p.u.) system on occasion to define the model
parameters.
xiii
About This Guide
What Is the Per Unit System?
The per unit system is widely used in the power system industry to express
values of voltages, currents, powers, and impedances of various power
equipment. It is mainly used for transformers and AC machines.
For a given quantity (voltage, current, power, impedance, torque, etc.) the per
unit value is the value related to a base quantity.
expressed in SI units
base value in p.u. = quantity
----------------------------------------------------------------------------------base value
Generally the following two base values are chosen:
• The base power = nominal power of the equipment
• The base voltage = nominal voltage of the equipment
All other base quantities are derived from these two base quantities. Once the
base power and the base voltage are chosen, the base current and the base
impedance are determined by the natural laws of electrical circuits.
base powerbase current = --------------------------------base voltage
2
base voltage( base voltage )
base impedance = --------------------------------= ----------------------------------------base current
base power
For a transformer with multiple windings, each having a different nominal
voltage, the same base power is used for all windings (nominal power of the
transformer). However, according to the above definitions, there are as many
base values as windings for voltages, currents, and impedances.
For AC machines, the torque and speed can be also expressed in p.u. The
following base quantities are chosen:
• The base speed = synchronous speed
• The base torque = torque corresponding at base power and synchronous
speed:
base power (3 phases) in watts
base torque = -----------------------------------------------------------------------------------base speed in radians/second
xiv
Units
Instead of specifying the rotor inertia in kg*m2, you would generally give the
inertia constant H defined as
energy stored in the rotor at synchronous speed in joules
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------H = kinetic
machine nominal power in VA
1
--- × J ⋅ w 2
2
H = -------------------------Pnom
The inertia constant is expressed in seconds. For large machines, this constant
is around 3 to 5 seconds. An inertia constant of 3 seconds means that the energy
stored in the rotating part could supply the nominal load during 3 seconds. For
small machines, H is lower. For example, for a 3 HP motor, it can be between
0.5 and 0.7 seconds.
Example 1: Three-Phase Transformer
Consider, for example, a three-phase two-winding transformer. The following
typical parameters could be provided by the manufacturer:
• Nominal power = 300 kVA total for three phases
• Nominal frequency = 60 Hz
• Winding 1: connected in wye, nominal voltage = 25 kV RMS line-to-line
resistance 0.01 p.u., leakage reactance = 0.02 p.u.
• Winding 2: connected in delta, nominal voltage = 600 V RMS line-to-line
resistance 0.01 p.u., leakage reactance = 0.02 p.u.
• Magnetizing losses at nominal voltage in % of nominal current:
Resistive 1%, Inductive 1%
The base values for each single phase transformer are first calculated:
• For winding 1:
Base power
300 kVA/3 = 100e3 VA/phase
Base voltage
25 kV/sqrt(3) = 14434 V RMS
Base current
100e3/14434 = 6.928 A RMS
Base impedance
14434/6.928 = 2083 Ω
xv
About This Guide
Base resistance
14434/6.928 = 2083 Ω
Base inductance
2083/(2π*60)= 5.525 H
• For winding 2:
Base power
300 kVA/3 = 100e3 VA
Base voltage
600 V RMS
Base current
100e3/600 = 166.7 A RMS
Base impedance
600/166.7 = 3.60 Ω
Base resistance
600/166.7 = 3.60 Ω
Base inductance
3.60/(2π*60) = 0.009549 H
The values of the winding resistances and leakage inductances expressed in SI
units are therefore
• For winding 1: R1= 0.01 * 2083 = 20.83 Ω; L1= 0.02*5.525 = 0.1105 H
• For winding 2: R2= 0.01 * 3.60 = 0.0360 Ω; L2= 0.02*0.009549 = 0.191 mH
For the magnetizing branch, magnetizing losses of 1% resistive and 1%
inductive mean a magnetizing resistance Rm of 100 p.u. and a magnetizing
inductance Lm of 100 p.u. Therefore, the values expressed in SI units referred
to winding 1 are
• Rm = 100*2083 = 208.3 kΩ
• Lm = 100*5.525 = 552.5 H
Example 2: Asynchronous Machine
Now consider the three-phase four-pole Asynchronous Machine in SI units
provided in the Machines library of powerlib. It is rated 3 HP, 220 V RMS
line-to-line, 60 Hz.
The stator and rotor resistance and inductance referred to stator are
• Rs = 0.435 Ω; Ls = 2 mH
• Rr = 0.816 Ω; Lr = 2 mH
The mutual inductance is Lm = 69.31 mH. The rotor inertia is J = 0.089 kg.m2.
xvi
Units
The base quantities for one phase are calculated as follows:
Base power
3 HP*746VA/3 = 746 VA/phase
Base voltage
220 V/sqrt(3) = 127.0 V RMS
Base current
746/127.0 = 5.874 A RMS
Base impedance
127.0/5.874 = 21.62 Ω
Base resistance
127.0/5.874 = 21.62 Ω
Base inductance
21.62/(2π*60)= 0.05735 H = 57.35 mH
Base speed
1800 rpm = 1800*(2π)/60 = 188.5 radians/second
Base torque (3-phase) 746*3/188.5 = 11.87 newton-meters
Using the above base values, you can compute the values in per units.
Rs= 0.435 / 21.62 = 0.0201 p.u. Ls= 2 / 57.35 = 0.0349 p.u.
Rr= 0.816 / 21.62 = 0.0377 p.u. Lr= 2 / 57.35 = 0.0349 p.u.
Lm = 69.31/57.35 = 1.208 p.u.
The inertia is calculated from inertia J, synchronous speed, and nominal
power.
1
--- × J ⋅ w 2
2
H = ------------------------ =
Pnom
1
--- × 0.089 × ( 188.5 ) 2
2
----------------------------------------------------- = 0.7065 seconds
3 × 746
If you open the dialog box of the Asynchronous Machine block in p.u. units
provided in the Machines library of powerlib, you find that the parameters in
p.u. are the ones calculated above.
Base Values for Instantaneous Voltage and Current Waveforms
When displaying instantaneous voltage and current waveforms on graphs or
oscilloscopes, you normally consider the peak value of the nominal sinusoidal
voltage as 1 p.u. In other words, the base values used for voltage and currents
are the RMS values given above multiplied by 2 .
xvii
About This Guide
Why Use the Per Unit System Instead of the Standard SI Units?
Here are the main reasons for using the per unit system:
• When values are expressed in p.u., the comparison of electrical quantities
with their “normal” values is straightforward.
For example, a transient voltage reaching a maximum of 1.42 p.u. indicates
immediately that this voltage exceeds the nominal value by 42%.
• The values of impedances expressed in p.u. stay fairly constant whatever the
power and voltage ratings.
For example, for all transformers in the 3 kVA to 300 kVA power range, the
leakage reactance varies approximately between 0.01 p.u. and 0.03 p.u.,
whereas the winding resistances vary between 0.01 p.u. and 0.005 p.u.,
whatever the nominal voltage. For transformers in the 300 kVA to 300 MVA
range, the leakage reactance varies approximately between 0.03 p.u. and
0.12 p.u., whereas the winding resistances vary between 0.005 p.u. and 0.002
p.u.
Similarly, for salient pole synchronous machines, the synchronous reactance
Xd is generally between 0.60 and 1.50 p.u., whereas the sub transient
reactance X'd is generally between 0.20 and 0.50 p.u.
It means that if you do not know the parameters for a 10 kVA transformer,
you are not making a major error by assuming an average value of 0.02 p.u.
for leakage reactances and 0.0075 p.u. for winding resistances.
• The calculations using the per unit system are simplified. When all
impedances in a multivoltage power system are expressed on a common
power base and on the nominal voltages of the different subnetworks, the
total impedance in p.u. seen at one bus is obtained by simply adding all
impedances in p.u., without taking into consideration the transformer ratios.
xviii
Typographical Conventions
Typographical Conventions
This manual uses some or all of these conventions.
Item
Convention
Example
Example code
Monospace font
To assign the value 5 to A,
enter
A = 5
Function names, syntax,
filenames, directory/folder
names, user input, items in
drop-down lists
Monospace font
The cos function finds the
cosine of each array element.
Buttons and keys
Boldface with book title caps
Press the Enter key.
Literal strings (in syntax
descriptions in reference
chapters)
Monospace bold for literals
f = freqspace(n,'whole')
Mathematical
expressions
Italics for variables
This vector represents the
polynomial p = x2 + 2x + 3.
MATLAB output
Monospace font
Syntax line example is
MLGetVar ML_var_name
Standard text font for functions,
operators, and constants
MATLAB responds with
A =
5
Menu and dialog box titles
Boldface with book title caps
Choose the File Options
menu.
New terms and for
emphasis
Italics
An array is an ordered
collection of information.
Omitted input arguments
(...) ellipsis denotes all of the
input/output arguments from
preceding syntaxes.
[c,ia,ib] = union(...)
String variables (from a
finite list)
Monospace italics
sysc = d2c(sysd,'method')
xix
About This Guide
xx
1
Modeling Simple Systems
SimPowerSystems operates in the Simulink environment. Therefore, before starting this user’s
guide, you should be familiar with Simulink. For help with Simulink, see the Using Simulink guide.
To master SimPowerSystems, you must learn how to model and simulate electrical circuits. This
chapter is organized into four tutorials, all based on a simple power system, that demonstrate basic
circuit modeling, analysis, and simulation.
Simulating a Simple Circuit (p. 1-2)
Build a simple circuit with SimPowerSystems blocks and
connect it to other Simulink blocks
Analyzing a Simple Circuit (p. 1-9)
Use the Powergui block and analyze static and
frequency-domain response
Simulating Transients (p. 1-19)
Create an electrical subsystem, simulate transients, and
discretize simple circuits
Introducing the Phasor Simulation
Method (p. 1-26)
Use the phasor method to analyze magnitudes and
phases in linear circuits
1
Modeling Simple Systems
Simulating a Simple Circuit
SimPowerSystems allows you to build and simulate electrical circuits
containing linear and nonlinear elements.
In this section you
• Explore the powerlib library of SimPowerSystems
• Learn how to build a simple circuit from the powerlib library
• Interconnect Simulink blocks with your circuit
The circuit below represents an equivalent power system feeding a 300 km
transmission line. The line is compensated by a shunt inductor at its receiving
end. A circuit breaker allows energizing and deenergizing of the line. In order
to simplify matters, only one of the three phases is represented. The
parameters shown in the figure are typical of a 735 kV power system.
300 km
transmission line
Rs_eq
2.0 Ω
Z_eq
424.4 kV RMS
0 degrees
60 Hz
R = 180.1 Ω
L = 26.525 mH
C = 117.84 µF
R = 0.011 Ω/km
L = 0.8674 mH/km
C = 13.41 nF/km
Q = 110 Mvars
quality factor:300
@ 424.4 kV
60 Hz
Figure 1-1: Circuit to Be Modeled with SimPowerSystems
Building the Electrical Circuit with powerlib Library
The graphical user interface makes use of the Simulink functionality to
interconnect various electrical components. The electrical components are
grouped in a special library called powerlib.
Open the SimPowerSystems library by entering the following command at the
MATLAB prompt:
powerlib
1-2
Simulating a Simple Circuit
This command displays a Simulink window showing icons of different block
libraries.
You can open these libraries to produce the windows containing the blocks to
be copied into your circuit. Each component is represented by a special icon
having one or several inputs and outputs corresponding to the different
terminals of the component:
1 From the File menu of the powerlib window, open a new window to contain
your first circuit and save it as circuit1.
2 Open the Electrical Sources library and copy the AC Voltage Source block
into the circuit1 window.
3 Open the AC Voltage Source dialog box by double-clicking the icon and
enter the Amplitude, Phase, and Frequency parameters according to the
values shown in Figure 1-1.
Note that the amplitude to be specified for a sinusoidal source is its peak
value (424.4e3*sqrt(2) volts in this case).
4 Change the name of this block from Voltage Source to Vs.
5 Copy the Parallel RLC Branch block, which can be found in the Elements
library of powerlib, set its parameters as shown in Figure 1-1, and name it
Z_eq.
1-3
1
Modeling Simple Systems
6 The resistance Rs_eq of the circuit can be obtained from the Parallel RLC
Branch block. Duplicate the Parallel RLC Branch block, which is already in
your circuit1 window, set the R parameter according to Figure 1-1, and set
the L and C parameters respectively to infinity (inf) and zero (0).
Once the dialog box is closed, notice that the L and C components have
disappeared so that the icon now shows a single resistor. The same result
would have been obtained with the Series RLC Branch block by setting L
and C respectively at zero and inf.
7 Name this block Rs_eq.
Resize the various components and interconnect blocks by dragging lines from
outputs to inputs of appropriate blocks.
In order to complete the circuit of Figure 1-1, you need to add a transmission
line and a shunt reactor. You add the circuit breaker later in “Simulating
Transients” on page 1-19.
The model of a line with uniformly distributed R, L, and C parameters
normally consists of a delay equal to the wave propagation time along the line.
This model cannot be simulated as a linear system because a delay corresponds
to an infinite number of states. However, a good approximation of the line with
a finite number of states can be obtained by cascading several PI circuits, each
representing a small section of the line.
A PI section consists of a series R-L branch and two shunt C branches. The
model accuracy depends on the number of PI sections used for the model. Copy
the PI Section Line block from the Elements library into the circuit1 window,
set its parameters as shown in Figure 1-1, and specify one line section.
1-4
Simulating a Simple Circuit
The shunt reactor is modeled by a resistor in series with an inductor. You could
use a Series RLC Branch block to model the shunt reactor. Set the R and L
values corresponding to the active and reactive power specified in Figure 1-1
(Q = 110 Mvar; P = 110/300 = 0.37 MW at V = 424.4 kV rms and f = 60 Hz).
You might find it more convenient to use a Series RLC Load block that allows
you to specify directly the active and reactive powers absorbed by the shunt
reactor.
Copy the Series RLC Load block, which can be found in the Elements library of
powerlib. Name this block 110 Mvar. Set its parameters as follows:
Vn
424.4e3 V
fn
60 Hz
P
110e6/300 W (quality factor = 300)
QL
110e6 vars
Qc
0
Note that, as no reactive capacitive power is specified, the capacitor disappears
on the block icon when the dialog box is closed. Interconnect the new blocks as
shown.
You need a Voltage Measurement block to measure the voltage at node B1.
This block is found in the Measurements library of powerlib. Copy it and name
it U1. Connect its positive input to the node B1 and its negative input to a new
Ground block.
1-5
1
Modeling Simple Systems
In order to observe the voltage measured by the Voltage Measurement block
named U1, a display system is needed. This can be any device found in the
Sinks library of Simulink.
Open the Sinks library of Simulink and copy the Scope block into your circuit1
window. If the scope were connected directly at the output of the voltage
measurement, it would display the voltage in volts. However, electrical
engineers in power systems are used to working with normalized quantities
(per unit system). The voltage is normalized by dividing the value in volts by a
base voltage corresponding to the peak value of the system nominal voltage. In
this case the scaling factor K is
1
K = -------------------------------------------3
424.4 × 10 × 2
Copy a Gain block from the Simulink library and set its gain as above. Connect
its output to the Scope block and connect the output of the Voltage
Measurement block to the Gain block. Duplicate this voltage measurement
system at the node B2, as shown below.
Interfacing the Electrical Circuit with Simulink
The Voltage Measurement block acts as an interface between the
SimPowerSystems blocks and the Simulink blocks. For the system shown
above, you implemented such an interface from the electrical system to the
1-6
Simulating a Simple Circuit
Simulink system. The Voltage Measurement blocks converts the measured
voltages into Simulink signals.
Note that the Current Measurement block from the Measurements library of
powerlib can also be used to convert any measured current into a Simulink
signal.
You can also interface from Simulink blocks to the electrical system. For
example, you can use the Controlled Voltage Source block to inject a voltage in
an electrical circuit. The voltage is then controlled by a Simulink signal.
Electrical Terminal Ports and Connection Lines SimPowerSystems is
part of the Physical Modeling environment. Its blocks often feature both
normal Simulink input and output ports > and special electrical terminal ports
.
• Lines that connect normal Simulink ports > are directional signal lines.
• Lines that connect terminal ports are special electrical connection lines.
These lines are nondirectional and can be branched. But you cannot connect
them to Simulink ports > or to normal Simulink signal lines.
1-7
1
Modeling Simple Systems
• You can connect Simulink ports > only to other Simulink ports and terminal
ports only to other terminal ports.
• Converting Simulink signals to electrical connections or vice versa requires
using a SimPowerSystems block that features both Simulink and terminal
ports.
Some SimPowerSystems blocks feature only one type of port.
Simulating Your Circuit
Now you can start the simulation from the Simulation menu. As expected,
voltage is sinusoidal with peak value of 1 p.u.
While the simulation is running, open the Vs block dialog box and modify the
amplitude. Observe the effect on the two scopes. You can also modify the
frequency and the phase. You can zoom in on the waveforms in the scope
windows by drawing a box around the region of interest with the left mouse
button.
Note To simulate this circuit, the default integration algorithm (ode45) was
used. However, for most applications of SimPowerSystems your circuits
contain switches and other nonlinear models. In such a case, you must specify
a different integration algorithm. This is discussed in “Simulating Transients”
on page 1-19, where a circuit breaker is added to your circuit.
1-8
Analyzing a Simple Circuit
Analyzing a Simple Circuit
In this section you
• Use the Powergui (graphical user interface) block
• Obtain the steady-state outputs of the system
• Analyze your circuit with power_analyze command
• Analyze an electrical circuit in the frequency domain
Steady-State Analysis
In order to facilitate the steady-state analysis of your circuit, a graphical user
interface (GUI) is provided in the powerlib library. Copy the Powergui block
into your circuit1 window and double-click the block icon to open it.
From the Analysis tools menu of Powergui, select Steady-State Voltages and
Currents. This opens the Steady State Tool window where the steady-state
phasors measured by the two measurement blocks are displayed in polar form.
1-9
1
Modeling Simple Systems
Each measurement output is identified by a string corresponding to the
measurement block name. The magnitudes of the phasors U1 and U2
correspond to the peak value of the sinusoidal voltages.
From the Steady State window you can also choose to display the steady-state
values of the source voltage or the steady-state values of states by selecting
either the Sources or the States check box.
The state variable names contain the name of the block where the inductor or
capacitor is found, preceded by the Il_ prefix for inductor currents or the Uc_
prefix for capacitor voltages.
The sign conventions used for the voltages and currents of sources and state
variables are determined by the orientation of the blocks:
• Inductor currents flowing in the arrow direction are considered positive.
• Capacitor voltages are Vblock output − Vblock input.
1-10
Analyzing a Simple Circuit
Note Depending on the exact position of the various blocks in your circuit1
diagram, the state variables might not be ordered in the same way as in the
preceding figure.
Now, from the Tools menu of Powergui, select Initial State Settings. The
initial values of the six state variables (three inductor currents and three
capacitor voltages) are displayed. These initial values are set in order to start
the simulation in steady state.
Frequency Analysis
The Measurements library of powerlib contains an Impedance Measurement
block that measures the impedance between any two nodes of a circuit. In the
following two sections you measure the impedance of your circuit between node
B2 and ground by using two methods:
1-11
1
Modeling Simple Systems
• Calculation from the state-space model
• Automatic measurement using the Impedance Measurement block and the
Powergui block
Obtaining the Impedance vs Frequency Relation from the State-Space
Model
To measure the impedance versus frequency at node B2, you need a current
source at node B2 providing a second input to the state-space model. Open the
Electrical Sources library and copy the AC Current Source block into your
model. Connect this source at node B2, as shown below. Set the current source
magnitude to zero and keep its frequency at 60 Hz. Rearrange the blocks as
follows:
Figure 1-2: AC Current Source at the B2 Node
Now compute the state-space representation of the model circuitl with the
power_analyze command. Enter the following command at the MATLAB
prompt.
[A,B,C,D,x0,states,inputs,outputs]=power_analyze('circuit1');
The power_analyze command returns the state-space model of your circuit in
the four matrices A, B, C, and D. x0 is the vector of initial conditions that you
just displayed with the Powergui block. The names of the state variables,
inputs, and outputs are returned in three string matrices.
1-12
Analyzing a Simple Circuit
states =
Il_110 Mvars
Uc_input PI Section Line
Il_ sect1 PI Section Line
Uc_output PI Section Line
Il_Z_eq
Uc_Z_eq
inputs =
U_Vs
I_AC Current Source
outputs =
U_U1
U_U2
Note that you could have obtained the names and ordering of the states, inputs,
and outputs directly from the Powergui block.
Once the state-space model of the system is known, it can be analyzed in the
frequency domain. For example, the modes of this circuit can be found from the
eigenvalues of matrix A (use the MATLAB eig command).
eig(A)
ans =
1.0e+05
-2.4972
-0.0001
-0.0001
-0.0002
-0.0002
-0.0000
*
+
+
-
0.0144i <– 229 Hz
0.0144i
0.0056i <– 89 Hz
0.0056i
This system has two oscillatory modes at 89 Hz and 229 Hz. The 89 Hz mode
is due to the equivalent source, which is modeled by a single pole equivalent.
The 229 Hz mode is the first mode of the line modeled by a single PI section.
1-13
1
Modeling Simple Systems
Note If you have Control System Toolbox installed, you can compute the
impedance of the network as a function of frequency by using the bode
function.
In the Laplace domain, the impedance Z2 at node B2 is defined as the transfer
function between the current injected at node B2 (input 2 of the system) and
the voltage measured at node B2 (output 2 of the system):
U2 ( s )Z2 ( s ) = --------------I2 ( s )
The impedance at node B2 for the 0 to 1500 Hz range can be calculated and
displayed as follows:
freq=0:1500;
w=2*pi*freq;
[mag1,phase1]=bode(A,B,C,D,2,w);
semilogy(freq,mag1(:,2));
Repeat the same process to get the frequency response with a 10 section line
model. Open the PI Section Line dialog box and change the number of sections
from 1 to 10. To calculate the new frequency response and superimpose it upon
the one obtained with a single line section, enter the following commands:
[A,B,C,D]=power_analyze('circuit1');
[mag10,phase10]=bode(A,B,C,D,2,w);
semilogy(freq,mag1(:,2),freq,mag10(:,2));
This is the resulting plot.
1-14
Analyzing a Simple Circuit
Impedance magnitude at node B2 (Ω)
105
229 Hz
104
One line section
103
10 line sections
89 Hz
102
101
100
0
500
1000
1500
Frequency (Hz)
Figure 1-3: Impedance at Node B2 as Function of Frequency
This graph indicates that the frequency range represented by the single line
section model is limited to approximately 150 Hz. For higher frequencies, the
10 line section model is a better approximation.
For a distributed parameter line model the propagation speed is
1 v = ---------------= 293,208 km/s
L⋅C
The propagation time for 300 km is therefore T = 300/293,208 = 1.023 ms and
the frequency of the first line mode is f1 = 1/4T = 244 Hz. A distributed
parameter line would have an infinite number of modes every 244 + n*488 Hz
(n = 1, 2, 3...). The 10 section line model simulates the first 10 modes. The first
three line modes can be seen in Figure 1-3 (244 Hz, 732 Hz, and 1220 Hz).
Obtaining the Impedance vs Frequency Relation from the Impedance
Measurement and Powergui blocks
The process described above to measure a circuit impedance has been
automated in SimPowerSystems. Open the Measurements library of powerlib,
1-15
1
Modeling Simple Systems
copy the Impedance Measurement block into your model, and rename it ZB2.
Connect the two inputs of this block between node B2 and ground as shown.
Figure 1-4: Measuring Impedance vs Frequency with the Impedance
Measurement Block
Now open the Powergui. In the Tools menu, select Impedance vs Frequency
Measurement. A new window opens, showing the list of Impedance
Measurement blocks available in your circuit.
In your case, only one impedance is measured, and it is identified by ZB2 (the
name of the ZB2 block) in the window. Fill in the frequency range by entering
0:2:1500 (zero to 1500 Hz by steps of 2 Hz). Select the logarithmic scale to
display Z magnitude. Select the Save data when updated check box and enter
ZB2 as the variable name to contain the impedance vs. frequency. Click the
Display/Save button.
1-16
Analyzing a Simple Circuit
When the calculation is finished, the window displays the magnitude and
phase as functions of frequency. The magnitude should be identical to the plot
(for one line section) shown in Figure 1-3. If you look in your workspace, you
should have a variable named ZB2. It is a two-column matrix containing
frequency in column 1 and complex impedance in column 2.
Now open the Simulation —> Simulation parameters dialog of your circuit1
model. On the Solver pane, select the ode23tb integration algorithm. Set the
relative tolerance to 1e-4 and keep auto for the other parameters. Set the stop
time to 0.05. Open the scopes and start the simulation.
Look at the waveforms of the sending and receiving end voltages on ScopeU1
and ScopeU2. As the state variables are automatically initialized, the system
starts in steady state and sinusoidal waveforms are observed.
1-17
1
Modeling Simple Systems
Finally open the Powergui. In the Tools menu, select Initial State Settings
and reset all the states to zero by selecting the To zero button and then the
Apply button. Restart the simulation and observe the transient when the line
is energized from zero.
Figure 1-5: Receiving End Voltage U2 with 10 PI Section Line
1-18
Simulating Transients
Simulating Transients
In this section you
• Learn how to create an electrical subsystem
• Simulate transients with a circuit breaker
• Compare time domain simulation results with different line models
• Learn how to discretize a circuit and compare results thus obtained with
results from a continuous, variable time step algorithm
One of the main uses of SimPowerSystems is to simulate transients in
electrical circuits. This can be done with either mechanical switches (circuit
breakers) or switches using power electronic devices.
First open your circuit1 system and delete the current source connected at
node B2. Save this new system as circuit2. Before connecting a circuit
breaker, you need to modify the schematic diagram of circuit2. As with
Simulink, SimPowerSystems allows you to group several components into a
subsystem. This feature is useful to simplify complex schematic diagrams.
Use this feature to transform the source impedance into a subsystem:
1 Select the two blocks identified as Rs_eq and Z_eq by surrounding them by
a box with the left mouse button and use the Edit —> Create subsystem
menu item. The two blocks now form a new block called Subsystem.
2 Using the Edit —> Mask subsystem menu item, change the icon of that
subsystem. In the Icon section of the mask editor, enter the following
drawing command:
1-19
1
Modeling Simple Systems
disp('Equivalent\nCircuit')
The icon is now “Equivalent Circuit,” as shown in the figure above.
3 Use the Format —> Show drop shadow menu item to get the appearance
shown in the figure. You can now double-click the Subsystem block and look
at its content.
4 Insert a circuit breaker into your circuit in order to simulate a line
energization by opening the Elements library of powerlib. Copy the Breaker
block into your circuit2 window.
The circuit breaker is a nonlinear element modeled by an ideal switch in series
with a resistance. Because of modeling constraints, this resistance cannot be
set to zero. However, it can be set to a very small value, say 0.001 Ω, that does
not affect the performance of the circuit.
1 Open the Breaker block dialog box and set its parameters as follows:
Ron
0.001 Ω
Initial state
0 (open)
Rs
inf
Cs
0
Switching times
[(1/60)/4]
2 Insert the circuit breaker in series with the sending end of the line, then
rearrange the circuit as shown in the previous figure.
3 Finally connect a Scope block, from the Sinks library of Simulink, at the
output of the Gain block measuring U2. Click the Scope Parameters icon
and select the Data history tab. Click the Save data to workspace button
and specify a variable name U2 to save the simulation results; then change
the Format option for U2 to be Array. Also, clear Limit rows to last to
display the entire waveform for long simulation times.
You are now ready to simulate your system.
1-20
Simulating Transients
Continuous, Variable Time Step Integration
Algorithms
Open the PI section Line dialog box and make sure the number of sections is
set to 1. Open the Simulation —> Simulation parameters dialog. As you now
have a system containing switches, you need a stiff integration algorithm to
simulate the circuit. In the Solver pane, select the variable-step stiff
integration algorithm ode23tb.
Keep the default parameters (relative tolerance set at 1e-3) and set the stop
time to 0.02 seconds. Open the scopes and start the simulation. Look at the
waveforms of the sending and receiving end voltages on ScopeU1 and ScopeU2.
Once the simulation is complete, copy the variable U2 into U2_1 by entering the
following command in the MATLAB window:
U2_1 = U2;
These two variables now contain the waveform obtained with a single PI
section line model.
Open the PI section Line dialog box and change the number of sections from
1 to 10. Start the simulation. Once the simulation is complete, copy the variable
U2 into U2_10.
Before modifying your circuit to use a distributed parameter line model, save
your system as circuit2_10pi, which you can reuse later.
Delete the PI section line model and replace it with a single-phase Distributed
Parameter Line block. Set the number of phases to 1 and use the same R, L, C,
and length parameters as for the PI section line (see Figure 1-1). Save this
system as circuit2_dist.
Restart the simulation and save the U2 voltage in the U2_d variable.
You can now compare the three waveforms obtained with the three line models.
Each variable U2_1, U2_10, and U2_d is a two-column matrix where the time is
in column 1 and the voltage is in column 2. Plot the three waveforms on the
same graph by entering the following command:
plot(U2_1(:,1), U2_1(:,2), U2_10(:,1),U2_10(:,2),
U2_d(:,1),U2_d(:,2));
These waveforms are shown in the next figure. As expected from the frequency
analysis performed during “Analyzing a Simple Circuit” on page 1-9, the single
1-21
1
Modeling Simple Systems
PI model does not respond to frequencies higher than 229 Hz. The 10 PI section
model gives a better accuracy, although high-frequency oscillations are
introduced by the discretization of the line. You can clearly see in the figure the
propagation time delay of 1.03 ms associated with the distributed parameter
line.
Figure 1-6: Receiving End Voltage Obtained with Three Different Line Models
Discretizing the Electrical System
An important feature of SimPowerSystems is its ability to simulate either with
continuous, variable step integration algorithms or with discrete solvers. For
small systems, variable time step algorithms are usually faster than fixed step
methods, because the number of integration steps is lower. For large systems
that contain many states or many nonlinear blocks such as power electronic
switches, however, it is advantageous to discretize the electrical system.
When you discretize your system, the precision of the simulation is controlled
by the time step. If you use too large a time step, the precision might not be
sufficient. The only way to know if it is acceptable is to repeat the simulation
with different time steps and find a compromise for the largest acceptable time
step. Usually time steps of 20 µs to 50 µs give good results for simulation of
1-22
Simulating Transients
switching transients on 50 Hz or 60 Hz power systems or on systems using
line-commutated power electronic devices such as diodes and thyristors. You
must reduce the time step for systems using forced-commutated power
electronic switches. These devices, the insulated-gate bipolar transistor
(IGBT), the field-effect transistor (FET), and the gate-turn-off thyristor (GTO)
are operating at high switching frequencies.
For example, simulating a pulse-width-modulated (PWM) inverter operating
at 8 kHz would require a time step of at least 1 µs.
You now learn how to discretize your system and compare simulation results
obtained with continuous and discrete systems. Open the circuit2_10pi
system that you saved from a previous simulation. This system contains 24
states and one switch. Open the Powergui and select Discretize electrical
model. Set the sample time to 25e-6 s. When you restart the simulation, the
power system is discretized using the Tustin method (corresponding to
trapezoidal integration) using a 25 µs sample time.
Open the Simulation —> Simulation parameters —> Solver dialog and set
the simulation time to 0.2 s. Start the simulation.
Note Once the system is discretized, there are no more continuous states in
the electrical system. So you do not need a variable-step integration method to
simulate. In the Simulation —> Simulation parameters —> Solver dialog,
you could have selected the Fixed-step and discrete (no continuous
states) options and specified a fixed step of 25 µs.
In order to measure the simulation time, you can restart the simulation by
entering the following commands:
tic; sim(gcs); toc
When the simulation is finished the elapsed time in seconds is displayed in the
MATLAB window.
To return to the continuous simulation, open the Powergui block and select
Continuous. If you compare the simulation times, you find that the discrete
system simulates approximately 3.5 times faster than the continuous system.
In order to compare the precision of the two methods, perform the following
three simulations:
1-23
1
Modeling Simple Systems
1 Simulate a continuous system, with Ts = 0.
2 Simulate a discrete system, with Ts = 25 µs.
3 Simulate a discrete system, with Ts = 50 µs.
For each simulation, save the voltage U2 in a different variable. Use
respectively U2c, U2d25, and U2d50. Plot the U2 waveforms on the same graph
by entering the following command:
plot(U2c(:,1), U2c(:,2), U2d25(:,1),U2d25(:,2),
U2d50(:,1),U2d(50:,2))
Using the zoom button of the graphics window, zoom in on the 4 to 12 ms
region. You see differences on the high-frequency transients. The 25 µs
compares reasonably well with the continuous simulation. However,
increasing the time step to 50 µs produces appreciable errors. The 25 µs time
step would therefore be acceptable for this circuit, while obtaining a gain of 3.5
on simulation speed.
1-24
Simulating Transients
3
2
Continuous
25us
50us
U2(v)
1
0
−1
−2
−3
4
5
6
7
8
time(s)
9
10
11
12
−3
x 10
Figure 1-7: Comparison of Simulation Results for Continuous and Discrete
Systems
1-25
1
Modeling Simple Systems
Introducing the Phasor Simulation Method
In this section, you
• Apply the phasor simulation method to a simple linear circuit
• Learn advantages and limitations of this method
Up to now you have used two methods to simulate electrical circuits:
• Simulation with variable time steps using the continuous Simulink solvers
• Simulation with fixed time steps using a discretized system
This section explains how to use a third simulation method: the phasor solution
method. This technique was introduced in Version 2.3.
When to Use the Phasor Solution
The phasor solution method is mainly used to study electromechanical
oscillations of power systems consisting of large generators and motors. An
example of this method is the simulation of a multimachine system in
“Three-Phase Systems and Machines” on page 2-24. However, this technique is
not restricted to the study of transient stability of machines. It can be applied
to any linear system.
If, in a linear circuit, you are interested only in the changes in magnitude and
phase of all voltages and currents when switches are closed or opened, you do
not need to solve all differential equations (state-space model) resulting from
the interaction of R, L, and C elements. You can instead solve a much simpler
set of algebraic equations relating the voltage and current phasors. This is
what the phasor solution method does. As its name implies, this method
computes voltages and currents as phasors. Phasors are complex numbers
representing sinusoidal voltages and currents at a particular frequency. They
can be expressed either in Cartesian coordinates (real and imaginary) or in
polar coordinates (amplitude and phase). As the electrical states are ignored,
the phasor solution method does not require a particular solver to solve the
electrical part of your system. The simulation is therefore much faster to
execute. You must keep in mind, however, that this faster solution technique
gives the solution only at one particular frequency.
1-26
Introducing the Phasor Simulation Method
Phasor Simulation of a Circuit Transient
You now apply the phasor solution method to a simple linear circuit. Open the
Demos library of powerlib. Open the Simple Demos library and select the
demo named “Transient Analysis.” A system named power_transient opens.
Figure 1-8: Simple Linear Circuit Built in SimPowerSystems
This circuit is a simplified model of a 60 Hz, 230 kV three-phase power system
where only one phase is represented. The equivalent source is modeled by a
voltage source (230 kV RMS / sqrt(3) or 132.8 kV RMS, 60 Hz) in series with its
internal impedance (Rs Ls). The source feeds an RL load through a 150 km
transmission line modeled by a single PI section (RL1 branch and two shunt
capacitances, C1 and C2). A circuit breaker is used to switch the load (75 MW,
20 Mvar) at the receiving end of the transmission line. Two measurement
blocks are used to monitor the load voltage and current.
The Powergui block at the lower left corner indicates that the model is
continuous. Start the simulation and observe transients in voltage and current
waveforms when the load is first switched off at t = 0.0333 s (2 cycles) and
switched on again at t = 0.1167 s (7 cycles).
1-27
1
Modeling Simple Systems
Invoking the Phasor Solution in the Powergui Block
You now simulate the same circuit using the phasor simulation method. This
option is accessible through the Powergui block. Open this block and select
Phasor simulation. You must also specify the frequency used to solve the
algebraic network equations. A default value of 60 Hz should already be
entered in the Frequency menu. Close the Powergui and notice that the word
Phasors now appears on the Powergui icon, indicating that the Powergui now
applies this method to simulate your circuit.
Restart the simulation. The magnitudes of the 60 Hz voltage and current are
now displayed on the scope. Waveforms obtained from the continuous
simulation and the phasor simulation are superimposed in this plot.
Figure 1-9: Waveforms Obtained with the Continuous and Phasor Simulation
Methods
1-28
Introducing the Phasor Simulation Method
Note that with continuous simulation, the opening of the circuit breaker occurs
at the next zero crossing of current following the opening order; whereas for the
phasor simulation, this opening is instantaneous. This is because there is no
concept of zero crossing in the phasor simulation.
Selecting Phasor Signal Measurement Formats
If you now double-click the Voltage Measurement block or the Current
Measurement block, you see that a menu allows you to output phasor signals
in four different formats: Complex, Real-Imag, Magnitude-Angle, or just
Magnitude (default choice). If you select Magnitude-Angle, both magnitude and
angle (in degrees) are multiplexed at the output of the measurement block. You
might need to demultiplex these two signals to send them on separate traces of
the scope. Note that the oscilloscope does not accept complex signals. You
should instead use the Real-Imag format.
The Complex format allows the use of complex operations and processing of
phasors without separating real and imaginary parts. Suppose for example
that you need to compute the power consumption of the load (active power P
and reactive power Q). The complex power S is obtained from the voltage and
current phasors as
*
1
S = P + jQ = --- ⋅ V ⋅ I
2
where I* is the conjugate of the current phasor. The 1/2 factor is required to
convert magnitudes of voltage and current from peak values to RMS values.
1-29
1
Modeling Simple Systems
Select the Complex format for both current and voltage and, using blocks from
the Simulink Math library, implement the power measurement as shown.
Figure 1-10: Power Computation Using Complex Voltage and Current
The Complex to Magnitude-Angle blocks are now required to convert complex
phasors to magnitudes before sending them to the scope.
The power computation system you just implemented is already built into
SimPowerSystems: the Active & Reactive Power (Phasor Type) block is
available in the Extras library under the Phasor collection of blocks.
1-30
2
Advanced Components
and Techniques
This chapter introduces methods and devices that enhance your power system simulations and make
them more realistic.
The first two tutorials illustrate power electronics, simple motors, and Fourier analysis. The third
tutorial demonstrates three-phase power systems, electrical machinery, load flow, and use of the
phasor solution method for transient stability studies of electromechanical systems. The fourth
explains how you can create and customize your own nonlinear blocks.
Introducing Power Electronics
(p. 2-2)
Use power electronics and transformers and vary circuit
initial conditions
Simulating Motor Drives (p. 2-11)
Model and discretize simple motors with specialized blocks.
Use the FFT tool of Powergui to perform harmonic analysis
Three-Phase Systems and Machines Use electrical machines and three-phase components
(p. 2-24)
Apply the phasor solution method to study of
electromechanical oscillations of power systems
Building and Customizing
Nonlinear Models (p. 2-40)
Model nonlinear systems and create your own blocks to
represent them
2
Advanced Components and Techniques
Introducing Power Electronics
In this section you
• Learn how to use power electronics components
• Learn how to use transformers
• Change initial conditions of a circuit
SimPowerSystems is designed to simulate power electronic devices. This
section uses a simple circuit based on thyristors as the main example.
Consider the circuit shown below. It represents one phase of a static var
compensator (SVC) used on a 735 kV transmission network. On the secondary
of the 735 kV /16 kV transformer, two variable susceptance branches are
connected in parallel: one thyristor-controlled reactor (TCR) branch and one
thyristor-switched capacitor (TSC) branch.
2-2
Introducing Power Electronics
2.7 Ω 71.65 mH
735kV ⁄
3
16 kV
70.5 mΩ
1.5 mΩ
18.7 mH
1.13 mH
424.4 kV rms
0 degrees
60 Hz
308.4 µF
Transformer parameters:
TCR
branch
TSC
branch
Nominal power 110 MVA
Primary: Rated voltage 424.4 kV
RMS; leakage reactance = 0.15 p.u.;
resistance = 0.002 p.u.
Secondary: Rated voltage 16 kV
RMS; leakage reactance = 0 p.u.;
resistance = 0.002 p.u.
Thyristor parameters:
Ron = 1 mΩ; Vf = 14*0.8 V (14
thyristors in series)
Snubber: Rs = 500W Cs = 0.15
µF
Magnetizing current at 1 p.u.
voltage: Inductive: 0.2% Resistive:
0.2%
Figure 2-1: One Phase of a TCR/TSC Static Var Compensator
The TCR and TSC branches are both controlled by a valve consisting of two
thyristor strings connected in antiparallel. An RC snubber circuit is connected
across each valve. The TSC branch is switched on/off, thus providing discrete
step variation of the SVC capacitive current. The TCR branch is phase
2-3
2
Advanced Components and Techniques
controlled in order to obtain a continuous variation of the net SVC reactive
current.
Now build two circuits illustrating the operation of the TCR and the TSC
branches.
Simulation of the TCR Branch
1 Open a new window and save it as circuit3.
2 Open the Power Electronics library and copy the Thyristor block into your
circuit3 model.
3 Open the Thyristor menu and set the parameters as follows:
Ron
1e-3
Lon
0
Vf
14*0.8
Rs
500
Cs
0.15e-6
Notice that the snubber circuit is integral to the Thyristor dialog box.
4 Rename this block Th1 and duplicate it.
5 Connect this new thyristor Th2 in antiparallel with Th1, as shown in Figure
2-2.
As the snubber circuit has already been specified with Th1, the snubber of
Th2 must be eliminated.
6 Open the Th2 dialog box and set the snubber parameters to
Rs
Inf
Cs
0
Notice that the snubber disappears on the Th2 icon.
2-4
Introducing Power Electronics
The linear transformer is located in the Elements library. Copy it, rename it to
TrA, and open its dialog box. Set its nominal power, frequency, and winding
parameters (winding 1 = primary; winding 2 = secondary) as shown in
Figure 2-1.
Note that the leakage reactance and resistance of each winding have to be
specified directly in per unit quantities. As there is no tertiary winding,
deselect Three windings transformer. Notice that winding 3 disappears on
the TrA block.
Finally, set the magnetizing branch parameters Rm and Xm at [500, 500].
These values correspond to 0.2% resistive and inductive currents.
Add a voltage source, series RL elements, and a Ground block. Set the
parameters as shown in Figure 2-1. Add a current measurement to measure
the primary current. Interconnect the circuit as shown in Figure 2-2.
Notice that the Thyristor blocks have an output identified by the letter m. This
output returns a Simulink vectorized signal containing the thyristor current
(Iak) and voltage (Vak). Connect a Demux block with two outputs at the m
output of Th1. Then connect the two demultiplexer outputs to a dual trace
scope that you rename Scope_Th1. (To create a second input to your scope, in
the Scope properties —> General menu item, set the number of axes to 2.)
Label the two connection lines Ith1 and Vth1. These labels are automatically
displayed on the top of each trace.
2-5
2
Advanced Components and Techniques
Figure 2-2: Simulation of the TCR Branch
You can now model the synchronized pulse generators firing thyristors Th1
and Th2. Copy two Simulink pulse generators into your system, name them
Pulse1 and Pulse2, and connect them to the gates of Th1 and Th2.
Now you have to define the timing of the Th1 and Th2 pulses. At every cycle a
pulse has to be sent to each thyristor α degrees after the zero crossing of the
thyristor commutation voltage. Set the Pulse1 and Pulse2 parameters as
follows:
Amplitude
1
Period
1/60 s
Pulse width (% of period)
1% (3.6 degrees pulses)
Phase Delay
1/60+T for Pulse1
1/60+1/120+T for Pulse2
The pulses sent to Th2 are delayed by 180 degrees with respect to pulses sent
to Th1. The delay T is used to specify the firing angle α. In order to get a 120
degree firing angle, specify T in the workspace by entering
2-6
Introducing Power Electronics
T = 1/60/3;
Now open the Simulation —> Simulation parameters dialog. Select the
ode23tb integration algorithm. Keep the default parameters but set the
relative tolerance to 1e-4 and the stop time to 0.1. Start the simulation. The
results are shown in Figure 2-3.
Note You could also choose to discretize your system. Try for example 50 µs
sample time. The simulation results should compare well with the continuous
system.
Figure 2-3: TCR Simulation Results
2-7
2
Advanced Components and Techniques
Simulation of the TSC Branch
You can now modify your circuit3 system and change the TCR branch to a
TSC branch. Save circuit3 as a new system and name it circuit4.
Connect a capacitor in series with the RL inductor and Th1/Th2 valve as shown
in Figure 2-4. Change the R, L, and C parameters as shown in Figure 2-1.
Connect a voltmeter and scope to monitor the voltage across the capacitor.
Contrary to the TCR branch, which was fired by a synchronous pulse
generator, a continuous firing signal is now applied to the two thyristors.
Delete the two pulse generators. Copy a Step block from the Simulink library
and connect its output at both gates of Th1 and Th2. Set its step time at 1/60/4
(energizing at the first positive peak of the source voltage). Your circuit should
now be similar to the one shown here.
Figure 2-4: Simulation of the TSC Branch
Open the three scopes and start the simulation.
As the capacitor is energized from zero, you can observe a low damping
transient at 200 Hz, superimposed with the 60 Hz component in the capacitor
2-8
Introducing Power Electronics
voltage and primary current. During normal TSC operation, the capacitor has
an initial voltage left since the last valve opening. In order to minimize the
closing transient with a charged capacitor, the thyristors of the TSC branch
must be fired when the source voltage is at maximum value and with the
correct polarity. The initial capacitor voltage corresponds to the steady-state
voltage obtained when the thyristor switch is closed. The capacitor voltage is
17.67 kVrms when the valve is conducting. At the closing time, the capacitor
must be charged at the peak voltage.
Uc = 17670 × 2 = 24989 V
You can now use the Powergui block to change the capacitor initial voltage.
Open the Powergui and select Initial States Setting. A list of all the state
variables with their default initial values appears. The value of the initial
voltage across the capacitor C (variable Uc_C) should be −0.3141 V. This voltage
is not exactly zero because the snubber allows circulation of a small current
when both thyristors are blocked. Now select the Uc_C state variable and enter
24989 in the upper right field. Then click the Apply button in order to make
this change effective.
Start the simulation. As expected the transient component of capacitor voltage
and current has disappeared. The voltages obtained with and without initial
voltage are compared in this plot.
2-9
2
Advanced Components and Techniques
Capacitor precharged (Uc0 = 24989 V)
5
Initial conditions calculated by power_analyze (Uc0 = −0.31 V)
x 10 4
4
3
2
1
0
-1
-2
-3
-4
-5
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05
Figure 2-5: Transient Capacitor Voltage With and Without Initial Charge
2-10
Simulating Motor Drives
Simulating Motor Drives
In this section you
• Use electrical machines and power electronics to simulate a simple motor
drive
• Learn how to use the Universal Bridge block
• Discretize your model and compare variable-step and fixed-step simulation
methods
• Learn how to use the Multimeter block
• Learn how to use the FFT tool
Variable speed control of AC electrical machines makes use of
forced-commutated electronic switches such as IGBTs, MOSFETs, and GTOs.
Asynchronous machines fed by pulse width modulation (PWM) voltage sourced
converters (VSC) are nowadays gradually replacing the DC motors and
thyristor bridges. With PWM, combined with modern control techniques such
as field-oriented control or direct torque control, you can obtain the same
flexibility in speed and torque control as with DC machines. This section shows
how to build a simple open loop DC drive controlling an asynchronous machine.
A more elaborate example of a PWM drive is presented in Chapter 3, “Case
Studies.” The SimPowerSystems circuit to simulate is shown in Figure 2-6. It
uses blocks from the Machines and Power Electronics libraries.
The Machines library contains four of the most commonly used three-phase
machines: simplified and complete synchronous machines, asynchronous
machine, and permanent magnet synchronous machine. Each machine can be
used either in generator or motor mode. Combined with linear and nonlinear
elements such as transformers, lines, loads, breakers, etc., they can be used to
simulate electromechanical transients in an electrical network. They can also
be combined with power electronic devices to simulate drives.
The Power Electronics library contains blocks allowing you to simulate diodes,
thyristors, GTO thyristors, MOSFETs, and IGBT devices. You could
interconnect several blocks together to build a three-phase bridge. For
example, an IGBT inverter bridge would require six IGBTs and six antiparallel
diodes.
In order to facilitate implementation of bridges, the Universal Bridge block
automatically performs these interconnections for you.
2-11
2
Advanced Components and Techniques
Figure 2-6: Circuit 5: PWM Control of an Induction Motor
Building and Simulating the PWM Motor Drive
Follow these steps to build a PWM-controlled motor.
Assembling and Configuring the Motor Blocks
In the first steps, you copy and set up the motor blocks.
1 Open a new window and save it as circuit5.
2 Open the Power Electronics library and copy the Universal Bridge block into
your circuit5 model.
2-12
Simulating Motor Drives
3 Open the Universal Bridge dialog and set its parameters as follows:
Power electronic device
IGBT/Diodes
Snubber
Rs
1e5 Ω
Cs
inf
Ron
1e-3 Ω
Forward voltages
Vf
0V
Vfd
0 V
Tf
1e-6 s
Tt
1e-6 s
Tail
Notice that the snubber circuit is integral to the Universal Bridge dialog box.
As the Cs capacitor value of the snubber is set to Inf (short-circuit), we are
using a purely resistive snubber. Generally, IGBT bridges do not use
snubbers; however, because each nonlinear element in SimPowerSystems is
modeled as a current source, you have to provide a parallel path across each
IGBT in order to allow connection to an inductive circuit (stator of the
asynchronous machine). The high resistance value of the snubber does not
affect the circuit performance.
4 Open the Machines library. Copy the Asynchronous Machine SI Units block
as well as the Machine Measurement Demux block into your circuit5
model.
5 Open the Asynchronous Machine menu and look at its parameters. They are
set for a 3 HP, 60 Hz machine with two pairs of poles. Its nominal speed is
therefore slightly lower than the synchronous speed of 1800 rpm, or ws=
188.5 rad/s.
6 Notice that the three rotor terminals a, b, and c are made accessible. During
normal motor operation these terminals should be short-circuited together.
2-13
2
Advanced Components and Techniques
In the Asynchronous Machine menu change the rotor type to Squirrel cage.
Notice that after this change the rotor connections are no longer accessible.
7 Open the Machine Measurement Demux block menu. When this block is
connected to a machine measurement output, it allows you to access specific
internal signals of the machine. First select the Asynchronous machine
type. Deselect all signals except the following three signals: is_abc (three
stator currents), wm (rotor speed), and Te (electromagnetic torque).
Loading and Driving the Motor
You now implement the torque-speed characteristic of the motor load. Assume
a quadratic torque-speed characteristic (fan or pump type load). The torque T
is then proportional to the square of the speed ω.
T = k×ω
2
The nominal torque of the motor is
3 × 746
T n = ------------------- = 11.87Nm
188.5
Therefore, the constant k should be
T
–4
11.87
k = ------n- = ----------------- = 3.34 × 10
2
2
188.5
ωs
1 Open the Math Operations library of Simulink and copy the Math Function
block into your circuit5 model. Open the block menu and enter the
expression of torque as a function of speed: 3.34e-4*u^2.
2 Connect the input of the Math Function block to the speed output of the
Machines Measurement Demux block, labeled wm, and its output to the
torque input of the motor, labeled Tm.
3 Open the Electrical Sources library and copy the DC Voltage Source block
into your circuit5 model. Open the block menu and set the voltage to 400 V.
2-14
Simulating Motor Drives
4 Open the Measurements library and copy a Voltage Measurement block into
your circuit5 model. Change the block name to Vab.
5 Using Ground blocks from the Elements library, complete the power
elements and voltage sensor interconnections as shown in Figure 2-6.
Controlling the Inverter Bridge with a Pulse Generator
In order to control your inverter bridge, you need a pulse generator. Such a
generator is available in the Extras library of powerlib.
1 Open the Extras/Discrete Control blocks library and copy the Discrete
3-Phase PWM Generator block into your circuit5 model. This block can be
used to generate pulses for a two-level or a three-level bridge. In addition the
block generates two sets of pulses (outputs P1 and P2) that can be sent to
two different three-arm bridges when the converter uses a twin bridge
configuration. In this case, use it as a two-level single-bridge PWM
generator. The converter operates in an open loop, and the three PWM
modulating signals are generated internally. Connect the P1 output to the
pulses input of the Universal Bridge block
2 Open the Discrete Three-Phase PWM Generator block dialog and set the
parameters as follows.
Type
2 level
Mode of operation
Un-synchronized
Carrier frequency
18*60Hz (1080 Hz)
Internal generation of modulating Selected
signals
Modulation index m
0.9
Output voltage frequency
60 Hz
Output voltage phase
0 degrees
Sample time
10e-6 s
3 Use the Edit —> Look Under Mask menu item of your model window to see
how the PWM is implemented. This control system is made entirely with
Simulink blocks. The block has been discretized so that the pulses change at
2-15
2
Advanced Components and Techniques
multiples of the specified time step. A time step of 10 µs corresponds to +/−
0.54% of the switching period at 1080 Hz.
One common method of generating the PWM pulses uses comparison of the
output voltage to synthesize (60 Hz in this case) with a triangular wave at
the switching frequency (1080 Hz in this case). This is the method that is
implemented in the Discrete 3-Phase PWM Pulse Generator block. The
line-to-line RMS output voltage is a function of the DC input voltage and of
the modulation index m as given by the following equation:
m
3
V LLrms = ----- × ------- Vdc = m × 0.612 × VDC
2
2
Therefore, a DC voltage of 400 V and a modulation factor of 0.90 yield the
220 Vrms output line-to-line voltage, which is the nominal voltage of the
asynchronous motor.
Displaying Signals and Measuring Fundamental Voltage and Current
1 You now add blocks measuring the fundamental component (60 Hz)
embedded in the chopped Vab voltage and in the phase A current. Open the
Extras/Discrete Measurements library of powerlib and copy the Discrete
Fourier block into your circuit5 model.
Open the Discrete Fourier block dialog and check that the parameters are
set as follows:
Fundamental frequency f1
60 Hz
Harmonic number
1
Initial input
[0 0]
Sample time
10e-6 s
Connect this block to the output of the Vab voltage sensor.
2-16
Simulating Motor Drives
2 Duplicate the Discrete Fourier block. In order to measure the phase A
current, you need to select the first element of the is_abc output of the ASM
Measurement Demux block.
Copy a Selector block from the Signals & Systems library of Simulink.
Open its menu and set Element to 1. Connect the Selector output to the
second Discrete Fourier block and its input to the is_abc output of the
Machines Measurement Demux block as shown in Figure 2-6.
3 Finally, add scopes to your model. Copy one Scope block into your circuit.
This scope is used to display the instantaneous motor voltage, currents,
speed, and electromagnetic torque. In the Scope Properties —> General
menu of the scope, set the following parameters:
Number of axes
4
Time range
0.05 s
Tick labels
bottom axis only
Connect the four inputs and label the four connection lines as shown in
Figure 2-6. When you start the simulation, these labels are displayed on top
of each trace.
In order to allow further processing of the signals displayed on the
oscilloscope, you have to store them in a variable. In the Scope
Parameters/Data history menu of the scope, set the following parameters:
Limit data point to last
deselected
Save data to workspace
selected
variable name
ASM
Format
Structure with time
After simulation, the four signals displayed on the scope are available in a
structure array named ASM.
4 Duplicate the four-input Scope and change its number of inputs to 2. This
scope is used to display the fundamental component of Vab voltage and Ia
2-17
2
Advanced Components and Techniques
current. Connect the two inputs to the outputs of the Fourier blocks. Label
the two connection lines as shown in Figure 2-6.
You are now ready to simulate the motor starting.
Simulating the PWM Motor Drive with Continuous Integration Algorithm
Open the Simulation —> Simulation parameters menu. Select the ode23tb
integration algorithm. Set the relative tolerance to 1e-4, the absolute tolerance
and the Max step size to auto, and the stop time to 1 s. Start the simulation.
The simulation results are shown in Figure 2-7.
The motor starts and reaches its steady-state speed of 181 rad/s (1728 rpm)
after 0.5 s. At starting, the magnitude of the 60 Hz current reaches 90 A peak
(64 A RMS) whereas its steady-state value is 10.5 A (7.4 A RMS). As expected,
the magnitude of the 60 Hz voltage contained in the chopped wave stays at
220 × 2 = 311V
Also notice strong oscillations of the electromagnetic torque at starting. If you
zoom in on the torque in steady state, you should observe a noisy signal with a
mean value of 11.9 N.m, corresponding to the load torque at nominal speed.
If you zoom in on the three motor currents, you can see that all the harmonics
(multiples of the 1080 Hz switching frequency) are filtered by the stator
inductance, so that the 60 Hz component is dominant.
2-18
Simulating Motor Drives
.
Figure 2-7: PWM Motor Drive; Simulation Results for Motor Starting at Full
Voltage
Using the Multimeter Block
The Universal Bridge block is not a conventional subsystem where all the six
individual switches are accessible. If you want to measure the switch voltages
and currents, you must use the Multimeter block, which gives access to the
bridge internal signals.
1 Open the Universal Bridge dialog and set the Measurement parameter to
Device currents.
2-19
2
Advanced Components and Techniques
2 Copy the Multimeter block from the Measurements library into your
circuit5 circuit. Double-click the Multimeter block. A window showing the
six switch currents appears.
3 Select the two currents of the bridge arm connected to phase A. They are
identified as
iSw1
Universal Bridge
iSw2
Universal Bridge
4 Click OK. The number of signals (2) is displayed in the multimeter icon.
5 Using a Demux block, send the two multimeter output signals to a two-trace
scope and label the two connection lines (Trace 1: iSw1 Trace 2: iSw2).
6 Restart the simulation. The waveforms obtained for the first 20 ms are
shown in this plot.
150
iSw1 (A)
100
50
0
−50
−100
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0.02
0.018
0.02
Diode1 IGBT2
IGBT1 Diode2
100
iSw2 (A)
50
0
−50
−100
−150
0
0.002
0.004
0.006
0.008
0.01
Time (s)
0.012
0.014
0.016
Figure 2-8: Currents in IGBT/Diode Switches 1 and 2
2-20
Simulating Motor Drives
As expected, the currents in switches 1 and 2 are complementary. A positive
current indicates a current flowing in the IGBT, whereas a negative current
indicates a current in the antiparallel diode.
Note Multimeter block use is not limited to the Universal Bridge block. All
the elements of the Electrical Sources and Elements libraries have a
Measurement parameter where you can select voltages, currents, and
saturable transformer fluxes. A judicious use of the Multimeter block reduces
the number of current and voltage sensors in your circuit, making it easier to
follow.
Discretizing the PWM Motor Drive
You might have noticed that the simulation using a variable-step integration
algorithm is relatively long. Depending on your computer, it might take some
minutes to simulate one second. In order to shorten the simulation time, you
can discretize your circuit and simulate at fixed simulation time steps.
Open the Powergui and select Discretize electrical model. Set the Sample
Time to 10e-6 s. When you restart the simulation, the power system,
including the asynchronous machine, is discretized at a 10 µs sample time.
As there are no more continuous states in the electrical system, you do not need
a variable-step integration method to solve this system. In the Simulation —>
Simulation parameters —> Solver dialog pane, select the Fixed-step and
discrete (no continuous states) options.
Start the simulation. Observe that the simulation is now approximately three
times faster than with the continuous system. Results compare well with the
continuous system.
Performing Harmonic Analysis Using the FFT Tool
The two Discrete Fourier blocks allow computation of the fundamental
component of voltage and current while simulation is running. If you would
like to observe harmonic components also you would need a Discrete Fourier
block for each harmonic. This approach is not convenient.
2-21
2
Advanced Components and Techniques
Now use the FFT tool of Powergui to display the frequency spectrum of voltage
and current waveforms. These signals are stored in your workspace in the ASM
structure array.
Open Powergui and select FFT Analysis. A new window opens. Set the
parameters specifying the analyzed signal, the time window, and the frequency
range as follows:
Structure
ASM
Input
Vab
Signal number
1
Start time
0.7 s
Number of cycles
2
(pull-down menu)
Display FFT window
Fundamental frequency
60 Hz
Max Frequency
5000 Hz
Frequency axis
Harmonic order
Display style
Bar (relative to Fund or DC)
The analyzed signal is displayed in the upper window. Click Display. The
frequency spectrum is displayed in the bottom window. See Figure 2-9.
2-22
Simulating Motor Drives
Figure 2-9: FFT Analysis of the Motor Line-to-Line Voltage
The fundamental component and total harmonic distortion (THD) of the Vab
voltage are displayed above the spectrum window. The magnitude of the
fundamental of the inverter voltage (312 V) compares well with the theoretical
value (311 V for m=0.9).
Harmonics are displayed in percent of the fundamental component. As
expected, harmonics occur around multiples of carrier frequency (n*18 +− k).
Highest harmonics (30%) appear at 16th harmonic (18 − 2) and 20th harmonic
(18 + 2). Note that the THD value (69%) has been computed for the specified 0
to 5000 Hz frequency range. If you recompute the FFT with a maximum
frequency range of 10000 Hz, you should see the THD increasing to 74% (5%
contribution in THD for the 5000 to 10000 Hz frequencies).
Finally, select input Ia instead of Vab and display its current spectrum.
2-23
2
Advanced Components and Techniques
Three-Phase Systems and Machines
In this section you
• Learn how to simulate a three-phase power system containing electrical
machines and other three-phase models
• Perform a load flow study and initialize machines to start simulation in
steady state by using the Load Flow and Machine Initialization option of
the Powergui
• Simulate the power system and observe its dynamic performance by using
both the standard solution technique using a continuous solver and the
Phasor Solution method
You now use three types of machines of the Electrical Machines library:
simplified synchronous machine, detailed synchronous machine, and
asynchronous machine. You interconnect these machines with linear and
nonlinear elements such as transformers, loads, and breakers to study the
transient stability of an uninterruptible power supply using a diesel generator.
Three-Phase Network with Electrical Machines
The two-machine system shown in this single line diagram is this section’s
main example:
25.0 kV t = 0.2 s
2.4 kV
ASM
1000 MVA
Q = 10
B1
5 MW
Fault t = 0.1 s
25/2.4 kV
Y/D 6 MVA
Diesel
B2
500 kvar
1 MW
Asynchronous
Motor
2250 HP
SM
Synchronous
Generator
3.125 MVA
Figure 2-10: Diesel Generator and Asynchronous Motor on Distribution
Network
2-24
Three-Phase Systems and Machines
This system consists of a plant (bus B2), simulated by a 1 MW resistive load
and a motor load (ASM) fed at 2400 V from a distribution 25 kV network
through a 6 MVA, 25/2.4 kV transformer, and from an emergency synchronous
generator/diesel engine unit (SM).
The 25 kV network is modeled by a simple R-L equivalent source (short-circuit
level 1000 MVA, quality factor X/R = 10) and a 5 MW load. The asynchronous
motor is rated 2250 HP, 2.4 kV, and the synchronous machine is rated 3.125
MVA, 2.4 kV.
Initially, the motor develops a mechanical power of 2000 HP and the diesel
generator is in standby, delivering no active power. The synchronous machine
therefore operates as a synchronous condenser generating only the reactive
power required to regulate the 2400 V bus B2 voltage at 1.0 p.u. At t = 0.1 s, a
three-phase to ground fault occurs on the 25 kV system, causing the opening of
the 25 kV circuit breaker at t = 0.2 s, and a sudden increase of the generator
loading. During the transient period following the fault and islanding of the
motor-generator system, the synchronous machine excitation system and the
diesel speed governor react to maintain the voltage and speed at a constant
value.
This system is modeled in a SimPowerSystems demo. Open the Demos library
of powerlib and double-click the demo called “Three-Phase Machines and Load
Flow.” A system named power_machines opens.
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Advanced Components and Techniques
Figure 2-11: Power System of Figure 2-10 Built with SimPowerSystems
The Synchronous Machine (SM) block uses standard parameters, whereas the
Asynchronous Machine (ASM) block uses S.I. parameters.
The other three-phase elements such as the inductive voltage source, the
Y grounded/Delta transformer, and the loads are standard blocks from the
Electrical Source and Elements libraries of powerlib. If you open the dialog
box of the Three-Phase Fault and Three-Phase Breaker blocks, you see how the
switching times are specified. The Machine Measurement Demux block
provided in the Machines library is used to demux the output signals of the SM
and ASM machines.
The SM voltage and speed outputs are used as feedback inputs to a Simulink
control system that contains the diesel engine and governor block as well as an
excitation block. The excitation system is the standard block provided in the
Machines library. The SM parameters as well as the diesel engine and
governor models were taken from reference [1].
2-26
Three-Phase Systems and Machines
1
wref (p.u.)
2
w (p.u.)
0.2s+1
0.0002s2+0.01s+1
CONTROL SYSTEM
K
0.25s+1
0.009s+1
1
0.0384s+1
TF1
TF2
ACTUATOR
Torque
1
s
Integrator
Td
ENGINE
1
Pmec (p.u.)
Note: The engine inertia is combined with the generator inertia
Figure 2-12: Diesel Engine and Governor System
If you simulate this system for the first time, you normally do not know what
the initial conditions are for the SM and ASM to start in steady state.
These initial conditions are
• SM block: Initial values of speed deviation (usually 0%), rotor angle,
magnitudes and phases of currents in stator windings, and initial field
voltage required to obtain the desired terminal voltage under the specified
load flow
• ASM block: Initial values of slip, rotor angle, magnitudes and phases of
currents in stator windings
Open the dialog box of the Synchronous Machine and Asynchronous Machine
blocks. All initial conditions should be set at 0, except for the initial SM field
voltage and ASM slip, which are set at 1 p.u. Open the three scopes
monitoring the SM and ASM signals as well as the bus B2 voltage. Start the
simulation and observe the first 100 ms before fault is applied.
As the simulation starts, note that the three ASM currents start from zero and
contain a slowly decaying DC component. The machine speeds take a much
longer time to stabilize because of the inertia of the motor/load and
diesel/generator systems. In our example, the ASM even starts to rotate in the
wrong direction because the motor starting torque is lower than the applied
load torque. Stop the simulation.
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Advanced Components and Techniques
Load Flow and Machine Initialization
In order to start the simulation in steady state with sinusoidal currents and
constant speeds, all the machine states must be initialized properly. This is a
difficult task to perform manually, even for a simple system. In the next section
you learn how to use the Load Flow and Machine Initialization option of the
Powergui to perform a load flow and initialize the machines.
Double-click the Powergui. In the Tools menu, click the Load Flow and
Machine Initialization button. A new window appears. In the upper right
window you have a list of the machines appearing in your system. Select the
SM 3.125 MVA machine. Note that for the Bus Type, you have a menu
allowing you to choose either PV Generator, PQ Generator, or Swing
Generator.
For synchronous machines you normally specify the desired terminal voltage
and the active power that you want to generate (positive power for generator
mode) or absorb (negative power for motor mode). This is possible as long as
you have a swing (or slack) bus that generates or absorbs the excess power
required to balance the active powers throughout the network.
The swing bus can be either a voltage source or any other synchronous
machine. If you do not have any voltage source in your system, you must
declare one of the machines as a swing machine. In the next section, you
perform a load flow with the 25 kV voltage source connected to bus B1, which
is used as a swing bus.
Load Flow Without a Swing Machine
In the Load Flow window, your SM Bus Type should already be initialized as
P & V generator, indicating that the load flow is performed with the machine
controlling its active power and terminal voltage. By default, the desired
Terminal Voltage UAB is initialized at the nominal machine voltage (2400
Vrms). Keep it unchanged and set the Active Power to zero. The synchronous
machine therefore absorbs or generates reactive power only in order to keep
terminal voltage at 1 p.u. Now select the ASM 2250 HP machine in the upper
right window. The only parameter that is needed is the Mechanical power
developed by the motor. Enter 2000*746 (2000 HP). You now perform the load
flow with the following parameters.
SM
Terminal Voltage
2-28
2400 Vrms
Three-Phase Systems and Machines
Active Power
0 kW
Mechanical Power
2000*746 W (2000 HP)
ASM
Click the Update Load Flow button. Once the load flow is solved, the three
phasors of line-to-line machine voltages as well as currents are updated as
shown on the next figure. Values are displayed both in SI units (volts RMS or
amperes RMS) and in p.u.
The SM active and reactive powers, mechanical power, and field voltage are
displayed.
P
0 W
Q
856 kvar or 856/3125=0.2739 p.u.
2-29
2
Advanced Components and Techniques
Pmec
844.2 W or 0.00027 p.u., representing
internal machine losses in stator windings
Ef (field voltage)
1.427 p.u.
The ASM active and reactive powers absorbed by the motor, slip, and torque
are also displayed.
P
1.515 MW (0.9024 p.u.)
Q
615 kvar (0.3662 p.u.)
Pmec
1.492 MW (2000 HP)
Slip
0.006119
Torque
7964 N.m (0.8944 p.u.)
Close the Load Flow window.
The ASM torque value (7964 N.m) should already be entered in the Constant
block connected at the ASM torque input. If you now open the SM and ASM
dialog boxes you can see the updated initial conditions. If you open the
Powergui, you can see updated values of the measurement outputs. You can
also click the Nonlinear button to obtain voltages and currents of the
nonlinear blocks. For example, you should find that the magnitude of the Phase
A voltage across the fault breaker (named Uc_3-Phase Fault/Breaker1) is
14.42 kV RMS, corresponding to a 24.98 kV RMS phase-to-phase voltage.
In order to start the simulation in steady state, the states of the Governor &
Diesel Engine and the Excitation blocks should also be initialized according to
the values calculated by the load flow. Open the Governor & Diesel Engine
subsystem, which is inside the Diesel Engine Speed and Voltage Control
subsystem. Notice that the initial mechanical power has been automatically set
to 0.0002701 p.u. Open the Excitation block and notice that the initial
terminal voltage and field voltage have been set respectively to 1.0 and 1.427
p.u.
Note that the load flow also initializes the Constant blocks connected at the
reference inputs (wref and vref) of the Governor and Excitation blocks as well
as the Constant block connected at the load torque input (Tm) of the
Asynchronous Machine block.
2-30
Three-Phase Systems and Machines
Open the three scopes displaying the internal signals of synchronous and
asynchronous machines and phase A voltage. Start the simulation. The
simulation results are shown in the following figure.
Figure 2-13: Simulation Results
Observe that during the fault, the terminal voltage drops to about 0.2 p.u., and
the excitation voltage hits the limit of 6 p.u. After fault clearing and islanding,
the SM mechanical power quickly increases from its initial value of 0 p.u. to 1
p.u. and stabilizes at the final value of 0.82 p.u. required by the resistive and
motor load (1.0 MW resistive load + 1.51 MW motor load = 2.51 MW =
2.51/3.125 = 0.80 p.u.). After 3 seconds the terminal voltage stabilizes close to
2-31
2
Advanced Components and Techniques
its reference value of 1.0 p.u. The motor speed temporarily decreases from 1789
rpm to 1635 rpm, then recovers close to its normal value after 2 seconds.
If you increase the fault duration to 12 cycles by changing the breaker opening
time to 0.3 s, notice that the system collapses. The ASM speed slows down to
zero after 2 seconds.
Load Flow With a Swing Machine
In this section you make a load flow with two synchronous machine types: a PV
generator and a swing generator. In your power_machines window, delete the
inductive source and replace it with the Simplified Synchronous Machine block
in p.u. that you find in the Machines library. Rename it SSM 1000MVA and
save this new system in your working directory as power_machines2.mdl.
Open the SSM 1000 MVA dialog box and enter the following parameters.
Connection type
3-wire Y
Pn(VA), Vn(Vrms), fn(Hz)
[1000e6 25e3 60]
H(s), Kd(), p ()
[inf 0 2]
R(p.u.), X(p.u.)
[0.1 1.0]
Init. cond.
Leave all initial conditions at zero.
As you specify an infinite inertia, the speed and therefore the frequency of the
machine are kept constant. Notice how easily you can specify an inductive
short-circuit level of 1000 MVA and a quality factor of 10 with the per unit
system.
Also, connect at inputs 1 and 2 of the SSM block two Constant blocks specifying
respectively the required mechanical power (Pmec) and its internal voltage (E).
These two constants are updated automatically according to the load flow
solution.
When there is no voltage source imposing a reference angle for voltages, you
must choose one of the synchronous machines as a reference. In a load flow
program, this reference is called the swing bus. The swing bus absorbs or
generates the power needed to balance the active power generated by the other
machines and the power dissipated in loads as well as losses in all elements.
2-32
Three-Phase Systems and Machines
Open the Powergui. In the Tools menu, select Load Flow and Machine
Initialization. Change the SSM Bus Type to Swing Generator. Specify the
load flow by entering the following parameters for the SM and ASM machines:
SM 1000 MVA:
Terminal Voltage UAB
2400 Vrms
Active Power
0 W
ASM 2250 HP:
Mechanical power
1.492e+06 W (2000 HP)
For the SSM swing machine you only have to specify the requested terminal
voltage (magnitude and phase). The active power is unknown. However, you
can specify an active power that is used as an initial guess and help load flow
convergence. Respecify the following SSM parameters:
Terminal Voltage
24984 Vrms
(this voltage obtained at bus B1 from the
previous load flow)
Phase of UAN voltage
0 degrees
Active Power guess
7.5e6 W
(estimated power = 6 MW (resistive load) + 1.5
MW motor load)
Click the Update Load Flow button. Once the load flow is solved the following
solution is displayed. Use the scroll bar of the left window to look at the solution
for each of the three machines.
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Advanced Components and Techniques
The active and reactive electrical powers, mechanical power, and internal
voltage are displayed for the SSM block.
P=7.542 MW; Q=-147 kvar;
Pmec=7.547 MW (or 7.547/1000=0.007547 p.u.);
Internal voltage E=1.0 p.u.
The active and reactive electrical powers, mechanical power, and field voltage
of the SM block are
P=0 W; Q=856 kvar;
Pmec=844 W; Vf=1.428 p.u.
The active and reactive powers absorbed by the motor, slip, and torque of the
ASM block are also displayed.
P=1.515MW; Q=615 kvar; Pmec=1.492 MW (2000 HP)
Slip=0.006119; Torque=7964 N.m
2-34
Three-Phase Systems and Machines
As expected, the solution obtained is exactly the same as the one obtained with
the R-L voltage source. The active power delivered by the swing bus is 7.54 MW
(6.0 MW resistive load + 1.51 MW motor load = 7.51 MW, the difference (0.03
MW) corresponding to losses in the transformer).
Restart the simulation. You should get the same waveforms as those of Figure
2-13.
Reference
[1] Yeager, K.E., and J.R.Willis, “Modeling of Emergency Diesel Generators in
an 800 Megawatt Nuclear Power Plant,” IEEE Transactions on Energy
Conversion, Vol. 8, No. 3, September, 1993.
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2
Advanced Components and Techniques
Using the Phasor Solution Method for Stability
Studies
Up to now, you have simulated a relatively simple power system consisting of
a maximum of three machines. If you increase complexity of your network by
adding extra lines, loads, transformers, and machines, the required simulation
time becomes longer and longer. Moreover, if you are interested in slow
electromechanical oscillation modes (typically between 0.02 Hz and 2 Hz on
large systems) you might have to simulate for several tens of seconds, implying
simulation times of minutes and even hours. The conventional continuous or
discrete solution method is therefore not practical for stability studies
involving low-frequency oscillation modes. In order to allow such studies, you
have to use the phasor technique (see “Introducing the Phasor Simulation
Method” on page 1-26).
For a stability study, we are not interested in the fast oscillation modes
resulting from the interaction of linear R, L, C elements and distributed
parameter lines. These oscillation modes, which are usually located above the
fundamental frequency of 50 Hz or 60 Hz, do not interfere with the slow
machine modes and regulator time constants. In the phasor solution method,
these fast modes are ignored by replacing the network’s differential equations
by a set of algebraic equations. The state-space model of the network is
therefore replaced by a transfer function evaluated at the fundamental
frequency and relating inputs (current injected by machines into the network)
and outputs (voltages at machine terminals). The phasor solution method uses
a reduced state-space model consisting of slow states of machines, turbines,
and regulators, thus dramatically reducing the required simulation time.
Continuous variable-step solvers are very efficient in solving this type of
problem. Recommended solvers are ode15s or ode23tb with a maximum time
step of one cycle of the fundamental frequency (1/60 s or 1/50 s).
Now apply the phasor solution method to the two-machine system you have
just simulated with the conventional method. Open the power_machines demo.
Double-click the Powergui. Select the Phasor simulation option. You must
also specify the fundamental frequency used to solve the algebraic network
equations. A default value of 60 Hz should already be entered in the
Frequency menu. Close the Powergui and notice that Phasors appears on
thee Powergui icon, indicating that this new method can be used to simulate
your circuit. In order to start the simulation in steady state, you must first
repeat the load flow and machine initialization procedure explained in the
previous section, “Load Flow and Machine Initialization” on page 2-28.
2-36
Three-Phase Systems and Machines
In the Simulation Parameters dialog, specify a Max step size of 1/60 s (one
cycle) and start the simulation.
Observe that simulation is now much faster. The results compare well with
those obtained in the previous simulation. A comparison of synchronous
machine and asynchronous machine signals is shown in Figure 2-14.
2-37
2
Advanced Components and Techniques
Figure 2-14: Comparison of Results for Continuous and Phasor Simulation
Methods
The phasor solution method is illustrated on more complex networks presented
in the Demos library. These demos are identified as
• Transient stability of two machines with PSS and SVC
• Performance of three PSS for interarea oscillations
2-38
Three-Phase Systems and Machines
The first demo illustrates the impact of power system stabilizers (PSS) and use
of a static var compensator (SVC) to stabilize a two-machine system. The
second demo compares the performance of three different types of power
system stabilizers on a four-machine, two-area system.
2-39
2
Advanced Components and Techniques
Building and Customizing Nonlinear Models
SimPowerSystems provides a wide collection of nonlinear models. It can
happen, however, that you need to interface your own nonlinear model with the
standard models provided in the powerlib library. This model could be a
simple nonlinear resistance simulating an arc or a varistor, a saturable
inductor, a new type of motor, etc.
In the following section you learn how to build such a nonlinear model. A
simple saturable inductance and a nonlinear resistance serve as examples.
Modeling a Nonlinear Inductance
Consider an inductor of 2 henries designed to operate at a nominal voltage,
Vnom = 120 V RMS, and a nominal frequency, fnom = 60 Hz. From zero to 120
V RMS the inductor has a constant inductance, L = 2 H. When voltage exceeds
its nominal voltage, the inductor saturates and its inductance is reduced to
Lsat = 0.5 H. The nonlinear flux-current characteristic is plotted in the next
figure. Flux and current scales are in per units. The nominal voltage and
nominal current are chosen as base values for the per-unit system.
2-40
Building and Customizing Nonlinear Models
Flux (p.u.)
1.25
Lsat = 0.5 H
1.0
L = 2.0 H
−2.0
−1.0
1.0
2.0
Current (p.u.)
Vnom ⋅ 2
2π ⋅ fnom
120 ⋅ 2
2π ⋅ 60
Flux: 1pu = ----------------------------- = ---------------------- = 0.450 V ⋅ s
−1.0
−1.25
Vnom ⋅ 2
L ⋅ 2π ⋅ fnom
120 ⋅ 2
4π ⋅ 60
Current: 1pu = ----------------------------------- = ---------------------- = 0.225 A
Figure 2-15: Flux-Current Characteristic of the Nonlinear Inductance
The current i flowing in the inductor is a nonlinear function of flux linkage ψ
that, in turn, is a function of v appearing across its terminals. These relations
are given by the following equations:
di
v = L ⋅ ------ = dψ
-------dt
dt
or
ψ =
∫ v ⋅ dt
ψ
i = ------------L(ψ)
The model of the nonlinear inductance can therefore be implemented as a
controlled current source, where current i is a nonlinear function of voltage v,
as shown.
2-41
2
Advanced Components and Techniques
v
i
v
1
--s
integrator
ψ
i
i=f(ψ)
Figure 2-16: Model of a Nonlinear Inductance
Figure 2-17 shows a circuit using a 2 H nonlinear inductance. The nonlinear
inductance is connected in series with two voltage sources (an AC Voltage
Source block of 120 volts RMS, 60 Hz, and a DC Voltage Source block) and a 5
ohm resistor.
All the elements used to build the nonlinear model have been grouped in a
subsystem named Nonlinear Inductance. The inductor terminals are labeled In
and Out. Notice that a second output returning the flux has been added to the
subsystem. You can use this Simulink output to observe the flux by connecting
it to a Simulink Scope block.
The nonlinear model uses two powerlib blocks and two Simulink blocks. The
two powerlib blocks are a Voltage Measurement block to read the voltage at
the inductance terminals and a Controlled Current Source block. The direction
of the arrow of the current source is oriented from input to output according to
the model shown in Figure 2-16.
The two Simulink blocks are an Integrator block computing the flux from the
voltage input and a Look-Up Table block implementing the saturation
characteristic i = f(ψ) described by Figure 2-15.
2-42
Building and Customizing Nonlinear Models
Nonlinear Inductance subsystem
Figure 2-17: Implementation of a Nonlinear Inductance
Two Fourier blocks from the Measurements library of powerlib_extras are
used to analyze the fundamental component and the DC component of the
current.
Using blocks of the powerlib and Simulink libraries, build the circuit of Figure
2-17. To implement the i =f(ψ) relation, specify the following vectors in the
Look-Up Table block.
Vector of input
values (flux)
[-1.25
Vector of output
values (current)
[-2 -1 1 2]*(120*sqrt(2)/(4π*60))
-1
1 1.25 ] *(120*sqrt(2)/(2π*60))
Save your circuit as circuit7.
2-43
2
Advanced Components and Techniques
Set the following parameters for the two sources.
AC source
Peak amplitude
120*sqrt(2)
Phase
90 degrees
Frequency
60 Hz
DC source
Amplitude
0 V
Adjust the simulation time to 1.5 s and select the ode33tb integration
algorithm with default parameters. Start the simulation.
As expected, the current and the flux are sinusoidal. Their peak values
correspond to the nominal values.
120 ⋅ 2- = 0.225 A
Peak ⋅ Current = ------------------------2 ⋅ 2π ⋅ 60
⋅ 2- = 0.450 V⋅ s
Peak ⋅ Flux = 120
--------------------2π ⋅ 60
Current and flux waveforms are shown.
2-44
Building and Customizing Nonlinear Models
1
Current (A)
VDC=1V
0.5
VDC=0V
0
−0.5
1.45
1.455
1.46
1.465
1.47
1.475
1.48
1.485
1.49
1.495
1.5
1.47
1.475
Time (s)
1.48
1.485
1.49
1.495
1.5
1
Flux (V.s)
VDC=1V
0.5
VDC=0V
0
−0.5
1.45
1.455
1.46
1.465
Figure 2-18: Current and Flux Waveforms Obtained with VDC = 0 V and
VDC = 1 V
Now change the DC voltage to 1 V and restart the simulation. Observe that the
current is distorted. The 1 V DC voltage is now integrated, causing a flux offset,
which makes the flux enter into the nonlinear region of the flux-current
characteristic (ψ > 0.450 V.s). As a result of this flux saturation, the current
contains harmonics. Zoom in on the last three cycles of the simulation. The
peak value of the current now reaches 0.70 A and the fundamental component
has increased to 0.368 A. As expected, the DC component of the current is 1 V/
0.5 Ω = 0.2. The current and flux waveforms obtained with and without
saturation are superimposed in Figure 2-18.
Customizing Your Nonlinear Model
Up to now, you have used a nonlinear model with fixed parameters. If you plan
to use this block in other circuits with different parameters (for example, an
inductance with a different voltage rating or a saturation characteristic
2-45
2
Advanced Components and Techniques
defined with more than two segments), it proves more convenient to enter the
block parameters in a dialog box, rather than modifying individual blocks of
your subsystem.
In the following section, you learn how to use the Simulink masking facility to
create a dialog box, an icon, and documentation for your model. For more
details, refer to the Using Simulink guide.
Block Initialization
Select the Nonlinear Inductance subsystem and in the Edit menu, select Edit
mask. The Mask editor window appears. Select the Parameters tab.
Add button
In the Mask type field, enter Nonlinear Inductance and click Apply.
The parameters that you have to specify are the nominal voltage, the
inductance in the linear region, and the flux-current characteristic (flux and
current vectors in p.u.).
Click Add. In the Prompt field, enter
Nominal voltage (Volts rms):
2-46
Building and Customizing Nonlinear Models
In the Variable field, enter the variable name associated with that field: Vnom.
Repeat the preceding steps to define the dialog boxes and associated variables
listed below.
Nominal frequency (Hz):
fnom
Unsaturated inductance (H):
L
Saturation characteristic [i1(p.u.) phi1(p.u.); i2 phi2; ...]:
sat
Select the Initialization tab. Enter the following MATLAB commands. This
code prepares the two vectors Current_vect and Flux_vect to be used in the
Look-Up Table block of the model.
% Define base current and Flux for p.u. system
I_base=Vnom*sqrt(2)/(L*2π*fnom);
Phi_base=Vnom*sqrt(2)/(2π*fnom);
% Check first two points of the saturation characteristic
if ~all(all(sat(1:2,:)==[0 0; 1 1])),
h=errordlg('The first two points of the characteristic must
be [0 0; 1 1]','Error');
uiwait(h);
end
% Complete negative part of saturation characteristic
[npoints,ncol]=size(sat);
sat1=[sat ; -sat(2:npoints,:)];
sat1=sort(sat1);
% Current vector (A) and flux vector (V.s)
Current_vect=sat1(:,1)*I_base;
Flux_vect=sat1(:,2)*Phi_base;
As the saturation characteristic is specified only in the first quadrant, three
lines of code are added to complete the negative part of the saturation
characteristic. Notice also how the validity of the first segment of the
saturation characteristic is verified. This segment must be defined by two
2-47
2
Advanced Components and Techniques
points [0 0; 1 1] specifying a 1 p.u. inductance (nominal value) for the first
segment.
Click the OK button to close the Mask Editor window. Double-click the icon of
your masked block. Its dialog opens with all fields empty. Enter the values as
shown here.
Before you can use the masked block, you must apply the two internal variables
defined in the initialization section of the Look-Up Table block. Select your
block and, in the Edit menu, select Look under mask.
The Nonlinear Inductance subsystem opens. Open the Look-Up Table block
dialog box and enter the following variable names in the two fields:
Vector of input values (flux)
Flux_vect
Vector of output values (current) Current_vect
Close the Nonlinear Inductance subsystem and start the simulation. You
should get the same waveforms as shown in Figure 2-18.
2-48
Building and Customizing Nonlinear Models
Block Icon
In this section you learn how to customize your block's icon and make it more
attractive.
Select your block and, in the Edit menu, select Edit mask. The Mask editor
window opens. Select the Icon tab.
In the Drawing commands section, you can specify any drawing that appears
in your block icon by using the plot function. You can, for example, plot the
flux-current characteristic of your inductance.
Remember that the currents and fluxes of the nonlinear characteristic are
stored respectively in the Current_vect and Flux_vect internal variables of
the masked block. Enter the following command in the Drawing commands
section.
plot(Current_vect,Flux_vect)
Click Apply and notice that the saturation characteristic is displayed on the
icon. Notice also that the input and output names have disappeared.
2-49
2
Advanced Components and Techniques
To make them visible, in the Icon transparency pop-up menu, select
Transparent. Click OK to close the Mask Editor window.
Block Documentation
In this section, you add documentation to your block dialog box. Select your
block and, in the Edit menu, select Edit Mask. The Mask Editor window
opens. Select the Documentation tab.
Enter in the Mask description the text shown in the dialog box of the next
figure. Then, click OK to close the Mask Editor window. The next time you
double-click your block, this description appears on the dialog box of the block.
2-50
Building and Customizing Nonlinear Models
Modeling a Nonlinear Resistance
The technique for modeling a nonlinear resistance is similar to the one used for
the nonlinear inductance.
A good example is a metal-oxide varistor (MOV) having the following V-I
characteristic:
v α
i = I o ⋅  ------
 V o
where
v, i =
Instantaneous voltage and current
Vo =
Protection voltage
Io =
Reference current used to specify the protection voltage
α=
Exponent defining the nonlinear characteristic (typically between
10 and 50)
The following figure shows an application of such a nonlinear resistance to
simulate a MOV used to protect equipment on a 120 kV network. In order to
keep the circuit simple, only one phase of the circuit is represented.
2-51
2
Advanced Components and Techniques
Nonlinear Resistance Subsystem
Figure 2-19: Nonlinear Resistance Applied on a 120 kV Network
Using blocks of the powerlib and Simulink libraries, build this circuit. Group
all components used to model the nonlinear model in a subsystem named
Nonlinear Resistance. Use an X-Y Graph block to plot the V-I characteristic of
the Nonlinear Resistance subsystem.
Notice that the model does not use a Look-Up Table block as in the case of the
nonlinear inductance model. As the analytical expression of current as a
function of voltage is known, the nonlinear I(V) characteristic is implemented
directly with a Math Function block from the Math Operations library of
Simulink.
This purely resistive model contains no states. It produces an algebraic loop in
the state-space representation of the circuit, as shown in the next figure. See
Chapter 5, “SimPowerSystems Block Reference,” for more details on how
SimPowerSystems works.
2-52
Building and Customizing Nonlinear Models
AC Voltage Source
block
u
State-space
matrices
Linear circuit
Current Measurement block
Voltage Measurement block
y
Algebraic loop
Controlled
Current Source
block
i
Nonlinear resistance
subsystem
v
Voltage Measurement
block
Figure 2-20: Algebraic Loop Introduced by the Nonlinear Resistance Model
Although Simulink can solve algebraic loops, they often lead to slow simulation
times. You should break the loop with a block that does not change the
nonlinear characteristic. Here a first-order transfer function H(s) = 1/(1+Ts) is
introduced into the system, using a fast time constant (T = 0.01 µs).
Use the technique explained for the nonlinear inductance block to mask and
customize your nonlinear resistance block as shown.
Figure 2-21: Dialog Box of the Nonlinear Resistance Block
2-53
2
Advanced Components and Techniques
Open the dialog box of your new masked block and enter the parameters shown
in Figure 2-21. Notice that the protection voltage Vo is set at 2 p.u. of the
nominal system voltage. Adjust the source voltage at 2.3 p.u. by entering the
following peak amplitude:
120e3/sqrt(3)*sqrt(2)*2.3
Save your circuit as circuit8.
Using the ode23tb integration algorithm, simulate your circuit8 system for
0.1 s. The results are shown below.
2-54
Building and Customizing Nonlinear Models
2000
Current (A)
1000
0
−1000
−2000
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0.01
0.02
0.03
0.04
0.05
Time (s)
0.06
0.07
0.08
0.09
0.1
5
x 10
3
Voltage (V)
2
1
0
−1
−2
−3
0
5
2.5
x 10
2
1.5
1
Voltage (V)
0.5
0
−0.5
−1
−1.5
−2
−2.5
−2000
−1500
−1000
−500
0
Current (A)
500
1000
1500
2000
Figure 2-22: Current and Voltage Waveforms and V-I Characteristic Plotted
by the X-Y Graph Block
2-55
2
Advanced Components and Techniques
Creating Your Own Library
Simulink lets you create your own libraries of SimPowerSystems blocks. To
create a library, in the File menu choose New Library. A new Simulink
window named Library: untitled opens. Now copy the Nonlinear Inductance
block of your circuit7 system and the Nonlinear Resistance block of your
circuit8 system into that library. Save this library as my_powerlib. Next
time you develop a new model, you can add it to your personal library. You can
also organize your library in different sublibraries according to their functions,
as is done in the powerlib library.
Figure 2-23: Nonlinear Inductance and Resistance Blocks in my_powerlib
One advantage of using a library is that all blocks that you copy from that
library are referenced to the library. In other words, if you make a correction
in your library block, the correction is automatically applied to all circuits
using that block.
Connecting Your Model with Other Nonlinear Blocks
You now learn how to avoid error messages that can appear with nonlinear
blocks when they are simulated by a current source. Obviously, a current
source cannot be connected in series with an inductor, another current source,
or an open circuit. Such circuit topologies are forbidden in SimPowerSystems.
Similarly, if your nonlinear model uses a Controlled Voltage Source block, this
model could not be short-circuited or connected across a capacitor.
Suppose, for example, that you want to study the inrush current in a nonlinear
inductance when it is energized on a voltage source. Using blocks from
2-56
Building and Customizing Nonlinear Models
powerlib library and my_powerlibrary, you can build the circuit shown here.
Change the Breaker block parameters as follows.
Snubber resistance Rs
inf (no snubber)
Snubber capacitance Cs
0
External control
Not selected
Switching times
[1/60]
Figure 2-24: Circuit Topology Causing an Error
If you try to simulate this circuit, you get the following error message.
This topology is forbidden because two nonlinear elements simulated by
current sources are connected in series: the Breaker block and the Nonlinear
Inductance block. To be able to simulate this circuit you must provide a current
path around one of the two nonlinear blocks. You could, for example, connect a
large resistance, say 1 MΩ, across the Breaker block or the Inductance block.
2-57
2
Advanced Components and Techniques
In this case, it is more convenient to choose the Breaker block because a series
RC snubber circuit is provided with the model. Open the Breaker block dialog
box and specify the following snubber parameters:
Snubber resistance Rs (ohms)
1e6
Snubber capacitance Cs (F)
inf
Notice that in order to get a purely resistive snubber you have to use an infinite
capacitance.
Note Using an inductive source impedance (R-L series) instead of a purely
resistive impedance would have produced another error message, because the
current source modeling the nonlinear inductance would have been in series
with an inductance, even with a resistive snubber connected across the
breaker. In such a case, you could add either a parallel resistance across the
source impedance or a large shunt resistance connected between one breaker
terminal and the source neutral terminal.
Make sure that the phase angle of the voltage source is zero. Use the ode23tb
integration algorithm and simulate the circuit for 1 second. Voltage and
current waveforms are shown here.
2-58
Building and Customizing Nonlinear Models
1.5
Current (A)
1
0.5
0
−0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0
0.1
0.2
0.3
0.4
0.5
Time (s)
0.6
0.7
0.8
0.9
1
Flux (V.s)
1
0.5
0
−0.5
Figure 2-25: Current and Flux Waveforms When Energizing the Nonlinear
Inductance with Maximum Flux Offset
Figure 2-25 shows that energizing the inductor at a zero crossing of voltage
results in a maximum flux offset and saturation.
2-59
2
Advanced Components and Techniques
2-60
3
Case Studies
These case studies provide detailed, realistic examples of how to use SimPowerSystems.
Series-Compensated Transmission
Network (p. 3-2)
Study of subsynchronous resonance in AC power
transmission
Chopper-Fed DC Motor Drive
(p. 3-21)
Study of a DC motor drive with armature voltage controlled
by a GTO thyristor chopper
Variable-Frequency Induction Motor Study of a PWM inverter-driven variable-frequency AC
induction motor in variable-voltage, variable-speed operation
Drive (p. 3-33)
HVDC System (p. 3-46)
Study of a high-voltage DC transmission link and
perturbations to analyze system response
3
Case Studies
Series-Compensated Transmission Network
The example described in this section illustrates phenomena related to
subsynchronous resonance in a series-compensated AC transmission network.
Description of the Transmission Network
The single diagram shown here represents a three-phase, 60 Hz, 735 kV power
system transmitting power from a power plant consisting of six 350 MVA
generators to an equivalent network through a 600 km transmission line. The
transmission line is split into two 300 km lines connected between buses B1,
B2, and B3.
6*350 MVA
13.8 kV/735 kV
D/Yg
MOV1
line 1; 300 km
CB1
Generators
13.8 kV
6*350 MVA
40%
330 Mvar
B1
100 MW
300 MVA
735 /230 /25 kV
Yg/Yg/D
CB2
250 MW
MOV2
line 2; 300 km
40%
735 kV
equivalent
30000 MVA
B3
330 Mvar
B2
Figure 3-1: Series and Shunt Compensated Network
In order to increase the transmission capacity, each line is series compensated
by capacitors representing 40% of the line reactance. Both lines are also shunt
compensated by a 330 Mvar shunt reactance. The shunt and series
compensation equipment is located at the B2 substation where a 300
MVA-735/230 kV transformer feeds a 230 kV-250 MW load.
Each series compensation bank is protected by metal-oxide varistors (MOV1
and MOV2). The two circuit breakers of line 1 are shown as CB1 and CB2.
3-2
Series-Compensated Transmission Network
This network is available in the power_3phseriescomp model. Load this model
and save it in your working directory as case1.mdl in order to allow further
modifications to the original system.
Compare the circuit modeled in SimPowerSystems (Figure 3-2) with the
schematic diagram of Figure 3-1. The generators are simulated with a
Simplified Synchronous Machine block. A Three-Phase Transformer (Two
Windings) block and a Three-Phase Transformer (Three Windings) block are
used to model the two transformers. Saturation is implemented on the
transformer connected at bus B2.
The B1, B2, and B3 blocks are Three-Phase V-I Measurement blocks taken
from the Measurements library. These blocks are reformatted and given a
black background color to give them the appearance of bus bars. They output
the three line-to-ground voltages and the three line currents. Open the dialog
boxes of B1 and B2. Note how the blocks are programmed to output voltages in
p.u. and currents in p.u./100 MVA. Notice also that the voltage and current
signals are sent to internal Goto blocks by specifying signal labels. The signals
are picked up by the From blocks in the Data Acquisition subsystem.
The fault is applied on line 1, on the line side of the capacitor bank. Open the
dialog boxes of the Three-Phase Fault block and of the Three-Phase Breaker
blocks CB1 and CB2. See how the initial breaker status and switching times
are specified. A line-to-ground fault is applied on phase A at t = 1 cycle. The two
circuit breakers that are initially closed are then open at t = 5 cycles,
simulating a fault detection and opening time of 4 cycles. The fault is
eliminated at t = 6 cycles, one cycle after the line opening.
3-3
3
Case Studies
Figure 3-2: Series-Compensated Network (power_3phseriescomp)
Series Compensation1 Subsystem
Now, open the Series Compensation1 subsystem of the power_3phseriescomp
model. The three-phase module consists of three identical subsystems, one for
each phase. A note indicates how the capacitance value and the MOV
protection level are calculated. Open the Series Compensation1/Phase A
subsystem. You can see the details of the connections of the series capacitor
and the Surge Arrester block (renamed MOV). The transmission line is 40%
series compensated by a 62.8 µF capacitor. The capacitor is protected by the
MOV block. If you open the dialog box of the MOV block, notice that it consists
of 60 columns and that its protection level (specified at a reference current of
500 A/column or 30 kA total) is set at 298.7 kV. This voltage corresponds to 2.5
times the nominal capacitor voltage obtained at a nominal current of 2 kA
RMS.
A gap is also connected in parallel with the MOV block. The gap is fired when
the energy absorbed by the surge arrester exceeds a critical value of 30 MJ. In
order to limit the rate of rise of capacitor current when the gap is fired, a
damping RL circuit is connected in series. Open the Energy & Gap firing
subsystem. It shows how you calculate the energy dissipated in the MOV by
integrating the power (product of the MOV voltage and current).
3-4
Series-Compensated Transmission Network
When the energy exceeds the 30 MJ threshold, a closing order is sent to the
Breaker block simulating the gap.
Figure 3-3: Series Compensation Module
Series Compensation1/PhaseA Subsystem:
3-5
3
Case Studies
Series Compensation1/PhaseA Subsystem/Energy & Gap firing:
Three-Phase Saturable Transformer Model
Open the 300 MVA 735/230 kV Transformer dialog box and notice that the
current-flux saturation characteristic is set at
[0 0 ; 0.0012 1.2; 1 1.45] in p.u.
These data are the current and flux values at points 1, 2, and 3 of the piecewise
linear approximation to the flux linkage curve shown here:
3-6
Series-Compensated Transmission Network
Bus B2
L1
R1
R
L2
Lm
Ls
m
R2
Ideal transformer
Nonlinear inductance (reactive power losses)
Linear resistance (active power losses)
Slope L S =
Ψ
Flux linkage (p.u.)
1.45 p.u.
1.2 p.u.
L ac – L 1
Point 3
Point 2
Slope
Lm = 1000 p.u.
point 1
0.0012 p.u.
1 p.u.
i
Current (p.u./300 MVA)
Figure 3-4: Saturable Transformer Model
The flux-current characteristic is approximated by the two segments shown in
the graph here. The saturation knee point is 1.2 p.u. The first segment
corresponds to the magnetizing characteristic in the linear region (for fluxes
below 1.2 p.u.). At 1 p.u. voltage, the inductive magnetizing current is
0.0010/1.0 = 0.001 p.u., corresponding to 0.1% reactive power losses.
The iron core losses (active power losses) are specified by the magnetization
resistance Rm = 1000 p.u., corresponding to 0.1% losses at nominal voltage.
The slope of the saturation characteristic in the saturated region is 0.25 p.u.
Therefore, taking into account the primary leakage reactance (L1 = 0.15 p.u.),
the air core reactance of the transformer seen from the primary winding is
0.4 p.u./300 MVA.
3-7
3
Case Studies
Setting the Initial Load Flow and Obtaining Steady
State
Before performing transient tests you must initialize your model for the
desired load flow. Use the load flow utility of the Powergui to obtain an active
power flow of 1500 MW out of the machine with a terminal voltage of 1 p.u.
(13.8 kV).
Open the Powergui and select Load Flow and Machine Initialization. A new
window appears. In the upper right window you have the name of the only
machine present in your system. Its Bus Type should be PV Generator and
the desired Terminal Voltage should already be set to the nominal voltage of
13800 V. In the Active Power field, enter 1500e6 as the desired output power.
Click the Execute load flow button. Once the load flow is solved, the phasors
of AB and BC machine voltages as well as currents flowing in phases A and B
are updated in the left window. The required mechanical power to drive the
machine is displayed in watts and in p.u., and the required excitation voltage
E is displayed in p.u.
Pmec
1.5159e9 W [0.72184 p.u.]
E/Vf
1.0075 p.u.
Notice that Constant blocks containing these two values are already connected
to the Pm and E inputs of the machine block. If you open the machine dialog box,
you see that the machine initial conditions (initial speed deviation dw = 0;
internal angle theta, current magnitudes, and phase angles) are automatically
transferred in the last line.
Once the load flow is performed, you can obtain the corresponding voltage and
current measurements at the different buses. In the Powergui, select Steady
State Voltages and Currents. You can observe, for example, the phasors for
phase A voltages at buses B1, B2, and B3 and the current entering line 1 at bus
B1.
3-8
B1/Va
6.088e5 V ; 18.22 degrees
B2/Va
6.223e5 V ; 9.26 degrees
B3/Va
6.064e5 V ; 2.04 degrees
B1/Ia
1560 A ; 30.50 degrees
Series-Compensated Transmission Network
The active power flow for phase A entering line 1 is therefore
P
a
608.8 kV 1.56 kA
= V ⋅ I ⋅ cos ( ϕ ) = ----------------------- ⋅ -------------------- cos ( 30.50 – 18.22 ) = 464 MW
a a
a
2
2
corresponding to a total of 464 * 3 = 1392 MW for the three phases.
Transient Performance for a Line Fault
In order to speed up the simulation, you need to discretize the network. The
sample time is specified in the Powergui block as a variable Ts. This sample
time Ts is also used in the Integrator block of the MOV energy calculator
controlling the gap.
In the MATLAB window, define the variable
Ts = 50e-6
Ensure that the simulation parameters are set as follows:
Stop time
0.2
Solver options Type
Fixed-step; discrete (no continuous state)
Fixed step size
Ts
Line-to-Ground Fault Applied on Line 1
Ensure that the fault breaker is programmed for a line-to-ground fault on
phase A. Start the simulation and observe the waveforms on the three scopes.
These waveforms are shown here:
3-9
3
Case Studies
(a)
3-10
Series-Compensated Transmission Network
(b)
Figure 3-5: Simulation Results for a Four-Cycle Line-to-Ground Fault at the
End of Line 1
The simulation starts in steady state. At the t = 1 cycle, a line-to-ground fault
is applied and the fault current reaches 10 kA (a: trace 3). During the fault, the
MOV conducts at every half cycle (b: trace 5) and the energy dissipated in the
MOV (b: trace 6) builds up to 13 MJ. At t = 5 cycles the line protection relays
open breakers CB1 and CB2 (see the three line currents on trace 2) and the
energy stays constant at 13 MJ. As the maximum energy does not exceed the
30 MJ threshold level, the gap is not fired. At the breaker opening, the fault
current drops to a small value and the line and series capacitance starts to
discharge through the fault and the shunt reactance. The fault current
extinguishes at the first zero crossing after the opening order given to the fault
breaker (t = 6 cycles). Then the series capacitor stops discharging and its
voltage oscillates around 220 kV (b: trace 4).
3-11
3
Case Studies
Three-Phase-to-Ground Fault Applied on Line 1
Open the Three-Phase Fault block dialog box. Select the Phase B Fault and
Phase C Fault, so that you now have a three-phase-to-ground fault.
Restart the simulation. The resulting waveforms are shown.
(a)
3-12
Series-Compensated Transmission Network
(b)
Figure 3-6: Simulation Results for a Four-Cycle Three-Phase-to-Ground Fault
at the End of Line 1
Note that during the fault the energy dissipated in the MOV (trace 6) builds up
faster than in the case of a line-to-ground fault. The energy reaches the 30 MJ
threshold level after three cycles, one cycle before the opening of the line
breakers. As a result, the gap is fired and the capacitor voltage (trace 4) quickly
discharges to zero through the damping circuit.
Frequency Analysis
One particular characteristic of series-compensated systems is the existence of
subsynchronous modes (poles and zeros of the system impedance below the
fundamental frequency). Dangerous resonances can occur if the mechanical
torsion modes of turbine/generator shafts are in the vicinity of the zeros of the
system impedance. Also, high subsynchronous voltages due to impedance poles
3-13
3
Case Studies
at subsynchronous frequencies drive transformers into saturation. The
transformer saturation due to subsynchronous voltages is illustrated at the
end of this case study. The torque amplification on a thermal machine is
illustrated in another demonstration (see the power_thermal model).
Now measure the positive-sequence impedance versus frequency seen from bus
B2.
The section “Analyzing a Simple Circuit” on page 1-9 in the “Modeling Simple
Systems” chapter explains how the Impedance Measurement block allows you
to compute the impedance of a linear system from its state-space model.
However, your case1 model contains several nonlinear blocks (machine and
saturation of transformers). If you connect the Impedance Measurement block
to your system, all nonlinear blocks are ignored. This is correct for the
transformer, but you get the impedance of the system with the machine
disconnected. Before measuring the impedance, you must therefore replace the
machine block with an equivalent linear block having the same impedance.
Delete the Simplified Synchronous Machine block from your case1 model and
replace it with the Three-Phase Source block from the Electrical Sources
library. Open the block dialog box and set the parameters as follows in order to
get the same impedance value (L = 0.22 p.u./ (6 * 350 MVA) Quality factor = 15).
Phase-to-phase rms voltage
13.8e3
Phase angle of phase A
0
Frequency (Hz)
60
Internal connection Yg
Specify impedance using
short-circuit level
3-phase short-circuit level
6*350e6
Base voltage
13.8e3
X/R ratio
15
Save your modified model as case1Zf.mdl.
Open the Measurements library of powerlib and copy the Impedance
Measurement block into your model. This block is used to perform the
impedance measurement. Connect the two inputs of this block between phase
A and phase B of the B2 bus. Measuring the impedance between two phases
3-14
Series-Compensated Transmission Network
gives two times the positive-sequence impedance. Therefore you must apply a
factor of 1/2 to the impedance in order to obtain the correct impedance value.
Open the dialog box and set the multiplication factor to 0.5.
In the Powergui, select Impedance vs Frequency Measurement. A new
window opens, showing your Impedance Measurement block name. Fill in the
frequency range by entering 0:500. Select the linear scales to display Z
magnitude vs. frequency plot. Click the Save data to workspace button and
enter Zcase1 as the variable name to contain the impedance vs. frequency.
Click the Display button.
When the calculation is finished, the magnitude and phase as a function of
frequency are displayed in the two graphs on the window. If you look in your
workspace, you should have a variable named Zcase1. It is a two-column
matrix containing frequency in column 1 and complex impedance in column 2.
The impedance as a function of frequency (magnitude and phase) is shown
here:
3-15
3
Case Studies
Figure 3-7: Impedance vs. Frequency Seen from Bus B2
You can observe three main modes: 9 Hz, 175 Hz, and 370 Hz. The 9 Hz mode
is mainly due to a parallel resonance of the series capacitor with the shunt
inductors. The 175 Hz and 370 Hz modes are due to the 600 km distributed
parameter line. These three modes are likely to be excited at fault clearing.
If you zoom in on the impedance in the 60 Hz region, you can find the system’s
short-circuit level at bus B2. You should find a value of 58 Ω at 60 Hz,
corresponding to a three-phase short-circuit power of (735 kV)2 / 58 = 9314
MVA.
3-16
Series-Compensated Transmission Network
Transient Performance for a Fault at Bus B2
The configuration of the substation circuit breakers normally allows clearing a
fault at the bus without losing the lines or the transformers. You now modify
your case1 model in order to perform a three-cycle, three-phase-to-ground fault
at bus B2:
1 Disconnect the Three-Phase Fault block and reconnect it so that the fault is
now applied on bus B2.
2 Open the Three-Phase Fault dialog box and make the following
modifications:
Phase A, Phase B, Phase C,
Ground Faults
All selected
Transition times
[2/60 5/60]
Transition status [1, 0, 1...]
(0/1)
You have now programmed a three-phase-to-ground fault applied at the t =
2 cycles.
3 Open the dialog boxes of circuit breakers CB1 and CB2 and make the
following modifications:
Switching of Phase A
Not selected
Switching of Phase B
Not selected
Switching of Phase C
Not selected
The circuit breakers are not switched anymore. They stay at their initial
state (closed).
4 In the Data Acquisition subsystem, insert a Selector block (from the
Simulink Signals & Systems library) in the Vabc_B2 output of bus B2
connected to the scope. Set the Elements parameter to 1. This allows you to
see the phase A voltage clearly on the scope.
3-17
3
Case Studies
5 You now add blocks to read the flux and the magnetization current of the
saturable transformer connected at bus B2.
Copy the Multimeter block from the Measurements library into your case1
model. Open the Transformer dialog box. In the Measurements pop-up
menu, select Flux and magnetization Current. Open the Multimeter block.
Verify that you have six signals available. Select flux and magnetization
current on phase A, and click OK.
6 You now have two signals available at the output of the Multimeter block.
Use a Demux block to send these two signals on a two-trace scope.
7 In the Simulation —> Simulation parameters dialog, change the stop time
to 0.5. This longer simulation time allows you to observe the expected
low-frequency modes (9 Hz). Start the simulation.
The resulting waveforms are plotted here:
3-18
Series-Compensated Transmission Network
3-19
3
Case Studies
Figure 3-8: Simulation Results for a Three-Cycle Three-Phase-to-Ground Fault
at Bus B2
The 9 Hz subsynchronous mode excited at fault clearing is clearly seen on the
phase A voltage at bus B2 (trace 1) and capacitor voltage (trace 3). The 9 Hz
voltage component appearing at bus B2 drives the transformer into saturation,
as shown on the transformer magnetizing current (trace 5). The flux in phase
A of the transformer is plotted on trace 4. At fault application the voltage at
transformer terminals drops to zero and the flux stays constant during the
fault.
At fault clearing, when the voltage recovers, the transformer is driven into
saturation as a result of the flux offset created by the 60 Hz and 9 Hz voltage
components. The pulses of the transformer magnetizing current appear when
the flux exceeds its saturation level. This current contains a 60 Hz reactive
component modulated at 9 Hz.
3-20
Chopper-Fed DC Motor Drive
Chopper-Fed DC Motor Drive
The example described in this section illustrates application of
SimPowerSystems to the operation of a DC motor drive in which the armature
voltage is controlled by a GTO thyristor chopper.
The objective of this example is to demonstrate the use of electrical blocks, in
combination with Simulink blocks, in the simulation of an electromechanical
system with a control system. The electrical part of the DC motor drive,
including the DC source, the DC motor, and the chopper, is built using blocks
from the Elements, Machines, and Power Electronics libraries. The DC
Machine block models both electrical and mechanical dynamics. The load
torque-speed characteristic and the control system are built using Simulink
blocks.
Description of the Drive System
A simplified diagram of the drive system is shown in the next figure. The DC
motor is fed by the DC source through a chopper that consists of the GTO
thyristor, Th1, and the free-wheeling diode D1. The DC motor drives a
mechanical load that is characterized by the inertia J, friction coefficient B, and
load torque TL (which can be a function of the motor speed).
Ia
Th1
DC Motor
Mechanical load
+
Vdc
+
−
La
D1
Va
−
Ra
Tm
J, B, TL
+
E
−
Figure 3-9: Chopper-Fed DC Motor Drive
In this diagram, the DC motor is represented by its equivalent circuit
consisting of inductor La and resistor Ra in series with the counter
electromotive force (emf) E.
3-21
3
Case Studies
The back reaction EMF is proportional to the motor speed
E = KE ω
where KE is the motor voltage constant and ω is the motor speed.
In a separately excited DC machine, the motor voltage constant KE is
proportional to the field current If
K E = L af I f
where Laf is the field-armature mutual inductance.
The torque developed by the DC motor is proportional to the armature current
Ia:
Tm = KT Ia
where KT is the motor torque constant.
The DC motor torque constant is equal to the voltage constant.
KT = KE
Thyristor Th1 is triggered by a pulse-width-modulated (PWM) signal to control
the average motor voltage. (See “Variable-Frequency Induction Motor Drive”
on page 3-33 for more details on pulse-width modulation.) Theoretical
waveforms illustrating the chopper operation are shown here:
3-22
Chopper-Fed DC Motor Drive
T
Th1
αT
Va
Vdc
Va (avg)
t
Ia
Ia (avg)
t
Figure 3-10: Waveforms Illustrating the Chopper Operation
The average armature voltage is a direct function of the chopper duty cycle α.
V a ( avg ) = αV dc
Note that this relation is valid only when the armature current is continuous.
In steady state, the armature average current is equal to
V a ( avg ) – E
I a ( avg ) = --------------------------------Ra
The peak-to-peak current ripple is
– αr
–r
– ( 1 – α )r
+e –e
)
Vdc ( 1 – e
∆i = ----------- ----------------------------------------------------------------------–r
Ra
1–e
3-23
3
Case Studies
where α is the duty cycle and r is the ratio between the chopper period and the
DC motor electrical time constant.
T
r = ----------------------( La ⁄ Ra )
In this case study, a variable-speed DC motor drive using a cascade control
configuration is considered. Here is a block diagram of this drive:
Vdc
+
−
+
Chopper Va
−
α
Current
controller
DC
motor
Current
sensor
Speed
sensor
Ia
+ −
Ia*
Speed
controller
ω
+
−
ω*
Speed reference
Figure 3-11: Variable-Speed DC Motor Drive
The motor torque is controlled by the armature current Ia, which is regulated
by a current control loop. The motor speed is controlled by an external loop,
which provides the current reference Ia* for the current control loop.
Modeling the DC Drive
Open the power_dcdrive model and save this model as case2.mdl in your
working directory so that you can make further modifications without altering
the original file.
The drive system diagram is built with blocks from the powerlib library
combined with Simulink blocks. The system diagram is shown here:
3-24
Chopper-Fed DC Motor Drive
Figure 3-12: DC Motor Drive Using SimPowerSystems (power_dcdrive)
With a Manual Switch block, you can select both the reference speed and the
load torque applied to the motor shaft in order to use either a constant value or
a step function. Initially the reference speed is set to a constant value of 120
rad/s and the load torque is also maintained constant at 5 N.m.
The DC motor represented by the DC Machine block is modeled in two separate
parts: electrical and mechanical. To view the Simulink model of the DC motor,
click the DC Machine block and use the Look under mask item in the model
Edit menu.
3-25
3
Case Studies
The mechanical subsystem is
The armature circuit is represented by an RL circuit in series with a controlled
voltage source, the value of which is KEω.
The field circuit is represented by an RL circuit.
3-26
Chopper-Fed DC Motor Drive
The mechanical part is represented by Simulink blocks, which implement the
following equation:
dω
T m = J -------- + Bω + sgn ( ω ) T L
dt
Set the DC machine parameters to the desired values by using the dialog box
of the DC Machine block.
You implement the load torque-speed characteristic using a Simulink Math
Function block.
The motor used in this case study is a separately excited, 5 HP/240 V DC motor
with the following parameters:
Ra
0.5 Ω
La
10 mH
KE
1.23 V/(rad/s)
KT
1.23 N.m/A
A 10 mH inductor (Ls) is connected in series with the DC motor to smooth out
the armature current. The constant excitation is implemented by the
connection of a DC Voltage Source block to the field winding.
The required trigger signal for the GTO thyristor is generated by a hysteresis
current controller, which forces the motor current to follow the reference within
+h/2 and −h/2 limits (h is the hysteresis band).
The current controller is a masked block that contains
2
Ia
1
Iref
Relay
1
g
The speed control loop uses a proportional-integral controller, which is
implemented by Simulink blocks.
3-27
3
Case Studies
Kp
1
wm
Ki
2
wref
1
Iref
1
s
Simulation of the DC Drive
Run the simulation by selecting Start from the Simulation menu in Simulink.
Set the simulation parameters in the Simulation parameters dialog as
follows.
Simulation time
Start Time: 0, Stop time: 1.2
Solver Type
Variable-step ode23tb (stiff/TR-BDF2)
Max Step Size
auto
Initial Step Size
auto
Relative Tolerance
1e-3
Absolute Tolerance
1e-3
The motor voltage, current waveforms, and motor speed are displayed on three
axes of the scope connected to the variables Va, Ia, and ω.
Starting the Drive
This test simulates the starting transient of the DC drive. The inertia of the
mechanical load is small in order to bring out the details of the chopper
commutation. The speed reference is 120 rad/s s, and you can observe the DC
motor speed and current.
The transient responses for the starting of the DC motor drive are shown in
Figure 3-13.
Note that you can save the final system state vector xFinal by selecting the
Workspace I/O —> Save to workspace —> Final state check box in the
Simulation parameters dialog. It can be used as the initial state in a
subsequent simulation so that the simulation can start under steady-state
conditions.
3-28
Chopper-Fed DC Motor Drive
Figure 3-13: Starting the DC Motor Drive
Steady-State Voltage and Current Waveforms
When the steady state is attained, you can stop the simulation. The DC motor
current and voltage waveforms obtained at the end of the starting test are
shown here:
3-29
3
Case Studies
Steady−state DC motor current and voltage
Armature current , A
10
8
6
4
2
0
1.19
1.191
1.192
1.193
1.194
1.195
Time , s
1.196
1.197
1.198
1.199
1.2
1.191
1.192
1.193
1.194
1.195
Time , s
1.196
1.197
1.198
1.199
1.2
Armature voltage , V
300
200
100
0
−100
1.19
Figure 3-14: Steady-State Motor Current and Voltage Waveforms
Speed Regulation Dynamic Performance
You can study the drive dynamic performance (speed regulation performance
versus reference and load torque changes) by applying two successive changes
of operating conditions to the DC drive: a step change in speed reference and a
step change in load torque.
Click the Torque Step block to step the load torque from 5 N.m to 25 N.m at t
= 1.2 s. Then click also the Speed Step block to step the reference speed from120
rad/s to 160 rad/s at t = 0.4 s. In order to start the simulation in steady state,
the final state vector obtained with the previous simulation can be used as the
initial condition. Copy the xFinal variable (state vector saved at the end of the
last simulation) into the xInitial variable. Select the Workspace I/O —>
Load from workspace O—> Initial state check box in the Simulation
parameters window and restart the simulation.
3-30
Chopper-Fed DC Motor Drive
The response of the DC motor drive to successive changes in speed reference
and load torque is plotted here:
DC Motor Drive − Speed regulator transient response
180
Motor speed , rad/s
170
160
150
140
130
120
110
0
0.2
0.4
0.6
0.8
1
Time , s
1.2
1.4
1.6
1.8
2
0
0.2
0.4
0.6
0.8
1
Time , s
1.2
1.4
1.6
1.8
2
35
Armature current , A
30
25
20
15
10
5
0
Figure 3-15: Dynamic Transient of the DC Motor Drive
Simulating with a Discretized System
Up to now you have performed all simulations using a continuous model of the
DC drive and a variable-step solver. You can also perform the same
simulations at fixed steps using a discretized system. Discretizing electronic
converters is advantageous because simulation is much faster than with a
continuous system.
As explained in the “Improving Simulation Performance” chapter, you cannot
discretize power electronic converters using forced-commutated devices such
as GTOs when these devices are simulated by individual blocks. However,
discretization is possible when the Universal Bridge block or the Three-Level
Bridge block is used to model the converter.
3-31
3
Case Studies
The discrete version of the DC drive has been saved in the
power_dcdrive_disc demo. Open this model. Note that the GTO block and the
Diode block have been replaced by the Universal Bridge block. Open the
Universal Bridge block menu and note that the number of arms has been set to
1. The specified type of power electronic device is GTO/Diodes. It means that
the converter consists of two GTO/Diode pairs (upper pair and lower pair)
connected in series. For the type of buck converter used in our case study, only
the upper GTO and the lower diode are used. Therefore no pulse is sent to the
lower GTO.
The system is discretized by means of the Powergui block, where a sample time
Ts has been specified. Define a variable Ts = 10e-6 in your MATLAB
Command Window. The control system and the DC machine is also discretized
using the same 10 µs sample time. Open the Simulation/Parameters menu
and notice that in the Solver section, Discrete (no continuous states) is
selected.
Start the simulation and observe motor starting. Note that simulation now
runs faster than with the continuous model. Results should compare well with
those presented on Figure 3-13 for the continuous model.
References
[1] Leonhard,W., Control of Electrical Drives, Springer-Verlag, Berlin 1996.
3-32
Variable-Frequency Induction Motor Drive
Variable-Frequency Induction Motor Drive
This case study examines a variable-frequency AC motor drive model. A
pulse-width-modulated (PWM) inverter is used as a variable-voltage,
variable-frequency source to drive an induction motor in variable-speed
operation.
You model the drive, including the motor, the power converter, and the speed
control system, by using SimPowerSystems and Simulink blocks. The drive
operation is studied for different operating conditions: starting, steady-state,
and transients.
The objective of this example is to demonstrate the use of Machines library and
Power Electronics library blocks in combination with Simulink blocks in the
simulation of a complex electromechanical system operating at high frequency.
The electrical part of the AC motor drive, including the PWM inverter, is built
using the Universal Bridge block. The induction motor is represented by the
Asynchronous Machine block, which models both electric and mechanical
dynamics. The control system, including current and speed regulators, is built
using Simulink blocks.
Description of the Induction Motor Drive
The induction motor requires a variable-frequency three-phase source for
variable-speed operation. You can realize this source by using a power
converter system consisting of a rectifier connected to an inverter through a DC
link.
The next figure shows a block diagram of the power circuit of a typical
variable-frequency induction motor drive.
3-33
3
Case Studies
Rectifier
Filter
L
60 Hz
power
grid
C
Inverter
+
Induction
motor
Vdc
−
DC link
V
f
Figure 3-16: Variable-Frequency Induction Motor Drive
The power grid AC voltage is converted into a fixed DC voltage by the rectifier.
The harmonics are filtered out by an LC filter to provide a smooth DC voltage,
which is then applied to the inverter input.
+
A
Vdc
B
−
C
Figure 3-17: Three-Phase IGBT Inverter
The inverter consists essentially of six power switches that can be metal-oxide
semiconductor field-effect transistors (MOSFET), gate turn-off thyristors
(GTO), or insulated gate bipolar transistors (IGBT), depending on the drive
power capacity and the inverter switching frequency (Hz). The preceding figure
shows a simplified diagram of a three-phase IGBT inverter.
The inverter converts the DC link voltage into an adjustable three-phase AC
voltage. Different control schemes can be used to control the inverter output
voltage and frequency. One of the most utilized schemes is pulse width
3-34
Variable-Frequency Induction Motor Drive
modulation (PWM) in which you obtain three-phase variable sinusoidal voltage
waveforms by modulating the on and off times of the power switches.
In industrial drive applications, the PWM inverter operates as a three-phase
variable-frequency, variable-voltage source with fundamental frequency
varying from zero to three times the motor nominal frequency.
In some control schemes where a three-phase, variable-frequency current
source is required, current control loops are added to force the motor currents
to follow an input reference (usually sinusoidal).
You can control the inverter-fed induction motor drive with various schemes
depending on the application, desired performance, and controller design
complexity. The most utilized schemes are
• Stator V/Hz control
• Stator currents and open loop flux control
• Vector control (field-oriented control)
• Direct torque control (DTC)
A Field-Oriented Variable-Speed Induction Motor
Drive
This case study illustrates a variable-speed induction motor drive using
field-oriented control. In this control scheme, a dq coordinates reference frame
locked to the rotor flux space vector is used to achieve decoupling between the
motor flux and torque. They can thus be controlled separately by stator
direct-axis current and quadrature-axis current respectively, as in a DC motor.
This figure shows a block diagram of a field-oriented induction motor drive:
3-35
3
Case Studies
Vdc
+
ia
PWM
inverter
−
ib
ic
Induction
motor
Current
controllers
Rotor flux
reference
|ψr|∗
iqs*
calculation
Torque
reference
ids*
calculation
|ψr|
ids*
Speed
sensor
ia* ib* ic*
iqs*
dq
θe
calculation
abc
θe
ω
Te*
Rotor flux
calculation
Speed
controller
ids
iqs
dq
+
abc
ω
−
ω∗
Speed
reference
Figure 3-18: Field-Oriented Variable-Frequency Induction Motor Drive
The induction motor is fed by a current-controlled PWM inverter, which
operates as a three-phase sinusoidal current source. The motor speed ω is
compared to the reference ω* and the error is processed by the speed controller
to produce a torque command Te*.
As shown below, the rotor flux and torque can be separately controlled by the
stator direct-axis current ids and quadrature-axis current iqs, respectively.
3-36
Variable-Frequency Induction Motor Drive
q
Is
iqs
ωe
ψr
ids
θe
θsl
θr
d Rotor flux axis
Rotor axis
a
Ir
Figure 3-19: Field-Oriented Control Principle
The stator quadrature-axis current reference iqs* is calculated from torque
reference Te* as
T e∗
2 2 Lr
i qs∗ = --- ⋅ --- ⋅ -------- ⋅ ---------------3 p L m ψ r est
where Lr is the rotor inductance, Lm is the mutual inductance, and |ψr|est is
the estimated rotor flux linkage given by
L m i ds
ψ r est = ---------------1 + τr s
where τr = Lr / Rr is the rotor time constant.
The stator direct-axis current reference ids* is obtained from rotor flux
reference input |ψr|*:
ψr ∗
i ds∗ = ----------Lm
3-37
3
Case Studies
The rotor flux position θe required for coordinates transformation is generated
from the rotor speed ωm and slip frequency ωsl:
θe =
∫ ( ωm + ωsl ) dt
The slip frequency is calculated from the stator reference current iqs* and the
motor parameters.
Lm Rr
ω sl = ---------------- ⋅ ------ ⋅ i qs∗
ψ r est L r
The iqs* and ids* current references are converted into phase current references
ia*, ib*, ic* for the current regulators. The regulators process the measured and
reference currents to produce the inverter gating signals.
The role of the speed controller is to keep the motor speed equal to the speed
reference input in steady state and to provide a good dynamic during
transients. It can be of proportional-integral type.
Modeling the Induction Motor Drive
Open the power_acdrive model and save it as case3.mdl in your working
directory so that you can make further modifications without altering the
original file.
The next figure shows the power_acdrive model in which blocks from
SimPowerSystems and Simulink are used to model the induction motor drive.
3-38
Variable-Frequency Induction Motor Drive
Figure 3-20: Variable-Speed Field-Oriented Induction Motor Drive
(power_acdrive)
The induction motor is modeled by an Asynchronous Machine block. The motor
used in this case study is a 50 HP, 460 V, four-pole, 60 Hz motor having the
following parameters:
Rs
0.087 Ω
Lls
0.8 mH
Lm
34.7 mH
Rr
0.228 Ω
Llr
0.8 mH
The reference speed and the load torque applied to the motor shaft can be both
selected by a Manual Switch block in order to use either a constant value or a
step function. Initially the reference speed is set a constant value of 120 rad/s
and the load torque is also maintained constant at 0 N.m
The current-controlled PWM inverter circuit is shown in Figure 3-20. The
IGBT inverter is modeled by a Universal Bridge block in which the Power
Electronic device and Port configuration options are selected as IGBT/Diode
3-39
3
Case Studies
and ABC as output terminals respectively. The DC link input voltage is
represented by a 780 V DC voltage source.
The current regulator, which consists of three hysteresis controllers, is built
with Simulink blocks. The motor currents are provided by the measurement
output of the Asynchronous Machine block.
2
Iabc
em
Mux
1
Iabc*
1
Pulses
em
The conversions between abc and dq reference frames are executed by the
abc_to_dq0 Transformation and dq0_to_abc Transformation blocks of Figure
3-20.
1
Teta
id
cos(u)
sin(u)
f(u)
2/3
1
Id
f(u)
2/3
2
Iq
Mux
2
Iabc
iq
3
cos(u)
abc_dq
ia
Teta
f(u)
1
sin(u)
Mux
2
Iq*
1
f(u)
Mux
ib
1
Iabc
dq_abc
1
1
Id*
ic
The rotor flux is calculated by the Flux_Calculation block of Figure 3-20.
1
Phir
3-40
34.7e−3
0.1557s+1
1
Id
Variable-Frequency Induction Motor Drive
The rotor flux position (θe) is calculated by the Teta Calculation block of Figure
3-20.
1
Iq
Mux
1
34.7e−3*u[1]/(u[2]*0.1557+1e−3)
1
2
Phir
2
3
Mux
s
1
Teta
wr
The stator quadrature-axis current reference (iqs*) is calculated by the
iqs*_Calculation block of Figure 3-20.
1
Te*
Mux
u[1]*0.341/(u[2]+1e−3)
2
Phir
1
Iq*
The stator direct-axis current reference (ids*) is calculated by the
id*_Calculation block of Figure 3-20.
1
Phir*
1/34.7e−
1
Id*
KF
The speed controller is of proportional-integral type and is implemented using
Simulink blocks.
Kp
1
w*
2
Ki
1
s
1
Te*
w
3-41
3
Case Studies
Simulating the Induction Motor Drive
In order to increase simulation speed, this model is discretized using a sample
time of 2 µs. The variable Ts = 2e-6 automatically loads into your workspace
when you open this model. This sample time Ts is used both for the power
circuit (Ts specified in the Powergui) and the control system.
Run the simulation by selecting Start from the Simulation menu in Simulink.
The motor voltage and current waveforms as well as the motor speed and
torque are displayed on four axes of the scope connected to the variables Vab,
Is, Te, and ω.
Starting the Drive
You can start the drive from a standstill by specifying [1,0,0,0,0,0,0,0] as
the initial conditions for the Asynchronous Machine block (initial slip = 1 and
no currents flowing in the three phases). The speed reference is 120 rad/s.
The motor speed, electromechanical torque, and currents observed during the
starting of the induction motor drive are shown in Figure 3-21.
Note that you can save the final system state vector xFinal by selecting the
Workspace I/O —> Save to workspace —> Final state check box in the
Simulation parameters dialog. It can be used as the initial state in a
subsequent simulation so that the simulation can start under steady-state
conditions.
3-42
Variable-Frequency Induction Motor Drive
Figure 3-21: Starting the Induction Motor Drive
Steady-State Voltage and Current Waveforms
When the steady state is attained, you can stop the simulation and zoom on the
scope signals.
This figure shows the motor voltage, current, and torque waveforms obtained
when the motor is running at no load (torque = 0 N.m) at a speed of 120 rad/s.
The 20 A band imposed by the hysteresis current regulator is clearly seen on
the three motor currents.
3-43
3
Case Studies
Figure 3-22: Steady-State Motor Current, Voltage, and Torque Waveforms
Speed Regulation Dynamic Performance
You can study the drive dynamic performance (speed regulation performance
versus reference and load torque changes) by applying two changing operating
conditions to the drive: a step change in speed reference and a step change in
load torque.
Use the Reference Speed selection switch and the Torque selection switch to set
speed reference steps from 120 rad/s to 160 rad/s at t = 0.2 s and the load torque
steps from 0 N.m to 200 N.m at t = 1.8 s. The final state vector obtained with
the previous simulation can be used as the initial condition so that the
simulation starts from steady state. Load the power_acdrive_init.mat file,
which creates the xInitial variable. Select the Workspace I/O —> Load from
workspace —> Initial state check box in the Simulation parameters dialog
and restart the simulation.
The response of the induction motor drive to successive changes in speed
reference and load torque is shown here:
3-44
Variable-Frequency Induction Motor Drive
Figure 3-23: Dynamic Performance of the Induction Motor Drive
References
[1] Leonhard, W., Control of Electrical Drives, Springer-Verlag, Berlin, 1996.
[2] Murphy, J. M. D., and Turnbull, F. G., Power Electronic Control of AC
Motors, Pergamon Press, Oxford, 1985.
[3] Bose, B. K., Power Electronics and AC Drives, Prentice-Hall, Englewood
Cliffs, N.J., 1986.
3-45
3
Case Studies
HVDC System
The final example described in this section illustrates modeling of a
high-voltage direct current (HVDC) transmission link [1]. Perturbations are
applied in order to examine the system performance [2]. The objectives of this
example are to demonstrate the use of the Universal Bridge block and the
Three-Phase Transformer (Three Windings) block in combination with
Simulink blocks in the simulation of a complete pole of a 12-pulse HVDC
transmission system. The electrical part representing the AC network is built
using three-phase blocks. The Discrete 12-Pulse HVDC control system is a
generic control available in the Discrete Control Blocks library of
powerlib_extras.
Description of the HVDC Transmission System
Open the power_hvdc12pulse model and save it as case4.mdl in order to allow
further modifications to the original system. This system is shown in Figure
3-24.
A 1000 MW (500 kV, 2 kA) DC interconnection is used to transmit power from
a 500 kV, 5000 MVA, 60 Hz network to a 345 kV, 10000 MVA, 50 Hz network.
The AC networks are represented by damped L-R equivalents with an angle of
80 degrees at fundamental frequency (60 Hz or 50 Hz) and at the third
harmonic.
The rectifier and the inverter are 12-pulse converters using two Universal
Bridge blocks connected in series. Open the two converter subsystems to see
how they are built. The converters are interconnected through a 300 km line
and 0.5 H smoothing reactors. The converter transformers (Wye grounded
/Wye/Delta) are modeled with Three-Phase Transformer (Three-Windings)
blocks. The transformer tap changers are not simulated. The tap position is
rather at a fixed position determined by a multiplication factor applied to the
primary nominal voltage of the converter transformers (0.90 on the rectifier
side; 0.96 on the inverter side).
From the AC point of view, an HVDC converter acts as a source of harmonic
currents. From the DC point of view, it is a source of harmonic voltages.
The order n of these characteristic harmonics is related to the pulse number p
of the converter configuration: n = kp ± 1 for the AC current and n = kp for the
direct voltage, k being any integer. In the example, p = 12, so that injected
harmonics on the AC side are 11, 13, 23, 25, and on the DC side are 12, 24.
3-46
HVDC System
Figure 3-24: HVDC System
AC filters are used to prevent the odd harmonic currents from spreading out on
the network. The filters are grouped in two subsystems. These filters also
appear as large capacitors at fundamental frequency, thus providing reactive
power compensation for the rectifier consumption due to the firing angle α. For
α = 30 degrees, the converter reactive power demand is approximately 60% of
the power transmitted at full load. Look under the AC filters subsystem mask
to see the high Q (100) tuned filters at the 11th and 13th harmonics and the
low Q (3), or damped filter, used to eliminate the higher order harmonics, e.g.,
23rd and up. Extra reactive power is also provided by capacitor banks.
Two circuit breakers are used to apply faults on the rectifier AC and DC sides.
The rectifier and inverter control systems use the Discrete 12-Pulse HVDC
Control block of the Discrete Control Blocks library of powerlib_extras.
The power system and the control system are both discretized with the same
sample time Ts.
Define parameter Ts = 50e-6 in your workspace before starting the
simulation.
3-47
3
Case Studies
Frequency Response of the AC and DC Systems
You now measure the frequency response of the AC systems (rectifier and
inverter sides) and of the DC line.
The section “Analyzing a Simple Circuit” on page 1-9 in the “Modeling Simple
Systems” chapter explains how the Impedance Measurement block allows you
to compute the impedance of a linear system from its state-space model. As the
thyristor valves of the converters are nonlinear blocks, they are ignored in the
impedance calculation and you get the impedances with the valves open.
Open the Measurements library, copy three Impedance Measurement blocks
into your model, and rename them Zrec, Zinv, and ZDC. Connect the two inputs
of Zrec and Zinv between phase A and phase B of the AC system on the rectifier
and inverter sides. Measuring the impedance between two phases gives two
times the positive-sequence impedance. Therefore you must apply a factor of
1/2 to the impedance in order to obtain the correct impedance value. Open the
two Impedance Measurement blocks and set the Multiplication factor to 0.5.
Finally, connect input 1 of the ZDC block between the DC line terminal and the
rectifier smoothing reactor, and connect input 2 to ground. Save your modified
model as case4Zf.mdl.
In the Powergui, select Impedance vs Frequency Measurement. A new
window opens, showing the three Impedance Measurement block names. Fill
in the Frequency range by entering 10:2:1500. Select the lin scale to display
the Z magnitude and lin scale for the frequency axis. Click the Save data to
workspace button and enter Zcase4 as the variable name to contain the
impedance vs. frequency. Click the Display button.
When the calculation is finished, the magnitude and phase as functions of
frequency measured by the three Impedance Measurement blocks are
displayed in the window. Your workspace should have a variable named
Zcase5. It is a four-column matrix containing frequency in column 1 and the
three complex impedances in columns 2, 3, and 4 with the same order as in the
window displaying the block names.
The magnitudes of the three impedances as a function of frequency are shown
here.
3-48
HVDC System
Figure 3-25: Positive-Sequence Impedances of the Two AC Networks and of
the DC Line
Note the two minimum impedances on the Z magnitudes of the AC systems.
These series resonances are created by the 11th and 13th harmonic filters.
They occur at 660 Hz and 780 Hz on the 60 Hz system. Note also that the
addition of 600 Mvar capacitive filters on the inductive systems creates
resonances (around 188 Hz on the rectifier side and 220 Hz on the inverter
side). Zoom in on the impedance magnitude in the 60 Hz region. You should
find a magnitude of 56.75 Ω for the 60 Hz system, corresponding to an effective
short-circuit level of 5002/56.75 = 4405 MVA on the rectifier side (5000 MVA 600 Mvar of filters).
For the DC line, note the series resonance at 240 Hz, which corresponds to the
main mode likely to be excited on the DC side, under large disturbances.
3-49
3
Case Studies
Description of the Control System
The control systems of the rectifier and of the inverter use the same 12-Pulse
HVDC Control block from the Discrete Control Blocks library of
powerlib_extras. The block can operate either in rectifier or inverter mode.
Use Look under mask to see how this block is built.
Inputs and Outputs
Input 1 (Vabc) is a vectorized signal of the three line-to-ground voltages
measured at the primary of the converter transformer. These three voltages
are used to synchronize the pulse generation on the line voltages. Inputs 2 and
3 are the DC line voltage (VdL) and current (Id). Note that the measured DC
currents (IdR and IdI in A) and DC voltages (VdLR and VdLI in V) are scaled to
p.u. (1 p.u. current = 2 kA; 1 p.u. voltage = 500 kV) before they are used in the
controllers.
Inputs 4 and 5 (Id_ref and Vd_ref) are the Vd and Id reference values in p.u.
The VdL and Id inputs are filtered before being processed by the regulators. A
first-order filter is used on the Id input and a second-order filter is used on the
VdL input. The filter parameters are shown in the dialog box of Figure 3-27.
Input 6 (Block) accepts a logical signal (0 or 1) used to block the converter when
Block = 1. Input 7 is also a logical signal that can be used for protection
purposes. If this signal is high (1), the firing angle is forced at the value defined
in the block dialog box.
The first two block outputs (PulseY and PulseD) contain the vectorized signals
of the six pulses to be sent to each of the six-pulse converters connected to the
wye and delta windings of the converter transformer. The third output (alpha)
is the firing delay angle in degrees ordered by the regulator. The fourth output
(Id_ref_lim) is the actual reference current value (value of Id_ref limited by
the VDCOL function as explained below). The fifth output (Mode) is an
indication of the actual state of the converter control mode or firing pulses. The
state is given by a number (from 0 to 5) as follows:
3-50
0
Blocked pulses
1
Current control
2
Voltage control
3
Alpha minimum limitation
HVDC System
4
Alpha maximum limitation
5
Forced or constant alpha
Synchronization System
The Discrete 12-Pulse HVDC Control block uses the primary voltages (input 1)
to synchronize and generate the pulses according to Vd_ref and Id_ref set
points (inputs 4 and 5). The synchronizing voltages are measured at the
primary side of the converter transformer because the waveforms are less
distorted. The firing command pulse generator is synchronized to the
fundamental frequency of the AC source. At the zero crossings of the
commutating voltages (AB, BC, CA), a ramp is reset. A firing pulse is generated
whenever the ramp value becomes equal to the desired delay angle provided by
the regulator. In order to improve the commutating voltages used by the pulse
generator, the primary voltages (Vabc) are filtered by a low Q second-order
band-pass filter centered at the fundamental system frequency. The base
system frequency and the filter bandwidth are defined in the block dialog box.
Steady-State V-I Characteristic
The Discrete 12-Pulse HVDC Control block implements this steady-state
characteristic:
3-51
3
Case Studies
DC voltage (Vd)
αmin. (normal AC rect. voltage)
Rectifier
Operating
point 1
Inverter
Vd_ref = 1 p.u.
Vd margin (0.05 p.u.)
Low AC rect. voltage
Operating point 2
(low AC voltage
at rectifier)
Id margin
(0.1 p.u.)
Id_ref = 1 p.u.
DC current (Id)
Figure 3-26: Rectifier and Inverter Steady-State Characteristics and VDCOL
Function
In normal operation, the rectifier controls the current at the Id_ref reference
value, whereas the inverter controls the voltage at the Vd_ref reference value.
The Id_margin and Vd_margin parameters are defined in the inverter dialog
box. They are set respectively at 0.1 p.u. and 0.05 p.u. The system normally
operates at point 1 as shown in the figure. However, during a severe
contingency producing a voltage drop on the AC network 1 feeding the rectifier,
the operating point moves to point 2. The rectifier therefore is forced to a
minimum α mode and the inverter is in current control mode.
Note In industrial controllers, the α angle at the inverter is normally limited
in order to keep a minimum γ angle, where
• γ = extinction angle = 180° − α − µ
• µ =commutation or overlap angle
The γ control required to avoid commutation failures is not implemented in
this version of the HVDC control. Nevertheless, a block taken from the
Discrete Control Blocks library of powerlib_extras is used to monitor γ. Such
a block could be used to control minimum γ.
3-52
HVDC System
VDCOL Function
Another important control function is implemented to change the reference
current according to the value of the DC voltage. This control, named Voltage
Dependent Current Order Limiter (VDCOL), automatically reduces the
reference current (Id_ref) set point when VdL decreases (as, for example,
during a DC line fault or a severe AC fault). Reducing the Id reference currents
also reduces the reactive power demand on the AC network, helping to recover
from fault. The VDCOL parameters of the Discrete 12-Pulse HVDC Control
block dialog box are explained by this diagram:
Id_ref actual (Id_ref_lim)
Id_ref = 1.0 p.u.
1.0 p.u.
Id_ref = 0.8 p.u.
IdMin*Id_ref
(0.3 p.u.*1.0)
(0.3 p.u.*0.8)
Id_ref = 0.027 p.u.
IdMinAbs
(0.08 p.u.)
Mininum Id_ref value
VdMin
(0.18 p.u.)
VdThresh
(0.6 p.u.)
DC line Voltage (VdL)
Figure 3-27: VDCOL Characteristic; Id_ref = f(VdL)
The Id_ref value starts to decrease when the Vd line voltage falls below a
threshold value VdThresh (0.6 p.u.). The actual reference current used by the
controllers is available at the fourth controller output, named Id_ref_lim.
IdMinAbs is the absolute minimum Id_ref value, set at 0.08 p.u. When the DC
line voltage falls below the VdThresh value, the VDCOL drops instantaneously
to Id_ref. However, when the DC voltage recovers, VDCOL limits the Id_ref
rise time with a time constant defined by parameter Tup (80 ms in the
example).
3-53
3
Case Studies
Current and Voltage Regulators
The rectifier and the inverter controls both have a voltage and a current
regulator operating in parallel calculating firing angles αv and αi. The effective
α angle is the minimum value of αv and αi. This angle is available at the third
block output, named alpha (deg). Both regulators are of the proportionalintegral type. They should have high enough gains for low frequencies (<10 Hz)
to maintain the current or voltage response equal to the reference current
(Id_ref_lim) or reference voltage (Vd_ref), as long as α is within the minimum
and maximum limits (5° < α < 165° for rectifier, 92° < α < 165° for inverter). The
regulator gains Kp and KI are adjusted during small perturbations in the
current reference. The following gains are used:
Current regulator
Kp = 92 deg/p.u.
Ki = 4500 deg/p.u./s
Voltage regulator
Kp = 35 deg/p.u.
Ki = 2250 deg/p.u./s
Another particularity of the regulator is the linearization of the proportional
gain. As the Vd voltage generated by the rectifier and the inverter is
proportional to cos(α), the ∆Vd variation due to a ∆α change is proportional to
sin(α). With a constant Kp value, the effective gain is therefore proportional to
sin(α). In order to keep a constant proportional gain, independent of the α
value, the gain is linearized by multiplying the Kp constant by 1/sin(α). This
linearization is applied for a range of α defined by two limits specified in the
dialog box (third line).
System Startup and Steady State
Notice that the system is discretized, using sample time Ts (you should already
have Ts = 50e-6 defined in your workspace).
The system is programmed to start and reach a steady state. Then a step is
applied to the reference current so you can observe the dynamic response of the
regulators.
Start the simulation and observe the signals on the rectifier and inverter
scopes. The waveforms are reproduced here:
3-54
HVDC System
Rectifier
α = 18 degrees
Inverter
α = 142 degrees
Figure 3-28: Startup of the DC System and Step Applied on the Reference
3-55
3
Case Studies
The reference current follows a ramp from zero to 1 p.u. (2 kA) in 0.4 s. Observe
that the DC current starts to build up at t = 20 ms, time at which the controller
and the pulse generators are deblocked. The DC current and voltages start
from zero and reach steady state in approximately 0.5 s. The rectifier controls
the current and the inverter controls the voltage. Trace 1 of both rectifier and
inverter scopes shows the DC line voltage (1 p.u. = 500 kV). Trace 2 shows the
reference current and the measured Id current (1 p.u. = 2 kA). During the ramp
the inverter is actually controlling the current (Trace 4: Mode = 1) to the value
of Id_ref_lim less the Current Margin (0.1 p.u.) and the rectifier tries to
control the current at Id_ref_lim. At the inverter, the control mode changes to
voltage control (Mode = 2) at t = 0.33 s and the rectifier becomes effectively in
control of the current. Once steady state is attained, the α firing angles are 18
degrees and 142 degrees respectively on the rectifier and inverter side. At the
inverter, the Gamma Measurement block monitors the extinction angle γ for
each thyristor of a six-pulse bridge (e.g., the bridge connected to the Wye
windings) by determining the elapsed time expressed in electrical degrees from
the end of current conduction to the zero crossing of the commutating voltage.
The minimum and filtered means of six γ values are shown in trace 5. In steady
state, the filtered mean γ is around 24.5 degrees. Then, at t = 0.6 s, a step is
applied to the reference current so that you can observe the dynamic response
of the regulators.
Comparison of Theoretical and Simulation Results in Steady-State
The main equations governing the steady-state operation of the DC system are
given here so that you can compare the theoretical values to the simulation
results.
The following expression relates the mean direct voltage Vd of a 12-pulse
bridge to the direct current Id and firing angle α:
Vd = 2 × ( Vdo × cos ( α ) – Rc × Id )
where Vdo is the ideal no-load direct voltage for a six-pulse bridge:
Vdo = ( 3 2 ⁄ π ) × Vc
Vc is the line-to-line RMS commutating voltage that is dependent on the AC
system voltage and the transformer ratio.
Rc is the equivalent commutating resistance
3-56
HVDC System
Rc = ( 3 ⁄ π ) × Xc
Xc is the commutating reactance or transformer reactance referred to the valve
side.
The following rectifier parameters were used in the simulation.
The Vc voltage must take into account the effective value of the voltage on the
500 kV bus and the transformer ratio. If you look at the waveforms displayed
on the AC_RECTIFIER scope, you find 0.96 p.u. when the direct current Id has
reached its steady state (1 p.u.).
If you open the rectifier transformer dialog box, you find a multiplication factor
of 0.90 applied to the primary nominal voltage. The voltage applied to the
inverter is therefore boosted by a factor of 1/0.90.
Vc = 0.96 * 200 kV/0.90 = 213.3 kV
Id = 2 kA
α = 18°
Xc = 0.24 p.u., based on 1200 MVA and 222.2 kV = 9.874 Ω
Therefore
Vdo = ( 3 2 ⁄ π ) × 213.3 = 288.1 kV
Rc = ( 3 ⁄ π ) × 9.874 = 9.429 Ω
Vd = 2 × (288.1 kV × cos ( 18° ) – 9.429 × 2 ) = 510 kV
This theoretical voltage corresponds well with the expected rectifier voltage
calculated from the inverter voltage and the voltage drop in the DC line.
Vd = VdL inverter + ( R DCline + R inductance ) × Id
Vd = 500 kV + (4.5 Ω + 1 Ω ) × 2 = 511 kV
The µ commutation or overlap angle can also be calculated. Its theoretical
value depends on α, the DC current Id, and the commutation reactance Xc.
3-57
3
Case Studies
Xc ⋅ Id ⋅ 2
µ = acos cos ( α ) – ------------------------------ – α
Vc
9.874 ⋅ 2 ⋅ 2
µ = acos cos ( 18° ) – ---------------------------------- – 18° = 16.9°
213.3
Now verify the commutation angle by plotting the currents in two valves,
showing for example current extinction in valve 1 and current buildup in valve
3 of one six-pulse bridge of the rectifier.
Open the rectifier subsystem. Then open the upper bridge dialog box and select
All voltages and currents for the Measurement parameter. Now copy the
Multimeter block from the Measurements library into your case4 model.
Double-click the Multimeter block. A window showing all the bridge voltages
and currents appears. Select the following signals:
uSw1
Rectifier/Universal Bridge
iSw1
Rectifier/Universal Bridge
iSw3
Rectifier/Universal Bridge
The number of signals (3) is displayed in the multimeter icon. Using a Demux
block, send the three multimeter output signals to a two-trace scope (Trace 1:
uSw1 Trace 2: iSw1 and iSw3). Restart the simulation. The waveforms
illustrating two cycles are shown in the following figure. The measured
commutation angle is 14 steps of 50 µs or 15.1° of a 60 Hz period. The resolution
with a 50 µs time step is 1.1°; this angle compares reasonably well with the
theoretical value.
3-58
HVDC System
5
uSw1 (V)
2
x 10
0
−2
−4
0.5
0.505
0.51
0.515
0.52
0.525
0.53
i Sw1 & Sw3 (A)
3000
2000
1000
0
−1000
0.5
µ = 15.1°
0.505
0.51
0.515
0.52
0.525
0.53
0.505
0.51
0.515
Time (s)
0.52
0.525
0.53
alphaR (deg)
25
20
15
10
0.5
Figure 3-29: Valve Voltage and Currents (Commutation from Valve 1 to
Valve 3)
Finally, to validate the γ measurement at the inverter, plot the valve 1 voltage
and current. Also plot the commutating voltage corresponding to the outgoing
valve 1 to be extinguished and the filtered mean value of γ as shown in Figure
3-30. (The filter is low-pass with a time constant of 20 ms.) Verify also that the
values of α, µ, and γ add up to 180°.
3-59
3
Case Studies
Figure 3-30: Current and Commutation Voltage of Valve 1 Showing γ
Response to a Step of Reference Current
At t = 0.6 s, a 0.2 p.u. step is applied to the reference current (decrease from
1 p.u. to 0.8 p.u.). At t = 0.75 s, another step is applied to set the reference back
to 1 p.u. Observe the response of the current regulator. It stabilizes in
approximately 0.1 s.
3-60
HVDC System
Rectifier
Inverter
Figure 3-31: Response to a 0.2 p.u. Step of the Reference Current
DC Line Fault
Disconnect the Step Up & Down block in order to eliminate the step
disturbance applied to the reference current. In the DC Fault and Forced Delay
blocks of the power_hvdc12pulse model, change the multiplication factor of 100
to 1, so that a fault is now applied at t = 0.6 s. Open the FAULT scope to observe
the fault current. Restart the simulation.
3-61
3
Case Studies
Rectifier
1.5
VdL (pu)
1
0.5
0
−0.5
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
0.6
0.7
0.8
0.9
Time (s)
1
1.1
1.2
1.3
Id & Idref (pu)
3
2
1
0
−1
0.5
alphaR (deg)
200
150
100
50
0
0.5
Inverter
Id & Idref (pu)
VdL (pu)
2
0
−2
0.5
1.5
alphaI (deg)
0.7
0.8
0.9
1
1.1
1.2
1.3
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
0.6
0.7
0.8
0.9
time (s)
1
1.1
1.2
1.3
1
0.5
0
−0.5
0.5
160
140
120
100
80
0.5
8000
ifalut DC (A)
0.6
6000
4000
2000
0
0.5
Figure 3-32: DC Line Fault on the Rectifier Side
3-62
HVDC System
At fault application (t = 0.6 s), the DC current increases to 2.3 p.u. and the DC
voltage falls to zero at the rectifier. This DC voltage drop is seen by the Voltage
Dependent Current Order Limiter (VDCOL), which reduces the reference
current to 0.3 p.u. at the rectifier. A DC current still continues to circulate in
the fault. Then, at t = 0.65 s, the rectifier α firing angle is forced to 165 degrees
when the signal applied to the ForcedAlpha input goes high. This signal would
normally be provided by the protection system not simulated here. The rectifier
now operates in inverter mode. The DC line voltage becomes negative and the
energy stored in the line is returned to the AC network, causing rapid
extinction of the fault current at its next zero crossing. Then α is released at
t = 0.7 s and the normal DC voltage and current recover in approximately 0.5 s.
AC Line-to-Ground Fault at the Rectifier
Now you modify the fault timings in order to apply a line-to-ground fault. In
the DC Fault and Forced Delay blocks of power_hvdc12pulse, change the
multiplication factor of 1 to 100, so that the DC fault is now eliminated. In the
A-G Fault block, change the multiplication factor in the switching times to 1,
so that a six-cycle line-to-ground fault is now applied at the rectifier. Restart
the simulation.
3-63
3
Case Studies
RECTIFIER signals
VdL (pu)
2
1
0
−1
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
0.6
0.7
0.8
0.9
1
1.1
1.2
0.6
0.7
0.8
0.9
1
1.1
1.2
Id & Id ref (pu)
3
2
1
0
0.5
Alpha (deg)
150
100
50
0
0.5
Time (s)
INVERTER signals
VdL (pu)
2
1
0
−1
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
0.6
0.7
0.8
0.9
1
1.1
1.2
0.6
0.7
0.8
0.9
1
1.1
1.2
Id & Id ref (pu)
3
2
1
0
0.5
Alpha (deg)
180
160
140
120
100
0.5
Time (s)
Figure 3-33: Rectifier, Inverter Signals for an AC Line Fault on Rectifier Side
3-64
HVDC System
1.5
Vabc (pu)
1
0.5
0
−0.5
−1
−1.5
0.5
0.6
0.7
0.8
0.6
0.7
0.8
0.9
1
1.1
1.2
0.9
1
1.1
1.2
100
Iabc (A)
50
0
−50
0.5
Time (s)
Figure 3-34: Voltages and Currents on the 60 Hz Side for an AC Line Fault on
the Rectifier Side
Notice the 120 Hz oscillations in the DC voltage and currents during the fault.
When the fault is cleared at t = 0.7 s, the VDCOL operates and reduces the
reference current to 0.3 p.u. The system recovers in approximately 0.4 s after
fault clearing.
References
[1] Arrilaga, J., High Voltage Direct Current Transmission, IEEE Power
Engineering Series 6, Peter Peregrinus, Ltd., 1983.
[2] Electromagnetic Transients Program (EMTP), Workbook IV (TACS),
EL-4651, Volume 4, Electric Power Research Institute, 1989.
3-65
3
Case Studies
3-66
4
Improving Simulation
Performance
SimPowerSystems gives you many tools to speed up your power system simulations. Depending on
your model, you can choose among continuous, discrete, and phasor integration methods. Simulink
and related products provide additional ways to enhance model performance, including code
generation, creating your own model libraries, and tuning block parameters.
How SimPowerSystems Works
(p. 4-2)
Overview of what SimPowerSystems does when it analyzes
and runs your models
Choosing an Integration Method
(p. 4-5)
Advantages and disadvantages of continuous, discrete, and
phasor simulation of power system models
Simulating with Continuous
Integration Algorithms (p. 4-7)
How to integrate continuous time power models with
SimPowerSystems
Simulating Discretized Electrical
Systems (p. 4-11)
How to solve discretized power models with
SimPowerSystems
Increasing Simulation Speed
(p. 4-14)
Ways to optimize simulation speed and efficiency, including
the Simulink Accelerator and Real-Time Workshop
The Nonlinear Model Library
(p. 4-16)
Using and modifying the powerlib_models library to model
nonlinear power components
Creating Your Own Library of
Models (p. 4-20)
Creating your own custom power system blocks with the
Simulink block masking feature
Changing Your Circuit Parameters
(p. 4-21)
Modifying SimPowerSystems block parameters during
simulation and automating with MATLAB scripts
4
Improving Simulation Performance
How SimPowerSystems Works
Once you have built your circuit with the blocks of powerlib, you can start the
simulation just like any other Simulink model. Each time you start the
simulation, a special initialization mechanism is called. This initialization
process computes the state-space model of your electric circuit and builds the
equivalent system that can be simulated by Simulink.
The power_analyze command is part of that process. It obtains the state-space
model and builds the Simulink model of your circuit. You can also call
power_analyze from the command line to obtain the state-space model of the
linear part of the circuit. When called by the initialization process,
power_analyze performs the following five steps as shown in Figure 4-1:
1 Sorts all SimPowerSystems blocks, gets the block parameters and evaluates
the network topology. The blocks are separated into linear and nonlinear
blocks, and each electrical node is automatically given a node number.
2 Once the network topology has been obtained, the state-space model (A, B,
C, D matrices) of the linear part of the circuit is computed by the
power_statespace command. All steady-state calculations and
initializations are performed at this stage.
If you have chosen to discretize your circuit, the discrete state-space model
is computed from the continuous state-space model, using the Tustin
method.
If you are using the phasor solution method, the state-space model is
replaced with the complex transfer matrix H(jω) relating inputs and outputs
(voltage and current phasors) at the specified frequency. This matrix defines
the network algebraic equations.
3 Builds the Simulink model of your circuit and stores it inside one of the
measurement blocks. This means that you need at least one measurement
block (Current Measurement block, Voltage Measurement block,
Three-Phase V-I Measurement block, or Multimeter block) in your model.
The connections between the equivalent circuit and measurements blocks
are performed by invisible links using the Goto and From blocks.
4-2
How SimPowerSystems Works
Simulink library
Draw circuit
powerlib library
Start simulation
1.
power_analyze
- Analyze network topology
- Get circuit parameters
2.
power_statespace
- Compute continuous state-space
model of linear circuit (A, B, C, D)
- Compute steady-state and
initial conditions
Continuous Discrete
Solution Method
Phasor
Solution
Discretize
(Tustin
method)
H(jω)
Matrix
3.
power_analyze
- Build the Simulink model
- Initialize nonlinear models
powerlib_models library
powergui
- Display steady state info.
- Change initial conditions
- Initialize machines (Load Flow)
- Compute impedance vs. frequency
Simulink
starts simulation
Figure 4-1: SimPowerSystems Flowchart
The Simulink model uses a State-Space block or an S-Function block to model
the linear part of the circuit. Predefined Simulink models are used to simulate
nonlinear elements. These models can be found in the powerlib_models
4-3
4
Improving Simulation Performance
library available with SimPowerSystems. Simulink Source blocks connected at
the input of the State-Space block are used to simulate the electrical source
blocks.
The next figure represents the interconnections between the different parts of
the complete Simulink model. The nonlinear models are connected in feedback
between voltage outputs and current inputs of the linear model.
Linear model
Sources
(inputs)
u State-space
matrices
i
Outputs from
measurements
blocks
y
v
Nonlinear models
Figure 4-2: Interconnection of Linear Circuit and Nonlinear Models
Once power_analyze has completed the initialization process, Simulink starts
the simulation. You can observe waveforms on scopes connected at the outputs
of your measurement blocks. Through the Powergui, you can access the LTI
viewer and obtain transfer functions of your system between any pair of input
and output. The Powergui also allows you to perform a FFT analysis of
recorded signals in order to obtain their frequency spectrum.
If you stop the simulation and drag a copy of the Powergui block into your
circuit window, you have access to the steady-state values of inputs, outputs,
and state variables displayed as phasors. You can also use the interface to
modify the initial conditions. The Powergui block interface allows you to
perform a load flow with circuits involving three-phase machinery and
initialize the machine models so that the simulation starts in steady state. This
feature avoids long transients due to mechanical time constants of machines.
The Powergui block allows you to specify the desired frequency range, visualize
impedance curves, and store results in your workspace for Impedance
Measurement blocks connected in your circuit.
4-4
Choosing an Integration Method
Choosing an Integration Method
Three solution methods are available through the Powergui block. These are:
• Continuous solution method using Simulink variable-step solvers
• Discretization for solution at fixed time steps
• Phasor solution method using Simulink variable-step solvers
Continuous versus Discrete Solution
One important feature of SimPowerSystems is its ability to simulate electrical
systems either with continuous variable-step integration algorithms or with a
fixed-step using a discretized system. For small size systems, the continuous
method is usually more accurate. Variable-step algorithms are also faster
because the number of steps is fewer than with a fixed-step method giving
comparable accuracy. When using line-commutated power electronics, the
variable-step, event-sensitive algorithms detect the zero crossings of currents
in diodes and thyristors with a high accuracy so that you do not observe any
current chopping. However, for large systems (containing either a large
number of states or nonlinear blocks), the drawback of the continuous method
is that its extreme accuracy slows down the simulation. In such cases, it is
advantageous to discretize your system. In the following two sections, we
explain these two methods, their advantages, and their limitations.
What do we mean by “small size” and “large size”? Although the distinction is
not sharp, you can consider small size a system that contains fewer than 30
electrical states and fewer than 6 electronic switches. Circuit breakers do not
affect the speed much, because unlike power electronic switches, which are
commutated at every cycle, these devices are operated only a couple of times
during a test.
Phasor Solution Method
If you are interested only in the changes in magnitude and phase of all voltages
and currents when switches are closed or opened, you don’t need to solve all
differential equations (state-space model) resulting from the interaction of R,
L, C elements. You can instead solve a much simpler set of algebraic equations
relating the voltage and current phasors. This is what the phasor solution
method does. As its name implies, this method computes voltages and currents
as phasors. The phasor solution method is particularly useful for studying
4-5
4
Improving Simulation Performance
transient stability of networks containing large generators and motors. In this
type of problem, we are interested in electromechanical oscillations resulting
from interactions of machine inertias and regulators. These oscillations
produce a modulation of the magnitude and phase of fundamental voltages and
currents at low frequencies (typically between 0.02 Hz and 2 Hz). Long
simulation times are therefore required (several tens of seconds). The
continuous or discrete solution methods are not appropriate for this type of
problem.
In the phasor solution method, the fast modes are ignored by replacing the
network differential equations by a set of algebraic equations. The state-space
model of the network is replaced by a complex matrix evaluated at the
fundamental frequency and relating inputs (currents injected by machines into
the network) and outputs (voltages at machine terminals). As the phasor
solution method uses a reduced state-space model consisting of slow states of
machines, turbines and regulators, it dramatically reduces the required
simulation time.
Continuous variable-step solvers are very efficient in solving this type of
problem. Recommended solvers are ode15s or ode23tb with a maximum time
step of one cycle of the fundamental frequency (1/60 s or 1/50 s).You must keep
in mind however that this faster solution technique gives the solution only in
the vicinity of the fundamental frequency.
4-6
Simulating with Continuous Integration Algorithms
Simulating with Continuous Integration Algorithms
Simulink provides a variety of solvers. Most of the variable-step solvers work
well with linear circuits. However circuits containing nonlinear models,
especially circuits with circuit breakers and power electronics, require stiff
solvers.
Choosing an Integration Algorithm
Fastest simulation speed is usually achieved with ode23tb or ode15s with
default parameters.
Solver
ode23tb or ode15s
Relative tolerance
1e-3
Absolute tolerance
auto
Maximum step siz
auto
Initial step size
auto
Maximum order
(for ode15s) = 5
Normally, you can choose auto for the absolute tolerance and the maximum
step size. In some occasions you might have to limit the maximum step size and
the absolute tolerance. Selecting too small a tolerance can slow down the
simulation considerably. The choice of the absolute tolerance depends on the
maximum expected magnitudes of the state variables (inductor currents and
capacitor voltages). For example, if you work with high-power converters
where expected voltage and currents are thousands of volts and amperes, an
absolute tolerance of 0.1 or even 1.0 should be sufficient. If you are working
with low-power circuits involving maximum values of 100 V and 10 A, you
should use a smaller absolute tolerance, such as 0.001 or 0.01.
Simulating Switches and Power Electronic Devices
Two methods are used for simulation of switches and power electronic devices:
• If the switch is purely resistive the switch model is considered as part of the
linear circuit. The state-space model of the circuit, including open and closed
switches, is therefore recalculated at each switch opening or closing,
producing a change in the circuit topology. This method is always used with
4-7
4
Improving Simulation Performance
the Breaker block and the Ideal Switch block because these elements do not
have internal inductance. It is also applied for the Diode block and the
Thyristor block, with Ron > 0 and Lon = 0, and for the Universal Bridge with
forced commutated devices.
• If the switch contains a series inductance (Diode and Thyristor with Lon > 0,
IGBT, MOSFET, or GTO), the switch is simulated as a current source driven
by voltage across its terminals. The nonlinear element (with a voltage input
and a current output) is then connected in feedback on the linear circuit, as
shown in Figure 4-2.
You have therefore the choice to simulate diodes and thyristors with or without
Lon internal inductance. In most applications, it is not necessary to specify an
inductance Lon. However, for circuit topologies resulting in zero commutation
or overlap angle, you have to specify a switch inductance Lon in order to help
commutation.
Consider for example the circuit shown in the following figure. This circuit is
available in the power_rectifier_ideal model. The thyristor bridge is fed
from an infinite source (zero impedance) so that the commutation between
thyristors is quasi instantaneous.
Figure 4-3: Three-Phase Thyristor Rectifier on Infinite Source
4-8
Simulating with Continuous Integration Algorithms
If you simulate this circuit without internal thyristor inductances (Lon = 0),
observe high current spikes flowing in the three lines. This happens because
during commutation two thyristors connected to the same positive or negative
terminal of the bridge are in conduction for a short period of time, applying a
line-to-line short circuit on the source (see Figure 4-4 following). During
commutation, the current is limited only by the internal resistance of
thyristors (with Ron = 0.01 ohms, the current reaches 7.35 kA (208* 2
*sin(30o) / (2*0.01) or 245 times the normal DC current of 30 A). These short
circuits can be avoided by using a small Lon = 1 µH in the thyristor model. If
you repeat the simulation, you get square current waveforms with a peak value
of 30 A.
If you zoom in on the line current during a commutation, you discover that the
commutation is not instantaneous. The commutation time depends on the Lon
value and the DC current.
4-9
4
Improving Simulation Performance
Lon = 0
iA & iB (A)
50
0
−50
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0
0.01
0.02
0.03
0.04
0.05
Time (s)
0.06
0.07
0.08
0.09
0.1
250
Vd (V)
200
150
100
50
0
Lon = 1mH
40
iA & iB (A)
20
0
−20
−40
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0
0.01
0.02
0.03
0.04
0.05
Time (s)
0.06
0.07
0.08
0.09
0.1
250
Vd (V)
200
150
100
50
0
Figure 4-4: Source Currents and DC Load Voltage with Lon = 0 and Lon = 1 µH
4-10
Simulating Discretized Electrical Systems
Simulating Discretized Electrical Systems
You implement discretization by dragging the Powergui block into your
system. The sample time is specified in the block dialog box. The electrical
system is discretized using the Tustin method, which is equivalent to a
fixed-step trapezoidal integration. In order to avoid algebraic loops, the
electrical machines are discretized using the Forward Euler method.
The precision of the simulation is controlled by the time step you choose for the
discretization. If you use too large a sample time, the precision might not be
sufficient. The only way to know if it is acceptable is to repeat the simulation
with different sample times or to compare with a continuous method and to
find a compromise for the largest acceptable sample time. Usually sample
times of 20 µs to 50 µs give good results for simulation of switching transients
on 50 Hz or 60 Hz power systems or on systems using line-commutated power
electronic devices such as diodes and thyristors. However, for systems using
forced-commutated power electronic switches, you must reduce the time step.
These devices, the insulated-gate-bipolar transistor (IGBT), the field-effect
transistor (FET), and the gate-turn-off thyristor (GTO) are usually operating
at high switching frequencies. For example, simulating a
pulse-width-modulated (PWM) inverter operating at 8 kHz requires a time
step of 1 µs or less.
Note that even if you discretize your electric circuit, you can still use a
continuous control system. However, the simulation speed is improved by use
of a discrete control system.
Limitations of Discretization with Nonlinear Models
There are a few limitations to discretizing nonlinear models.
Discretization of individual forced-commutated electronic devices is not
allowed
Discretization of circuits containing forced-commutated power electronic
devices (IGBT, GTO, or MOSFET) is permitted only with the Universal Bridge
block. Discretization of circuits containing individual forced-commutated
devices is not allowed. For example, an attempt to discretize the buck DC
chopper circuit saved in the power_buckconv model produces a warning
message:
4-11
4
Improving Simulation Performance
Figure 4-5: A Circuit Containing Individual Forced Commutated Electronic
Switches Cannot be Discretized
In this circuit, the opening of the GTO forces a quasi instantaneous conduction
of the freewheeling diode. If the circuit was discretized, the diode would be fired
with one step delay, and the inductive current chopping would produce large
overvoltages. However, for conventional converter topologies as in the case of
the Universal Bridge, the switch interactions are known in advance. For
example, in a six-switch IGBT/Diode inverter (Figure 4-6 following), opening of
IGBT1 causes instantaneous conduction of diode D2 in the same arm. As the
circuit topology is predetermined, it is possible to force firing of the diode in the
same step that the IGBT opens. You should use a continuous method if you
prefer to use individual IGBT and Diode blocks to simulate a complete inverter.
4-12
Simulating Discretized Electrical Systems
+
IGBT1
A
B
Vdc
C
D2
Figure 4-6: IGBT Inverter Simulated by the Universal Bridge
Minimal load is required at machine terminals
When using electrical machines in discrete systems, you might have to use a
small parasitic resistive load, connected at the machine terminals, in order to
avoid numerical oscillations. Large sample times require larger loads. The
minimum resistive load is proportional to the sample time. As a rule of thumb,
remember that with a 25 µs time step on a 60 Hz system, the minimum load is
approximately 2.5% of the machine nominal power. For example, a 200 MVA
synchronous machine in a power system discretized with a 50 µs sample time
requires approximately 5% of resistive load or 10 MW. If the sample time is
reduced to 20 µs, a resistive load of 4 MW should be sufficient.
Lon = 0 is used for diodes and thyristors in discrete circuits
Diodes and thyristors used in a discretized circuit must have a zero internal
inductance. If you discretize a circuit containing diodes or thyristors with Lon
> 0, SimPowerSystems prompts you with a warning indicating that Lon will be
reset to zero.
4-13
4
Improving Simulation Performance
Increasing Simulation Speed
Once the proper method (continuous, discrete, or phasor), solver type, and
parameters have been selected, there are additional steps you can take to
optimize your simulation speed:
• Discretize your electric circuit and your control system. You can even use a
larger sample time for the control system, provided that it is a multiple of the
smallest sample time.
• Simulating large systems or complex power electronic converters can be time
consuming. If you have to repeat several simulations from a particular
operating point, you can save time by specifying a vector of initial states in
the Simulation —> Simulation parameters —> Workspace IO dialog pane.
This vector of initial conditions must have been saved from a previous
simulation run.
• Reducing the number of open scopes and the number of points saved in the
scope also helps in reducing the simulation time.
• If you have the Simulink Performance Tools option installed, you can use the
Accelerator. The performance gain obtained with the Accelerator varies with
the size and complexity of your model. Typically you can expect performance
improvements by factors of two to 10.
Using Accelerator Mode and Real-Time Workshop
The Simulink Accelerator mode is explained in the Simulink user’s guide.
The Simulink Accelerator speeds up the execution of Simulink models by
replacing the interpreted M code running beneath the Simulink blocks with
compiled code as your model executes. The Simulink Accelerator uses portions
of Real-Time Workshop (RTW) to generate this code on the fly. Although the
Simulink Accelerator uses RTW technology, Real-Time Workshop is not
required to run it. Also, if you do not have your own C compiler installed, you
can use the lcc C compiler provided with MATLAB.
To activate the Simulink Accelerator, select Accelerator instead of Normal in
the Simulation menu of your model window. Alternatively, select Accelerator
in the pull-down menu to the right and below the Simulation menu.
The following table shows typical performance gains obtained with
discretization and Simulink Accelerator applied on the following two demos: a
4-14
Increasing Simulation Speed
DC drive using a chopper and the AC-DC converter using a three-phase,
three-level voltage-sourced converter. Two versions of the DC drive model are
provided in the Demos library: a continuous version, power_dcdrive, and a
discrete version, power_dcdrive_disc. The AC-DC converter is available as
the power_3levelVSC demo.
Simulation Time in Seconds*
Simulation Method
DC drive
AC-DC converter
(Stop time = 1 s)
(Stop time = 0.15 s)
Continuous: ode23tb
default parameters
175
—
Discrete
23 (Ts = 10 µs)
25 (Ts = 5 µs)
Discrete + Accelerator
10 (Ts = 10 µs)
8.4 (Ts = 5 µs)
* Simulation times obtained on a Pentium II 500 MHz processor, with 128MB
of RAM
The table shows how discretizing your circuit boosts the simulation speed by a
factor of 7.6 for the DC drive. Using the Accelerator mode, an additional factor
of 2.3 performance gain is obtained. For complex power electronic converter
models, the Accelerator provides performance gains up to factors of 10.
To take full advantage of the performance enhancements made possible by
converting your models to code, you must use Real-Time Workshop to generate
stand-alone C code. You can then compile and run this code and, with xPC
Target, also run it on a target PC operating the xPC Target real-time kernel.
4-15
4
Improving Simulation Performance
The Nonlinear Model Library
The building blocks used to assemble the Simulink model of the nonlinear
circuit are stored in a library named powerlib_models. You do not normally
need to work with the powerlib_models library. However, you might have to
look inside the models or modify them for particular applications. You can
access that library by entering powerlib_models in the MATLAB Command
Window.
Figure 4-7: The powerlib_models Library
The Continuous Library
The Continuous library contains two types of blocks:
• Current sources simulating continuous machine models, surge arrester,
saturable transformer, and distributed parameter lines
• Switching logics used for purely resistive power electronic devices: breaker,
diode, three-level bridge, thyristor, universal bridge, and individual
forced-commutated devices
4-16
The Nonlinear Model Library
Nonlinear Blocks Simulated by Current Sources
These blocks use a voltage input (output of the state-space model of the linear
circuit) and their current output is fed into the state-space model. For complex
models, such as electrical machines requiring several inputs and outputs,
vectorized signals are used. Useful internal signals are also returned by most
of the models in a measurement output vector m.
For example, the Asynchronous Machine model is stored in the block named
asynchronous_machine. The model uses as inputs a vector of four voltages, two
rotor voltages and two stator voltages, respectively: (VabR, VbcR, VabS, VbcS).
It returns a vector of four currents, two rotor currents and two stator currents,
respectively: (IaR, IbR, IaS, IbS). The model also returns a measurement
output vector of 20 signals. When the Asynchronous Machine block is used
from powerlib this measurement output vector is accessible through the m
output of the machine icon. You can get details on the model inputs and outputs
from the documentation of powerlib and powerlib_models block icons.
4-17
4
Improving Simulation Performance
Logics for Switches and Power Electronic Devices
For switches and power electronic devices, the blocks contain only the logic
returning the status (open or closed) of the switch. The switch status is passed
to an S-function, which recomputes the state-space model of the linear circuit
each time that a switch status is changed. The m output is a vector returning
the switch current and voltage. The i output returns the tail current of
forced-commutated devices such as IGBTs and GTOs. All the switch logics are
vectorized. This means that a single model is used by power_analyze to
simulate all the devices having the same type.
The Discrete Library
The Discrete library contains the discrete versions of the continuous models
described above.
The Phasors Library
The Phasors library contains the phasor versions of some of the continuous
models described above. See the “Modeling Simple Systems” chapter for more
details on the phasor simulation.
The Switch Current Source Library
This library contains models of power electronic devices, which are simulated
by a current source external to the linear circuit.
These devices are the diode and the thyristor with Lon > 0, and the three
forced-commutated devices: gate-turn-off thyristor (GTO),
metal-oxide-semiconductor field-effect transistor (MOSFET), and the
insulated-gate-bipolar transistor (IGBT). All these models are continuous and
contain an internal inductance, allowing you to handle fast transitions of
forced-commutated converters. As for electrical machines, these models use a
4-18
The Nonlinear Model Library
voltage input (output of the state-space model of the linear circuit) and their
current output is fed into the state-space model. All these models are
vectorized.
Limitations of the Nonlinear Models
Because nonlinear models are simulated as current sources, they cannot be
connected in series with inductors and their terminals cannot be left open.
If you feed a machine through an inductive source, power_analyze prompts you
with an error message. You can avoid this by connecting large resistances in
parallel with the source inductances or across the machine terminals.
A series RC snubber circuit is included in the model of the Breaker block and
power electronics blocks. You should not have any problems if you keep these
snubber circuits in service. The snubber can be changed to a single resistance
by setting Cs to Inf, or to a single capacitor by setting Rs = 0. To eliminate the
snubber, specify Rs = Inf or Cs = 0.
Modifying the Nonlinear Models of the
powerlib_models Library
To use your own powerlib_models library, you must first copy the
powerlib_models.mdl file into your working directory or any other directory.
If you are using a directory different from the current directory, you must
specify this new directory in the MATLAB search path before the standard
blockset directory.
Then you can customize this new powerlib_models library, as long as you do
not change the names of the blocks, the number of inputs and outputs, and the
number of parameters in their dialog boxes. The next time you run the
simulation, these modifications take effect in your circuit.
4-19
4
Improving Simulation Performance
Creating Your Own Library of Models
SimPowerSystems provides a variety of basic building blocks to build more
complex electric blocks. Using the masking feature of Simulink, you can
assemble several elementary blocks of powerlib into a subsystem, build your
own parameter dialog box, create the desired block icon, and place this new
block in your personal library.
The “Modeling Simple Systems” chapter explained how to build a nonlinear
model using a Voltage Measurement block and a Controlled Current Source
block. The proposed examples (a nonlinear inductance and a nonlinear
resistance) were relatively simple. Using the same principle, you can develop
much more complex models using several controlled current sources, or even
controlled voltage sources. Refer to the tutorial “Building and Customizing
Nonlinear Models” on page 2-40.
4-20
Changing Your Circuit Parameters
Changing Your Circuit Parameters
Each time that you change a parameter of the powerlib blocks, you have to
restart the simulation in order to evaluate the state-space model and update
the parameters of the nonlinear models. However, you can change any source
parameter (Magnitude, Frequency, or Phase) during the simulation. The
modification takes place as soon as you apply the modification or close the
source block menu.
As for the Simulink blocks, all the powerlib block parameters that you specify
in the dialog box can contain MATLAB expressions using symbolic variable
names. Before running the simulation, you must assign a value to each of these
variables in your MATLAB workspace. This allows you to perform parametric
studies by changing the parameter values in a MATLAB script.
Example of MATLAB Script Performing a Parametric
Study
Suppose that you want to perform a parametric study in a circuit named
my_circuit to find the impact of varying an inductance on switching
transients. You want to find the highest overvoltage and the inductance value
for which it occurred.
The inductance value of one of the blocks contains variable L1, which should be
defined in your workspace. L1 is varied in 10 steps from 10 mH to 100 mH and
the values to be tested are saved in a vector, L1_vec. The voltage waveform to
be analyzed is stored in a ToWorkspace block in matrix format with V1 variable
name.
You can write a MATLAB M-file that loops on the 10 inductance values and
displays the worst case.
L1_vec= (10:10:100)*1e-3; % 10 inductances values 10/100 mH
V1_max=0;
for i=1:10
L1=L1_vec(i);
fprintf('Test No %d L1= %g H\n', i, L1);
sim('my_circuit'); % performs simulation
% memorize worst case
if max(abs(V1))>V1_max,
imax=i;
V1_max=max(abs(V1));
4-21
4
Improving Simulation Performance
end
end
fprintf('Maximum overvoltage= %g V occured for L1=%g H\n', V1_max,
L1_vec(imax));
4-22
5
SimPowerSystems Block
Reference
This chapter contains complete information on every block in SimPowerSystems. Refer to this
chapter when you need to find detailed information on a particular block.
Blocks – By Category (p. 5-2)
The SimPowerSystems blocks summarized by block
library
Blocks – Alphabetical List (p. 5-9)
The SimPowerSystems blocks listed alphabetically by
name
PLEASE RGENERAT
5
SimPowerSystems Block Reference
Blocks – By Category
The SimPowerSystems main library, powerlib, organizes its blocks into
libraries according to their behavior. The powerlib window displays the block
library icons and names. This section lists all SimPowerSystems blocks
arranged by library.
Use the Simulink Library Browser or the SimPowerSystems library to access
the blocks directly, guided by this hierarchical library list.
The main SimPowerSystems powerlib block library window contains the
Powergui block that opens a graphical user interface for the steady-state
analysis of electrical circuits.
Electrical Sources Library
Contains blocks that generate electric signals.
Elements Library
Contains linear and nonlinear circuit elements.
Phasor Elements Library
Contains specialized circuit elements for phasor analysis
Power Electronics Library
Contains power electronics devices.
Machines Library
Contains power machinery models.
Measurements Library
Contains blocks for the current and voltage measurements.
Extras Library
Contains three-phase blocks and specialized measurement and control blocks.
You can also open this library by entering powerlib_extras at the command
line.
5-2
Blocks – By Category
Demos Library
Contains useful demos and case studies.
Nonlinear Simulink Blocks for SimPowerSystems Models
The nonlinear Simulink blocks of powerlib are stored in a special block library
named powerlib_models. These masked Simulink models are used by
SimPowerSystems to build the equivalent Simulink model of your circuit. See
the “Improving Simulation Performance” chapter for a description of the
powerlib_models library.
5-3
5
SimPowerSystems Block Reference
Creating Electrical Sources
AC Current Source
Implement a sinusoidal current source
AC Voltage Source
Implement a sinusoidal voltage source
Controlled Current Source
Implement a controlled current source
Controlled Voltage Source
Implement a controlled voltage source
DC Voltage Source
Implement a DC voltage source
Three-Phase Programmable
Voltage Source
Implement a three-phase voltage source with programmable time
variation of amplitude, phase, frequency, and harmonics
Three-Phase Source
Implement a three-phase source with internal R-L impedance
Creating Circuit Elements
5-4
Breaker
Implement a circuit breaker opening at current zero crossing
Connection Port
Create a terminal port for a subsystem
Distributed Parameter Line
Implement an N-phases distributed parameter line model with
lumped losses
Ground
Provide a connection to the ground
Linear Transformer
Implement a two- or three-windings linear transformer
Mutual Inductance
Implement a magnetic coupling between two or three windings
Neutral
Implement a local common node in the circuit
Parallel RLC Branch
Implement a parallel RLC branch
Parallel RLC Load
Implement a linear parallel RLC load
PI Section Line
Implement a single-phase transmission line with lumped
parameters
Saturable Transformer
Implement a two- or three-windings Saturable Transformer
Series RLC Branch
Implement a series RLC branch
Series RLC Load
Implement a linear series RLC load
Surge Arrester
Implement a metal-oxide surge arrester
Blocks – By Category
Three-Phase Breaker
Implement a three-phase circuit breaker opening at current zero
crossing
Three-Phase Dynamic Load
Implements a three-phase dynamic load with active power and
reactive power as a function of voltage or controlled from an
external input
Three-Phase Fault
Implement a programmable phase-to-phase and phase-to-ground
fault breaker system
Three-Phase Mutual
Inductance Z1-Z0
Implement a three-phase RL impedance with mutual coupling
between phases and allow specification in the form of positive- and
zero-sequence parameters
Three-Phase Parallel RLC
Branch
Implement a three-phase parallel RLC branch
Three-Phase Parallel RLC
Load
Implement a three-phase parallel RLC load with selectable
connection
Three-Phase PI Section Line
Implement a three-phase transmission line section with lumped
parameters
Three-Phase Series RLC
Branch
Implement a three-phase series RLC branch
Three-Phase Series RLC Load Implement a three-phase series RLC load with selectable
connection
Three-Phase Transformer 12
Terminals
Implement three single-phase, two-winding transformers where
all terminals are accessible
Three-Phase Transformer
(Two Windings)
Implement a three-phase transformer with two windings
Three-Phase Transformer
(Three Windings)
Implement a three-phase transformer with three windings
Zigzag Phase-Shifting
Transformer
Implement a zigzag phase-shifting transformer with secondary
winding connection
5-5
5
SimPowerSystems Block Reference
Modeling with Phasor Elements
Static Var Compensator
Implement a phasor model of a three-phase, three-wire static var
compensator
Modeling Power Electronics Components
Diode
Implement a diode model
GTO
Implement a gate-turn-off (GTO) thyristor model
Ideal Switch
Implement an ideal switch model
IGBT
Implement an insulated-gate-bipolar-transformer (IGBT) model
MOSFET
Implement a metal-oxide-semiconductor-field-effect-transistor
(MOSFET) model
Three-Level Bridge
Implement a three-level neutral point clamped (NPC) power
converter
Thyristor
Implement a thyristor model
Universal Bridge
Implement a universal three-phase bridge converter
Modeling Electrical Machines
Asynchronous Machine
Model the dynamics of a three-phase asynchronous machine
(induction machine)
DC Machine
Model a separately excited DC machine.
Excitation System
Provide an excitation system for the synchronous machine and
regulate its terminal voltage in generating mode
Generic Power System
Stabilizer
Provide a generic power system stabilizer for the synchronous
machine and regulate its electrical power
Hydraulic Turbine and
Governor
Model a hydraulic turbine and a proportional-integral-derivative
governor system
Machine Measurement Demux Split machine measurement signal into separate signals
Multiband Power System
Stabilizer
5-6
Implement a multiband power system stabilizer
Blocks – By Category
Permanent Magnet
Synchronous Machine
Model the dynamics of a three-phase permanent magnet
synchronous machine with sinusoidal flux distribution
Simplified Synchronous
Machine
Model the dynamics of a simplified three-phase synchronous
machine
Steam Turbine and Governor
Implement a steam turbine and governor system
Synchronous Machine
Model the dynamics of a three-phase round-rotor or salient-pole
synchronous machine
Measuring Electrical Circuits
Current Measurement
Measure a current in a circuit
Impedance Measurement
Measure the impedance in a circuit as a function of the frequency
Multimeter
Measure voltage and current in SimPowerSystems blocks
Three-Phase V-I Measurement Measure three-phase currents and voltages in a circuit
Voltage Measurement
Measure a voltage in a circuit
Analyzing Electrical Circuits
Powergui
Graphical user interface for the analysis of circuits and systems
Additional Useful Blocks
Signal Measurements
abc_to_dq0 Transformation
Perform a Park transformation from the three-phase (abc)
reference frame to the dq0 reference frame
Active & Reactive Power
Measure the active and reactive powers of a voltage-current pair
dq0_to_abc Transformation
Perform a Park transformation from the dq0 reference frame to
the three-phase (abc) reference frame
Fourier
Fourier analyze a signal
RMS
Measure the root mean square (RMS) value of a signal
5-7
5
SimPowerSystems Block Reference
Three-Phase Sequence
Analyzer
Measure the positive-, negative-, and zero-sequence components of
a three-phase signal
Total Harmonic Distortion
Measure the total harmonic distortion of a voltage or current
signal containing harmonics
Signal and Pulse Sources
5-8
PWM Generator
Generate pulses for a carried-based Pulse Width Modulator
(PWM)
Synchronized 6-Pulse
Generator
Implement a synchronized pulse generator to fire the thyristors of
a six-pulse converter
Synchronized 12-Pulse
Generator
Implement a synchronized pulse generator to fire the thyristors of
a twelve-pulse converter
Timer
Generate a signal changing at specified transition times
Blocks – Alphabetical List
Blocks – Alphabetical List
5
abc_to_dq0 Transformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12
AC Current Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-18
Active & Reactive Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-20
AC Voltage Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24
Asynchronous Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26
Breaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-39
Connection Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-44
Controlled Current Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-46
Controlled Voltage Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-49
Current Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-53
DC Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-55
DC Voltage Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-61
Diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-63
Discrete System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-68
Distributed Parameter Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-69
dq0_to_abc Transformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-77
Excitation System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-79
Fourier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-82
Generic Power System Stabilizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-86
Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-90
GTO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-91
Hydraulic Turbine and Governor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-98
Ideal Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-103
IGBT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-108
Impedance Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-116
Linear Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-118
Machine Measurement Demux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-123
MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-127
Multiband Power System Stabilizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-132
Multimeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-140
Mutual Inductance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-146
Neutral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-151
Parallel RLC Branch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-153
Parallel RLC Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-157
Permanent Magnet Synchronous Machine . . . . . . . . . . . . . . . . . . . . . . . 5-160
5-9
5
PI Section Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Powergui . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PWM Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Saturable Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Series RLC Branch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Series RLC Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Simplified Synchronous Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Static Var Compensator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Steam Turbine and Governor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Surge Arrester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Synchronized 6-Pulse Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Synchronized 12-Pulse Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Synchronous Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Three-Phase Breaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Three-Level Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Three-Phase Dynamic Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Three-Phase Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Three-Phase Mutual Inductance Z1-Z0 . . . . . . . . . . . . . . . . . . . . . . . . . .
Three-Phase Parallel RLC Branch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Three-Phase Parallel RLC Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Three-Phase PI Section Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Three-Phase Programmable Voltage Source . . . . . . . . . . . . . . . . . . . . . .
Three-Phase Sequence Analyzer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Three-Phase Series RLC Branch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Three-Phase Series RLC Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Three-Phase Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Three-Phase Transformer 12 Terminals . . . . . . . . . . . . . . . . . . . . . . . . .
Three-Phase Transformer (Two Windings) . . . . . . . . . . . . . . . . . . . . . . .
Three-Phase Transformer (Three Windings) . . . . . . . . . . . . . . . . . . . . . .
Three-Phase V-I Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Thyristor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Total Harmonic Distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Universal Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Voltage Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Zigzag Phase-Shifting Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5-10
5-166
5-171
5-192
5-199
5-202
5-214
5-218
5-221
5-229
5-239
5-249
5-255
5-263
5-270
5-285
5-289
5-298
5-303
5-308
5-311
5-313
5-316
5-319
5-324
5-329
5-331
5-334
5-338
5-340
5-347
5-353
5-357
5-365
5-367
5-369
5-379
5-381
Blocks – Alphabetical List
power_analyze . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3
power_init . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-11
power_statespace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-12
5-11
abc_to_dq0 Transformation
Purpose
5abc_to_dq0 Transformation
Library
Extras/Measurements
Perform a Park transformation from the three-phase (abc) reference frame to
the dq0 reference frame
A discrete version of this block is available in the Extras/Discrete
Measurements library.
Description
The abc_to_dq0 Transformation block computes the direct axis, quadratic axis,
and zero sequence quantities in a two-axis rotating reference frame for a
three-phase sinusoidal signal. The following transformation is used:
2
V d = --- ( V a sin ( ωt ) + V b sin ( ωt – 2π ⁄ 3 ) + V c sin ( ωt + 2π ⁄ 3 ) )
3
2
V q = --- ( V a cos ( ωt ) + V b cos ( ωt – 2π ⁄ 3 ) + V c cos ( ωt + 2π ⁄ 3 ) )
3
1
V 0 = --- ( V a + V b + V c )
3
where ω = rotation speed (rad/s) of the rotating frame.
The transformation is the same for the case of a three-phase current; you
simply replace the Va, Vb, Vc, Vd, Vq, and V0 variables with the Ia, Ib, Ic, Id, Iq,
and I0 variables.
This transformation is commonly used in three-phase electric machine models,
where it is known as a Park transformation. It allows you to eliminate
time-varying inductances by referring the stator and rotor quantities to a fixed
or rotating reference frame. In the case of a synchronous machine, the stator
quantities are referred to the rotor. Id and Iq represent the two DC currents
flowing in the two equivalent rotor windings (d winding directly on the same
axis as the field winding, and q winding on the quadratic axis), producing the
same flux as the stator Ia, Ib, and Ic currents.
You can use this block in a control system to measure the positive-sequence
component V1 of a set of three-phase voltages or currents. The Vd and Vq (or Id
and Iq) then represent the rectangular coordinates of the positive-sequence
component.
You can use the Math Function block and the Trigonometric Function block to
obtain the modulus and angle of V1:
5-12
abc_to_dq0 Transformation
V1 =
2
Vq + Vd
2
∠V 1 = atan2 ( V q ⁄ V d )
This measurement system does not introduce any delay, but, unlike the
Fourier analysis done in the Sequence Analyzer block, it is sensitive to
harmonics and imbalances.
Dialog Box and
Parameters
Inputs and
Outputs
abc
Connect to the first input the vectorized sinusoidal phase signal to be
converted [phase A phase B phase C].
sin_cos
Connect to the second input a vectorized signal containing the [sin(ωt)
cos(ωt)] values, where ω is the rotation speed of the reference frame.
dq0
The output is a vectorized signal containing the three sequence
components [d q o].
5-13
abc_to_dq0 Transformation
Example
The power_3phsignaldq demo uses a Discrete Three-Phase Programmable
Source block to generate a 1 p.u., 15 degrees positive sequence voltage. At 0.05
second the positive sequence voltage is increased to 1.5 p.u. and at 0.1 second
an imbalance is introduced by the addition of a 0.3 p.u. negative sequence
component with a phase of −30 degrees. The magnitude and phase of the
positive-sequence component are evaluated in two different ways:
• Sequence calculation of phasors using Fourier analysis
• abc-to-dq0 transformation
5-14
abc_to_dq0 Transformation
Start the simulation and observe the instantaneous signals Vabc (Scope1), the
signals returned by the Sequence Analyzer (Scope2), and the abc-to-dq0
transformation (Scope3).
5-15
abc_to_dq0 Transformation
Note that the Sequence Analyzer, which uses Fourier analysis, is immune to
harmonics and imbalance. However, its response to a step is a one-cycle ramp.
The abc-to-dqo transformation is instantaneous. However, an imbalance
produces a ripple at the V1 and Phi1 outputs.
5-16
abc_to_dq0 Transformation
See Also
dq0_to_abc Transformation
5-17
AC Current Source
Purpose
5AC Current Source
Library
Electrical Sources
Description
The AC Current Source block implements an ideal AC current source. The
positive current direction is indicated by the arrow in the block icon. The
generated current I is described by the following relationship:
Implement a sinusoidal current source
I = A sin ( ωt + φ )
ω = 2πf
φ = Phase in radians
Negative values are allowed for amplitude and phase. A zero frequency
specifies a DC current source. You cannot enter a negative frequency; Simulink
returns an error in that case, and the block displays a question mark in the
block icon. You can modify the first three block parameters at any time during
the simulation.
Dialog Box and
Parameters
Peak amplitude
The peak amplitude of the generated current, in amperes (A).
5-18
AC Current Source
Phase
The phase in degrees (deg).
Frequency
The source frequency in hertz (Hz).
Sample time
The sample period in seconds (s). The default is 0, corresponding to a
continuous source.
Measurements
Select Current to measure the current flowing through the AC Current
Source block.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurement is identified by a label
followed by the block name.
Measurement
Label
Current
Isrc:
Example
The power_accurrent demo uses two AC Current Source blocks in parallel to
sum two sinusoidal currents in a resistor.
See Also
Controlled Current Source, Multimeter
5-19
Active & Reactive Power
Purpose
5Active & Reactive Power
Library
Extras/Measurements
Measure the active and reactive powers of a voltage-current pair
A discrete version of this block is available in the Extras/Discrete
Measurements library.
Description
The Active & Reactive Power block measures the active power P and reactive
power Q associated with a periodic voltage-current pair that can contain
harmonics. P and Q are calculated by averaging the V I product with a running
average window over one cycle of the fundamental frequency, so that the
powers are evaluated at fundamental frequency.
t
1
P = ---T
∫
( V ( ωt ) × I ( ωt ) ) dt
(t – T)
t
1
Q = ---T
∫
( V ( ωt ) × I ( ωt – π ⁄ 2 ) ) dt
(t – T)
where T = 1/(fundamental frequency).
A current flowing into an RL branch, for example, produces positive active and
reactive powers.
As this block uses a running window, one cycle of simulation has to be
completed before the output gives the correct active and reactive powers.
The discrete version of this block, available in the Extras/Discrete
Measurements library, allows you to specify the initial input voltage and
current (magnitude and phase). For the first cycle of simulation the outputs are
held constant using the values specified by the initial input parameters.
5-20
Active & Reactive Power
Dialog Box and
Parameters
Fundamental frequency (Hz)
The fundamental frequency, in hertz, of the instantaneous voltage and
current.
Inputs and
Outputs
The first input is the instantaneous voltage. The second input is the
instantaneous current. The output is a vector [P Q] of the active and reactive
powers.
Example
The power_transfo demo simulates a three-winding distribution transformer
rated at 75 kVA:14400/120/120 V. The transformer primary winding is
connected to a high-voltage source of 14400 Vrms. Two identical inductive
5-21
Active & Reactive Power
loads (20 kW-10 kvar) are connected to the two secondary windings. A third
capacitive load (30 kW-20 kvar) is fed at 240 V.
Initially, the circuit breaker in series with Load 2 is closed, so that the system
is balanced. When the circuit breaker opens, a current starts to flow in the
neutral path as a result of the load imbalance.
The active power computed from the primary voltage and current is measured
by an Active & Reactive Power block. When the breaker opens, the active power
decreases from 70 kW to 50 kW.
5-22
Active & Reactive Power
5-23
AC Voltage Source
Purpose
5AC Voltage Source
Library
Electrical Sources
Description
The AC Voltage Source block implements an ideal AC voltage source. The
generated voltage U is described by the following relationship:
Implement a sinusoidal voltage source
U = A sin ( ωt + φ )
ω = 2πf
φ = Phase in radians
Negative values are allowed for amplitude and phase. A 0 frequency specifies
a DC voltage source. Negative frequency is not allowed; otherwise Simulink
signals an error, and the block displays a question mark in the block icon. You
can modify the first three block parameters at any time during the simulation.
Dialog Box and
Parameters
Peak amplitude
The peak amplitude of the generated voltage, in volts (V).
Phase
The phase in degrees (deg).
5-24
AC Voltage Source
Frequency
The source frequency in hertz (Hz).
Sample time
The sample period in seconds (s). The default is 0, corresponding to a
continuous source.
Measurements
Select Voltage to measure the voltage across the terminals of the AC
Voltage Source block.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurement is identified by a label
followed by the block name.
Measurement
Label
Voltage
Usrc:
Example
The power_acvoltage demo uses two AC Voltage Source blocks at different
frequencies connected in series across a resistor. The sum of the two voltages
is read by a Voltage Measurement block.
See Also
Controlled Voltage Source, DC Voltage Source, Multimeter
5-25
Asynchronous Machine
Purpose
5Asynchronous Machine
Library
Machines
Description
The Asynchronous Machine block operates in either generator or motor mode.
The mode of operation is dictated by the sign of the mechanical torque (positive
for motoring, negative for generating). The electrical part of the machine is
represented by a fourth-order state-space model and the mechanical part by a
second-order system. All electrical variables and parameters are referred to the
stator. This is indicated by the prime signs in the machine equations given
below. All stator and rotor quantities are in the arbitrary two-axis reference
frame (dq frame). The subscripts used are defined as follows:
5-26
Model the dynamics of a three-phase asynchronous machine, also known as an
induction machine
Subscript
Definition
d
d axis quantity
q
q axis quantity
r
Rotor quantity
s
Stator quantity
l
Leakage inductance
m
Magnetizing inductance
Asynchronous Machine
Electrical System
+
Vqs
ωϕ
Rs + ds
− Lls
iqs
Lm
L'lr (ω−−ωr)ϕ'dr
+
i'qr
R'r
+
V'qr
−
−
ωϕ L L' (ω−ωr)ϕ'qr
Rs − qs
lr
+ ls
+ −
+
R'r
Lm
V'dr
Vds ids
i'dr
+
−
−
d axis
q axis
d
V qs = R s i qs + ------ ϕ qs + ωϕ ds
dt
ϕ qs = L s i qs + L m i′ qr
ϕ ds = L s i ds + L m i′ dr
d
V ds = R s i ds + ------ ϕ ds – ωϕ qs
dt
d
V′ qr = R′ r i′ qr + ------ ϕ′ qr + ( ω – ω r )ϕ′ dr
dt
d
V′ dr = R′ r i′ dr + ------ ϕ′ dr – ( ω – ω r )ϕ′ qr
dt
T e = 1.5p ( ϕ ds i qs – ϕ qs i ds )
where
ϕ′ qr = L′ r i′ qr + L m i qs
ϕ′ dr = L′ r i′ dr + L m i ds
L s = L ls + L m
L′ r = L′ lr + L m
Mechanical System
1
d
ω = -------- ( T e – Fω m – T m )
2H
dt m
d
θ = ωm
dt m
The Asynchronous Machine block parameters are defined as follows (all
quantities are referred to the stator):
Parameter
Definition
Rs, Lls
Stator resistance and leakage inductance
R'r, L'lr
Rotor resistance and leakage inductance
Lm
Magnetizing inductance
5-27
Asynchronous Machine
5-28
Parameter (Continued)
Definition (Continued)
Ls, L'r
Total stator and rotor inductances
Vqs, iqs
q axis stator voltage and current
V'qr, i'qr
q axis rotor voltage and current
Vds, ids
d axis stator voltage and current
V'dr, i'dr
d axis rotor voltage and current
ϕqs, ϕds
Stator q and d axis fluxes
ϕ'qr, ϕ'dr
Rotor q and d axis fluxes
ωm
Angular velocity of the rotor
θm
Rotor angular position
p
Number of pole pairs
ωr
Electrical angular velocity (ωm x p)
θr
Electrical rotor angular position (θm x p)
Te
Electromagnetic torque
Tm
Shaft mechanical torque
J
Combined rotor and load inertia coefficient. Set
to infinite to simulate locked rotor.
H
Combined rotor and load inertia constant. Set to
infinite to simulate locked rotor.
F
Combined rotor and load viscous friction
coefficient
Asynchronous Machine
Dialog Boxes
and
Parameters
You can choose between two Asynchronous Machine blocks to specify the
electrical and mechanical parameters of the model.
Rotor type
Specifies the branching for the rotor windings.
5-29
Asynchronous Machine
Reference frame
Specifies the reference frame that is used to convert input voltages (abc
reference frame) to the dq reference frame, and output currents (dq
reference frame) to the abc reference frame. You can choose among the
following reference frame transformations:
- Rotor (Park transformation)
- Stationary (Clarke or αβ transformation)
- Synchronous
The following relationships describe the abc-to-dq reference frame
transformations applied to the Asynchronous Machine phase-to-phase
voltages.
V qs
V abs
1
= --- 2 cos θ cos θ + 3 sin θ
3
V ds
2 sin θ sin θ – 3 cos θ V bcs
V′ qr
1
= --- 2 cos β cos β+ 3 sin β
3
V′ dr
2 sin β sin β – 3 cos β
V′ abr
V′ bcr
In the preceding equations, θ is the angular position of the reference frame,
while β = θ – θ r is the difference between the position of the reference
frame and the position (electrical) of the rotor. Because the machine
windings are connected in a three-wire Y configuration, there is no
homopolar (0) component. This also justifies the fact that two line-to-line
input voltages are used inside the model instead of three line-to-neutral
voltages. The following relationships describe the dq-to-abc reference
frame transformations applied to the Asynchronous Machine phase
currents.
5-30
Asynchronous Machine
i as
i bs
i′ ar
i′ br
=
=
cos θ
sin θ
– cos θ + 3 sin θ
------------------------------------------2
– 3 cos θ – sin θ
------------------------------------------2
cos β
sin β
– cos β + 3 sin β
-------------------------------------------2
– 3 cos β – sin β
------------------------------------------2
i qs
i ds
i′ qr
i′ dr
i cs = – i as – i bs
i′ cr = – i′ ar – i′ br
The following table shows the values taken by θ and β in each reference
frame (θe is the position of the synchronously rotating reference frame).
Reference Frame
θ
β
Rotor
θr
0
Stationary
0
−θr
Synchronous
θe
θe − θr
The choice of reference frame affects the waveforms of all dq variables. It
also affects the simulation speed and in certain cases the accuracy of the
results. The following guidelines are suggested in [1]:
- Use the stationary reference frame if the stator voltages are either
unbalanced or discontinuous and the rotor voltages are balanced (or 0).
- Use the rotor reference frame if the rotor voltages are either unbalanced
or discontinuous and the stator voltages are balanced.
- Use either the stationary or synchronous reference frames if all voltages
are balanced and continuous.
Nominal power, L-L volt, and freq.
The nominal apparent power Pn (VA), RMS line-to-line voltage Vn (V), and
frequency fn (Hz).
5-31
Asynchronous Machine
Stator
The stator resistance Rs (Ω or p.u.) and leakage inductance Lls (H or p.u.).
Rotor
The rotor resistance Rr' (Ω or p.u.) and leakage inductance Llr' (H or p.u.),
both referred to the stator.
Mutual inductance
The magnetizing inductance Lm (H or p.u.).
Inertia, friction factor, and pairs of poles
For the SI units dialog box: the combined machine and load inertia
coefficient J (kg.m2), combined viscous friction coefficient F (N.m.s), and
pole pairs p.
For the p.u. units dialog box: the inertia constant H (s), combined viscous
friction coefficient F (p.u.), and pole pairs p.
Initial conditions
Specifies the initial slip s, electrical angle θe (degrees), stator current
magnitude (A or p.u.), and phase angles (degrees):
[slip, th, ias, ibs, ics, phaseas, phasebs, phasecs]
For the wound-rotor machine, you can also specify optional initial values
for the rotor current magnitude (A or p.u.), and phase angles (degrees):
[slip, th, ias, ibs, ics, phaseas, phasebs, phasecs, iar, ibr, icr,
phasear, phasebr, phasecr]
For the squirrel cage machine, the initial conditions can be computed by
the load flow utility in the Powergui block.
Note Depending on the dialog box you choose to use, SimPowerSystems
automatically converts the parameters you enter into per unit parameters.
The Simulink model of the Asynchronous Machine block uses p.u. parameters.
Inputs and
Outputs
5-32
The stator terminals of the Asynchronous Machine block are identified by the
A, B, and C letters. The rotor terminals are identified by the a, b, and c letters.
Asynchronous Machine
Note that the neutral connections of the stator and rotor windings are not
available; three-wire Y connections are assumed.
You must be careful when you connect ideal sources to the machine’s stator. If
you choose to supply the stator via a three-phase Y-connected infinite voltage
source, you must use three sources connected in Y. However, if you choose to
simulate a delta source connection, you must only use two sources connected in
series.
The Simulink input of the block is the mechanical torque at the machine’s
shaft. When the input is positive, the asynchronous machine behaves as a
motor. When the input is negative, the asynchronous machine behaves as a
generator.
The Simulink output of the block is a vector containing 21 signals. They are, in
order (refer to the preceding description section, all currents flowing into
machine).
Signal
Definition
1 to 3
Rotor currents i'ra, i'rb, and i'rc
4 to 9
i'qr, i'dr, ϕ'qr, ϕ'dr, v'qr, and v'd
10 to 12
Stator currents isa, isb and isc
13 to 18
iqs, ids, ϕqs, ϕds, vqs, and vds
19 to 21
ωm, Te, and θm
5-33
Asynchronous Machine
You can demultiplex these signals by using the Machines Measurement
Demux block provided in the Machines library.
Limitations
The Asynchronous Machine block does not include a representation of iron
losses and saturation.
Example
The power_pwm demo illustrates the use of the Asynchronous Machine block in
motor mode. It consists of an asynchronous machine in an open-loop speed
control system.
The machine’s rotor is short-circuited, and the stator is fed by a PWM inverter,
built with Simulink blocks and interfaced to the Asynchronous Machine block
through the Controlled Voltage Source block. The inverter uses sinusoidal
pulse-width modulation, which is described in [2]. The base frequency of the
sinusoidal reference wave is set at 60 Hz and the triangular carrier wave’s
frequency is set at 1980 Hz. This corresponds to a frequency modulation factor
mf of 33 (60 Hz x 33 = 1980). It is recommended in [2] that mf be an odd multiple
of three and that the value be as high as possible.
The 3 HP machine is connected to a constant load of nominal value (11.9 N.m).
It is started and reaches the set point speed of 1.0 p.u. at t = 0.9 second.
The parameters of the machine are those found in the SI Units dialog box
above, except for the stator leakage inductance, which is set to twice its normal
value. This is done to simulate a smoothing inductor placed between the
inverter and the machine. Also, the stationary reference frame was used to
obtain the results shown.
5-34
Asynchronous Machine
Open the power_pwm demo. Note in the simulation parameters that a small
relative tolerance is required because of the high switching rate of the inverter.
Run the simulation and observe the machine’s speed and torque.
5-35
Asynchronous Machine
The first graph shows the machine’s speed going from 0 to 1725 rpm (1.0 p.u.).
The second graph shows the electromagnetic torque developed by the machine.
Because the stator is fed by a PWM inverter, a noisy torque is observed.
However, this noise is not visible in the speed because it is filtered out by the
machine’s inertia, but it can also be seen in the stator and rotor currents, which
are observed next.
5-36
Asynchronous Machine
Finally, look at the output of the PWM inverter. Because nothing of interest
can be seen at the simulation time scale, the graph concentrates on the last
moments of the simulation.
5-37
Asynchronous Machine
References
[1] Krause, P.C., O. Wasynczuk, and S.D. Sudhoff, Analysis of Electric
Machinery, IEEE Press, 1995.
[2] Mohan, N., T.M. Undeland, and W.P. Robbins, Power Electronics:
Converters, Applications, and Design, John Wiley & Sons, Inc., New York,
1995, Section 8.4.1.
See Also
5-38
Machine Measurement Demux, Powergui
Breaker
Purpose
5Breaker
Library
Elements
Description
The Breaker block implements a circuit breaker where the opening and closing
times can be controlled either from an external Simulink signal (external
control mode), or from an internal control timer (internal control mode).
Implement a circuit breaker opening at the current zero crossing
The arc extinction process is simulated by opening the breaker device when the
current passes through 0 (first current zero crossing following the transition of
the Simulink control input from 1 to 0).
When the breaker is closed it behaves as a resistive circuit. It is represented by
a resistance Ron. The Ron value can be set as small as necessary in order to be
negligible compared with external components (typical value is 10 mΩ). When
the breaker is open it has an infinite resistance.
If the Breaker block is set in external control mode, a Simulink input appears
on the block icon. The control signal connected to the Simulink input must be
either 0 or 1: 0 to open the breaker, 1 to close it. If the Breaker block is set in
internal control mode, the switching times are specified in the dialog box of the
block.
If the breaker initial state is set to 1 (closed), SimPowerSystems automatically
initializes all the states of the linear circuit and the Breaker block initial
current so that the simulation starts in steady state.
A series Rs-Cs snubber circuit is included in the model. It can be connected to
the circuit breaker. If the Breaker block happens to be in series with an
inductive circuit, an open circuit or a current source, you must use a snubber.
5-39
Breaker
Dialog Box and
Parameters
Breaker resistance Ron
The internal breaker resistance, in ohms (Ω). The Breaker resistance Ron
parameter cannot be set to 0.
Initial state
The initial state of the breaker. A closed contact is displayed in the block
icon when the Initial state parameter is set to 1, and an open contact is
displayed when it is set to 0.
Snubber resistance Rs
The snubber resistance, in ohms (Ω). Set the Snubber resistance Rs
parameter to inf to eliminate the snubber from the model.
5-40
Breaker
Snubber capacitance Cs
The snubber capacitance, in farads (F). Set the Snubber capacitance Cs
parameter to 0 to eliminate the snubber, or to inf to get a resistive
snubber.
Switching times
Specifies the vector of switching times when using the Breaker block in
internal control mode. At each switching time the Breaker block opens or
closes depending on its initial state. For example, if the Initial state
parameter is 0 (open), the breaker closes at the first switching time, opens
at the second switching time, and so on. The Switching times parameter
is not visible in the dialog box if the External control of switching times
parameter is selected.
External control of switching times
If selected, adds a Simulink input to the Breaker block for external control
of the switching times of the breaker. The switching times are defined by a
logical signal (0 or 1) connected to the Simulink input.
Measurements
Select Branch voltage to measure the voltage across the Breaker block
terminals.
Select Branch current to measure the current flowing through the
Breaker block. If the snubber device is connected to the breaker model, the
measured current is the one flowing through the breaker contacts only.
Select Branch voltage and current to measure the breaker voltage and
the breaker current.
Place a Multimeter block in your model to display the selected
measurements during the simulation.
In the Available Measurements list box of the Multimeter block, the
measurement is identified by a label followed by the block name:
Measurement
Label
Branch voltage
Ub:
Branch current
Ib:
5-41
Breaker
Limitations
When the block is connected in series with an inductor or another current
source, you must add the snubber circuit. In most applications you can use a
resistive snubber (Snubber capacitance parameter set to inf) with a large
resistor value (Snubber resistance parameter set to 1e6 or so). Because of
modeling constraints, the internal breaker inductance Ron cannot be set to 0.
You must use a stiff integration algorithm to simulate circuits with the
Breaker block. ode23tb or ode15s with default parameters usually gives the
best simulation speed.
Example
The power_breaker demo illustrates a circuit breaker connected in series with
a series RL circuit on a 60 Hz voltage source. The switching times of the
Breaker block are controlled by a Simulink signal. The breaker device is
initially closed and an opening order is given at t = 1.5 cycles, when current
reaches a maximum. The current stops at the next zero crossing, then the
breaker is reclosed at a zero crossing of voltage at t = 3 cycles.
Simulation produces the following results.
5-42
Breaker
Note that the breaker device opens only when the load current has reached
zero, after the opening order.
See Also
Three-Phase Breaker, Three-Phase Fault
5-43
Connection Port
Purpose
5Connection Port
Library
Elements
Description
The Connection Port block, placed inside a subsystem composed of
SimPowerSystems blocks, creates a Physical Modeling open round connector
port on the boundary of the subsystem. Once connected to a connection line,
the port becomes solid • . Once you begin the simulation, the solid port •
becomes an electrical terminal port, an open square .
Create a Physical Modeling connector port for a subsystem
You connect individual SimPowerSystems blocks and subsystems made of
SimPowerSystems blocks to one another with SimPowerSystems connection
lines, instead of normal Simulink signal lines. These are anchored at the open,
round connector ports . Subsystems constructed of SimPowerSystems blocks
automatically have such open round connector ports. You can add additional
connector ports by adding Connection Port blocks to your subsystem.
Dialog Box and
Parameters
Port number
This field labels the subsystem connector port created by the block.
Multiple connector ports on the boundary of a single subsystem require
different numbers as labels. The default value for the first port is 1.
Port location on parent subsystem
Choose which side of the parent subsystem boundary the port is placed.
The choices are left or right. The default is left.
5-44
Connection Port
See Also
In Simulink, see Creating Subsystems.
5-45
Controlled Current Source
Purpose
5Controlled Current Source
Library
Electrical Sources
Description
The Controlled Current Source block provides a current source controlled by a
Simulink signal. The positive current direction is as shown by the arrow in the
block icon.
Implement a controlled current source
You can initialize the Controlled Current Source block with a specific AC or DC
current. If you want to start the simulation in steady state, the block input
must be connected to a signal starting as a sinusoidal or DC waveform
corresponding to the initial values.
Dialog Box and
Parameters
5-46
Controlled Current Source
Initialize
If selected, initializes the Controlled Current Source block with the
specified Initial current, Initial phase, and Initial frequency
parameters.
Source type
The Source type parameter is not visible if the Initialize parameter is not
selected.
The type of current source. Select AC to initialize the Controlled Current
Source Block as an AC current source. Select DC to initialize the Controlled
Current Source block as a DC current.
Initial current
The Initial current parameter is not visible in the dialog box if the
Initialize parameter is not selected. The initial peak current for the
initialization of the source, in amperes (A).
Initial phase
The initial phase for the initialization of the source, in degrees. The Initial
phase parameter is not visible in the dialog box if the Source type
parameter is set to DC.
Initial frequency
The initial frequency for the initialization of the source, in hertz (Hz). The
Initial frequency parameter is not visible in the dialog box if the Source
type parameter is set to DC.
Measurements
Select Current to measure the current flowing through the Controlled
Current Source block.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurement is identified by a label
followed by the block name:
Measurement
Label
Current
Isrc:
5-47
Controlled Current Source
Example
The power_controlcurr demo uses a Controlled Current Source to generate a
60 Hz current modulated at 5 Hz.
Simulation produces the following waveforms:
See Also
5-48
AC Current Source, Controlled Voltage Source, Multimeter
Controlled Voltage Source
Purpose
5Controlled Voltage Source
Library
Electrical Sources
Description
The Controlled Voltage Source block provides a voltage source controlled by a
Simulink signal.
Implement a controlled voltage source
You can initialize the Controlled Voltage Source block with a specific AC or DC
voltage. If you want to start the simulation in steady state, the Simulink input
must be connected to a signal starting as a sinusoidal or DC waveform
corresponding to the initial values.
Dialog Box and
Parameters
Initialize
If selected, initializes the Controlled Voltage Source block with the
specified Initial voltage, Initial phase, and Initial frequency
parameters.
5-49
Controlled Voltage Source
Source type
The Source type parameter is not available if the Initialize parameter is
not selected.
The type of voltage source. Select AC to initialize the Controlled Voltage
Source block with an AC voltage source. Select DC to initialize the
Controlled Voltage Source Block with a DC voltage.
Initial voltage
The Initial voltage parameter is not available if the Initialize parameter
is not selected. The initial voltage for the initialization of the source, in
amperes (A).
Initial phase
The Initial phase parameter is not available if the Source type parameter
is set to DC. The initial phase for the initialization of the source, in degrees.
Initial frequency
The initial frequency for the initialization of the source, in hertz (Hz). The
Initial frequency parameter is not available in the dialog box if the
Source type parameter is set to DC.
Measurements
Select Voltage to measure the voltage across the terminals of the
Controlled Voltage Source block.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurement is identified by a label
followed by the block name:
Example
5-50
Measurement
Label
Voltage
Usrc:
The power_controlvolt demo uses Controlled Voltage Source blocks to
generate a 60 Hz sinusoidal voltage containing a third harmonic. One
Controlled Voltage Source block is initialized as a 120 V AC voltage source with
an initial frequency of 60 Hz and initial phase set to 0. The second Controlled
Voltage Source block is not initialized.
Controlled Voltage Source
At t = 0.0333 s a 100 V-180 Hz sinusoidal signal is added to the 120 V Simulink
signal. The resulting capacitor voltages are compared on a Scope block.
5-51
Controlled Voltage Source
The Vc voltage starts in steady state, whereas the Vc1 voltage contains a DC
offset.
See Also
5-52
AC Current Source, Controlled Current Source, Multimeter
Current Measurement
Purpose
5Current Measurement
Library
Measurements
Description
The Current Measurement block is used to measure the instantaneous current
flowing in any electrical block or connection line. The Simulink output provides
a Simulink signal that can be used by other Simulink blocks.
Measure a current in a circuit
Dialog Box and
Parameters
Output signal
Specifies the format of the output signal when the block is used in a phasor
simulation. The Output signal parameter is disabled when the block is not
used in a phasor simulation. The phasor simulation is activated by a
Powergui block placed in the model.
Set to Complex to output the measured current as a complex value. The
output is a complex signal.
Set to Real-Imag to output the real and imaginary parts of the measured
current. The output is a vector of two elements.
Set to Magnitude-Angle to output the magnitude and angle of the
measured current. The output is a vector of two elements.
Set to Magnitude to output the magnitude of the measured current. The
output is a scalar value.
Example
The power_currmeasure demo uses four Current Measurement blocks to read
currents in different branches of a circuit. The two scopes display the same
current.
5-53
Current Measurement
See Also
5-54
Powergui, Three-Phase V-I Measurement, Voltage Measurement
DC Machine
Purpose
5DC Machine
Library
Machines
Description
This block implements a separately excited DC machine. An access is provided
to the field terminals (F+, F−) so that the machine model can be used as a
shunt-connected or a series-connected DC machine. The torque applied to the
shaft is provided at the Simulink input TL.
Implement a separately excited DC machine
The armature circuit (A+, A−) consists of an inductor La and resistor Ra in
series with a counter-electromotive force (CEMF) E.
The CEMF is proportional to the machine speed.
E = KE ω
KE is the voltage constant and ω is the machine speed.
In a separately excited DC machine model, the voltage constant KE is
proportional to the field current If:
K E = L af I f
where Laf is the field-armature mutual inductance.
The electromechanical torque developed by the DC machine is proportional to
the armature current Ia.
Te = KT Ia
where KT is the torque constant. The sign convention for Te and TL is
T e T L> 0 : Motor mode
T e T L< 0 : Generator mode
The torque constant is equal to the voltage constant.
KT = KE
5-55
DC Machine
The armature circuit is connected between the A+ and A− ports of the DC
Machine block. It is represented by a series Ra La branch in series with a
Controlled Voltage Source and a Current Measurement block.
Armature circuit
Field circuit
5-56
DC Machine
Mechanical part:
The field circuit is represented by an RL circuit. It is connected between the F+
and F− ports of the DC Machine block.
The mechanical part computes the speed of the DC machine from the net
torque applied to the rotor. The speed is used to implement the CEMF voltage
E of the armature circuit.
The mechanical part is represented by Simulink blocks that implement the
equation
dω
J -------- = T e – sgn ( ω )T L – B m ω – T f
dt
where J = inertia, Bm = viscous friction coefficient, and Tf = Coulomb friction
torque.
Measurements
Four internal signals are multiplexed on the Simulink measurement output
vector returning
• Rotor speed in rad/s
5-57
DC Machine
• Armature current in A
• Field current in A
• Electromechanical torque in N.m
Dialog Box and
Parameters
Armature resistance and inductance [Ra La]
The armature resistance Ra, in ohms, and the armature inductance La, in
henries.
Field resistance and inductance [Rf Lf]
The field resistance Rf, in ohms, and the field inductance Lf, in henries.
Field armature mutual inductance Laf
The field armature mutual inductance, in henries.
5-58
DC Machine
Total inertia J
The total inertia of the DC machine, in kg.m2.
Viscous friction coefficient Bm
The total friction coefficient of the DC machine, in N.m.s.
Coulomb friction torque Tf
The total Coulomb friction torque constant of the DC machine, in N.m.
Initial speed
Specifies an initial speed for the DC machine, in rad/s, in order to start the
simulation with a specific initial speed. To start the simulation in steady
state, the initial value of the input torque signal TL must be proportional
to the initial speed.
Example
The power_dcmotor demo illustrates the starting of a 5 HP 240 V DC machine
with a three-step resistance starter.
5-59
DC Machine
The Motor Starter subsystem is
References
Analysis of Electric Machinery, Krause et al., pp. 89-92.
See Also
Asynchronous Machine, Synchronous Machine
5-60
DC Voltage Source
Purpose
5DC Voltage Source
Library
Electrical Sources
Description
The DC Voltage Source block implements an ideal DC voltage source. The
positive terminal is represented by a plus sign on one port. You can modify the
voltage at any time during the simulation.
Implement a DC voltage source
Dialog Box and
Parameters
Amplitude
The amplitude of the source, in volts (V).
Measurements
Select Voltage to measure the voltage across the terminals of the DC
Voltage Source block.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurement is identified by a label
followed by the block name:
Measurement
Label
Voltage
Usrc:
5-61
DC Voltage Source
Example
The power_dcvoltage demo illustrates the simulation of the transient
response of a first-order RC circuit.
See Also
AC Voltage Source, Controlled Voltage Source
5-62
Diode
Purpose
5Diode
Library
Power Electronics
Description
The diode is a semiconductor device that is controlled by its own voltage Vak
and current Iak. When a diode is forward biased (Vak>0), it starts to conduct
with a small forward voltage Vf across it. It turns off when the current flow into
the device becomes 0. When the diode is reverse biased (Vak<0), it stays in the
off state.
Implement a diode model
The Diode block is simulated as a resistor, an inductor, and a DC voltage source
connected in series with a switch. The switch is controlled by the voltage Vak
and current Iak.
K
anode
cathode
Iak
SW
Diode
Logic
Ron
Lon
Vf
+
+
A
A
−
Vak
−
K
Vak
Iak
The Diode block also contains a series Rs-Cs snubber circuit that can be
connected in parallel with the diode device (between nodes A and K).
The static VI characteristic of this model is shown in the following figure.
Iak
On state
slope = 1/Ron
Off state
Vf
Vak
5-63
Diode
Dialog Box and
Parameters
Resistance Ron
The diode internal resistance Ron, in ohms (Ω). The Resistance Ron
parameter cannot be set to 0 when the Inductance Lon parameter is set
to 0.
Inductance Lon
The diode internal inductance Lon, in henries (H). The Inductance Lon
parameter cannot be set to 0 when the Resistance Ron parameter is set
to 0.
Forward voltage Vf
The forward voltage of the diode device, in volts (V).
5-64
Diode
Initial current Ic
Specifies an initial current flowing in the diode device. It is usually set to 0
in order to start the simulation with the diode device blocked. If the Initial
Current IC parameter is set to a value greater than 0, the steady state
calculation of SimPowerSystems considers the initial status of the diode as
closed.
Initializing all states of a power electronic converter is a complex task.
Therefore, this option is useful only with simple circuits.
Snubber resistance Rs
The snubber resistance, in ohms (Ω). Set the Snubber resistance Rs
parameter to inf to eliminate the snubber from the model.
Snubber capacitance Cs
The snubber capacitance in farads (F). Set the Snubber capacitance Cs
parameter to 0 to eliminate the snubber, or to inf to get a resistive
snubber.
Show measurement port
If selected, adds a Simulink output to the block returning the diode current
and voltage.
Inputs and
Outputs
The anode of the diode is identified with the letter a and the cathode is
identified by the letter k. The Simulink output is a measurement output vector
[Iak Vak] returning the diode current and voltage.
Assumptions
The Diode block implements a macromodel of a diode device. It does not take
and Limitations into account either the geometry of the device or the complex physical processes
underlying the state change [1]. The leakage current in the blocking state and
the reverse-recovery (negative) current are not considered. In most circuits, the
reverse current does not affect converter or other device characteristics.
Depending on the value of the inductance Lon, the diode is modeled either as a
current source (Lon > 0) or as a variable topology circuit (Lon = 0). The Diode
block cannot be connected in series with an inductor, a current source, or an
open circuit, unless its snubber circuit is in use. See the “Improving Simulation
Performance” chapter for more details on this topic.
5-65
Diode
You must use a stiff integrator algorithm to simulate circuits containing
diodes. ode23tb or ode15s with default parameters usually gives the best
simulation speed.
The inductance Lon is forced to 0 if you choose to discretize your circuit.
Example
The power_diode demo illustrates a single pulse rectifier consisting of a Diode
block, an RL load, and an AC Voltage source block.
Simulation produces the following results.
5-66
Diode
References
[1] Rajagopalan, V., Computer-Aided Analysis of Power Electronic Systems,
Marcel Dekker, Inc., New York, 1987.
[2] Mohan, N., T.M. Undeland, and W.P. Robbins, Power Electronics:
Converters, Applications, and Design, John Wiley & Sons, Inc., New York,
1995.
See Also
Thyristor, Universal Bridge
5-67
Discrete System
Purpose
5Discrete System
Library
powerlib
Description
The Discrete System block, in previous versions of SimPowerSystems, served
to discretize the state-space model of an electrical model. Discrete time models
are used for the linear elements as well as for the nonlinear blocks of the
Elements, Machines, and Power Electronics libraries of powerlib.
Discretize the state-space model of a circuit
Note This block is now obsolete. Use the Powergui block to replace this block.
See Also
5-68
Powergui
Distributed Parameter Line
Purpose
5Distributed Parameter Line
Library
Elements
Description
The Distributed Parameter Line block implements an N-phase distributed
parameter line model with lumped losses. The model is based on the Bergeron’s
traveling wave method used by the Electromagnetic Transient Program
(EMTP) [1]. In this model, the lossless distributed LC line is characterized by
two values (for a single-phase line): the surge impedance Zc = L ⁄ C and the
phase velocity v = 1 ⁄ LC .
Implement an N-phase distributed parameter transmission line model with
lumped losses
The model uses the fact that the quantity e+Zi (where e is line voltage and i is
line current) entering one end of the line must arrive unchanged at the other
end after a transport delay of τ = d ⁄ v , where d is the line length. By lumping
R/4 at both ends of the line and R/2 in the middle and using the current
injection method of SimPowerSystems, the following two-port model is derived.
is
es
ir
Ish
Z
Irh
Z
er
1+h 1
1–h 1
I sh ( t ) =  ------------- ---- e ( t – τ ) + hi r ( t – τ ) +  ------------- ---- e s ( t – τ ) + hi s ( t – τ )
 2  Z r
 2  Z
1+h 1
1–h 1
I rh ( t ) =  ------------- ---- e s ( t – τ ) + hi s ( t – τ ) +  ------------- ---- e r ( t – τ ) + hi r ( t – τ )
 2  Z
 2  Z
where Z = Z C + R
---4
,
R
Z C – ---4
h = -----------------R
Z C + ---4
,
ZC =
L- , and
--C
τ = d LC .
For multiphase line models, modal transformation is used to convert line
quantities from phase values (line currents and voltages) into modal values
5-69
Distributed Parameter Line
independent of each other. The previous calculations are made in the modal
domain before being converted back to phase values.
In comparison to the PI section line model, the distributed line represents wave
propagation phenomena and line end reflections with much better accuracy.
See the comparison between the two models in the Example section.
Dialog Box and
Parameters
Number of phases N
Specifies the number of phases, N, of the model. The block icon dynamically
changes according to the number of phases that you specify. When you
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Distributed Parameter Line
apply the parameters or close the dialog box, the number of inputs and
outputs is updated.
Frequency used for RLC specifications
Specifies the frequency used to compute the resistance R, inductance L,
and capacitance C matrices of the line model.
Resistance per unit length
The resistance R per unit length, as an N-by-N matrix in ohms/km (Ω/km).
For a symmetrical line, you can either specify the N-by-N matrix or the
sequence parameters. For a two-phase or three-phase continuously
transposed line, you can enter the positive and zero-sequence resistances
[R1 R0]. For a symmetrical six-phase line you can enter the sequence
parameters plus the zero-sequence mutual resistance [R1 R0 R0m].
For asymmetrical lines, you must specify the complete N-by-N resistance
matrix.
Inductance per unit length
The inductance L per unit length, as an N-by-N matrix in henries/km
(H/km).
For a symmetrical line, you can either specify the N-by-N matrix or the
sequence parameters. For a two-phase or three-phase continuously
transposed line, you can enter the positive and zero-sequence inductances
[L1 L0]. For a symmetrical six-phase line, you can enter the sequence
parameters plus the zero-sequence mutual inductance [L1 L0 L0m].
For asymmetrical lines, you must specify the complete N-by-N inductance
matrix.
Capacitance per unit length
The capacitance C per unit length, as an N-by-N matrix in farads/km
(F/km).
For a symmetrical line, you can either specify the N-by-N matrix or the
sequence parameters. For a two-phase or three-phase continuously
transposed line, you can enter the positive and zero-sequence capacitances
[C1 C0]. For a symmetrical six-phase line you can enter the sequence
parameters plus the zero-sequence mutual capacitance [C1 C0 C0m].
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Distributed Parameter Line
For asymmetrical lines, you must specify the complete N-by-N capacitance
matrix.
Line length
The line length, in km.
Measurements
Select Phase-to-ground voltages to measure the sending end and
receiving end voltages for each phase of the line model.
Place a Multimeter block in your model to display the selected
measurements during the simulation.
In the Available Measurements list box of the Multimeter block, the
measurement is identified by a label followed by the block name:
Measurement
Label
Phase-to-ground voltages,
sending end
Us_ph1_gnd:, Us_ph2_gnd:,
Us_ph3_gnd:, etc.
Phase-to-ground voltages,
receiving end
Ur_ph1_gnd:, Ur_ph2_gnd:,
Ur_ph3_gnd:, etc.
Limitations
This model does not represent accurately the frequency dependence of RLC
parameters of real power lines. Indeed, because of the skin effects in the
conductors and ground, the R and L matrices exhibit strong frequency
dependence, causing an attenuation of the high frequencies.
Example
The power_monophaseline demo illustrates a 200 km line connected on a 1 kV,
60 Hz infinite source. The line is deenergized and then reenergized after 2
cycles. The simulation is performed simultaneously with the Distributed
Parameter Line block and with the PI Section Line block.
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Distributed Parameter Line
The receiving end voltage obtained with the Distributed Parameter Line block
is compared with the one obtained with the PI Section Line block (two
sections).
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Distributed Parameter Line
Open the Powergui. Click the Impedance vs Frequency Measurement
button. A new window appears, listing the two Impedance Measurement blocks
connected to your circuit. Set the parameters of Impedance vs Frequency
5-74
Distributed Parameter Line
Measurement to compute impedance in the [0,2000] Hz frequency range,
select the two measurements in the list, then click the Update button.
The distributed parameter line shows a succession of poles and zeros equally
spaced, every 486 Hz. The first pole occurs at 243 Hz, corresponding to
frequency f = 1/(4 * T) where
T = traveling time = l LC = 1.028 ms
The PI section line only shows two poles because it consists of two PI sections.
Impedance comparison shows that a two-section PI line gives a good
approximation of the distributed line for the 0 to 350 Hz frequency range.
5-75
Distributed Parameter Line
References
[1] Dommel, H., “Digital Computer Solution of Electromagnetic Transients in
Single and Multiple Networks,” IEEE Transactions on Power Apparatus and
Systems, Vol. PAS-88, No. 4, April, 1969.
See Also
PI Section Line
5-76
dq0_to_abc Transformation
Purpose
5dq0_to_abc Transformation
Library
Extras/Measurements
Perform a Park transformation from the dq0 reference frame to the abc
reference frame
A discrete version of this block is available in the Extras/Discrete
Measurements library.
Description
The dq0_to_abc Transformation block performs the reverse of the so-called
Park transformation, which is commonly used in three-phase electric machine
models. It transforms three quantities (direct axis, quadratic axis, and
zero-sequence components) expressed in a two-axis reference frame back to
phase quantities. The following transformation is used:
V a = V d sin ( ωt ) + V q cos ( ωt ) + V 0
V b = V d sin ( ωt – 2π ⁄ 3 ) + V q cos ( ωt – 2π ⁄ 3 ) + V 0
V c = V d sin ( ωt + 2π ⁄ 3 ) + V q cos ( ωt + 2π ⁄ 3 ) + V 0
where
ω = rotation speed (rad/s) of the rotating frame
The transformation is the same for the case of a three-phase current; you
simply replace the Va, Vb, Vc, Vd, Vq, and V0 variables with the Ia, Ib, Ic, Id, Iq,
and I0 variables.
The dq0_to_abc Transformation block is used in the model of the Synchronous
Machine block where the stator quantities are referred to the rotor. The Park
transformation then eliminates time-varying inductances by referring the
stator and rotor quantities to a fixed or rotating reference frame. The Id and Iq
currents represent the two DC currents flowing in the two equivalent rotor
windings (d winding on the same axis as the field winding, and q winding in
quadratic) producing the same flux as the stator Ia, Ib, and Ic currents.
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dq0_to_abc Transformation
Dialog Box and
Parameters
Inputs and
Outputs
dq0
Connect to the first input a vectorized signal containing the sequence
components [d q 0] to be converted.
sin_cos
Connect to the second input a vectorized signal containing the [sin(ωt)
cos(ωt)] values, where ω is the rotation speed of the reference frame.
abc
The output is a vectorized signal containing the three-phase sinusoidal
quantities [phase A phase B phase C].
Example
See the demo of the abc_to_dq0 Transformation block for an example using the
dq0_to_abc Transformation block.
See Also
abc_to_dq0 Transformation
5-78
Excitation System
Purpose
5Excitation System
Library
Machines
Description
The Excitation System block is a Simulink system implementing a DC exciter
described in [1], without the exciter’s saturation function. The basic elements
that form the Excitation System block are the voltage regulator and the exciter.
Provide an excitation system for the synchronous machine and regulate its
terminal voltage in generating mode
The exciter is represented by the following transfer function between the
exciter voltage Vfd and the regulator’s output ef:
V fd
1
--------- = -----------------------ef
Ke + sTe
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Excitation System
Dialog Box and
Parameters
Low-pass filter time constant
The time constant Tr, in seconds (s), of the first-order system that
represents the stator terminal voltage transducer.
Regulator gain and time constant
The gain Ka and time constant Ta, in seconds (s), of the first-order system
representing the main regulator.
Exciter
The gain Ke and time constant Te, in seconds (s), of the first-order system
representing the exciter.
5-80
Excitation System
Transient gain reduction
The time constants Tb, in seconds (s), and Tc, in seconds (s), of the
first-order system representing a lead-lag compensator.
Damping filter gain and time constant
The gain Kf and time constant Tf, in seconds (s), of the first-order system
representing a derivative feedback.
Regulator output limits and gain
Limits Efmin and Efmax are imposed on the output of the voltage
regulator. The upper limit can be constant and equal to Efmax, or variable
and equal to the rectified stator terminal voltage Vtf times a proportional
gain Kp. If Kp is set to 0, the former applies. If Kp is set to a positive value,
the latter applies.
Initial values of terminal voltage and field voltage
The initial values of terminal voltage Vt0 (p.u.) and field voltage Vf0 (p.u.).
When set correctly, they allow you to start the simulation in steady state.
Initial terminal voltage should normally be set to 1 p.u. Both Vt0 and Vf0
values are automatically updated by the load flow utility of the Powergui
block.
Example
See the Hydraulic Turbine and Governor block.
Inputs and
Outputs
The first input of the block is the desired value of the stator terminal voltage.
The following two inputs are the vq and vd components of the terminal voltage.
The fourth input can be connected to a power system stabilizer to provide
additional stabilization of power system oscillations. All inputs are in p.u. The
output of the block is the field voltage Vf for the Synchronous Machine block
(p.u.).
References
[1] “Recommended Practice for Excitation System Models for Power System
Stability Studies,” IEEE Standard 421.5-1992, August, 1992.
See Also
Generic Power System Stabilizer, Hydraulic Turbine and Governor, Multiband
Power System Stabilizer, Steam Turbine and Governor, Synchronous Machine
5-81
Fourier
Purpose
5Fourier
Library
Extras/Measurements
Perform a Fourier analysis of a signal
A discrete version of this block is available in the Extras/Discrete
Measurements library.
Description
The Fourier block performs a Fourier analysis of the input signal over a
running window of one cycle of the fundamental frequency of the signal. The
Fourier block can be programmed to calculate the magnitude and phase of the
DC component, the fundamental, or any harmonic component of the input
signal.
Recall that a signal f(t) can be expressed by a Fourier series of the form
∞
a
f ( t ) = -----0- +
2
∑
a n cos ( nωt ) + b n sin ( nωt )
n=1
where n represents the rank of the harmonics (n = 1 corresponds to the
fundamental component). The magnitude and phase of the selected harmonic
component are calculated by the following equations:
Hn =
2
an + bn
2
bn
∠H n = atan  ------
 a n
where
t
2
a n = ---T
∫
f ( t ) cos ( nωt ) dt
(t – T)
t
2
b n = ---T
∫
f ( t ) sin ( nωt ) dt
(t – T)
1
T = ---f1
5-82
f 1 : Fundamental frequency
Fourier
As this block uses a running average window, one cycle of simulation has to be
completed before the outputs give the correct magnitude and angle. The
discrete version of this block allows you to specify the initial magnitude and
phase of the output signal. For the first cycle of simulation the outputs are held
to the values specified by the initial input parameter.
Dialog Box and
Parameters
Fundamental frequency f1
The fundamental frequency, in hertz, of the input signal.
Harmonic n (0 = DC; 1 = fundamental; 2 = 2nd harm; ...)
Specify the harmonic component you want to perform the Fourier analysis.
Enter 0 if you want to analyze the DC component. Enter 1 if you want to
analyze the fundamental frequency, or enter a number corresponding to
the desired harmonic.
Inputs and
Outputs
signal
Connect to the signal to be analyzed. Typical input signals are voltages or
currents measured by Current Measurement blocks or Voltage
Measurement blocks.
magnitude
The first output returns the magnitude of the harmonic component
specified, in the same units as the input signal.
5-83
Fourier
phase
The second output returns the phase, in degrees, of the harmonic
component specified.
Example
The power_transfosat demo shows the energization of a 450 MVA three-phase
transformer on a 500 kV network. The power system is simulated by an
equivalent circuit consisting of an inductive source having a short-circuit
power of 3000 MVA and a parallel RC load.
The load capacitance is set to produce a resonance at 240 Hz (fourth harmonic).
A Fourier block is used to measure the fourth harmonic content of phase A of
the primary voltage.
The Fourier block measures a high level fourth harmonic in the voltage (on the
second trace of Scope1) because of the fourth harmonic content of the current
injected into the network resonating at that particular frequency (240 Hz).
5-84
Fourier
5-85
Generic Power System Stabilizer
Purpose
5Generic Power System Stabilizer
Library
Machines
Description
The Generic Power System Stabilizer (PSS) block can be used to add damping
to the rotor oscillations of the synchronous machine by controlling its
excitation. The disturbances occurring in a power system induce
electromechanical oscillations of the electrical generators. These oscillations,
also called power swings, must be effectively damped to maintain the system
stability. The output signal of the PSS is used as an additional input (vstab) to
the Excitation System block. The PSS input signal can be either the machine
speed deviation, dw, or its acceleration power, Pa = Pm − Peo (difference
between the mechanical power and the electrical power).
Implement a generic power system stabilizer for the synchronous machine
The Generic Power System Stabilizer is modeled by the following nonlinear
system:
To ensure a robust damping, the PSS should provide a moderate phase advance
at frequencies of interest in order to compensate for the inherent lag between
the field excitation and the electrical torque induced by the PSS action.
The model consists of a low-pass filter, a general gain, a washout high-pass
filter, a phase-compensation system, and an output limiter. The general gain
K determines the amount of damping produced by the stabilizer. The washout
high-pass filter eliminates low frequencies that are present in the dw signal
and allows the PSS to respond only to speed changes. The phase-compensation
system is represented by a cascade of two first-order lead-lag transfer functions
used to compensate the phase lag between the excitation voltage and the
electrical torque of the synchronous machine.
5-86
Generic Power System Stabilizer
Dialog Box and
Parameters
Sensor time constant
The time constant, in seconds (s), of the first-order low-pass filter used to
filter the block’s input signal.
Gain
The overall gain K of the generic power system stabilizer.
Wash-out time constant
The time constant, in seconds (s), of the first-order high-pass filter used by
the washout system of the model.
Lead-lag #1 time constants: [Tnum Tden]
The numerator time constant T1n and denominator time constant T1d, in
seconds (s), of the first lead-lag transfer function.
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Generic Power System Stabilizer
Lead-lag #2 time constants: [Tnum Tden]
The numerator time constant T2n and denominator time constant T2d, in
seconds (s), of the second lead-lag transfer function.
Output limits: [Vsmin Vsmax]
The limits VSmin and VSmax, in p.u., imposed on the output of the
stabilizer.
Initial input
The initial DC voltage, in p.u., of the block’s input signal. Specification of
this parameter is required to initialize all states and start the simulation
in steady state with vstab set to zero.
Plot frequency response
If selected, a plot of the frequency response of the stabilizer is displayed
when you click the Apply button.
Magnitude in dB
The Magnitude in dB parameter is not visible if the Plot frequency
response is not selected. If selected, the magnitude of the frequency
response is plotted in dB.
Frequency range
The Frequency range parameter is not visible in the dialog box if the Plot
frequency response is not selected. Specify the frequency range used to
plot the frequency response of the stabilizer.
Inputs and
Outputs
In
Two types of signals can be used at the input In:
- The synchronous machine speed deviation dw signal (in p.u.)
- The synchronous machine acceleration power Pa = Pm − Peo (difference
between the machine mechanical power and output electrical power (in
p.u.))
Vstab
The output is the stabilization voltage (in p.u.) to connect to the Vstab
input of the Excitation System block used to control the terminal voltage of
the synchronous machine.
5-88
Generic Power System Stabilizer
Example
See the help text of the power_PSS demo model.
References
Kundur, P., Power System Stability and Control, McGraw-Hill, 1994, Section
12.5.
See Also
Multiband Power System Stabilizer
5-89
Ground
Purpose
5Ground
Library
Elements
Description
The Ground block implements a connection to the ground.
Example
The power_ground demo shows an application of the Ground block.
See Also
Neutral
5-90
Provide a connection to the ground
GTO
Purpose
5GTO
Library
Power Electronics
Description
The gate turn-off (GTO) thyristor is a semiconductor device that can be turned
on and off via a gate signal. Like a conventional thyristor, the GTO thyristor
can be turned on by a positive gate signal (g > 0). However, unlike the
thyristor, which can be turned off only at a zero crossing of current, the GTO
can be turned off at any time by the application of a gate signal equal to 0.
Implement a gate turn off (GTO) thyristor model
The GTO thyristor is simulated as a resistor Ron, an inductor Lon, and a DC
voltage source Vf connected in series with a switch. The switch is controlled by
a logical signal depending on the voltage Vak, the current Iak, and the gate
signal g.
anode
g
gate
K
cathode
A
Iak
SW
GTO
Logic
Ron
Lon
Vf
+
+
A
−
Vak
−
K
Vak
Iak
g
The Vf, Ron, and Lon parameters are the forward voltage drop while in
conduction, the forward conducting resistance, and the inductance of the
device. The GTO block also contains a series Rs-Cs snubber circuit that can be
connected in parallel with the GTO device (between terminal ports A and K).
The GTO thyristor turns on when the anode-cathode voltage is greater than Vf
and a positive pulse signal is present at the gate input (g > 0). When the gate
signal is set to 0, the GTO thyristor starts to block but its current does not stop
instantaneously.
5-91
GTO
Iak
On state
On to Off
if G goes to 0
Off to On
if G goes to 1
Off state
Off state
Vf
Vak
Because the current extinction process of a GTO thyristor contributes
significantly to the turnoff losses, the turnoff characteristic is built into the
model. The current decrease is approximated by two segments. When the gate
signal becomes 0, the current Iak first decreases from the value Imax (value of
Iak when the GTO thyristor starts to open) to Imax/10, during the fall time (Tf),
and then from Imax/10 to 0 during the tail time (Tt). The GTO thyristor turns
off when the current Iak becomes 0. The latching and holding currents are not
considered.
Iak
Imax
Itail = 0.1 Imax
t
G
Tf
Tt
1
t
5-92
GTO
Dialog Box and
Parameters
Resistance Ron
The internal resistance Ron, in ohms (Ω).
Inductance Lon
The internal inductance Lon, in henries (H). The Inductance Lon
parameter cannot be set to 0.
5-93
GTO
Forward voltage Vf
The forward voltage of the GTO thyristor device, in volts (V).
Current 10% fall time
The current fall time Tf, in seconds (s).
Current tail time
The current tail time Tt, in seconds (s).
Initial current Ic
You can specify an initial current flowing in the GTO thyristor. It is usually
set to 0 in order to start the simulation with the device blocked.
If the Initial Current IC parameter is set to a value greater than 0, the
steady state calculation of SimPowerSystems considers the initial status of
the GTO as closed. Initializing all states of a power electronic converter is
a complex task. Therefore, this option is useful only with simple circuits.
Snubber resistance Rs
The snubber resistance, in ohms (Ω). Set the Snubber resistance Rs
parameter to inf to eliminate the snubber from the model.
Snubber capacitance Cs
The snubber capacitance, in farads (F). Set the Snubber capacitance Cs
parameter to 0 to eliminate the snubber, or to inf to get a resistive
snubber.
Show measurement port
If selected, add a Simulink output to the block returning the GTO current
and voltage.
Inputs and
Outputs
The input port (g) is a Simulink signal applied to the gate of the GTO thyristor.
The output port (m) is a Simulink measurement vector [Iak Vak] returning the
GTO thyristor current and voltage.
Assumptions
The GTO block implements a macromodel of a real GTO thyristor. It does not
and Limitations take into account either the geometry of the device or the underlying physical
processes of the device [1].
The GTO block requires a continuous application of the gate signal (g > 0) in
order to be in the on state (with Iak > 0). The latching current and the holding
5-94
GTO
current are not considered. The critical value of the derivative of the reapplied
anode-cathode voltage is not considered.
The GTO block is modeled as a current source. It cannot be connected in series
with an inductor, a current source, or an open circuit, unless its snubber circuit
is in use. In order to avoid an algebraic loop, you cannot set the inductance Lon
to 0.
Each GTO block adds an extra state to the electrical circuit model. Circuits
containing GTO blocks cannot be discretized. In order to discretize circuits
using GTO converters, use the Universal Bridge block or the Three-Level
Bridge block. See the “Improving Simulation Performance” chapter for more
details on this topic.
You must use a stiff integrator algorithm to simulate circuits containing GTO
blocks. ode23tb or ode15s with default parameters usually gives the best
simulation speed.
Example
The power_buckconv demo illustrates the use of the GTO block in a buck
converter topology. The basic polarized snubber circuit is connected across the
GTO block. The snubber circuit consists of a capacitor Cs, a resistor Rs, and a
diode Ds. The parasitic inductance Ls of the snubber circuit is also taken into
consideration.
The parameters of the GTO block are those found in the dialog box section,
except for the internal snubber, which is not used (Rs = inf; Cs = 0). The
switching frequency is 1000 Hz and the pulse width is 216 degrees (duty cycle:
60%).
5-95
GTO
Run the simulation. Observe the GTO voltage and current as well as the load
voltage and current.
5-96
GTO
References
[1] Mohan, N., T.M. Undeland, and W.P. Robbins, Power Electronics:
Converters, Applications, and Design, John Wiley & Sons, Inc., New York,
1995.
See Also
IGBT, MOSFET, Three-Level Bridge, Thyristor, Universal Bridge
5-97
Hydraulic Turbine and Governor
Purpose
5Hydraulic Turbine and Governor
Library
Machines
Description
The Hydraulic Turbine and Governor block implements a nonlinear hydraulic
turbine model, a PID governor system, and a servomotor [1].
Model a hydraulic turbine and a proportional-integral-derivative (PID)
governor system
The hydraulic turbine is modeled by the following nonlinear system.
The gate servomotor is modeled by a second-order system.
5-98
Hydraulic Turbine and Governor
Dialog Box and
Parameters
Servo-motor
The gain Ka and time constant Ta, in seconds (s), of the first-order system
representing the servomotor.
Gate opening limits
The limits gmin and gmax (p.u.) imposed on the gate opening, and vgmin
and vgmax (p.u./s) imposed on gate speed.
Permanent droop and regulator
The static gain of the governor is equal to the inverse of the permanent
droop Rp in the feedback loop. The PID regulator has a proportional gain
Kp, an integral gain Ki, and a derivative gain Kd. The high-frequency gain
of the PID is limited by a first-order low-pass filter with time constant
Td (s).
Hydraulic turbine
The speed deviation damping coefficient β and water starting time Tw (s).
5-99
Hydraulic Turbine and Governor
Droop reference
Specifies the input of the feedback loop: gate position (set to 1) or electrical
power deviation (set to 0).
Initial mechanical power
The initial mechanical power Pm0 (p.u.) at the machine’s shaft. This value
is automatically updated by the load flow utility of the Powergui block.
Inputs and
Outputs
The first two inputs are the desired speed and mechanical power. The third and
fourth inputs are the machine’s actual speed and electrical power. The fifth
input is the speed deviation. Inputs 2 and 4 can be left unconnected if you want
to use the gate position as input to the feedback loop instead of the power
deviation. All inputs are in p.u. The outputs of the block are mechanical power
Pm for the Synchronous Machine block and gate opening (both in p.u.).
Example
This power_turbine demo illustrates the use of the Synchronous Machine
associated with the Hydraulic Turbine and Governor (HTG) and Excitation
System blocks. It also demonstrates the use of the load flow tool of the
Powergui block to initialize machine currents and initial mechanical power of
the HTG block. A three-phase generator rated 200 MVA, 13.8 kV, 112.5 rpm is
connected to a 230 kV network through a Delta-Y 210 MVA transformer. The
system starts in steady state with the generator supplying 150 MW of active
power. At t = 0.1 s, a three-phase to ground fault occurs on the 230 kV bus of
the transformer. The fault is cleared after six cycles (t = 0.2 s).
In order to start the simulation in steady state, you must initialize the
Synchronous Machine block for the desired load flow. Open the Powergui and
select Load flow and machine initialization. The machine Bus type should
be already initialized as PV generator, indicating that the load flow is
performed with the machine controlling the active power and its terminal
voltage. Specify the desired values by entering the following parameters:
• Terminal voltage U AB (Vrms) = 13800
• Active power (watts) = 150e6
5-100
Hydraulic Turbine and Governor
Then click the Update Load Flow button. Once the load flow has been solved,
the line-to-line machine voltages as well as the phase currents flowing out of
the machine. The machine reactive power, mechanical power, and field voltage
requested to supply the electrical power should also be displayed:
• Q = 3.4 Mvar
• Pmec = 150.32 MW (0.7516 p.u.)
• Field voltage Vf = 1.291 p.u.
The load flow also initializes the HTG and Excitation System blocks. Open the
HTG block menu and notice that the initial mechanical power is set to 0.5007
p.u. (100.14 MW). Then open the Excitation System block menu and note that
the initial terminal voltage and field voltage are set respectively to 1.0 and
1.291 p.u. Open the four scopes and start the simulation. The simulation starts
in steady state.
5-101
Hydraulic Turbine and Governor
Observe that the terminal voltage Va is 1.0 p.u. at the beginning of the
simulation. It falls to about 0.4 p.u. during the fault and returns to nominal
quickly after the fault is cleared. This quick response in terminal voltage is due
to the fact that the Excitation System output Vf can go as high as 11.5 p.u.,
which it does during the fault. The speed of the machine increases to 1.01 p.u.
during the fault, then it oscillates around 1 p.u. as the governor system
regulates it. The speed takes much longer than the terminal voltage to
stabilize, mainly because the rate of valve opening/closing in the governor
system is limited to 0.1 p.u./s.
References
[1] IEEE Working Group on Prime Mover and Energy Supply Models for
System Dynamic Performance Studies, “Hydraulic Turbine and Turbine
Control Models for Dynamic Studies,” IEEE Transactions on Power Systems,
Vol. 7, No. 1, February, 1992, pp. 167-179.
See Also
Excitation System, Steam Turbine and Governor, Synchronous Machine
5-102
Ideal Switch
Purpose
5Ideal Switch
Library
Power Electronics
Description
The Ideal Switch block does not correspond to a particular physical device.
When used with appropriate switching logic, it can be used to model simplified
semiconductor devices such as a GTO or a MOSFET, or even a power circuit
breaker with current chopping. The switch is simulated as a resistor Ron in
series with a switch controlled by a logical gate signal g.
Implement an ideal switch device
+
2
Terminal
1
Terminal
g
Gate
1
−
V12
I12
SW
Ron
2
Switch
Logic
g
The Ideal Switch block is fully controlled by the gate signal (g > 0 or g = 0). It
has the following characteristics:
• Blocks any forward or reverse applied voltage with 0 current flow when g = 0
• Conducts any bidirectional current with quasi-zero voltage drop when g > 0
• Switches instantaneously between on and off states when triggered
The Ideal Switch block turns on when a positive signal is present at the gate
input (g > 0). It turns off when the gate signal equals 0 (g = 0).
The Ideal Switch block also contains a series Rs-Cs snubber circuit that can be
connected in parallel with the ideal switch (between nodes 1 and 2).
5-103
Ideal Switch
I12
On state
On to Off
if g goes to 0
Off state
Off to On
if g goes to 1
slope = 1/ Ron
Off to On
if g goes to 1
On to Off
if g goes to 0
On state
Dialog Box and
Parameters
5-104
Off state
V12
Ideal Switch
Internal Resistance Ron
The internal resistance of the switch device, in ohms (Ω). The Internal
resistance Ron parameter cannot be set to 0.
Initial state
The initial state of the Ideal Switch block. The initial status of the Ideal
Switch block is taken into account in the steady-state calculation of
SimPowerSystems.
Snubber resistance Rs
The snubber resistance, in ohms (Ω). Set the Snubber resistance Rs
parameter to inf to eliminate the snubber from the model.
Snubber capacitance Cs
The snubber capacitance in farads (F). Set the Snubber capacitance Cs
parameter to 0 to eliminate the snubber, or to inf to get a resistive
snubber.
Show measurement port
If selected, add a Simulink output to the block returning the ideal switch
current and voltage.
Inputs and
Outputs
The input port (g) controls the opening and closing of the switch. The output
port (m) is a measurement output vector [Iak Vak] returning the Ideal Switch
block current and voltage.
Assumptions
The Ideal Switch block is modeled as a current source. It cannot be connected
and Limitations in series with an inductor, a current source, or an open circuit, unless its
snubber circuit is in use. See the “Improving Simulation Performance” chapter
for more details on this topic.
You must use a stiff integrator algorithm to simulate circuits containing Ideal
Switch blocks. ode23tb or ode15s with default parameters usually gives the
best simulation speed.
Example
The power_switch demo uses the Ideal Switch block to switch an RLC circuit
on an AC source (60 Hz). The switch, which is initially closed, is first opened at
t = 50 ms (3 cycles) and then reclosed at t = 138 ms (8.25 cycles). The Ideal
Switch block has 0.01 ohms resistance and no snubber is used.
5-105
Ideal Switch
Run the simulation and observe the inductor current, the switch current, and
the capacitor voltage. Notice the high-frequency overvoltage produced by
inductive current chopping. Note also the high switch current spike when the
switch is reclosed on the capacitor at maximum source voltage.
5-106
Ideal Switch
References
Mohan, N., T.M. Undeland, and W.P. Robbins, Power Electronics: Converters,
Applications, and Design, John Wiley & Sons, Inc., New York, 1995.
See Also
Breaker
5-107
IGBT
Purpose
5IGBT
Library
Power Electronics
Description
The IGBT block implements a semiconductor device controllable by the gate
signal. The IGBT is simulated as a series combination of a resistor Ron,
inductor Lon, and a DC voltage source Vf in series with a switch controlled by
a logical signal (g > 0 or g = 0).
Implement an insulated gate bipolar transistor (IGBT)
Emitter
C
IC
g
Gate
SW
Ron
Lon
Vf
+
+
E
C
Collector
−
VCE
−
E
IC
IGBT
Logic
VCE
g
Emitter
g
Gate
C
IC
SW
IGBT
Logic
Ron
Lon
Vf
+
+
E
C
Collector
−
VCE
−
E
IC
VCE
g
The IGBT turns on when the collector-emitter voltage is positive and greater
than Vf and a positive signal is applied at the gate input (g > 0). It turns off
5-108
IGBT
when the collector-emitter voltage is positive and a 0 signal is applied at the
gate input (g = 0).
The IGBT device is in the off state when the collector-emitter voltage is
negative. Note that many commercial IGBTs do not have the reverse blocking
capability. Therefore, they are usually used with an antiparallel diode.
The IGBT block contains a series Rs-Cs snubber circuit, which is connected in
parallel with the IGBT device (between terminals C and E).
IC
On state
Turn-off
(g = 0)
Turn-on
(g > 0)
Off state
Vf
Off state
VCE
The turn-off characteristic of the IGBT model is approximated by two
segments. When the gate signal falls to 0, the collector current decreases from
Imax to 0.1 Imax during the fall time (Tf), and then from 0.1 Imax to 0 during
the tail time (Tt).
5-109
IGBT
G
1
t
0
IC
Imax
0.1Imax
Tf Tt
5-110
t
IGBT
Dialog Box and
Parameters
Resistance Ron
The internal resistance Ron, in ohms (Ω).
Inductance Lon
The internal inductance Lon, in henries (H). The Inductance Lon
parameter cannot be set to 0.
5-111
IGBT
Forward voltage Vf
The forward voltage of the IGBT device, in volts (V).
Current 10% fall time
The current fall time Tf, in seconds (s).
Current tail time
The current tail time Tt, in seconds (s).
Initial current Ic
You can specify an initial current flowing in the IGBT. It is usually set to 0
in order to start the simulation with the device blocked.
If the Initial Current IC parameter is set to a value greater than 0, the
steady state calculation of SimPowerSystems considers the initial status of
the IGBT as closed. Initializing all states of a power electronic converter is
a complex task. Therefore, this option is useful only with simple circuits.
Snubber resistance Rs
The snubber resistance, in ohms (Ω). Set the Snubber resistance Rs
parameter to inf to eliminate the snubber from the model.
Snubber capacitance Cs
The snubber capacitance in farads (F). Set the Snubber capacitance Cs
parameter to 0 to eliminate the snubber, or to inf to get a resistive
snubber.
Show measurement port
If selected, add a Simulink output to the block returning the diode IGBT
current and voltage.
Inputs and
Outputs
The input port (g) is a logical Simulink signal applied to the gate. The output
port is a measurement vector [Ic Vce] returning the IGBT current and voltage.
Assumptions
The IGBT block implements a macromodel of the real IGBT device. It does not
and Limitations take into account either the geometry of the device or the complex physical
processes [1].
The IGBT block is modeled as a current source. It cannot be connected in series
with an inductor, a current source, or an open circuit, unless its snubber circuit
is in use. In order to avoid an algebraic loop, you cannot set the IGBT block
5-112
IGBT
inductance Lon to 0. Each IGBT block adds an extra state to the electrical
circuit model. See the “Improving Simulation Performance” chapter for more
details on this topic.
Circuits containing individual IGBT blocks cannot be discretized. However,
discretization is permitted for IGBT/Diode bridges simulated with the
Universal Bridge block or the Three-Level Bridge block.
You must use a stiff integrator algorithm to simulate circuits containing
IGBTs. ode23tb or ode15s with default parameters usually gives the best
simulation speed.
Example
The power_igbtconv demo illustrates the use of the IGBT block in a boost
DC-DC converter. The IGBT is switched on and off at a frequency of 10 kHz to
transfer energy from the DC source to the load (RC). The average output
voltage (VR) is a function of the duty cycle (α) of the IGBT switch:
1
V R = ------------- V dc
1–α
L
+
Vdc
−
D1
+
Q1
C
R
VR
−
5-113
IGBT
In our example, α = 0.5 so that the theoretical value of VR is 200 V, assuming
no voltage drop across the diode and the IGBT.
Run the simulation and observe the inductor current (IL), the IGBT collector
current (IC), the diode current (ID), the IGBT device collector-emitter voltage
(VCE), and the load voltage (VR).
The load voltage (197 V) is slightly lower than the theoretical value (200 V)
mainly because of the forward voltage (Vf) of the diode (0.8 V) and of the IGBT
(Vf = 1 V).
5-114
IGBT
References
[1] Mohan, N., T.M. Undeland, and W.P. Robbins, Power Electronics:
Converters, Applications, and Design, John Wiley & Sons, Inc., New York,
1995.
See Also
GTO, MOSFET, Three-Level Bridge, Thyristor
5-115
Impedance Measurement
Purpose
5Impedance Measurement
Library
Measurements
Description
The Impedance Measurement block measures the impedance between two
nodes of a linear circuit as a function of the frequency. It consists of a current
source Iz, connected between inputs one and two of the Impedance
Measurement block, and a voltage measurement Vz, connected across the
terminals of the current source. The network impedance is calculated as the
transfer function H(s) from the current input to the voltage output of the
state-space model.
Measure the impedance of a circuit as a function of frequency
Vz ( s )
H ( s ) = ------------Iz ( s )
The impedance (magnitude and phase) as function of frequency is displayed by
using the Impedance vs Frequency Measurement tool of the Powergui block.
The measurement takes into account the initial states of the Breaker and Ideal
Switch blocks. It also allows impedance measurements with Distributed
Parameter Line blocks in your circuit.
Dialog Box and
Parameter
Multiplication factor
If you plan to use the Impedance Measurement block in a three-phase
circuit, you can use the Multiplication factor parameter to rescale the
measured impedance. For example, measuring the impedance between two
5-116
Impedance Measurement
phases of a three-phase circuit gives two times the positive-sequence
impedance. Therefore you must apply a multiplication factor of 1/2 to the
impedance in order to obtain the correct positive-sequence impedance
value.
Similarly, to measure the zero-sequence impedance of a balanced
three-phase circuit, you can connect the Impedance Measurement block
between ground or neutral and the three phases connected together.
In that case, you are measuring one third of the zero-sequence impedance
and you must apply a multiplication factor of 3 to obtain the correct
zero-sequence value.
Limitations
The only nonlinear blocks that are taken into account during the impedance
measurement are the Breaker, Three-Phase Breaker, Three-Phase Fault, Ideal
Switch, and Distributed Parameter Line blocks. All other nonlinear blocks,
such as machines and power electronic devices, are not considered, and they
are disconnected during the measurement.
If you plan to connect the Impedance Measurement block in series with an
inductance, a current source, or any nonlinear element, you must add a large
resistor across the terminals of the block, because the Impedance
Measurement block is simulated as a current source block.
Example
See the Powergui block reference page for an example using the Impedance
Measurement block.
See Also
Powergui
5-117
Linear Transformer
Purpose
5Linear Transformer
Library
Elements
Description
The Linear Transformer block model shown consists of three coupled windings
wound on the same core.
Implement a two-winding or three-winding linear transformer
R1
L1
Lm
L2
R2
L3
R3
Rm
The model takes into account the winding resistances (R1 R2 R3) and the
leakage inductances (L1 L2 L3), as well as the magnetizing characteristics of
the core, which is modeled by a linear (Rm Lm) branch.
The Per Unit Conversion
In order to comply with industry, you must specify the resistance and
inductance of the windings in per unit (p.u.). The values are based on the
transformer rated power Pn, in VA, nominal frequency fn, in Hz, and nominal
voltage Vn, in Vrms, of the corresponding winding. For each winding, the per
unit resistance and inductance are defined as
R ( Ω )R ( p.u. ) = -------------R base
L(H)
L ( p.u. ) = --------------L base
The base resistance and base inductance used for each winding are
5-118
Linear Transformer
2
Vn )
R base = (--------------Pn
R base
L base = -------------2 π fn
For the magnetization resistance Rm and inductance Lm, the p.u. values are
based on the transformer rated power and on the nominal voltage of winding 1.
For example, the default parameters of winding 1 specified in the dialog box
section give the following bases:
2
( 735e3 ⁄ ( 3 ) )
R base = ---------------------------------------- = 720.3Ω
250e6
720.3
L base = --------------- = 1.91H
2 π 60
Suppose that the winding 1 parameters are R1 = 1.44 Ω and L1 = 0.1528 H; the
corresponding values to be entered in the dialog box are
1.44Ω
R 1 = ------------------- = 0.002 p.u.
720.3Ω
0.1528H
L 1 = ----------------------- = 0.08 p.u.
1.91H
To specify a magnetizing current of 0.2% (resistive and inductive) based on
nominal current, you must enter per unit values of 1/0.002 = 500 p.u. for the
resistance and the inductance of the magnetizing branch. Using the base
values calculated previously, these per unit values correspond to Rm = 8.6e5
ohms and Lm = 995 henries.
5-119
Linear Transformer
Dialog Box and
Parameters
Nominal power and frequency
The nominal power rating Pn in volt-amperes (VA) and frequency fn, in
hertz (Hz), of the transformer.
Winding 1 parameters
The nominal voltage V, in volts RMS, resistance, and leakage inductance
in p.u. The p.u. values are based on the nominal power Pn and on V1.
Winding 2 parameters
The nominal voltage V2 in volts RMS, resistance, and leakage inductance
in p.u. The p.u. values are based on the nominal power Pn and on V2.
Three windings transformer
If selected, implements a linear transformer with three windings;
otherwise, it implements a two-windings transformer.
5-120
Linear Transformer
Winding 3 parameters
The Winding 3 parameters parameter is not available if the Three
windings transformer parameter is not selected.
The nominal voltage in volts RMS (Vrms), resistance, and leakage
inductance in p.u. The p.u. values are based on the nominal power Pn and
on V3.
Magnetization resistance and reactance
The resistance and inductance simulating the core active and reactive
losses, both in p.u. The p.u. values are based on the nominal power Pn and
on V1. For example, to specify 0.2% of active and reactive core losses, at
nominal voltage, use Rm = 500 p.u. and Lm = 500 p.u.
Measurements
Select Winding voltages to measure the voltage across the winding
terminals of the Linear Transformer block.
Select Winding currents to measure the current flowing through the
windings of the Linear Transformer block.
Select Magnetization current to measure the magnetization current of
the Linear Transformer block.
Select All voltages and currents to measure the winding voltages and
currents plus the magnetization current.
Place a Multimeter block in your model to display the selected
measurements during the simulation.
In the Available Measurements list box of the Multimeter block, the
measurements are identified by a label followed by the block name.
Measurement
Label
Winding voltages
Uw1:, Uw2:, Uw3:
Winding currents
Iw1:, Iw2:, Iw3:
Magnetization current
Imag:
5-121
Linear Transformer
Note To implement a quasi-ideal transformer model, set the winding
resistances and inductances to 0, and the magnetization inductance Lm to
inf. The Rm value must have a finite value. Use a large value such as 1e4
(0.01% losses).
Limitations
Windings can be left floating (that is, not connected to the rest of the circuit).
However, an internal resistor is automatically added between the floating
winding and the main circuit. This internal connection does not affect voltage
and current measurements.
Example
The power_transformer demo shows a typical residential distribution
transformer network feeding line-to-neutral and line-to-line loads.
See Also
Mutual Inductance, Saturable Transformer, Three-Phase Transformer (Two
Windings), Three-Phase Transformer (Three Windings)
5-122
Machine Measurement Demux
Purpose
5Machine Measurement Demux
Library
Machines
Description
The Machine Measurement Demux block is used to demux the measurement
signals of the Simplified Synchronous Machine, the Synchronous Machine, the
Asynchronous Machine, and the Permanent Magnet Synchronous Machine
blocks.
Split measurement signal of machine models into separate signals
The Machine Measurement Demux block is connected directly to the
measurement output of the machine blocks. You select the type of machine
connected to the block and you select the measurements you want to observe.
An output is added to the block for each measurement in the list.
Dialog Box and
Parameters
Machines Measurement Demux dialog: Simplified synchronous type
5-123
Machine Measurement Demux
Machines Measurement Demux dialog: Synchronous type
5-124
Machine Measurement Demux
Machines Measurement Demux dialog: Asynchronous type
5-125
Machine Measurement Demux
Machines Measurement Demux dialog: Permanent magnet synchronous type
Machine Type
Set to Simplified synchronous to display the measurement list for the
Simplified Synchronous Machine block.
Set to Synchronous to display the measurement list for the Synchronous
Machine block.
Set to Asynchronous to display the measurement list for the Asynchronous
Machine block.
Set to Permanent magnet synchronous to display the measurement list for
the Permanent Magnet Synchronous Machine block.
Measurement list
Select the block parameters you want to output.
See Also
5-126
Asynchronous Machine, Permanent Magnet Synchronous Machine, Simplified
Synchronous Machine, Synchronous Machine
MOSFET
Purpose
5MOSFET
Library
Power Electronics
Description
The metal-oxide semiconductor field-effect transistor (MOSFET) is a
semiconductor device controllable by the gate signal (g > 0) if its current Id is
positive (Id > 0). The MOSFET device is connected in parallel with an internal
diode that turns on when the MOSFET device is reverse biased (Vds < 0). The
model is simulated as a series combination of a variable resistor (Rt) and
inductor (Lon) in series with a switch controlled by a logical signal (g > 0 or
g = 0).
Implement a MOSFET model
ID
SW
Ron
Lon
Vf
+
+
d
−
VDS
−
S
S
Source
d
Drain
g
MOSFET
Logic
Id
VDS
Gate
g
The MOSFET device turns on when the drain-source voltage is positive and a
positive signal is applied at the gate input (g > 0).
With a positive current flowing through the device, the MOSFET turns off
when the gate input becomes 0. If the current Id is negative (Id flowing in the
internal diode) and without a gate signal (g = 0), the MOSFET turns off when
the current Id becomes 0 (Id = 0).
Note that the on state resistance Rt depends on the drain current direction:
• Rt = Ron if Id > 0, where Ron represents the typical value of the forward
conducting resistance of the MOSFET device.
• Rt = Rd if Id < 0, where Rd represents the internal diode resistance.
The MOSFET block also contains a series Rs-Cs snubber circuit that can be
connected in parallel with the MOSFET (between nodes d and s).
5-127
MOSFET
Id
On state
Rt = Ron
On to Off
if g = 0
Off state
Off to On
if g >0
Rt = Rd
On state
Dialog Box and
Parameters
5-128
Off state
Vds
MOSFET
Resistance Ron
The internal resistance Ron, in ohms (Ω).
Inductance Lon
The internal inductance Lon, in henries (H). The Inductance Lon
parameter cannot be set to 0.
Internal diode resistance Rd
The internal resistance of the internal diode, in ohms (Ω).
Initial current Ic
You can specify an initial current flowing in the MOSFET device. It is
usually set to 0 in order to start the simulation with the device blocked.
If the Initial Current IC parameter is set to a value greater than 0, the
steady state calculation of SimPowerSystems considers the initial status of
the MOSFET as closed. Initializing all states of a power electronic
converter is a complex task. Therefore, this option is useful only with
simple circuits.
Snubber resistance Rs
The snubber resistance, in ohms (Ω). Set the Snubber resistance Rs
parameter to inf to eliminate the snubber from the model.
Snubber capacitance Cs
The snubber capacitance, in farads (F). Set the Snubber capacitance Cs
parameter to 0 to eliminate the snubber, or to inf to get a resistive
snubber.
Show measurement port
If selected, add a Simulink output to the block returning the MOSFET
current and voltage.
Inputs and
Outputs
The input port is a logical signal applied to the gate. The output port is a
measurement vector [Id Vds] returning the MOSFET device current and
voltage.
Assumptions
The MOSFET block implements a macromodel of the real MOSFET device. It
and Limitations does not take into account either the geometry of the device or the complex
physical processes [1].
5-129
MOSFET
The MOSFET block is modeled as a current source. It cannot be connected in
series with an inductor, a current source, or an open circuit, unless its snubber
circuit is in use. In order to avoid an algebraic loop, you cannot set the
MOSFET block inductance Lon to 0. Each MOSFET block adds an extra state
to the electrical circuit model. See the “Improving Simulation Performance”
chapter for more details on this topic.
Circuits containing individual MOSFET blocks cannot be discretized. However
discretization is permitted for MOSFET/Diode bridges simulated with the
Universal Bridge block or the Three-Level Bridge block.
You must use a stiff integrator algorithm to simulate circuits containing
MOSFETs. ode23tb or ode15s with default parameters usually gives the best
simulation speed.
Example
5-130
The power_mosconv demo illustrates the use of the MOSFET block in a
zero-current quasi-resonant switch converter. In such a converter, the current
produced by the Lr-Cr resonant circuit flows through the MOSFET and
internal diode. The negative current flows through the internal diode that
turns off at 0 current [1]. The switching frequency is 2 MHz and the pulse width
is 72 degrees (duty cycle: 20%).
MOSFET
Run the simulation and observe the gate pulse signal, the MOSFET current,
the capacitor voltage, and the diode current on the four-trace Scope block.
References
[1] Mohan, N., T.M. Undeland, and W.P. Robbins, Power Electronics:
Converters, Applications, and Design, John Wiley & Sons, Inc., New York,
1995.
See Also
Diode, GTO, Ideal Switch, Three-Level Bridge, Thyristor, Universal Bridge
5-131
Multiband Power System Stabilizer
Purpose
5Multiband Power System Stabilizer
Library
Machines
Description
The disturbances occurring in a power system induce electromechanical
oscillations of the electrical generators. These oscillations, also called power
swings, must be effectively damped to maintain the system’s stability.
Electromechanical oscillations can be classified in four main categories:
Implement a multiband power system stabilizer
• Local oscillations: between a unit and the rest of the generating station and
between the latter and the rest of the power system. Their frequencies
typically range from 0.8 to 4.0 Hz.
• Interplant oscillations: between two electrically close generation plants.
Frequencies can vary from 1 to 2 Hz.
• Interarea oscillations: between two major groups of generation plants.
Frequencies are typically in a range of 0.2 to 0.8 Hz.
• Global oscillation: characterized by a common in-phase oscillation of all
generators as found on an isolated system. The frequency of such a global
mode is typically under 0.2 Hz.
The need for effective damping of such a wide range, almost two decades, of
electromechanical oscillations motivated the concept of the multiband power
system stabilizer (MB-PSS).
As its name reveals, the MB-PSS structure is based on multiple working bands.
Three separate bands are used, respectively dedicated to the low-,
intermediate-, and high-frequency modes of oscillations: the low band is
typically associated with the power system global mode, the intermediate with
the interarea modes, and the high with the local modes.
Each of the three bands is made of a differential bandpass filter, a gain, and a
limiter (see Figure ). The outputs of the three bands are summed and passed
through a final limiter producing the stabilizer output Vstab. This signal then
modulates the set point of the generator voltage regulator so as to improve the
damping of the electromechanical oscillations.
To ensure robust damping, the MB-PSS should include a moderate phase
advance at all frequencies of interest to compensate for the inherent lag
5-132
Multiband Power System Stabilizer
between the field excitation and the electrical torque induced by the MB-PSS
action.
VLMAX
∆ω B-I
KB
FB
VLMI
VSTMA
VIMAX
KI
∑
FI
Speed
Transducers
∆ω
VIMIN
KH
∆ωH
VVstab
ST
VSTMIN
VH
FH
VH
Conceptual Representation
VLMAX
∆ω L-
∆ω
KB1
KB11+sTB1
1+sTB2
1+sTB3
1+sTB4
1+sTB5
1+sTB6
KB2
KB17+sTB7
1+sTB8
1+sTB9
1+sTB10
1+sTB11
1+sTB12
KI1
KI11+sTI1
1+sTI3
1+sTI5
1+sTI2
1+sTI4
1+sTI6
KI2
KI17+sTI7
1+sTI9
1+sTI11
1+sTI8
1+sTI10
1+sTI12
KH1
KH11+sTH1
1+sTH2
1+sTH3
1+sTH4
1+sTH5
1+sTH6
KH2
KH17+sTH7
1+sTH8
1+sTH9
1+sTH10
1+sTH11
1+sTH12
Speed
Transducers
∆ω H
∑
KB
VLMIN
Low
Band
∑
KI
∑
VST
Vstab
VSTMIN
VIMIN
Intermediate
Band
∑
VSTMAX
VIMAX
VHMAX
KH
VHMIN
High
Band
Internal Specifications
5-133
Multiband Power System Stabilizer
The MB-PSS is represented by the IEEE St. 421.5 PSS 4B type model [2],
illustrated in Figure , with built-in speed transducers whose parameters are
fixed according to manufacturer’s specifications.
Generally, only a few of the lead-lag blocks in Figure should be used in a given
PSS application. Two different approaches are available to configure the
settings in order to facilitate the tuning process:
1 Simplified settings:
Only the first lead-lag block of each frequency band is used to tune the
Multiband Power System Stabilizer block. The differential filters are
assumed to be symmetrical bandpass filters respectively tuned at the center
frequency FL, FI, and FH. The peak magnitude of the frequency responses
(Figure ) can be adjusted independently through the three gains KL, KI, and
KH. Only six parameters are therefore required for a simplified tuning of the
MB-PSS.
2 Detailed settings:
The designer is free to use all the flexibility built into the MB-PSS structure
to achieve nontrivial controller schemes and to tackle even the most
constrained problem (for example, multi unit plant including an
intermachine mode, in addition to a local mode and multiple interarea
modes). In this case, all the time constants and gains appearing in Figure
have to be specified in the dialog box.
5-134
Multiband Power System Stabilizer
Dialog Box and
Parameters
Simplified Settings Mode
Global gain
The overall gain K of the multiband power system stabilizer.
Low frequency band: [FL KL]
The center frequency, in hertz, and peak gain of the low-frequency
bandpass filter.
Intermediate frequency band: [FI KI]
The center frequency, in hertz, and peak gain of the intermediatefrequency bandpass filter.
5-135
Multiband Power System Stabilizer
High frequency band: [FH KH]
The center frequency, in hertz, and peak gain of the high-frequency
bandpass filter.
Signal limits [VLmax VImax VHmax VSmax]
The limits imposed on the output of the low-, intermediate-, and
high-frequency bands and the limit VSmax imposed on the output of the
stabilizer, all in p.u.
Plot frequency response
If selected, a plot of the frequency response of the stabilizer is displayed
when you click the Apply button.
5-136
Multiband Power System Stabilizer
Detailed Settings Mode
Low frequency gains: [KL1 KL2 KL]
The gains of the positive and negative branches of the differential filter in
the low-frequency band and the overall gain KL of the low-frequency band,
in p.u.
5-137
Multiband Power System Stabilizer
Low frequency time constants
The time constants, in seconds, of the lead-lag blocks in the positive and
negative branches of the low-frequency filter. You need to specify the
following twelve time constants and two gains:
[TB1 TB2 TB3 TB4 TB5 TB6 TB7 TB8 TB9 TB10 TB11 TB12 KB11 KB17]
Set KB11 to 0 in order to make the first block of the positive filter branch a
washout block. Set KB11 to 1 in order to make the block a lead-lag block.
Set KB17 to 0 in order to make the first block of the negative filter branch
a washout block. Set KB17 to 1 in order to make the block a lead-lag block.
Intermediate frequency gains: [KI1 KI2 KI]
The gains of the positive and negative branches of the differential filter in
the intermediate-frequency band and the overall gain KI of the
intermediate-frequency band, in p.u.
Intermediate frequency time constants
The time constants, in seconds, of the lead-lag blocks in the positive and
negative branches of the intermediate-frequency filter. You need to specify
the following twelve time constants and two gains:
[TI1 TI2 TI3 TI4 TI5 TI6 TI7 TI8 TI9 TI10 TI11 TI12 KI11 KI17]
Set KI11 to 0 in order to make the first block of the positive filter branch a
washout block. Set KI11 to 1 in order to make the block a lead-lag block.
Set KI17 to 0 in order to make the first block of the negative filter branch a
washout block. Set KI17 to 1 in order to make the block a lead-lag block.
High frequency gains: [KH1 KH2 KH]
The gains of the positive and negative branches of the differential filter in
the high-frequency band and the overall gain KI of the high-frequency
band, in p.u.
High frequency time constants
The time constants, in seconds, of the lead-lag blocks in the positive and
negative branches of the high-frequency filter. You need to specify the
following twelve time constants and two gains:
[TH1 TH2 TH3 TH4 TH5 TH6 TH7 TH8 TH9 TH10 TH11 TH12 KH11 KH17]
5-138
Multiband Power System Stabilizer
Set KH11 to 0 in order to make the first block of the positive filter branch a
washout block. Set KH11 to 1 in order to make the block a lead-lag block.
Set KH17 to 0 in order to make the first block of the negative filter branch
a washout block. Set KH17 to 1 in order to make the block a lead-lag block.
Signal limits [VLmax VImax VHmax VSmax]
The limits imposed on the output of the low-, intermediate-, and
high-frequency bands and the limit VSmax imposed on the output of the
stabilizer, all in p.u.
Plot frequency response
If selected, a plot of the frequency response of the stabilizer is displayed
when you click the Apply button.
Input and
Output
dw
Connect to the first input the synchronous machine speed deviation dw
signal (in p.u.).
Vstab
The output is the stabilization voltage, in p.u., to connect to the vstab input
of the Excitation System block used to control the terminal voltage of the
Synchronous Machine block.
Example
See the help text of the power_PSS demo model.
References
[1] Grondin, R., I. Kamwa, L. Soulieres, J. Potvin, and R. Champagne, “An
approach to PSS design for transient stability improvement through
supplementary damping of the common low frequency,” IEEE Transactions on
Power Systems, 8(3), August 1993, pp. 954-963.
[2] IEEE recommended practice for excitation system models for power system
stability studies: IEEE St. 421.5-2002 (Section 9).
See Also
Generic Power System Stabilizer
5-139
Multimeter
Purpose
5Multimeter
Library
Measurements
Description
The Multimeter block is used to measure voltages and currents of the
measurements described by the dialog boxes of SimPowerSystems blocks.
Measure the voltages and currents specified in dialog boxes of
SimPowerSystems blocks
The powerlib blocks listed in the following table have a special parameter
(Measurements) that allows you to measure voltages or currents related to the
block. Choosing voltages or currents through this measurement parameter is
equivalent to connecting an internal voltage or current measurement block
inside your blocks. The measured signals can be observed through a
Multimeter block placed in your circuit.
Drag the Multimeter block into the top-level system of your circuit and
double-click the icon to open the dialog box.
5-140
Block Name
Block Name
AC Current Source
PI Section Line
AC Voltage Source
Saturable Transformer
Breaker
Series RLC Branch
Controlled Current
Source
Series RLC Load
Controlled Voltage
Source
Surge Arrester
DC Voltage Source
Three-Level Bridge
Distributed Parameter
Line
Three-Phase Load (Series and Parallel)
Linear Transformer
Three-Phase Branch (Series and Parallel)
Mutual Inductance
Three-Phase Transformer (Two and Three
Windings)
Multimeter
Block Name (Continued)
Block Name (Continued)
Parallel RLC Branch
Universal Bridge
Parallel RLC Load
Zigzag Phase-Shifting Transformer
Sign Conventions for Voltages and Currents
When you measure a current using a Current Measurement block, the positive
direction of current is indicated on the block icon (positive current flowing from
+ terminal to – terminal). Similarly, when you measure a voltage using a
Voltage Measurement block, the measured voltage is the voltage of the +
terminal with respect to the – terminal. However, when voltages and currents
of blocks from the Elements library are measured using the Multimeter block,
the voltage and current polarities are not immediately obvious because blocks
might have been rotated and there are no signs indicating polarities on the
block icons.
Unlike Simulink signal lines and input and output ports, the Physical
Modeling connection lines and terminal ports of SimPowerSystems lack
intrinsic directionality. The voltage and current polarities are determined, not
by line direction, but instead by block orientation. To find out a block
orientation, first click the block to select it. Then enter the following command:
get_param(gcb,'Orientation')
The following table indicates the polarities of the currents and voltages
measured with the Multimeter block for single-phase and three-phase RLC
elements (branches or loads), surge arresters, and single-phase and
three-phase breakers. The table also indicates the polarities of their state
variables (inductor currents and capacitor voltages).
Block Orientation
Positive Current
Direction
Measured Voltage
right
left —> right
Vleft – Vright
left
right —> left
Vright – Vleft
5-141
Multimeter
Block Orientation
(Continued)
Positive Current
Direction (Continued)
Measured Voltage
(Continued)
down
top —> bottom
Vtop – Vbottom
up
bottom —> top
Vbottom – Vtop
The natural orientation of the blocks (that is, their orientation in the Element
library) is right for horizontal blocks and down for vertical blocks.
For single-phase transformers (linear or saturable), with the winding
connectors appearing on the left and right sides, the winding voltages are the
voltages of the top connector with respect to the bottom connector whatever the
block orientation (right or left). The winding currents are the currents entering
the top connector.
For three-phase transformers, the voltage polarities and positive current
directions are indicated by the signal labels used in the Multimeter block. For
example, Uan_w2 = phase A-to-neutral voltage of the Y connected winding #2,
Iab_w1 = winding current flowing from A to B in the delta-connected winding
#1.
5-142
Multimeter
Dialog Box and
Parameters
Available Measurements
The Available Measurements list box shows the measurements in the
Multimeter block. Use the >> button to select measurements from the
Available Measurements list box. Click the Update button to refresh the
list of available measurements in the Multimeter block.
The measurements in the list box are identified by the name of the block
where the measurement is done. The type of measurement (voltage
measurement, current measurement, or flux) is defined by a label
preceding the block name. See the reference sections of blocks listed in the
previous table for a description of these measurements.
5-143
Multimeter
Selected Measurements
The Selected Measurements list box shows the measurements sent to the
output of the block. You can reorder the measurements by using the Up,
Down, and Remove buttons. The +/– button allows you to reverse the
polarity of any selected measurement.
Plot selected measurements
If selected, displays a plot of selected measurements using a MATLAB
figure window. The plot is generated when the simulation stops.
Output type
Specifies the format of the output signals when the block is used in a
phasor simulation. The Output signal parameter is disabled when the
block is not used in a phasor simulation. The phasor simulation is activated
by a Powergui block placed in the model.
Set to Complex to output the selected measurements as complex values.
The outputs are complex signals.
Set to Real-Imag to output the real and imaginary parts of the
measurements. For each selected measurement, the multimeter outputs
the real and imaginary parts.
Set to Magnitude-Angle to output the magnitude and angle of the selected
measurements. For each selected measurement, the multimeter outputs
the magnitude and angle values.
Set to Magnitude to output the magnitude of the selected measurements.
5-144
Multimeter
Example
The power_compensated demo uses a Multimeter block to measure the voltage
across the secondary winding of a Saturable Transformer block and the
currents flowing through two Series RLC Load blocks.
A Multimeter block is dragged into the model. In the dialog box of the 250 MVA
block, set the Measurements parameter to All measurements (V,I,flux). In
the 110 Mvar block, set it to Branch voltage and in the 110 Mvar1 block, set
it to Branch voltage and current.
The output of the Multimeter block is connected to a Scope block in order to
display the measurements during the simulation. In addition, you can select
the Plot selected measurements parameter to display a plot of selected
measurements when simulation stops.
Open the Multimeter block dialog box and select the signals you want to
observe, as shown on the Dialog Box and Parameters section. Notice the labels
used to define the available measurements in the Multimeter block. See the
reference section of the Saturable Transformer block and Series RLC Load
block for a description of these labels.
Start the simulation. After 0.4 seconds, the simulation stops and a MATLAB
figure window opens to display the selected measurements in the Multimeter
block.
See Also
Current Measurement, Voltage Measurement
5-145
Mutual Inductance
Purpose
5Mutual Inductance
Library
Elements
Description
The Mutual Inductance block implements a magnetic coupling among three
separate windings. Specify the self-resistance and inductance of each winding
on the first three entries of the dialog box and the mutual resistance and
inductance in the last entry.
Implement a magnetic coupling between two or three windings
The electrical model for this block is given below:
R1-Rm
L2-Lm R2-Rm
L1-Lm
Lm
Rm
L3-Lm R3-Rm
Ideal
transformer
1:1:1
5-146
Mutual Inductance
Dialog Box and
Parameters
Winding 1 self impedance
The self-resistance and inductance for winding 1, in ohms (Ω) and henries
(H).
Winding 2 self impedance
The self-resistance and inductance for winding 2, in ohms (Ω) and henries
(H).
Three windings Mutual Inductance
If selected, implements three coupled windings; otherwise, it implements
two coupled windings.
Winding 3 self impedance
The Winding 3 self impedance parameter is not available if the Three
windings Mutual Inductance parameter is not selected. The
self-resistance and inductance in ohms (Ω) and henries (H) for winding 3.
5-147
Mutual Inductance
Mutual impedance
The mutual resistance and inductance between windings, in ohms (Ω) and
henries (H). If the mutual resistance and reactance are set to [0 0], the
block implements three separate inductances with no mutual coupling.
Measurements
Select Winding voltages to measure the voltage across the winding
terminals.
Select Winding currents to measure the current flowing through the
windings.
Select Winding voltages and currents to measure the winding voltages
and currents.
Place a Multimeter block in your model to display the selected
measurements during the simulation.
In the Available Measurements list box of the Multimeter block, the
measurements are identified by a label followed by the block name.
Inputs and
Outputs
Measurement
Label
Winding voltages
Uw1:, Uw2:, Uw3:
Winding currents
Iw1:, Iw2:, Iw3:
Winding 1 is connected between input 1 and output 1 of the Mutual Inductance
block. Winding 2 is connected between input 2 and output 2 and winding 3, if
defined, is connected between input 3 and output 3.
The input ports of the Mutual Inductance block are at the same instantaneous
polarity.
Limitations
Because of modeling constraints, the following restrictions apply:
R 1, R 2, R 3 ≠ R m
L 1, L 2, L 3 ≠ L m
Negative values are allowed for the self- and mutual inductances as long as the
self-inductances are different from the mutual inductance.
5-148
Mutual Inductance
Windings can be left floating (not connected by an impedance to the rest of the
circuit). However an internal resistor between the floating winding and the
main circuit is automatically added. This internal connection does not affect
voltage and current measurements.
Example
The power_mutual demo uses three coupled windings to inject a third harmonic
voltage into a circuit fed at 60 Hz.
Simulation produces the following load voltage waveform:
5-149
Mutual Inductance
See Also
5-150
Linear Transformer, Saturable Transformer, Three-Phase Mutual Inductance
Z1-Z0
Neutral
Purpose
5Neutral
Library
Elements
Description
The Neutral block implements a common node with a specific node number.
You can use this block to create a floating neutral or to interconnect two points
without drawing a connection line.
Implement a common node in the circuit
Dialog Box and
Parameters
Node number
Specify a number of the neutral node. If the Node number parameter is set
to 0, the Neutral block makes a connection to ground. The node number is
displayed next to the block icon.
5-151
Neutral
Example
The power_neutral demo uses three Neutral blocks. One Neutral block is used
to refer a Voltage Measurement block to the ground (node 0).
See Also
Ground
5-152
Parallel RLC Branch
Purpose
5Parallel RLC Branch
Library
Elements
Description
The Parallel RLC Branch block implements a single resistor, inductor, and
capacitor or a parallel combination of these. To eliminate either the resistance,
inductance, or capacitance of the branch, the R, L, and C values must be set
respectively to infinity (inf), infinity (inf), and 0. Only existing elements are
displayed in the block icon.
Implement a parallel RLC branch
Negative values are allowed for resistance, inductance, and capacitance.
Dialog Box and
Parameters
Resistance R
The branch resistance, in ohms (Ω).
Inductance L
The branch inductance, in henries (H).
Capacitance C
The branch capacitance, in farads (F).
5-153
Parallel RLC Branch
Measurements
Select Branch voltage to measure the voltage across the Parallel RLC
Branch block terminals.
Select Branch current to measure the total current (sum of R, L, C
currents) flowing through the Parallel RLC Branch block.
Select Branch voltage and current to measure the voltage and the
current of the Parallel RLC Branch block.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurement is identified by a label
followed by the block name.
Example
Measurement
Label
Branch voltage
Ub:
Branch current
Ib:
The power_paralbranch demo is used to obtain the frequency response of an
eleventh-harmonic filter (tuned frequency at 660 Hz) connected on a 60 Hz
power system:
The network impedance in the Laplace domain is
5-154
Parallel RLC Branch
2
V(s)
RLCs + Ls + R
Z ( s ) = ------------ = ------------------------------------------2
I(s)
LCs + RCs
To obtain the frequency response of the impedance you have to get the
state-space model (A B C D matrices) of the system.
This system is a one input (Is) and one output (Vs) system.
Note If you have the Control System Toolbox installed, you can get the
transfer function Z(s) from the state-space matrices and the bode function.
[A,B,C,D] = power_analyze('power_paralbranch');
freq = logspace(1,4,500);
w = 2*pi*freq;
[Zmag,Zphase] = bode(A,B,C,D,1,w);
subplot(2,1,1)
loglog(freq,Zmag)
grid
title('11th harmonic filter')
xlabel('Frequency, Hz')
ylabel('Impedance Z')
subplot(2,1,2)
semilogx(freq,Zphase)
xlabel('Frequency, Hz')
ylabel('phase Z')
grid
You can also use the Impedance Measurement block and the Powergui block to
plot the impedance as a function of frequency.
5-155
Parallel RLC Branch
See Also
5-156
Multimeter, Parallel RLC Load, Powergui, Series RLC Branch, Series RLC
Load
Parallel RLC Load
Purpose
5Parallel RLC Load
Library
Elements
Description
The Parallel RLC Load block implements a linear load as a parallel
combination of RLC elements. At the specified frequency, the load exhibits a
constant impedance. The active and reactive powers absorbed by the load are
proportional to the square of the applied voltage.
Implement a linear parallel RLC load
Only elements associated with nonzero powers are displayed in the block icon.
Dialog Box and
Parameters
Nominal voltage Vn
The nominal voltage of the load, in volts RMS (Vrms).
Nominal frequency fn
The nominal frequency, in hertz (Hz).
5-157
Parallel RLC Load
Active power P
The active power of the load, in watts.
Inductive reactive power QL
The inductive reactive power QL, in vars. Specify a positive value, or 0.
Capacitive reactive power QC
The capacitive reactive power QC, in vars. Specify a positive value, or 0.
Measurements
Select Branch voltage to measure the voltage across the Parallel RLC
Load block terminals.
Select Branch current to measure the current flowing through the
Parallel RLC Load block.
Select Branch voltage and current to measure the voltage and the
current of the Parallel RLC Load block.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurement is identified by a label
followed by the block name.
Example
5-158
Measurement
Label
Branch voltage
Ub:
Branch current
Ib:
The power_paralload demo uses a parallel RLC load block to implement a
load.
Parallel RLC Load
See Also
Multimeter, Parallel RLC Branch, Series RLC Branch, Series RLC Load
5-159
Permanent Magnet Synchronous Machine
Purpose
5Permanent Magnet Synchronous Machine
Library
Machines
Description
The Permanent Magnet Synchronous Machine block operates in either
generator or motor mode. The mode of operation is dictated by the sign of the
mechanical torque (positive for motor mode, negative for generator mode). The
electrical and mechanical parts of the machine are each represented by a
second-order state-space model. The model assumes that the flux established
by the permanent magnets in the stator is sinusoidal, which implies that the
electromotive forces are sinusoidal.
Model the dynamics of a three-phase permanent magnet synchronous machine
with sinusoidal flux distribution
The block implements the following equations expressed in the rotor reference
frame (qd frame).
Electrical System
Lq
d
1
R
i d = ------- v d – ------- i d + ------- pω r i q
dt
Ld
Ld
Ld
Ld
λpω
1
R
d
i q = ------ v q – ------ i q – ------- pω r i d – -------------r
Lq
Lq
dt
Lq
Lq
T e = 1.5p [ λi q + ( L d – L q )i d i q ]
where (all quantities in the rotor reference frame are referred to the stator)
5-160
L q, L d
q and d axis inductances
R
Resistance of the stator windings
iq, id
q and d axis currents
vq, vd
q and d axis voltages
ωr
Angular velocity of the rotor
λ
Amplitude of the flux induced by the permanent magnets of
the rotor in the stator phases
Permanent Magnet Synchronous Machine
p
Number of pole pairs
Te
Electromagnetic torque
Mechanical System
1
d
ω = --- ( T e – Fω r – T m )
J
dt r
dθ
= ωr
dt
where
J
Combined inertia of rotor and load
F
Combined viscous friction of rotor and load
θ
Rotor angular position
Tm
Shaft mechanical torque
5-161
Permanent Magnet Synchronous Machine
Dialog Box and
Parameters
Resistance
The stator resistance R (Ω).
Inductances
The d-axis and q-axis stator inductances Ld (H) and Lq (H).
Flux induced by magnets
The constant flux λ (Wb) induced in the stator windings by the magnets.
Inertia, friction factor and pairs of poles
The combined machine and load inertia coefficient J (kg.m2), combined
viscous friction coefficient F (N.m.s), and pole pairs p.
Inputs and
Outputs
5-162
The first three inputs are the electrical connections of the machine’s stator. The
fourth input is the mechanical torque at the machine’s shaft (Simulink signal).
This input should normally be positive because the Permanent Magnet
Synchronous Machine block is usually used as a motor. Nevertheless, you can
apply a negative torque input if you choose to use the block in generator mode.
Permanent Magnet Synchronous Machine
The block outputs a vector containing the following 10 signals (all currents
flowing into machine):
Signal
Definition
1 to 3
Line currents ia, ib, and ic, in A
4 and 5
q and d axis currents iq and id, in A
6 and 7
q and d axis voltages vq and vd, in V
8
Rotor mechanical speed ωr, in rad/s
9
Rotor mechanical angle θ, in rad
10
Electromagnetic torque Te, in N.m
You can demultiplex these signals by using the Machines Measurement
Demux block provided in the Machines library.
Assumption
The Permanent Magnet Synchronous Machine block assumes a linear
magnetic circuit with no saturation of the stator and rotor iron. This
assumption can be made because of the large air gap usually found in
permanent magnet synchronous machines.
Example
This power_pmmotor demo illustrates the use of the Permanent Magnet
Synchronous Machine block in motoring mode with a closed-loop control
system built entirely in Simulink. The interfacing is done using Controlled
Voltage Source blocks from the Electrical Sources library. The complete system
consists of a PWM inverter built with ideal switches (Simulink Relay blocks).
Two control loops are used; the inner loop is used to regulate the motor line
currents and the outer loop regulates the motor’s speed. More elaborate and
efficient control schemes for the Permanent Magnet Synchronous Machine
block can be found, for instance, in [1]. The mechanical torque applied at the
motor’s shaft is originally 3 N.m (nominal) and steps to 1 N.m at t = 0.04
5-163
Permanent Magnet Synchronous Machine
seconds. The parameters of the machine are those found in the dialog box
section.
Set the simulation parameters as follows:
• Integrator type: stiff, ode15s
• Stop time: 0.06
• Integration options: Use default options, except for absolute tolerance that
you can set to 1e-3
Run the simulation and observe the motor’s torque, speed, and currents.
5-164
Permanent Magnet Synchronous Machine
The torque climbs to nearly 32 N.m when the motor starts but stabilizes
rapidly to its nominal value (3 N.m), until the step is applied, at which point
the torque oscillates slightly before stabilizing to its new value (1 N.m). As for
the speed, you can see that it stabilizes quite fast at start-up and is not affected
by the load step.
The currents are initially high when the machine starts, like the torque, but
stabilize quickly to their nominal values until the step is applied, at which
point they oscillate before stabilizing to a lower value, corresponding to the
load torque decrease.
References
[1] Grenier, D., L.-A. Dessaint, O. Akhrif, Y. Bonnassieux, and B. LePioufle,
“Experimental Nonlinear Torque Control of a Permanent Magnet Synchronous
Motor Using Saliency,” IEEE Transactions on Industrial Electronics, Vol. 44,
No. 5, October 1997, pp. 680-687.
5-165
PI Section Line
Purpose
5PI Section Line
Library
Elements
Description
The PI Section Line block implements a single-phase transmission line with
parameters lumped in PI sections.
Implement a single-phase transmission line with lumped parameters
For a transmission line, the resistance, inductance, and capacitance are
uniformly distributed along the line. An approximate model of the distributed
parameter line is obtained by cascading several identical PI sections, as shown
in the following figure.
Section1
R
C/2
R
L
C
R
L
C
C
L
C/2
Unlike the Distributed Parameter Line block, which has an infinite number of
states, the PI section linear model has a finite number of states that permit you
to compute a linear state-space model. The number of sections to be used
depends on the frequency range to be represented.
A good approximation of the maximum frequency range represented by the PI
line model is given by the following equation:
f max = Nv
-------8l
where
5-166
N
Number of PI sections
v
Propagation speed in km/s = 1 ⁄ LC L in H/km, C in F/km
l
Line length in km
PI Section Line
For example, for a 100 km aerial line having a propagation speed of 300,000
km/s, the maximum frequency range represented with a single PI section is
approximately 375 Hz. For studying interactions between a power system and
a control system, this simple model could be sufficient. However for switching
surge studies involving high-frequency transients in the kHz range, much
shorter PI sections should be used. In fact, you can obtain the most accurate
results by using a distributed parameters line model.
Dialog Box and
Parameters
Frequency used for RLC specifications
Frequency used to compute the line parameters, in hertz (Hz).
Resistance per unit length
The resistance per unit length of the line, in ohms/km (Ω).
Inductance per unit length
The inductance per unit length of the line, in henries/km (H/km).
5-167
PI Section Line
Capacitance per unit length
The capacitance per unit length of the line, in farads/km (F/km).
Length
The line length in km.
Number of pi sections
The number of PI sections. The minimum value is 1.
Measurements
Select Input and output voltages to measure the sending end (input
port) and receiving end (output port) voltages of the line model.
Select Input and output voltages to measure the sending end and
receiving end currents of the line model.
Select All voltages and currents to measure the sending end and
receiving end voltages and currents of the line model.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurement is identified by a label
followed by the block name.
Example
5-168
Measurement
Label
Sending end voltage (block input)
Us:
Receiving end voltage (block output)
Ur:
Sending end current (input current)
Is:
Receiving end current (output current)
Ir:
The power_piline demo shows the line energization voltages and currents of
a PI section line.
PI Section Line
The results obtained with the line modeled by one PI section of 100 km and 10
PI sections of 10 km are shown.
5-169
PI Section Line
See Also
5-170
Distributed Parameter Line
Powergui
Purpose
5Powergui
Library
powerlib
Description
The Powergui block provides useful graphical user interface (GUI) tools for the
analysis of SimPowerSystems models. Copy the Powergui block into the top
level of your model and double-click the block to open the interface.
Graphical user interface for the analysis of circuits and systems
What the Powergui Block Does
The Powergui block allows you to choose one of three methods to solve your
circuit:
1 Continuous method, which uses a variable step solver from Simulink
2 Discretization of the electrical system for a solution at fixed time steps
3 Phasor solution method
The Powergui block also allows you to
• Display steady-state values of measured current and voltages as well as all
state variables (inductor currents and capacitor voltages) in a circuit.
• Modify the initial states in order to start the simulation from any initial
conditions. The names of the state variables are the name of the block where
the capacitor or the inductor is found, preceded by the Uc_ label for capacitor
voltages and by the IL_ label for the inductor currents.
• Perform load flows and initialize three-phase networks containing
three-phase machines so that the simulation starts in steady state. This
option is available with circuits containing the following types of machines:
Simplified Synchronous Machine, Synchronous Machine, or Asynchronous
Machine (squirrel cage) blocks.
• Display impedance versus frequency plots when Impedance Measurement
blocks are present in your circuit.
• Perform FFT analysis of the simulation results.
• Generate the state-space model (SS) of your system (if you have the Control
System Toolbox installed) and automatically open the LTI Viewer interface
for time and frequency domain responses
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Powergui
• Generate a report containing steady-state values of the measurement blocks,
the sources, the nonlinear models, and the states of your circuit. The report
is saved in a file with the.rep extension.
• Model the hysteresis characteristic of the Saturable Transformer blocks.
Dialog Boxes
and
Parameters
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Powergui
Simulation
Type
Phasor simulation
If selected, SimPowerSystems performs a phasor simulation of the model,
at the frequency specified by the Frequency parameter.
Frequency (Hz)
Specify the frequency used by SimPowerSystems to perform the phasor
simulation of the model. The Frequency field is gray if Phasor simulation
is not selected.
Discretize electrical model
If selected, SimPowerSystems performs a discretization of the model. The
sample time is specified by the Sample time parameter.
Sample time(s)
Specify the sample time used to discretize the electrical circuit. Set the
Sample time parameter to a value greater than 0. The icon displays the
value of the sample time. If sample time is specified as 0, discretization is
not performed, and the continuous solution method is used. The Sample
time field is gray if the Discretize electrical model parameter is not
selected.
Continuous
If selected, SimPowerSystems performs a continuous solution of the model.
Show messages during simulation
If selected, the command line echo messages of SimPowerSystems are
enabled during the analysis and simulation of the model.
Analysis Tools
Steady-State Voltages and Currents
Open a window that displays the steady-steady-state voltages and currents
of the model.
Initial States Setting
Open a window that allows you to display and modify initial voltages and
currents of the model.
Load Flow and Machine Initialization
Open a window to perform load flow and machine initialization.
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Powergui
Use LTI Viewer
Open a window to use the LTI Viewer of the Control System Toolbox.
Impedance vs Frequency Measurement
Open a window that allows you to display the impedance versus frequency
measurements performed by the Impedance Measurement blocks of the
model.
FFT Analysis
Open a window to use the FFT analysis tool.
Generate Report
Open a window and generate a report of the steady-state calculations.
Hysteresis Design Tool
Open a window to design a hysteresis characteristic for the saturable core
of the Saturable Transformer block and the Three-Phase Transformer
blocks (two- and three-windings).
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Powergui
Steady-State Voltages and Currents GUI
Steady state values
Display measurements of steady-state voltages and currents in the model.
Units
Set the Units parameter to Peak values to display the peak values of the
selected values. Set the Units parameter to RMS to display the
root-mean-square (RMS) values of the selected values.
Frequency
Allows you to choose the frequency, in hertz (Hz), that you want for display
of the voltage and current phasors. The Frequency parameter lists all the
different frequencies of the electrical sources of the model.
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Powergui
States
If selected, the window displays the steady-state phasors of the capacitor
voltages and inductor currents of the circuit. The default is unselected.
Measurements
If selected, the window displays the steady-state voltage and current
phasors of the measurement blocks of the circuit. The default is selected.
Sources
If selected, the window displays the steady-state voltage and current
phasors of the electrical sources of the circuit. The default is unselected.
Nonlinear elements
If selected, the window displays the steady-state voltages and currents of
the nonlinear blocks of the circuit. The default is unselected.
Format
In the pull-down menu, choose the format in which you want your
measurements displayed. The floating point option is displayed in
mantissa-exponent form with five significant figures. The best of option
displays with four significant figures and uses mantissa-exponent form
only for numbers larger than 9999. The final option is displayed in plain
numbers with two figures to the right of the decimal point. The default is
floating point.
Reload Steady State Values
Recompute and redisplay the steady-state measurements.
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Powergui
Initial States Setting GUI
Initial state values for simulation
Display names of model state variables and their initial values.
Set selected state
Enter a value here to set the initial value of the variable selected in the
Initial state values for simulation list.
Reset all states
If To Steady State is selected, sets all initial state values to steady-state
values. If To Zero is selected, sets all variables to zero.
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Powergui
Reload states
If From File is selected, allows you to choose a previously saved file storing
the model’s states. If From Diagram is selected, sets all initial state values
to their current values (either steady state values or last modified values).
Apply
Apply the chosen settings to the simulation.
Revert
Reapply the model’s original settings from when this GUI was opened.
Save Initial States
Save the model’s initial state settings in a file.
Format
In the pull-down menu, choose the format in which you want your
measurements displayed. The floating point option is displayed in
mantissa-exponent form with five significant figures. The best of option
displays with four significant figures and uses mantissa-exponent form
only for numbers larger than 9999. The final option is displayed in plain
numbers with two figures to the right of the decimal point. The default is
floating point.
Sort values by
Select order of displayed initial state values. Selecting Default order
displays the value by block order in the diagram. Selecting State number
displays the values according to the states’ ordering in the state-space
model. Selecting Type displays the values grouped by capacitors and
inductors. The default is Default order.
Sign Conventions for Voltages and Currents
Unlike Simulink signal lines and input and output ports, the Physical
Modeling connection lines and terminal ports of SimPowerSystems lack
intrinsic directionality. The voltage and current polarities are determined, not
by line direction, but instead by block orientation. To find out a block
orientation, first click on the block to select it. Then enter the following
command:
get_param(gcb,'Orientation')
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Powergui
The following table indicates the polarities of the currents and voltages for
single-phase and three-phase RLC elements (branches or loads), surge
arresters, and single-phase and three-phase breakers. The table also indicates
the polarities of their state variables (inductor currents and capacitor
voltages).
Block
Orientation
Positive Current
Direction
Measured
Voltage
right
left —> right
Vleft – Vright
left
right —> left
Vright – Vleft
down
top —> bottom
Vtop – Vbottom
up
bottom —> top
Vbottom – Vtop
The natural orientation of the blocks (that is, their orientation in the Element
library) is right for horizontal blocks and down for vertical blocks.
For single-phase transformers (linear or saturable), with the winding
connectors appearing on the left and right sides, the winding voltages are the
voltages of the top connector with respect to the bottom connector whatever the
block orientation (right or left). The winding currents are the currents entering
the top connector. For three-phase transformers, the voltage polarities and
positive current directions are indicated by the signal labels used in the
Multimeter block.
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Powergui
Load Flow and Machine Initialization GUI
Machine load flow
Displays load flow characteristics of the machine selected in the Machines
field.
Machines
Display the names of the Simplified Synchronous Machines, the
Synchronous Machines, the Asynchronous Machine, and the Three-Phase
Dynamic Load blocks of your model. Select a machine or a load in the list
box in order to set its parameters for the load flow.
Bus type
If Bus type is set to P&V Generator, you can set the desired terminal
voltage and active power of the machine. If Bus type is set to PQ
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Powergui
generator, you can set the desired active and reactive powers. If Bus type
is set to Swing Bus, you can set the desired terminal voltage, enter an active
power guess, and specify the phase of the UAN terminal voltage of the
machine.
If you select an Asynchronous Machine block machine, you only have to
enter the desired mechanical power delivered by the machine. If you select
a Three-Phase Dynamic Load block, you have to specify the active and
reactive powers consumed by the load.
Terminal voltage UAB
Specify the terminal line-to-line voltage of the selected machine.
Active power
Specify the active power of the selected machine or load.
Active power guess
Specify active power guess to start iterations when the specified machine
bus type is Swing Bus.
Reactive power
Specify the reactive power of the selected machine or load.
Phase of UAN voltage
This parameter is activated only when the bus type is Swing Bus.
Specify the phase of the phase-to-neutral voltage of phase A of the selected
machine.
Mechanical power
In motor mode, specify the mechanical power developed by the squirrel
cage induction machine. In generator mode, specify the mechanical power
absorbed by the machine as a negative number.
Load flow frequency
Specify the frequency to be used in the load flow calculations (normally 60
Hz or 50 Hz).
Load flow initial condition
Normally, you should keep the default setting Auto to let the load flow
automatically adjust the initial conditions before starting iterations. If you
select Start from previous solution, the load flow starts with initial
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Powergui
conditions corresponding to the previous solution. Try this option if the
load flow fails to converge after a change has been made to the power and
voltage settings of the machines or to the circuit parameters.
Update Circuit & Measurements
Update the list of machines, voltage and current phasors, as well as the
powers in the load flow window if you have made a change in your model
while the load flow window is open. The new voltages and powers displayed
in the load flow window are computed by using the machine currents
obtained from the last load flow (the three currents stored in the Initial
conditions parameter of the machine blocks).
Execute Load Flow
Executes the load flow calculations for the given load flow parameters.
Use LTI Viewer GUI
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Powergui
System inputs
Lists the inputs of the state-space model of your circuit. Select the inputs
to be used by the LTI Viewer.
System outputs
Lists the outputs of the state-space model of your circuit. Select the outputs
to be used by the LTI Viewer.
Open New LTI Viewer
Generate the state-space model of the circuit and opens the LTI viewer for
the selected system inputs and outputs.
Impedance vs Frequency Measurement GUI
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Powergui
Measurement
Lists the Impedance Measurement blocks of the model. Select the blocks
for which you want to obtain the frequency response. Use the CTRL key to
select several impedances to be displayed on the same plot.
Axis
Range (Hz)
Specify the frequency vector, in hertz (Hz). You can specify in that field any
valid MATLAB expression defining a vector of frequencies; for example,
0:2:1000 or linspace(0,1000,500). The default is logspace(0,3,50).
Logarithmic Impedance/Linear Impedance
Choose logarithmic or linear scale for the vertical impedance scale.
Logarithmic Frequency/Linear Frequency
Choose logarithmic or linear scale for the horizontal frequency scales.
Grid
If selected, a grid is displayed for the two plots. Default is unselected.
Save data when updated
If selected, data are saved in a variable in the workspace. The name of the
variable is defined by the Workspace variable name parameter. The
complex impedances are saved in an array together with the corresponding
frequencies. Frequency is saved in column 1 and impedances are saved in
the next columns. Default is unselected.
Display/Save or Update
Click to initially display the impedance versus frequency measurement
and, if the Save data when updated check box is selected, save the data to
your workspace.
Click to start the impedance versus frequency measurement again and
display results after multiple runs of your model.
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Powergui
FFT Analysis GUI
Structure
Lists the structures with time variables that are present in your
workspace. These structures are generated by the Scope or To Workspace
blocks in your model. Use the pull-down menu to select the variable you
want to analyze.
Input
Select the input signal of the selected structure with time variables
specified in the Structure field. Structures with time variables with
multiple inputs can be generated by a Scope block having multiple input
ports.
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Powergui
Signal Number
Specify the index of the selected input signal specified by the Input
parameter. For example, the Signal Number parameter allows you to
select the phase A signal of a three-phase signal connected to input 2 of a
Scope block.
Start time(s)
Specify the start times for the FFT analysis.
Number of cycles
Specify the number of cycles for the FFT analysis.
Display FFT window/Display entire signal
In the pulldown menu, select Display entire signal to display the entire
selected signal in the upper plot. Select Display FFT window to display
only the portion of the signal where the FFT analysis is performed.
Fundamental frequency
Specify the fundamental frequency, in hertz (Hz), for the FFT analysis.
Max Frequency
Specify the maximum frequency, in hertz (Hz), for the FFT analysis.
Frequency axis
In the pull-down menu, select Hertz to display the spectrum frequency axis
in hertz. Select Harmonic order to display the spectrum frequency axis in
harmonic order relative to the fundamental frequency.
Display style
In the pull-down menu, select Bar (relative to Fund. or DC) to display the
spectrum as a bar graph relative to the fundamental frequency. Select Bar
(relative to specified base) to display the spectrum as a bar graph relative
to the base defined by the Base value parameter.
Select List (relative to Fund. or DC) to display the spectrum as a list in %
relative to the fundamental or DC component. Select List (relative to
specified base) to display the spectrum as a list in % relative to the base
value defined by the Base value parameter.
Base value
Enter a base value for the display of harmonics.
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Powergui
Display
Display the FFT analysis results for the selected measurement.
Generate Report GUI
Items to include in the report
In the check boxes, select any combination of measurements to include in
the generated report, Steady state, Initial states, and Machine load flow.
The default is unselected for all three.
Frequency to include in the report
Select the frequency or frequencies to include in the generated report, 60
Hz or All. The default is 60 Hz.
Units
Set the Units parameter to Peak values to display the peak values of the
selected values. Set the Units parameter to RMS to display the
root-mean-square (RMS) values of the selected values.
Format
In the pull-down menu, choose the format in which you want your
measurements displayed. The floating point option is displayed in
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Powergui
mantissa-exponent form with five significant figures. The best of option
is displayed with four significant figures and uses mantissa-exponent form
only for numbers larger than 9999. The final option is displayed in plain
numbers with two figures to the right of the decimal point. The default is
floating point.
Create Report
Generate a report and save it to a file.
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Powergui
Hysteresis Design Tool GUI
To learn more about hysteresis modeling, see the Saturable Transformer block
reference pages.
5-189
Powergui
Segments
In the pull-down menu, specify the number of linear segments used to
define the right side of the hysteresis loop. The left side of the loop is the
symmetric image of the right side.
Remanent flux Fr
Specify the remanent flux point of the hysteresis characteristic (flux at zero
current).
Saturation Flux Fs
Specify the saturation flux point where the hysteresis loop becomes a
single-valued saturation curve.
Saturation current Is
Specify the saturation current point where the hysteresis loop becomes a
single-valued saturation curve. The saturation region is defined by the
Saturation region currents parameter.
Coercive current Ic
Specify the coercive current point of the hysteresis characteristic.
dF/dl at coercive current
Set the slope of the flux at the coercive current point (current at zero flux).
Saturation region currents
Specify the vector of current values that define the saturation
characteristic. The number of specified points must be the same as for the
Saturation region fluxes parameter. You only need to specify the positive
part of the characteristic.
Saturation region fluxes
Specify the vector of flux values that define the saturation characteristic.
The number of specified points must be the same as for the Saturation
region currents parameter. You only need to specify the positive part of
the characteristic.
Transfo Nominal Parameters
Specify the nominal parameters (nominal power in VA, nominal voltage of
winding 1 in volts RMS, and nominal frequency in Hz) used in the
conversion of the hysteresis parameters.
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Powergui
Parameter units
Convert the fluxes and currents that define the hysteresis characteristic
from SI to p.u. or from p.u. to SI.
Zoom around the hysteresis
If selected, zoom the plot around the hysteresis curve. The default is
selected.
Example
Open the demos of SimPowerSystems and double-click the Powergui block
contained in the model. For each demo, you can use the tools of the Powergui
to look at the initial values and steady-state values of the inductor currents and
capacitor voltages. For demos containing machines, you can edit and perform
a machine load flow analysis.
See Also
Multimeter, Saturable Transformer
5-191
PWM Generator
Purpose
5PWM Generator
Library
Extras/Control Blocks
Generate pulses for a carrier-based two-level pulse width modulator (PWM) in
converter bridge
A discrete version of this block is available in the Extras/Discrete Control
Blocks library.
Description
The PWM Generator block generates pulses for carrier-based pulse width
modulation (PWM) converters using two-level topology. The block can be used
to fire the forced-commutated devices (FETs, GTOs, or IGBTs) of single-phase,
two-phase, three-phase, two-level bridges or a combination of two three-phase
bridges.
The number of pulses generated by the PWM Generator block is determined by
the number of bridge arms you have to control:
• Two pulses are generated for a one-arm bridge. Pulse 1 fires the upper device
and pulse 2 fires the lower device (shown for the IGBT device).
+
{
Pulse 1
Pulse 2
Upper device
2
Lower device
A
arm
5-192
1
−
PWM Generator
• Four pulses are generated for a two-arm bridge. Pulses 1 and 3 fire the upper
devices of the first and second arm. Pulses 2 and 4 fire the lower devices.
+
{
Pulse 1
Pulse 2
Pulse 3
1
3
2
4
A
B
Pulse 4
arm1
−
arm2
• Six pulses are generated for a three-arm bridge. Pulses 1, 3, and 5 fire the
upper devices of the first, second, and third arms. Pulses 2, 4, and 6 fire the
lower devices.
{
+
Pulse 1
1
3
5
2
4
6
Pulse 2
Pulse 3
Pulse 4
Pulse 5
Pulse 6
A
B
C
arm1
arm2
−
arm3
• Twelve pulses are generated for a double three-arm bridge. The first six
pulses (1 to 6) fire the six devices of the first three-arm bridge and the last
six pulses (7 to 12) fire the six devices of the second three-arm bridge.
For each arm the pulses are generated by comparing a triangular carrier
waveform to a reference modulating signal. The modulating signals can be
generated by the PWM generator itself, or they can be a vector of external
signals connected at the input of the block. One reference signal is needed to
generate the pulses for a single- or a two-arm bridge, and three reference
signals are needed to generate the pulses for a three-phase, single or double
bridge.
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PWM Generator
The amplitude (modulation), phase, and frequency of the reference signals are
set to control the output voltage (on the AC terminals) of the bridge connected
to the PWM Generator block.
The two pulses firing the two devices of an arm bridge are complementary. For
example, pulse 4 is low (0) when pulse 3 is high (1). This is illustrated in the
next two figures.
The following figure displays the two pulses generated by the PWM Generator
block when it is programmed to control a one-arm bridge.
Pulse 1
Pulse 2
The triangular carrier signal is compared with the sinusoidal modulating
signal. When the carrier is greater than the modulating signal, pulse 1 is high
(1) and pulse 2 is low (0).
For a single-phase two-arm bridge the modulating signal used for arm 2 is the
negative of modulating signal used for arm 1 (180 degrees phase shift). For a
three-phase six-arm bridge the three modulating signals used for bridge 2 are
the negative of the modulating signals applied to bridge 1.
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PWM Generator
The following figure displays the six pulses generated by the PWM Generator
block when it is programmed to control a three-arm bridge.
pulse 1
pulse 2
pulse 3
pulse 4
pulse 5
pulse 6
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PWM Generator
Dialog Box and
Parameters
Generator Mode
Specify the number of pulses to generate. The number of pulses is
proportional to the number of bridge arms to fire. Select for example
Double 3-arm bridges (12 pulses) to fire the self-commutated devices
of two six-pulse bridges connected in a twelve-pulse bridge configuration.
Carrier frequency
The frequency, in hertz, of the carrier triangular signal.
Internal generation of modulating signal
If selected, the modulating signal is generated by the block. Otherwise,
external modulating signals are used for pulse generation.
Modulation index (0 < m < 1)
The Modulation index parameter is visible only if the Internal
generation of modulating signal (s) parameter is selected.
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PWM Generator
The amplitude of the internal sinusoidal modulating signal. The
Modulation index must be greater than 0, and lower than or equal to 1.
This parameter is used to control the amplitude of the fundamental
component of the output voltage of the controlled bridge.
Frequency of output voltage
The Frequency of output voltage (Hz) parameter is visible only if the
Internal generation of modulating signal (s) parameter is selected.
The frequency, in hertz, of the internal modulating signals. This parameter
is used to control the fundamental frequency of the output voltage of the
controlled bridge.
Phase of output voltage
The Phase of output voltage parameter is visible only if the Internal
generation of modulating signal (s) parameter is selected.
The phase, in degrees, of the internal modulating signal. This parameter is
used to control the phase of the fundamental component of the output
voltage of the controlled bridge.
Inputs and
Outputs
Signal(s)
The input is not visible when Internal generation of modulating signal
(s) is selected.
The input is the vector of modulating signals when Internal generation of
modulating signal is not selected. Connect this input to a single-phase
sinusoidal signal when the block is used to control a single- or a two-arm
bridge, or to a three-phase sinusoidal signal when the PWM Generator
block is controlling one or two three-phase bridges.
Pulses
The output contains the two, four, six, or twelve pulse signals used to fire
the self-commutated devices (MOSFETs, GTOs, or IGBTs) of single-phase,
two-phase, or three-phase bridges or a combination of two three-phase
bridges.
Example
See the power_1phPWM and power_3phPWM demos for examples of single-phase
and three-phase two-level inverters.
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PWM Generator
See Also
5-198
Universal Bridge
RMS
Purpose
5RMS
Library
Extras/Measurements
Measure the root mean square (RMS) value of a signal
A discrete version of this block is available in the Extras/Discrete
Measurements library.
Description
This block measures the root mean square value of an instantaneous current
or voltage signal connected to the input of the block. The RMS value of the
input signal is calculated over a running average window of one cycle of the
specified fundamental frequency.
t
RMS ( f ( t ) ) =
1
---T
∫
f( t)
2
(t – T)
f ( t ): input signal, T = 1/fundamental frequency
as this block uses a running average window, one cycle of simulation has to be
completed before the output gives the correct value. The discrete version of this
block allows you to specify the initial magnitude of inputs. For the first cycle of
simulation the output is held to the RMS value of the specified initial input.
Dialog Box and
Parameters
Fundamental frequency
The fundamental frequency, in hertz, of the input signal.
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RMS
Example
In the power_controlvolt demo, you can add an RMS block as shown below to
measure the RMS value of the capacitor voltage. The Controlled Voltage
Source block introduces a third harmonic (180 Hz) in the voltage at t = 0.4
seconds.
At the beginning of the simulation, the RMS block needs one cycle of the
fundamental frequency (60Hz) to calculate the RMS value of the voltage. At
t = 0.4 seconds the RMS value slightly increases because of the addition of the
third harmonic in the signal. Again, the RMS block needs one cycle of the
fundamental signal to stabilize and give the correct result.
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RMS
5-201
Saturable Transformer
Purpose
5Saturable Transformer
Library
Elements
Description
The Saturable Transformer block model shown consists of three coupled
windings wound on the same core.
Implement a two- or three-winding saturable transformer
R1
L1
Lsat
L2
R2
L3
R3
Rm
The model takes into account the winding resistances (R1 R2 R3) and the
leakage inductances (L1 L2 L3) as well as the magnetizing characteristics of
the core, which is modeled by a resistance Rm simulating the core active losses
and a saturable inductance Lsat.
You can choose one of the following two options for the modeling of the
nonlinear flux-current characteristic
1 Model saturation without hysteresis. The total iron losses (eddy current +
hysteresis) are modeled by a linear resistance, Rm.
2 Model hysteresis and saturation. Specification of the hysteresis is done by
means of the Hysteresis Design Tool of the Powergui block. The eddy
current losses in the core are modeled by a linear resistance, Rm.
Note Modeling the hysteresis requires additional computation load and
therefore slows down the simulation. The hysteresis model should be reserved
for specific applications where this phenomenon is important.
5-202
Saturable Transformer
Saturation Characteristic Without Hysteresis
When the hysteresis is not modeled, the saturation characteristic of the
Saturable Transformer block is defined by a piecewise linear relationship
between the flux and the magnetization current.
phi
phi
3
4
3
Residual
flux
2
4
2
phi0
1
1
i
i
−2
(a) No residual flux can
be specified.
(b) A residual flux can be
specified between points
2 and −2.
Therefore, if you want to specify a residual flux, phi0, the second point of the
saturation characteristic should correspond to a null current, as shown in the
figure (b).
The saturation characteristic is entered as (i, phi) pair values in per units,
starting with pair (0, 0). SimPowerSystems converts the vector of fluxes Φpu
and the vector of currents Ipu into standard units to be used in the saturation
model of the Saturable Transformer block:
Φ = Φ pu Φ base
I = I pu I base
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Saturable Transformer
where the base flux linkage (Φbase) and base current (Ibase) are the peak values
obtained at nominal voltage power and frequency:
Pn
I base = -------- 2
V1
V1
Φ base = ------------ 2 (Flux linkage in volts-seconds)
2πf n
The base flux is defined as the peak value of the sinusoidal flux (in webers)
when winding 1 is connected to a 1 p.u. sinusoidal voltage source (nominal
voltage). The Φ base value defined above represents the base flux linkage (in
volt-seconds). It is related to the base flux by the following equation
Φ base = Base flux × number of turns of winding 1
When they are expressed in p.u., the flux and the flux linkage have the same
value.
Saturation Characteristic with Hysteresis
The magnetizing current I is computed from the flux Φ obtained by integrating
voltage across the magnetizing branch. The static model of hysteresis defines
the relation between flux and the magnetization current evaluated in DC,
when the eddy current losses are not present.
The hysteresis model is based on a semiempirical characteristic, using an
arctangent analytical expression Φ(I) and its inverse I(Φ) to represent the
operating point trajectories. The analytical expression parameters are
obtained by curve fitting empirical data defining the major loop and the
single-valued saturation characteristic. The Hysteresis design tool of the
Powergui block is used to fit the hysteresis major loop of a particular core type
to basic parameters. These parameters are defined by the remanent flux (Φr),
5-204
Saturable Transformer
the coercive current (Ic), and the slope (dΦ/dI) at (0, Ic) point as shown in the
next figure.
The major loop half cycle is defined by a series of N equidistant points
connected by line segments. The value of N is defined in the Hysteresis design
tool of the Powergui block. Using N = 256 yields a smooth curve and usually
gives satisfactory results.
The single-valued saturation characteristic is defined by a set of current-flux
pairs defining a saturation curve which should be asymptotic to the air core
inductance Ls.
The main characteristics of the hysteresis model are summarized below:
1
A symmetrical variation of the flux produces a symmetrical current
variation between −Imax and +Imax, resulting in a symmetrical hysteresis
loop whose shape and area depend on the value of Φmax. The major loop is
produced when Φmax is equal to the saturation current (Φs). Beyond that
point the characteristic reduces to a single-valued saturation characteristic.
2 In transient conditions, an oscillating magnetizing current produces minor
asymmetrical loops, as shown in the next figure, and all points of operation
5-205
Saturable Transformer
are assumed to be within the major loop. Loops once closed have no more
influence on the subsequent evolution.
The trajectory starts from the initial (or residual) flux point, which must lie on
the vertical axis inside the major loop. You can specify this initial flux value
phi0, or it is automatically adjusted so that the simulation starts in steady
state.
The Per Unit Conversion
In order to comply with industry practice, you must specify the resistance and
inductance of the windings in per unit (p.u.). The values are based on the
transformer rated power Pn in VA, nominal frequency fn in Hz, and nominal
voltage Vn, in Vrms, of the corresponding winding. For each winding the per
unit resistance and inductance are defined as
R(Ω)
R ( p.u. ) = --------------R base
L ( H )L ( p.u. ) = -------------L base
The base resistance and base inductance used for each winding are
5-206
Saturable Transformer
2
Vn )
R base = (--------------Pn
R base
L base = -------------2 π fn
For the magnetization resistance Rm, the p.u. values are based on the
transformer rated power and on the nominal voltage of winding 1.
The default parameters of winding 1 specified in the dialog box section give the
following base values:
2
( 735e3 ⁄ 3 )
R base = ------------------------------------ = 720.3Ω
250e6
720.3
L base = --------------- = 1.91H
2 π 60
For example, if winding 1 parameters are R1 = 1.44 Ω and L1 = 0.1528 H, the
corresponding values to enter in the dialog box are
1.44Ω = 0.002 p.u.
R 1 = ------------------720.3Ω
0.1528H- = 0.08 p.u.
L 1 = ---------------------1.91H
5-207
Saturable Transformer
Dialog Box and
Parameters
Nominal power and frequency
The nominal power rating, Pn, in volt-amperes (VA), and frequency, in
hertz (Hz), of the transformer.
Winding 1 parameters
The nominal voltage in volts RMS, resistance, and leakage inductance in
p.u. for winding 1.
Winding 2 parameters
The nominal voltage in volts RMS, resistance, and leakage inductance in
p.u. for winding 2.
5-208
Saturable Transformer
Three windings transformer
If selected, specify a saturable transformer with three windings; otherwise
it implements a two windings transformer.
Winding 3 parameters
The Winding 3 parameters are not available if the Three windings
transformer parameter is not selected. The nominal voltage in volts RMS,
resistance, and leakage inductance in p.u. for winding 3.
Saturation characteristic
Specify a series of magnetizing current (p.u.) - flux (p.u.) pairs starting with
(0,0).
Core loss resistance and initial flux
Specify the active power dissipated in the core by entering the equivalent
resistance Rm in p.u. For example, to specify a 0.2% of active power core
loss at nominal voltage, use Rm = 500 p.u. You can also specify the initial
flux phi0 (p.u). This initial flux becomes particularly important when the
transformer is energized. If phi0 is not specified, the initial flux is
automatically adjusted so that the simulation starts in steady state. When
simulating hysteresis, Rm models the eddy current losses only.
Simulate hysteresis
Select to model hysteresis saturation characteristic instead of a
single-valued saturation curve.
Hysteresis data MAT file
The Hysteresis data MAT file parameter is visible only if the Simulate
hysteresis parameter is selected.
Specify a .mat file containing the data to be used for the hysteresis model.
When you open the Hysteresis Design tool of the Powergui, the default
hysteresis loop and parameters saved in the hysteresis.mat file are
displayed. Use the File —> Load a model menu of the Hysteresis Design
tool to load another .mat file. Use the File —> Save this model menu of
the Hysteresis Design tool to save your model in a new .mat file.
Measurements
Select Winding voltages to measure the voltage across the winding
terminals of the Saturable Transformer block.
5-209
Saturable Transformer
Select Winding currents to measure the current flowing through the
windings of the Saturable Transformer block.
Select Flux and excitation current (Im + IRm) to measure the flux
linkage, in volt seconds (V.s), and the total excitation current including
iron losses modeled by Rm.
Select Flux and magnetization current (Im) to measure the flux
linkage, in volt seconds (V.s), and the magnetization current, in amperes
(A), not including iron losses modeled by Rm.
Select All measurement (V, I, Flux) to measure the winding voltages,
currents, magnetization currents, and the flux linkage.
Place a Multimeter block in your model to display the selected
measurements during the simulation.
In the Available Measurements list box of the Multimeter block, the
measurements are identified by a label followed by the block name.
Measurement
Label
Winding voltages
Uw1:, Uw2:, Uw3:
Winding currents
Iw1:, Iw2:, Iw3:
Excitation current
Iexc:
Magnetization current
Imag:
Flux linkage
Flux:
Inputs and
Outputs
The winding terminals of Input 1, output 1, and output 3 (if it exists) are at the
same instantaneous polarity.
Limitations
Windings can be left floating (that is, not connected by an impedance to the rest
of the circuit). However, the floating winding is connected internally to the
main circuit through a resistor. This invisible connection does not affect voltage
and current measurements.
5-210
Saturable Transformer
Example
The power_xfosaturable demo illustrates the energization of one phase of a
three-phase 450 MVA, 500/230 kV transformer on a 3000 MVA source. The
transformer parameters are
Nominal power Pn = 150e6 VA
and frequency
Winding 1
parameters
fn = 60 Hz
V1 = 500e3 Vrms/sqrt(3)
R1 = 0.002 p.u.
L1 = 0.08 p.u
V2 = 230e3 Vrms/sqrt(3)
R2 = 0.002 p.u.
L2 = 0.08 p.u.
(primary)
Winding 2
parameters
(secondary)
Saturation
characteristic
[0 0; 0.0 1.2; 1.0 1.52]
Core loss
resistance and
initial flux
Rm = 500 p.u.
phi0 = 0.8 p.u.
Simulation of this circuit illustrates the saturation effect on the transformer
current and voltage.
5-211
Saturable Transformer
As the source is resonant at the fourth harmonic, you can observe a high fourthharmonic content in the secondary voltage. In this circuit, the flux is calculated
in two ways:
• By integrating the secondary voltage
• By using the Multimeter block
The simulation results demonstrate these points:
References
Casoria, S., P. Brunelle, and G. Sybille, “Hysteresis Modeling in the
MATLAB/Power System Blockset,” Electrimacs 2002, École de technologie
supérieure, Montreal, 2002.
Frame, J.G., N. Mohan, and Tsu-huei Liu, “Hysteresis modeling in an
Electro-Magnetic Transients Program,” presented at the IEEE PES winter
meeting, New York, January 31 to February 5, 1982.
5-212
Saturable Transformer
See Also
Linear Transformer, Multimeter, Mutual Inductance, Powergui, Three-Phase
Transformer (Two Windings), Three-Phase Transformer (Three Windings)
5-213
Series RLC Branch
Purpose
5Series RLC Branch
Library
Elements
Description
The Series RLC Branch block implements a single resistor, inductor, or
capacitor, or a series combination of these. To eliminate either the resistance,
inductance, or capacitance of the branch, the R, L, and C values must be set
respectively to 0, 0, and infinity (inf). Only existing elements are displayed in
the block icon.
Implement a series RLC branch
Negative values are allowed for resistance, inductance, and capacitance.
Dialog Box and
Parameters
Resistance
The branch resistance, in ohms (Ω).
Inductance
The branch inductance, in henries (H).
Capacitance
The branch capacitance, in farads (F).
5-214
Series RLC Branch
Measurements
Select Branch voltage to measure the voltage across the Series RLC
Branch block terminals.
Select Branch current to measure the current flowing through the Series
RLC Branch block.
Select Branch voltage and current to measure the voltage and the
current of the Series RLC Branch block.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurement is identified by a label
followed by the block name.
Example
Measurement
Label
Branch voltage
Ub:
Branch current
Ib:
Obtain the frequency response of a fifth-harmonic filter (tuned frequency = 300
Hz) connected on a 60 Hz power system. This example is available in the
power_seriesbranch model.
The network impedance in the Laplace domain is
5-215
Series RLC Branch
2
( s )- = -----------------------------------------LCs + RCs + 1
Z(s) = V
----------Cs
I(s)
To obtain the frequency response of the impedance you have to get the
state-space model (A B C D matrices) of the system.
This system is a one-input (Vsource) and one-output (Current Measurement
block) system.
Note If you have the Control System Toolbox installed, you can use the bode
function to get the transfer function Z(s) from the state-space matrices as
follows:
[A,B,C,D] = power_analyze('power_seriesbranch');
freq = logspace(1,4,500);
w = 2*pi*freq;
[Ymag,Yphase] = bode(A,B,C,D,1,w);
% invert Y(s) to get Z(s)
Zmag = 1./Ymag;
Zphase = -Yphase;
subplot(2,1,1)
loglog(freq,Zphase)
grid
title('5th harmonic filter')
xlabel('Frequency, Hz')
ylabel('Impedance Zmag')
subplot(2,1,2)
semilogx(freq,Zphase)
xlabel('Frequency, Hz')
ylabel('phase Z')
grid
You can also use the Impedance Measurement block and the Powergui block to
plot the impedance as a function of frequency. In order to measure the
impedance you must disconnect the voltage source.
5-216
Series RLC Branch
See Also
Multimeter, Parallel RLC Branch, Parallel RLC Load, Series RLC Load
5-217
Series RLC Load
Purpose
5Series RLC Load
Library
Elements
Description
The Series RLC Load block implements a linear load as a series combination of
R L C elements. At the specified frequency, the load exhibits a constant
impedance. The active and reactive powers absorbed by the load are
proportional to the square of the applied voltage. Only elements associated
with nonzero powers are displayed in the block icon.
Implement a linear series RLC load
Dialog Box and
Parameters
Nominal voltage Vn
The nominal voltage of the load, in volts RMS.
Nominal frequency fn
The nominal frequency, in hertz.
Active power P
The active power of the load, in watts.
5-218
Series RLC Load
Inductive reactive power QL
The inductive reactive power QL, in vars. Specify a positive value, or 0.
Capacitive reactive power QC
The capacitive reactive power QC, in vars. Specify a positive value, or 0.
Measurements
Select Branch voltage to measure the voltage across the Series RLC Load
block terminals.
Select Branch current to measure the current flowing through the Series
RLC Load block.
Select Branch voltage and current to measure the voltage and the
current of the Series RLC Load block.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurement is identified by a label
followed by the block name:
Example
Measurement
Label
Branch voltage
Ub:
Branch current
Ib:
The power_seriesload demo uses a Series RLC Load block to implement a
simple load.
5-219
Series RLC Load
See Also
5-220
Multimeter, Parallel RLC Branch, Parallel RLC Load, Series RLC Branch
Simplified Synchronous Machine
Purpose
5Simplified Synchronous Machine
Library
Machines
Description
The Simplified Synchronous Machine block models both the electrical and
mechanical characteristics of a simple synchronous machine.
Model the dynamics of a simplified three-phase synchronous machine
The electrical system for each phase consists of a voltage source in series with
an RL impedance, which implements the internal impedance of the machine.
The value of R can be zero but the value of L must be positive.
The Simplified Synchronous Machine block implements the mechanical system
described by
t
1
∆ω ( t ) = -------- ( Tm – Te ) dt – K d∆ω ( t )
2H
∫
0
ω ( t ) = ∆ω ( t ) + ω 0
where
∆ω = Speed variation with respect to speed of operation
H = Constant of inertia
Tm = Mechanical torque
Te = Electromagnetic torque
Kd = Damping factor representing the effect of damper windings
ω ( t ) = Mechanical speed of the rotor
ω 0 = Speed of operation (1 p.u.)
Although the parameters can be entered in either SI units or per unit in the
dialog box, the internal calculations are done in per unit. The following block
diagram illustrates how the mechanical part of the model is implemented.
Notice that the model computes a deviation with respect to the speed of
operation, and not the absolute speed itself.
5-221
Simplified Synchronous Machine
Tm (p.u.)
+
Te (p.u.)
−
1
1/2H
1/s
+
∆ω
ω (p.u.)
+
−
Kd
The Kd damping coefficient simulates the effect of damper windings normally
used in synchronous machines. When the machine is connected to an infinite
network (zero impedance), the variation of machine power angle delta (δ)
resulting from a change of mechanical power (Pm) can be approximated by the
following second-order transfer function:
2
2
δ ⁄ P m = ( ω s ⁄ 2H ) ⁄ ( s + 2ζω n s + ω n )
where
δ
Power angle delta: angle of internal voltage E with respect to
terminal voltage, in radians
Pm
Mechanical power in p.u.
ωn
Frequency of electromechanical oscillations =
ω s ⋅ P max ⁄ ( 2H ) in rad/s
ζ
Damping ratio = ( K d ⁄ 4 ) 2 ⁄ ( ω s ⋅ H ⋅ P max )
Electrical frequency in rad/s
ωs
5-222
Pmax
Maximum power in p.u. transmitted through reactance X at
terminal voltage Vt and internal voltage E. Pmax = V t ⋅ E ⁄ X
(p.u.) where Vt, E, and X are in p.u.
H
Inertia constant(s)
Kd
Damping factor (p.u._of_torque / p.u._of_speed)
Simplified Synchronous Machine
This approximate transfer function, which has been derived by assuming sin(δ)
= δ, is valid for small power angles (δ < 30 degrees). It follows from the above ζ
expression that the Kd value required to obtain a given ζ damping ratio is
K d = 4ζ ω s ⋅ H ⋅ P max ⁄ 2
Dialog Box and
Parameters
In the powerlib library you can choose between the SI units or the p.u. units
Simplified Synchronous Machine blocks to specify the electrical and
mechanical parameters of the model.
:
Connection type
Specify the number of wires used in three-phase Y connection: either
three-wire (neutral not accessible) or four-wire (neutral is accessible).
5-223
Simplified Synchronous Machine
Nominal power, L-L voltage, and frequency
The nominal apparent power Pn (VA), frequency fn (Hz), and RMS
line-to-line voltage Vn (V). Used to compute nominal torque and convert SI
units to p.u.
Inertia, friction factor and pairs of poles
The inertia (J in kg.m2 or H in seconds) damping factor (Kd) and number
of pairs of poles (p). The damping factor should be specified in (p.u. of
torque)/(p.u. of speed) in both machine dialog boxes (in p.u. and in SI).
Internal impedance
The resistance R (Ω or p.u.) and reactance L (H or p.u.) for each phase.
Initial conditions
The initial speed deviation (% of nominal), rotor angle (degrees), line
current magnitudes (A or p.u.), and phase angles (degrees). These values
can be computed by the load flow utility of the Powergui block.
Note These two blocks simulate exactly the same simplified synchronous
machine model; the only difference is the way of entering the parameter units.
Inputs and
Outputs
5-224
The first input of the Simplified Synchronous Machine block is the mechanical
power supplied to the machine. This input can be a constant or the output of
the Hydraulic Turbine and Governor block. The frequency of the internal
voltage sources depends on the mechanical speed of the machine. The
amplitude of these voltages is given by the second input of the block, which can
be a constant or the output of a voltage regulator. If you use SI units these two
inputs should be in watts and volts phase-to-phase RMS. If you use p.u. both
inputs should be in p.u.
Simplified Synchronous Machine
The first three outputs are the electrical terminals of the stator. The last
output of the block is a vector containing the following 12 signals:
Signal
Definition
1 to 3
Line currents (flowing out of the machine) ia, ib, ic
4-6
Terminal voltages va, vb, vc
7-9
Internal voltages ea, eb, ec
10
Mechanical angle θ
11
Rotor speed ω
12
Electrical power Pe
You can demultiplex these signals by using the Machines Measurement
Demux block in the Machines library.
Assumptions
The electrical system of the Simplified Synchronous Machine block consists
solely of a voltage source behind a synchronous reactance and resistance. All
the other self- and magnetizing inductances of the armature, field, and
damping windings are neglected. The effect of damper windings is
approximated by the damping factor Kd. The three voltage sources and RL
impedance branches are Y-connected (three wires or four wires). The load
might or might not be balanced.
Example
The power_simplealt demo uses the Simplified Synchronous Machine block to
represent a 1000 MVA, 315 kV, 60 Hz equivalent source connected to an
infinite bus (Three-Phase Programmable Voltage Source block). The Simplified
Synchronous Machine (SI Units) block is used as a synchronous generator. The
internal resistance and reactance are set respectively to 0.02 p.u. (1.9845 Ω)
and 0.2 p.u. (X = 19.845 Ω; L = 0.0526 H). The inertia of the machine is J =
168,870 kg.m2, corresponding to an inertia constant H = 3 s. The electrical
frequency is ωs = 2*π*60/2 = 377 rad/s. The machine has two pairs of poles such
that its synchronous speed is 2*π*60/2 = 188.5 rad/s or 1800 rpm.
The Load Flow option of the Powergui has been used to initialize the machine
in order to start simulation in steady state with the machine generating 500
5-225
Simplified Synchronous Machine
MW. The required internal voltage computed by the load flow is 1.0149 p.u.
Therefore an internal voltage E = 315e3*1.0149 = 319,690 Vrms
phase-to-phase is specified in the Constant block connected to the E input. The
maximum power that can be delivered by the machine with a terminal voltage
Vt = 1.0 p.u. and an internal voltage E = 1.0149 p.u. is Pmax = Vt*E/X =
1.0149/0.2 = 5.0745 p.u.
The damping factor Kd is adjusted in order to obtain a damping ratio ζ = 0.3.
According to the formula given in the Description section, the required Kd
value is K d = 4ζ ( ω s ⋅ H ⋅ P max ) ⁄ 2 = 64.3 .
Two Fourier blocks are used to measure the power angle δ. This angle is
computed as the difference between the phase angle of phase A internal voltage
and the phase angle of phase A terminal voltage.
In this demo, a step is performed on the mechanical power applied to the shaft.
The machine is initially running in steady state with a mechanical power of
505 MW (mechanical power required for an output electrical power of 500 MW,
5-226
Simplified Synchronous Machine
considering the resistive losses). At t = 0.5 s the mechanical power is suddenly
increased to 1000 MW.
Run the demo and observe the electromechanical transient on the Scope block
displaying the power angle δ in degrees, the machine speed in rpm, and the
electrical power in MW. Simulation results are shown in the following figure.
For an initial electrical power Pe = 500 MW (0.5 p.u.), the load angle δ is 5.65
degrees, which corresponds to the expected value:
V t ⋅ E ⋅ sin δ 1.0 ⋅ 1.0149 ⋅ sin ( 5· .65° )
Pe = ------------------------------- = ----------------------------------------------------------------- = 0.5 p.u.
X
0.2
As the mechanical power is stepped from 0.5 p.u. to 1.0 p.u., the load angle
increases and goes through a series of underdamped oscillations (damping
5-227
Simplified Synchronous Machine
ratio ζ = 0.3) before stabilizing to its new value of 11.3 degrees. The frequency
of the oscillations is given by
f n = ( 1 ⁄2π ) ⋅ ω s ⋅ P max ⁄ ( 2H ) = 2.84 Hz
See Also
5-228
Excitation System, Hydraulic Turbine and Governor, Machine Measurement
Demux, Powergui, Steam Turbine and Governor, Synchronous Machine
Static Var Compensator
Purpose
5Static Var Compensator
Library
Phasor Elements
Description
The Static Var Compensator (SVC) is a device of the Flexible AC Transmission
Systems (FACTS) family using power electronics to control power flow on
power grids. The SVC regulates voltage at its terminal by controlling the
amount of reactive power injected into or absorbed from the power system.
When system voltage is low, the SVC generates reactive power (SVC
capacitive). When system voltage is high, it absorbs reactive power (SVC
inductive). The variation of reactive power is performed by switching
three-phase capacitor banks and inductor banks connected on the secondary
side of a coupling transformer. Each capacitor bank is switched on and off by
three thyristor switches (Thyristor Switched Capacitor or TSC). Reactors are
either switched on-off (Thyristor Switched Reactor or TSR) or phase-controlled
(Thyristor Controlled Reactor or TCR).
e
Implement a phasor model of a three-phase, three-wire static var compensator
The figure below shows a single-line diagram of a static var compensator and
a simplified block diagram of its control system.
Primary voltages
Vm
Voltage
Measurement
Voltage
Regulator
B
Secondary voltages
Vref
Pulses
TCR
Synchronizing Unit
Pulse Generator
n_TSC Distribution
Unit
α
TSC
Control System
Single-line Diagram of an SVC and Its Control System Block Diagram
The control system consists of
• A measurement system measuring the positive-sequence voltage to be
controlled
5-229
Static Var Compensator
• A voltage regulator that uses the voltage error (difference between the
measured voltage Vm and the reference voltage Vref) to determine the SVC
susceptance B needed to keep the system voltage constant
• A distribution unit that determines the TSCs (and eventually TSRs) that
must be switched in and out, and computes the firing angle α of TCRs
• A synchronizing system and a pulse generator that send appropriate pulses
to the thyristors
The Static Var Compensator block is a phasor model, and you must use it with
the phasor simulation method, activated with the Powergui block. It can be
used in three-phase power systems together with synchronous generators,
motors, and dynamic loads to perform transient stability studies and observe
impact of the SVC on electromechanical oscillations and transmission capacity.
This model does not include detailed representations of the power electronics,
the measurement system, or the synchronization system. These systems are
approximated rather by simple transfer functions and delays that yield a
correct representation at the system’s fundamental frequency.
SVC V-I Characteristic
The SVC can be operated in two different modes:
• In voltage regulation mode (the voltage is regulated within limits as
explained below)
• In var control mode (the SVC susceptance is kept constant)
When the SVC is operated in voltage regulation mode, it implements the
following V-I characteristic.
5-230
Static Var Compensator
Vref
Slope Xs
V
Blmax
Bcmax
Capacitive
Inductive
Reactive Current
I
SVC V-I characteristic
As long as the SVC susceptance B stays within the maximum and minimum
susceptance values imposed by the total reactive power of capacitor banks
(Bcmax) and reactor banks (Blmax), the voltage is regulated at the reference
voltage Vref. However, a voltage droop is normally used (usually between 1%
and 4% at maximum reactive power output), and the V-I characteristic has the
slope indicated in the figure. The V-I characteristic is described by the
following three equations:
V = Vref + Xs ⋅ I
SVC is in regulation range (−Bcmax < B < Blmax)
I
V = – ----------------Bc max
SVC is fully capacitive (B = Bcmax)
I V = ---------------Bl max
SVC is fully inductive (B = Blmax)
where
V
Positive sequence voltage (p.u.)
I
Reactive current (p.u./Pbase) (I > 0 indicates an inductive
current)
Xs
Slope or droop reactance (p.u./Pbase)
5-231
Static Var Compensator
Bcmax
Maximum capacitive susceptance (p.u./Pbase) with all TSCs in
service, no TSR or TCR
Blmax
Maximum inductive susceptance (p.u./Pbase) with all TSRs in
service or TCRs at full conduction, no TSC
Pbase
Three-phase base power specified in the block dialog box
SVC Dynamic Response
When the SVC is operating in voltage regulation mode, its response speed to a
change of system voltage depends on the voltage regulator gains (proportional
gain Kp and integral gain Ki), the droop reactance Xs, and the system strength
(short-circuit level).
For an integral-type voltage regulator (Kp = 0), if the voltage measurement
time constant Tm and the average time delay Td due to valve firing are
neglected, the closed-loop system consisting of the SVC and the power system
can be approximated by a first-order system having the following closed-loop
time constant:
1
T c = -------------------------------------Ki ⋅ ( Xs + Xn )
where
Tc
Closed loop time constant
Ki
Proportional gain of the voltage regulator (p.u._B/p.u._V/s)
Xs
Slope reactance p.u./Pbase
Xn
Equivalent power system reactance (p.u./Pbase)
This equation demonstrates that you obtain a faster response speed when the
regulator gain is increased or when the system short-circuit level decreases
(higher Xn values). If you take into account the time delays due to voltage
measurement system and valve firing, you obtain an oscillatory response and,
eventually, an instability with too weak a system or too large a regulator gain.
5-232
Static Var Compensator
Dialog Box and
Parameters
Mode of operation
Specifies the SVC mode of operation. Select either Voltage regulation or
Var control (fixed susceptance Bref).
Nominal voltage
The nominal phase-to-phase voltage in Vrms.
Reactive power limits [Qc Ql]
The maximum SVC reactive powers at 1 p.u. voltage, in vars. Enter a
positive value for the capacitive reactive power Qc (vars generated by the
SVC) and a negative value for the inductive reactive power Ql (vars
absorbed by the SVC).
5-233
Static Var Compensator
Three-phase base power Pbase
Three-phase base power, in VA, used to specify the following parameters in
p.u.: droop reactance Xs, gains Kp and Ki of the voltage PI regulator, and
reference susceptance Bref. This base power is also used to normalize the
output B susceptance signal.
Reference voltage Vref
This parameter is not visible when the Mode of operation parameter is set
to Var Control.
Reference voltage, in p.u., used by the voltage regulator.
Droop Xs
This parameter is not visible when the Mode of operation parameter is set
to Var Control.
Droop reactance, in p.u./Pbase, defining the slope of the V-I characteristic.
Voltage regulator [Kp Ki]
This parameter is not visible when the Mode of operation parameter is set
to Var Control.
Proportional gain, in (p.u. of B)/(p.u. of V), and integral gain, in
p.u._B/p.u._V/s, of the voltage regulator.
Bref for var control mode
This parameter is not visible when the Mode of operation parameter is set
to Voltage regulation.
Reference susceptance, in p.u./Pbase, when the SVC is operating in var
control mode.
Time constant of voltage measurement system Tm
This parameter is not visible when the Mode of operation parameter is set
to Var Control.
Time constant, in seconds, of the first-order low-pass filter simulating the
measurement system response time to a change of the fundamental
voltage. A 1/2-cycle time constant can be used to approximate the transfer
function of a Fourier-based measurement system using a one-cycle running
average.
5-234
Static Var Compensator
Average time delay due to thyristor valves firing Td
Average time delay simulating the noninstantaneous variation of thyristor
fundamental current when the distribution unit sends a switching order to
the pulse generator. Because pulses have to be synchronized with thyristor
commutation voltages, this delay normally varies between 0 and 1/2 cycle.
The suggested average value is 1/4 cycle.
Inputs and
Outputs
A B C
The three terminals of the static var compensator.
B (p.u.)
Simulink signal of the SVC susceptance, in p.u./Pbase. In voltage control
mode, this control signal is the output of the voltage regulator. In var
control mode, this value is the Bref value specified by the user. A positive
value indicates that the SVC is capacitive. A negative value indicates that
the SVC is inductive.
Vm (p.u.)
Simulink signal of the positive-sequence measured voltage, in p.u. This
control signal is the output of the voltage measurement system.
Example
The power_SVC demo illustrates the steady-state and dynamic performance of
an SVC regulating voltage on a 500 kV, 60 Hz, 3000 MVA system. The Static
Var Compensator block models a +200 Mvar/−100 Mvar SVC.
5-235
Static Var Compensator
Open the SVC block menu and look at its parameters. The SVC is set to
Voltage regulation mode with a reference voltage Vref = 1.0 pu. The voltage
droop reactance is 0.03 p.u./200 MVA, so that the voltage varies from 0.97 p.u.
to 1.015 p.u. when the SVC current goes from fully capacitive to fully inductive.
Double-click the blue block located below the Scope block to display the SVC
V-I characteristic.
The Three-Phase Programmable Voltage Source is used to vary the system
voltage and observe the SVC performance. Initially the source is generating its
nominal voltage (500 kV). Then, voltage is successively decreased (0.97 p.u. at
t = 0.1 s), increased (1.03 p.u. at t = 0.4 s) and finally returned to nominal
voltage (1 p.u. at t = 0.7 s).
Start the simulation and observe the SVC dynamic response to voltage steps
on the Scope. Waveforms are reproduced on the figure below. Trace 1 shows the
actual positive-sequence susceptance B1 and control signal output B of the
voltage regulator. Trace 2 shows the actual system positive-sequence voltage
V1 and output Vm of the SVC measurement system.
5-236
Static Var Compensator
The SVC response speed depends on the voltage regulator integral gain Ki
(proportional gain Kp is set to zero), system strength (reactance Xn), and droop
(reactance Xs).
As mentioned above, neglecting the voltage measurement time constant Tm
and the average time delay Td due to valve firing, the system can be
approximated by a first-order system having a closed-loop time constant:
1
T c = -------------------------------------Ki ⋅ ( Xs + Xn )
5-237
Static Var Compensator
With given system parameters (Ki = 300; Xn = 0.0667 p.u./200 MVA; Xs = 0.03
p.u./200 MVA), the closed-loop time constant is Tc = 0.0345 s.
If you increase the regulator gain or decrease the system strength, Tm and Td
are no longer negligible, and you instead observe an oscillatory response and
eventually instability. The figure below compares the SVC susceptance (B
output of the voltage regulator) for two different short-circuit levels: 3000 VA
and 600 MVA.
See Also
5-238
Powergui, Thyristor
Steam Turbine and Governor
Purpose
5Steam Turbine and Governor
Library
Machines
Description
The Steam Turbine and Governor block implements a complete
tandem-compound steam prime mover, including a speed governing system, a
four-stage steam turbine, and a shaft with up to four masses.
Model the dynamics of a speed governing system, steam turbine, and
multimass shaft
The speed governing system consists of a proportional regulator, a speed relay,
and a servomotor controlling the gate opening. It is similar to one of the models
proposed in [1].
The steam turbine has four stages, each modeled by a first-order transfer
function. The first stage represents the steam chest while the three other
stages represent either reheaters or crossover piping. The boiler is not modeled
5-239
Steam Turbine and Governor
and boiler pressure is constant at 1.0 p.u. Fractions F2 to F5 are used to
distribute the turbine power to the various shaft stages:
The shaft models a four-mass system, which is coupled to the mass in the
Synchronous Machine model for a total of five masses. The machine’s mass is
labeled mass #1. The mass in the Steam Turbine and Governor block, which is
closest to the machine’s mass, is mass #2, while the mass farthest from the
machine is mass #5. The shaft is characterized by mass inertias H, damping
factors D, and rigidity coefficients K. If you choose to simulate a single-mass
shaft, the entire four-mass shaft subsystem in the Steam Turbine and
Governor block is disabled and all the torque from the turbine is added together
and applied to the machine’s mass:
5-240
Steam Turbine and Governor
5-241
Steam Turbine and Governor
Dialog Box and
Parameters
Generator type
Specifies rotor type: single mass or multimass tandem-compound. If you
choose a single-mass system, the multimass shaft subsystem in the Steam
5-242
Steam Turbine and Governor
Turbine and Governor block is disabled and the turbine’s output torques
are summed together and applied to the single mass in the Synchronous
Machine block.
Regulator gain, permanent droop, dead zone
The gain Kp, permanent droop Rp (p.u.), and dead-zone width Dz (p.u.). Set
gain to 3 if you want to use the steam flow feedback loop. Otherwise, set
gain to 1.
Speed relay and servo-motor time constants
The speed relay and gate servomotor time constants Tsr (s) and Tsm (s).
Gate opening limits
The minimum and maximum gate opening speed vgmin and vgmax (both
in p.u./s), and minimum and maximum gate opening gmin and gmax (both
in p.u.).
Steam turbine time constants
The turbine time constants T2 to T5 (s). Numbered consistently with
turbine torque fractions and mass numbers; i.e., T5 is the time constant of
the first turbine stage, which models the steam chest.
Turbine torque fractions
The turbine torque fractions F2 to F5. Must total 1, otherwise an error
message appears. Fraction numbers correspond to mass numbers; i.e., F2
is the fraction of torque to be applied to mass #2 of the multimass shaft.
Coefficient of inertia; Stiffness coefficient; Damping factors
Only visible if generator type is multimass. Coefficients of inertia H2 to H5
(s), stiffness coefficients K12 to K45 (p.u./rad), and damping factors D2 to
D5 (p.u. torque / p.u. speed deviation) are associated with the masses of
the multimass shaft. K12 corresponds to the rigidity coefficient between
masses #1 and #2, and so on.
Note If you do not want to simulate all four masses in the multimass shaft,
simply set the inertia of unwanted masses to 0. The rigidity coefficient and
damping factor corresponding to omitted masses are not considered. When
masses are not simulated, the remaining system is “compressed” toward the
generator; i.e., if only two masses are used (excluding the generator), they are
5-243
Steam Turbine and Governor
masses #2 and #3. The input data for the masses considered are shifted
accordingly. In any case, inertias must be consistent with torque fractions.
You cannot set an inertia to 0 and set the corresponding torque fraction to a
nonzero value. However, you can set a torque fraction to 0 and set the
corresponding mass inertia to a nonzero value.
Initial power and generator rotor angle
If the shaft is multimass, enter the initial mechanical power Pm0 (p.u.) and
initial generator angle θe0 (degrees). If the shaft is single mass, enter only
initial mechanical power.
Initial mechanical power is automatically updated by the load flow utility
of the Powergui block. Initial angle is also computed by the load flow utility
and is written in the associated Synchronous Machine block dialog box.
Inputs and
Outputs
The first input is the speed reference, in p.u. It is normally connected to a
Constant block with the value set to 1.0 p.u.
The second input is the electrical power reference, in p.u. It is set to a constant
value corresponding to the initial active power drawn from the Synchronous
Machine block connected to the Steam Turbine and Governor block.
The third input is the generator’s speed, in p.u. This is one of the signals in the
last output of the Synchronous Machine model (internal variables).
The fourth input is the generator’s power angle deviation. It is also one of the
signals in the last output of the Synchronous Machine model (internal
variables).
The first output is a vector containing the speed deviations, in p.u., of masses
#5 to #2, in that order.
The second output is also a vector containing the torques, in p.u., transmitted
by masses #5 to #2.
The third output is the gate opening in p.u.
The fourth output is the mechanical power, in p.u., that you must connect to
the first input of a Synchronous Machine block.
5-244
Steam Turbine and Governor
Example
The power_thermal demo illustrates the use of the Steam Turbine and
Governor block. This system is an IEEE benchmark used to study
subsynchronous resonance and particularly torque amplification after a fault
on a series-compensated power system [2]. It consists in a single generator
connected to an infinite bus via two transmission lines, one of which is series
compensated. The subsynchronous mode introduced by the compensation
capacitor after a fault has been applied and cleared excites the oscillatory
torsional modes of the multimass shaft and the torque amplification
phenomenon can be observed. Open the Simulink diagram by typing
power_thermal.
This system is slightly different from the one presented in [2]. Since we are
using the Synchronous Machine mass as the first mass, we cannot model the
exciter’s mass as is done in [2]. Therefore, our system has only three masses,
representing the generator’s rotor (mass #1) and the turbine’s low and high
pressure stages (masses #2 and #3, respectively).
In order to start the simulation in steady state, you must first initialize the
synchronous machine and steam turbine by using the Load Flow and
Machine Initialization utility of the Powergui. Set the generator as a PV
generator with initial power of 100 kW (1e5 W) or 0.0167% of nominal power.
5-245
Steam Turbine and Governor
This is done to simulate an initially unloaded generator. The load flow returns
initial mechanical power of 100,020 W. This value was converted into p.u. by
dividing it by the generator’s nominal VA rating (600e6 VA) and the result was
entered as the first initial condition in the Steam Turbine and Governor block.
The second initial condition is the generator’s initial angle. This value is
computed by the load flow and is written in the initial conditions vector of the
generator. The Steam Turbine and Governor block is now correctly initialized.
The electrical power (load) reference, the second input of the Steam Turbine
and Governor block, is set to the desired electrical power supplied by the
generator, in p.u. (1e5/600e6, or 0.1/600).
This test is performed without regulators. The speed governing system is
forced to output a constant value by setting the gate opening limits very close
to each other, around the initial gate opening, which is also the initial
mechanical power in p.u. (100 010/600e6, or 0.00016668 p.u.). The machine’s
excitation voltage is also set to a constant value (1.00358 p.u.), which is
computed by the load flow.
Run the simulation. Once the simulation is completed, observe the mass speed
deviations and torques and the fault current.
5-246
Steam Turbine and Governor
.
The peak values of all these signals correspond within 3% to those given in
Table 5, case 1A, of [2]. The torque amplification is clearly observed on all
masses of the shaft system. The high-pressure mass (#3) transmits a peak
torque of 1.91 p.u. to the low-pressure mass (#2), while the low-pressure mass
transmits a peak torque of 4.05 p.u. to the generator’s rotor (mass #1).
References
[1] IEEE committee report, “Dynamic models for steam and hydro turbines in
power system studies,” IEEE Transactions on Power Apparatus and Systems,
Vol. PAS-92, No. 6, 1973, pp. 1904-1915.
[2] IEEE Subsynchronous resonance working group, “Second benchmark
model for computer simulation of subsynchronous resonance,” IEEE
Transactions on Power Apparatus and Systems, Vol. PAS-104, No. 5, 1985,
pp. 1057-1066.
5-247
Steam Turbine and Governor
See Also
5-248
Excitation System, Hydraulic Turbine and Governor, Powergui, Synchronous
Machine
Surge Arrester
Purpose
5Surge Arrester
Library
Elements
Description
The Surge Arrester block implements a highly nonlinear resistor used to
protect power equipment against overvoltages. For applications requiring high
power dissipation, several columns of metal-oxide discs are connected in
parallel inside the same porcelain housing. The nonlinear V-I characteristic of
each column of the surge arrester is modeled by a combination of three
exponential functions of the form
Implement a metal-oxide surge arrester
I 1 ⁄ αi
V
----------- = k i  ---------
 I ref
V ref
The protection voltage obtained with a single column is specified at a reference
current (usually 500 A or 1 kA). Default parameters k and α given in the dialog
box fit the average V-I characteristic provided by the main metal-oxide arrester
manufacturers and they do not change with the protection voltage. The
required protection voltage is obtained by adding discs of zinc oxide in series in
each column.
This V-I characteristic is graphically represented as follows (on a linear scale
and on a logarithmic scale).
V
log(V/Vref)
α1
α2
α3
α3
Vref
nIref
α2
α1
log(I/Iref)
α1
nIref
I
n = Number of columns in parallel
5-249
Surge Arrester
Dialog Box and
Parameters
Protection voltage Vref
The protection voltage of the Surge Arrester block, in volts (V).
Number of columns
The number of metal-oxide disc columns. The minimum is one.
Reference current per column Iref
The reference current of one column used to specify the protection voltage,
in amperes (A).
Segment 1 characteristics
The k and α parameters of segment 1.
Segment 2 characteristics
The k and α parameters of segment 2.
5-250
Surge Arrester
Segment 3 characteristics
The k and α characteristics of segment 3.
Measurements
Select Branch voltage to measure the voltage across the Surge Arrester
block terminals.
Select Branch current to measure the current flowing through the Surge
Arrester block.
Select Branch voltage and current to measure the surge arrester voltage
and current.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurement is identified by a label
followed by the block name.
Measurement
Label
Branch voltage
Ub:
Branch current
Ib:
Limitations
The Surge Arrester block is modeled as a current source driven by the voltage
appearing across its terminals. Therefore, it cannot be connected in series with
an inductor or another current source. As the Surge Arrester block is highly
nonlinear, a stiff integrator algorithm must be used to simulate the circuit.
ode15s or ode23tb with default parameters usually gives the best simulation
speed. For continuous simulation, in order to avoid an algebraic loop, the
voltage applied to the nonlinear resistance is filtered by a first-order filter with
a time constant of 0.01 microseconds. This very fast time constant does not
significantly affect the result accuracy. When the Surge Arrester block is used
in a discrete system, a time delay of one simulation step is used. This delay can
cause numerical oscillations if the sample time is too large.
Example
The power_arrester demo illustrates the use of metal-oxide varistors (MOV)
on a 735 kV series-compensated network. Only one phase of the network is
represented. The capacitor connected in series with the line is protected by a
30 column arrester. At t = 0.03 seconds, a fault is applied at the load terminals.
5-251
Surge Arrester
The current increases in the series capacitor and produces an overvoltage that
is limited by the Surge Arrester block. Then the fault is cleared at t = 0.1
seconds.
At fault application, the resulting overvoltage makes the MOV conduct. The
waveforms displayed by Umov and Imov measurements as well as the V-I
characteristic plotted by the X-Y scope are shown below:
5-252
Surge Arrester
5-253
Surge Arrester
See Also
5-254
Multimeter
Synchronized 6-Pulse Generator
Purpose
5Synchronized 6-Pulse Generator
Library
Extras/Control Block
Implement a synchronized pulse generator to fire the thyristors of a six-pulse
converter
A discrete version of this block is available in the Extras/Discrete Control
Blocks library.
Description
The Synchronized 6-Pulse Generator block can be used to fire the six thyristors
of a six-pulse converter. The output of the block is a vector of six pulses
individually synchronized on the six thyristor voltages. The pulses are
generated alpha degrees after the increasing zero crossings of the thyristor
commutation voltages.
The figures below display the synchronization of the six pulses for an alpha
angle of 0 degrees. The pulses are generated exactly at the zero crossings of the
three line-to-line synchronization voltages.
5-255
Synchronized 6-Pulse Generator
Vbc
Vca
Vab
synchronization
voltages
pulse 1
pulse 2
pulse 3
pulse 4
pulse 5
pulse 6
The Synchronized 6-Pulse Generator block can be configured to work in
double-pulsing mode. In this mode two pulses are sent to each thyristor: a first
pulse when the alpha angle is reached, then a second pulse 60 degrees later,
when the next thyristor is fired.
5-256
Synchronized 6-Pulse Generator
The figures below display the synchronization of the six pulses for an alpha
angle of 30 degrees and with double-pulsing mode. Notice that the pulses are
generated 30 degrees after the zero crossings of the line-to-line.
Vbc
Vca
Vab
synchronization
voltages
pulse 1
pulse 2
pulse 3
pulse 4
pulse 5
pulse 6
The pulse ordering at the output of the block corresponds to the natural order
of commutation of a three-phase thyristor bridge. When you connect the
Synchronized 6-Pulse Generator block to the pulses input of the Universal
Bridge block (with the thyristors as the power electronic device), the pulses are
sent to the thyristors in the following order:
5-257
Synchronized 6-Pulse Generator
{
1
Pulse 1
Pulse 2
Pulse 3
Pulse 4
Pulse 5
Pulse 6
A
B
C
Converter
AC terminals
3
+
5
Converter
DC terminals
4
6
2
−
When you build your own three-phase thyristor bridge with single thyristor
blocks, you need to connect the pulse signals of the Synchronized 6-Pulse
Generator block to the gate inputs of the corresponding thyristors.
Dialog Box and
Parameters
Frequency of synchronization voltages
The frequency, in hertz, of the synchronization voltages. It usually
corresponds to the frequency of the network.
Pulse width
The width of the pulses, in degrees.
5-258
Synchronized 6-Pulse Generator
Double pulsing
If selected, the generator sends to each thyristor a first pulse when the
alpha angle is reached, and then a second pulse 60 degrees later when the
next thyristor in the sequence is fired.
Inputs and
Outputs
alpha_deg
Input 1 is the alpha firing signal, in degrees. This input can be connected
to a Constant block, or it can be connected to a controller system to control
the pulses of the generator.
AB, BC, CA
Inputs 2, 3, and 4 are the phase-to-phase synchronization voltages Vab,
Vbc, and Vca. The synchronization voltages should be in phase with the
three phase-phase voltages at the converter AC terminals.
Synchronization voltages are normally derived at the primary windings of
the converter transformer. If the converter is connected to the delta
winding of a Wye/Delta transformer, the synchronization voltages should
be the phase-to-ground voltages of the primary windings.
Freq
Available only with the discrete version of the Synchronized 6-Pulse
Generator. This input should be connected to a constant block containing
the fundamental frequency, in hertz, or to a PLL tracking the frequency of
the system.
block
Input 5 allows you to block the operation of the generator. The pulses are
disabled when the applied signal is greater than zero.
pulses
The output contains the six pulse signals.
Example
The power_sixpulses demo uses a Synchronized 6-Pulse Generator block to
fire the thyristors of a six-pulse thyristor bridge. The bridge is fed by a
5-259
Synchronized 6-Pulse Generator
three-phase voltage source (200 V peak line-to-ground or 245 V RMS
line-to-line) and it is connected to a resistive load.
A first simulation is performed with an alpha angle of 0 degrees. Open the
Constant block connected at input 1 of the Synchronized 6-Pulse Generator
block and set its value to 0. Start the simulation. The average voltage is
3 2
3 2
V dc = ----------- E = ----------- 245 = 331 volts
π
π
The six thyristor voltages are displayed in the next figure. The resulting DC
voltage at the output of the rectifier is also displayed (average value of 331 V).
5-260
Synchronized 6-Pulse Generator
Now change the value of the alpha angle to 30 degrees and start the simulation.
Notice that the waveforms of the thyristor voltages look different from the
previous case. The thyristors start conducting 30 degrees after their
commutation voltage becomes positive and the resulting DC voltage at the
output of the rectifier is lower. Its average value is now
3 2
3 2
V dc = ----------- E cos ( α ) = ----------- 245 cos ( 30° ) = 286 volts
π
π
5-261
Synchronized 6-Pulse Generator
The thyristor voltages and DC voltage for alpha = 30 degrees are
The figures show that the mean value of the DC voltage can be controlled by
the alpha angle applied to the Synchronized 6-Pulse Generator block.
See Also
The power_hvdc demo illustrates the use of the Discrete Synchronized 6-Pulse
Generator block.
Synchronized 12-Pulse Generator
5-262
Synchronized 12-Pulse Generator
Purpose
5Synchronized 12-Pulse Generator
Library
Extras/Control Blocks
Implement a synchronized pulse generator to fire the thyristors of a
twelve-pulse converter
A discrete version of this block is available in the Extras/Discrete Control
Blocks library.
Description
The Synchronized 12-Pulse Generator block generates two vectors of six pulses
synchronized on the twelve thyristor commutation voltages. The first set of
pulses, denoted PY, is sent to the six-pulse bridge connected to the wye
secondary winding of the Y/Y/Delta converter transformer. It is generated
alpha degrees after the zero crossing of the phase-to-phase synchronization
voltages. The second set of pulses, denoted PD, is sent to the six-pulse bridge
connected to the delta secondary winding of the converter transformer. It lags
the PY pulses by 30 degrees.
The figure below shows the three synchronization voltages and the first three
pulses of the two output vectors.The synchronization voltages are the three
phase-to-ground voltages Va, Vb, Vc measured on the primary side (Y) of the
Y/Y/Delta converter transformer.
5-263
Synchronized 12-Pulse Generator
Vb
Vc
Va
Phase-to-ground
Synchronization
voltages
pulse PD 1
pulse PD 2
pulse PD 3
.
.
.
pulse PY 1
pulse PY 2
pulse PY 3
.
The phase-to-ground A,B, and C voltages are provided to the generator, and the
two sets of phase-to-phase synchronization voltages required by the two
six-pulse bridges are generated internally.
The ordering of the pulses in the two outputs of the block corresponds to the
natural order of commutation of a three-phase thyristor bridge. When you
connect the Synchronized 12-Pulse Generator block outputs to the pulse inputs
5-264
Synchronized 12-Pulse Generator
of the Universal Bridge blocks (with the thyristor device), the pulses are sent
to the thyristors in the following way:
{
{
1
Pulse PY 1
3
5
+
Pulse PY 2
Pulse PY 3
Pulse PY 4
Pulse PY 5
A
B
C
Y converter
4
6
2
1
3
5
Pulse PY 6
−
Pulse PD 1
Pulse PD 2
Pulse PD 3
Pulse PD 4
Pulse PD 5
Pulse PD 6
A
B
C
+
D converter
4
6
2
−
5-265
Synchronized 12-Pulse Generator
Dialog Box and
Parameters
Frequency of synchronization voltages
The frequency, in hertz, of the synchronization voltages. It usually
corresponds to the frequency of the network.
Pulse width
The width of the pulses, in degrees.
Double pulsing
If selected, the generator sends to each thyristor a first pulse when the
alpha angle is reached, and then a second pulse 60 degrees later when the
next thyristor in the sequence is fired. The double pulsing is applied
separately on the two vectors of pulses.
5-266
Synchronized 12-Pulse Generator
Inputs and
Outputs
alpha_deg
Input 1 is the alpha firing signal, in degrees. This input can be connected
to a Constant block, or it can be connected to a controller system to control
the pulses of the generator.
A, B, C
Inputs 2, 3, and 4 are the phase-to-ground synchronization voltages Va, Vb,
and Vc. The synchronization voltages should be measured at the primary
side of the converter transformer.
Freq
Available only with the discrete version of the Synchronized 6-Pulse
Generator. This input should be connected to a constant block containing
the fundamental frequency, in hertz, or to a PLL tracking the frequency of
the system.
block
Input 5 allows you to block the operation of the generator. The pulses are
disabled when the applied signal is greater than zero.
PY
Output 1 contains the six-pulse signals to be sent to the six-pulse thyristor
converter connected to the Y secondary winding of the converter
transformer.
PD
Output 2 contains the six-pulse signals to be sent to the six-pulse thyristor
converter connected to the Delta (D) secondary winding of the converter
transformer.
Example
In the power_twelvepulses demo a Synchronized 12-Pulse Generator block is
used to fire the thyristors of a twelve-pulse thyristor bridge built with two
six-pulse bridges. The bridge is fed by a three-winding three-phase transformer
(500 kV / 200 kV / 200 kV). The Y-connected secondary feeds the first six-pulse
bridge. The Delta secondary feeds the second bridge. The transformer is
assumed to be ideal (no leakage reactances, no resistance). The expected DC
voltage obtained for alpha = 0 is
5-267
Synchronized 12-Pulse Generator
3 2
V dc = 2 ----------- 200 kV = 540 kV
π
The two bridge rectifiers are connected in series and a 300 km DC line is
connected to the rectifier.
A first simulation is performed with an alpha angle of 0 degrees. Open the
Constant block connected at input 1 of the Synchronized 12-Pulse Generator
block and set its value to 0. Start the simulation. The voltages of the thyristors
of the D thyristor Converter block are displayed in the next figure. The
5-268
Synchronized 12-Pulse Generator
resulting DC voltage at the input terminal of the transmission line is also
displayed (average value = 540 kV).
Compare the DC voltage generated by the Synchronized 12-Pulse Generator
with the DC voltage you obtained with the Synchronized 6-Pulse Generator.
Notice that the ripple in the DC voltage waveform is lower. The rectifier
voltage contains the harmonics 12*k (k = 1,2,...).
See Also
The power_hvdc12pulse demo illustrates the use of the Discrete Synchronized
12-Pulse Generator block.
Synchronized 6-Pulse Generator
5-269
Synchronous Machine
Purpose
5Synchronous Machine
Library
Machines
Description
The Synchronous Machine block operates in generator or motor modes. The
operating mode is dictated by the sign of the mechanical power (positive for
generator mode, negative for motor mode). The electrical part of the machine
is represented by a sixth-order state-space model and the mechanical part is
the same as in the Simplified Synchronous Machine block.
Model the dynamics of a three-phase round-rotor or salient-pole synchronous
machine
The model takes into account the dynamics of the stator, field, and damper
windings. The equivalent circuit of the model is represented in the rotor
reference frame (qd frame). All rotor parameters and electrical quantities are
viewed from the stator. They are identified by primed variables. The subscripts
used are defined as follows:
• d,q: d and q axis quantity
• R,s: Rotor and stator quantity
• l,m: Leakage and magnetizing inductance
• f,k: Field and damper winding quantity
The electrical model of the machine is
ω φ
Rs + R −d Ll
+
Vq
−
iq
q1
L’ lk
L’
1
R’ kq
l kq
Lmq
i ’ kq1
2
R’
k
i’
k
q axis
+
−
q2
q2
5-270
+
Vd
+
V’kq2
−
with the following equations.
ω φ
Rs − R +q Ll
V’kq1
−
id
Lmd
d
L’ lk
L’
i’ kd
lfd
R’
f
i’
f
d
d axis
+
R’ kd
V’kd
−
d
+
V’fd
−
Synchronous Machine
d
V d = R s i d + ------ ϕ d – ω R ϕ q
dt
d
V q = R s i q + ------ ϕ q + ω R ϕ d
dt
d
V′ fd = R′ fd i′ fd + ------ ϕ′ fd
dt
d
V′ kd = R′ kd i′ kd + ------ ϕ′ kd
dt
d
V′ kq1 = R′ kq1 i′ kq1 + ------ ϕ′ kq1
dt
ϕ d = L d i d + L md ( i′ fd + i′ kd )
ϕ q = L q i q + L mq i′ kq
ϕ′ fd = L′ fd i′ fd + L md ( i d + i′ kd )
ϕ′ kd = L′ kd i′ kd + L md ( i d + i′ fd )
ϕ′ kq1 = L′ kq1 i′ kq1 + L mq i q
ϕ′ kq2 = L′ kq2 i′ kq2 + L mq i q
d
V′ kq2 = R′ kq2 i′ kq2 + ------ ϕ′ kq2
dt
Note that this model assumes currents flowing into the stator windings. The
measured stator currents returned by the Synchronous Machine block (Ia, Ib,
Ic, Id, Iq) are the currents flowing out of the machine.
Dialog Box and
Parameters
In the powerlib library you can choose between three Synchronous Machine
blocks to specify the parameters of the model.
5-271
Synchronous Machine
Fundamental Parameters in SI Units
Rotor type
Specify rotor type: Salient-pole or Round (cylindrical). This choice affects
the number of rotor circuits in the q-axis (damper windings).
Nominal power, voltage, frequency, and field current
The total three-phase apparent power Pn (VA), RMS line-to-line voltage
Vn (V), frequency fn (Hz), and field current ifn (A).
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Synchronous Machine
The nominal field current is the current that produces nominal terminal
voltage under no-load conditions. This model was developed with all
quantities viewed from the stator. The nominal field current makes it
possible to compute the transformation ratio of the machine, which allows
you to apply the field voltage viewed from the rotor, as in real life. This also
allows the field current, which is a variable in the output vector of the
model, to be viewed from the rotor. If the value of the nominal field current
is not known, you must enter 0 or leave it blank. Since the transformation
ratio cannot be determined in this case, you have to apply the field voltage
as viewed from the stator and the field current in the output vector is also
viewed from the stator.
Stator
The resistance Rs (Ω), leakage inductance Lls (H), and d-axis and q-axis
magnetizing inductances Lmd (H) and Lmq (H).
Field
The field resistance Rf' (Ω) and leakage inductance Llfd' (H), both referred
to the stator.
Dampers
The d-axis resistance Rkd' (Ω) and leakage inductance Llkd' (H), the q-axis
resistance Rkq1' (Ω) and leakage inductance Llkq1' (H), and (only if round
rotor) the q-axis resistance Rkq2' (Ω) and leakage inductance Llkq2' (H).
All these values are referred to the stator.
Inertia, friction factor, and pole pairs
The inertia coefficient J (kg.m2), damping coefficient D (N.m.s./rad), and
number of pole pairs p.
Initial conditions
The initial speed deviation ∆ω (% of nominal speed), electrical angle of the
rotor θe (degrees), line current magnitudes ia, ib, ic (A) and phase angles
pha, phb, phc (degrees), and the initial field voltage Vf (V).
You can specify the initial field voltage in one of two ways. If you know the
nominal field current (first line, last parameter), enter in the dialog box the
initial field voltage in volts DC referred to the rotor. Otherwise, enter a zero
as nominal field current, as explained earlier, and specify the initial field
voltage in volts DC referred to the stator. You can determine the nominal
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Synchronous Machine
field voltage viewed from the stator by selecting the Display Vfd which
produces a nominal Vt check box at the bottom of the dialog box.
Simulate saturation
Specifies whether magnetic saturation of rotor and stator iron is to be
simulated or not.
Saturation parameters
The no-load saturation curve parameters. Magnetic saturation of stator
and rotor iron is modeled by a nonlinear function (in this case a polynomial)
using points on the no-load saturation curve. You must enter a 2-by-n
matrix, where n is the number of points taken from the saturation curve.
The first row of this matrix contains the values of field currents, while the
second row contains values of corresponding terminal voltages. The first
point (first column of the matrix) must correspond to the point where the
effect of saturation begins.
You must select the Simulate saturation check box to simulate saturation.
This check box allows you to enter the matrix of parameters for simulating
the saturation. If you do not want to model saturation in your simulation,
do not select the Simulate saturation check box. In this case the
relationship between ifd and Vt obtained is linear (no saturation).
Display Vfd which produces a nominal Vt
Select to determine the nominal field voltage viewed from the stator.
As an example, without saturation, a typical curve might be as shown below.
Here ifn is 1087 A and Vn is 13800 V RMS line-to-line, which is also 11268 V
peak line-to-neutral.
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Synchronous Machine
Saturation is modeled by fitting a polynomial to the curve corresponding to the
matrix of points you enter. The more points you enter, the better the fit to the
original curve.
The next figure illustrates goodness of fit graphically (the diamonds are the
actual points entered in the dialog box).
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Synchronous Machine
In this particular case, the following values were used:
5-276
ifn
1087 A
ifd
[695.64, 774.7, 917.5, 1001.6, 1082.2, 1175.9, 1293.6, 1430.2,
1583.7] A
Vt
[9660, 10623, 12243, 13063, 13757, 14437, 15180, 15890, 16567] V
Synchronous Machine
Fundamental Parameters in p.u.
Rotor type
Specifies rotor type: Salient-pole or Round (cylindrical).
Nominal power, L-L voltage, and frequency
Total three-phase apparent power (VA), RMS line-to-line voltage (V),
frequency (Hz), and field current (A).
This line is identical to the first line of the fundamental parameters in SI
dialog box, except that you do not specify a nominal field current. This
value is not required here because we do not need the transformation ratio.
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Synchronous Machine
Since rotor quantities are viewed from the stator, they are converted to p.u.
using the stator base quantities derived from the preceding three nominal
parameters.
Stator; Field; Dampers
Contain exactly the same parameters as in the previous dialog box, but
they are expressed here in p.u. instead of SI units.
Coefficient of inertia, friction factor, and pole pairs
The inertia constant H (s), where H is the ratio of energy stored in the rotor
at nominal speed over the nominal power of the machine, the damping
coefficient D (p.u. torque/p.u. speed deviation), and the number of pole
pairs p.
Initial conditions; Simulate saturation; Saturation parameters
The same initial conditions and saturation parameters as in the S.I. units
dialog box, but all values are expressed in p.u. instead of SI units. For
saturation, the nominal field current multiplied by the d-axis magnetizing
inductance and nominal RMS line-to-line voltage are the base values for
the field current and terminal voltage, respectively.
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Synchronous Machine
Standard Parameters in p.u.
Rotor type; Nominal power, L-L voltage, and frequency
The same parameters as the fundamental p.u. dialog box.
Reactances
The d-axis synchronous reactance Xd, transient reactance Xd', and
subtransient reactance Xd'', the q-axis synchronous reactance Xq,
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Synchronous Machine
transient reactance Xq' (only if round rotor), and subtransient reactance
Xq'', and finally the leakage reactance Xl (all in p.u.).
d-axis time constants; q-axis time constant(s)
Specify the time constants you supply for each axis: either open-circuit or
short-circuit.
Time constants
The d-axis and q-axis time constants (all in s). These values must be
consistent with choices made on the two previous lines: d-axis transient
open-circuit (Tdo') or short-circuit (Td') time constant, d-axis subtransient
open-circuit (Tdo'') or short-circuit (Td'') time constant, q-axis transient
open-circuit (Tqo') or short-circuit (Tq') time constant (only if round rotor),
q-axis subtransient open-circuit (Tqo'') or short-circuit (Tq'') time constant.
Stator resistance
The stator resistance Rs (p.u.).
Coefficient of inertia, friction factor, and pole pairs; Initial conditions;
Simulate saturation; Saturation parameters
The same parameters as the fundamental parameters in p.u. dialog box.
Note These three blocks simulate exactly the same synchronous machine
model; the only difference is the way of entering the parameter units.
Inputs and
Outputs
The units of inputs and outputs vary according to which dialog box was used to
enter the block parameters. For the nonelectrical connections, there are two
possibilities. If the first dialog box (fundamental parameters in SI units) is
used, the inputs and outputs are in SI units (except for dw in the vector of
internal variables, which is always in p.u., and angle θ, which is always in rad).
If the second or third dialog boxes is used, the inputs and outputs are in p.u.
The first input is the mechanical power at the machine’s shaft. In generating
mode, this input can be a positive constant or function or the output of a prime
mover block (see the Hydraulic Turbine and Governor or Steam Turbine and
Governor blocks). In motoring mode, this input is usually a negative constant
or function.
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Synchronous Machine
The second input of the block is the field voltage. This voltage can be supplied
by a voltage regulator in generator mode (see the Excitation System block). It
is usually a constant in motor mode.
If you use the model in SI fundamental units, the field voltage Vf should be
entered in volts DC if nominal field current Ifn is specified or in volts referred
to stator if Ifn is not specified. To obtain the Vfd producing nominal voltage,
select the last check box of the dialog box. If you use the model in p.u. Standard
or in p.u. Fundamental units, Vf should be entered in p.u. (1 p.u. of field voltage
producing 1 p.u. of terminal voltage at no load).
The first three outputs are the electrical terminals of the stator. The last
output of the block is a vector containing 21 signals. They are, in order:
Signal
Definition
1-3
Stator currents (flowing out of machine) isa, isb, and isc
4-5
q- and d-axis stator currents (flowing out of machine) iq,
id
6-8
Field and damper winding currents (flowing into
machine) ifd, ikq, and ikd
9 - 10
q- and d-axis magnetizing fluxes ϕmq, ϕmd
11 - 12
q- and d-axis stator voltages vq, vd
13
Rotor angle deviation ∆θ with respect to a synchronous
rotating frame
14
Rotor speed ωr
15
Total electrical power Pe, including losses in stator,
field, and damper windings
16
Rotor speed deviation dω
17
Rotor mechanical angle θ (degrees)
18
Electromagnetic torque Te
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Synchronous Machine
Signal
Definition (Continued)
19
Load angle δ (electrical degrees)
20
Output active power Peo
21
Output reactive power Qeo
You can demultiplex these signals by using the Machine Measurement Demux
block provided in the Machines library.
Example
5-282
The power_syncmachine demo illustrates the use of the Synchronous Machine
block in motor mode. The simulated system consists of an industrial grade
synchronous motor (150 HP (112 kVA), 762 V) connected to a network with a
10 MVA short-circuit level. In order to start simulation in steady state, the
machine is initialized using the Load Flow and Machine Initialization option
of the Powergui. The machine is initialized for an output electrical power of −50
kW (negative value for motor mode), corresponding to a mechanical power of
−48.9 kW. The corresponding values of mechanical power and field voltage
have been automatically entered by the Load Flow analysis into the Pm Step
block and in the Vf Constant block. The Pm Step block has been programmed
in order to apply a sudden increase of mechanical power from −48.9 kW to −60
kW at time t = 0.1 s.
Synchronous Machine
Run the simulation and observe the RMS current, RMS voltage, speed, load
angle δ and output electrical power of the motor.
5-283
Synchronous Machine
Since this is a four-pole machine, the nominal speed is 1800 rpm. The initial
speed is 1800 rpm as prescribed. After the load has increased from 48.9 kW to
100 kW at t = 0.1 s, the machine speed oscillates before stabilizing to 1800 rpm.
The load angle (angle between terminal voltage and internal voltage) increases
from −21 degrees to −53 degrees.
References
[1] Krause, P.C., Analysis of Electric Machinery, McGraw-Hill, 1986, Section
12.5.
[2] Kamwa, I., et al., “Experience with Computer-Aided Graphical Analysis of
Sudden-Short-Circuit Oscillograms of Large Synchronous Machines,” IEEE
Transactions on Energy Conversion, Vol. 10, No. 3, September 1995.
See Also
5-284
Excitation System, Hydraulic Turbine and Governor, Machine Measurement
Demux, Powergui, Simplified Synchronous Machine, Steam Turbine and
Governor
Three-Phase Breaker
Purpose
5Three-Phase Breaker
Library
Elements
Description
The Three-Phase Breaker block implements a three-phase circuit breaker
where the opening and closing times can be controlled either from an external
Simulink signal (external control mode), or from an internal control timer
(internal control mode).
Implement a three-phase circuit breaker opening at the current zero crossing
The Three-Phase Breaker block uses three Breaker blocks connected between
the inputs and the outputs of the block. You can use this block in series with
the three-phase element you want to switch. See the Breaker block reference
pages for details on the modeling of the single-phase breakers.
If the Three-Phase Breaker block is set in external control mode, a control
input appears in the block icon. The control signal connected to this input must
be either 0 or 1, 0 to open the breakers, 1 to close them. If the Three-Phase
Breaker block is set in internal control mode, the switching times are specified
in the dialog box of the block. The three individual breakers are controlled with
the same signal.
Series Rs-Cs snubber circuit are included in the model. They can be optionally
connected to the three individual breakers. If the Three-Phase Breaker block
happens to be in series with an inductive circuit, an open circuit or a current
source, you must use the snubbers.
5-285
Three-Phase Breaker
Dialog Box and
Parameters
Initial status of breakers
The initial status of the breakers. The initial status is the same for the
three breakers. Depending on the initial status, the icon shows a closed
contact or an open contact.
Switching of phase A
If selected, the switching of phase A is activated. If not selected, the
breaker of phase A stays in its initial status specified in the Initial status
of breakers parameter.
5-286
Three-Phase Breaker
Switching of Phase B
If selected, the switching of phase B is activated. If not selected, the
breaker of phase B stays in its initial status specified in the Initial status
of breakers parameter.
Switching of phase C
If selected, the switching of phase C is activated. If not selected, the
breaker of phase C stays in its initial status specified in the Initial status
of breakers parameter.
Transition times(s)
The Transition times(s) parameter is not visible in the dialog box if the
External control of switching times parameter is selected.
Specify the vector of switching times when using the Three-Phase Breaker
block in internal control mode. At each transition time the selected
breakers opens or closes depending to their initial state.
External control of switching times
If selected, adds a fourth input port to the Three-Phase Breaker block for
an external control of the switching times of the breakers. The switching
times are defined by a Simulink signal (0-1 sequence).
Breakers resistance Ron
The internal breaker resistances, in ohms (Ω). The Breaker resistance
Ron parameter cannot be set to 0.
Snubbers resistance Rp
The snubber resistances, in ohms (Ω). Set the Snubber resistance Rp
parameter to inf to eliminate the snubbers from the model.
Snubbers capacitance Cp
The snubber capacitances, in farads (F). Set the Snubber capacitance Cp
parameter to 0 to eliminate the snubbers, or to inf to get resistive
snubbers.
Measurements
Select Breaker voltages to measure the voltage across the three internal
breaker terminals.
5-287
Three-Phase Breaker
Select Breaker currents to measure the current flowing through the three
internal breakers. If the snubber devices are connected, the measured
currents are the ones flowing through the breakers contacts only.
Select Breaker voltages and currents to measure the breaker voltages
and the breaker currents.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurements is identified by a label
followed by the block name and the phase:
Measurement
Label
Breaker voltages
Ub <block name> /Breaker A: Ub <block
name> /Breaker B:
Ub <block name> /Breaker C.
Breaker currents
Ib <block name> /Breaker A: Ib <block
name> /Breaker B:
Ib <block name> Breaker C.
Inputs and
Outputs
The three inputs A, B, and C and the three outputs a, b, and c are the breaker
terminals. Breaker A is connected between input 1 and output 1, breaker B is
connected between input 2 and output 2, and breaker C is connected between
input 3 and output 3. If the Three-Phase Breaker block is set in external control
mode, the Simulink input 4 appears and it is used to control the opening and
closing of the three internal breakers.
Example
See the power_3phlinereclose and power_3phseriescomp demos for circuits
using the Three-Phase Breaker block.
See Also
Breaker, Multimeter, Three-Phase Fault
5-288
Three-Level Bridge
Purpose
5Three-Level Bridge
Library
Power Electronics
Description
The Three-Level Bridge block implements a three-level power converter that
consists of one, two, or three arms of power switching devices. Each arm
consists of four switching devices (Q1 to Q4) along with their antiparallel
diodes (D1 to D4) and two neutral clamping diodes (D5 and D6) as shown.
Implement a three-level neutral point clamped (NPC) power converter with
selectable topologies and power switching devices
+Vdc
Q1
D1
Q1
D2
Q2
Q4
Q2
D2
B
D3
Q3
D3
D4
D6
Q4
D4
D6
D1
D5
D2
A
Q3
Q1
D5
D5
Q2
D1
C
Q3
D3
D6
Q4
D4
−Vdc
N
The type of power switching device (IGBT, GTO, MOSFET, or ideal switch) and
the number of arms (one, two, or three) are selectable from the dialog box.
When the ideal switch is used as the switching device, the Three-Level Bridge
block implements an ideal switch bridge having a three-level topology as
shown.
5-289
Three-Level Bridge
+Vdc
Sw1
A
Sw3
−Vdc
N
Dialog Box and
Parameters
5-290
B
C
Sw3
Sw3
Sw2
Sw1
Sw1
Sw2
Sw2
Three-Level Bridge
Number of bridge arms
Determine the bridge topology: one, two, or three arms.
Snubber resistance Rs
The snubber resistance, in ohms (Ω). Set the Snubber resistance Rs
parameter to inf to eliminate the snubbers from the model.
Snubber capacitance Cs
The snubber capacitance, in farads (F). Set the Snubber capacitance Cs
parameter to 0 to eliminate the snubbers, or to inf to get a resistive
snubber.
For forced-commutated devices (GTO, IGBT, or MOSFET) the Three-Level
Bridge block operates satisfactorily with resistive snubbers as long as the
firing pulses are sent to the switching devices.
If the firing pulses to forced-commutated devices are blocked, the bridge
operates as a diode rectifier. In this condition, you must use appropriate
values of Rs and Cs. If the model is discretized, you can use the following
formulas to compute approximate values of Rs and Cs:
Ts
Rs > 2 ------Cs
Pn
Cs < --------------------------------------2
1000 ( 2πf )Vn
where
P n = Nominal power of single- or three-phase converter (VA)
Vn = Nominal line-to-line AC voltage (Vrms)
f = Fundamental frequency (Hz)
T s = Sample Time (s)
These Rs and Cs values are derived from the following two criteria:
- The snubber leakage current at fundamental frequency is less than 0.1%
of nominal current when power electronic devices are not conducting.
5-291
Three-Level Bridge
- The RC time constant of snubbers is higher than two times the sample
time Ts.
Note that the Rs and Cs values that guarantee numerical stability of the
discretized bridge can be different from actual values used in the physical
circuit.
Power electronic device
Select the type of power electronic device to use in the bridge.
Internal resistance Ron
Internal resistance of the selected devices and diodes, in ohms (Ω).
Forward voltages [Device Vf, Diode Vfd]
The forward voltage of the selected devices (for GTO or IGBT only) and of
the antiparallel and clamping diodes, in volts.
Measurements
Select All Device currents to measure the current flowing through all
the components (Q1 to Q4 and D1 to D6). If the snubber devices are defined,
the measured currents are those flowing through the power electronic
devices only.
Select Phase-to-neutral and DC voltages to measure the terminal
voltages (AC and DC) of the Three-Level Bridge block.
Select All voltages and currents to measure all voltages and currents
defined for the Three-Level Bridge block.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurement list
5-292
Three-Level Bridge
box of the Multimeter block, the measurement is identified by a label
followed by the block name.
Inputs and
Outputs
Measurement
Label
Device currents for
MOSFET, IGBT, and
GTO
IQ1x:, IQ2x:, IQ3x:, IQ4x:, ID1x:,
ID2x:, ID3x:, ID4x:, ID5x:, ID6x:
or
Device currents for
Ideal Switch, where x =
a, b, or c
ISw1x:, ISw2x:, ISw3x:
Terminal voltages
Uan:, Ubn:, Ucn:, Udc+:, Udc-:
The Pulses input accepts a Simulink-compatible vectorized gating signal
containing four pulses (Q1 to Q4) for each arm of the converter. For instance,
if a three-arm topology is selected, the input vector must contain twelve pulses
and the ordering must be as follows: Q1 of leg A, Q2 of leg A, …, Q4 of leg C.
Note In the case of the ideal switch converter, the Q1 pulse is sent to Sw1,
the Q4 pulse to Sw2, and a logical AND operation is performed on the Q2 and
Q3 pulses and the result sent to Sw3.
Assumptions
Turn-on and turn-off times (Fall time, Tail time) of power switching devices are
and Limitations not modeled in the Three-Level Bridge block.
Example
The power_3levelVSC demo illustrates the use of the Three-Level Bridge block
in an AC-DC converter consisting of a three-phase IGBT-based voltage sourced
converter (VSC). The converter is pulse-width modulated (PWM) to produce a
500 V DC voltage (+/− 250V). In this example the converter chopping frequency
is 1620 Hz and the power system frequency is 60 Hz.
5-293
Three-Level Bridge
IGBT Bridge
Transformer
Three-phase
600 V
60 Hz
supply
+
Inductor
N
500 Vdc
load
−
−
Capacitor
The VSC is controlled in a closed loop by two PI regulators in order to maintain
a DC voltage of 500 V at the load while maintaining a unity input power factor
for the AC supply.
The initial conditions for a steady-state simulation are generated by running
an initial simulation to steady state for an integer number of cycles of 60 Hz.
The final states (both SimPowerSystems and Simulink controller states) are
saved in a vector called xInitial. This vector, as well as the sample times
(Ts_Power and Ts_Control) are saved in the power_3levelVSC_xinit.mat file.
5-294
Three-Level Bridge
When you open this model, the initial condition vector xInitial and the
sample times saved in the MAT file are automatically loaded in the workspace.
Start the simulation. The monitored signals start in steady state.
Observe the following signals:
• The DC voltage (Vdc Scope block)
• The primary voltage and current of phase A of the AC supply (VaIa Scope
block)
• The device currents of leg A of the IGBT bridge (Ia_Devices Scope block
inside the Measurements & Signals subsystem)
• The line-to-line terminal voltage of the VSC (Vab_VSC Scope block)
At 50 ms, a 200 kW load is switched in. You can see that the dynamic response
of the DC regulator to the sudden load variation from 200 kW to 400 kW is
satisfactory. The DC voltage reverts to 500 V within 2 cycles and the unity
power factor on the AC side is maintained.
At 100 ms, a stop-pulsing signal is activated and the pulses normally sent to
the converter are blocked. You can see that the DC voltage drops to 315 V. A
drastic change in the primary current waveform can also be observed. When
the pulses are blocked, the Three-Level Bridge block operation becomes similar
to a three-phase diode bridge.
5-295
Three-Level Bridge
The following two figures summarize the results of the simulation. The first
figure shows the operation of the AC-DC converter during the load variation
and when the pulses are blocked.
5-296
Three-Level Bridge
The second figure shows the current flowing in the various devices of the IGBT
bridge when the converter is feeding 500 Vdc to a 200-kW load.
See Also
Multimeter
5-297
Three-Phase Dynamic Load
Purpose
5Three-Phase Dynamic Load
Library
Elements
Description
The Three-Phase Dynamic Load block implements a three-phase, three-wire
dynamic load whose active power P and reactive power Q vary as function of
positive-sequence voltage. Negative- and zero-sequence currents are not
simulated. The three load currents are therefore balanced, even under
unbalanced load voltage conditions.
Implements a three-phase dynamic load with active power and reactive power
as a function of voltage or controlled from an external input
The load impedance is kept constant if the terminal voltage V of the load is
lower than a specified value Vmin. When the terminal voltage is greater than
the Vmin value, the active power P and reactive power Q of the load vary as
follows:
V
P ( s ) = P o  ------
 V o
np ( 1
V
Q ( s ) = Q o  ------
 V o
+ T p1 s )
-------------------------( 1 + T p2 s )
nq ( 1
+ T q1 s )
-------------------------( 1 + T q2 s )
where
• Vo is the initial positive sequence voltage.
• Po and Qo are the initial active and reactive powers at the initial voltage Vo.
• V is the positive-sequence voltage.
• np and nq are exponents (usually between 1 and 3) controlling the nature of
the load.
• Tp1 and Tp2 are time constants controlling the dynamics of the active power
P.
• Tq1 and Tq2 are time constants controlling the dynamics of the reactive
power Q.
For a constant current load, for example, you set np to 1 and nq to 1, and for
constant impedance load you set np to 2 and nq to 2.
5-298
Three-Phase Dynamic Load
Dialog Box and
Parameters
Nominal L-L voltage and frequency
Specifies the nominal phase-to-phase voltage, in volts RMS, and nominal
frequency, in hertz, of the load.
Active and reactive power at initial voltage
Specifies the initial active power Po, in watts, and initial reactive power
Qo, in vars, at the initial voltage Vo. If the load flow utility of the Powergui
is used to initialize the dynamic load and start simulation in steady state,
5-299
Three-Phase Dynamic Load
these parameters are automatically updated according to P and Q set
points specified for the load.
Initial positive-sequence voltage Vo
Specifies the magnitude and phase of the initial positive-sequence voltage
of the load. If the load flow utility of the Powergui is used to initialize the
dynamic load and start simulation in steady state, these two parameters
are automatically updated according to values computed by the load flow.
External control of PQ
If selected, the active power and reactive power of the load are defined by
an external Simulink vector of two signals.
Parameters [np nq]
Specifies the np and nq parameters that define the nature of the load.
Time constants [Tp1 Tp2 Tq1 Tq2]
Specifies the time constants controlling the dynamics of the active power
and the reactive power.
Minimum voltage Vmin
Specifies the minimum voltage at which the load dynamics commences.
The load impedance is constant below this value.
Inputs and
Outputs
Inputs A, B, and C are the three terminals of the load. If External control of
PQ is selected, a fourth input, labeled PQ, appears. This Simulink input is used
to control the active and reactive powers of the load from a vector of two signals
[P Q].
The m output is a vector containing the following three signals:
positive-sequence voltage (p.u.); active power P (W); and reactive power Q
(vars).
Example
5-300
The power_dynamicload model uses a Three-Phase Dynamic Load block
connected on a 500 kV, 60 Hz power network. The network is simulated by its
Thevenin equivalent (voltage source behind a R-L impedance corresponding to
a three-phase short-circuit level of 2000 MVA). The source internal voltage is
modulated in order to simulate voltage variation during a power swing. As the
dynamic load is a nonlinear model simulated by current sources, it cannot be
Three-Phase Dynamic Load
connected to an inductive network (R-L in series). Therefore, a small resistive
load (1 MW) has been added in parallel with the dynamic load.
In order to start the simulation in steady state, you must specify the correct
initial positive-sequence voltage Vo (magnitude and phase) corresponding to
the desired Po and Qo values. You use the load flow utility to find this voltage
and initialize the dynamic load. Open the Powergui and select Load Flow and
Machine Initialization. Specify the desired active power and reactive powers
for the dynamic load (50 MW, 25 Mvar):
Active Power = 50e6; Reactive Power = 25e6.
Then press the Update Load Flow button.Once the load flow has been solved
the three phase-to-phase voltages of the dynamic load (0.9844 p.u.) as well as
its line currents are displayed. The phase angle of the phase-to-neutral load
voltage Uan is also displayed (−1.41 degrees). This angle corresponds to the
angle of the positive-sequence voltage. If you now open the Three-Phase
Dynamic Load dialog box, notice that the values of Po, Qo, and Vo have been
updated.
5-301
Three-Phase Dynamic Load
Start the simulation and observe load voltage, P&Q powers, and current on
Scope1. Observe that simulation starts in steady state. At t = 0.2 s, when
voltage modulation is initiated, P and Q start to increase (trace 2), but, as np
and nq are set to 1, the load current (trace 3) stays constant. When voltage falls
below 0.7 p.u. the load behaves as a constant impedance. Therefore load
current follows this voltage variation.
Observe on Scope2 variations of instantaneous voltages and currents. Also,
notice that computed P and Q displayed on Scope3 are the same as P and Q
internal signals returned by the Dynamic Load measurement output.
The signals displayed on the Scope1 block are shown below.
5-302
Three-Phase Fault
Purpose
5Three-Phase Fault
Library
Elements
Description
The Three-Phase Fault block implements a three-phase circuit breaker where
the opening and closing times can be controlled either from an external
Simulink signal (external control mode), or from an internal control timer
(internal control mode).
Implement a programmable phase-to-phase and phase-to-ground fault breaker
system
The Three-Phase Fault block uses three Breaker blocks that can be
individually switched on and off to program phase-to-phase faults,
phase-to-ground faults, or a combination of phase-to-phase and ground faults.
Ron
A
Ron
Rg
B
Ron
C
The ground resistance Rg is automatically set to 106 ohms when the ground
fault option is not programmed. For example, to program a fault between the
phases A and B you need to select the Phase A Fault and Phase B Fault block
parameters only. To program a fault between the phase A and the ground, you
need to select the Phase A Fault and Ground Fault parameters and specify a
small value for the ground resistance.
If the Three-Phase Fault block is set in external control mode, a control input
appears in the block icon. The control signal connected to the fourth input must
be either 0 or 1, 0 to open the breakers, 1 to close them. If the Three-Phase
Fault block is set in internal control mode, the switching times and status are
specified in the dialog box of the block.
Series Rp-Cp snubber circuits are included in the model. They can be optionally
connected to the fault breakers. If the Three-Phase Fault block is in series with
an inductive circuit, an open circuit or a current source, you must use the
snubbers.
5-303
Three-Phase Fault
Dialog Box and
Parameters
Phase A Fault
If selected, the fault switching of phase A is activated. If not selected, the
breaker of phase A stays in its initial status. The initial status of the phase
A breaker corresponds to the complement of the first value specified in the
vector of Transition status. The initial status of the fault breaker is
usually 0 (open). However, it is possible to start a simulation in steady
state with the fault initially applied on the system. For example, if the first
5-304
Three-Phase Fault
value in the Transition status vector is 0, the phase A breaker is initially
closed. It opens at the first time specified in the Transition time(s) vector.
Phase B Fault
If selected, the fault switching of phase B is activated. If not selected, the
breaker of phase B stays in its initial status. The initial status of the phase
B breaker corresponds to the complement of the first value specified in the
vector of Transition status.
Phase C Fault
If selected, the fault switching of phase C is activated. If not selected, the
breaker of phase C stays in its initial status. The initial status of the phase
C breaker corresponds to the complement of the first value specified in the
vector of Transition status.
Fault resistances Ron
The internal resistance, in ohms (Ω), of the phase fault breakers. The Fault
resistances Ron parameter cannot be set to 0.
Ground Fault
If selected, the fault switching to the ground is activated. A fault to the
ground can be programed for the activated phases. For example, if the
Phase C Fault and Ground Fault parameters are selected, a fault to the
ground is applied to the phase C. The ground resistance is set internally to
1e6 ohms when the Ground Fault parameter is not selected.
Ground resistance Rg
The Ground resistance Rg (ohms) parameter is not visible if the Ground
Fault parameter is not selected. The ground resistance, in ohms (Ω). The
Ground resistance Rg (ohms) parameter cannot be set to 0.
External control of fault timing
If selected, adds a fourth input port to the Three-Phase Fault block for an
external control of the switching times of the fault breakers. The switching
times are defined by a Simulink signal (0 or 1) connected to the fourth input
port of the block.
Transition status
Specify the vector of switching status when using the Three-Phase Breaker
block in internal control mode. The selected fault breakers open (0) or close
5-305
Three-Phase Fault
(1) at each transition time according to the Transition status parameter
values.
The initial status of the breakers corresponds to the complement of the first
value specified in the vector of switching status.
Transition times(s)
Specify the vector of switching times when using the Three-Phase Breaker
block in internal control mode. At each transition time the selected fault
breakers opens or closes depending to the initial state. The Transition
times (s) parameter is not visible in the dialog box if the External control
of switching times parameter is selected.
Snubbers resistance Rp
The snubber resistances, in ohms (Ω). Set the Snubbers resistance Rp
parameter to inf to eliminate the snubbers from the model.
Snubbers capacitance Cp
The snubber capacitances, in farads (F). Set the Snubbers capacitance Cp
parameter to 0 to eliminate the snubbers, or to inf to get resistive
snubbers.
Measurements
Select Fault voltages to measure the voltage across the three internal
fault breaker terminals.
Select Fault currents to measure the current flowing through the three
internal breakers. If the snubber devices are connected, the measured
currents are the ones flowing through the breakers contacts only.
Select Fault voltages and currents to measure the breaker voltages and
the breaker currents.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
5-306
Three-Phase Fault
box of the Multimeter block, the measurements are identified by a label
followed by the block name and the phase:
Measurement
Label
Fault voltages
Ub <block name> /Fault A: Ub <block name>
/Fault B: Ub <block name> /Fault C.
Fault currents
Ib <block name> /Fault A: Ib <block name>
/Fault B: Ib <block name> /Fault C.
Inputs and
Outputs
The inputs 1, 2, and 3 are the fault breaker terminals connected respectively to
phases A, B, and C. The breakers are connected between inputs 1, 2, and 3 and
the internal ground resistor. If the Three-Phase Fault block is set in external
control mode, Simulink input 4 appears and is used to control the opening and
closing of the three internal breakers.
Example
See the power_3phseriescomp demo for a circuit using the Three-Phase Fault
block.
See Also
Breaker, Multimeter, Three-Phase Breaker
5-307
Three-Phase Mutual Inductance Z1-Z0
Purpose
5Three-Phase Mutual Inductance Z1-Z0
Library
Elements
Description
The Three-Phase Mutual Inductance Z1-Z0 block implements a three-phase
balanced inductive and resistive impedance with mutual coupling between
phases. This block performs the same function as the three-winding Mutual
Inductance block. For three-phase balanced power systems, it provides a more
convenient way of entering system parameters in terms of positive- and
zero-sequence resistances and inductances than the self- and mutual
resistances and inductances.
Implement a three-phase impedance with mutual coupling among phases
Dialog Box and
Parameters
Positive-sequence parameters
The positive-sequence resistance R1, in ohms (Ω), and the
positive-sequence inductance L1, in henries (H).
Zero-sequence parameters
The zero-sequence resistance R0, in ohms (Ω), and the zero-sequence
inductance L0, in henries (H).
Example
5-308
The power_3phmutseq10 demo illustrates the use of the Three-Phase Mutual
Inductance Z1-Z0 block to build a three-phase inductive source with different
values for the positive-sequence impedance Z1 and the zero-sequence
impedance Z0. The programmed impedance values are Z1 = 1+j1 Ω and Z0 =
Three-Phase Mutual Inductance Z1-Z0
2+j2 Ω. The Three-Phase Programmable Voltage Source block is used to
generate a 1-volt, 0-degree, positive-sequence internal voltage. At t = 0.1 s, a 1volt, 0-degree, zero-sequence voltage is added to the positive-sequence voltage.
The three source terminals are short-circuited to ground and the resulting
positive-, negative-, and zero-sequence currents are measured using the
Discrete 3-Phase Sequence Analyzer block.
The current waveforms and their sequence components (magnitude and phase)
are displayed on the Scope block. The resulting waveforms are shown on the
following figure.
5-309
Three-Phase Mutual Inductance Z1-Z0
The polar impedance values are Z1 =
2 ∠45° Ω and Z0 = 2 2 ∠45° Ω
Therefore, the positive- and zero-sequence currents displayed on the scope are
I1 = V1 ⁄ Z1 = 1 ⁄ ( 2 ∠45° ) = 0.7071 A ∠– 45°
I0 = V0 ⁄ Z0 = 1 ⁄ ( 2 2 ∠45° ) = 0.3536 A ∠– 45°
The transients observed on the magnitude and the phase angle of the
zero-sequence current when the zero-sequence voltage is added (at t = 0.1 s) are
due to the Fourier measurement technique used by the Discrete 3-Phase
Sequence Analyzer block. As the Fourier analysis uses a running average
window of one cycle, it takes one cycle for the magnitude and phase to stabilize.
See Also
5-310
Mutual Inductance
Three-Phase Parallel RLC Branch
Purpose
5Three-Phase Parallel RLC Branch
Library
Elements
Description
The Three-Phase Parallel RLC Branch block implements three balanced
branches consisting each of a resistor, an inductor, a capacitor, or a parallel
combination of these. To eliminate either the resistance, inductance, or
capacitance of each branch, the R, L, and C values must be set respectively to
infinity (inf), infinity (inf), and 0. Only existing elements are displayed in the
block icon.
Implement a three-phase parallel RLC branch
Negative values are allowed for resistance, inductance, and capacitance.
Dialog Box and
Parameters
Resistance R
The branch resistances, in ohms (Ω).
Inductance L
The branch inductances, in henries (H).
Capacitance C
The branch capacitances, in farads (F).
5-311
Three-Phase Parallel RLC Branch
Measurements
Select Branch voltages to measure the three voltages across the
Three-Phase Parallel RLC Branch block terminals.
Select Branch currents to measure the three total currents (sum of R, L,
C currents) flowing through the Three-Phase Parallel RLC Branch block.
Select Branch voltages and currents to measure the three voltages and
the three currents of the Three-Phase Parallel RLC Branch block.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurements are identified by a label
followed by the block name.
See Also
5-312
Measurement
Label
Branch voltages of
phases A, B, and C
Ub1: , Ub2: , Ub3:
Branch currents of
phases A, B, and C
Ib1: , Ib2: , Ib3:
Multimeter, Three-Phase Parallel RLC Load, Three-Phase Series RLC Branch,
Three-Phase Series RLC Load
Three-Phase Parallel RLC Load
Purpose
5Three-Phase Parallel RLC Load
Library
Elements
Description
The Three-Phase Parallel RLC Load block implements a three-phase balanced
load as a parallel combination of RLC elements. At the specified frequency, the
load exhibits a constant impedance. The active and reactive powers absorbed
by the load are proportional to the square of the applied voltage.
Implement a three-phase parallel RLC load with selectable connection
Only elements associated with nonzero powers are displayed in the block icon.
Dialog Box and
Parameters
5-313
Three-Phase Parallel RLC Load
Configuration
The connection of the three phases. Select one of the following four
connections:
Y(grounded)
Neutral is grounded.
Y(floating)
Neutral is not accessible.
Y(neutral)
Neutral is made accessible through a
fourth connector.
Delta
Three phases connected in delta
The block icon is updated according to the load connection.
Nominal phase-to-phase voltage Vn
The nominal phase-to-phase voltage of the load, in volts RMS (Vrms).
Nominal frequency fn
The nominal frequency, in hertz (Hz).
Active power P
The three-phase active power of the load, in watts (W).
Inductive reactive power QL
The three-phase inductive reactive power QL, in vars. Specify a positive
value, or 0.
Capacitive reactive power QC
The three-phase capacitive reactive power QC, in vars. Specify a positive
value, or 0.
Measurements
Select Branch voltages to measure the three voltages across each phase
of the Three-Phase Parallel RLC Load block terminals. For a Y connection,
these voltages are the phase-to-ground or phase-to-neutral voltages. For a
delta connection, these voltages are the phase-to-phase voltages.
Select Branch currents to measure the three total currents (sum of R, L,
C currents) flowing through each phase of the Three-Phase Parallel RLC
Load block. For a delta connection, these currents are the currents flowing
in each branch of the delta.
5-314
Three-Phase Parallel RLC Load
Select Branch voltages and currents to measure the three voltages and
the three currents of the Three-Phase Parallel RLC Load block.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurements are identified by a label
followed by the block name.
Measurement
Branch voltages
Label
Y(grounded): Uag, Ubg, Ucg
Ub1: , Ub2: , Ub3:
Y(floating): Uan, Ubn, Ucn
Y(neutral): Uan, Ubn, Ucn
Delta: Uab, Ubc, Uca
Branch currents
Y(grounded): Ia, Ib, Ic
Ib1: , Ib2: , Ib3:
Y(floating): Ia, Ib, Ic
Y(neutral): Ia, Ib, Ic
Delta: Iab, Ibc, Ica
See Also
Multimeter, Three-Phase Dynamic Load, Three-Phase Parallel RLC Branch,
Three-Phase Series RLC Branch, Three-Phase Series RLC Load
5-315
Three-Phase PI Section Line
Purpose
5Three-Phase PI Section Line
Library
Elements
Description
The Three-Phase PI Section Line block implements a balanced three-phase
transmission line model with parameters lumped in a PI section.
Implement a three-phase transmission line section with lumped parameters
Contrary to the Distributed Parameter Line model where the resistance,
inductance, and capacitance are uniformly distributed along the line, the
Three-Phase PI Section Line block lumps the line parameters in a single PI
section as shown in the figure below where only one phase is represented.
R
C/2
L
C/2
The line parameters R, L, and C are specified as positive- and zero-sequence
parameters that take into account the inductive and capacitive couplings
between the three phase conductors as well as the ground parameters. This
method of specifying line parameters assumes that the three phases are
balanced.
Using a single PI section model is appropriate for modeling short transmission
lines or when the frequency range of interest is limited around the
fundamental frequency. You can obtain a more accurate model by cascading
several identical blocks. See the PI Section Line documentation for
explanations of the maximum frequency range that can be achieved by a PI line
model.
5-316
Three-Phase PI Section Line
Dialog Box and
Parameters
Frequency used for R L C specification
The frequency used for specification of line parameters, in hertz (Hz). This
is usually the nominal system frequency (50 Hz or 60 Hz).
Positive- and zero-sequence resistances
The positive- and zero-sequence resistances in ohms/kilometer (Ω/km).
Positive- and zero-sequence inductances
The positive- and zero-sequence inductances in henries/kilometer (H/km).
Positive- and zero-sequence capacitances
The positive- and zero-sequence capacitances in farads/kilometer (F/km).
Line section length
The line section length in kilometers (km).
Example
The power_triphaseline demo illustrates voltage transients at the receiving
end of a 200 km line when only phase A is energized. Voltages obtained with
5-317
Three-Phase PI Section Line
two line models are compared: 1) the Distributed Parameters Line block and 2)
a PI line model using two Three-Phase PI Section Line blocks.
See Also
5-318
Distributed Parameter Line, PI Section Line
Three-Phase Programmable Voltage Source
Purpose
Implement a three-phase voltage source with programmable time variation of
amplitude, phase, frequency, and harmonics
Library
Electrical Sources
Description
Use this block to generate a three-phase sinusoidal voltage with time-varying
parameters. You can program the time variation for the amplitude, phase, or
frequency of the fundamental component of the source. In addition, two
harmonics can be programmed and superimposed on the fundamental signal.
5Three-Phase Programmable Voltage Source
Dialog Box and
Parameters
5-319
Three-Phase Programmable Voltage Source
Positive-sequence
The amplitude in volts RMS phase-to-phase, the phase in degrees, and the
frequency in hertz of the positive-sequence component of the three
voltages.
Time variation of
Specify the parameter for which you want to program the time variation.
Select None if you do not want to program the time variation of the source
parameters. Select Amplitude if you want to program the time variation of
the amplitude. Select Phase if you want to program the time variation of
the phase. Select Frequency if you want to program the time variation of
the frequency.
Note that the time variation applies on the three phases of the source
except when the Type of variation parameter is set to Table of
amplitude-pairs, in which case you can apply a variation on phase A only.
Type of variation
Specify the type of variation that is applied on the parameter specified by
the Time variation of parameter. Select Step to program a step variation.
Select Ramp to program a ramp variation. Select Modulation to program a
modulated variation. Select Table of amplitude-pairs to program a
series of step changes of amplitudes at specific times.
Step magnitude
This parameter is only visible if the Type of Variation parameter is set to
Step.
Specify the amplitude of the step change. The variation of amplitude is
specified in p.u. of the positive-sequence amplitude.
Rate of change
This parameter is only visible if the Type of Variation parameter is set to
Ramp.
Specify the rate of change, in volt/seconds. The rate of change of voltage is
specified in (p.u of the positive-sequence voltage)/second.
Amplitude of the modulation
This parameter is only visible if the Type of variation parameter is set to
Modulation.
5-320
Three-Phase Programmable Voltage Source
Specify the amplitude of the modulation for the source parameter specified
in the Time variation of parameter. When the varying quantity is the
voltage amplitude, the amplitude of the modulation is specified in p.u. of
the positive-sequence amplitude.
Frequency of the modulation
This parameter is only visible if the Type of variation parameter is set to
Modulation.
Specify the frequency of the modulation for the source parameter specified
in the Time variation of parameter.
Variation timing(s)
Specify the time, in seconds, when the programmed time variation takes
effect and the time when it stops.
Fundamental and/or Harmonic generation
If selected, two harmonics can be programmed to be superimposed on the
fundamental voltage of the source.
A: [Order Amplitude Phase Seq]
This parameter is only visible if the Fundamental and/or Harmonic
generation check box is selected.
Specify the order, amplitude, phase, and the type of sequence (1 =
positive-sequence; 2 = negative-sequence; 0 = zero-sequence) of the first
harmonic to be superimposed on the fundamental signal. The voltage of the
harmonic is specified in p.u. of the positive-sequence voltage.
Specify 1 for the harmonic order and 0 or 2 for the sequence to produce a
voltage imbalance without harmonics.
B: [Order Amplitude Phase Seq]
This parameter is only visible if the Fundamental and/or Harmonic
generation check box is selected.
Specify the order, amplitude, phase, and the type of sequence (0 = zero
sequence, 1 = positive sequence, 2 = negative sequence) of the second
harmonic to be superimposed on the fundamental signal. The voltage of the
harmonic is specified in p.u. of the positive-sequence voltage.
5-321
Three-Phase Programmable Voltage Source
Specify 1 for the harmonic order and 0 or 2 for the sequence to produce a
voltage unbalance without harmonics.
Variation Timing(s)
This parameter is only visible if the Fundamental and/or Harmonic
generation check box is selected.
Specify the time, in seconds, when the harmonic generation is
superimposed on the fundamental signal and the time when it stops.
Inputs and
Outputs
Output connectors 1, 2, and 3 are the three source terminals of phases A, B, and
C. The input connector is the neutral point. This neutral can be left open
(ungrounded wye connection) or grounded (grounded wye connection).
Example
The power_3phsignalseq circuit illustrates the use of the Three-Phase
Programmable Voltage Source block to produce a step variation of the
positive-sequence voltage and to inject harmonics into the circuit.
A 25 kV, 100 MVA short-circuit level, equivalent network feeds a 5 MW, 2 Mvar
capacitive load. The internal voltage of the source is controlled by the Discrete
3-phase Programmable Voltage Source block.
A positive sequence of 1.0 p.u., 0 degrees is specified for the fundamental
signal. At t = 0.05 s a step of 0.5 p.u. is applied on the positive-sequence voltage
magnitude, then at t = 0.1 s, 0.08 p.u. of fifth harmonic in negative sequence is
added to the 1.5 p.u. voltage.
The three-phase voltage and current are measured at the output of the source
impedance. Two Discrete Sequence Analyzer blocks are used to measure the
positive-sequence fundamental component and the negative-sequence fifth
harmonic of the three-phase voltage.
5-322
Three-Phase Programmable Voltage Source
See Also
Three-Phase Source
5-323
Three-Phase Sequence Analyzer
Purpose
5Three-Phase Sequence Analyzer
Library
Extras/Measurements
Measure the positive-, negative-, and zero-sequence components of a
three-phase signal
A discrete version of this block is available in the Extras/Discrete
Measurements library
Description
The Three-Phase Sequence Analyzer block outputs the magnitude and phase
of the positive- (denoted by the index 1), negative- (index 2), and zero-sequence
(index 0) components of a set of three balanced or unbalanced signals. The
signals can contain harmonics or not. The three sequence components of a
three-phase signal (voltages V1 V2 V0 or currents I1 I2 I0) are computed as
follows:
2
1
V 1 = --- ( V a + a ⋅ V b + a ⋅ V c )
3
2
1
V 2 = --- ( V a + a ⋅ V b + a ⋅ V c )
3
1
V 0 = --- ( V a + V b + V c )
3
where
V a, V b, V c = three voltage phasors at specified frequency
a = e
j2π ⁄ 3
= 1 ∠120degree complex operator
A Fourier analysis over a sliding window of one cycle of the specified frequency
is first applied to the three input signals. It evaluates the phasor values Va, Vb,
and Vc at the specified fundamental or harmonic frequency. Then the
transformation is applied to obtain the positive sequence, negative sequence,
and zero sequence.
The Three-Phase Sequence Analyzer block is not sensitive to harmonics or
imbalances. However, as this block uses a running average window to perform
the Fourier analysis, one cycle of simulation has to be completed before the
outputs give the correct magnitude and angle. For example, its response to a
step change of V1 is a one-cycle ramp.
5-324
Three-Phase Sequence Analyzer
The discrete version of this block allows you to specify the initial magnitude
and phase of the output signal. For the first cycle of simulation the outputs are
held to the values specified by the initial input parameter.
You can modify any parameter during the simulation in order to obtain the
different sequence and harmonic components of the input signals.
Dialog Box and
Parameters
Fundamental frequency f1
The fundamental frequency, in hertz, of the three-phase input signal.
Harmonic n
Specify the harmonic component from which you want to evaluate the
sequences. For DC, enter 0. For fundamental, enter 1.
5-325
Three-Phase Sequence Analyzer
Sequence
Specify which sequence component the block outputs. Select Positive to
calculate the positive sequence, select Negative to calculate the negative
sequence, select 0 to compute the zero sequence of the fundamental or
specified harmonic of the three-phase input signal. Select Positive
Negative Zero to get all the sequences.
Inputs and
Outputs
abc
Connect to the input the vectorized signal of the three [a b c] sinusoidal
signals.
Mag
The first output gives the magnitude (peak value) of the specified sequence
component.
Phase
The second output gives the phase in degrees of the specified component(s).
Example
The power_3phsignalseq demo illustrates the use of the Discrete Sequence
Analyzer block to measure the fundamental and harmonic components of a
three-phase voltage. A 25kV, 100 MVA short-circuit level, equivalent network
feeds a 5 MW, 2 Mvar capacitive load. The internal voltage of the source is
controlled by the Discrete 3-phase Programmable Voltage Source block.
A positive sequence of 1.0 p.u., 0 degrees is specified for the fundamental
signal. At t = 0.05 s a step of 0.5 p.u. is applied on the positive-sequence voltage
magnitude, then at t = 0.1 s, 0.08 p.u. of fifth harmonic in negative sequence is
added to the 1.5 p.u. voltage.
Two Discrete Three-Phase Sequence Analyzer blocks are used to measure the
positive-sequence fundamental component and the negative-sequence fifth
harmonic of the three-phase voltage.
5-326
Three-Phase Sequence Analyzer
As the Three-Phase Sequence Analyzer blocks use Fourier analysis, their
response time is delayed by one cycle of the fundamental frequency.
5-327
Three-Phase Sequence Analyzer
5-328
Three-Phase Series RLC Branch
Purpose
5Three-Phase Series RLC Branch
Library
Elements
Description
The Three-Phase Series RLC Branch block implements three balanced
branches consisting each of a resistor, an inductor, or a capacitor or a series
combination of these. To eliminate either the resistance, inductance, or
capacitance of each branch, the R, L, and C values must be set respectively to
0, 0, and infinity (inf). Only existing elements are displayed in the block icon.
Implement a three-phase series RLC branch
Negative values are allowed for resistance, inductance, and capacitance.
Dialog Box and
Parameters
Resistance R
The branch resistances, in ohms (Ω).
Inductance L
The branch inductances, in henries (H).
Capacitance C
The branch capacitances, in farads (F).
5-329
Three-Phase Series RLC Branch
Measurements
Select Branch voltages to measure the three voltages across the
Three-Phase Series RLC Branch block terminals.
Select Branch currents to measure the three currents flowing through the
Three-Phase Series RLC Branch block.
Select Branch voltages and currents to measure the three voltages and
the three currents of the Three-Phase Series RLC Branch block.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurements are identified by a label
followed by the block name.
See Also
5-330
Measurement
Label
Branch voltages
of phases A, B, and C
Ub1: , Ub2: , Ub3:
Branch currents
of phases A, B, and C
Ib1: , Ib2: , Ib3:
Multimeter, Three-Phase Parallel RLC Branch,Three-Phase Parallel RLC
Load, Three-Phase Series RLC Load
Three-Phase Series RLC Load
Purpose
5Three-Phase Series RLC Load
Library
Elements
Description
The Three-Phase Series RLC Load block implements a three-phase balanced
load as a series combination of RLC elements. At the specified frequency, the
load exhibits a constant impedance. The active and reactive powers absorbed
by the load are proportional to the square of the applied voltage.
Implement a three-phase series RLC load with selectable connection
Only elements associated with nonzero powers are displayed in the block icon.
Dialog Box and
Parameters
5-331
Three-Phase Series RLC Load
Configuration
The connection of the three phases. Select one of the following four
connections:
Y(grounded)
Neutral is grounded.
Y(floating)
Neutral is not accessible.
Y(neutral)
Neutral is made accessible through a
fourth connector.
Delta
Three phases connected in delta
The block icon is updated according to the load connection.
Nominal phase-to-phase voltage Vn
The nominal phase-to-phase voltage of the load, in volts RMS (Vrms).
Nominal frequency fn
The nominal frequency, in hertz (Hz).
Active power P
The three-phase active power of the load, in watts (W).
Inductive reactive power QL
The three-phase inductive reactive power QL, in vars. Specify a positive
value, or 0.
Capacitive reactive power Qc
The three-phase capacitive reactive power QC, in vars. Specify a positive
value, or 0.
Measurements
Select Branch voltages to measure the three voltages across each phase
of the Three-Phase Series RLC Load block terminals. For a Y connection,
these voltages are the phase-to-ground or phase-to-neutral voltages. For a
delta connection, these voltages are the phase-to-phase voltages.
Select Branch currents to measure the three total currents (sum of R, L,
C currents) flowing through each phase of the Three-Phase Series RLC
Load block. For a delta connection, these currents are the currents flowing
in each branch of the delta.
5-332
Three-Phase Series RLC Load
Select Branch voltages and currents to measure the three voltages and
the three currents of the Three-Phase Series RLC Load block.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurements are identified by a label
followed by the block name.
Measurement
Branch voltages
Label
Y(grounded): Uag, Ubg, Ucg
Ub1: , Ub2: , Ub3:
Y(floating): Uan, Ubn, Ucn
Y(neutral): Uan, Ubn, Ucn
Delta: Uab, Ubc, Uca
Branch currents
Y(grounded): Ia, Ib, Ic
Ib1: , Ib2: , Ib3:
Y(floating): Ia, Ib, Ic
Y(neutral): Ia, Ib, Ic
Delta: Iab, Ibc, Ica
See Also
Multimeter, Three-Phase Dynamic Load, Three-Phase Parallel RLC Branch,
Three-Phase Parallel RLC Load, Three-Phase Series RLC Branch
5-333
Three-Phase Source
Purpose
5Three-Phase Source
Library
Electrical Sources
Description
The Three-Phase Source block implements a balanced three-phase voltage
source with an internal R-L impedance. The three voltage sources are
connected in Y with a neutral connection that can be internally grounded or
made accessible. You can specify the source internal resistance and inductance
either directly by entering R and L values or indirectly by specifying the source
inductive short-circuit level and X/R ratio.
Implement a three-phase source with internal R-L impedance
Dialog Box and
Parameters
Phase-to-phase rms voltage
The internal phase-to-phase voltage in volts RMS (Vrms)
5-334
Three-Phase Source
Phase angle of phase A
The phase angle of the internal voltage generated by phase A, in degrees.
The three voltages are generated in positive sequence. Thus, phase B and
phase C internal voltages are lagging phase A respectively by 120 degrees
and 240 degrees.
Frequency
The source frequency in hertz (Hz).
Internal connection
The internal connection of the three internal voltage sources. The block
icon is updated according to the source connection.
Select one of the following three connections:
Y
The three voltage sources are connected in Y to an
internal floating neutral.
Yn
The three voltage sources are connected in Y to a
neutral connection which is made accessible through a
fourth terminal.
Yg
The three voltage sources are connected in Y to an
internally grounded neutral.
Specify impedance using short-circuit level
Select to specify internal impedance using the inductive short-circuit level
and X/R ratio.
3-phase short-circuit level at base voltage
The three-phase inductive short-circuit power, in volts-amperes (VA), at
specified base voltage, used to compute the internal inductance L. This
parameter is available only if Specify impedance using short-circuit
level is selected.
5-335
Three-Phase Source
The internal inductance L (in H) is computed from the inductive
three-phase short-circuit power Psc (in VA), base voltage Vbase (in Vrms
phase-to-phase), and source frequency f (in Hz) as follows:
2
( Vbase )
1
L = ------------------------- ⋅ --------Psc
2πf
Base voltage
The phase-to-phase base voltage, in volts RMS, used to specify the
three-phase short-circuit level. The base voltage is usually the nominal
source voltage. This parameter is available only if Specify impedance
using short-circuit level is selected.
X/R ratio
The X/R ratio at nominal source frequency or quality factor of the internal
source impedance. This parameter is available only if Specify impedance
using short-circuit level is selected.
The internal resistance R (in Ω) is computed from the source reactance X
(in Ω) at specified frequency, and X/R ratio as follows:
X
2πfL
R = ----------------- = ----------------(X ⁄ R)
(X ⁄ R)
Source resistance
This parameter is available only if Specify impedance using
short-circuit level is not selected.
The source internal resistance in ohms (Ω).
Source inductance
This parameter is available only if Specify impedance using
short-circuit level is not selected.
The source internal inductance in henries (H).
Note Either resistance or inductance of the source can be set to zero, but not
both at the same time. The block icon is updated accordingly.
5-336
Three-Phase Source
Example
See the power_3phseriescomp demo, which uses a Three-Phase Source block to
model a portion of a 735 kV system with a simplified R-L source. The source
impedance is specified by using the three-phase short-circuit level (30,000
MVA) and X/R ratio (X/R = 10).
See Also
Three-Phase Programmable Voltage Source
5-337
Three-Phase Transformer 12 Terminals
Purpose
Implement three single-phase, two-winding transformers where all terminals
are accessible
Library
Elements
Description
The Three-Phase Transformer 12 Terminals block implements three
single-phase, two-winding linear transformers where all the twelve winding
connectors are accessible. The block can be used in place of the Three-Phase
Transformer (Two Windings) block to implement a three-phase transformer
when primary and secondary are not necessarily connected in Y or Delta.
5Three-Phase Transformer 12 Terminals
Dialog Box and
Parameters
[Three-phase rated power Frequency]
The total nominal power of the three phases, in volt-amperes (VA), and the
nominal frequency, in hertz (Hz).
5-338
Three-Phase Transformer 12 Terminals
Winding 1: [phase voltage R X]
The nominal voltage of the three primary windings (labeled 1) in volts RMS
(Vrms), the winding resistances, in p.u., and the winding leakage
reactances, in p.u.
Winding 2: [phase voltage R X]
The nominal voltage of the three secondary windings (labeled 2) in volts
RMS (Vrms), the winding resistances, in p.u., and the winding leakage
reactances, in p.u.
Magnetizing branch: [Rm Xm]
The resistance and reactance simulating the core active and reactive
losses, both in p.u. For example, to specify 0.2% of active and reactive core
losses, at nominal voltage, use Rm = 500 p.u. and Lm = 500 p.u. Lm can be
set to inf (no reactive core losses), but Rm must have a finite value.
Note Refer to the Linear Transformer block documentation for explanations
on the per unit system.
Example
See the power_3phPWM demo for an example of use of the Three-Phase
Transformer 12 Terminals block in a three-phase double-bridge
voltage-sourced converter.
See Also
Linear Transformer, Three-Phase Transformer (Two Windings)
5-339
Three-Phase Transformer (Two Windings)
Purpose
5Three-Phase Transformer (Two Windings)
Library
Elements
Description
The Three-Phase Transformer (Two Windings) block implements a
three-phase transformer using three single-phase transformers. You can
simulate the saturable core or not simply by setting the appropriate check box
in the parameter menu of the block. See the Linear Transformer block and
Saturable Transformer block sections for a detailed description of the electrical
model of a single-phase transformer.
Implement a three-phase transformer with configurable winding connections
The two windings of the transformer can be connected in the following manner:
•Y
• Y with accessible neutral
• Grounded Y
• Delta (D1), delta lagging Y by 30 degrees
• Delta (D11), delta leading Y by 30 degrees
Note The D1 and D11 notations refer to the following clock convention. It
assumes that the reference Y voltage phasor is at noon (12) on a clock display.
D1 and D11 refer respectively to 1 PM (delta voltages lagging Y voltages by
−30 degrees) and 11 AM (delta voltages leading Y voltages by +30 degrees).
The block takes into account the connection type you have selected, and the
icon of the block is automatically updated. An input port labeled N is added to
the block if you select the Y connection with accessible neutral for winding 1. If
you ask for an accessible neutral on winding 2, an extra output port labeled n
is generated.
The saturation characteristic, when activated, is the same as the one described
for the Saturable Transformer block, and the icon of the block is automatically
updated. If the fluxes are not specified, the initial values are automatically
adjusted so that the simulation starts in steady state.
The leakage inductance and resistance of each winding are given in p.u. based
on the transformer nominal power Pn and on the nominal voltage of the
5-340
Three-Phase Transformer (Two Windings)
winding (V1 or V2). For an explanation of per units, refer to the Linear
Transformer and Saturable Transformer block reference pages.
Dialog Box and
Parameters
Nominal power and frequency
The nominal power rating, in volt-amperes (VA), and nominal frequency,
in hertz (Hz), of the transformer.
Winding 1 (ABC) connection
The winding connections for winding 1.
Winding parameters
The phase-to-phase nominal voltage in volts RMS, resistance, and leakage
inductance in p.u. for winding 1.
5-341
Three-Phase Transformer (Two Windings)
Winding 2 (abc) connection
The winding connections for winding 2.
Winding parameters
The phase-to-phase nominal voltage in volts RMS, resistance, and leakage
inductance in p.u. for winding 2.
Saturable core
If selected, implements a saturable three-phase transformer.
Magnetization resistance Rm
The magnetization resistance Rm, in p.u.
Magnetization reactance Lm
The Magnetization reactance Lm parameter is not visible in the dialog
box if the Saturable core parameter is selected.
The magnetization inductance Lm, in p.u., for a nonsaturable core.
Saturation characteristic
This parameter is visible only if the Saturable core parameter is selected.
The saturation characteristic for the saturable core. Specify a series of
current/ flux pairs (in p.u.) starting with the pair (0,0).
Simulate hysteresis
Select to model a saturation characteristic including hysteresis instead of
a single-valued saturation curve.
Hysteresis data MAT file
This parameter is visible only if the Simulate hysteresis parameter is
selected.
Specify a .mat file containing the data to be used for the hysteresis model.
When you open the Hysteresis Design tool of the Powergui, the default
hysteresis loop and parameters saved in the hysteresis .mat file are
displayed. Use the File —> Load a model menu of the Hysteresis Design
tool to load another .mat file. Use the File —> Save this model menu of
the Hysteresis Design tool to save your model in a new .mat file.
5-342
Three-Phase Transformer (Two Windings)
Specify initial fluxes
If selected, the initial fluxes are defined by the [phi0A phi0B phi0C]
parameter.
[phi0A phi0B phi0C]
Specify initial fluxes for each phase of the transformer. This parameter is
visible only if the Specify initial fluxes and Saturable core parameters
are selected.
Measurements
Select Winding voltages to measure the voltage across the winding
terminals of the Three-Phase Transformer block.
Select Winding currents to measure the current flowing through the
windings of the Three-Phase Transformer block.
Select Fluxes and excitation currents (Im + IRm) to measure the flux
linkage, in volt seconds (V.s), and the total excitation current including
iron losses modeled by Rm (for saturable transformers only).
Select Fluxes and magnetization currents (Im) to measure the flux
linkage, in volt seconds (V.s), and the magnetization current, in amperes
(A), not including iron losses modeled by Rm (for saturable transformers
only).
Select All measurements (V, I, Flux) to measure the winding voltages,
currents, magnetization currents, and the flux linkages.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurements are identified by a label
followed by the block name.
5-343
Three-Phase Transformer (Two Windings)
If the Winding 1 ABC connection parameter is set to Y, Yn, or Yg, the
labels are as follows).
Measurement
Label
Winding 1 voltages
Uan_w1:, Ubn_w1:, Ucn_w1:
or
Uag_w1:, Ubg_w1:, Ucg_w1:
Winding 1 currents
Ian_w1:, Ibn_w1:, Icn_w1:
or
Iag_w1:, Ibg_w1:, Icg_w1:
Fluxes
Flux_A:, Flux_B:, Flux_C:
Magnetization
currents
Imag_A:, Imag_B:, Imag_C:
Excitation currents
Iexc_A:, Iexc_B:, Iexc_C:
The same labels apply for winding 2, except that 1 is replaced by 2 in the
labels.
If the Winding 1 ABC connection parameter is set to Delta (D11) or
Delta (D1), the labels are as follows.
Example
5-344
Measurement
Label
Winding 1 voltages
Uab_w1:, Ubc_w1:, Uca_w1:
Winding 1 currents
Iab_w1:, Ibc_w1:, Ica_w1:
Flux linkages
Flux_A:, Flux_B:, Flux_C:
Magnetization currents
Imag_A:, Imag_B:, Imag_C:
Excitation currents
Iexc_A:, Iexc_B:, Iexc_C:
The power_transfo3ph circuit uses the Three-Phase Transformer block where
the saturable core is simulated. Both windings are connected in a Y grounded
Three-Phase Transformer (Two Windings)
configuration. Note that the neutral points of the two windings are internally
connected to the ground.
The 500 kV/ 230 kV saturable transformer is energized on the 500 kV system.
Remanent fluxes of 0.8 p.u., −0.4 p.u., and 0.4 p.u. have been specified
respectively for phases A, B, and C.
Run the simulation and observe inrush currents due to core saturation.
5-345
Three-Phase Transformer (Two Windings)
See Also
5-346
Linear Transformer, Multimeter, Saturable Transformer, Three-Phase
Transformer (Three Windings)
Three-Phase Transformer (Three Windings)
Purpose
5Three-Phase Transformer (Three Windings)
Library
Elements
Description
This block implements a three-phase transformer by using three single-phase
transformers with three windings. You can simulate the saturable core or not
simply by setting the appropriate check box in the parameter menu of the
block. See the Linear Transformer and Saturable Transformer block sections
for a detailed description of the electrical model of a single-phase transformer.
Implement a three-phase transformer with configurable winding connections
The three windings of the transformer can be connected in the following
manner:
•Y
• Y with accessible neutral (for windings 1 and 3 only)
• Grounded Y
• Delta (D1), delta lagging Y by 30 degrees
• Delta (D11), delta leading Y by 30 degrees
Note The D1 and D11 notations refer to the following clock convention. It
assumes that the reference Y voltage phasor is at noon (12) on a clock display.
D1 and D11 refer respectively to 1 PM (delta voltages lagging Y voltages by
−30 degrees) and 11 AM (delta voltages leading Y voltages by +30 degrees).
The block takes into account the connection type you select, and the icon of the
block is automatically updated. An input port labeled N is added to the block if
you select the Y connection with accessible neutral for winding 1. If you ask for
an accessible neutral on winding 3, an extra outport port labeled n3 is
generated.
The saturation characteristic, when activated, is the same as the one described
for the Saturable Transformer block, and the icon of the block is automatically
updated. If the fluxes are not specified, the initial values are automatically
adjusted so that the simulation starts in steady state.
The leakage inductances and resistance of each winding are given in p.u. based
on the transformer nominal power Pn and on the nominal voltage of the
5-347
Three-Phase Transformer (Three Windings)
winding (V1, V2, or V3). For an explanation of per units, refer to the Linear
Transformer and Saturable Transformer block reference pages.
Dialog Box and
Parameters
Nominal power and frequency
The nominal power rating, in volt-amperes (VA), and nominal frequency,
in hertz (Hz), of the transformer.
Winding 1 (ABC) connection
The winding connection for winding 1.
5-348
Three-Phase Transformer (Three Windings)
Winding parameters
The phase-to-phase nominal voltage in volts RMS, resistance, and leakage
inductance in p.u. for winding 1.
Winding 2 (abc2) connection
The winding connection for winding 2.
Winding parameters
The phase-to-phase nominal voltage in volts RMS, resistance, and leakage
inductance in p.u. for winding 2.
Winding 3 (abc3) connection
The winding connection for winding 3.
Winding parameters
The phase-to-phase nominal voltage in volts RMS, resistance, and leakage
inductance in p.u. for winding 3.
Saturable core
If selected, implements a saturable three-phase transformer.
Magnetization resistance Rm
The magnetization resistance Rm, in p.u.
Magnetization reactance Lm
The magnetization inductance Lm, in p.u., for a nonsaturable core. The
Magnetization reactance Lm parameter is not visible in the dialog box if
the Saturable core parameter is selected.
Saturation characteristic
This parameter is visible only if the Saturable core parameter is selected.
The saturation characteristic for the saturable core. Specify a series of
current/ flux pairs (in p.u.) starting with the pair (0,0).
Simulate hysteresis
Select to model a saturation characteristic including hysteresis instead of
a single-valued saturation curve.
Hysteresis data MAT file
This parameter is visible only if the Simulate hysteresis parameter is
selected.
5-349
Three-Phase Transformer (Three Windings)
Specify a .mat file containing the data to be used for the hysteresis model.
When you open the Hysteresis Design tool of the Powergui, the default
hysteresis loop and parameters saved in the hysteresis .mat file are
displayed. Use the File —> Load a model menu of the Hysteresis Design
tool to load another .mat file. Use the File —> Save this model menu of
the Hysteresis Design tool to save your model in a new .mat file.
Specify initial fluxes
If selected, the initial fluxes are defined by the [phi0A phi0B phi0C]
parameter.
[phi0A phi0B phi0C]
Specifies initial fluxes for each phase of the transformer. This parameter is
visible only if the Specify initial fluxes and Saturable core parameters
are selected.
Measurements
Select Winding voltages to measure the voltage across the winding
terminals of the Three-Phase Transformer block.
Select Winding currents to measure the current flowing through the
windings of the Three-Phase Transformer block.
Select Fluxes and excitation currents (Im + IRm) to measure the flux
linkage, in volt seconds (V.s), and the total excitation current including
iron losses modeled by Rm (for saturable transformers only).
Select Fluxes and magnetization currents (Im) to measure the flux
linkage, in volt seconds (V.s), and the magnetization current, in amperes
(A), not including iron losses modeled by Rm (for saturable transformers
only).
Select All measurements (V, I, Flux) to measure the winding voltages,
currents, magnetization currents, and the flux linkages.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurements are identified by a label
followed by the block name.
5-350
Three-Phase Transformer (Three Windings)
If the Winding 1 ABC connection parameter is set to Y, Yn, or Yg, the
labels are as follows.
Measurement
Label
Winding 1 voltages
Uan_w1:, Ubn_w1:, Ucn_w1:
or
Uag_w1:, Ubg_w1:, Ucg_w1:
Winding 1 currents
Ian_w1:, Ibn_w1:, Icn_w1:
or
Iag_w1:, Ibg_w1:, Icg_w1:
Flux linkages
Flux_A:, Flux_B:, Flux_C:
Magnetization currents
Imag_A:, Imag_B:, Imag_C:
Excitation currents
Iexc_A:, Iexc_B:, Iexc_C:
The same labels apply for winding 2 and winding 3, except that the 1 is
replaced by 2 or by 3 in the labels.
If the Winding 1 ABC connection parameter is set to Delta (D11) or
Delta (D1), the labels are as follows.
Measurement
Label
Winding 1 voltages
Uab_w1:, Ubc_w1:, Uca_w1:
Winding 1 currents
Iab_w1:, Ibc_w1:, Ica_w1:
Flux linkages
Flux_A:, Flux_B:, Flux_C:
Magnetization currents
Imag_A:, Imag_B:, Imag_C:
Excitation currents
Iexc_A:, Iexc_B:, Iexc_C:
5-351
Three-Phase Transformer (Three Windings)
Example
The power_transfo3wdn circuit uses two Three-Phase Transformer blocks.
Two Multimeter blocks are used to measure the phase A voltage (or AB for
delta connections) of each winding.
See Also
Linear Transformer, Multimeter, Saturable Transformer, Three-Phase
Transformer (Two Windings)
5-352
Three-Phase V-I Measurement
Purpose
5Three-Phase V-I Measurement
Library
Measurements
Description
The Three-Phase V-I Measurement block is used to measure three-phase
voltages and currents in a circuit. When connected in series with three-phase
elements, it returns the three phase-to-ground or phase-to-phase voltages and
the three line currents.
Measure three-phase currents and voltages in a circuit
The block can output the voltages and currents in per unit (p.u.) values or in
volts and amperes. If you choose to measure the voltages and currents in p.u.,
the Three-Phase V-I Measurement block does the following conversions:
V abc (volts)
V abc (p.u.) = --------------------------------------V baseLL
 --------------------
-⋅ 2


3
I abc (amperes)
I abc (p.u.) = --------------------------------------------------P base


 ---------------------------------- ⋅ 2
 V baseLL ⋅ 3

where VbaseLL is the base line-to-line voltage in volts RMS and Pbase is the
three-phase base power in volts-amperes. The two base values VbaseLL and
Pbase are specified in the Three-Phase Measurement block menu.
The steady-state voltage and current phasors measured by the Three-Phase
V-I Measurement block can be obtained from the Powergui block by selecting
Steady-State Voltages and Currents. The phasor magnitudes displayed in
the Powergui stay in peak or RMS values even if the output signals are
converted to p.u.
5-353
Three-Phase V-I Measurement
Dialog Box and
Parameters
Voltage measurement
Select no if you do not want to measure three-phase voltage. Select
phase-to-ground if you want to measure the phase-to-ground voltages.
Select phase-to-phase if you want to measure the phase-to-phase
voltages.
Use a label
If selected, the voltage measurements are sent to a labeled signal. Use a
From block to read the voltages. The Goto tag of the From block must
5-354
Three-Phase V-I Measurement
correspond to the label specified by the Signal label parameter. If not
selected, the voltage measurements are available via the Vabc output of the
block.
Signal label
Specifies a label tag for the voltage measurements.
Voltages in p.u.
If selected, the three-phase voltages are measured in p.u. Otherwise they
are measured in volts.
Base voltage (Vrms phase-phase)
The base voltage, in volts RMS, used to convert the measured voltages in
p.u. The Base voltage (Vrms phase-phase) parameter is not visible in the
dialog box if Voltages in p.u. is not selected.
Current measurement
Select yes if you want to measure the three-phase currents that flow
through the block.
Use a label
If selected, the current measurements are sent to a labeled signal. Use a
From block to read the currents. The Goto tag of the From block must
correspond to the label specified by the Signal label parameter. If not
selected, the current measurements are available via the Iabc output of the
block.
Signal label
Specifies a label tag for the current measurements.
Currents in p.u.
If selected, the three-phase currents are measured in p.u. Otherwise they
are measured in amperes.
Base power (VA 3 phase)
The three-phase base power, in volt-ampere (VA), used to convert the
measured currents in p.u. The Base power (VA 3 phase) parameter is not
visible in the dialog box if Currents in p.u. is not selected.
5-355
Three-Phase V-I Measurement
Output signal
Specifies the format of the measured signals when the block is used in a
phasor simulation. The Output signal parameter is disabled when the
block is not used in a phasor simulation. The phasor simulation is activated
by a Powergui block placed in the model.
Set to Complex to output the measured voltages and currents as complex
values. The outputs are complex signals.
Set to Real-Imag to output the real and imaginary parts of the measured
voltages and currents.
Set to Magnitude-Angle to output the magnitudes and angles of the
measured voltages and currents.
Set to Magnitude to output the magnitudes of the measured voltages and
currents. The output is a scalar value.
Inputs and
Outputs
A, B, C
a, b, c
Inputs A, B, C and outputs a, b, c are the phase connectors of the
measurement block. Connect the Three-Phase V-I Measurement block in
series with other three-phase electrical blocks.
Vabc
Simulink port Output 1 is a vector containing the three measured
phase-to-ground or phase-to-phase voltages. The Vabc output disappears
when the Use a label parameter is selected or when the Voltage
measurement menu is set to no.
Iabc
Simulink port Output 2 is a vector containing the three measured line
currents. The Iabc output disappears when the Use a label parameter is
selected or when the Current measurement menu is set to no.
Example
5-356
See the power_3phseriescomp demo for a circuit using the Three-Phase V-I
Measurement block.
Thyristor
Purpose
5Thyristor
Library
Power Electronics
Description
The thyristor is a semiconductor device that can be turned on via a gate signal.
The thyristor model is simulated as a resistor Ron, an inductor Lon, and a DC
voltage source Vf, connected in series with a switch. The switch is controlled by
a logical signal depending on the voltage Vak, the current Iak, and the gate
signal g.
Implement a thyristor model
K
Cathode
g
Iak
SW
Ron
Gate
Thyristor
Logic
Lon
Vf
+
+
A
Anode
A
−
Vak
−
K
Vak
Iak
g
The Thyristor block also contains a series Rs-Cs snubber circuit that can be
connected in parallel with the thyristor device.
The static VI characteristic of this model is shown below.
Iak
Off state
On state
Off-to-On
if g > 0
Il
Vf
Off state
Vak
5-357
Thyristor
The thyristor device turns on when the anode-cathode Vak voltage is greater
than Vf and a positive pulse signal is applied at the gate input (g > 0). The pulse
height must be greater than 0 and last long enough to allow the thyristor anode
current to become larger than the latching current Il.
The thyristor device turns off when the current flowing in the device becomes
0 (Iak = 0) and a negative voltage appears across the anode and cathode for at
least a period of time equal to the turnoff time Tq. If the voltage across the
device becomes positive within a period of time less than Tq, the device turns
on automatically even if the gate signal is low (g = 0) and the anode current is
less than the latching current. Furthermore, if during turn-on, the device
current amplitude stays below the latching current level specified in the dialog
box, the device turns off after the gate signal level becomes low (g = 0).
The turnoff time Tq represents the carrier recovery time: it is the time interval
between the instant the anode current has decreased to 0 and the instant when
the thyristor is capable of withstanding positive voltage Vak without turning
on again.
Dialog Boxes
and
Parameters
5-358
Thyristor Model and Detailed Thyristor Model
In order to optimize simulation speed, two models of thyristors are available:
the thyristor model and the detailed thyristor model. For the thyristor model,
the latching current Il and recovery time Tq are assumed to be 0.
Thyristor
Resistance Ron
The thyristor internal resistance Ron, in ohms (Ω). The Resistance Ron
parameter cannot be set to 0 when the Inductance Lon parameter is set
to 0.
Inductance Lon
The thyristor internal inductance Lon, in henries (H). The Inductance
Lon parameter cannot be set to 0 when the Resistance Ron parameter is
set to 0.
Forward voltage Vf
The forward voltage of the thyristor, in volts (V).
5-359
Thyristor
Initial current Ic
When the Inductance Lon parameter is greater than 0, you can specify an
initial current flowing in the thyristor. It is usually set to 0 in order to start
the simulation with the thyristor blocked.
You can specify an Initial current Ic value corresponding to a particular
state of the circuit. In such a case all states of the linear circuit must be set
accordingly. Initializing all states of a power electronic converter is a
complex task. Therefore, this option is useful only with simple circuits.
Snubber resistance Rs
The snubber resistance, in ohms (Ω). Set the Snubber resistance Rs
parameter to inf to eliminate the snubber from the model.
Snubber capacitance Cs
The snubber capacitance in farads (F). Set the Snubber capacitance Cs
parameter to 0 to eliminate the snubber, or to inf to get a resistive
snubber.
Show measurement port
If selected, add a Simulink output to the block returning the thyristor
current and voltage.
5-360
Thyristor
Latching current Il
The latching current of the detailed thyristor model, in amperes (A).
Turn-off time Tq
The turnoff time Tq of the detailed thyristor model, in amperes (A).
Inputs and
Outputs
The Thyristor block consists of two inputs and two outputs. The first input and
output are the thyristor terminals connected respectively to anode (a) and
5-361
Thyristor
cathode (k). The second input (g) is a Simulink logical signal applied to the gate.
The second output (m) is a Simulink signal output vector [Iak Vak] returning
the thyristor current and voltage.
Assumptions
The Thyristor block implements a macromodel of the real thyristor. It does not
and Limitations take into account either the geometry of the device or complex physical
processes that model the behavior of the device [1, 2]. The forward breakover
voltage and the critical value of the derivative of the reapplied anode-cathode
voltage are not considered by the model.
Depending on the value of Inductance Lon, the Thyristor block is modeled
either as a current source (Lon > 0) or as a variable topology circuit (Lon = 0).
See the “Improving Simulation Performance” chapter for more details.
As the Thyristor block is modeled as a current source, it cannot be connected in
series with an inductor, a current source, or an open circuit, unless a snubber
circuit is used.
When simulating a continuous model, you must use a stiff integrator algorithm
to simulate circuits containing thyristors. ode23tb or ode15s with default
parameters usually gives the best simulation speed.
The inductance Lon is forced to 0 if you choose to discretize your circuit.
Example
In the power_thyristor demo a single-pulse thyristor rectifier is used to feed
an RL load. The gate pulses are obtained from a pulse generator synchronized
on the source voltage. The following parameters are used:
R
1 Ω
L
10 mH
Thyristor block:
5-362
Ron
0.001 W
Lon
0 H
Vf
0.8 V
Rs
20 Ω
Cs
4e-6 F
Thyristor
The firing angle is varied by a pulse generator synchronized on the voltage
source. Run the simulation and observe the load current and load voltage, as
well as the thyristor current and voltage.
5-363
Thyristor
References
[1] Rajagopalan, V., Computer-Aided Analysis of Power Electronic Systems,
Marcel Dekker, Inc., New York, 1987.
[2] Mohan, N., T.M. Undeland, and W.P. Robbins, Power Electronics:
Converters, Applications, and Design, John Wiley & Sons, Inc., New York,
1995.
See Also
5-364
Diode, Universal Bridge
Timer
Purpose
5Timer
Library
Extras/Control Blocks, Extras/Discrete Control Blocks
Description
The Timer block generates a signal changing at specified transition times. Use
this block to generate a logical signal (0 or 1 amplitudes) and control the
opening and closing times of power switches like the Breaker block and the
Ideal Switch block. You can also use this block to generate a signal whose
amplitude changes by steps at specified transition times.
Generate a signal changing at specified transition times
Dialog Box and
Parameters
Time(s)
The transition times, in seconds, when the output of the block changes its
value as defined by the Amplitude parameter. The Time(s) parameter
must be a vector of the same length as the vector defined in the Amplitude
parameter. The definition of the time 0 is optional. If a signal is not
specified at time 0, the output is kept at zero until the first transition time
specified in the Amplitude vector.
Amplitude
The vector of amplitudes of signal to be generated by the Timer block. The
amplitude is kept constant between transition times defined in the Time(s)
vector.
5-365
Timer
Inputs and
Outputs
The output is a signal changing by steps at specified transition times.
Example
See the power_breaker model for a circuit using the Timer block to control a
circuit breaker.
5-366
Total Harmonic Distortion
Purpose
5Total Harmonic Distortion
Library
Extras/Measurements
Measure the total harmonic distortion (THD) of a signal
A discrete version of this block is available in the Extras/Discrete
Measurements library.
Description
The Total Harmonic Distortion block measures the total harmonic distortion
(THD) of a periodic distorted signal. The signal can be a measured voltage or
current.
The THD is defined as the root mean square (RMS) value of the total harmonics
of the signal, divided by the RMS value of its fundamental signal. For example,
for currents, the THD is defined as
IH
total harmonic distortion (THD) = ----IF
where
IH =
2
2
I2 + I3 + … + In
2
I n : RMS value of the harmonic n
I F : RMS value of the fundamental current
It follows that the THD has a value comprised between zero and 1. It is null for
a pure sinusoidal voltage or current.
5-367
Total Harmonic Distortion
Dialog Box and
Parameters
Fundamental frequency
The frequency, in hertz, of the fundamental signal.
Inputs and
Outputs
5-368
Connect to the first input the voltage or current you want to measure the total
harmonic distortion. The output returns the THD of the input signal.
Universal Bridge
Purpose
5Universal Bridge
Library
Power Electronics
Description
The Universal Bridge block implements a universal three-phase power
converter that consists of up to six power switches connected in a bridge
configuration. The type of power switch and converter configuration are
selectable from the dialog box.
Implement a universal power converter with selectable topologies and power
electronic devices
The Universal Bridge block allows simulation of converters using both
naturally commutated (or line-commutated) power electronic devices (diodes or
thyristors) and forced-commutated devices (GTO, IGBT, MOSFET).
The Universal Bridge block is the basic block for building two-level
voltage-sourced converters (VSC).
Diode and Thyristor bridges:
+
+
1
3
5
1
3
5
4
6
2
A
B
C
A
B
C
4
6
2
−
−
5-369
Universal Bridge
GTO-Diode and IGBT-Diode bridges:
+
1
3
+
5
A
B
C
1
3
5
2
4
6
A
B
C
2
6
4
−
−
MOSFET-Diode and Ideal Switch bridges:
+
1
3
+
5
A
B
C
1
3
5
2
4
6
A
B
C
2
4
6
−
−
Note The device numbering is different if the power electronic devices are
naturally commutated or forced-commutated. For a naturally commutated
converter, numbering follows the natural order of commutation.
5-370
Universal Bridge
Dialog Box and
Parameters
Number of bridge arms
Set to 1 or 2 to get a single-phase converter (two or four switching devices).
Set to 3 to get a three-phase converter connected in Graetz bridge
configuration (six switching devices).
Snubber resistance Rs
The snubber resistance, in ohms (Ω). Set the Snubber resistance Rs
parameter to inf to eliminate the snubbers from the model.
Snubber capacitance Cs
The snubber capacitance, in farads (F). Set the Snubber capacitance Cs
parameter to 0 to eliminate the snubbers, or to inf to get a resistive
snubber.
5-371
Universal Bridge
In order to avoid numerical oscillations when your system is discretized,
you need to specify Rs and Cs snubber values for diode and thyristor
bridges. For forced-commutated devices (GTO, IGBT, or MOSFET), the
bridge operates satisfactorily with purely resistive snubbers as long as
firing pulses are sent to switching devices.
If firing pulses to forced-commutated devices are blocked, only antiparallel
diodes operate, and the bridge operates as a diode rectifier. In this
condition appropriate values of Rs and Cs must also be used.
When the system is discretized, use the following formulas to compute
approximate values of Rs and Cs:
Ts
Rs > 2 ------Cs
Pn
Cs < --------------------------------------2
1000 ( 2πf )Vn
where
P n = Nominal power of single or three phase converter (VA)
Vn = Nominal line-to-line AC voltage (Vrms)
f = Fundamental frequency (Hz)
T s = Sample Time (s)
These Rs and Cs values are derived from the following two criteria:
- The snubber leakage current at fundamental frequency is less than 0.1%
of nominal current when power electronic devices are not conducting.
- The RC time constant of snubbers is higher than two times the sample
time Ts.
These Rs and Cs values that guarantee numerical stability of the
discretized bridge can be different from actual values used in a physical
circuit.
5-372
Universal Bridge
Power electronic device
Select the type of power electronic device to use in the bridge.
Ron
Internal resistance of the selected device, in ohms (Ω).
Lon
Internal inductance, in henries (H), for the diode or the thyristor device.
When the bridge is discretized, the Lon parameter must be set to zero.
Forward voltage Vf
This parameter is available only when the selected Power electronic
device is Diodes or Thyristors.
Forward voltage, in volts (V), across the device when it is conducting.
Forward voltages [Device Vf, Diode Vfd]
This parameter is available when the selected Power electronic device is
GTO/Diodes or IGBT/Diodes.
Forward voltages, in volts (V), of the forced-commutated devices (GTO,
MOSFET, or IGBT) and of the antiparallel diodes.
[Tf (s) Tt (s)]
Fall time Tf and tail time Tt, in seconds (s), for the GTO or the IGBT
devices.
Measurements
Select Device voltages to measure the voltages across the six power
electronic device terminals.
Select Device currents to measure the currents flowing through the six
power electronic devices. If antiparallel diodes are used, the measured
current is the total current in the forced-commutated device (GTO,
MOSFET, or IGBT) and in the antiparallel diode. A positive current
therefore indicates a current flowing in the forced-commutated device and
a negative current indicates a current flowing in the diode. If snubber
devices are defined, the measured currents are the ones flowing through
the power electronic devices only.
Select UAB UBC UCA UDC voltages to measure the terminal voltages (AC
and DC) of the Universal Bridge block.
5-373
Universal Bridge
Select All voltages and currents to measure all voltages and currents
defined for the Universal Bridge block.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements
menu of the Multimeter block, the measurement is identified by a label
followed by the block name.
Inputs and
Outputs
Measurement
Label
Device voltages
Usw1:, Usw2:,Usw3:,Usw4:,Usw5:,Usw6:
Branch current
Isw1:, Isw2:, Isw3:, Isw4:, Isw5:, Isw6:
Terminal voltages
Uab:, Ubc):, Uca:, Udc:
A B C +
The three AC connectors and the two DC connectors of the bridge.
g
The gate input, except for the case of a diode bridge. The g input accepts a
Simulink vector gating signal containing two, four, or six pulse trains,
depending on the number of bridge arms (1, 2, or 3). The gating signals are
sent to the power switches according to the number shown in the diagrams
above.
Note The pulse ordering in the vector of the gate signals corresponds to the
switch number indicated in the six circuits shown in the Description section.
For the diode and thyristor bridges, the pulse ordering corresponds to the
natural order of commutation. For all other forced-commutated switches,
pulses are sent to upper and lower switches of phases A, B, and C with the
following order: [A upper A lower B upper B lower C upper C lower].
Assumptions
Universal Bridge blocks can be discretized for use in a discrete time step
and Limitations simulation. In this case, the internal commutation logic of the Universal Bridge
takes care of the commutation between the power switches and the diodes in
the converter arms.
5-374
Universal Bridge
Note In a converter built with individual forced-commutated power
components (GTOs, MOSFETs, IGBTs), discretization of the model is not
available. See the “Improving Simulation Performance” chapter for more
details.
Example
The power_bridges demo illustrates the use of two Universal Bridge blocks in
an ac/dc/ac converter consisting of a rectifier feeding an IGBT inverter through
a DC link. The inverter is pulse-width modulated (PWM) to produce a
three-phase 50 Hz sinusoidal voltage to the load. In this example the inverter
chopping frequency is 2000 Hz.
Rectifier
Filter
L
60 Hz
power
grid
C
Inverter
+
Vdc
−
Filters
A
Three-phase load
B
C
DC link
The IGBT inverter is controlled with a PI regulator in order to maintain a 1 p.u.
voltage (380 Vrms, 50 Hz) at the load terminals.
5-375
Universal Bridge
A Multimeter block is used to observe commutation of currents between diodes
1 and 3 in the diode bridge and between IGBT/Diodes switches 1 and 2 in the
IGBT bridge.
Start simulation. After a transient period of approximately 40 ms, the system
reaches a steady state. Observe voltage waveforms at DC bus, inverter output,
and load on Scope1. The harmonics generated by the inverter around multiples
of 2 kHz are filtered by the LC filter. As expected the peak value of the load
voltage is 537 V (380 V RMS).
In steady state the mean value of the modulation index is m = 0.77, and the
mean value of the DC voltage is 780 V. The fundamental component of 50 Hz
voltage buried in the chopped inverter voltage is therefore
Vab = 780 V * 0.612 * 0.80 = 382 V RMS
Observe diode currents on trace 1 of Scope2, showing commutation from diode
1 to diode 3. Also observe on trace 2 currents in switches 1 and 2 of the
IGBT/Diode bridge (upper and lower switches connected to phase A). These two
currents are complementary. A positive current indicates a current flowing in
the IGBT, whereas a negative current indicates a current flowing in the
antiparallel diode.
5-376
Universal Bridge
5-377
Universal Bridge
See Also
5-378
Diode, GTO, Ideal Switch, IGBT, MOSFET, Multimeter,Three-Level Bridge,
Thyristor
Voltage Measurement
Purpose
5Voltage Measurement
Library
Measurements
Description
The Voltage Measurement block measures the instantaneous voltage between
two electric nodes. The output provides a Simulink signal that can be used by
other Simulink blocks.
Measure a voltage in a circuit
Dialog Box and
Parameters
Output signal
Specifies the format of the output signal when the block is used in a phasor
simulation. The Output signal parameter is disabled when the block is not
used in a phasor simulation. The phasor simulation is activated by a
Powergui block placed in the model.
Set to Complex to output the measured current as a complex value. The
output is a complex signal.
Set to Real-Imag to output the real and imaginary parts of the measured
current. The output is a vector of two elements.
Set to Magnitude-Angle to output the magnitude and angle of the
measured current. The output is a vector of two elements.
Set to Magnitude to output the magnitude of the measured current. The
output is a scalar value.
5-379
Voltage Measurement
Example
The power_voltmeasure demo uses three Voltage Measurement blocks to read
voltages.
See Also
Current Measurement, Powergui, Three-Phase V-I Measurement
5-380
Zigzag Phase-Shifting Transformer
Purpose
5Zigzag Phase-Shifting Transformer
Library
Elements
Description
The Zigzag Phase-Shifting Transformer block implements a three-phase
transformer with a primary winding connected in a zigzag configuration and a
configurable secondary winding. The model uses three single-phase, threewinding transformers. The primary winding connects the windings 1 and 2 of
the single-phase transformers in a zigzag configuration. The secondary
winding uses the windings 3 of the single phase transformers, and they can be
connected in one of the following ways:
Implement a zigzag phase-shifting transformer with a configurable secondary
winding connection
•Y
• Y with accessible neutral
• Grounded Y
• Delta (D1), delta lagging Y by 30 degrees
• Delta (D11), delta leading Y by 30 degrees
Note The D1 and D11 notations refer to the following clock convention. It
assumes that the reference Y voltage phasor is at noon (12) on a clock display.
D1 and D11 refer respectively to 1 PM (lagging Y by −30 degrees) and 11 AM
(leading Y by +30 degrees).
If the secondary winding is connected in Y, the secondary phase voltages are
leading or lagging the primary voltages by the Phi phase angle specified in the
parameters of the block. If the secondary winding is connected in delta (D11),
an additional phase shift of +30 degrees is added to the phase angle. If the
secondary winding is connected in delta (D1), a phase shift of −30 degrees is
added to the phase angle.
The block takes into account the connection type you have selected and the icon
of the block is automatically updated. An output port labeled N is added to the
block if you select the Y connection with accessible neutral for the secondary
winding.
5-381
Zigzag Phase-Shifting Transformer
The saturation characteristic, when activated, is the same as the one described
for the Saturable Transformer block.
Dialog Box and
Parameters
Nominal power and frequency
The nominal power rating, in volt-amperes (VA), and nominal frequency,
in hertz (Hz), of the transformer.
5-382
Zigzag Phase-Shifting Transformer
Primary (zigzag) nominal voltage Vp
The phase-to-phase nominal voltage in volts RMS, for the primary winding
of the transformer.
Secondary nominal voltage and phase shift
The phase-to-phase nominal voltage, in volts RMS, and the phase shift, in
degrees, for the secondary winding of the transformer.
Secondary winding (abc) connection
The winding connection for the secondary winding.
Winding 1 (zigzag): [R1 L1]
The resistance and leakage inductance of the windings 1 of the
single-phase transformers used to implement the primary winding of the
Zigzag Phase-Shifting Transformer.
Winding 2 (zigzag): [R2 L2]
The resistance and leakage inductance of the windings 2 of the
single-phase transformers used to implement the primary winding of the
Zigzag Phase-Shifting Transformer.
Winding 3 (secondary): [R1 L1]
The resistance and leakage inductance of the windings 3 of the
single-phase transformers used to implement the secondary winding of the
Zigzag Phase-Shifting Transformer.
Saturable core
If selected, implements a saturable core.
Magnetization resistance Rm
This parameter is visible only if the Saturable core check box is selected.
The magnetization resistance Rm, in p.u, when the saturation is
simulated.
Magnetizing branch: [Rm(p.u.) Lm(p.u.)]
The Magnetizing branch parameter is not visible in the dialog box if the
Saturable core check box is selected.
The magnetization resistance Rm and inductance Lm, in p.u., when the
saturation is not simulated.
5-383
Zigzag Phase-Shifting Transformer
Saturation characteristic
This parameter is visible only if the Saturable core check box is selected.
The saturation characteristic for the saturable core. Specify a series of
current/ flux pairs (in p.u.) starting with the pair (0,0).
Measurements
Select Winding voltages to measure the voltage across the winding
terminals of the Three-Phase Transformer block.
Select Winding currents to measure the current flowing through the
windings of the Three-Phase Transformer block.
Select Fluxes and excitation currents (Im + IRm) to measure the flux
linkage, in volt-seconds (V.s), and the total excitation current including
iron losses modeled by Rm (for saturable transformers only).
Select Fluxes and magnetization currents (Im) to measure the flux
linkage, in volt-seconds (V.s), and the magnetization current, in amperes
(A), not including iron losses modeled by Rm (for saturable transformers
only).
Select All measurements (V, I, Flux) to measure the winding voltages,
currents, magnetization currents, and the flux linkages.
Place a Multimeter block in your model to display the selected
measurements during the simulation. In the Available Measurements list
box of the Multimeter block, the measurements are identified by a label
followed by the block name.
The labels used in the Multimeter are as follows.
Measurement
Label
Phase voltages of primary (zigzag)
UA:, UB:, UC:
Phase currents of primary (zigzag)
IA:, IB:, IC:
Phase voltages of secondary (Y, Yn or
Yg)
Uan:, Ubn:, Ucn:
or
Uag:, Ubg:, Ucg:
Phase voltages of secondary (delta)
5-384
Uab:, Ubc:, Uca:
Zigzag Phase-Shifting Transformer
Measurement (Continued)
Label (Continued)
Phase currents of secondary (Y, Yn,
or Yg)
Ian:, Ibn:, Icn:
or
Iag:, Ibg:, Icg:
Example
Phase currents of secondary (delta)
Iab:, Ibc:, Ica:
Fluxes
Flux_a:, Flux_b:,
Flux_c:
Excitation currents
Iexc_a:, Iexc_b:,
Iexc_c:
Magnetization currents
Imag_a:, Imag_b:,
Imag_c:
See the help text of the power_48pulsegtoconverter demo.
In this model, a 48-pulse GTO converter is built with four Three-Level Bridge
blocks and four Zigzag Phase-Shifting Transformer blocks. Harmonic
neutralization is obtained by use of appropriate phase shifts introduced by the
Zigzag connections (+7.5/−7.5 degrees) and of secondary winding connections
(Y or Delta).
See Also
Multimeter, Three-Phase Transformer (Three Windings)
5-385
Zigzag Phase-Shifting Transformer
5-386
6
SimPowerSystems
Command Reference
This table indicates the tasks performed by the commands described in this chapter.
Command
Purpose
power_analyze
Analyze an electric circuit built with SimPowerSystems
power_init
Set the initial states values of an electrical circuit
power_statespace
Compute the linear state-space model of an electrical circuit
power_analyze
Purpose
6power_analyze
Analyze an electric circuit built with SimPowerSystems
Syntax
sps = power_analyze('sys','structure')
sps = power_analyze('sys','sort')
sps = power_analyze('sys','ss')
[A,B,C,D,x0,states,inputs,outputs,uss,xss,yss,freqyss,Hlin]=
power_analyze( sys );
power_analyze('sys','net')
Description
The power_analyze command computes the equivalent state-space model of
the specified electrical model built with SimPowerSystems. It evaluates the A,
B, C, D standard matrices of the state-space system described by the equations
x· = Ax + Bu
y = Cx + Du
where the state variables contained in the x vector are the inductor currents
and capacitor voltages. Nonlinear elements are simulated by current sources
driven by the voltages across the nonlinear elements.
The inputs of the system contained in the u vector are the voltage and current
sources plus the current sources simulating the nonlinear elements. The
outputs of the system contained in the y vector are the voltage and current
measurements plus the voltages across the nonlinear elements.
The following conventions are used for inputs:
• Source current flowing in the arrow direction is positive.
• Positive source voltage is indicated by a + sign on the icon.
The sign conventions used for voltages and currents (state variables x and
measurement outputs y) are explained below.
Sign Conventions for Voltages and Currents
When you measure a current using a Current Measurement block, the positive
direction of current is indicated on the block icon (positive current flowing from
+ terminal to – terminal). Similarly, when you measure a voltage using a
Voltage Measurement block, the measured voltage is the voltage of the +
terminal with respect to the – terminal. However, when voltages and currents
6-2
power_analyze
of blocks from the Elements library are measured using the Multimeter block,
the voltage and current polarities are not so evident because blocks might have
been rotated and there are no signs indicating polarities on the block icons.
Unlike the Simulink signal lines and input and output ports, the Physical
Modeling connection lines and terminal ports of SimPowerSystems lack an
intrinsic directionality. The voltage and current polarities are determined
instead by the block orientation. To find out the block orientation, first click the
block to select it. Then enter the following command:
get_param(gcb, Orientation )
The following table gives the polarities of the currents and voltages measured
with the Multimeter block for single-phase and three-phase RLC elements
(branches or loads), surge arresters, and single-phase and three-phase
breakers. The table also indicates the polarities of the corresponding state
variables (inductor currents and capacitor voltages).
Block
Orientation
Positive Current
Direction
Measured
Voltage
right
left —> right
Vleft – Vright
left
right —> left
Vright – Vleft
down
top —> bottom
Vtop – Vbottom
up
bottom —> top
Vbottom – Vtop
The natural orientation of the blocks (that is, their orientation in the Element
library) is right for horizontal blocks and down for vertical blocks.
For single-phase transformers (linear or saturable), with the winding ports
appearing on the left and right sides, the winding voltages are the voltages of
the top terminal port with respect to the bottom terminal port, whatever the
block orientation (right or left). The winding currents are the currents entering
the top port.
For three-phase transformers, the voltage polarities and positive current
directions are indicated by the signal labels used in the Multimeter block. For
example, Uan_w2 = phase A-to-neutral voltage of the Y connected winding #2,
6-3
power_analyze
Iab_w1= winding current flowing from A to B in the delta connected winding
#1.
Output
Arguments:
Structure
6-4
sps = power_analyze('sys','structure') creates a structure array sps with
fields and values describing the model sys.
The fields of the structure array are defined in the following order.
Field
Description
circuit
Name of the model
states
char array of state variable names
inputs
char array of system input names
outputs
char array of system output names
A
nstates-by-nstates state-space A matrix
B
nstates-by-ninput state-space B matrix
C
noutput-by-nstates state-space C matrix
D
noutput-by-ninput state-space D matrix
x0
nstates-by-1 vector of initial conditions
Aswitch
A matrix including closed switches
Bswitch
B matrix including closed switches
Cswitch
C matrix including closed switches
Dswitch
D matrix including closed switches
x0switch
Vector of initial values of switch currents
uss
ninput-by-nfreq steady-state values of inputs
xss
nstates-by-nfreq steady-state values of states
yss
noutput-by-nfreq steady-state values of outputs
power_analyze
Field (Continued)
Description (Continued)
Hlin
nfreq-by-noutput-by-ninput transfer function of
impedances
frequencies
1-by-nfreq vector of input source frequencies
LoadFlow
Load flow information for circuits with machines
OscillatoryModes
Oscillatory modes of linear part of the system
The table uses the following conventions:
• nstates is the number of states.
• ninput is the number of inputs.
• noutput is the number of outputs.
• nfreq is the number of input source frequencies.
states is a string matrix containing names of the state variables. Each line of
states begins with a prefix Uc_ for capacitor voltages or Il_ for inductor
currents, followed by the name of the block in which the element (C or L) is
found. See “Sign Conventions for Voltages and Currents” on page 6-22 for
inductor current directions and capacitor voltage polarities. A string is added
to this prefix for blocks containing more than two inductances or capacitors.
For example, the Linear Transformer blocks produce four lines in the states
matrix, one for each of the three leakage inductances, with prefixes
Il_winding_x:, where x is the winding number of the transformer, and one
line for the magnetization inductance with the prefix Il_Lm:.
inputs is a string matrix containing names of the inputs of the system. Each
line of inputs begins with a prefix U_ for voltage sources or I_ for current
sources, followed by the name of the source block. A string can be added to the
prefix for blocks containing more than one source. For example, the
Synchronous Machine block produces two current inputs with prefixes I_A:
and I_B: (phase A and phase B machine currents).
outputs is a string matrix containing names of the outputs of the state-space
system (vector y). Each line of outputs begins with a prefix U_ for voltage
outputs or I_ for current outputs, followed by the name of the block that
produces the output. A string can be added to the prefix for blocks containing
6-5
power_analyze
more than one source. For example, the Synchronous Machine block produces
two voltage outputs with prefixes U_AB: and U_BC: (two machine
phase-to-phase voltages). See “Sign Conventions for Voltages and Currents” on
page 6-22 for current directions and voltage polarities.
A,B,C,D are the state-space matrices of the linear part of the model.
x0 is a vector containing the initial conditions of the state variables listed in the
states variable.
uss, xss, and yss are complex matrices containing the steady-state values of
inputs, states and outputs. If voltage and current sources all generate the same
frequency, these are column vectors. If sources with different frequencies are
used, each column of the matrices corresponds to a frequency contained in the
frequencies vector.
frequencies is a row vector containing the input source frequencies ordered
by increasing values.
Hlin is the complex transfer impedance three-dimensional array
(nfreq-by-noutput-by ninput) of the linear system corresponding to the
frequencies contained in the frequencies vector. For a particular frequency,
Hlin is defined by
yss(:,ifreq) = Hlin(ifreq,:,:) * uss(:,ifreq)
Output
Arguments:
Sort
6-6
sps = power_analyze('sys','sort') returns a structure array sps with the
following fields related to the interconnection of SimPowerSystems blocks in a
model. The fields are defined in the following order.
Field
Description
circuit
Name of the model
SampleTime
Sample time for discrete systems
RlcBranch
rlc matrix in the power_statespace format
RlcBranchNames
List of blocks containing the state variable
SourceBranch
Source matrix in the power_statespace format
SourceBranchNames
Names of the blocks defined as sources
power_analyze
Field (Continued)
Description (Continued)
InputNames
Names of the inputs of the system
OutputNames
Names of the outputs of the system
OutputExpressions
Output expression in the power_statespace
format
OutputMatrix
Output expression in matrix format (internal)
MeasurementBlocks
Names of the voltage and current measurement
blocks
[A,B,C,D,x0,states,inputs,outputs,uss,xss,yss,frequencies,Hlin] =
power_analyze('sys') returns the state-space calculations in separate
variables.
sps = power_analyze('sys','ss') creates a continuous state-space model of
the model sys with matrices A, B, C, D. You must have Control System Toolbox
installed for this option. The output is a state-space object.
Output
Arguments:
Net
power_analyze('sys','net') generates a netlist stored in a file, sys.net. The
file contains the node numbers automatically generated by power_analyze, as
well as parameter values of all linear elements. See the formats described in
the power_statespace reference page.
Example
Obtain the state-space matrices and steady-state voltages and currents for the
power_netsim2 circuit.
6-7
power_analyze
Recapture
R
R
The command
sps = power_analyze('power_netsim2','structure')
returns the state-space model in the sps structure variable.
sps.A =
1.0e+04 *
0
6.2500
-0.0083 -1.4250
sps.uss =
0
1000
sps.xss =
1.0e+02 *
4.8392 - 5.1314i
0.0310 + 0.0292i
sps.yss =
1.0e+02 *
8.5535 - 1.6287i
0
sps.inputs =
6-8
power_analyze
I_Breaker
U_Source
sps.outputs =
U_Breaker
I_Current Measurement
The inductor current of the 51 ohms-12 mH block and the capacitor voltage of
the 120 ohms-16 uF block are the two state variables in this circuit. The
Breaker block is a nonlinear element that is represented by a current source
(the first input) driven by the voltage across its terminals (the first output).
See Also
power_statespace, power_init, Powergui
6-9
power_init
Purpose
6power_init
Set the initial state values of a model built with SimPowerSystems
Syntax
power_init('sys','look')
power_init('sys','reset')
power_init('sys','steady')
power_init('sys','set',X0)
power_init('sys','setb','StateVariableName',Value)
Description
power_init('sys','look') displays the current initial states for the specified
system.
power_init('sys','reset') resets to zero the initial states of the specified
system.
power_init('sys','steady') sets the initial states of the specified system in
order to start the simulation in steady state.
power_init('sys','set',X0) sets the initial state values of the model sys to
the specified vector X0. The ordering of the states variable is given by the
power_init('sys','look') command.
power_init('sys','setb','StateVariableName',Value) sets the initial
state of the variable specified in 'StateVariableName' to Value. The names of
the variables states are given by the power_init('sys','look') command.
Example
The following commands reset to zero the initial state values of the
power_filter demo.
power_filter
power_init('power_filter','reset')
This command returns the names of the states and their current values.
power_init('power_filter','look')
Initial states for a particular case:
Il_5th Harm. Filter = 0
Uc_5th Harm. Filter = 0
Il_Zsource
= 0
See Also
6-10
power_analyze, Powergui
power_statespace
Purpose
6power_statespace
Synopsis
You must call power_statespace with a minimum of seven input arguments.
Compute the state-space model of a linear electrical circuit
[A,B,C,D,states,x0,x0sw,rlsw,u,x,y,freq,Asw,Bsw,Csw,Dsw,Hlin] =
power_statespace(rlc,switches,source,line_dist,yout,y_type,unit)
You can also specify optional arguments. To use these optional arguments, the
number of input arguments must be 12, 13, 14 or 16.
[A,B,C,D,states,x0,x0sw,rlsw,u,x,y,freq,Asw,Bsw,Csw,Dsw,Hlin] =
power_statespace(rlc,switches,source,line_dist,yout,y_type,unit,
net_arg1,net_arg2,net_arg3,...,netsim_flag,fid_outfile,
freq_sys,ref_node,vary_name,vary_val)
Description
The power_statespace command computes the state-space model of a linear
electrical circuit expressed as
·
x = Ax + Bu
y = Cx + Du
where x is the vector of state-space variables (inductor currents and capacitor
voltages), u is the vector of voltage and current inputs, and y is the vector of
voltage and current outputs.
When you build a circuit from SimPowerSystems blocks of the powerlib
library, power_statespace is automatically called by the power_analyze
command. power_statespace is also available as a stand-alone command for
expert users. This allows you to generate state-space models without using the
SimPowerSystems block modeling interface and to access options that are not
available through powerlib. For example, using power_statespace, you can
model transformers and mutual inductances with more than three windings.
The linear circuit can contain any combination of voltage and current sources,
RLC branches, multiwinding transformers, mutually coupled inductances, and
switches. The state variables are inductor currents and capacitor voltages.
The state-space representation (matrices A,B,C,D, and vector x0) computed by
power_statespace can then be used in a Simulink system, via a State-Space
block, to perform simulation of the electrical circuit (see the “Example” on
page 6-22). Nonlinear elements (mechanical or power electronic switches,
6-11
power_statespace
transformer saturation, machines, distributed parameter lines, etc.) can be
connected to the linear circuit.
These Simulink models are interfaced with the linear circuit through voltage
outputs and current inputs of the state-space model. You can find the models
of the nonlinear elements provided with SimPowerSystems in the
powerlib_models library (see the “Improving Simulation Performance”
chapter).
Input
Arguments
The number of input arguments must be 7, 12, 13, 14, or 16. Arguments 8 to 16
are optional. The first seven arguments that must be specified are
• rlc: Branch matrix specifying the network topology as well as the resistance
R, inductance L, and capacitance C values. See format below.
• switches: Switch matrix. Specify an empty variable if no switches are used.
See format below.
• source: Source matrix specifying the parameters of the electrical voltage and
current sources. Specify an empty variable if no sources are used. See format
below.
• line_dist: Distributed parameter line matrix. Specify an empty variable if
no distributed lines are used. See format below.
• yout: String matrix of output expressions. See format below.
• y_type: Integer vector indicating output types (0 for voltage output, 1 for
current output).
• unit: String specifying the units to be used for R, L, and C values in the rlc
matrix. If unit = 'OHM', R L C values are specified in ohms Ω at the
fundamental frequency specified by freq_sys (default value is 60 Hz). If
unit = 'OMU', R L C values are specified in ohms (Ω), millihenries (mH),
and microfarads (µF).
The last nine arguments are optional. The first three are used to pass
arguments from the power_analyze command. Hereafter, only the arguments
to be specified when power_statespace is used as a stand-alone command are
described:
• net_arg1, net_arg2, net_arg3: Used to pass arguments from
power_analyze. Specify an empty variable [] for each of these arguments.
6-12
power_statespace
• netsim_flag: Integer controlling the messages displayed during the
execution of power_statespace. Default value is 0.
If netsim_flag = 0, the version number, number of states, inputs, outputs,
and modes are displayed. Output values are displayed in polar form for each
source frequency.
If netsim_flag = 1, only version number, number of states, inputs, and
outputs are displayed.
If netsim_flag = 2, no message is displayed during execution.
• fid_outfile: File identifier of the power_statespace output file containing
parameter values, node numbers, steady-state outputs, and special
messages. Default value is 0.
• freq_sys: Fundamental frequency (Hz) considered for specification of XL
and XC reactances if unit is set to 'OHM'. Default value is 60 Hz.
• ref_node: Reference node number used for ground of PI transmission lines.
If -1 is specified, the user is prompted to specify a node number.
• vary_name: String matrix containing the symbolic variable names used in
output expressions. These variables must be defined in your MATLAB
workspace.
• vary_val: Vector containing the values of the variable names specified in
vary_name.
Output
Arguments
• A,B,C,D: state-space matrices of the linear circuit with all switches open.
A(nstates, nstates) , B(nstates, ninput),
C(noutput, nstates) , D(noutput, ninput),
where nstates is the number of state variables, ninput is the number of
inputs, and noutput is the number of outputs.
• states: String matrix containing the names of the state variables. Each
string has the following format:
Inductor currents: Il_bxx_nzz1_zz2
Capacitor voltages: Uc_bxx_nzz1_zz2
where
xx = branch number
zz1 = first node number of the branch
zz2 = second node number of the branch
6-13
power_statespace
The last lines of the states matrix, which are followed by an asterisk, indicate
inductor currents and capacitor voltages that are not considered as state
variables. This situation arises when inductor currents or capacitor voltages
are not independent (inductors forming a cut set – for example, inductors
connected in series – or capacitors forming a loop). The currents and voltages
followed by asterisks can be expressed as a linear combination of the other
state variables:
• x0: Column vector of initial values of state variables considering the open or
closed status of switches.
• x0sw: Vector of initial values of switch currents.
• rlsw: Matrix (nswitch,2) containing the R and L values of series switch
impedances in ohms (Ω) and henries (H). nswitch is the number of switches
in the circuit.
• u,x,y: Matrices u(ninput,nfreq), x(nstates,nfreq), and y(noutput,nfreq)
containing the steady-state complex values of inputs, states, and outputs.
nfreq is the length of the freq vector. Each column corresponds to a different
source frequency, as specified by the next argument, freq.
• freq: Column vector containing the source frequencies ordered by increasing
frequency.
• Asw,Bsw,Csw,Dsw: State-space matrices of the circuit including the closed
switches. Each closed switch with an internal inductance adds one extra
state to the circuit.
• Hlin: Three-dimensional array (nfreq, noutput, ninput) of the nfreq
complex transfer impedance matrices of the linear system corresponding to
each frequency of the freq vector.
Format of the
RLC Input
Matrix
Two formats are allowed:
• Six columns: Implicit branch numbering. Branch numbers correspond to the
RLC line numbers.
• Seven columns: Explicit branch numbering. Branch number Nobr is assigned
by the user.
Each line of the RLC matrix must be specified according to the following format.
[node1, node2, type, R, L, C, Nobr] for RLC branch or line branch
[node1, node2, type, R, L, C, Nobr] for transformer magnetizing branch
6-14
power_statespace
[node1, node2, type, R, L, U, Nobr] for transformer winding
[node1, node2, type, R, L, U, Nobr] for mutual inductances
• node1: First node number of the branch. The node number must be positive
or zero. Decimal node numbers are allowed.
• node2: Second node number of the branch. The node number must be positive
or zero. Decimal node numbers are allowed.
• type: Integer indicating the type of connection of RLC elements, or, if
negative, the transmission line length:
type = 0: Series RLC element
type = 1: Parallel RLC element
type = 2: Transformer winding
type = 3: Coupled (mutual) winding
If type is negative, the transmission line is modeled by a PI section of length
|type|. See details below.
For a mutual inductor or a transformer having N windings, N+1 consecutive
lines must be specified in RLC matrix:
1 N lines with type = 2 or type = 3; (one line per winding). Each line
specifies R/L/U or R/Xl/Xc where [R/L, R/Xl = winding resistance and
leakage reactance for a transformers or winding resistance and self
reactance for mutually coupled windings. U is the nominal voltage of
transformer winding (specify 0 if type = 3).
2 One extra line with type = 1 for the magnetizing branch of a transformer
(parallel Rm/Lm or Rm/Xm) or one line with type = 0 for a mutual impedance
(series Rm/Lm or Rm/Xm).
For a transformer magnetizing branch or a mutual impedance, the first node
number is an internal node located behind the leakage reactance of the first
winding. The second node number must be the same as the second node
number of the first winding.
To model a saturable transformer, you must use a nonlinear inductance
instead of the linear inductance simulating the reactive losses. Set the Lm/Xm
value to 0 (no linear inductance) and use the Saturable Transformer block, set
with proper flux-current characteristics.
6-15
power_statespace
This block can be found in the powerlib_models/Continuous library. It must
be connected to the linear part of the system (State-Space block or S-function)
between a voltage output (voltage across the magnetizing branch) and a
current input (current source injected into the transformer internal node). See
the “Example” on page 6-22.
If type is negative, its absolute value specifies the length (km) of a
transmission line simulated by a PI section. For a transmission line, the R/L/C
or R/Xl/Xc values must be specified in Ω/km, mH/km, and µF/km, or in Ω/km.
Parameter
Description
R
Branch resistance (Ω)
Xl
Branch inductive reactance (Ω at freq_sys) or transformer
winding leakage reactance (Ω at freq_sys)
L
Branch inductance (mH)
Xc
Branch capacitive reactance (Ω at freq_sys). The negative
sign of Xc is optional.
C
Capacitance (µF)
U
Nominal voltage of transformer winding. The same units
(volts or kV) must be used for each winding. For a mutual
inductance (type=3), this value must be set to zero.
Zero value for R, L or Xl, C or Xc in a series or parallel branch indicates
that the corresponding element does not exist.
The following restrictions apply for transformer winding R-L values. Null
values are not allowed for secondary impedances if some transformer
secondaries form loops (as in a three-phase delta connection). Specify a very
low value for R or L or both (e.g., 1e-6 p.u. based on rated voltage and power)
to simulate a quasi-ideal transformer. The resistive and inductive parts of the
magnetizing branch can be set to infinite (no losses; specify Xm = Rm = inf).
Format of the
Source Input
Matrix
6-16
Three formats are allowed:
power_statespace
• Five columns: All sources are generating the same frequency specified by
freq_sys.
• Six columns: The frequency of each source is specified in column 6.
• Seven columns: The seventh column is used to specify the type of nonlinear
element modeled by the current source.
Each line of the source matrix must be specified according to the following
format:
[ node1, node2, type, amp, phase, freq, model ]
• node1, node2: Node numbers corresponding to the source terminals. These
are the polarity conventions:
- Voltage source: node1 is the positive terminal.
- Current source: Positive current flowing from node1 to node2 inside the
source.
• type: Integer indicating the type of source: 0 for voltage source, 1 for current
source.
• amp: Amplitude of the AC or DC voltage or current (V or A).
• phase: Phase of the AC voltage or current (degree).
• freq: Frequency (Hz) of the generated voltage or current. Default value is 60
Hz. For a DC voltage or current source, specify phase = 0 and freq = 0. amp
can be set to a negative value. The generated signals are
amp * sin(2π*freq*t + phase) for AC, amp for DC.
• model: Integer specifying the type of nonlinear element modeled by the
current source (saturable inductance, thyristor, switch, ...). Used by
power_analyze only.
Order in Which Sources Must Be Specified
The commands that compute the state-space representation of a system expect
the sources in a certain order. You must respect this order in order to obtain
correct results. You must be particularly careful if the system contains any
switches. This is the proper ordering of sources:
1 The currents from all switches that have a null inductance (Lon = 0), if any.
6-17
power_statespace
2 The currents from all nonlinear models that have a finite inductance
(switches with Lon > 0, the magnetizing inductance in saturable
transformers, etc.), if any.
3 All other voltage and current sources in any order, if any.
Refer to the Example section below for an example illustrating proper ordering
of sources for a system containing nonlinear elements.
Format of the
Switches Input
Matrix
Switches are nonlinear elements simulating mechanical or electronic devices
such as circuit breakers, diodes, or thyristors. Like other nonlinear elements,
they are simulated by current sources driven by the voltage appearing across
their terminals. Therefore, they cannot have a null impedance. They are
simulated as ideal switches in series with a series R-L circuit. Various models
of switches (circuit breaker, ideal switch, and power electronic devices) are
available in the powerlib_models library. They must be interconnected to the
linear part of the system through appropriate voltage outputs and current
inputs.
The switch parameters must be specified in a line of the switches matrix in
seven different columns, according to the following format.
[ node1, node2, status, R, L/Xl, no_I , no_U ]
Parameter
Description
node1,
node2
Node numbers corresponding to the switch terminals
status
Code indicating the initial status of the switch at t = 0:
0 = open; 1 = closed
R
Resistance of the switch when closed (Ω)
L/Xl
Inductance of the switch when closed (mH) or inductive
reactance (Ω at freq_sys)
For these last two fields, you must use the same units as those specified
for the RLC matrix. Either field can be set to 0, but not both.
6-18
power_statespace
The next two fields specify the current input number and the voltage output
number to be used for interconnecting the switch model to the State-Space
block. The output number corresponding to the voltage across a particular
switch must be the same as the input number corresponding to the current
from the same switch (see Example section below):
• no_I: Current input number coming from the output of the switch model
• no_U: Voltage output number driving the input of the switch model
Format of the
Line_Dist
Matrix
The distributed parameter line model contains two parts:
1 A linear part containing current sources and resistances that are connected
at the line sending and receiving buses together with the linear circuit.
2 A nonlinear part available in the distributed_param_line block of the
powerlib_models/Continuous library. This block performs the
phase-to-mode transformations of voltage and currents and simulates the
transmission delays for each mode. The distributed_param_line block must
be connected to appropriate voltage outputs and current inputs of the linear
part of the system. The line parameters have to be specified in the
line_dist matrix and also in the distributed_param_line block.
Each row of the line_dist matrix is used to specify a distributed parameter
transmission line. The number of columns of line_dist depends on the
number of phases of the transmission line.
For an nphase line, the first (4 + 3 * nphase + nphase^2) columns are used.
For example, for a three-phase line, 22 columns are used.
6-19
power_statespace
[nphase, no_I, no_U, length, L/Xl, Zc, Rm, speed, Ti]
Parameter
Description
nphase
Number of phases of the transmission line
no_I
Input number in the source matrix corresponding to the first
current source Is_1 of the line model. Each line model uses
2*nphase current sources specified in the source matrix as
follows:
Is_1, Is_2, ..., Is_nphase for the sending end followed
by
Ir_1, Ir_2, ..., Ir_nphase for the receiving end.
nu_U
Output number of the state-space corresponding to the first
voltage output Vs_1 feeding the line model. Each line model
uses 2*nphase voltage outputs in the source matrix as
follows:
Vs_1, Vs_2, ..., Vs_nphase for the sending end followed by
Vr_1, Vr_2, ..., Vr_nphase for the receiving end.
length
Length of the line (km)
Zc
Vector of the nphase modal characteristic impedances (Ω)
Rm
Vector of the nphase modal series resistances (Ω/km)
speed
Vector of the nphase modal propagation speeds (km/s)
Ti
Transformation matrix from mode to phase currents such
that Iphase = Ti * Imod. The nphase * nphase matrix
must be given in vector format,
[col_1, col_2,... col_nphase].
6-20
power_statespace
Format of the
Yout Matrix
The desired outputs are specified by a string matrix yout. Each line of the yout
matrix must be an algebraic expression containing a linear combination of
states and state derivatives, specified according to the following format:
Parameter
Description
Uc_bn
Capacitor voltage of branch n
Il_bn
Inductor current of branch n
dUc_bn
Derivative of Uc_bn or Il_bn
Un, In
Source voltage or current specified by line n of the source
matrix
U_nx1_x2
Voltage between nodes x1 and x2 = Ux1 -Ux2
I_bn
Current in branch n flowing from node1 to node2 (See
format of RLC matrix). For a parallel RLC branch, I_bn
corresponds to the total current IR + IL + IC.
I_bn_nx
Current flowing into node x of a PI transmission line
specified by line n of the RLC matrix. This current includes
the series inductive branch current and the capacitive shunt
current.
Each output expression is built from voltage and current variable names
defined above, their derivatives, constants, other variable names, parentheses
and operators (+ − ∗ / ^), in order to form a valid MATLAB expression. For
example:
yout =
char(['R1*I_b1+Uc_b3-L2*dIl_b2','U_n10_20','I2+3*I_b5']);
If variable names are used (R1 and L2 in the above example), their names and
values must be specified by the two input arguments vary_name and vary_val.
6-21
power_statespace
Sign Conventions for Voltages and Currents
Parameter
Sign Convention
I_bn, Il_bn, In
Branch current, inductor current of branch n, or
current of source #n is oriented from node1 to node2
I_bn_nx
Current at one end (node x) of a PI transmission line.
If x = node1, the current is entering the line. If x =
node2, the current is leaving the line.
Uc_bn, Un
Voltage across capacitor or source voltage
(Unode1 - Unode2)
U_nx1_x2
Voltage between nodes x1 and x2 = Ux1 − Ux2.
Voltage of node x1 with respect to node x2.
Order in Which Outputs Must Be Specified
The commands that compute the state-space representation of a system expect
the outputs to be in a certain order. You must respect this order in order to
obtain correct results. You must be particularly careful if the system contains
any switches. The following list gives the proper ordering of outputs:
1 The voltages across all switches that have a null inductance (Lon = 0), if any
2 The currents of all switches that have a null inductance (Lon = 0), if any, in
the same order as the voltages above
3 The voltages across all nonlinear models that have a finite inductance
(switches with Lon > 0, the magnetizing inductance in saturable
transformers, etc.)
4 All other voltage and current measurements that you request, in any order
Refer to the Example section below for an example illustrating proper ordering
of outputs for a system containing nonlinear elements.
Example
6-22
The following circuit consists of two sources (one voltage source and one
current source), two series RLC branches (R1-L1 and C6), two parallel RLC
branches (R5-C5 and L7-C7), one saturable transformer, and two switches (Sw1
and Sw2). Sw1 is initially closed whereas Sw2 is initially open. Three
measurement outputs are specified (I1, V2, and V3). This circuit has seven
power_statespace
nodes numbered 0, 1, 2, 2.1, 10, 11, and 12. Node 0 is used for the ground. Node
2.1 is the internal node of the transformer where the magnetization branch is
connected.
I1
1
R1 L1
2
Rt1
Lt1
2.1
Rt2
10
11
Sw1
100 V
0 deg.
60 Hz
Rm
U1
Lsat
U2
R5
2A
-30deg.
180 Hz
Sw2 C6
12
C5 V2
C7
L7
V3
0
Saturable Transformer
R1 = 0.1 Ω
L1 = 1.0 mH
Rt1 = 0.05 Ω; Lt1 = 1.5 mH; U1 =100 V
Rt2 = 0.20 Ω; Lt2 = 0.0 mH; U2=200 V
Rm = 1000 Ω
C5 = 1 µF; R5 = 200 Ω
C6 = 1 nF
C7 = 2 µF; L7 = 0.5 H
Sw1: R=0.01 Ω; L = 0H; initial state = closed
Sw2: R=0.1 Ω; L = 0H; initial state = open
Linear state space. You can use the power_statespace command to find the
state-space model of the linear part of the circuit. The nonlinear elements Sw1,
Sw2, and Lsat must be modeled separately by means of current sources driven
by the voltages appearing across their terminals. Therefore you must provide
three additional current sources and three additional voltage outputs for
interfacing the nonlinear elements to the linear circuit.
You can find the state-space model of the circuit by entering the following
commands in a MATLAB script file. The example is available in the
power_circ2ss.m file. Notice that an output text file named
power_circ2ss.net containing information on the system is requested in the
call to power_statespace.
unit='OMU'; % Units = ohms, mH, and uF
rlc=[
6-23
power_statespace
%N1N2
1 2
2 0
10 0
2.10
11 0
11 12
12 0
];
typeR
L
0
0.1 1
2
0.051.5
2
0.200
1
10000
1
200 0
0
0
0
1
0
500
source=[
%N1N2 typeU/I
10 11 1
0
11 12 1
0
2.10
1
0
1 0
0
100
0 10 1
2
];
C(uF)/U(V)
0
%R1 L1
100 %transfo Wind.#1
200 %transfo Wind.#2
0
%transfo mag. branch
1
%R5 C5
1e-3%C6
2
%L7 C7
phasefreq
0
0
%Sw1
0
0
%Sw2
0
0
%Saturation
0
60 %Voltage source
-30 180 %Current source
switches=[
%N1N2 statusR(ohm)L(mH)I#U# #
10 11 1
0.010
1
1
%Sw1
11 12 0
0.1 0
2
2
%Sw2
];
%outputs
%
% Both switches have Lon=0, so their voltages must be the first
outputs,
% immediately followed by their currents (in the same order as the
voltages).
% The voltage across all nonlinear models that don't have L=0
follow
% (in this case the saturable transformer's magnetizing inductor).
% The measurements that you request follow, in any order.
%
y_u1='U_n10_11';%U_Sw1= Voltage across Sw1
y_u2='U_n11_12';%U_Sw2= Voltage across Sw2
y_i3='I1'; %I1= Switch current Sw1
y_i4='I2'; %I2= Switch current Sw2
6-24
power_statespace
y_u5='U_n2.1_0';%U_sat= Voltage across saturable reactor
y_i6='I_b1';%I1 measurement
y_u7='U_n11_0';%V2 measurement
y_u8='U_n12_0';%V3 measurement
yout=char(y_u1,y_u2,y_i3,y_i4,y_u5,y_i6,y_u7,y_u8);% outputs
y_type=[0,0,1,1,0,1,0,0];%output types; 0=voltage 1=current
% Open file that contains power_statespace output information
fid=fopen('power_circ2ss.net','w');
[A,B,C,D,states,x0,x0sw,rlsw,u,x,y,freq,Asw,Bsw,Csw,Dsw,Hlin]=
power_statespace(rlc,switches,source,[],yout,y_type,unit,[],[],
[],0,fid);
Command line messages. While power_statespace is executing, the following
messages are displayed.
Computing state space representation of linear electrical circuit
(V2.0)...
(4 states ; 5 inputs ; 7 outputs)
Oscillatory modes and damping factors:
F=159.115Hz zeta=4.80381e-08
Steady state outputs @ F=0 Hz :
y_u1= 0Volts
y_u2= 0Volts
y_i3= 0Amperes
y_i4= 0Amperes
y_u5= 0Volts
y_i6= 0Amperes
y_u7= 0Volts
y_u8= 0Volts
Steady state outputs @ F=60 Hz :
y_u1 = 0.009999 Volts < 3.168 deg.
y_u2 = 199.4 Volts < -1.148 deg.
y_i3 = 0.9999 Amperes < 3.168 deg.
y_i4 = 0 Amperes < 0 deg.
y_u5 = 99.81 Volts < -1.144 deg.
6-25
power_statespace
y_i6 = 2.099 Amperes < 2.963 deg.
y_u7 = 199.4 Volts < -1.148 deg.
y_u8 = 0.01652 Volts < 178.9 deg.
Steady
y_u1 =
y_u2 =
y_i3 =
y_i4 =
y_u5 =
y_i6 =
y_u7 =
y_u8 =
state outputs @ F=180 Hz :
0.00117 Volts < 65.23 deg.
22.78 Volts < 52.47 deg.
0.117 Amperes < 65.23 deg.
0 Amperes < 0 deg.
11.4 Volts < 53.48 deg.
4.027 Amperes < 146.5 deg.
22.83 Volts < 52.47 deg.
0.0522 Volts < 52.47 deg.
State space output. The names of the state variables are returned in the states
string matrix.
states
states =
Il_b2_n2_2.1
Uc_b5_n11_0
Uc_b6_n11_12
Il_b7_n12_0
Il_b1_n1_2*
Uc_b7_n12_0*
Although this circuit contains a total of six inductors and capacitors, there are
only four state variables. The names of the state variables are given by the first
four lines of the states matrix. The last two lines are followed by an asterisk
indicating that these two variables are a linear combination of the state
variables. The dependencies can be viewed in the output file
power_circ2ss.net.
The following capacitor voltages are dependent:
Uc_b7_n12_0 = + Uc_b5_n11_0 - Uc_b6_n11_12
The following inductor currents are dependent:
Il_b1_n1_2 = + Il_b2_n2_0
The A,B,C,D matrices contain the state-space model of the circuit without
nonlinear elements (all switches open). The x0 vector contains the initial state
values considering the switch Sw1 closed. The Asw, Bsw, Csw, and Dsw matrices
6-26
power_statespace
contain the state-space model of the circuit considering the closed switch Sw1.
The x0sw vector contains the initial current in the closed switch.
A
A =
-4.0006e+05
0
0
-4995
0 -4992.5
0
2
0
0
0 -499.25
04.9925e+05
-2
0
Asw
Asw =
-80.999 -199.99
4.9947e+05 -5244.7
4.9922e+05 -5242.1
0
2
0
0
0 -499.25
04.9925e+05
-2
0
The system source frequencies are returned in the freq vector.
freq
freq =
0
60
180
The corresponding steady-state complex outputs are returned in the (6-by-3) y
matrix where each column corresponds to a different source frequency.
For example, you can obtain the magnitude of the six voltage and current
outputs at 60 Hz as follows:
abs(y(:,2))
ans =
0.0099987
199.42
0.99987
0
99.808
2.0993
199.41
0.016519
6-27
power_statespace
The initial values of the four state variables are returned in the x0 vector. You
must use this vector in the State-Space block to start the simulation in steady
state.
x0
x0 =
2.3302
14.111
14.07
3.1391e-05
The initial values of switch currents are returned in x0sw. To start the
simulation in steady state, you must use these values as initial currents for the
nonlinear model simulating the switches.
x0sw
x0sw =
0.16155
0
The Simulink diagram of the circuit shown in the following figure is available
in the power_circ2ss_slk model. If no resistive switches had been used, the
linear part of the circuit could have been simulated with the State-Space block
of the Simulink/Continuous library. However, as resistive switches are used,
the sfun_psbcontc S-function is used instead of the State-Space block. This
S-function reevaluates the state-space matrices during simulation when the
circuit topology is changing (after a switch is opened or closed). Appropriate
inputs and outputs are used to connect the switch and saturable reactance
models to the linear system. Notice that the status of each switch is fed back
from the breaker to the S-function, after the inputs mentioned earlier. You can
find the breaker and saturable_transformer blocks in the
powerlib_models/Continuous library containing all the nonlinear continuous
models used by SimPowerSystems. As the breaker model is vectorized, a single
block is used to simulate the two switches Sw1 and Sw2.
If you use the powerlib library to build your circuit, the same Simulink system
is generated automatically by the power_analyze command. The powerlib
version of this system is also available in the power_circ2ss_sps model and is
shown below.
6-28
power_statespace
power_circ2ss_slk.mdl Example Diagram
power_circ2ss_sps.mdl Example Diagram
See Also
power_analyze
6-29
power_statespace
6-30
Index
A
abc_to_dq0 Transformation block 5-12
AC Current Source block 5-18
AC transmission network 3-2
AC Voltage Source block 5-24
Active & Reactive Power block 5-20
analysis
power_analyze command 6-2
analyze
Powergui block graphical interface 5-171
Asynchronous Machine
per unit system 5-29
Asynchronous Machine block 5-26
B
block diagrams
creating 1-2
blocks
nonlinear 4-16
powerlib block library 1-3
Breaker block 5-39
C
circuit
building a simple 1-2
circuit breaker 5-39
commands
power_analyze 6-2
power_init 6-10
power_statespace 6-11
connecting blocks 1-6
Connection Port block 5-44
Control System Toolbox 1-14
control systems
analyzing with the Control System Toolbox
1-14
speed control system 5-34
Controlled Current Source block 5-46
Controlled Voltage Source block 5-49
Current Measurement block 5-53
D
DC Machine block 5-55
DC Voltage Source block 5-61
Demos model library 5-3
Diode block 5-63
Discrete System block 5-68
display signals 1-6
distributed parameter line
propagation speed 1-15
Distributed Parameter Line block 5-69
dq0_to_abc Transformation block 5-77
drives
DC motor 3-21
variable-frequency induction motor 3-46
E
electrical circuits 1-1
Electrical Sources block library 5-2
Elements block library 5-2
examples
buck converter 5-95
distributed parameter line 5-72
modulated current source 5-48
permanent magnet synchronous machine
5-163
PWM inverter 5-34
I-1
Index
surge arresters in series-compensated network
5-251
synchronous machine in motoring mode
5-282
zero-current-quasi-resonant switch converter
5-113, 5-130
Excitation System block 5-79
Extras block library 5-2
L
linear and nonlinear elements 1-2
Linear Transformer block 5-118
lines
connection lines 1-7
signal lines 1-7
M
F
Fourier block 5-82
frequency analysis 5-155
G
Generic Power System Stabilizer block 5-86
Ground block 5-90
GTO block 5-91
GTO system 3-21
H
HVDC system 3-46
Hydraulic Turbine and Governor block 5-98
I
Ideal Switch block 5-103
IGBT block 5-108
Impedance Measurement block 5-116
interconnections
between electric and Simulink blocks 1-2
interface
between Simulink and SimPowerSystems
1-6
I-2
Machine Measurement Demux block 5-123
Machines block library 5-2
measurements
current 5-53
voltage 5-379
Measurements block library 5-2
models
limitations with nonlinear 4-16
nonlinear model library 4-16
MOSFET
inverter 3-34
MOSFET block 5-127
Multiband Power System Stabilizer block 5-132
Multimeter block 5-140
Mutual Inductance block 5-146
N
Neutral block 5-151
P
Parallel RLC Branch block 5-153
Parallel RLC Load block 5-157
per unit system 1-6
Permanent Magnet Synchronous Machine block
5-160
Phasor Elements block library 5-2
Index
PI section line
frequency response 1-15
PI Section Line block 5-166
ports
Simulink ports 1-7
terminal ports 1-7
Power Electronics block library 5-2
power system 1-2
Power Systems Blockset 1-1
power_analyze command 6-2
power_init command 6-10
power_statespace command 6-11
Powergui block 5-171
powerlib library 1-2
pulse-width modulation 3-33
PWM Generator block 5-192
PWM inverter 5-34
R
RMS block 5-199
S
Saturable Transformer block 5-202
saturable transformer model 3-6
Series RLC Branch block 5-214
Series RLC Load block 5-218
series-compensated transmission network 3-2
Simplified Synchronous Machine block 5-221
simulation
modifying block parameter 1-8
speed 4-21
sinusoidal source 1-3
snubber circuits
in Diode block 5-63
in GTO block 5-91
state variable
names 1-11
state-space model
obtaining state-space matrices 6-7
Static Var Compensator block 5-229
Steam Turbine and Governor block 5-239
Surge Arrester block 5-249
Synchronized 12-Pulse Generator block 5-263
Synchronized 6-Pulse Generator block 5-255
synchronous machine
with regulators 3-33
Synchronous Machine block 5-270
T
Three-Level Bridge block 5-289
Three-Phase Breaker block 5-285
Three-Phase Dynamic Load block 5-298
Three-Phase Fault block 5-303
Three-Phase Mutual Inductance Z1-Z0 block
5-308
Three-Phase Parallel RLC Branch block 5-311
Three-Phase Parallel RLC Load block 5-313
Three-Phase PI Section Line block 5-316
Three-Phase Programmable Voltage Source block
5-319
Three-Phase Sequence Analyzer block 5-324
Three-Phase Series RLC Branch block 5-329
Three-Phase Series RLC Load block 5-331
Three-Phase Source block 5-334
Three-Phase Transformer (Three Windings) block
5-347
Three-Phase Transformer (Two Windings) block
5-340
Three-Phase Transformer 12 Terminals block
5-338
Three-Phase V-I Measurement block 5-353
I-3
Index
Thyristor block 5-357
Timer block 5-365
Total Harmonic Distortion block 5-367
transformers
linear 5-118
three-phase 3-6
transmission lines
propagation time 1-15
U
Universal Bridge block 5-369
V
Voltage Measurement block 5-379
Z
Zigzag Phase-Shifting Transformer block 5-381
I-4