Simulation and Analysis of Photovoltaic Stand-Alone Systems Tulika Dutta Roy

Simulation and Analysis of Photovoltaic Stand-Alone Systems Tulika Dutta Roy
Simulation and Analysis of Photovoltaic
Stand-Alone Systems
Tulika Dutta Roy
Department of Electrical Engineering
National Institute of Technology, Rourkela
Rourkela-769008, Odisha, India.
May 2013
Simulation and Analysis of Photovoltaic
Stand- Alone Systems
A Thesis Submitted in Partial Fulfilment of the
Requirements for the Degree of
Master of Technology
in
Electrical Engineering
by
Tulika Dutta Roy
(Roll no-211EE2130)
Under the Guidance of
Prof. Somnath Maity
Department of Electrical Engineering
National Institute of Technology, Rourkela
Rourkela-769008, Odisha, India
May 2013
Dedicated to
My Maa
ACKNOWLEDGEMENTS
First and foremost, I am truly indebted to my supervisor Prof. Somnath
Maity for his inspiration, excellent guidance and unwavering confidence
through my study, without which this thesis would not be in its present form.
I also thank him for their gracious encouragement throughout the work. I am
also very much obliged to Prof. A. K. Panda Head of the Department of
Electrical Engineering, NIT Rourkela for providing all the possible facilities
towards this work. Thanks also to other faculty members in the department. I
would like to thank Pratik, Shradda, Tusar, Avinash, Prangya and research
scholars’ electrical engg. department for their enjoyable and helpful company
I had with. My wholehearted gratitude to my parents, Da, Boudi, Mishti and
Ritun for their encouragement and support.
Tulika Dutta Roy
Roll no.-211ee2130
Rourkela, May 2013
ABSTRACT
Energy saving is biggest issue now a days, renewable energy is playing a big
role in producing electricity, among them wind and solar are popular renewable
energy sources. Fast tracking of global maximum power point (MPP) is a
challenge, many research is going on this direction.
MPP highly depends on atmospheric conditions, so our maximum power
point tracking (MPPT) technique should be good enough to track MPP in dynamic
atmospheric conditions. Perturb and Observer (P & O) and Incremental
conductance (INC) are widely used MPPT techniques, we used INC method and
simulated solar photovoltaic system in dynamic atmospheric conditions.
Partial shading gives local MPPs and one global MPP, power loss occur in a
shaded module because of that efficiency reduces, most of the conventional MPPT
are failed to track global MPP ,to deal with this problem two kind of control
strategies found in literature
first one modular MPPT and second one two
controller structure.
MPP also highly depends on the load, as the load changes MPP changes.
Extra power need to store because sometimes load requirement is lesser than the
generation, in this situation a battery is needed and in night time when PV module
not able to generate, power can draw from the battery.
In this thesis we have discussed about the INC MPPT method for different
atmospheric conditions and partial shading.
LIST OF FIGURES
Figure No.
Figure description
Page No.
Figure 1.1
PV module with boost converter
3
Figure 1.2
Block diagram of partial shaded module
4
Figure 1.3
Circuit diagram of partially shaded module connected in series
5
Figure 2.1
Unregulated standalone system with DC load
7
Figure 2.2
Regulated standalone system with DC load
8
Figure 2.3
Regulated standalone system with battery and DC load
8
Figure 2.4
Regulated standalone system with battery, AC and DC loads
9
Figure 2.5
Grid interactive PV system
9
Figure 2.6
Hybrid system
10
Figure 3.1
PV cell structure
11
Figure 3.2
PV array, cell and module
12
Figure 3.3
Equivalent circuit of practical PV device
13
Figure 3.4
I-V curve of PV panel
15
Figure 3.5
P-V curve of PV panel
15
Figure 4.1
The concept of load-mismatch and MPP tracking
16
Figure 5.1
Buck converter interface with PV system
19
Figure 5.2
Boost converter interface with PV system
19
Figure 5.3
PV system
20
Figure 5.4
Duty cycle control of DC-DC converter
22
Figure 5.5
Output power curve of boost converter
23
Figure 5.6
Output voltage curve of boost converter
23
Figure 6.1
P-V curve
24
Figure 6.2
INC algorithm
25
Figure 6.3
Irradiance effect on P-V characteristics at constant temperature
26
(25°C)
Figure 6.4
Irradiance effect on output power of boost converter at constant
26
temperature (25°C)
Figure 6.5
Different irradiance condition and constant temperature
27
Figure 6.6
Temperature effect on P-V curve at constant irradiance
27
(1000W/m2)
Figure 6.7
Temperature effect on output power of boost converter at constant
28
irradiance (1000W/m2)
Figure 6.8
Different temperature condition and constant irradiance
28
Figure 7.1
Module IV curves
30
Figure 7.2
Array IV curve
30
Figure 7.3
Module PV curves
30
Figure 7.4
Array PV curve
31
Figure 7.5
Analogue implementation of MPPT
34
Figure 7.6
Power output curve in partial shading condition
34
LIST OF TABLES
3.1
7.1
Module Ratings
23
Principle of operation of controller
\
44
CONTENTS
1. Introduction…………………………………………………………………...1
1.1Motivation…………………………………………………………………...1
1.2 Literature Review……………………………………………………………2
1.3 System under consideration…………………………………………………3
1.4 Objective and scope of this dissertation…………………………………….5
2. Classification of solar photovoltaic system…………………………………..7
2.1 Introduction solar PV system………………………………………………7
2.2 Types of PV system………………………………………………………..7
2.2.1Stand-alone PV systems……………………………………………7
2.2.2Grid interactive PV systems………………………………………..9
2.2.3Hybrid system……………………………………………………..10
3. Modeling and simulation of PV array……………………………………...11
3.1Modeling of PV array…………………………………………………...11
3.2Parameters of PV array affected by the Temperature and irradiance…..13
3.3Module rating used for simulation……………………………………...14
3.4Simulation results of one module…………………………………….....14
4. Maximum power point tracking techniques………………………………..16
5. DC-DC converters……………………………………………………………19
5.1Components comparison………………………………………………..19
5.2Modeling of PV system with boost converter…………………………..21
5.3Simulation results……………………………………………………….23
6. Incremental conductance method…………………………………………...24
6.1 Mathematical description……………………………………………….24
6.2 Varying insolation condition…………………………………………....26
6.3 Varying temperature condition………………………………………….27
7. Partial shading………………………………………………………………..29
7.1 Modeling of partial shading phenomena in PV system………………...30
7.2 Analog implementation of MPPT………………………………………32
8. Conclusion…………………………………………………………………….36
8.1 Summary……………………………………………………………….36
8.2 Future research directions………………………………………………36
8.3 References………………………………………………………………36
CHAPTER 1
Introduction
1.1 Motivation
In 21st century energy crises, drag every researchers concentration towards the renewable
energies, renewable energy is a source of clean and green energy. Among all renewable energies
photovoltaic (PV) and wind are considered to be good sources of energy. Many researches are
going on in the area of PV system, big challenge in this area is to track maximum power point
(MPP) in the dynamic atmospheric conditions and shading condition because MPP varies with
change in temperature and insolation.
To track maximum power point, technique use called maximum power point tracking
technique (MPPT).In literature we found many MPPT tracking techniques in which main
concentration is towards the fast tracking of MPP and operate PV system in global maximum
power point.
Perturb and observer (P&O) and incremental conductance (INC), these two methods are
frequently found in literature because of its easy implementation and effective tracking. In this
thesis we described about INC. Boost converter is used as intermediate converter to perform
switching and regulated output. In many literatures it has proved that boost converter has more
advantages over the buck converter.
To understand PV system easily, it is operated under the constant load condition and
avoids battery. Battery is used to store extra power from PV system. Partial shading is problem
which interrupts PV system to operate in global MPP and system efficiency reduces because of
this. Effect of partial shading in I-V and P-V curves also explained in this thesis.
Analog implementation of MPPT makes system’s transient response faster and it is
cheaper, this also discussed with results.
1
1.2 Literature review
Many literatures are on the topic modelling of solar photovoltaic (PV) array M. G.
Villalva et.al. [1] proposed a method of modelling and simulation of photovoltaic arrays. The
main objective of this paper was to find the parameters of nonlinear I-V equation. In this paper
effect of temperature and irradiation on the parameters of the I-V equation also discussed. S. J.
Chiang et.al. [8] introduces a residential photovoltaic energy storage system, in which the PV
power is controlled by a DC-DC controller with MPPT and transferred to a small battery energy
storage system. C. Rodriguez et.al. [7] derived an analytic solution for finding the point which is
in a close vicinity of the MPP.
T. Esram et.al. [2] discussed and compared different MPPT techniques available in
literature and explained about nineteen MPPT methods. The author has given summary of these
MPPT techniques and their implementation methods which serve as a useful guide in choosing
the right MPPT method for specific PV systems. Shading is a big problem in the photovoltaic
system W. Xiao et.al. [3] discussed the topologies used for photovoltaic power systems to
optimize the operation of MPPT. The author proposed an individual power interface for each
photovoltaic module and recommended a structure suitable for the photovoltaic features and
MPPT to minimize the performance reduction caused by non-ideal conditions.
M. Chen et.al. [12] proposed an accurate, intuitive, and comprehensive electrical model
to capture the entire dynamic characteristics of a battery, from nonlinear open-circuit voltage,
current, temperature, cycle number, and storage time-dependent capacity to transient response.
I.-S. Kim et.al. [13] proposed a sliding mode controller for the single-phase grid connected
photovoltaic system. The sliding mode controller has been constructed based on a time-varying
sliding surface to control the inductor current and solar array power simultaneously. R. Gules
et.al. [14] analysed, designed and implemented a parallel connected MPPT system for a standalone photovoltaic power generation.
A. Safari et.al. [11] discussed incremental conductance (INC) method and practical
implementation of this method. H. Patel et.al. [15] have discussed about specifically partial
shading condition and extensive study about the partial shading condition has been done by the
author. They made a generalised programme for PV array simulation.
2
1.3 The system under consideration
PV system under constant temperature and irradiation
As shown in Figure 1.1 system consist of a PV module, DC-DC boost converter, MPPT with
constant resistive load. Boost converter consist of two switches S1 and S2, an inductor L, two
capacitors C1 and C2 and load resistance R. Switches are operate by control logic, develop by
MPPT. Matlab coding is use to make MPPT, its purpose is to track maximum power so that PV
module utilizes maximum.
Figure 1.1: PV module with boost converter
PV system under constant temperature and varying irradiation
Dynamic atmospheric condition affects the output of PV panel, so output of boost converter also,
our purpose is to track maximum power deliver by the module in any atmospheric conditions.
Our MPPT should be robust enough to track MPP. System discussed in previous section is for
3
constant atmospheric condition, same system consider again but for different irradiations and
constant temperature.
PV system under varying temperature and constant irradiation
Temperature is inversely proportional to the voltage, so as the temperature increases voltage
decreases, it affects the output power.
PV system under partial shading condition
Figure 1.2 shows two modules in a array , one module is shaded, because of shaded module P-V
and I-V curve changes; we will have one local maxima and other global maxima. How this
partial shading condition is affecting the P-V and I-V curves we will discuss in this section.
Figure 1.3 shows the circuit diagram of partial shaded module.
Figure 1.2: Block diagram of partial shaded module
4
Figure 1.3: Circuit diagram of partially shaded module connected in series
Analog implementation of MPPT
Analog implementation of MPPT is faster and cheaper, MPPT consist of differentiator,
comparator, XOR gate and D flip flop.
1.4 Objective and scope of this dissertation
Objective of this thesis is to check incremental conductance (INC) algorithm in dynamic
atmospheric conditions, INC method is capable of tracking maximum power point or not. For
efficient tracking or utilize PV array fully, it need to operate in maximum power point. For that
5
INC method is implemented first with constant temperature, constant irradiation, after constant
temperature; varying irradiation and varying temperature; constant irradiation.
Partial shading of array is a big problem because in this condition we have many local
maxima and one global maxima, so it’s tough to get global maxima in P-V curve. In this we
simulated two modules one is fully shaded and other is partially shaded, P-V curve and I-V
curves plotted in this situation.
Analog implementation of MPPT is easy, cheap and faster.
In chapter 2, we described what PV system is and types of PV system, we concentrated
on PV stand-alone system. We discuss, what are differences in stand-alone, grid connected and
hybrid photovoltaic system.
In chapter 3, modeling of the solar photovoltaic system has discussed, how the
parameter of PV equation depends on the temperature and irradiation has been discussed.
In chapter 4, MPPT techniques are described, why we have chosen INC method,
although we found many MPPT techniques in literature but INC method is simple and easy to
implement. In this chapter we discussed various MPPT techniques.
In chapter 5, which type of DC-DC converter used is discussed, it’s purpose to find
accurate and cost effective DC-DC converter for PV system for perfect modeling. State space
equation is derived for boost converter with PV system.
In chapter 6, INC method is discussed in brief advantage of this method over other
methods. Results of simulation for steady and dynamic atmospheric condition are also discuss in
this chapter.
In chapter 7, discuss the phenomena of partial shading with two modules and three
modules of PV array and its simulation results has shown.
6
CHAPTER 2
Classifications of solar photovoltaic system
2.1 Introduction solar PV system
PV system is design to give the electric supply to load and load can be ac type or dc type. Supply
can be needed in day time or evening time or both time. PV system can give supply only in day
time for night hours we needed supply for that we have batteries, where power can store and
utilize [13].
2.2 Types of PV system
2.2.1 Stand-alone PV system
Depending on the type of load, cost, resources availability and requirements of the load
stand-alone system divided into several categories, which are describe below
a)
Unregulated standalone system with DC load
Usually this type of system is for low power applications. A PV system is directly connected to
the load without any MPPT controller, night hours it will not provide any supply because of the
absence of the battery.
Figure 2.1: Unregulated standalone system with DC load
7
b)
Regulated standalone system with DC load
Figure 2.2: Regulated standalone system with DC load
It is similar to unregulated standalone system with DC load but basic difference between this and
previous one that this system requires a MPPT technique. Usually system with MPPT should
have one battery otherwise extra power will be waste.
c)
Regulated standalone system with battery and DC load
Figure 2.3: Regulated standalone system with battery and DC load
Most common configuration PV array, battery, MPPT and DC load. Battery use to store the extra
power of PV system, this will increase the cost of PV system. A charge controller is must for this
type of system because battery life is less compare to PV module, extra charging deep
discharging can reduce the life of battery [12].
8
d)
Regulated standalone system with battery, AC and DC loads
Figure 2.4: Regulated standalone system with battery, AC and DC loads
This system is similar to previous one but here AC load can also draw the power from PV system
and inverter (DC to AC converter) is require, it will increase the cost.
2.2.2 Grid interactive PV system
Grid connected PV system is a system when grid is connected to PV system .In this type
of system consist PV array and inverter. Figure 2.5 shows grid connected PV system. Grid
connected system deals with AC. Grid connected system deals with very high power applications,
so is tough to store this much of power in battery [13].
Figure 2.5: Grid interactive PV system
9
2.2.3 Hybrid system
When PV system is use in conjunction with diesel generator, wind generator, micro turbines, fuel
cells etc., system is called hybrid system
Figure 2.6: Hybrid system
10
CHAPTER 3
Modeling of PV array and simulation
3.1 Modeling of PV array
PV array consist several modules, modules made of cells, each PV cell generates approximately
2W of power. Cells connected in series to increase voltage rating, these are connected in parallel
to increase current rating. Figure 3.2 shows PV cell, module and array.
Photovoltaic cell
Solar cells are the building blocks of the PV system. It is made up of semiconductor, when light
strikes to the surface of semiconductor electron knocked off, it collected from metal connected to
this cell.
Photovoltaic module
Power generated by cell is very less so number of cells connected in series to increase power
rating. Diode can be antiparallel connected to avoid the damage caused by partial shading.
Photovoltaic array
Power generated by a module is not sufficient for some applications, so module can be connected
in series or parallel, to meet desire value.
Figure 3.1: PV cell structure
11
Figure 3.2: PV array, cell and module
PV cell and array model represented in electrical equivalent circuit shown in Figure
3.2 .It is represented by the PV equation (3.1)
[
(
)
]
(3.1)
Where I and I0 the photovoltaic output and saturation currents of array respectively and Vt is the
thermal voltage of array ,Rs is the series equivalent resistance Rp is the parallel equivalent
resistance ,a is the diode ideality factor, Vpv and Ipv are the photovoltaic output voltage and
current respectively. I current generated from the light.
To increase voltage rating of array Ns cell connected in series than thermal voltage
Vt=NskT/q. To increase output current of the PV array Np cell connected in
parallel .I=I,cellNp,I0=I0,cellNp
In literature we found single diode, two diode and three diode model. Single diode model
is a good combination of simplicity and accuracy. For considering various effects extra diodes
consider. For power electronics practitioner single diode model is accurate and easy for doing
analysis.
12
Figure 3.3: Equivalent circuit of practical PV device
3.2 Parameters of PV array affected by the Temperature and irradiance
(
)
(3.2)
t generated current at nominal condition (25ºC and 1000 W/m2)
Where
= Short circuit current/temperature coefficient
=
(Actual and nominal temperature respectively)
G = irradiation on the device surface
= nominal irradiation
( )
Where
[
(
)]
(3.3)
Bandgap energy of semiconductor
= Saturation current in nominal condition
(3.4)
Where
k= Boltzmann constant (1.3806503 × 10−23 J/K)
q = electron charge (1.60217646 × 10−19 C)
13
Conclusions from above equations and literature
 Diode saturation current ( ), PV current (
) and thermal voltage ( ) are temperature
dependent.
 PV current (


) directly proportional to the irradiance
gives accurate shape between mpp and open circuit voltage
a expresses the degree of ideality of the diode and it is totally empirical, any initial value
of a can be chosen in order to adjust the model
3.3 Module ratings use for simulation
We use Solarex MSX -60 parameters for simulation, whose parameter ratings are given below:
Table 3.1 Module Ratings
Typical peak power (Pp)
60W
Voltage @ peak power (Vpp)
17.1V
Current @ peak power (Ipp)
3.5 A
Guaranteed minimum peak power
58W
Short-circuit current (Isc)
3.8A
Open-circuit voltage (Voc)
21.1V
Temperature
coefficient
of
open-circuit -(80±10)mV/ºC
voltage
Temperature
coefficient
of
short-circuit (0.065±0.015)%/ºC
current
Approximate
effect of temperature on power
–(0.5±0.05)%/ºC
3.4 Simulation results of one module
3.4.1 I-V curve of PV panel
I-V (Current-Voltage) curve originated from the equation (3.1) for particular value of the voltage
current value we get and plot the curve this curve gives at what value of the voltage what should
be the current. When the Ipv=0 we will get open circuit voltage (Voc) of PV panel, when Voc=0
14
we will get short circuit current (Isc).In I-V curve star point represents the maximum power point
corresponding voltage Vmpp and corresponding current Impp .
4
3.5
Current (A)
3
2.5
2
1.5
1
0.5
0
0
5
10
15
20
25
Voltage (V)
Figure 3.4: I-V curve of PV panel
3.4.2 P-V curve of PV panel
Multiplication of output current and output voltage gives the output power, at particular value of
current (Impp) and voltage (Vmpp), will give maximum power Pmpp. Figure 3.5 shows P-V (PowerVoltage) curve of PV panel, star point shows the maximum power point of the panel.
60
Power (W)
50
40
30
20
10
0
0
5
10
15
Voltage (V)
Figure 3.5: P-V curve of PV panel
15
20
CHAPTER 4
Maximum power point tracking technique
PV system’s efficiency depends on MPPT [2].MPPT is the most important in PV system;
efficient tracking is the key issue. Many literature we found who has taken care of irradiation
and temperature changes because these are key factors of shifting of MPP, in chapter 3 we
already have described about the effect of temperature and irradiation on the parameters of
current equation, roughly we can say temperature is inversely proportional and irradiation
directly proportional to output power. In partial shading condition we have multiple local
maxima and one global maxima and it’s tough to track the global maxima through one MPPT,
without using it in distributed manner. Fast tracking of MPPT is also a big problem.
Figure 4.1: The concept of load-mismatch and MPP tracking
16
Figure 4.1 Maximum power hyperbola BP intersects I-V curve at point B, load mismatch can
cause PV array to operate in sub-optimal point. Actual load line intersects I-V curve in I, ideal
load curve in B [4].
Few MPPT methods we discussed below
A. Hill climbing
Figure 3.5 shows PV curve, a hill climbing method is method to track the power through
perturbation in duty cycle. Perturbation in duty cycle will continue unless maximum power
reaches. Fixed step size can be use but oscillation around the MPP may occur, variable step size
will be beneficial but its though to vary the step size, as we reach closer to the MPP step size
decreases.
B. Perturb and observe (P&O)
P&O is similar to the hill climbing method only one difference is that hill climbing method deals
with perturbation in duty cycle and P&O method deals with perturbation in voltage.
Disadvantage of this method is it is unable to track MPP in varying weather conditions.
C. Incremental conductance (INC)
Increment in conductance in I-V curve is the basis of this method, we already know
At maximum power point
0……… (4.1)
.......................................... (4.2)
Since
………………………….... (4.3)
So
This technique we will briefly discuss in chapter 6.
D. Fractional open-circuit voltage
Voc and Vmpp are directly proportional
k
……………………...… (4.4)
17
k ≌ 7 % to 78% , for measuring
converter should off. Frequently we have to do this, it
causes power loss and efficiency is less and this method is not useful in partial shading
condition. Advantage of this method it is easy to implement and it is cheap.
E. Fractional short-circuit current
This method is similar to fractional open circuit voltage method .current Impp is
proportional to Isc
k
……………………..(4.5)
k ≌ 78% to 92 % .measuring Isc during operation is though need one extra switch. It will
increase the cost and calculated value is also not so accurate.
18
CHAPTER 5
DC-DC converters
DC to DC converters are used for converting one level of input voltage to other level of
DC output voltage. DC-DC converter consist of inductor, capacitors and switches,
DC-DC Converter interface with PV system is very essential for that we need a good
converter. These converters play a role of charge controller, MPP trackers and PV interface with
load. We have many types’ isolated and non-isolated converters among that buck and boost nonisolated DC-DC converters frequently use in literature, because of their easy structure and less
components .Figure 5.1 and figure 5.2 shows buck and boost DC-DC converter with their PV
interface [3].Among these two boost converter is advantageous [3],[9].
Figure 5.1: Buck converter interface with PV system
Figure 5.2: Boost converter interface with PV system
19
5.1Components comparison
Not very significant comparison between inductor of boost and buck converter ,boost converter
require greater value inductor .As we compare the capacitor value buck converter requires a huge
and bulky capacitor to remove ripple from the PV current, boost converter can handle ripple with
less value capacitor.
MOSFET current rating of boost converter is less as compare to buck converter because
in buck converter MOSFET connected with the source directly and heavy current flow through it,
in boost converter less current flow through it.
A blocking diode is requiring to protect reverse current from load side at light load
condition otherwise PV panel can burn or damage, in boost converter it has freewheeling diode
but in buck converter it’s require.
5.2Modeling of PV system with boost converter
Figure 5.3: PV system
State space modelling is very useful in small signal and DC analysis.
Taking figure 5.3 system under consideration .Below equations describe the operation
̇ (t)
(t)
(t)
(t) (t)……….. (5.1)
(t)
(t) (t)…….. (5.2)
20
Where j=1, during dT and j=2 during d’T, where d is the duty ratio, defined as
is it’s compliment [16].
(t)
State vector x(t)= [ (t) ]………………(5.3)
(t)
Input vector u(t)=[
(t)]……………………(5.4)
ON mode
()
(t)………………… (5.5)
()
()
()
………………… (5.6)
(t)
(t)…… (5.7)
(t)……….................. (5.8)
OFF mode
()
(t)
()
(t)……………….. (5.9)
()
()
(t)………….. (5.10)
(t)
(t)…… (5.11)
(t)……..(5.12)
21
, d’
0
[ 0
0
0
0
[ 0 ],
0] ,
0
0
0
[0] ,
0 ],
[
0
[0
0
[0 0
],
[0
]
0 0]
[0 0 0 ]
0
Small signal AC state equation
̂ ()
̂ (t)
̂(t)
̂( )
̂
̂(t)
̂ (t)
()
̂(t)
̂ (t)
̂ (t)
̂ (t)………….. (5.13)
̂ (t)……… (5.14)
̂ (t)………….. (5.15)
̂ (t)…………… (5.16)
5.3Control of DC-DC converters
The output of DC-DC converters controlled by switch ON-OFF the controllable switch with
constant frequency TS=TON+TOFF. d=TON/TOFF is the duty cycle. MPPT will generate a signal
which is compared with constant frequency ramp signal, a square wave is generated after it and
its fed to DC-DC converter.
Figure 5.4 Duty cycle control of DC-DC converter
22
5.4Simulation results
PV module is simulated with MPPT with boost converter and out output voltage, output power
curve is plotted and these are constant with some ripple in output. Figure 5.5 shows out-put
power of boost converter and Figure 5.6 shows output voltage of boost converter.
70
Power (W)
60
50
40
30
20
10
0
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0.09
0.1
Time (sec)
Figure 5.5: output power curve of boost converter
25
Voltage (V)
20
15
10
5
0
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Time (sec)
Figure 5.6: output voltage curve of boost converter
23
CHAPTER 6
Incremental conductance method
6.1 Mathematical description
Basic of INC method comes from P&O algorithm. In P-V curve as shown in figure 6.1, slope is
positive, negative and zero in left, right and peak point respectively [11].
Figure 6.1: PV curve
At maximum power point
Since
So
24
0…….. (6.1)
… (6.2)
….. (6.4)
Because
>0
left side of the curve
<0
right side of the curve
0
peak of the curve
So
>
left side of the curve
<
right side of the curve
peak of the curve
According to above expression algorithm is implemented for MPPT, instead of P-V curve, I-V
curve is use in these. Figure 6.2 shows the algorithm of this method
Figure 6.2: INC algorithm
25
Simulation has been done using INC method for various insolation and temperature change
conditions and results has been plotted.
6.2 Varying insolation condition
Figure 6.3 shows the P-V curve in different insolation conditions, star point shows peak power of
each curve, as insolation increases peak power shifted upwards.
60
1000W/m2
Power (W)
50
900W/m2
800W/m2
40
700W/m2
30
20
10
0
0
5
10
15
20
25
Voltage (V)
Figure 6.3: Irradiance effect on P-V characteristics at constant temperature (25°C)
Figure 6.4 shows output power of boost converter as the insolation increases power increases and
INC method is properly tracking the MPP with change in insolation
80
1000W/m2
900W/m2
70
Output Power (W)
800W/m2
60
2
700W/m
50
40
30
20
10
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
Time (sec)
Figure 6.4: Irradiance effect on output power of boost converter at constant temperature (25°C)
26
Figure 6.5 is plotted to verify the results that out power are tracking exact the input power or not.
Dashed line is P-V curve of panel output and continuous line is output power verses time and it
is tracking exactly the input power.
70
60
y axis - Output power of boost converter
----Input power of boost converter
Power (W)
50
40
30
20
10
0
0
5
10
15
20
Voltage (V)
Figure 6.5: Different irradiance condition and constant temperature
6.3 Varying temperature condition
Figure 6.6 shows the P-V curve in different temperature conditions, star point shows peak power
of each curve, as temperature increases peak power shifted downwards.
60
25°C
55°C
50
Power (W)
85°C
40
115°C
30
20
10
0
0
5
10
15
20
25
Voltage (V)
Figure 6.6: Temperature effect on P-V curve at constant irradiance (1000W/m2)
27
Figure 6.7 shows output power of boost converter as the temperature increases power decreases
and INC method is properly tracking the MPP with change in temperature.
80
25°C
Output Power (W)
70
55°C
85°C
60
115°C
50
40
30
20
10
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
Time (sec)
Figure 6.7: Temperature effect on output power of boost converter at constant irradiance
(1000W/m2)
Figure 6.8 is platted to verify the results that out power are tracking exact the input power or not.
Dashed line is P-V curve of panel output and continuous line is output power verses time and it
is tracking exactly the input power.
60
Output power of boost converter
Power (W)
50
----Input power of boost converter
40
30
20
10
0
2
4
6
8
10
12
14
16
18
Voltage (V)
Figure 6.8: Different temperature condition and constant irradiance
28
20
CHAPTER 7
Partial shading
Partial shading occurs in PV system or cell because of dirt, neighbor building, aging effect of
module etc. Shaded cell gives less power output and it’s tough to consider the shading of each
and every cell analysis will become tougher, so considering the effect of shading in module, we
simulated.
We have considered two modules one is shaded and one is full illuminated, and check the
how out P-V and I-V curve affected. Figure 1.2 shows partial shading phenomena. When one cell
is shaded, cell become reverse bias, breakdown voltage can occur in this situation, which can
cause serious damage in the cell, so anti parallel diode connected in series to bypass the current.
Figure 7.2 and figure 7.4 shows how P-V and I-V curve will look like in this case.
Why we need to simulate PV array in partial shading condition because P-V curve had
multiple local peak and a global peak, so MPPT should be good enough to track this global peak.
So in partial shading condition I-V and P-V curve will give essential information for designing
MPPT.
7.1 Modeling of partial shading phenomena in PV system
We can code or give a modeling approach to check partial shading effect in P-V and I-V curves,
modeling is little bit easy. Modeling approach of PV system having following advantages
 Helps researchers to predict the effect of irradiation and temperature change in P-V and IV curves.
 Different configuration can be check with its efficiency of PV system
 Different configuration can be check with different MPPT approach.
Two module output in shading condition
Two module is simulated in shading condition one is getting 1000 W/m2 and other one is getting
100 W/m2.Figure 7.2 and Figure 7.4 clearly shows how the I-V curve and P-V curve change
respectively in partial shading condition.
29
4
Module current (A)
3.5
1000 W/m2
3
2.5
2
1.5
100 W/m2
1
0.5
0
0
5
10
15
20
25
Module voltage (V)
Figure 7.1 Module IV curves
Array output current (A)
4
3.5
3
2.5
2
1.5
1
0.5
0
0
5
10
15
20
25
30
35
Array output voltage (V)
Figure 7.2:Array IV curve
60
1000 W/m2
Module power (W)
50
40
30
100 W/m2
20
10
0
0
5
10
15
Module voltage (V)
Figure 7.3: Module PV curves
30
20
25
Array output power (W)
60
50
40
30
20
10
0
0
5
10
15
20
25
30
35
Array output voltage (V)
Figure 7.4: Array PV curve
Three modules in array in shading condition
Figure 7.5 shows three modules getting different irradiations, connected in series. How the
output P-V and I-V curve affected by partial shading shown in figure 7.6.
90
4
I-V curve
3.5
70
P-V curve
3
Power (W)
60
2.5
50
2
40
1.5
30
1
20
0.5
10
0
0
-10
0
Current (A)
80
10
20
30
40
50
60
-0.5
70
Voltage (V)
Figure 7.5: output P-V and I-V curve of PV array in shading condition for three modules
31
7.2 Analog implementation of MPPT
Control strategy
MPPT can perform in analog or digital both domains, analog domain is faster than digital
domain because don’t need I-V and P-V plot and cheaper also, partial shading occur
instantaneous, so faster response of MPPT is require [18].
As MPP depends on temperature, noise, irradiation, aging and other factors, so we can write
⋯……….. (7.1)
Where µ1, µ2 are the noise terms. Neglecting the effect of noise In P-V curve for maximum
0
power
Therefore
>0
{ 0
<0
f
f
f
<
………. (7.2)
>
Where Vmpp is the voltage where power is maximum.
> 0 and
So when
<
voltage should increase to achieve Vmpp, if
voltage should operate in same point and
>0
{ 0
<0
f
f
f
< 0 and
>
0 and
, decrease the voltage.
<
…………. (7.3)
>
According to equation 7.3, obvious control strategy ̇
k(
) where k is a positive
coefficient, associated with speed of controller. From equation 7.2 and 7.3 we can write ̇
k
, to implement this we need
̇
̇
at
an
,we have equation 7.1 after neglecting noise term
̇
̇
k ̇ ,but this is very though to implement because ̇ appear in denominator and
, ̇
0, singularity occur. If we make ̇ =0 we may lose vital information related
to sign.
32
̇
We can use signum function sgn x= -1 if x<0, 0 if x=0 and1 if x>0,sgn ( ̇ )←sgn ( ̇ ) where
← denotes RHS of equation gives information to LHS but x=0 again creates problem and we can
write if x≥0 so sgn x=1 and to avoid division we use sgn ( ̇ ) ← sgn ( ̇ ) sgn ( ̇ )
Practical implementation
Power will get through simple multiplication of current and voltage p = v i and and ̇ ̇ will get
through differentiator, after that comparator to compare the condition and Boolean expression
use to execute by XOR gate. High frequency can damage the switch to control that D flip flop is
used.
Table 7.1 Principle of operation of controller
Comparator output
̇
̇
X
X
S
Switch
v
≤
>0
>0
1
1
0
Opens
Increase
≤
≤0
≤0
0
0
0
Opens
Increase
>
>0
>0
1
0
1
Closes
Decrease
>
≤0
≤0
0
1
1
Closes
Decrease
Condition
33
Figure 7.6: Analog implementation of MPPT
Output power curve
100
Power (W)
80
60
40
20
0
0
0.5
1
1.5
2
2.5
Time (sec)
Figure 7.7: Power output curve in partial shading condition
34
3
-3
x 10
CHAPTER 8
Conclusion
8.1. Summary
There are many MPPT techniques available in both digital and analog domains. Although the
INC method reported earlier has proved it’s important, still it is unable to track maximum power
under partial shading condition.
In partial shading condition array output P-V and I-V curve are drastically changed and there
exist multiple local minima and one global maxima power point. In such situations, it is difficult
to track the global maximum point. It is therefore necessary one to look for an intelligent
solution, which cannot be solved by available MPPT controllers for partial shading conditions.
With his views, in this thesis, we propose a module integrated converters structures. This is
achieved by using the self-controlled (implemented in analog domain) dedicated modular dc-dc
converter architecture. The analog implementation of MPPT is easy, faster and cheaper.
Moreover, in order to show its tracking performance, system has also been evaluated for different
loading conditions.
8.2Future research directions
Battery is very much requires in stand- alone systems so study based on battery and varying load
condition can study.
State space modelling of PV system has been done, stability analysis can be done controller may
design based on modeling.
8.3References
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37
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