Verification of ZVS Boost Converter with Resonant circuit &

Verification of ZVS Boost Converter with Resonant circuit &
Verification of ZVS Boost Converter with Resonant circuit &
Modelling of an Accurate Two-Diode PV Array System Simulator
using MATLAB Simulink
ASHISH MEHER (110EE0206)
PRATEEK K LENKA (110EE0203)
MANISH BHAGAT (110EE0191)
Department of Electrical Engineering
National Institute of Technology, Rourkela
Page 1
END SEMESTER REPORT
Verification of ZVS Boost Converter with Resonant circuit &
Modelling of an Accurate Two-Diode PV Array System Simulator
using MATLAB Simulink
A Thesis Submitted in Partial Fulfilment of the Requirements for the Degree of
Bachelor of Technology in “Electrical Engineering”
By:
ASHISH MEHER (110EE0206)
PRATEEK K LENKA (110EE0203)
MANISH BHAGAT (110EE0191)
Under the Supervision of
Prof. K. Ratna Subhashini
Department of Electrical Engineering
National Institute of Technology, Rourkela
Odisha, India-769008
May- 2014
Page 2
DEPARTMENT OF ELECTRICAL ENGINEERING
NATIONAL INSTITUTE OF TECHNOLOGY
ROURKELA, ODISHA, INDIA-769008
CERTIFICATE
This is to certify that the thesis entitled “Verification of ZVS Boost
Converter with Resonant circuit & Modelling of an Accurate Two-Diode
PV Array System Simulator using MATLAB Simulink”, submitted by
Ashish Meher(110EE0206), Prateek Kumar Lenka(110EE0203) & Manish
Bhagat(110EE0191) in partial fulfilment of the requirements for the
award of Bachelor of Technology in Electrical Engineering during
session 2013-2014 at National Institute of Technology, Rourkela. A bonafide
record of research work carried out by them under my supervision and
guidance.
The candidates have fulfilled all the prescribed requirements.
The thesis which is based on candidates’ own work, have not submitted
elsewhere for a degree/diploma.
In my opinion, the thesis is of standard required for the award of a
bachelor of technology degree in Electrical Engineering.
Place: Rourkela
K. Ratna Subhashini
Dept. of Electrical Engineering,
National institute of Technology,
Rourkela-769008, ODISHA.
Page 3
Electrical Engineering Department
National Institute Of Technology -Rourkela
ACKNOWLEDGEMENTS
We would like to express our sincere thanks to our project supervisor Prof. B.
Chitti Babu, Department of Electrical Engineering, N.I.T. Rourkela, for his
constant support, timely help, guidance & sincere co-operation during the entire
period of our work. We are grateful to him for providing all the necessary
facilities during the course of the project work.
We would also like to thank Prof. (Mrs.) K. Ratna Subhashini, Assistant
Professor, NIT Rourkela, for the help provided during various stages of the
project.
Finally, an honourable mention goes to our friends & families for their
understanding and support in order to complete this project. Without the
help of those mentioned above, this project could not have been completed.
Ashish Meher (110EE0206)
Prateek K. Lenka (110EE0203)
Manish Bhagat (110EE0191)
B.Tech (Electrical Engineering)
Page 4
Dedicated to
Our Parents
Page 5
ABSTRACT
This thesis proposes a MATLAB Simulink simulator for Photo Voltaic (PV)
Array system. The main contribution is the utilisation of a Two-Diode model to
represent a PV cell. This model is preferred because of its better accuracy at low
irradiance levels. A PV of Kyocera (KC200GT) 50*10 Array is taken & the
characteristics curves are plotted. The same simulator can be interfaced with
MPPT algorithms & Power Electronics converters for better efficiency. The PV & I-V Curves of this simulator is found in exact with that given by the
manufacturers. It is expected that the proposed work can be very useful for PV
professionals who require a simple, fast & accurate PV simulator in order to
design their systems. A detailed analysis of a resonant circuit based softswitching boost-converter for PV applications is also performed. The converter
operates at Zero Voltage Switching (ZVS) turn-on and turn-off of the main
switch, & Zero Current Switching (ZCS) turn-on and ZVS turn-off of the
auxiliary switch due to resonant circuit incorporated into the circuit. Detailed
operation of the converters, analysis of various modes, simulation as well as
experimental results for the design has also been aptly presented. ZVS & ZCS
technique is chosen; as it eliminates switching losses and
noise due to
discharging of junction capacitances. The systems are modelled & simulated in
MATLAB 2013a 64-bit version and the output waveforms are shown.
Page 6
ABBREVIATIONS AND ACRONYMS
PV
-
Photo Voltaic
PVA
-
Photo Voltaic Array
SPV
-
Solar Photo Voltaic
ZVS
-
Zero Voltage Switching
ZCS
-
Zero Current Switching
MOSFET
-
Metal Oxide Semiconductor Field Effect Transistor
MATLAB
-
MATrix LABoratory
MPPT
-
Maximum Power Point Tracking
EMI
-
Electro Magnetic Interference
PWM
-
Pulse Width Modulation
Page 7
Table of Contents
ACKNOWLEDGEMENTS ...................................................................................................................... 4
ABSTRACT ......................................................................................................................................... 6
ABBREVIATIONS AND ACRONYMS ..................................................................................................... 7
LIST OF FIGURES .............................................................................................................................. 10
LIST OF TABLES ................................................................................................................................ 10
Chapter 1 ........................................................................................................................................ 11
Introduction .................................................................................................................................... 11
1.1 Introduction: .......................................................................................................................... 12
1.2 Converter Topology Used For Pv Systems: ............................................................................. 13
1.3 Literature Survey: .................................................................................................................. 14
1.4 Motivation: ............................................................................................................................ 15
1.5 Thesis Objective: .................................................................................................................... 15
1.6 Thesis Outline: ....................................................................................................................... 15
1.7 Road Maps: ............................................................................................................................ 16
Chapter 2 ........................................................................................................................................ 17
Photovoltaic Systems ...................................................................................................................... 17
2.1 Photovoltaic Groupings: ......................................................................................................... 18
2.1.1 Photovoltaic cell:............................................................................................................. 18
2.1.2 Photovoltaic module: ...................................................................................................... 19
2.1.3 Photovoltaic Array: ......................................................................................................... 19
2.2 Working of a PV cell: .............................................................................................................. 20
2.3 Characteristics of a PV cell (Two-Diode Model): ..................................................................... 20
Chapter 3 ........................................................................................................................................ 23
Modelling of PV array ...................................................................................................................... 23
3.1 Representation of PV devices: ................................................................................................ 24
3.1.1. Single diode model:........................................................................................................ 24
3.1.2. Two diode model: .......................................................................................................... 25
3.2 Improved Computational Method: .......................................................................................... 25
3.3 Determination of the
&
Values:.................................................................................. 26
3.4 Simulation Results: ................................................................................................................ 27
Page 8
Chapter 4 ........................................................................................................................................ 30
DC Chopper Circuits......................................................................................................................... 30
4.1 Introduction: .......................................................................................................................... 31
4.2 Boost Converter: .................................................................................................................... 31
Chapter 5 ........................................................................................................................................ 33
Soft Switching of DC-DC
Boost Converter .............................................................................................................................. 33
5.1 Introductions: ........................................................................................................................ 34
5.2 Soft Switching In Boost Converters:........................................................................................ 34
5.3 Analysis of Various Operations Intervals:- .............................................................................. 35
A. Interval 1 (
−
):............................................................................................................. 35
B. Interval 2 (
−
): ............................................................................................................. 36
C. Interval 3 (
−
): ............................................................................................................. 36
D. Interval 4 (
−
): ............................................................................................................ 37
E. Interval 5 (
−
): ............................................................................................................. 37
F. Interval 6 (
−
): ............................................................................................................. 38
G. Interval 7 (
−
): ............................................................................................................ 38
H. Interval 8 (
−
): ............................................................................................................ 39
I. Interval 9 (
−
): .............................................................................................................. 39
5.4 Theory of Main & Auxiliary Switch:- ....................................................................................... 40
Chapter 6 ........................................................................................................................................ 41
Experimental Results
& Conclusions.................................................................................................................................. 41
6.1 PV Modelling Conclusions: ..................................................................................................... 42
6.2 Soft Switching Boost Converter Results: ................................................................................. 42
6.3 Simulation Results of Soft Switching Boost Converter: ........................................................... 43
6.4 Soft Switching Boost Converter Conclusions:.......................................................................... 45
BIBLIOGRAPHY: ............................................................................................................................... 46
Page 9
LIST OF FIGURES
Fig. 1: Basic PV cell structure
17
Fig. 2: Photovoltaic Hierarchy
18
Fig. 3: Characteristics of a PV cell
19
Fig. 4: Two diode model of PV cell
20
Fig. 5: Single diode model of PV cell
13
Fig. 6: PV simulator Block in Simulink
26
Fig. 7: Input parameter window of Kyocera (KG200GT) 50*10 Array
26
Fig. 8: Curves I-V of Kyocera @different Temp & @different Irradiation
27
Fig. 9: Curves P-V of Kyocera @different Temp & @different Irradiation
27
Fig. 10: Curves I-V & P-V of Kyocera for shading pattern
27
Fig. 11: Relative Error for
28
&
Fig. 12: Fly back mode boost converter
31
Fig. 13: Output Voltage waveforms of Boost Converter
31
Fig. 14: The topology for Soft-Switching Boost Converter
33
Fig. 15: Theoretical waveforms for Soft Switching Converter
34
Fig. 16: Soft Switching Boost Converter Simulink Circuit
43
Fig. 17: Various Simulation Result Waveforms
44
Fig. 18: Load Current & Voltage Waveforms
45
LIST OF TABLES
Table No. 1: ISTC Specifications for the 3 Modules used in experiments
28
Table No. 2: Parameters for Proposed Two-Diode Model
28
Table No. 3: Parameters used for the Simulation of Soft switching Boost converter
42
Page 10
Chapter
1
Introduction
Page 11
Chapter 1
1.1 Introduction:
Most important worries in our power industry is the continuously
increasing power requirement but the unavailability of adequate resources to
encounter its requirement by using the conventional sources of energy.
Power demand has increased for the non-conventional sources of energies
should be used along with the conventional systems to fulfil the energy
demands. Non-conventional energy sources like solar energy and wind energy
are the leading sources of energy; which are mainly used in this favour to
extract green energy. The daily usage of fossil fuels has affected its deposit
to be decreased drastically and has critically affected the environment, thus
depleting the biosphere & resulting the global warming.
Solar energy is profusely obtainable on earth that has made it conceivable
to harvest & utilize it suitably. Solar energy may be a grid connected generating
unit or a standalone one depending on the availability of a grid nearby. As a
result it can be implemented to power the rural areas; where the accessibility of
grids is very less. Another advantage of using solar energy is the transportable
operation wherever & whenever necessary.
Photovoltaic (PVs) are arrays/module (combination of smallest unit
called cells) that contain a semiconductor material, which converts solar energy
into electrical energy. PV systems include multiple components like mechanical
and electrical connections and mountings and various means of regulating and
(if required) modifying the electrical outputs. Materials which are used in
photovoltaic applications are poly-crystalline silicon, mono-crystalline silicon,
micro-crystalline silicon (amorphous) and cadmium telluride. The current and
voltage that available at the PV device output terminals can be directly used to
feed any small loads like lighting systems or small DC motors.
This PV array can also be interfaced with MPPT algorithm & power
electronic converters to extract maximum power.
Due to the further development in the direction of power electronics, it
has also been possible to further reduce the losses during switching in the
converters, which are being used along with the PV array/module.
Page 12
1.2 Converter Topology Used For Pv Systems:
In order to feed the power from non-conventional energy sources like
photovoltaic array/module, DC-DC converters has played an important role
during interfacing & to supply required AC or DC power. Hence for efficient
load management it is necessary that the interfacing converter should be highly
efficient. Here DC-DC Boost converter is taken, which is the most popular
topology for obtaining the constant value of high DC output. Because of its
simplicity which leads to high reliability & high efficiency at lower cost.
Due to overlapping of current & voltage waveforms, in case of the
hard switching boost converters, during switching and the reverse recovery
of the diode, there lies a high amount of switching loss with each of the
switching cycle.
In order to eliminate the above shortcomings, new power electronics
circuits are being based on resonant and soft-switching technologies. Hence an
increase in the efficiency of the system is obtained as to the non-overlapping
of the voltage and current waveforms during switching. This results in the
decrease in output ripples at higher values of frequencies. Also, it is possible
to use smaller values of inductors and capacitors, with the increase in
frequencies, which results in the reduction of the components sizes and thus
increasing the power density.
This thesis highlights on a soft switching technique which provides ZVS turnon and turn-off for the main switch & ZCS turn-on and ZVS turn-off with the
use of resonant circuit by the auxiliary switch. An anti-parallel diode is added
across the main switch in order to make the voltage zero across it before current
starts to builds, thus making ZVS turn-on process and a capacitor is connected
across it to reduce the rate of rise of voltage across the main switch, thus
making ZVS turn-off process. The auxiliary switch operates with ZCS using
the resonance circuit. This soft switching method is selected over other methods
used for soft-switching because the resonant circuit implemented for this
performs dual operation. It not only makes ZVS turn-off of the main
switch and auxiliary switch but also ensures the ZCS turn-on of the auxiliary
switch. Hence, along with the conduction losses of the auxiliary switch,
the switching losses are also drastically decreased.
Page 13
1.3 Literature Survey:
The utilization of solar energy has been looked upon by many scientists
all around the world. It has been known that solar cell operates at very less
efficiency (up to 19% max.) and thus there is a need of best control mechanism
to increase the efficiency of the solar cell. In this area researchers have
developed what are now called as the Maximum Power Point Tracking (MPPT)
algorithms.
Mummadi Veerachary has given a detailed report on the use of a SEPIC
converter in the area of photovoltaic power control. In his thesis he used a twoinput converter for accomplishing the maximum power extraction from the solar
cell.
M. G. Villalva in his both reports has presented a comprehensive method
to model a solar cell using Simulink. His results were quite similar to the
characteristics of the solar cell output plots.
P. S. Revankar has even included the variation of sun’s inclination to
track down the maximum possible power from the incoming solar radiations.
The control mechanism changes the position of the panel such that the incoming
solar radiations are always perpendicular to it.
M. Berrera has compared seven different algorithms for maximum power
point tracking using two different solar irradiation functions to depict the
variation of the output power in both cases using the MPPT algorithms and
optimized MPPT algorithms.
Ramos Hernanz has also successfully presented the modelling of a solar
cell and the variation of the current-voltage curve and the power-voltage
curve due the solar irradiation changes and the change in ambient
temperature.
Soft-switching technique was developed in the middle of 1980s. Power
electronic engineers who were familiar with phase-controlled thyristor
converters already know that switching loss in this class of converters is
much less or negligible, thus contributes to the high conversion efficiency.
Page 14
1.4 Motivation:
Photovoltaic power control is one of the burning research fields
these days. Researchers are round the clock to develop better solar cell
materials and efficient control mechanisms. The challenge of the project and
the new area of study were the motivations behind the project. In India, there
are nearly 300 sunny days in a year & abundant solar energy is available in
nearly most parts of the country, both in the urban/rural areas.
But still we have lots of distance to cover, in order to effectively utilise
the solar power. In contrast to fossil fuels, it became a cheap and effective
solution for both commercial & domestic use. With the day-by-day increasing
demand for the renewable energy sources, the productivity of photovoltaic
modules/ array has advanced dramatically in recent years. Its efficient
usage has led to increasing the role of photovoltaic technology as reliable and
robust means of harnessing renewable energy.
1.5 Thesis Objective:
The following objectives are being achieved at the completion of the project:
1) To design an exact Two-diode Photovoltaic Array system simulator using
the Simulink models; which will be more user-friendly & to observe its
characteristics.
2) To design & analyse the operation of Boost converter.
3) To study the soft-switching technique of DC-DC Boost converter &
detailed analysis of its operations.
1.6 Thesis Outline:
The thesis has been broadly divided into 6 chapters. The first chapter
includes the introduction, converter topology, literature survey, motivation,
objectives & road-maps. Chapter 2 is based on PV characteristic. Chapter 3
deals with the modelling of PV Array. Chapter 4 consists of chopper circuit &
hardware verification of Boost converter. Chapter 5 deals with the soft
switching techniques & various modes of operation. Chapter 6 shows the results
of the Simulink model & the conclusions drawn.
Page 15
1.7 Road Maps:
The project has been started from the month of January 2014, when the
results of PV array (i.e. the accurate P-V & I-V Characteristics) were obtained.
In the same month the accuracy was checked by applying the same model to
five PV modules of different kind. In February the results were verified under
Partial Shadings conditions & hardware implementation of Boost converter was
done. In subsequent months the MATLAB model of the boost converter along
with ZVS switching method being simulated & the results were obtained.
Page 16
Chapter
2
Photovoltaic Systems
Page 17
Chapter 2
The effect of the photoelectric was first founded by a French physicist,
Edmund Bequerel in back 1839. He noted that certain materials have property
to produce small amounts of electric current when exposed to the sunlight. In
1905, Albert Einstein demonstrated the nature of light & the photoelectric effect
which has become the basic principle for photovoltaic technology. The first
photovoltaic module was built by Bell Laboratories in back 1954.
2.1 Photovoltaic Groupings:
PV system consists of 3 types of groups; namely:
2.1.1 Photovoltaic cell
2.1.2 Photovoltaic module
2.1.3 Photovoltaic Array
2.1.1 Photovoltaic cell:
PV cells are basically a diode made of semiconductor materials. Like a
diode, this PV cells also has a p-n junction & produces electricity when directly
exposed to sun-light. PV cell are basically made up of various types of semiconductor materials like mono-crystalline, poly-crystalline, amorphous & thin
film. Mono-crystalline and Poly-crystalline silicon are widely used for the
commercial use because of high efficiency.
Fig. 1 – PV Basic cell structure
Page 18
2.1.2 Photovoltaic module:
A single PV cell is incapable to produce the power for general purpose.
Therefore by inter-connecting several PV cell in parallel (for high current
requirements) & in series (for high voltage requirements) can fetch us the
required power. Normally a series connection is chosen, which is mainly
recognized as a module. A module normally comprise of 36 or 72 cells. The
modules consist of a transparent front side & an encapsulated PV cell at the
back side. The front side materials are usually made up from low-iron and
tempered glass. The overall efficiency of a PV module is less than that of a PV
cell. This is due to the fact that some radiations are reflected by the glass surface
cover, thus by reducing the overall efficiency of the module.
2.1.3 Photovoltaic Array:
Photo-voltaic array is made by inter-connecting many modules in series
& parallel manner to meet the power requirement. The energy generated by a
single module is hardly enough to use for commercial purpose. So modules are
linked in many ways; like Series-Parallel, Bridge-Linked & Totally Crossed
Tied; to supply the load with at most efficiency. In metropolitan areas, normally
the arrays are attached on the roofs. Also for the agricultural purpose, the array
output can be directly supplied to a DC motor.
Fig. 2 - Hierarchy of Photovoltaic
Page 19
2.2 Working of a PV cell:
Photoelectric effect is the elementary principle of working of a PV cell. It
can be described as the phenomenon in which a semi-conductor diode absorbs a
certain wavelength of sun light mainly of UV/Infrared/visible regions & ejects
an electron. When the sunbeam falls on PV cell surface, some part of the solar
energy are being scattered & reflected, while others are absorbed by this
material. If the absorbed solar energy is much greater than the band gap energy
of the semi-conductor material, then an electron migrates from valence band
into the conduction band. By this process, lots of hole-electron pairs are
generated inside the semiconductor. The electrons formed by this process are
much mobile to move by the action of small electric potential. These free
electrons are enforced to move in a particular direction by the action of electric
field created in the PV cells. These free electrons thus forms current and that
can be drained out for peripheral use by attaching a metal plate on the top and
the bottom of PV cell. This current and the voltage are basically responsible for
the necessary output power.
2.3 Characteristics of a PV cell (Two-Diode Model):
PV characteristic consists of mainly three important points namely; Open
circuit voltage (Voc), short circuit current (Isc) and Maximum power point
(Impp, Vmpp, Pmpp) i.e. the maximum powers that can be extracted from a PV
cell are at the maximum power point. Usually manufacturers provide these
parameters in their datasheets for a particular PV cell or module at a particular
temperature & irradiance (i.e. @STP- 25°C & 1000w/m²). By using these
parameters we can construct a simple model but for designing an accurate
model more information are needed.
Fig. 3 -PV cell Characteristics
Page 20
Fig. 4 –Two diode model of PV cell
The Equation of characteristic for the above PV cell is specified by:
=
−
∗ exp
−1 −
∗ exp
−1 −(
)
(1)
Where;
= Photocurrent or Light-generated Current: It is the current generated
directly by incident of sunbeams on the PV cell. This current also varies linearly
with the sun irradiation and depends on the temperature;
=(
_
+
∆ )
(2)
= Light-generated current at nominal condition
_
= Short-circuit current coefficient
= Actual sun irradiance (in
)
= irradiance under STC
∆ = It is the variance between actual temp. & nominal temp. (in Kelvin)
i.e. ∆ = ( −
&
)
are the dark saturation currents of diode 1 and diode 2
&
=
are the thermal voltages of diode 1 and diode 2
&
=
(3)
Page 21
Where,
K= Boltzmann constant = 1.3806503 × 10
q = electron charge = 1.607 × 10
J/K
C
T = Nominal Temperature = 298.15 K
&
represent the diode ideal constants
&
= Due to the presence of internal resistances, (like contact resistances
& manufacturing defects) the power loss takes place in the cell. These internal
resistances can be isolated into series resistance, and parallel resistance,
.
For the ideal case,
would be “zero” &
would be “infinity”.
Under STC:
= 1000
&
= 25°
(4)
Page 22
Chapter
3
Modelling of PV array
Page 23
Chapter 3
3.1 Representation of PV devices:
In this chapter, we will enlighten the basic models of PV array and their
advantages and disadvantages over each other’s. Then, we will go through a
new method to extract the unknown parameters using known ones.
The PV devices are essentially represented in two different models viz.
3.1.1. Single diode model
3.1.2. Double diode model
3.1.1. Single diode model:
In a single diode model, there is a current source in parallel to a diode. The
current source signifies the light-generated current,
that varies linearly with
the solar irradiation. This is the simplest and most widely used model for
simulations as it offers a good compromise between simplicity, reliability and
accuracy. Figure below indicates the single diode model circuit.
Fig. 5 –Single diode model of PV cell
Disadvantages:
The single diode models were based on the postulation that the recombination
losses are absent in the depletion region. But, in a real solar cell, the
recombination loss represents a significant loss, especially at low voltages.
Whereas in two-diode model the insertion of an additional diode increases the
preciseness.
Page 24
3.1.2. Two diode model:
In this model an additional diode is attached in parallel to the single diode
model circuit. This diode is incorporated to provide an even more accurate &
precise I-V characteristic curve that also deliberates for the difference in flow of
current at low current values due to charge recombination in the depletion
region of the semi-conductor. (Two diode model figure No. 2)
The characteristic equation for PV cell is given by:
=
−
∗ exp
−1 −
∗ exp
−1 −(
)
(5)
(Note: All the parameters are explained in previous chapter)
The
term in the above equation, recompenses the recombination loss in the
depletion region.
Although greater accurateness can be achieved by using this model; but it
requires the working out of seven parameters, namely
, , , , ,
&
.
To shorten the calculation we have assumed
=1&
= 2. These values are
guesstimate of the Schokley-Read-Hall recombination in space charge layer.
3.2 Improved Computational Method:
To further simplify, both the
=
=
(
are set to be equal in magnitude:
∆ )
_
∆
_
{(
&
)/ }∗
(6)
= the open-circuit voltage coefficient (presented from data-sheets)
The equalisation shortens the computation as no iteration is required.
According to the Shockley’s Diffusion Theory;
Must be unity & (
+
)/ = 1
(7)
Page 25
Hence the above equation again simplifies to:
=
(
=
∆ )
_
(8)
∆
_
Up to this five parameters of this model are easily calculated, i.e.
,
& the values of ,
are achieved through iteration.
3.3 Determination of the
&
,
,
,
Values:
The residual two parameters
& are attained through successive iteration.
The idea is to maximize the power point (
) matching; i.e. to match the
calculated peak power (
, ) & the experimental/ manufacturer peak power
(
while concurrently
, ) by iteratively increasing the value of
manipulating the value of
.
Under maximum power-point condition,
=
(
[
{
can be written as
)
}
=
Where,
(9)
]
,
[exp
=
[exp
− 1]
+
(10)
− 1]
The initial circumstances for both resistances are given below:
=0
&
=
−
(11)
Page 26
3.4 Simulation Results:
Fig. 6 –PV simulator Block in Simulink
Fig. 7 –Input parameter window of Kyocera (KG200GT) 50*10 Array
Page 27
1000 W/m2
25 degC
80
80
800 W/m2
50 degC
60
I (A)
I (A)
60
40
40
400 W/m2
75 degC
20
200 W/m2
20
0
0
500
1000
V (V)
0
0
1500
500
1000
V (V)
1500
Fig. 8 – Curves I-V of Kyocera @different Temp & @different Irradiation
4
x 10
x 10
25 degC
10
4
1000 W/m2
10
800 W/m2
8
P (W)
P (W)
8
6
50 degC
4
600 W/m2
6
400 W/m2
4
75 degC
2
2
200 W/m2
0
0
500
1000
V (V)
0
0
1500
500
1000
V (V)
1500
Fig. 9 – Curves P-V of Kyocera @different Temp & @different Irradiation
P-V @ Shading
I-V @ Shading pattern
120
8
Power (in P)
Current (in A)
100
6
4
80
60
40
2
20
0
0
10
20
Voltage (in V)
30
0
0
10
20
Voltage (in V)
30
Fig. 10 – Curves I-V & P-V of Kyocera for shading pattern
Page 28
Multi-crystalline
BP Solar
MSX-60
Kyocera
KG200GT
Shell
S36
Monocrystalline
SP-70
01
3.8 A
8.21 A
2.3 A
4.7 A
2.68 A
02
21.1 V
32.9 V
21.4 V
21.4 V
23.3 V
03
3.5 A
7.61 A
2.18 A
4.25 A
2.41 A
04
17.1 V
26.3 V
16.5 V
16.5 V
16.6 V
05
-80 mV/°C
-123 mV/°C
-76 mV/°C
-76 mV/°C
-100mV/°C
06
3 mA/°C
3.18 mA/°C
1 mA/°C
2 mA/°C
0.35 mA/°C
07
36
54
36
36
36
Sl.No
Parameter
Thin-Film
ST-40
Table No: 01 – ISTC Specifications for the 3 Modules used in experiments
Multi-crystalline
BP Solar
MSX-60
Kyocera
KG200GT
Shell
S36
Monocrystalline
SP-70
01
3.8 A
8.21 A
2.3 A
4.7 A
2.68 A
02
21.1 V
32.9 V
21.4 V
21.4 V
23.3 V
03
3.5 A
7.61 A
2.18 A
4.25 A
2.41 A
04
17.1 V
26.3 V
16.5 V
16.5 V
16.6 V
4.7455e-10
4.1659e-10
2.0769e-10
4.2441e-10
3.1048e-11
06
3.8
8.21
2.3
4.7
2.68
07
167.9843
145.8896
836.4395
89.9532
189.9195
08
0.34
0.32
0.90
0.38
1.53
Sl.No
05
Parameter
=
Thin-Film
ST-40
Table No: 02 – Parameters for Proposed Two-Diode Model
Fig. 11 – Relative Error for
&
Page 29
Chapter
4
DC Chopper Circuits
Page 30
Chapter 4
4.1 Introduction:
Now-a-days DC power sources are widely used many
industrial
applications. Variable DC voltage sources however, perform better in order to
extract power at maximum efficiency. Examples of such DC system are subway
cars, battery-operated vehicles, trolley buses, battery charging etc.
A chopper is a static device that transforms directly a fixed dc voltage to
an adjustable dc output voltage. A chopper can also be assumed of as dcequivalent of an AC transformer as they act in the same identical manner.
Since a chopper comprises one stage transformation, these are more effective.
The power semiconductor devices which is used for the chopper circuit
can be thyristor, power MOSFET, power BJT, GTO or IGBT. Like transformer,
a chopper circuit can also be used to step-up or step-down the stationary input
voltage.
Here, the Boost converter topology is used for obtaining a constant value
of high DC output voltage.
4.2 Boost Converter:
A boost converter (step-up converter) is a DC-to-DC power
converter with an output voltage greater than its input voltage. It is a part
of switched-mode
power
supply
(SMPS)
containing
at
least
two semiconductor switches (a diode and a transistor) and at least one energy
storage constituent, a capacitor/ an inductor, or the two in combinations. Filters
prepared of capacitors (occasionally in blend with inductors) are usually added
to the output of the converter to shrink output voltage ripples.
There are two modes of action namely;
 Continuous Mode: When a boost converter works in this mode, the
current through the inductor never decreases to zero.
 Discontinuous Mode: If the ripple amplitude of the current is too high,
the inductor may be entirely discharged before the completion of the
entire commutation cycle. This is commonly occur under light loads
conditions. In this case, the current through the inductor falls to zero
during part of the operation.
Page 31
Fig. 12 – Fly back mode boost converter
A pulse was used to mimic the operation of the control chip with an ontime of 9.83 µs and off-time of 6.1 µs. The circuit was simulated with a 120Ω
resister connected across the output capacitor. The result of the simulation has
been included below, which shows the waveform of the voltage at the switching
mode of the converter. The output voltage level is at 12V. The power efficiency
of the circuit exceed 70% for the load range of 120-145Ω.
Equation Involved:
=
Where,
(
(12)
)
K=
= Duty- Cycle of the converter
Test Results:
Fig. 13 – Output Voltage waveforms of Boost Converter
Page 32
Chapter
5
Soft Switching of DC-DC
Boost Converter
Page 33
5.1 Introductions:
Converters which use the conventional way of switching phenomenon are
known as Hard Switching converters. When the switch is turn-on, the voltage
across the switch tends to decrease while the current increases; which results in
considerable switching losses.
Soft switching technique can be incorporated to reduce EMI, switching &
conduction losses and switching stresses. If the semiconductor device is
prepared to turn off or turn on when current or voltage is zero, then the product
of voltage and current during transition period is zero which results to the zero
power loss.
5.2 Soft Switching In Boost Converters:
PV array can be interfaced with DC-DC Boost converter with soft
switching technique & MPPT tracker to extract maximum efficient power.
Fig. 14 – The topology for Soft-Switching Boost Converter
Page 34
The following assumptions are considered for the operation & analysis of
the circuit:
 Large input inductor to make the input current constant
 Large output capacitor to make output voltage constant
Fig. 15 – Theoretical waveforms for Soft Switching Converter
5.3 Analysis of Various Operations Intervals:A. Interval 1 (
−
):
In the commencement of this interval, the auxiliary switch
is turned on
with ZCS process while the main switch remains off. A resonant loop consisting
of
- - - is formed because of the resonance between
and .
The current in
reaches zero (soft turn-off) at the end of the period. Now,
when the current through
becomes equals to the current through , mode 1
ends.
Page 35
B. Interval 2 (
−
):
In this interval, switch
will remains on, while the current through
increases due to the resonance. The drain voltage of main switch
tries to drop as the snubber capacitor discharges. This interval finishes
when the voltage across
drops to zero.
C. Interval 3 (
−
):
In this interval, the anti-parallel diode across the main switch
is
turned on; by making the voltage across main switch to zero thus ensuring ZVS
turn-on process. The interval ends when current across the main inductor equals
to that of the resonant inductor current.
Page 36
D. Interval 4 (
−
):
In this interval, the main switch
is being turned on at zero voltage
condition and henceforth, there are no switching losses through it. The resonant
capacitor
is charged uninterruptedly in this interval. The load current is
constantly provided by the output capacitor.
E. Interval 5 (
−
):
In this mode, the current drifts through the anti-parallel diode of
.
Hence, the switch
is turned off certifying ZVS process. Thus, there is no
switching loss in
during the turn-off period. This period finishes when
resonant capacitor
is being fully charged.
Page 37
F. Interval 6 (
−
):
In this interval, the current drifts through the auxiliary diode
instead of
anti-parallel diode of switch
. This interval split ends, when the main switch
is turned off.
G. Interval 7 (
−
):
In this interval, the main switch
is turned-off by ZVS process
under the assistance of snubber capacitor
. During this time energy is
being stored in the capacitor
. This interval finishes when
is charged
fully.
Page 38
H. Interval 8 (
−
):
Here, in this interval, the resonant inductor
starts to discharge and
the energy is transported to the load over the output diode (
). This interval
derives to an end when
is discharged fully. Because of the ZVS method, the
output diode doesn’t involve any switching losses and the power losses.
I. Interval 9 (
−
):
During this interval, all the switches are turned off and the whole current
propagates through
to the load. Hence this interval finishes when
is
turned on.
Page 39
5.4 Theory of Main & Auxiliary Switch:-
The duty-cycle of auxiliary switch is such that it forces the main switch to
activate with soft switching. When the auxiliary switch is made turn-on then it
forms a resonant loop between
& . ZVS process is mainly initiated during
turning on of the auxiliary switch. The PWM pulses of the main switch have to
make a delay than that of auxiliary switch. Soft switching with resonance is
achieved by properly turning on the switches. During the suspension time
auxiliary switch must remain turn on.
The least delay time must be fulfilled by the subsequent equation:
≥
+
√(
)
(13)
The voltage conversion equation is defined as:
≈
(
)
(14)
where,
=
Duty cycle of the main switch
=
Duty cycle of the auxiliary switch
Page 40
Chapter
6
Experimental Results
& Conclusions
Page 41
6.1 PV Modelling Conclusions:
After going through the three arrays (i.e. Multi-crystalline, Monocrystalline & Thin-Film) used in the above experiment, we are concluded,
regarding the effect of temperature & irradiance, that temperature mainly affects
the voltage whereas irradiance affects the current across PV Module.
It was observed from the P-V or I-V curves of
 Figure-8(i) that open-circuit voltage drops with the rise in temperature.
 Figure-8(ii) that short-circuits current drops with reduction in irradiation
which is understandable since, they retain a linear relationship.
 Figure-9(i) that with the rise in temperature the maximum power-point
drops.
 Figure-9(ii) that with the reduction in irradiation also the maximum
power-point decreases.
It has also been observed (from Fig. 11) that, under the STC (Standard Testing
Conditions) irradiance level, there is a very slight difference in the
values
among the three models. When irradiance is reduced then substantial
abnormality is witnessed with
&
models; similarly for
.
Hence, from the above comparisons & simulation results it was concluded that
the Proposed Two-Diode Model perfectly calculates
under all conditions.
This simulator can also be interfaced with MPPT algorithm & power electronic
converters to extract maximum power.
6.2 Soft Switching Boost Converter Results:
The following table shows all the parameters used during the simulation
& designing. The simulation is executed under resonant switching frequency
(i.e. 160 KHz) & a rated power of 230W.
PV Array has an output voltage of 18V. A 10Ω load is attached across the
output of the soft switching Boost converter.
Page 42
Parameters
Output Voltage
Rated Power
Main Inductor
Resonant Inductor
Resonant Capacitor
Snubber Capacitance
Switching Frequency
Input Capacitor
Output Capacitor
Label
Value
48.8 V
230 W
200 uH
10 uH
100 nF
0.3 uF
160 KHz
50 uF
470 uF
L
Table No: 03 – Parameters used for the Simulation of Soft switching Boost converter
As we know that, resonance is formed between an inductor ( ) & a
capacitor ( ) if the switching is done at resonance frequency ( ).
=2
=
= 10
From the above equation, switching frequency (
(15)
=
) is obtained as 160KHz.
6.3 Simulation Results of Soft Switching Boost Converter:
The MATLAB simulated soft switching Boost converter circuit is presented
below.
Fig. 16 – Soft Switching Boost Converter Simulink Circuit
Page 43
Simulation results of main switch current & voltage waveforms are
shown in the following figure ensuring the ZVS turn-on & turn-off process. The
slope in the voltage waveform indicates ZVS turn-off whereas anti-parallel
diode ensures ZVS turn-on.
The reversing of current across auxiliary switch depicts ZCS turn-on due
to resonance & the anti-parallel diode ensures the ZVS turn-off of the auxiliary
switch & the resonant capacitor.
Fig. 17 – Simulation Result Waveforms: Gating Signal to Main Switch, Gating Signal
to Aux. Switch, Voltage across the Main Switch, Voltage across the Aux. Switch, Current
through the Main Switch, Current through the Aux. Switch, Current through the Main
Inductor, Current through Resonant Inductor & Voltage across the Resonant Capacitor resp.
Page 44
The output current (
) & output voltage (
10Ω load are also obtained & shown below:
) waveforms across the
Fig. 18 – Load Current & Voltage Waveforms
6.4 Soft Switching Boost Converter Conclusions:
An auxiliary resonant circuit ensuring Soft switching Boost converter
along with the two diode equivalent model of PV Array has been discussed in
this thesis. The simulation results ensure the soft switching of both the switches,
thus eliminating switching losses, conduction losses, electric stresses & EMI.
Proper design of inductor must be taken for appropriate soft switching as the
inductor plays a very vital role in the design of Boost converter. A proper
difference can be perceived in the effectiveness of Hard Switching & Soft
Switching converters. This method of soft switching can be used for low power
DC equipment mainly in telecom services. This soft switching method not only
eliminates the losses but also increase the overall efficiency of PV systems thus
making the overall system to cost-effective & reliable to use.
Page 45
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[1]
IEEE Standard Definitions of Terms for Solar Cells, 1969
[2]
Gwinyai Dzimano, B.S. “Modeling of Photovoltaic Systems”, The Ohio
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[3]
Ryan C. Campbell, A Circuit-based Photovoltaic Array Model for Power System
Studies, Pg.1 Student Member, IEEE.
[4]
H. J. M¨oller, Semiconductors for Solar Cells. Norwood, MA: Artech House, 1993.
[5]
W. Xiao, W. G. Dunford, and A. Capel, “A novel modeling method for photovoltaic
cells,” in Proc. IEEE 35th Annu. Power Electron. Spec. Conf. (PESC), 2004, vol. 3,
pp. 1950–1956.
[6]
N. Jain,”A Zero Voltage Switching Boost Converter using a Soft Switching Auxiliary
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[7]
G. Walker, “Evaluating MPPT converter topologies using a matlab PV model,” J.
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[8]
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IEEE Transaction on Power Electronics, Vol. 24, No. 5, Pg.1198-1204, May 2009.
[9]
A.S. Sedra & K.C. Smith, Microelectronic Circuits. London, U.K. Oxford Univ.
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[10]
Daniel S.H. Chan, member IEEE and Jacob C.H. Phang, member IEEE, “Analytical
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from I- V Characteristics”,IEEE transactions on electron devices, Vol.ED-34 No.2
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[11]
R. Gurunathan and A. K. S. Bhat, “A zero-voltage transition boost converter
using a zero-voltage switching auxiliary circuit,” IEEE Trans. on Power
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[12]
S.H. Park, G.R. Cha, Y.C. Jung and C.Y. Won, “Design and application for
PV generation system using a soft switching boost converter with SARC,” IEEE
Trans. on Industrial Electronics, vol. 57, no. 2, pp515-522, February (2010).
State
Page 46
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