Simscape Getting Started Guide

Simscape Getting Started Guide
Simscape™
Getting Started Guide
R2015a
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Simscape™ Getting Started Guide
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Revision History
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New for Version 2.0 (Release 2007b)
Revised for Version 2.1 (Release 2008a)
Revised for Version 3.0 (Release 2008b)
Revised for Version 3.1 (Release 2009a)
Revised for Version 3.2 (Release 2009b)
Revised for Version 3.3 (Release 2010a)
Revised for Version 3.4 (Release 2010b)
Revised for Version 3.5 (Release 2011a)
Revised for Version 3.6 (Release 2011b)
Revised for Version 3.7 (Release 2012a)
Revised for Version 3.8 (Release 2012b)
Revised for Version 3.9 (Release 2013a)
Revised for Version 3.10 (Release 2013b)
Revised for Version 3.11 (Release 2014a)
Revised for Version 3.12 (Release 2014b)
Revised for Version 3.13 (Release 2015a)
Contents
1
Product Fundamentals
Simscape Product Description . . . . . . . . . . . . . . . . . . . . . . . . .
Key Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1-2
1-2
Creating a New Simscape Model . . . . . . . . . . . . . . . . . . . . . . .
Recommended Blocks and Solvers . . . . . . . . . . . . . . . . . . . . .
Data Logging Settings for New Model . . . . . . . . . . . . . . . . . .
1-3
1-3
1-5
Evaluating Performance of a DC Motor . . . . . . . . . . . . . . . . .
1-7
v
1
Product Fundamentals
• “Simscape Product Description” on page 1-2
• “Creating a New Simscape Model” on page 1-3
• “Evaluating Performance of a DC Motor” on page 1-7
1
Product Fundamentals
Simscape Product Description
Model and simulate multidomain physical systems
Simscape provides an environment for modeling and simulating physical systems
spanning mechanical, electrical, hydraulic, and other physical domains. It provides
fundamental building blocks from these domains that you can assemble into models
of physical components, such as electric motors, inverting op-amps, hydraulic valves,
and ratchet mechanisms. Because Simscape components use physical connections, your
models match the structure of the system you are developing.
Simscape models can be used to develop control systems and test system-level
performance. You can extend the libraries using the MATLAB® based Simscape
language, which enables text-based authoring of physical modeling components,
domains, and libraries. You can parameterize your models using MATLAB variables and
expressions, and design control systems for your physical system in Simulink®. To deploy
your models to other simulation environments, including hardware-in-the-loop (HIL)
systems, Simscape supports C-code generation.
Key Features
• Single environment for modeling and simulating mechanical, electrical, hydraulic,
thermal, and other multidomain physical systems
• Libraries of physical modeling blocks and mathematical elements for developing
custom components
• MATLAB based Simscape language, enabling text-based authoring of physical
modeling components, domains, and libraries
• Physical units for parameters and variables, with all unit conversions handled
automatically
• Ability to simulate models that include blocks from related physical modeling
products without purchasing those products
• Support for C-code generation
1-2
Creating a New Simscape Model
Creating a New Simscape Model
In this section...
“Recommended Blocks and Solvers” on page 1-3
“Data Logging Settings for New Model” on page 1-5
Recommended Blocks and Solvers
Simscape models require certain blocks to be present in the model configuration, such
as a Solver block, or domain-specific reference blocks. Other blocks, although not
required, are highly likely to be needed, such as Simulink-PS Converter and PS-Simulink
Converter blocks. An easy way to start a new Simscape model is by using the ssc_new
function.
When you type ssc_new at the MATLAB Command prompt, the software opens the
main Simscape library and creates a new model prepopulated with certain blocks, as
shown in the following illustration.
1-3
1
Product Fundamentals
By default, the model name is not specified, the model contains a Solver Configuration
block with the default solver set to ode23t, a Simulink-PS Converter block, and a PSSimulink Converter block connected to a Scope block.
You can use the ssc_new function arguments to specify the model name, add a domainspecific reference block, and change the default solver. See the ssc_new reference page
for details. For example, typing
ssc_new('rotor1','rotational','ode15s')
creates the following model.
1-4
Creating a New Simscape Model
After using ssc_new, continue developing your model by copying the blocks, as needed,
and adding other blocks from the Simscape libraries.
For electrical models, you can also use the Creating A New Circuit example as a template
for a new model. This example creates a new electrical model and opens an Electrical
Starter Palette, which contains links to the most often used electrical components. Open
the example by typing ssc_new_elec in the MATLAB Command Window and use
File > Save As to save it under the desired model name. Then delete the unwanted
components and add new ones from the Electrical Starter Palette and from Simscape
libraries.
Data Logging Settings for New Model
Using data logging is a best practice for Simscape models because it provides access to
important simulation and analysis tools. Therefore, the ssc_new function automatically
turns on data logging for the whole model. It uses the default workspace variable name
1-5
1
Product Fundamentals
simlog to store simulation data, and limits the data to the last 10000 points to avoid
slowing down simulation.
When you create a new model using ssc_new, the model has the following data logging
configuration:
• Log simulation data — All.
• Log simulation statistics — Off.
• Open viewer after simulation — Off.
• Workspace variable name — simlog.
• Decimation — 1.
• Limit data points — On.
• Data history (last N steps) — 10000.
For information on what these settings mean and how to change them, see “Data Logging
Options”.
1-6
Evaluating Performance of a DC Motor
Evaluating Performance of a DC Motor
This example shows how to simulate systems that span electrical and mechanical
domains. You learn how to model physical components with Simscape blocks, connect
them into a realistic model, use Simulink blocks as well, and then simulate and modify a
motor model.
The model is based on a Faulhaber Series 0615 DC-Micromotor. The model uses
equivalent circuit parameters for the 1.5V motor to verify manufacturer-quoted noload speed, no-load current, and stall torque. You can use the model to assess motor
performance in a given application by adding the requisite mechanical load model.
Explore the Model
1
To open the Permanent Magnet DC Motor example model, type ssc_dcmotor in the
MATLAB Command Window.
1-7
1
Product Fundamentals
Main Model Window
The main model window contains a DC Motor subsystem with two electrical and two
mechanical rotational ports.
For improved readability of block diagrams, each Simscape domain uses a distinct
default color and line style for the connection lines. In this block diagram, for
example, the electrical circuit is indicated by the dark-blue color of the connection
lines, while the connection lines between the mechanical rotational ports are lightgreen. Physical signal lines are brown.
The electrical ports of the motor connect to the electrical circuit, which consists of
an Electrical Reference block, representing an electrical ground, a 1.5 V DC voltage
source, and a current sensor. The current sensor connects, through a PS-Simulink
Converter block, to a Simulink scope labeled Motor Current.
1-8
Evaluating Performance of a DC Motor
On the mechanical side, a Mechanical Rotational Reference block represents a
reference point for the other elements. An ideal rotational motion sensor connects,
through a PS-Simulink Converter block, to a Simulink scope labeled RPM.
The motor load is represented by an Ideal Torque Source block, which on one side
connects to a Mechanical Rotational Reference block, and on the other side to the
motor shaft. A regular Simulink Step source provides the control signal. A SimulinkPS Converter block converts the control signal into a physical signal and applies it to
the control port of the Ideal Torque Source block.
The diagram also contains a Solver Configuration block, which is required in any
Simscape model. It contains parameters relevant to numerical algorithms for
Simscape simulations.
2
Double-click the DC Motor subsystem to open it.
1-9
1
Product Fundamentals
DC Motor Subsystem
The motor consists of an electrical circuit and a mechanical rotational circuit,
connected by the Rotational Electromechanical Converter block. The electrical circuit
consists of a Rotor Resistance block and an Inductance block L. It contains two
electrical ports, corresponding to the V+ and V- electric terminals of the motor. The
mechanical circuit contains a Rotational Friction block, Motor Inertia J, and two
mechanical rotational ports, C and R, corresponding to the motor case and rotor,
respectively. Notice how the C and R ports of the Friction block and the Rotational
Electromechanical Converter block are connected to the C and R ports of the motor,
to preserve the correct direction of variables in the Physical Network.
1-10
Evaluating Performance of a DC Motor
Run the Model
1
2
3
Double-click the Motor Current and RPM scopes to open them. During simulation,
these windows display the motor current and shaft speed, respectively, as functions
of time.
In the toolbar of the model window, click
to start the simulation. The Simscape
solver evaluates the model, calculates the initial conditions, and runs the simulation.
This process might take a few seconds. The message in the bottom-left corner of the
model window provides the status.
Examine the simulation results in the Motor Current and RPM scope windows.
1-11
1
Product Fundamentals
For the first 0.1 seconds, the motor has no external load, and the speed builds up
to the no-load value. Then at 0.1 seconds, the stall torque is applied as a load to the
motor shaft. Zooming in on the RPM and Motor Current scopes shows that the model
matches the manufacturer parameters for no-load speed, no-load current, and stall
torque.
Change the Supply Voltage
Reduce the supply voltage to 1.25 volts (to simulate the battery running down) and vary
the load torque to find the maximum torque at this reduced voltage.
1
1-12
Double-click the 1.5V DC Voltage Source block. Set Constant voltage to 1.25 V.
Evaluating Performance of a DC Motor
2
Run the simulation. Note the effect of reduced voltage on the no-load speed.
1-13
1
Product Fundamentals
3
Try varying the load torque to find the maximum torque at this reduced voltage.
Double-click the Step source block, enter different final values for the input signal,
and rerun the simulation.
The next illustration shows the simulation results for Final value set to -0.2e-3,
which corresponds to (1.25/1.5)*0.24mNm, as the magnitude of the torque-speed
curve is proportional to voltage for a DC motor.
1-14
Evaluating Performance of a DC Motor
Change the Motor Load
Replace the torque source with a simple mechanical load, for example, a fan, for which
the torque is defined by alpha*speed^2, where alpha is -1e-10 Nm/(rad/s)^2.
1
Delete the Step source and the Simulink-PS Converter block from the model.
2
In the Simscape block library, open Foundation Library > Physical Signals >
Functions.
3
Drag the PS Product block and the PS Gain block to the model window.
4
Connect the blocks as shown in the following illustration. To rotate a block, select it
and press Ctrl+R.
1-15
1
Product Fundamentals
1-16
5
Double-click the Gain block to open its dialog box. Enter Gain value of -1e-10 and
click OK.
6
Run the simulation and assess motor performance with the new load.
Evaluating Performance of a DC Motor
1-17
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