 Open Access
 Total Downloads : 48
 Authors : Keerti Yadav , Dr. Anuprita Mishra
 Paper ID : IJERTV7IS030154
 Volume & Issue : Volume 07, Issue 03 (March 2018)
 DOI : http://dx.doi.org/10.17577/IJERTV7IS030154
 Published (First Online): 22032018
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Comparative Analysis of Two Wellknown Maximum Power Point Tracking Techniques for Photovoltaic Cell
Keerti Yadav M.Tech. student Department of EEE
Technocrats Institute of Technology Bhopal (M. P.) India
Anuprita Mishra Professor Department of EEE
Technocrats Institute of Technology Bhopal (M. P.) India
AbstractThis paper provides a comparative analysis of widely used maximum power point technique (MPPT) i.e. Perturb and observe MPPT and Incremental Conductance MPPT used in photovoltaic application. A boost converter is used to stepup the voltage of the PV cell to a required DClink voltage. A complete analysis of the boost converter has been described in this paper.
Keywords PV cell; Boost converter; DClink; MPPT

INTRODUCTION
Due to the limited resources of fossil fuel, the development of renewable energy sources is rising now days. The main advantages of these renewable energy sources are (a) it is plenty of available in nature, (b) ecofriendly and (c) recyclable. There are many renewable energy sources such as wind energy, solar energy, hydro energy and tidal energy. To harness electrical energy from renewable energy sources, power conditioning unit (PCU) is required. PCU comprises of one or more than one power electronic converter (PEC). DCmicro grids (Figure 1) are one of the most useful techniques where the renewable energy source is connected to the load with the help of a DC bus [1]. Design of DCmicro grid has been studied in [13].
incremental conductance. Both MPPT are hillclimbing algorithm and true MPPT. Simulation results are provided to illustrate the functionality of the MPPT techniques.
This paper is organized as follows. Section II provides the mathematical modeling of PV cell. Section III presents the functionality of different maximum power point tracking algorithms. Section IV presents details of switched mode power converter. Section V provides simulation results. Section VI concludes the paper.

MATHEMATICAL MODEL OF PV CELL
The photovoltaic system converts sunlight directly to electricity without having any disastrous effect on our environment. The basic segment of PV array is PV cell, which is just a simple pn junction device. Figure 2 shows the electrical equivalent circuit of PV cell.
The ideal PV cell consists of a constant current source and a diode whereas the practical PV cell consists of additional series Rs and parallel resistance Rp . Modeling of PV cell is
summarized in [24].
Rs
Ipv Rp
Id
Fig. 2. Circuit diagram of PV cell
The basic equation which describes the IV characteristics of an ideal PV cell can be represented as
Fig. 1. Block diagram of DCgrid
I I pv Id
(1)
Photovoltaic cell is one of the most widely used renewable
Where
I pv
is current of PV cell and Id
is Shockley diode
energy. The photovoltaic cell provides electrical energy when
equation which can be represented as
solar irradiance is incident on it. To extract maximum power
I
qV
from PV cell, maximum power point tracking technique is used.
d Io exp akT 1
(2)
This paper provides a detailed design and analysis of two well known MPPT algorithms such as perturb and observe and
Therefore, IV characteristics of an ideal PV cell can be represented as
I I
qV
power. Additional power harvested from the modules is then
pv Io exp akT 1
(3)
made available as increased battery charge current. MPPT can
Where Io the leakage is current of diode, q is electron charge, K is Boltzmann constant and T is temperature of pn junction (Kelvin)
In practice, the series and parallel equivalent characteristics of PV cell can be represented as
be used in conjunction with a mechanical tracking system, but the two systems are completely different. Figure 3 displays the concept of MPPT. Figure 4 shows the classification of MPPT algorithms.
I I
qV
V Rs I
(4)
pv Io exp akT 1 R
p
Where Rs is series resistance and Rp
is parallel resistance
Vt is thermal resistance of PV cell and Ns is number of cells
connected in series. The thermal resistance of PV cell can be represented as
V Ns kT t q
The current of the PV cell is dependent on solar irradiance and temperature. The relation between the PV current and temperature can be represented as
G
Fig. 3. The concept of MPPT
I pv I pv,n KI T
Gn
(5)
where
I pv,n
is light generated current at nominal operating
condition (25Â°C,1000W/m2),
r is the difference of
temperature (Actual and nominal temperature), G is the
irradiance of the surface and Gn
is the nominal irradiance The
relationship of diode saturation current with temperature can be represented as
T 3 qE 1 1
I I
n exp g
(6)
o o,n T
ak T T
n
The nominal saturation current can be expressed as
Io,n
Isc,n
V
(7)
exp oc,n 1
aVt ,n
The modified nominal saturation current can be represented as
Isc,n KV T
Fig. 4. Classification of different MPPT Techniques
A comparative analysis of different MPPT techniques have
Io,n
V K
(8)
been studied in [512].
exp oc,n I T 1
aVt

MAXIMUM POWER POINT TRACKING Maximum Power Point Tracking, frequently referred to as MPPT, is an electronic system that operates the Photovoltaic

Perturb Observe MPPT
One of the most widely used MPPT is Perturb and Observe (P&O) MPPT because it is true MPPT, independent of PV panel, can be implemented using both analog and digital circuit and the technique doesnt require periodic tuning. The
dP
(PV) modules in a manner that allows the modules to produce all the power they are capable of. MPPT is not a mechanical
main principle of (P&O) MPPT is the checking of
dV
slope.
tracking system that physically moves the modules to make them point more directly at the sun. MPPT is a fully electronic system that varies the electrical operating point of the modules so that the modules are able to deliver maximum available
The slope is positive at the left of MPP and the slope is negative
at the right of MPP [15]. This can be mathematically expressed as
0 dP 0 dV 0
V Vmpp V Vmpp V Vmpp
(9)
Initially the voltage and current of PV module is measured using respective voltage and current sensors and the power is calculated. Change of power and change of voltage is calculated and if the change of power dP 0 and also dV 0 then the duty cycle increases by a fraction of D and for negative slope the duty cycle decreases by a fraction of D . Figure 5 shows the flow chart of perturb and observe MPPT.
Fig. 6. Flow chart of classical incremental conductance MPPT
The efficiency of MPPT technique can be calculated using the following formula
Ppv
P
mppt
mppt
100
(10)
Fig. 5. Flow chart of classical perturbobserve MPPT

Incremental Conductance MPPT
Figure 6 shows the flow chart of incremental conductance MPPT. The Incremental conductance method eliminates the drawbacks of thePerturb and Observe method. It uses the advantage that the derivate of the power with respect to the voltage at the maximum power point is zero. The incremental conductance can determine that the MPPT has reached the MPP and stop perturbing the operating point. If this condition is not met, the direction in which the MPPT operating point must be perturbed can be calculated.


POWER ELECTRONIC INTERFACE FOR PV MODULE Power electronic interface for PV module is illustrated in Figure

PEI comprises of sensors, MPPT algorithms, PWM module, DCDC converter and resistive load.
Fig. 7. Block diagram of PEI for PV based generation
The circuit diagram of DCDC boost converter is shown in Fig.

DCDC boost converter is a nonminimum phase system which means the output voltage to duty cycle transfer function of boost converter has a zero in right half of Splane. This characteristic makes the controller design more complicated.
D
rL L
rC
R
Vdc S
C
400
Power (W)
300
200
100
0
0 20 40 60 80 100 120
Voltage (V)
5
Current (A)
4
3
Fig. 8. Circuit diagram of boost converter
2
The transfer function of boost converter can be represented as 1
L
1 sr C 1 s
0
0 20 40 60 80 100 120
Voltage (V)
v s V c 1 D2 R r
G s o
in l
boost
d s 1 D2
1 s
RrLC R rc L
s2 LCR
Fig. 9. PV and VI plot for PV cell
R r r 1 D2 R r 1 D2 R
c L L TABLE I: SPECIFICATION OF SPR305WHT PM MODULE
Parameters
Variable
Value
Number of cells per module
Nc
96
Number of series connected module
Ns
4
Number of parallel strings
Np
1
Opencircuit voltage
Voc
64.2V
Shortcircuit current
Isc
5.96 A
Maximum Power
Pmp
305W
Series resistance
Rs
0.037998
Parallel resistance
Rp
993.5
Saturation current
Isat
1.1753e8A
Photovoltaic current
Iph
5.9602A
The resonant frequency of the LC circuit of the converter can
1 D
be represented as o
LC
The righthalfzero frequency of the converter can be
represented as
R2 1 D 2
rc rL
RHP
R rc L L
There are different methods to eliminate the RHPZ characteristics. One such method is injected absorbed current method. The transfer function of boost converter using IAC method can be represented as
V 1
2
1 2 L DT
in
1 s
s Ts .
p
V 1 D
G s
1 D R 2
Module type: SunPower SPR305WHT
IAC
1 kW/
m2
0.75 k
W/m2
0.5 k
W/m2
2
0.25 k
W/m
2 T
1 s
1
L s
s2
LC 6
1 D R 2 2
Current (A)
1 D 4


SIMULATION RESULTS
Figure 9 represents the PV curve of the PV module under consideration. Form the Figure it can deduce that power in PV system is increased at certain point with the voltage. After a certain value of V, the power of the PV system started to fall. This paper considers a SPR305WHT PV module. This is manufactured by Sun Power. PV and VI characteristics of SPR305WHT module with varying solar irradiance is shown in Fig. 10. When 66 parallel strings and 5 series module of the said scheme is connected, the VI and PV characteristics of the solar module is shown in Fig. 11. The electrical response of the PV module changes with change in ambient temperature. Fig. 12 shows the PV and VI characteristics of the solar module with varying temperature.
2
0
0 10 20 30 40 50 60 70
Voltage (V)
Power (W)
/m2
0.75
kW/m2
0.5 k
W/m2
0.25
kW/m2
300 1 kW
200
100
0
0 10 20 30 40 50 60 70
Voltage (V)
Fig. 10. PV and VI characterisitics of SPR305WHT module
400
Current (A)
300
200
100
0
Array type: SunPower SPR305WHT; 5 series modules; 66 parallel strings
1 kW/
m2
0.75 k
W/m2
0.5 k
W/m2
0.25 k
W/m2
0 50 100 150 200 250 300 350
Voltage (V)

CONCLUSION
This paper provides a detailed analysis and comparative analysis of two wellknown MPPT algorithms for PV cell. A 300W PV module is considered and a DCmicro grid has been designed. Detailed simulation results have been provided. The electrical voltage of PV cell gets changed due to change in solar irradiance and ambient temperature. The comparative analysis of two MPPT algorithms are shown using simulation.
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