SIMULATION OF GRID CONNECTED PHOTOVOLTAIC SYSTEM WITH MAXIMUM POWERPOINT TRACKING

SIMULATION OF GRID CONNECTED PHOTOVOLTAIC SYSTEM WITH MAXIMUM POWERPOINT TRACKING
SIMULATION OF GRID CONNECTED
PHOTOVOLTAIC SYSTEM WITH MAXIMUM
POWERPOINT TRACKING
A thesis submitted in partial fulfilment of the
requirement for the degree of
Bachelor of Technology
in
Electrical Engineering
By
ABHISEK DASH (111EE0209)
DEPARTMENT OF ELECTRICAL ENGINEERING
NATIONAL INSTITUTE OF TECHNOLOGY
ROURKELA
2015
SIMULATION OF GRID CONNECTED
PHOTOVOLTAIC SYSTEM WITH MAXIMUM
POWERPOINT TRACKING
A thesis submitted in partial fulfilment of the
requirement for the degree of
Bachelor of Technology
in
Electrical Engineering
By
ABHISEK DASH (111EE0209)
Under the guidance of
Prof. Sandip Ghosh
DEPARTMENT OF ELECTRICAL ENGINEERING
NATIONAL INSTITUTE OF TECHNOLOGY
ROURKELA
2015
ii
NATIONAL INSTITUTE OF TECHNOLOGY
ROURKELA
CERTIFICATE
This is to for the certification that the work in this project report entitled “Simulation of
grid connected photovoltaic system with maximum power point tracking” by ABHISEK
DASH has been carried out under my supervision in partial fulfilment of the
requirements for the degree of Bachelor of Technology in Electrical Engineering,
National Institute of Technology, Rourkela and is a reliable and genuine work carried
out by him under my supervision and guidance.
To the best of my knowledge, this work has not been submitted to any other
university/institute for the award of any degree or diploma.
Place: Rourkela
Date: 10/05/2015
Prof. Sandip Ghosh
Department of Electrical Engineering
National Institute of Technology Rourkela, Orissa
769008
iii
ACKNOWLEDGEMENT
I convey my sincere gratitude to Prof. Sandip Ghosh, my guide and supervisor, for giving me
an opportunity to work under his supervision. I will always be grateful to him for his
invaluable guidance and constant motivation and inspiration.
I am extremely thankful to my friend Subodh Mishra, Kishan Patel, for their help and
constant support throughout the course of this work.
Finally, I would definitely not forget to extend my sincere heartfelt thanks to all the lab incharges and staff members of the department and my fellow classmates for their help and
support.
Place: Rourkela
Date: 10/05/12015
ABHISEK DASH
(111EE0209)
iv
ABSTRACT
Solar renewable energy harvesting is the demand of the century because of the huge energy
requirement of the world today. India being a home to a huge population witnesses high
Incident Solar radiations throughout the year. Planning has been made to produce at least 20
Gigawatts of high quality solar power by the year 2020. Energy harvested from the sun is a
necessarily a valuable source but still most it part goes unutilised in Indian subcontinent
although being a tropical region. The main obstacle for the wide usage of solar Photovoltaic
systems is their efficiency which is very low (20-25% for single crystal 10-15% for
polycrystalline and 3-5% for amorphous silicon solar cells [1]) and high cost of
manufacturing. In main objective behind the work in this thesis lies in extracting maximum
harvestable power from a Photovoltaic module and use the energy for a DC application as
well as the grid connection of the generated power so that the surplus power unutilised in the
load can be transferred to the grid. Maximum Power Point Tracking (MPPT), use of Boost
converter and the importance of bridge inverter have been the main investigation in this
project. Also the grid connection along with supply to a three phase load using bridge inverter
and PWM has been shown. First SIMULINK software is used to model the photovoltaic cell.
Then MPPT interfacing is done with a boost converter and resistive load and finally through
an inverter connected to the 3 phase grid. All simulations have been done in SIMULINK
software of MATLAB.
v
TABLE OF CONTENTS
COVER PAGE
ii
CIRTIFICATE
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
TABLE OF CONTENTS
vi
LIST OF FIGURES
vii-viii
CHAPTER 1: INTRODUCTION
1
1.1 THE NEED FOR RENEWABLE ENERGY
1
1.2 SOLAR POWER
1
1.3 MOTIVATION
2
1.4 OBJECTIVE
2
CHAPTER 2: LITERATURE REVIEW
3
CHAPTER 3: MODELLING OF PV SYSTEM
4
3.1 PHOTOVOLTAIC SYSTEM COMPONENTS
4
3.2 SIMULINK MODEL OF PV PANEL
5
3.3 BOOST CONVERTER
7
3.4 MAXIMUM POWER POINT TRACKING ALGORITHMS
9
3.5 PERTURB & OBSERVE
9
3.6 SIMULATIONS PLOTS AND RESULTS
11
CHAPTER 4: CONCLUSION & FUTURE WORK
18
4.1 CONCLUSION
18
4.2 FUTURE WORK
18
REFERENCES
19
vi
LIST OF FIGURES
Fig 1:-Single diode model of a PV cell
Fig 2:- Masked simulink model of a pv panel
Fig 3:- Unmasked simulink model of a pv panel
Fig 4: Voltage vs time plot of the solar panel
Fig 5: Current vs Voltage plot of the solar panel
Fig 6: Power vs Voltage plot of the solar panel
Fig 7(a):- Current (Y axis) vs Voltage(X axis) characteristic plot of the solar panel;
Fig 7(b):- Power(Y axis)
vs Voltage(X axis) characteristic plot of the solar panel.
Fig 8:-Simulink model of a Boost Converter 5v to 12v DC
Fig 9:-Duty Ratio vs Time plot of the boost converter
Fig 10: Current output Vs Time plot of the boost converter
Fig 11: Voltage output vs Time plot of the boost converter
Fig 12:- Flow chart for Perturb & Observe (P&O) algorithm
Fig 13 Simulink model of MPPT using P&O algorithm (a) masked and (b) unmasked
Fig 14:- Simulink Model of Solar Cell without MPPT
Fig 15:- Plot of open circuit Voltage (V) vs. time(s) of Solar Cell without MPPT
Fig 16:- Plot of Short Circuit Current (A) vs. time(s) of Solar Cell without MPPT
Fig 17:- Simulink Model of Solar Cell without MPPT
Fig 18:- Plot of Load Voltage (V) Vs time(s) of Solar Cell without MPPT
Fig 19:- Plot of Load Current (A) Vs time (s) of Solar Cell without MPPT
Fig 20:- Simulink Model of Solar Cell with MPPT and Boost Converter
Fig 21:- (a) Plot of the Gate pulse Output From MPPT (b) Plot of the Power Output of The
PV module
Fig22:- (a) Plot of the Load Voltage Vs Time (b) Plot of the Load Current Vs Time
Fig 23:-Plot of the Power output vs time of the PV model (a) without MPPT (b) with MPPT
and Boost converter
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Fig. 24:- Simulink Model of Solar Cell with MPPT and Boost Converter connected to the
Grid
Fig. 25:- Plot of (a) Gate pulse and (b) Power Output of the Solar Cell vs time
Fig. 26:- Plot of (a) Voltage and (b) Current waveforms of the Solar Cell vs time
Fig. 27:- Plot of (a) Current & (b) Voltage Output of Boost Converter of the PV Cell vs time
Fig. 28:- Plot of (a) Voltage output from the PWM generator and (b) Current Output from
Grid connection wrt time
Fig. 29:- Zoomed Plot of (a) Voltage output from the PWM generator and (b) Current Output
from Grid connection wrt time ( 0.2s to 0.205s )
viii
Chapter 1
INTRODUCTION
1.1 The need for Renewable Energy
The various sources of renewable energy are tides, sunlight, rain, geothermal energy and
wind. These resources can be naturally replenished and never go out of stock. Generally the
prime source of energy these days come directly or indirectly from fossil fuels which are
slowly getting exhausted from the earth storage unlike these renewable resources which are
inexhaustible in nature. With time and development people around the world have been
searching for nonconventional sources for long term fulfilment of their basic energy demand.
With rapidly increasing population and growing consumption of fossil fuel the pollution
caused to the environment also increases , hence there is a urgent need of Clean and Green
Mechanisms which are now popularly adopted by nations throughout the world. The clean
and no pollution consumption of these renewable energy is what attracted the current globe
and hence a huge capital is investment is being done for harvesting these resources.
1.2 Solar power
The rising power demand of day to day life cannot only be maintained by using conventional
energy recourses due to its unavailability. Along with conventional systems the demand for
renewable sources has increased to meet the energy demand. Renewable sources like solar
energy and wind energy are the prime energy sources which are being utilized in this regard.
The continuous use of fossil fuels has drastically affected the environment depleting the
biosphere and causing global warming.
Harvesting Solar energy is possible because of it’s abundantly availability. Solar energy can
be a standalone generating unit or can be a grid connected generating unit depending on the
availability of a grid nearby. Since the availability of grid is very low at rural areas the use of
renewable sources is maximum over there. Another importance of using solar energy is the
portable operation, can be used everywhere as per the necessity.
The present energy crisis can be tackled by developing power efficiently and can be extracted
from the incoming solar radiation. The power conversion techniques have been greatly
reduced in the past few years. To withstand the high power demand the development in
1
power electronics and material science has helped technicians to come up very brief but
powerful systems. The increased power density is the major disadvantage of these systems.
Trend has set in for the use of multi-input converter units that can effectively handle the
voltage fluctuations. But due to high production cost and the low efficiency of these systems
they can hardly compete in the competitive markets as a prime power generation source.
The constant increase in the development of the solar cells manufacturing technology would
definitely make the use of these technologies possible on a wider basis than what the scenario
is presently. The use of the newest power control mechanisms called the Maximum Power
Point Tracking (MPPT) algorithms has led to the increase in the efficiency of operation of the
solar modules and thus is effective in the field of utilization of renewable sources of energy.
The conversion of solar energy was originated by the British astronomer John Herschel who
famously used a solar thermal collector box to cook food during an expedition to Africa.
Solar energy has two major applications. Firstly, the captured heat can be used as solar
thermal energy, with applications in space heating. Another alternative is the conversion of
incident solar radiation to electrical energy, which is the most usable form of energy. This
can be achieved with the help of solar PV cells or with concentrating solar power plants.
1.3 MOTIVATION
Photovoltaic power control is one of the modern research fields in these days. Researchers
have given their best to develop better solar cell materials and efficient control mechanisms.
The modern day challenge of the project and the latest technology study were the motivations
behind the project.
1.4 OBJECTIVE
The primary focus will remain on the effect of Maximum Power Point Tracking and load
matching and its successfully implement using the Simulink models.For obtaining the
maximum power point operation, the modelling the PV module, boost converter, design of
the discrete PWM generator and bridge inverter circuitry in Simulink and interfacing of these
with the MPPT algorithm would be of prime importance of the work.
2
Chapter 2
LITERATURE REVIEW
While a solar panel has the capacity to convert only 30-40% of incident energy on it to useful
electrical energy experiment show that the efficiencies of various types and makes of solar
panel varies from 3%(amorphous grade silicon solar cells) to 25 % (single crystal silicon
solar cells) [1][2]. Therefore in order to increase the power output of the PV system there is a
need of various algorithms and tracking systems. There are different techniques for MPPT
such as Hill climbing method (P&O), Fractional Short Circuit Current, Incremental
conductance, Neural Network Control, Fractional Open Circuit Voltage, etc. The simplicity
of implementation and short duration of operation makes Perturb and observe (P&O) and
Incremental conductance algorithms popular .Economic factors also play a major role for
using P&O because they are cheaper. Incremental Conductance has an advantage over P&O
algorithm that is when there is an unusual change in weather or Insolation level ie when the
Maximum power point changes in continuous basis P&O calculates the wrong value of MPP
because it detects it as a perturbation change which is avoided to a large extent in IC method
because two samples of voltage are taken. But, counterbalancing the higher efficiency factor
of IC & its high complexity as compared to P&O boost the implementation cost by a visible
margin. Complexity and efficiency has to be settled for a compromising balance. Another
notable thing is that the type of converter used also affects the efficiency to a large extent.
buck type topology staying at the top of the list, followed by buck-boost converter and boost
topology residing at the lower end. While making the grid connection one has to also take
care of the inverter and load requirement and the type of source connected to avoid losses and
harmonics which may damage the PV system itself. Solar energy capture and harvest has
been the topic of research since Einstein discovered the Photoelectric effect and won noble
prize in physics 1905. The material he used in his experiment was primarily selenium coated
with thin gold layer. But after that a lot of researchers have been putting together their nights
and days for further technological improvement in the field solar energy worldwide. From
silicon solar cells to gallium arsenide, Cadmium sulphide- Cadmium telluride have been used
for manufacturing purpose. Apart from the hardware improvement researchers have also
come up with advance electronics and logical operations for increasing the overall efficiency.
Hence MPPT algorithms were developed which not only enhanced the efficiency but also
gave a very effective control mechanism to the whole system.
3
Chapter 3
Modelling of PV system
3.1 Photovoltaic System Components:Photovoltaic cell
A photovoltaic cell or photoelectric cell is a semiconductor device basically a P-N junction
diode that converts light to electrical energy by photovoltaic effect [1]. When photon particles
of light having energy greater than the band gap of the valence electron is bombarded to the
junction electron hole pairs are generated which when acted upon by internal electric field
result in a photocurrent. PV cell is basically a current source [2] where current is produced by
the variation of photons not the voltage.
PV module
It consists of a large number of P cells arranged in series or parallel or a mixture of both to
meet the consumption demand. PV modules of various materials and enhanced efficiencies
and of desired size are available in the market.
PV modelling
Typically a solar cell can be modelled by a current source and an inverted diode connected in
parallel to it. The PV cell has its own series and shunt resistance. Series resistance is due to
the diode resistance(of the bulk material) & resistance of metal contacts whereas parallel
resistance represents the electron hole recombination before t reaches the load.
Fig 1:-Single diode model of a PV cell
4
A current source (I) along with a diode and series resistance (Rs) is considered. The shunt
resistance (Rsh) in parallel is very high, has a negligible effect and can be neglected. The
output current from the photovoltaic array can be given by
I=ISC – Id
----eqn 1
Id=I0(eqVd/kT-1)
----eqn 2
Where Io is the reverse saturation current of the diode, q is the electron charge, Vd is the
voltage across the diode, k is Boltzmann constant (1.38 * 10-19 J/K) and T is the junction
temperature in Kelvin (K)
I=Isc-I0(eqVd/kT-1)
----eqn3
Using suitable approximations,
I=Isc-I0(eq((V+IRs/nkT-1)
----eqn4
Where, I is the photovoltaic cell current, V is the PV cell voltage, T is the temperature (in
Kelvin)
and n is the diode ideality factor [3] In order to model the solar panel accurately we can use
two diode model but in this project our scope of study is limited to the single diode model
[3][4]. Also, the shunt resistance is very high and can be neglected during the course of our
study.
3.2 SIMULINK MODEL of PV panel (Masked and Unmasked):-
Fig 2:- Masked simulink model of a pv panel
5
Fig 3:- Unmasked simulink model of a pv panel
Figure 4: Voltage vs time plot of the solar panel
Figure 5: Current vs Voltage plot of the solar panel
6
Figure 6 : Powervs Voltage plot of the solar panel
Figure 7(a):- Current (Y axis) vsVoltage(X axis) characteristic plot of the solar panel;
Figure 7(b):- Power(Y axis) vs Voltage(X axis) characteristic plot of the solar panel.
3.3 Boost Converter
The major disadvantage of a Buck type converter is the switch is at the output of PV panel so
when it’s ON it transfers power but when Off no output to the PV panel occurs which implies
the operating point remains near the open circuit voltage which is a loss [5] . This issue is not
there in boost converter mechanism. In a boost converter the Load matching is done by
varying the resistance of the input side by altering the Duty ratio for which a DC-DC
converter [6] is required. Basically this is called Tracking. Another purpose of using a Boost
regulator in spite of the fact that it has a lower efficiency than its counterparts is that this DCDC converter can be used to feed a load or a system with higher voltage demand thus
justifying its name.
7
Fig 8:-Simulink model of a Boost Converter 5v to 12v DC:Converter Parameters: L = 80 µH, RL = 80 m-ohm ,C = 1.68 µF, Rc = 5 m-ohm,fs = 100
KHz, Vg = 5 ,D = 0.61, Load R = 120 ohm,Vout = 12V
Figure 9 :Duty Ratio vs Time plot of the boost converter
Figure 10: Current output Vs Time plot of the boost converter
8
Figure 11: Voltage output vs Time plot of the boost converter
3.4 Maximum Power Point Tracking Algorithms
An overview of MPPT
The efficiency of a Solar PV module is measured to be not more than 30%. As seen from the
Power vs Voltage curve the module has to operate at a specific range of voltage values in
order to extract maximum power thus improving the efficiency. The Max Power Transfer
Theory says that maximum power can be extracted from a source when the load impedance
matches the source impedance (the Thevenin equivalent impedance). There are basically 3
methods to derive peak power operation electrically. The first method [7] is by measuring
dV/dI ie the dynamic impedance by injecting a periodic signal current (small magnitude) and
increasing the operating voltage until it equals the static impedance V/I. The second method
is by increasing the operating voltage until dP/dV ie (slope of the P vs V curve) is positive
[7][8]. In most of the cells a ratio between the maximum power voltage and open circuit
voltage is maintained and experimentally found to be near 0.72.in the third method this idea
is the key for MPPT [6]. From the above method what we can infer is that our basic motive
can be achieved by matching the impedances by duty cycle alteration of the boost converter
switch and obtain higher value of output voltage.
3.5 Perturb & Observe
Perturb & Observe (P&O) is one of the simple technique that uses a voltage sensor [8][9], to
sense the voltage of Photovoltaic array voltage which reduces the implementation cost and
9
hence easy to operate. The of this algorithm has a very less time complexity but when it
reaches close to the maximum power point it perturbs on both the directions without stopping
[9]. An appropriate error limit is to be set or a wait function can be added when MPP is
reached thus increasing the time complexity of the algorithm.
Fig 12:- Flow chart for Perturb & Observe (P&O) algorithm:-
10
3.6 SIMULATIONS PLOTS AND RESULTS
Fig:-13 Simulink model of MPPT using P&O algorithm (a)masked and (b)unmasked
Fig 13. (a)
Fig 13. (b)
11
Fig. 14:- Simulink Model of Solar Cell without MPPT
Input Parameters :Temperature in deg Celsius =25 ,Incident Solar Radiation in Watt per meter square: - 500
Fig. 15:- Plot of Open Circuit Voltage (V) vs. time(s) of Solar Cell without MPPT
Fig. 16:- Plot of Short Circuit Current (A) vs. time(s) of Solar Cell without MPPT
12
Fig. 17:- Simulink Model of Solar Cell without MPPT
Input Parameters :Temperature in deg Celsius =25
Incident Solar Radiation in Watt per meter square: - 500
Circuit parameters :R1 = 1 ohm
C= 0.002 F
Load resistance R = 1 ohm
Fig. 18:- Plot of Load Voltage(V) Vs time(s) of Solar Cell without MPPT
13
Fig. 19:- Plot of Load Current (A) Vs time (s) of Solar Cell without MPPT
Fig. 20:- Simulink Model of Solar Cell with MPPT and Boost Converter
Input Parameters :Temperature in deg celcius =25
Incident Solar Radiation in Watt per meter square :- 500
Circuit parameters :R1 = 1 ohm
C= 0.002 F
Inductance L = 0.01 H
Load resistance R = 1 ohm
14
Fig. 21:- (a) Plot of the Gate pulse Output From MPPT (b) Plot of the Power Output of The
PV module
Fig. 22:- (a) Plot of the Load Voltage Vs Time (b) Plot of the Load Current Vs Time
Comparison between the Power output of the Two models one without
MPPT and other with MPPT and Boost Converter
Fig 23:-Plot of the Power output vs time of the PV model (a) without MPPT (b) with MPPT
and Boost converter
15
Fig. 24:- Simulink Model of Solar Cell with MPPT and Boost Converter connected to the
Grid [12]
Fig. 25:- Plot of (a) Gate pulse and (b) Power Output of the Solar Cell vs time
Fig. 26:- Plot of (a) Voltage and (b) Current waveforms of the Solar Cell vs time
16
Fig. 27:- Plot of (a) Current and (b) Voltage Output from Boost Converter of the Solar Cell vs
time
Fig. 28:- Plot of (a) Voltage output from the PWM generator and (b) Current Output from
Grid connection wrt time
Fig. 29:- Zoomed Plot of (a) Voltage output from the PWM generator and (b) Current Output
from Grid connection wrt time (0.2s to 0.205s)
17
Chapter 4
CONCLUSION & FUTURE WORK
4.1 CONCLUSION
The no-load voltage and the short circuit current of the solar module are found to 85V and
12.7 A respectively. The power output of the module when a resistive load of 1 ohm (which
made the output current and voltage waveforms look similar) was used was calculated to be
150W. There after interfacing MPPT and boost converter the DC power extracted was raised
to 320W. The frequency of operation was 10 KHz which was set by using a repeating saw
tooth generator. For generating the pulse signal a repeating sequence generator was used in
the MPPT to provide gate pulse to the IGBT switch. A slight change in the incident solar
radiation alters the position of the maximum power point the PvsV curve as a result the duty
cycle has to be constantly changed in accordance with the solar incident radiation [11]. Use
of a constant value of Duty ratio will make the system less efficient as the peak power point
may not be tracked [11]. A three phase Load with Phase to phase Y (grounded) nominal
phase to phase voltage (Vrms) 300V with nominal frequency of 50 Hz and active power
consumption of 0.001 W was used . The three phase source was taken to be 300v phase to
phase and frequency of 50 Hz. Type of the source is also Y grounded. The output of the boost
converter is fed to the universal bridge that acts like an inverter circuitry. A discrete PWM
generator was used to give triggering signal to the inverter [12]. A sinusoidal three phase
current wave form with peak value of around 40Amps is obtained. Matlab and Simulink have
been used for various plots and value calculations. The waveforms obtained from the
Simulink models have been shown for comparison. Small values of error are still appearing
in the curves accounting to power losses (mostly switching loss or loss in the boost converter
circuitry mainly due to loss in capacitor or inductor [12]).
4.2 FUTURE WORK
Future work to this project will include the removal of harmonics [12] in the grid connection
system as well as operation of the PV system in variable environmental and physical
conditions like change in solar irradiation or sudden altering in atmospheric temperature.
Further improvement can be made by enhancing the energy exchange with the local electrical
grid in order to stabilise the energy curve. Design of more generalised solar cell with variable
inputs of incident solar radiation and atmospheric temperature can be designed using
Simulink instead of predefined constant values.
18
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