SIMULATION AND ANALYSIS OF PHOTOVOLTAIC SYSTEM USING VIRTUAL INSTRUMENTATION

SIMULATION AND ANALYSIS OF PHOTOVOLTAIC SYSTEM USING VIRTUAL INSTRUMENTATION
SIMULATION AND ANALYSIS OF
PHOTOVOLTAIC SYSTEM USING VIRTUAL
INSTRUMENTATION
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
Master of Technology
in
Electrical Engineering
By
K.K.Tejaswini
(Roll No-213EE5355)
Department of Electrical Engineering
National Institute of Technology, Rourkela
Rourkela-769008, Odisha,India.
May 2015
SIMULATION AND ANALYSIS OF
PHOTOVOLTAIC SYSTEM USING VIRTUAL
INSTRUMENTATION
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
Master of Technology
in
Electrical Engineering
By
K.K.Tejaswini
(Roll No-213EE5355)
Under the Guidance of
Dr.S.Gopalakrishna
Department of Electrical Engineering
National Institute of Technology, Rourkela
Rourkela-769008, Odisha, India.
May 2015
Department of Electrical Engineering
National Institute of Technology, Rourkela
CERTIFICATE
This is to certify that the Thesis Report entitled SIMULATION AND ANALYSIS OF
PHOTOVOLTAIC SYSTEM USING VIRTUAL INSTRUMENTATION submitted by
K.K.Tejaswini (213EE5355) of Electrical Engineering during May 2015 at National
Institute of Technology Rourkela is an authentic work by her under my supervision and
guidance.
Place: Rourkela
Dr. S. Gopalakrishna
Date: 25/05/2015
Assistant professor
Department of Electrical Engineering
National institute of technology, Rourkela
ACKNOWLEDGEMENT
I am thankful to my project supervisor Dr.S.Gopalakrishna, Department of Electrical
Engineering, N.I.T. Rourkela, for his support, guidance, co-operation during the entire period
of my work. I am grateful to Prof.A.K.Panda, Head of the Department, Electrical Engineering
for providing all the necessary facilities during the project work. I also express my gratitude
to Prof. K. B. Mohanthy for providing facilities towards this work. I am also thankful to
A.Divya for her enjoyable and helpful company.
K.K.Tejaswini
Roll No: 213EE5355
Rourkela, May, 2015
I
ABSTRACT
Renewable energy sources demand has been increasing rapidly due to their abundance
in nature, environment friendly and also serves as decentralized power sources in rural areas.
Solar energy is one such renewable energy source which produces electricity by means of
photovoltaic effect. The disadvantage of solar energy is its output power depends on factors
like temperature, intensity of sun light, sun angle of incidence. To extract maximum power
from the solar array it has to be operated at maximum power point (MPP).
Virtual Instrumentation (VI) is widely used in testing, measurement and control
application as it is easy to understand and implement. In this thesis, maximum power point
tracking (MPPT) of solar array is demonstrated using a virtual instrument (VI) created in
LabVIEW. Voltage and current signals sensed from photo voltaic (PV) array are fed as input
to the VI and control signal is obtained as output. The duty cycle of a buck converter which is
placed between solar array and the load is controlled using the control signal. Incremental
conductance (INC) algorithm is used for creating a LabVIEW VI that tracks maximum
power. Faster tracking of power in the range of millisecond is observed.
II
LIST OF FIGURES
Figure No
Figure description
Page No
Figure 2.1
Unregulated standalone system with DC load
5
Figure 2.2
Regulated standalone system with DC load
5
Figure 2.3
Regulated standalone system with battery and DC load
6
Figure 2.4
Regulated standalone system with battery, AC and DC loads
7
Figure 2.5
Grid interactive PV system
7
Figure 2.6
Hybrid system
8
Figure 3.1
Equivalent single diode model of solar cell
10
Figure 3.2
I-V curve of solar array under STC
11
Figure3.3
P-V curve of solar array under STC
12
Figure 3.4
I-V curve with different irradiations and at temperature of 25˚C
14
Figure 3.5
I-V curve under different temperatures at irradiation of 1000W/m²
14
Figure 4.1
Circuit diagram of buck converter
16
Figure 4.2
Buck converter waveforms
18
Figure 5.1
I-V and P-V curves of solar module indicating the MPP
19
Figure 6.1
P-V curve explaining the incremental conductance method
22
Figure 6.2
Block diagram of PV module with MPPT controller
23
Figure 6.3
Flow chart of incremental conductance method.
24
Figure 6.4
MPPT using INC method under STC
25
Figure 6.5
Output voltage of solar module during MPPT using INC method
25
under STC
Figure 6.6
Output current of solar module during MPPT using INC method
25
under STC
Figure 6.7
MPPT under varying irradiation and constant temperature of 25˚C
26
using INC method
Figure 6.8
MPPT under varying temperature and constant irradiation of
1000 W/m² using INC method
III
27
Figure 7.1
Block diagram of MPPT using LabVIEW
29
Figure 7.2
Circuit diagram of hardware implementation of MPPT
30
Figure 7.3
Picture showing hardware components for MPPT implementation
31
Figure 7.4
Array power waveform of solar panel with varying duty cycle
32
Figure 7.5
Array power waveform of MPPT using INC method
33
Figure 7.6
Array output current during MPPT
33
Figure 7.7
Array output voltage during MPPT
34
IV
LIST OF TABLES
3.1
Module ratings
10
7.2
Solar array specifications used for hardware implementation
28
V
CONTENTS
1. INTRODUCTION.......................................................................................... 1
1.1 Introduction .................................................................................................. 1
1.2. Motivation ................................................................................................... 1
1.2 Literature survey .......................................................................................... 2
1.3 Objective and Scope .................................................................................... 3
2. CLASSIFICATION OF PHOTOVOLTAIC SYSTEM .............................. 4
2.1 Solar photovoltaic system ............................................................................ 4
2.2 Types of photovoltaic systems ..................................................................... 4
2.2.1 Stand-alone PV system .......................................................................... 4
2.2.2 Grid interactive PV system .................................................................... 7
2.2.3 Hybrid system ........................................................................................ 8
3. MODELLING AND SIMULATION OF SOLAR CELL ........................... 9
3.1 Modeling of Solar cell ................................................................................. 9
3.2 Characteristics of solar array ..................................................................... 11
3.3 Dependency on temperature and irradiation .............................................. 12
4. BUCK CONVERTER .................................................................................. 15
4.1 Introduction to buck converter................................................................... 15
4.2 Modes of operation .................................................................................... 16
VI
4.3 Waveforms ................................................................................................. 17
5. MAXIMUM POWER POINT TRACKING TECHNIQUE
(MPPT)
............................................................................................................................. 18
5.1 Maximum power point tracking ................................................................ 18
5.2 MPPT methods .......................................................................................... 19
6. SIMULATION OF MPPT ........................................................................... 21
6.1 Mathematical description of INC method ................................................. 21
6.2 Simulation of MPPT using INC method ................................................... 23
6.3 Simulation of INC MPPT method under varying irradiation .................... 25
6.4 Simulation of INC MPPT method under varying temperature ................. 25
7. HARDWARE IMPLEMENTATION OF INC MPPT METHOD .......... 26
7.1 Hardware system description ..................................................................... 26
7.2 Determining maximum power of solar array in LabVIEW....................... 30
7.3 MPPT using INC method .......................................................................... 31
8. CONCLUSION.............................................................................................. 33
8.1 Summary .................................................................................................... 33
8.2 Future scope ............................................................................................... 33
8.3 References .................................................................................................. 33
VII
Chapter 1
1. INTRODUCTION
1.1 Introduction
Due to the depletion of non-renewable sources of energy and increase in demand for
electricity man has to search for alternative sources like renewable energy sources. Solar
energy is one such renewable sources of energy which works on the principle of photovoltaic
effect. Solar cell is the main element which converts solar energy into electrical energy. Solar
cells are connected in series or parallel depending on requirement to form solar module. Solar
modules are again connected in series or parallel depending on the current and voltage
requirement to form solar array. Solar cell provides clean and pollution free energy unlike
traditional source of energy like coal, diesel, natural gas, nuclear energy. It is has certain
disadvantage of low efficiency compared to other renewable sources of energy. This problem
is overcome by using maximum power point tracking (MPPT) technique as discussed in this
work.
1.2. Motivation
The efficiency of solar array is very less under normal operating conditions and also
further decreases with varying load, environmental conditions. To increase the efficiency of
solar array different control algorithms called Maximum Power Point Tracking (MPPT) are
being used now a days. The objective of all these algorithms is to match the source
impedance with that of load impedance such that maximum power is delivered from the array
[3]. This impedance matching is achieved by using pulse width modulation of dc to dc
converters which are used between solar array and load. One of the widely used methods for
this purpose is Incremental conductance (INC) method. This MPPT method is being
1
implemented in analog and digital domain. Although analog method works faster, digital
method is easy to implement and modify.
Digital method is being widely implemented by using different types of controllers
like DSP processor, Microprocessor, Microcontrollers etc., where the MPPT algorithm is
written as a coded program. However, graphical programming is simpler to understand,
implement and modify. Matlab/Simulink and LabVIEW are software that are used to acquire
data from real world, process the data and generate output that is either displayed or send to
output port as control signal. In this paper, a simulation study is carried out implementing
INC method in MATLAB Simulink. Having obtained simulation results on MPPT in
Simulink, the same is implemented in hardware using LabVIEW software.
1.2 Literature survey
Many literatures are available on the topic of modeling and MPPT of solar array. M.
G. Villalva et.al. [1] Proposed method to model the solar cell and the main objective is to find
the parameters of solar cell I-V equation. In this paper the effect of temperature and
irradiation on the parameters of solar cell is also discussed. Chiang et.al. [2] introduced
domestic photovoltaic energy storage system, in which the output PV power is controlled by
a DC-DC converter with MPPT controller and transferred to a small battery.
T. Esram et.al. [2] explained and compared different MPPT techniques available in
literature. The author has given summary of these MPPT techniques and their implementation
methods which helped in choosing the appropriate MPPT method for given PV systems. A.
Safari et.al.[11]
discussed incremental conductance (INC) method and practical
implementation of this method. R. Gules et.al. [10] analysed, designed and implemented a
parallel connected MPPT system for a stand -alone photovoltaic power generation.
2
1.3 Objective and Scope
The overall objectives and scope of the work can be summarized as follows

Studying the I-V (Current-Voltage) and P-V (Power-Voltage) characteristics of solar
array under different temperature and irradiation.

Simulating the maximum power point tracking (MPPT) using incremental
conductance method (INC) in MATLAB Simulink.

Determining maximum power point of solar array in LabVIEW.

Hardware implementation of maximum power point using incremental conductance
method in LabVIEW.
In chapter 2, we described various types of solar photovoltaic systems and also seen
difference between grid connected PV system and hybrid PV system.
In chapter 3, modeling of solar cell and the dependency of solar cell characteristics on
irradiation and temperature is seen.
In chapter 4, the modes of operation of buck converter used for MPPT technique has
been discussed.
In chapter 5, various MPPT techniques are described with their advantages and
disadvantages.
In chapter 6, mathematical description of MPPT is given and INC MPPT technique has
been chosen for tracking MPP and variation of MPP with change in temperature and
irradiation is observed.
In chapter 7, MPPT is implemented using hardware components and LabVIEW software
by INC algorithm
3
Chapter 2
2. CLASSIFICATION OF PHOTOVOLTAIC SYSTEM
2.1 Solar photovoltaic system
Photovoltaic system is meant to generate electricity from the solar cells and supply to the ac
or dc load. The photovoltaic system can supply energy only during day time, if we want
electricity during night time battery storage system must be used.
2.2 Types of photovoltaic systems
2.2.1 Stand-alone PV system
The Stand-Alone PV System consists of battery storage system to provide power to the load
when there is no sunlight. The array of solar panels must be large enough to provide power to
all loads at the site and recharge the batteries [10].
a) Unregulated standalone system with DC load
In this type the solar panel is directly connected to the DC load and the solar panel is not
operated always at its maximum power since there is no controller. This is usually used for
low power applications. This type of system can only provide energy during day time but not
night time since there is any energy storage system available. Figure 2.1 shows the diagram
of unregulated standalone system with DC load.
4
DC load
PV panel
Figure 2.1: Unregulated standalone system with DC load
b) Regulated standalone system with DC load
In this type of system a DC-DC converter is installed between PV panel and DC load as
shown in figure 2.2. The duty cycle of the switch used in DC-DC converter is controlled by
MPPT controller so that the solar panel always gives out maximum power.
DC-DC
converter
with MPPT
controller
PV panel
Figure 2.2: Regulated standalone system with DC load
5
DC load
c) Regulated standalone system with battery and DC load
The difference between this and previous system is that the extra power delivered by the solar
panel is stored in the battery storage system as shown in figure 2.3. When the solar panel is
unable to supply power to load then battery supplies the required power. A charge controller
is must for this type of system because battery life is less compare to PV module and also the
cost of the system increases.
DC-DC converter with
MPPT controller
DC load
PV panel
Battery
Figure 2.3: Regulated standalone system with battery and DC load
d) Regulated standalone system with battery, AC and DC loads
This system is similar to the previous one but the ac load also draws power from the system
as shown in figure 2.4 so an inverter is essential so the cost and complexity increases.
6
DC-DC
converter with
MPPT
controller
DC-AC
converter
PV panel
AC load
DC load
Battery
Figure 2.4: Regulated standalone system with battery, AC and DC loads
2.2.2 Grid interactive PV system
This type of system consists of PV panel interacted with grid through inverter. The excess
power left after the load utilization is fed to the grid as shown in figure 2.5.
PV
panel
Charge
controller
Inverter
Figure 2.5: Grid interactive PV system
7
Load
2.2.3 Hybrid system
In this the PV system is used in interaction with wind generator, diesel generators, micro
turbines etc., as shown in figure 2.6.
DC Bus
PV
panel
Load
DC-DC
converter
Rectifier
Inverter
Battery
Figure 2.6: Hybrid system
8
Diesel
generator
Chapter 3
3. MODELLING AND SIMULATION OF SOLAR CELL
3.1 Modeling of Solar cell
Solar cell works on the principle of photo-voltaic effect by which light energy is
converted to electrical energy. There is single diode model, two diode model and three diode
model to represent the equivalent circuit of solar cell [4]. Single diode model is simple and
accurate so for power electronics practitioners it helps for easy analysis. The well-known
single diode model of solar cell is shown in figure 3.1.The photo current Iph generated
depends upon irradiation and temperature. The basic equation describing I-V characteristics
of solar cell is given by [6]:
 q V  R I 

s 
 


 V  R sI
AKT
 1 
I  Iph  I0 e
R sh






I
Load current (A)
Iph
Generated current from PV cell (A)
I0
Reverse saturation current of diode (A)
V
Load voltage (V)
Rsh
Shunt resistance (ῼ)
Rs
Series resistance (ῼ)
K
Boltzmann constant (1.38 × 10-23J/K)
q
Charge of electron (1.6x10-19 C)
A
Curve fitting factor
9
……… (3.1)
In equation (3.1) usually Rsh will be very high so the term containing it will be
neglected. From this we can see that current from solar cell depends upon temperature. Iph is
light generated current which accounts for the electron-hole pairs formed and this depends on
the irradiance. The standard test conditions (STC) for solar cell is irradiation of 1000 W/m²,
temperature of 25˚C, Air Mass of 1.5
I
+
Rs
Rsh
Iph
V
Id
-
.
Figure 3.1: Equivalent single diode model of solar cell
Solar MSX-60 has been used for the simulation whose parameters are given below:
Table 3.1 Module ratings
Typical maximum power (Pp)
60 W
Open circuit voltage (Voc)
21.1 V
Short circuit current (Isc)
3.8 A
Voltage at peak power (Vpp)
17.1 V
Current at peak power (Ipp)
3.5 A
Temperature coefficient of Voc
- 0.00379 / ˚C
Temperature coefficient of Isc
0.00065 /˚C
10
3.2 Characteristics of solar array
3.2.1 I-V curve of PV array
I-V curve of the solar array shown in figure 3.2 is plotted by varying the load resistance under
STC in MATLAB simulink. When IPV=0 then we will get the open circuit voltage (Voc) of
solar panel and when VPV=0 then we get the short circuit current (Isc). In the figure 3.2 the
star point indicates the maximum power point of the solar panel under STC with
corresponding voltage VPP and current IPP.
Figure 3.2: I-V curve of solar module under STC
3.2.2 P-V curve of solar array
The output power of solar module is obtained by multiplying output voltage and output
current and at some point the maximum power is obtained. Figure 3.3 shows the P-V curve of
solar module operated under STC and star mark shows the maximum power.
11
Figure3.3: P-V curve of solar module under STC
3.3 Dependency on temperature and irradiation
The voltage and current of a PV module change with irradiance and temperature.
Hence, the effect temperature and irradiation must be taken into consideration in the PV
module model. The mathematical expressions for short circuit current and open circuit
voltage of solar array at any temperature and irradiation are given below:
I
SC
I

 S
1    T  T

SC , ref 
ref  S

ref


S




V
  T  T
V
1  a ln
ref 
OC
OC, ref 
S

ref


Voc,ref
Open circuit voltage under STC (V)
Isc,ref
Short circuit current under STC (A)
12
…………… (3.2)
…………… (3.3)
Isc
Short circuit current (A)
Voc
Open circuit voltage (V)
T
PV module temperature (˚C)
Tref
PV array temperature under STC (˚C)
S
Solar irradiance (W/m²)
Sref
Irradiance under STC (W/m²)
α
Temperature coefficient of ISC (/˚C)
β
Temperature coefficient of VOC (/˚C)
a
Irradiance correction factor of Voc.
So from equation (3.2), equation (3.3) as temperature increases open-circuit voltage
decreases and it has negligible effect on short circuit current. As irradiation increases the
short circuit current increases and it has negligible effect on open-circuit voltage. Figure 3.4;
figure 3.5 are simulated under different irradiation and different temperature respectively
13
Simulation study:
Figure 3.4: I-V curve with different irradiations and at temperature of 25˚C
In figure 3.4 I-V curves are drawn at irradiations of 1000 W/m2, 900 W/m2, 800 W/m2
at a temperature of 25˚C. As the irradiation increases short circuit current increases but has
negligible effect on open-circuit voltage.
Figure 3.5: I-V curve under different temperatures at irradiation of 1000W/m²
In the figure 3.5 I-V curves is drawn at temperatures of 25˚C, 35˚C, 45˚C and at
constant irradiation of 1000 W/m².as temperature increases the open circuit voltage decreases
and there is a negligible increase in short circuit current.
14
Chapter 4
4. BUCK CONVERTER
4.1 Introduction to buck converter
Buck converter steps down the input source voltage to the required value of output voltage.
The essential components of buck converter are inductor, diode, high frequency switch and
capacitor as shown in figure 4.1. These are connected in such a manner to supply voltage at a
lower level compared to the input voltage. The control strategy is change of the duty cycle of
the switch which causes the voltage change [13].
IL
L
Q1
IO
IS
Vin
C
D1
IC
Figure 4.1: Circuit diagram of buck converter
15
LOAD
Where
IS
source current (A)
IC
current through capacitor C (A)
IL
current through inductor L (A)
IO
load current (A)
4.2 Modes of operation
There are two modes of operation of buck converter. The charging mode in which the switch
Q1 is closed and the inductor L stores energy. The discharging mode in which the switch is
open and the inductor L supplies energy to the load thought the source is disconnected from
load.
4.2.1 Charging mode
In charging mode of operation the switch Q1 is closed and the inductor L gets charged from
source Vin .The current in the inductor L raises exponentially but for simplicity it has been
taken as linear [13]. The capacitor acts as a filter to make the output current almost constant.
4.2.2 Discharging mode
In discharging mode of operation the switch Q1 is opened and the load gets disconnected
from the source. The diode gets forward biased and the energy required by the load is
supplied by the inductor L. The current in the inductor L discharges exponentially and
assumed to be linear for simplicity.
16
4.3 Waveforms
Figure 4.2: Buck converter waveforms [13]
17
Chapter 5
5. MAXIMUM POWER POINT TRACKING TECHNIQUE
(MPPT)
5.1 Maximum power point tracking
From figure 5.1 solar arrays has non-linear current-voltage and power-voltage
characteristics that varies with irradiation and temperature. In order to track the maximum
power point of the solar array the MPPT technique plays a prominent role in the PV systems.
The job of a MPPT technique in a photovoltaic (PV) system is to continuously tune the
system so that solar array operates always at maximum power point irrespective of weather
or load conditions [12].
Figure 5.1: I-V and P-V curves of solar cell indicating the maximum power point [3]
Basic principle:
According to maximum power transfer theorem, the power delivered to the load is maximum
when the impedance of source matches the impedance of load. Thus, the impedance seen
from the converter side matches the internal impedance of the solar array.
18
5.2 MPPT methods
There are various methods to track the maximum power point; some of them are given below
[11]:
1. Perturb and observe method
Perturb and observe method deals with the change of voltage to track the maximum power
and it is simple and cheap. The disadvantage is that it cannot track the maximum power
efficiently under varying weather conditions.
2. Incremental conductance method (INC)
INC method is based on the I-V curve of the solar module. Incremental conductance method
deals with the change in the duty cycle of the converter used between the solar panel and load
to track the maximum power point. This method requires both current and voltage sensor so it
is costly and complex.INC method can track the MPP efficiently under varying weather
conditions.
3. Fractional open circuit voltage method
The open circuit voltage of solar module is directly proportional to the voltage at maximum
power
K ≅
% to
V
C
=K V
… … … … … . . 5.
%.In this method the converter switch needs to be opened frequently which
results in power loss. This method is less efficient and cannot be used for partial shading
purpose.
19
4. Fractional short circuit current method
Short circuit current of solar module is directly proportional to the current at maximum power
K ≅
% to
ISC = K I
… … … … … . . 5.
% .in this method to measure the ISC one extra switch is needed and it is not
an accurate method to track MPP.
20
Chapter 6
6. SIMULATION OF MPPT
6.1 Mathematical description of INC method
Incremental conductance technique has been used to track the maximum power point
in which the incremental value of conductance is equal to the instantaneous value of
conductance at maximum power point. This is based on the I-V curve of the solar cell.
Figure 6.1: P-V curve explaining the incremental conductance method
From figure 6.1 Where G=-I/V, ∆G=dI/dV
dI/dV=-I/V at MPPT
dI/dV<-I/V to the right side of MPPT
dI/dV>-I/V to the left side of MPPT
In INC method the instantaneous voltage and current from solar array is sensed and if
the value of instantaneous conductance of solar array equal to incremental value of
conductance solar array then the operating point is at MPP, if the value of instantaneous
conductance of solar array is greater than incremental conductance of solar array then the
21
operating point is to the right of MPP, if value of instantaneous conductance of solar array is
less than incremental conductance of solar array then the operating point is to the left of MPP
[11] . In this way maximum power point is tracked by changing the duty cycle of MOSFET
of buck converter in turn changing the voltage and current of solar array. The block diagram
of the MPPT method is shown in figure 6.2.
Figure 6.2: Block diagram of PV cell with MPPT controller
22
Flow chart in figure 6.3 explains the process for achieving the MPP using INC method
Figure 6.3: Flow chart of incremental conductance method.
6.2 Simulation of MPPT using INC method
Buck converter has been used and the maximum power point has been tracked according to
the flow chart shown in figure 6.2. Using MATLAB Simulink and the parameters of solar
module used for simulation is given in Table.3.1. Output voltage, output power, output
current curve is plotted and these are constant with some ripple in output. Figure 6.4 shows
out-put power of solar module, figure 6.5 shows output voltage of solar module, figure 6.6
shows output current of solar module.
23
Power (W)
Time(S)
Voltage (V)
Figure 6.4: MPPT using INC method under STC
Time(s)
Current (A)
Figure 6.5: Output voltage of solar module during MPPT using INC method under STC
Time(s)
Figure 6.6: Output current of solar module during MPPT using INC method under STC
24
6.3 Simulation of INC MPPT method under varying irradiation
Figure 6.7 shows output power of solar module as the irradiation increases power increases
and INC method is properly tracking the MPP with change in irradiation.
1000 W/m²
900 W/m²
Power (W)
800 W/m²
Time(s)
Figure 6.7: MPPT under varying irradiation and constant temperature of 25˚C using
INC method
6.4 Simulation of INC MPPT method under varying temperature
Figure 6.8 shows output power of solar module as the temperature increases power decreases
and INC method is properly tracking the MPP with change in temperature.
˚C
˚C
Power (W)
˚C
Time(s)
Figure 6.8: MPPT under varying temperature and constant irradiation of 1000 W/m² using
INC method
25
Chapter 7
7. HARDWARE IMPLEMENTATION OF INC MPPT
METHOD
7.1 Hardware system description
MPPT is practically demonstrated by using an illuminated solar panel with ratings given
in the table 7.1
Table 7.1 Solar array specifications used for hardware implementation
PV module type
1220
Typical peak power
20 W
Open circuit voltage
21.90 V
Short circuit current
1.25 A
Current at peak power
1.16 A
Voltage at peak power
17.25 V
Power tolerance
±5%
Electrical parameters tolerance
±10%
The panel is illuminated by two incandescent bulbs of 100 W rating each from a
single phase ac supply of 230 V. A fixed resistor of 150 Ω is used as a load. A non-isolated
buck converter [9] is used for impedance matching. Solar panel is connected at the input
terminals of the buck converter and load resistor at the output as shown in block diagram
figure 7.1. The buck converter consists of a MOSFET IRFZ44N that is connected at the low
voltage side. The source is connected to ground and hence the triggering pulse magnitude is
low.
26
Figure 7.1: Block diagram of MPPT using LabVIEW
For generation of PWM signal for MOSFET a saw-tooth signal and a control signal
are necessary. SG3524 generates saw-tooth signal of different frequencies depending upon
the values of resistor (�� and capacitor (�� connected at pin numbers 6 and 7 respectively
[8]. The frequency (f) of saw-tooth signal generated by SG3524 is given by equation (7.1).
�≈
.
�� ��
…………………..
.
The permissible value of �� ranges from 1.8 K٠to 100 K٠and permissible value of
�� ranges from 0.001 µF to 0.1 µF. So the frequency of saw-tooth signal ranges from 130 Hz
to 722 KHz. The value of frequency chosen for this work is approximately 50 KHz that is
adjusted by using variable resistance pot as shown in figure 7.2.The saw-tooth signal has
maximum value of 3.68 V and minimum voltage of 0.72 V.
27
Figure 7.2:. Circuit diagram of hardware implementation of MPPT
Array voltage and current are given as inputs to a data acquisition device (NI
USB6009). The data acquisition device is connected to a PC with LabVIEW software as
shown in figure 7.3. Solar array voltage is sensed using potentiometer that reduces the
voltage to a level that is within the input voltage rating of USB6009. Solar array current is
sensed using current transducer LA-55P whose output voltage is proportional to the array
current. These voltages (one proportional to array voltage and other to array current) are
processed using INC algorithm implemented in LabVIEW and a control signal is generated.
This control signal is given as voltage output using USB6009 at a rate of 150 samples
per second. This control signal is restricted between the same limits as that of saw-tooth
signal magnitude (3.68 V-0.72 V).This ensures the duty cycle of triggering pulse between 0
and 1. LM311P compares the control signal, saw-tooth signal and gives triggering pulses of
same frequency as saw-tooth signal for MOSFET of buck converter.
28
Control
circuit
USB 6009
acquiring
voltage
and
current
Current
sensor
USB 6009
generating
control
signal
Buck
converter
Figure 7.3: Picture showing hardware components for MPPT implementation
29
7.2 Determining maximum power of solar array in LabVIEW
Since the solar panel is not illuminated from sunlight directly so the power output
from solar panel will be less than normal peak power so we have to find the maximum power
before proceeding to the MPPT. This can be done using LABVIEW in which the load is
changed by means of changing duty cycle by 0.01 and determining the MPP.
Figure 7.4: Array power waveform of solar panel with varying duty cycle
From the figure 7.4 maximum array power obtained is about 0.365 mW. Now when this is
operated using INC method output power tracked must be 0.365 mW.
30
7.3 MPPT using INC method
Figure 7.5: Array power waveform of MPPT using INC method
Figure 7.6: Array output current during MPPT
31
Figure 7.7: Array output voltage during MPPT
Thus the maximum power has been tracked using INC method in LABVIEW. From
figure 7.4, figure 7.5; figure 7.5 the maximum power is tracked within 100 ms and the
maximum power is 0.365 mW at a current of 0.0365 mA and voltage of 10 V.
32
Chapter 8
8. CONCLUSION
8.1 Summary
The maximum power point of solar array can be rapidly tracked by using incremental
conductance method under normal and also varying weather conditions. In the hardware
implementation of MPPT the pulses given to MOSFET are not exactly square wave at lower
value of duty cycles so the power is not becoming zero at lower duty cycles .In order to avoid
that voltage driver circuit has to be used. In this work MPPT is implemented by considering
the maximum power derived from figure 7.4.
8.2 Future scope
The work done in this project can be implemented to track the maximum power point of solar
array under varying weather conditions using LabVIEW. MPPT of solar array cannot be
implemented under partial shaded conditions using INC method. Module integrated
converters has to be used to track MPPT under partially shaded conditions.
8.3 References
1. M. G. Villalva, J. R. Gazoli, and E. R. Filho, “Comprehensive approach to modeling and
simulation of photovoltaic arrays,”IEEE Trans. on power Electron. vol. 24, no. 5, May 2009.
2. S. J. Chiang, K. T. Chang, and C. Y. Yen, “Residential photovoltaic energy storage system,
”IEEE Trans. on Ind. Electron.,vol. 45, no. 3, pp. 385-394, June 1998.
3. M.
chen and G.
A.
Rincon-mora, “Accurate electrical battery model capable of
predicting runtime and I-V performance,” IEEE Trans. on Energy convers., vol. 21,no. 2,June
2006.
33
4. Paul A. Lynn, “Electricity from sunlight”third edition,Pearson publications,2009.
5. M. Berrera, A. Dolara, ”Experimental test of seven widely-adopted MPPT algorithms”,
IEEE Bucharest Power Tech Conference, 2009.
6. A. K. Mukerjee and N. Thakur, Photovoltaic systems analysis and design, PHI
Learning private limited,2011.
7. R. J. Wai, Wen-Hung and C. Y. Lin, “High performance stand-alone photovoltaic
generation System,” IEEE Trans. on Ind. Electron., vol. 55,no. 1,Jan. 2008.
8. Data sheet of regulated pulse width modulators SG3524 by national instruments.
9. Raju.N,Mariappan.V,Jeyaprakash.K,Sathya.A, “Teaching Aids in SMPC Construction
Project in the Curriculum of Switched Mode Power Conversion”, IISC, Bangalore.
10. R. Gules, J.D.P. Pacheco, H.L. Hey and J. Imhoff, “A maximum power point tracking
system
with parallel connection for PV stand
–alone applications,”
IEEE Trans. on
Ind.Electron., vol. 55, no. 7, July 2008.
11. A Safari and S. Mekhilef,“Simulation and hardware implementation of Incremental
conductance MPPT with direct Control Method using Cuk converter,” IEEE Trans. on
Ind. Electron.,vol. 58, no. 4, April 2011.
12. T. Esram and P. L. Chapman, “Comparison of photovoltaic array maximum power point
tracking techniques,” IEEE Trans. on Energy Conversion, vol. 22, no. 2, June 2007.
13. Muhammed H. Rashid, "Power Electronics: Circuits, Devices, and Applications",second
edition ,Pearson publications,ISBN- 10: 013678996X,1993.
34
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