Study and Analysis of Distributed Maximum Power Point Vadigi Chaitanya

Study and Analysis of Distributed Maximum Power Point  Vadigi Chaitanya
Study and Analysis of Distributed Maximum Power Point
Tracking Under Partial Shading Conditions.
Vadigi Chaitanya
710ee3074
Department of Electrical Engineering
National Institute of Technology
Distributed Maximum Power Point Tracking Under
Partial Shading Conditions.
A Thesis submitted in partial fulfilment of the requirements for the degree of
M.Tech Dual Degree in Electrical Engineering.
By
Vadigi Chaitanya
710ee3074
Under the guidance of
Prof. Susovon Samanta
Department of Electrical Engineering
National Institute of Technology
Rourkela-769008 (Odisha).
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Electrical Engineering Department
National Institute of Technology Rourkela.
CERTIFICATE
This is to certify that the dissertation report/thesis titled “Distributed Maximum Power Point
Tracking Under Partial Shading Conditions”, submitted to the National Institute of
Technology, Rourkela by Vadigi Chaitanya (Roll. No. 710EE3074) for the award of Master
of Technology in Electrical Engineering, is a bona fide record of research work carried out by
him under my supervision and guidance.
The candidate has fulfilled all the prescribed requirements. The dissertation report/thesis which
is based on candidate’s own work, has not submitted elsewhere for a degree. The draft
report/thesis is of standard required for the award of a Master of Technology in Electrical
Engineering.
Date:
Place: Rourkela
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Prof. Susovon Samanta
Supervisor
ACKNOWLEDGEMENT
For the development of the project of “Distributed Maximum Power Point Tracking Under
Partial Shading Conditions”, I would like to extend my gratitude and sincere thanks to Prof.
Susovon Samanta, Department of Electrical Engineering for his constant motivation and
support during the course of my work in the last one year. I truly appreciate and value his
esteemed guidance and encouragement of the project.
Especially I want to acknowledge the help of K.Muralidhar, Dept. of Electrical Engineering
for his valuable suggestions. I would also like to extend my gratitude to my friends, especially
K.Prudhavi Nag and S.Harsha Vardhan who have patiently extended all sorts of help for
accomplishing this undertaking.
VADIGI CHAITANYA (710EE3074)
Department of Electrical Engineering,
National Institute of Technology,
Rourkela – 769008.
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ABSTRACT
Photovoltaic (PV) energy generation is becoming an increasingly widespread means of
producing clean and renewable power. In PV systems, long strings of photovoltaic modules
are found to be vulnerable to shading effects, causing significant reduction in the system power
output. To overcome this, distributed maximum power point-tracking (abbreviated as DMPPT)
schemes have been proposed, in which individual dc–dc converters are connected to each PV
module to enable module-wise maximum power extraction. The development of a distributed
maximum power point tracking (DMPPT) photovoltaic (PV) system enables us to compensate
the shading effect and the PV module mismatching as well as to increase the overall output
power. The two main concepts to implement DMMPT systems are series and parallel
configuration which describes the connection of the output terminals of the converters. Both
systems are studied intensively. Output side sensor based DMPPT system has also been
studied. It is also proved that parallel configuration is virtually free of any cross coupling
effects.
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CONTENTS
ABSTRACT
5
CONTENTS
6
LIST OF FIGURES
8
ABBREVIATIONS AND ACRONYMS
10
Chapter 1: Introduction
11
1.1 Introduction
12
1.2 Motivation
13
1.3 Thesis Objectives
14
1.4 Organisation of Thesis
15
Chapter 2: Modelling of PV system
17
2.1 Characteristics of PV array
18
2.2 Operation of Boost converter
19
2.3 Maximum Power-Point Tracking
22
2.3.1 Perturb and Observe algorithm
24
Chapter 3: DMPPT and Mathematical Analysis of Cross-Coupling Effects
26
3.1 Distributed Maximum Power Point Tracking
27
3.2 Mathematical Analysis of Cross-Coupling Effects
29
3.2.1 Analysis of parallel configuration
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30
3.3 Results and Discussions
Chapter 4: Output side sensor based PV system
4.1 output side sensor based MPPT
33
40
41
4.1.1 Results and Discussions
43
4.2 Output side sensor based DMPPT
45
4.2.1 Results and Discussions
46
Conclusion
49
Bibliography
50
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LIST OF FIGURES
Figure 1 PV cell equivalent circuit
18
Figure 2 PV cell P-V, I-V characteristics
19
Figure 3 Boost converter when the switch is closed
20
Figure 4 Boost converter when the switch is open
20
Figure 5 Operating Point control using Duty cycle
21
Figure 6 PV system implementing MPPT
23
Figure 7 Flowchart of P&O algorithm
24
Figure 8 PV system in series DMPPT configuration
27
Figure 9 PV system in parallel DMPPT configuration
28
Figure 10 Equivalent circuit for a parallel DMPPT system
30
Figure 11 DMPPT system in parallel configuration
34
Figure 12 output voltage after boosting for lower insulation
35
Figure 13 Output voltage for higher insulation
35
Figure 14 Final power obtained by parallel connected DMPPT modules
36
Figure 15 DMPPT in series configuration
37
Figure 16 power obtained from higher insulation module at steady state
38
Figure 17 output voltage for module 1
38
Figure 18 output voltage for module 2
39
Figure 19 power received by load
39
Figure 20 Power vs Duty cycle characteristics
41
Figure 21 Output voltage at steady state after DC-AC conversion
43
Figure 22 Output current at steady state after DC-AC conversion
43
Figure 23 Power from the solar module after reaching steady state
44
Figure 24 Power received by tracking the MPP by the load
44
Figure 25 Power obtained from lower insulation module after reaching steady state
46
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Figure 26 Output current at steady state after DC-AC conversion
46
Figure 27 Output power of output sensor based DMPPT
47
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ABBREVIATIONS AND ACRONYMS
PWM
-
Pulse Width Modulation
AC
-
Alternating Current
DC
-
Direct Current
MPP
-
Maximum Power Point
MPPT
-
Maximum Power Point Tracking
DMPPT
-
Distributed Maximum Power Point Tracking
MATLAB
-
MATrix LABoratory
PV
-
Photo Voltaic
SCPVM
-
Self-controlled Photo Voltaic Module
P&O
-
Perturb and Observe
CC
-
Constant Current
CV
-
Constant Voltage
I
-
Current
V
-
Voltage
p
-
Power
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CHAPTER
1
Introduction
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1.1 Introduction:
The increasing concern over environmental issues and the advantages that photovoltaic energy
generation provides, if compared to other renewable energy sources, especially in terms of
maintenance and reliability, attracted interest and remarkable investments in PV technology in
the last decade. A PV field is comprised of a number of series connected strings that are
arranged in parallel. Generally, cells in a PV field are assumed to be of the same type, or
sometimes equal, but such a hypothesis is no longer valid when tolerances of manufacturing
and aging-related parametric drift are accounted for. Moreover, due to possible different
orientations of modules and to shadowing effects, the PV field very often works in mismatching
conditions, and the possibility that some cells in a module or some modules in a string are
potentially able to deliver strongly different currents is very high. To avoid one shadowed cell
from narrowing the current path in a string, thus lowering the other ones in the series and
reducing the overall power production of the whole string, bypass diodes are usually placed in
antiparallel to small groups of series-connected cells. In case of mismatching, this arrangement
helps to increase the power production of the PV field but makes its power versus voltage graph
multimodal. The detection of the absolute maximum power point (MPP) of the PV field in such
a characteristic makes much more complicated because of the presence of more than one peak.
Operation in any other point of the characteristic, due to fault of the MPP tracking (MPPT)
technique in presence of mismatch conditions, results in a consistent drop in the overall
system’s efficiency. In order to overcome such a setback, a switching converter connected to
each module and performing the MPPT operation can be used. This method is referred to as
distributed maximum power point tracking (DMPPT).
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A number of PV modules are usually connected in series to supply the input voltage to the
inverter within its operating range, and similar strings are connected in parallel to get the
desired output power. As a first-order approximation, it is possible to model the dc–ac
conversion stage as a voltage source with a series resistance. In fact, a PV inverter is capable
of sinking any amount current in a certain range while keeping its input voltage regulated to a
fixed average value. This hypothesis greatly simplifies system’s analysis because each string
forms an independent loop with the equivalent model of the dc–ac conversion stage, and the
analysis of the circuit can be simplified by adopting to the analysis of a single string of N selfcontrolled PV modules (SCPVM).
1.2 Motivation:
As the time progresses, the demand of power is increasing gradually and on the contrary the
fossil fuels used for power generation are decreasing rapidly. Alongside the reason of
inadequate resources, the methods that are used for power generation by fossil fuels are not
even eco-friendly and they are causing global warming and greenhouse effects. Now would be
the proper time to initiate the usage of renewable energy resources on very large scale.
The renewable energy resources that are available to us are Solar Energy, Hydro Energy and
Wind Energy. They are rich in quantity, pollution free, distributed all through the earth and
recyclable. Hydro Energy generation, Wind Energy generation are of course two of the main
sources of renewable energies, but the disadvantage in Hydro Energy is that, it is seasonal
dependent and in Wind energy is that it depends on geographical location. On the contrary,
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Solar Energy is widespread all over the globe and all the time. Also most of the remote areas
have not been connected to the grid and they do not have power supply. These areas can
generate power on their own using renewable resources such as solar energy. The amount of
irradiance and temperature vary from location to location and from time to time but under given
conditions Solar Energy system can be installed. Photo Voltaic energy system is the most direct
way to convert the solar radiation into electricity based on photovoltaic effect. Despite high
initial costs, they have already been implemented in many areas. Research is going into this
area to develop the efficient control mechanism and provide better control. Recent
developments in the technology of batteries and solar panel efficiencies offers a better
performance. So the overall installation cost of photovoltaic charging system reduces. And
therefore, the time is not so far that almost any and every middle class person can afford a solar
panel at home for at least some basic requirements.
In the light of above points, it is clear that Solar Energy plays an important role in the
forthcoming future. So, it is our duty to learn, implement and improvise the idea as early as
possible, so that it becomes a very useful tool to our future generations.
3.1 Thesis Objectives:
Objectives here in this project are:

To study the solar cell model and observe its characteristics.

To study the proposed DC-DC boost converter and its operation.

To study MPPT algorithms and method to generate PWM wave according to the output
of MPPT algorithm.
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
To study how to use boost converter to implement the proposed MPPT and DMPPT
systems.

To study the comparison between the conventional MPPT method and the proposed
DMPPT method in terms of efficiency improvement.

Matlab Simulink implementation of solar panel, its interface with boost converter,
using MPPT algorithms and generating suitable PWM wave for the control of Boost
converter, its scaling to DMPPT.

To observe the results of simulation, how the system is detecting the maximum power
point, its improvement while using DMPPT under partial shading conditions.

To implement output sensor based DMPPT and observe its operation.
 To prove that there are virtually no cross coupling effects in parallel connection of
DMPPT systems.
1.4 Organisation of Thesis:
The thesis is partitioned into five chapters along with the chapter of introduction at the
beginning. Each chapter is unique and is presented along with the required theory to encompass
it.
Chapter 2. This section deals with PV Array Characteristics and its modelling. First, the
equivalent circuit of the solar cell is made. Then power versus voltage and current versus
voltage characteristics curves of solar panel are studied. This section discusses Boost converter,
its circuit and its operation are presented along with the necessary illustrations. This chapter
also deals with the Maximum Power Point Tracking (MPPT) systems and the algorithms used
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to implement it. . Here P&O algorithm is discussed for designing the MPPT controller to track
the maximum power point and operate at this point.
Chapter 3. This section deals with Distributed Maximum Power Point Tracking (DMPPT)
systems and how the efficiency of a solar panel is improved by DMPPT under partial shading
condition. This section deals with analysis of DMPPT system with boost converter by StateSpace modelling. Initially state space modelling of MPPT system is derived, thus obtaining
A,B,C and D matrices for the later evaluations, which is further extended to parallel connected
DMPPT system and proving that there are virtually no cross couplings in parallel connected
DMPPT system. Results and discussion with DMPPT in parallel and series configuration has
been presented.
Chapter 4. This section deals with output side sensor based PV system. It has been discussed
about how this would allow reduction in the use of hardware thus affecting the installation cost.
Implementation of this system in Simulink has been presented and corresponding results and
discussions has been presented.
The final conclusion of the project is presented after these chapters concluded by the list of
sources referred in the Bibliography.
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CHAPTER
2
Modelling of PV system
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2.1 Characteristics of PV array:
The electrical equivalent model of a Photo-Voltaic cell consists of a current source and a diode
connected in parallel (Fig. 1).The PV cell behaves as a highly nonlinear current source and its
output voltage is limited. It is known from the PV-cell power versus voltage characteristics that
the power generated reaches its maximum under a precise loading. A module consist of a
number of solar cells which are arranged in parallel and series to increase voltage and current
levels of module. The electrical equivalent circuit of a solar cell is shown in Figure 1. It is
comprised of a series resistance, a parallel resistance, diode and light driven current source.
Here I and V denote current and voltage generated by the solar cell, 𝐼𝑝ℎ (A) denotes current
generated by solar cell, 𝑅𝑠 represents series resistance (Ω), and 𝑅𝑠ℎ represents shunt resistance
(Ω).
Figure 1 PV cell equivalent circuit
When load connected to panel is changed, then corresponding value of voltage and current
changes. Temperature, irradiation and internal characteristic of module affects the P-V
characteristics of the module. Irradiation on a module directly affect charge carriers of module.
So current generated by the module changes according to irradiation of the module. When
intensity of light changes, its corresponding temperature of module changes. So current
generated by the module also influenced by temperature. The constant current region (CC),
where the current of PV-cell stays almost constant from the voltage region (CV), where the
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voltage of PV-cell remains relatively constant is separated by the maximum power point
(MPP). Since the terminal voltage and current of PV-cell are both proportional to ambient
conditions, the loading must be controlled to extract maximum power under all operating
conditions. This process is known as MPP tracking.
Figure 2 PV cell P-V, I-V characteristics
2.2 Operation of Boost Converter:
It has been noted that the output characteristics of any solar module are nonlinear and depends
highly on the solar irradiation and temperature. To maximize the power extracted from solar
module, it has to be operated at fixed value of voltage and current representing a definite value
of load. For this DC-DC converter circuit is needed to operate our intended load and extracting
maximum power from the panel. Here in this project a boost converter is used.
There are particularly, two modes of operation of a boost converter which are based on the
operation of the switch of boost converter. The first mode is when the inductor is charging
when the switch is closed. The second mode when the inductor is discharging when the switch
is open.
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In this operation mode, the switch is closed. The inductor is charged from the source through
the switch. The charging current is actually exponential but for our simplicity it is assumed to
be linear. The diode helps restricting the flow of current from the source to the load and power
supply to the load is provided by the discharging of the capacitor.
Figure 3 Boost converter when the switch is closed
In discharging operation mode, the switch is closed and the diode is forward biased. The
inductor is now discharged. The discharging inductor and the source charges the capacitor and
supplies the load demand too. The load current variation is usually very small and which is
assumed constant throughout the two modes.
Figure 4 Boost converter when the switch is open
For a boost converter,
𝑉𝑜𝑢𝑡 =
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𝑉𝑖𝑛
1−𝐷
Where 𝑉𝑜𝑢𝑡 is the output voltage of boost converter, 𝑉𝑖𝑛 is the input voltage of boost converter
and 𝐷 (0< 𝐷 <1) is the duty ratio of boost converter.
If load 𝑅𝐿 is connected on the output side of boost converter, then the output power drawn is
2
2
𝑉𝑜𝑢𝑡
𝑉𝑖𝑛
1
=(
)
𝑅𝐿
1 − 𝐷 𝑅𝐿
𝑉𝑖𝑛 2
=
𝑅𝐿 (1 − 𝐷)2
Which must be equal to the power delivered by the solar panel 𝑉𝑖𝑛 𝐼𝑖𝑛 .
⇒ 𝑉𝑖𝑛 𝐼𝑖𝑛 =
⇒
𝑉𝑖𝑛 2
𝑅𝐿 (1 − 𝐷)2
𝐼𝑖𝑛
1
=
𝑉𝑖𝑛 𝑅𝐿 (1 − 𝐷)2
Figure 5 Operating Point control using Duty cycle
𝐼
Value of 𝑉𝑖𝑛 represents the slope of operating point in I-V characteristics graph. Thus by above
𝑖𝑛
equation, it can be controlled by controlling the duty ratio considering load resistance at a fixed
value.
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Hence with the increase of the duty ratio, voltage of solar panel (i.e. input voltage of DC-DC
boost converter) decreases and current from the panel increases. Also with the decrease of the
duty ratio, voltage of panel increases and current from the panel decreases.
This is the method to control the boost converter for attaining the required maximum power
point (MPP).
2.3 Maximum Power Point Tracking:
The method that any grid connected inverter and solar battery chargers adopt to get the
maximum possible power from the photovoltaic (PV) modules is called Maximum power point
tracking (MPPT). Analysis based on the I-V curve shows that photovoltaic cells have a
complex relationship among irradiance (𝑤𝑎𝑡𝑡/𝑚2 ), temperature and resistance of the panel
that introduces non-linear output efficiency. The intention of the MPPT system is to monitor
the output of the module and apply the proper resistance (load) to obtain maximum possible
power from the ambient environmental conditions. Generally, MPPT devices are integrated
into the power conversion systems. Whenever AC power is needed, install inverters that
convert the DC-power to AC-power. The voltage and current corresponding to MPP are called
as MPP voltage (𝑉𝑚𝑝𝑝 ) and MPP current (𝐼𝑚𝑝𝑝 ) respectively.
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Figure 6 PV system implementing MPPT
For a given value of ambient operational conditions, PV cells have a particular operating point
which gives the values of the current (𝐼𝑚𝑝𝑝 ) and Voltage (𝑉𝑚𝑝𝑝 ) of the cell that result in
maximum power output. From circuit theory it can be shown that the power delivered from the
𝑑𝐼
panel is at optimal level when the derivative (𝑑𝑉) i.e., the slope of the I-V curve is equal to
𝐼
𝑑𝑃
the negative ratio of (𝑉) where𝑑𝑉 = 0. This is known as the maximum power point (MPP) of
module at those conditions and occurs at the knee point of I-V curve.
MPPT controllers follow any one of the methods to detect the MPP. Various algorithms are
available that can be implemented to detect this point and the choice may depend on the
operating conditions of solar array. Some of the MPPT algorithms are Perturb and observe
algorithm, Incremental conductance algorithm, Current Sweep method, Constant Voltage
method etc.
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2.3.1 Perturb and Observe algorithm:
Figure 7 Flowchart of P&O algorithm
For the development of MPPT in this project, Perturb and Observe algorithm has been used.
The working of algorithm is as follows: voltage and current of the solar panel is measured
initially. After some time, by measuring the change in voltage and change in current, change
in power is measured. Depending on whether the change in power is positive or negative,
increase or decrease the module voltage as given in the algorithm is followed. If both the
change in power and change in voltage is positive the panel voltage is increased. If change in
voltage is negative and change in power is also negative, increase the module voltage. If either
change in voltage or change in power is positive and the other one is negative, then decrease
the module voltage. Overall algorithm is presented in figure 7.
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Using the signal given by the Perturb and Observe algorithm, the duty ratio of the boost
converter is controlled, there by controlling the increase and decrease of voltage of the solar
panel. So when the insulation level changes, as the maximum power point changes from the
point the module is operating at, this algorithm detects the change and accordingly gives the
signal to the boost converter to reach the maximum power point.
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CHAPTER
3
DMPPT and Mathematical
Analysis of Cross-Coupling
Effects
Page | 26
3.1 Distributed Maximum Power Point Tracking:
Utilising a switching converter between the PV panel and the load is a general method to
implement MPP tracking. The converter is useful in changing the levels of voltage and current
for transferring power between the PV panel and the intended load. A converter which would
transfer power from low voltage to high voltage is needed while interfacing any individual PV
module, since the PV module voltage is most usually insufficient for the suitable operation of
the inverter. Moreover, occurance of non-uniform illumination especially in constructed
environment is quite frequent, causing partially shaded PV modules of whose global maximum
power point occur at a significantly lower voltage than that of uniform illumination condition.
Each string of a panel contains a number of PV modules connected in series, thus increasing
the voltage of string which would be enough for the operation of inverter. These strings have
been seen to be potentially vulnerable to the mentioned shading effects whence the generated
power of the string is limited by shaded module e.g., by obstacles nearby or clouds. Each
module has to carry equal current due to the series connection which forces the operating point
of some modules away from the MPP. To overcome this, DMPPT systems have been proposed.
Here each individual PV module has a dedicated interfacing DC-DC converter.
Figure 8 PV system in series DMPPT configuration
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DMPPT converters are the front part in a two-stage conversion. Here the DC power produced
by the PV modules is transferred into the AC utility grid by means of an inverter. The two stage
structure thus contains a high-voltage dc-link between the DC-DC converters and the inverter.
There would be a number of individual converters that would transfer power into the common
dc-link. There are two general structures of DMPPT systems that are used. They are presented
in figure 8 and figure 9 representing the series configuration and the parallel configuration
respectively. In the series configuration, the outputs of individual DC-DC converters are
connected in series. Thus the dc-link voltage is spread between the converter output terminals.
While in the parallel configuration, the output terminals of the DC-DC converters are
connected parallel to the input of an inverter.
Figure 9 PV system in parallel DMPPT configuration
As observed in figures 8 and 9, although each module is independently connected to a dedicated
converter, they in turn are sharing either a common voltage (in parallel connection) or a
common current (in series connection). This result in a cross coupling effect. When the current
or duty ratio of second module is changed, it results in turbulence of voltage of first panel. Vice
versa, when the current or duty ratio of first module is changed, it ends up effecting the voltage
of second module. These cross couplings are undesirable and there are methods to eliminate
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these cross couplings. These cross couplings are usually prominent in series DMPPT
configuration. Where as in parallel configuration, the effect of cross couplings is much less as
the system doesn’t introduce the cross couplings but only the load does. While in series
configuration, the system itself introduces cross couplings. Hence one could say that parallel
configuration is virtually free of these cross coupling effects.
3.2 Mathematical analysis of Cross-Couplings:
A linear model of a converter is needed in order to analyse the switched-mode converter
operation suitably. In general the State-Space averaging technique usage is quite common to
obtain a small-signal model explaining the operation of the circuit.
In this technique of State-Space averaging, each of the sub circuits obtained from switching
process are analysed separately and by using the Kirchoff’s laws, the equations required are
developed. In this State-Space model a function is developed to relate the output variables and
input variables and state variables. In order to get an averaged State-Space model, it is needed
to average these equations over the switching periods according to the active time of subcircuit. The time invariant model is thus obtained. When the averaged equations are subjected
to linearization at specific operating point, final linear model is obtained. Depending on the
value of resistances, inductance and capacitance values, and the circuit, obtaining the matrices
A, B, C, D.
𝑆𝑋(𝑠) = 𝐴𝑋(𝑠) + 𝐵𝑈(𝑠)
𝑌(𝑠) = 𝐶𝑋(𝑠) + 𝐷𝑈(𝑠)
The output variable can be solved from the above two equations as
𝑌(𝑠) = [𝐶(𝑠𝐼 − 𝐴)−1 𝐵 + 𝐷]𝑈(𝑠)
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𝑌(𝑠) = 𝐺(𝑠)𝑈(𝑠)
The equations are linearized around
𝑈𝑖𝑛 = (𝑟𝐿 + 𝑟𝑑𝑠 + 𝐷 ′ 𝑟𝑑 )𝐼𝐿1 + 𝐷′(𝑈𝑜 + 𝑈𝐷 )
𝐼𝐿1 = 𝐼𝑖𝑛 , 𝐼𝑜 = 𝐷 ′ 𝐼𝑖𝑛
𝑈𝐶1 = 𝑈𝑖𝑛 , 𝑈𝐶2 = 𝑈𝑜
The averaged equations obtained from the Kirchoff’s laws are manipulated to get the StateSpace model.
𝐺 = [𝐶(𝑠𝐼 − 𝐴)−1 𝐵 + 𝐷] =
1
∆𝐿1 𝐶1
(𝑅𝑒𝑞 + 𝑠𝐿1 − 𝑟𝐶1 )(1 + 𝑠𝑟𝐶1 𝐶1 )
𝐷′
[
∆𝐿1 𝐶1
𝐷′
∆𝐿1 𝐶1
2
(1 + 𝑠𝑟𝐶1 𝐶1 )
𝑈𝑒𝑞
(1 + 𝑠𝑟𝐶1 𝐶1 )
𝐷′ 𝑠
𝑠𝐶
− [ ∆𝐿 + 1+𝑠𝑟 2
1
𝐶2 𝐶2
]
− ∆𝐿
−
3.2.1 Analysis of parallel configuration:
Figure 10 Equivalent circuit for a parallel DMPPT system
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𝐼𝑃𝑉
∆
1 𝐶1
(1 + 𝑠𝑟𝐶1 𝐶1 )
𝑅𝑒𝑞
𝐷 ′ 𝑈𝑒𝑞
[𝑠 2 + 𝑠 ( 𝐿 − 𝐿
1
1 𝐼𝑃𝑉
)+𝐿
1
1 𝐶1
]
]
Writing in State-Space form,
𝑋̇ = 𝐴𝑋 + 𝐵𝑈
𝑌 = 𝐶𝑋 + 𝐷𝑈
Solving the equations, we get,
𝑖𝑖𝑛1
𝑢𝑖𝑛1
𝑏1
0
𝑏2
𝑏3
0
𝑖𝑖𝑛2
𝑢𝑖𝑛2 = 0
𝑏4
𝑏5
0
𝑏6
𝑢𝑜
𝑏8
𝑏9
𝑏10
𝑏11 ]
[ 𝑖𝑜 ]
[𝑏7
̂1
𝑑
̂2 ]
[𝑑
Where,
𝑏1 = [− (
𝑠𝑟𝐶11
𝑟𝐶
𝑅𝑒𝑞1 − 𝑟𝐶11 1
1
+
) 11 + (𝑠 +
)
] + 𝑟𝐶11
∆1
𝐶11 ∆1 𝐿11
𝐿11
𝐶11
𝐷1′
1
𝑏2 =
(𝑠𝑟𝐶11 +
)
𝐿11 ∆1
𝐶11
𝑏3 =
𝑏4 = [− (
−𝑈𝑒𝑞1
1
(𝑠𝑟𝐶11 +
)
𝐿11 ∆1
𝐶11
𝑠𝑟𝐶12
𝑟𝐶
𝑅𝑒𝑞2 − 𝑟𝐶12 1
1
+
) 12 + (𝑠 +
)
] + 𝑟𝐶12
∆2
𝐶12 ∆2 𝐿12
𝐿12
𝐶12
𝐷2′
1
𝑏5 =
(𝑠𝑟𝐶12 +
)
𝐿12 ∆2
𝐶12
𝑏6 =
Page | 31
−𝑈𝑒𝑞2
1
(𝑠𝑟𝐶12 +
)
𝐿12 ∆2
𝐶12
𝑏7 =
𝐷1′
1
(𝑠𝑟𝐶11 +
)
𝐿11 ∆1
𝐶11
𝐷2′
1
𝑏8 =
(𝑠𝑟𝐶12 +
)
𝐿12 ∆2
𝐶12
𝑠𝐷1′
𝐷2′
𝑠𝐶21
𝑠𝐶22
𝑏9 = − (
+
+
+
)
𝐿11 ∆1 𝐿12 ∆2 1 + 𝑠𝑟𝐶21 𝐶21 1 + 𝑠𝑟𝐶22 𝐶22
𝑏10 =
𝑏11
𝑠𝐷1′ 𝑈𝑒𝑞1
− 𝐼𝐿11
𝐿11 ∆1
𝑠𝐷2′ 𝑈𝑒𝑞2
=
− 𝐼𝐿12
𝐿12 ∆2
Where,
𝑈𝑒𝑞1 = 𝑢𝑜 + 𝑈𝐷1 + (𝑟𝑑1 − 𝑟𝑑𝑠1 )𝐼𝑖𝑛1
𝑅𝑒𝑞1 = 𝑟𝐿11 + 𝑟𝐶11 + 𝐷𝑟𝑑𝑠1 + 𝐷′ 𝑟𝑑1
𝑈𝑒𝑞2 = 𝑢𝑜 + 𝑈𝐷2 + (𝑟𝑑2 − 𝑟𝑑𝑠 2 )𝐼𝑖𝑛2
𝑅𝑒𝑞2 = 𝑟𝐿12 + 𝑟𝐶12 + 𝐷𝑟𝑑𝑠2 + 𝐷′ 𝑟𝑑2
̂2 . Similarly
Hence, from the above zeroes, it is observed that 𝑢𝑖𝑛1 is independent of 𝑖𝑖𝑛2 and 𝑑
̂1 . Any change in 𝑖𝑖𝑛2 and 𝑑
̂2 doesn’t affect 𝑢𝑖𝑛1 and any
𝑢𝑖𝑛2 is independent of 𝑖𝑖𝑛1 and 𝑑
̂1 doesn’t affect 𝑢𝑖𝑛2 . Hence, virtually there are no cross couplings in
change in 𝑖𝑖𝑛1 and 𝑑
parallel connected DMPPT system.
Page | 32
3.3 Results and Discussions:
The voltage and current signals are sampled using zero order hold. Then change in voltage and
change in power is measured. If both the change in power and change in voltage is positive
then D state is decreased. If change in voltage is negative and change in power is also negative,
it will decrease the D state. If either change in voltage or change in power is positive and the
other one is negative, then it increases the value of D state. Now this signal is compared with
a repeating sequence which produces the required pulse width modulated (PWM) wave through
which the switch of boost converter is controlled.
The distributed maximum power point tracking (DMPPT) under partial shading conditions is
simulated in parallel configuration and the shading condition is generated by providing
different insulation levels to the modules. Now each MPPT tracker connected to the modules
detect the required maximum power point and generate corresponding PWM signals which
controls the respective boost converters. Hence different points will be detected independently
by each module. Input voltage of both modules will be different and the currents flowing
through each modules will also be different from each other so that each will be detecting their
corresponding maximum power point. Both the converters are finally connected together in
parallel DMPPT configuration and it is connected to an inverter which in turn is either
connected to the grid or a load can be connected after smoothening the waveform. Thus
DMPPT is used to get more efficiency from the panel, the downside being more usage of
equipment, in turn effecting the economy of installation. DMPPT system in parallel
configuration is presented in fig.11
Page | 33
Figure 11 DMPPT system in parallel configuration
Page | 34
Figure 12 output voltage after boosting for lower insulation
The input voltage is being controlled by the corresponding MPPT algorithm for tracking of
maximum power point. The input voltage is controlled while the output voltage after boosting
is reaching its value corresponding to the power that is produced by both the modules.
Figure 13 Output voltage for higher insulation
Page | 35
Here it is seen that the output voltage after boosting is similar to the output voltage of lower
insulation. It is because they both are connected in parallel. Whereas input voltage of both
modules doesn’t seem similar because each one is operated by different boost converters so as
to extract maximum power from each module.
Figure 14 Final power obtained by parallel connected DMPPT modules
Finally after tracking MPP from each module and converting it by boost converter and
connecting them in parallel, the tracking of final maximum power from the panel is observed
in figure 14. DC-AC conversion is done if the load needs alternating current. Otherwise load
can directly be connected to the output of DC-DC converter.
Page | 36
Figure 15 DMPPT in series configuration
Page | 37
Figure 16 power obtained from higher insulation module at steady state
Figure 15 shows the DMPPT system in series configuration. Hence output voltage will be
different for different modules but output current remains same. Power obtained from higher
insulation modules is shown in fig.16
Figure 17 output voltage for module 1
Page | 38
Figure 18 output voltage for module 2
Output voltage for higher insulation is shown in fig.17 and the output voltage for lower
insulation is shown in fig.18
Figure 19 power received by load
Power received by the load is the aggregate of the power received from both converters. Its
plot is shown in fig.19
Page | 39
CHAPTER
4
Output side sensor based
DMPPT
Page | 40
4.1 Output side sensor based MPPT:
Conventional method is tracking the maximum power point by taking the voltage of module
and current of the module as inputs to the MPP tracker. This chapter presents another way to
detect the maximum power point of the module i.e., by having an MPP tracker based on sensing
the output of converter rather than sensing the output of solar module.
Since, a tracker on the output side has been used, the MPP tracker which is used in earlier
chapters cannot be used here, because the variation of duty cycle is not same as that of earlier
one. Hence, in order to determine how to design the MPP tracker, power obtained at the output
of converter versus duty cycle of converter graph has been drawn.
600
power received
500
400
300
200
100
0
0
0.1
0.2
0.3
0.4
0.5
0.6
duty cycle (D)
0.7
0.8
0.9
1
Figure 20 Power vs Duty cycle characteristics
From the obtained graph, it is evident that as the duty cycle is increased, the power obtained
keeps on increasing until one point and from then on power obtained keeps deducing until zero.
So, by properly keeping the value of duty cycle at the optimum point, the maximum power
point can be tracked. The description of the algorithm used to detect the maximum power point
is as follows: measure the change in power and change in D i.e., finding out whether ∆𝑃 , ∆𝐷
Page | 41
are positive or not. If both are positive or both are negative then ∆𝐷 is increased for the next
duty cycle. If one of them is positive and the other is negative then ∆𝐷 is decreased for the
next duty cycle. Thus it keeps on increasing or decreasing the duty ratio depending on the
algorithm and finally the MPP point is obtained as steady state is reached.
The remaining system that is used will remain same as the one that is used in previous chapters.
The solar panel is connected to the boost converter which adjusts the duty ratio according to
the load and the maximum power point. The difference comes in the algorithm used in the MPP
tracker and the position of MPP tracker which is placed at the output side of boost converter
thus sensing the output voltage and output current and changing the duty cycle accordingly.
Page | 42
4.1.1 Results and discussion:
Figure 21 Output voltage at steady state after DC-AC conversion
Figure 22 Output current at steady state after DC-AC conversion
The output voltage and the output current shown in the figures 21 and 22 are obtained after
DC-AC conversion. The MPP tracker tracks the MPP point and correspondingly adjusts the
duty cycle necessarily thus boosting the input voltage.
Page | 43
Figure 23 Power from the solar module after reaching steady state
Figure 24 Power received by tracking the MPP by the load
The power obtained from the panel in the figure 23 is adjusted accordingly to get maximum
power from the output sensing and the final power received by the load is shown in figure 24.
Page | 44
4.2 output side sensor based DMPPT:
Similar to that of output sensor based MPPT, here output sensor based DMPPT is implemented
by sensing the output voltage of converter and output current of the converters. Here in
DMPPT, each module is provided a separate converter so that even under partial shading
conditions maximum power could be extracted from each module separately. Here in output
sensor based DMPPT, the output of each converter is tracked and feed it to the corresponding
output based MPP tracker. The tracker used in section 4.1 is used here also. The change in
output power of each converter is measured and comparing it with the change in duty cycle, if
both are positive then ∆𝐷 is increased for the next duty cycle. If both are negative then ∆𝐷 is
increased for the next duty cycle. If one is negative and the other one is positive, ∆𝐷 is
decreased for next duty cycle.
The benefit of using output sensor based DMPPT in parallel configuration is that since the
output voltage of all the converters is same in parallel connected DMPPT system, the output
voltage of any single module can be sampled and it would be given it to all the MPP trackers.
So, the amount of hardware needed for this one is lesser when compared to the conventional
DMPPT system. Thus hardware is saved in turn affecting the money needed to implement the
system. In this system, one voltage sensor and more than one current sensor are needed, where
as in conventional system, more than one voltage sensor and more than one current source are
needed. Similarly, output sensor based MPPT can also be implemented for series configuration
also where only one current sensor is needed and more than one voltage sensors are needed.
Page | 45
4.2.1 Results and Discussion:
Figure 25 Power obtained from lower insulation module after reaching steady state
Figure 26 Output current at steady state after DC-AC conversion
Page | 46
Figure 27 Output power of output sensor based DMPPT
The power obtained from the two modules is different from one another because the insulation
level for one module is higher than that of the other module. The output voltage remains same
to all the modules as they are connected in parallel. The power received by the load which is
shown in fig.27 is the aggregate of power from both the modules. Thus current received by the
load is the sum of currents provided by all modules. The voltage received by the load after DCAC conversion is shown.
Page | 47
Conclusion
And
Bibliography
Page | 48
Conclusion:
 Some new trends in practice for improvising the solar energy production have been
discussed.
 A special importance on perturb and observe method is being given.
 State Space modelling of boost converter is derived.
 An acceptable Mathematical analysis of why there are virtually no cross coupling
effects in the parallel configuration of DMPPT is presented.
 How the DMPPT technique effectively improves the efficiency of solar power is
discussed.
 Output side sensor based DMPPT system has been studied and how it helps in reducing
the hardware thereby reducing the overall installation cost is discussed.
 Various simulation results have been presented and checked based on theoretical
learning. The plots obtained have been shown accordingly.
Page | 49
Bibliography
[1] J.Viinamaki, J.Jokipii, T.Messo, T.Suntio, M.Sitbon and A.Kuperman, "Comprehensive dynamic
analysis of photovoltaic generator interfacing DC–DC boost power stage," IET Renewable Power
Generation, Sept. 2014.
[2] A. Kalirasu and S. S. Dash, "Simulation of Closed Loop Controlled Boost Converter for Solar
Installation," Serbian Journal of Electrical Engineering, vol. 7, no. 1, pp. 121-130, 2010.
[3] A. KumarVerma, B. Singh and S. Kaushik, "An Isolated Solar Power Generation using Boost
Converter and Boost Inverter,," in Proc. National Conference on Recent Advances in
Computational Technique in Electrical Engineering, SLITE, Longowal (India), March, 2010.
[4] N. Femia, G. Lisi, G. Petrone, G. Spagnuolo and a. M. Vitelli, "Distributed Maximum Power Point
Tracking of Photovoltaic Arrays: Novel Approach and System Analysis," EEE transactions on
Industrial Electronics, July, 2008.
[5] S. K. a. R. A. J. Farah Kazan, "A Novel Approach for Maximum Power Point Tracking of a PV
Generator with Partial Shading," in IEEE Mediterranean Electrotechnical Conference, April, 2014.
[6] G. Suman, B. Kumar, M. Kumar, B. Babu and K.R.Subhashini, "Modeling, Analysis and Design of
Synchronous Buck Converter using State Space Averaging Technique for PV Energy System," in
ISED-Conference , 2012.
[7] J. Huusari and T. Suntio, "Origin of Cross-Coupling Effects in Distributed DC–DC Converters in
Photovoltaic Applications," IEEE on Power Electronics, vol. 28, no. 10, Oct. 2013.
Page | 50
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