1. technology and computing

National Conference on Recent Trends in Engineering & Technology
Overview of various methods for MPPT of a pv cell
and implementation of incremental conductance
method
J. B. Borad#1, A. R. Patel*2
#1
Electrical Dept. ,#1Gujrat Technological University
B.V.M. College, V .V. Nagar India
[email protected]
*2
Asst. Prof. Electrical Dept.,
B.V.M. College, V. V. Nagar India
[email protected]
Abstract—Due to the limitations in the energy available from
conventional sources, worldwide attentation is being focused on
renewable sources of energy. Especially, the energy obtained
from solar arrays and the fuel cells, becomes more and more
important. Solar power plant became a peak research topic in
India as well as over seas. Basic parts of a solar power plant are
PV cell series, Dc-to-Dc converter and grid connection (to load).
How to achieve high step-up and high efficiency DC/DC
converters is the major consideration in the renewable power
applications due to the low voltage of PV arrays and fuel cells.
Paper is all about various method of MPPT of a PV cell. And
implementation of incremental conductance method for close
boost converter for solar installation. Circuit models for close
loop systems are developed using the blocks of simulink in PSIM.
The simulation results are compared with the theoretical results.
This paper represents that by using incremental conductance
method maximum power is obtained in any condition.
parts. The power produced by solar panel depends on two factors
which are irradiation and temperature. As irradiation and temperature
level changes rapidly, the voltage produced fluctuates and becomes
inconstant. Fig. 1 shows the block diagram of solar system for PV
grid connected.
Keywords— Boost converter, solar panel, photovoltaic cell,
Modelling and control
II. MPPT OF A SOLAR ENERGY
I. INTRODUCTION
Using renewable energy is no longer only recommended from the
environmental point of view to tackle climate change and air
pollution but also from economic point of view, because renewable
energy is becoming huge business on global scale as the global clean
energy race is on. There are also several other reasons why
developing countries should focus on renewable energy as one of the
best available energy options. For instance, developing countries
could especially use renewable energy in distant, rural areas because
in these areas producing renewable energy locally is economically
more viable energy option compared to generating energy from fossil
fuels (because of high transmission and distribution costs).
Photovoltaic (PV) sources are used today in many applications such
as satellite power systems, battery charging, home appliances and
many more. PV is becoming more famous in the world of power
generation because they have the advantages of free pollution, low
maintenance, and no noise and wear due to the absence of moving
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Fig 1: Block diagram of solar system for PV grid connected [Ref 2]
The output characteristics of photovoltaic arrays are
nonlinear and change with the cell‘s temperature and solar irradiance.
For a given conditions there is a unique point in which the array
produces maximum output power. This point is called maximum
power point (MPP) which varies depending of cell temperature and
present irradiation level. To obtain the maximum power from a
photovoltaic array, a maximum power point tracker (MPPT) is used.
The Perturbation and observation is one of the most commonly used
MPPT methods for its simplicity and ease of implementation. The
P&O works well when the irradiance change slowly but it presents
drawbacks such as slow response speed, oscillation around the MPP
in steady state, and even tracking in wrong way under rapidly
changing atmospheric conditions.
There are various methods for obtaining maximum power
tracking for pv cell discussed as below:
1) PERTURB AND OBSERVE METHOD
The P&O method is based on an adaptive algorithm which
automatically adjusts the reference voltage step size to achieve
B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology
dynamic response and search MPP under rapidly changing conditions
by exploiting networks capabilities.
The perturb and observe (P&O) best operation conditions
are investigated in order to identify the edge efficiency performances
of this most popular maximum power point tracking (MPPT)
technique for photovoltaic (PV) applications. P&O may guarantee
top-level efficiency, provided that a proper predictive (by means of a
parabolic interpolation of the last three operating points) and adaptive
(based on the measure of the actual power) hill climbing strategy is
adopted. The characteristic slop during a perturbation cycle provide
the best information concerning how much the operating point is far
from the MPP in steady state, but when a variation occur suddenly ,
this information will alter the behaviour of the algorithm and cause it
divergence by moving the operating point far from the MPPT. This
problem can be solved if the algorithm acquires a skill which allows
the detection of the working conditions variations and its extents
also.
It is well known that any atmospheric condition variation
induce a proportional PV array output power variation.
connected in parallel with the individual solar cells, connecting the
cells in parallel will increase the effective capacitance seen by the
MPPT. From this, the difference in MPPT efficiency between the
parasitic capacitance and incremental conductance algorithms should
be at a maximum in a high-power solar array with many parallel
modules.
3 ) VOLTAGE BASED PEAK POWER TRACKING METHOD
The basis for the constant voltage (CV) algorithm is the
observation from I–V curves that the ratio of the array‘s maximum
power voltage as shown in fig. 2, VMPP, to its open-circuit voltage,
VOC, is approximately constant.
Fig 2: Constant voltage algorithm
2) PARASITIC CAPACITANCE METHOD
The parasitic capacitance algorithm is similar to
incremental conductance, except that the effect of the solar cells‘
parasitic junction capacitance CP, which models charge storage in
the p–n junctions of the solar cells, is included. By adding this
capacitance to the lighted diode equation, Equation, and representing
the capacitance using
 dV 
i (t )  C 

 dt 
Equation is obtained.
 dV p
I  I L  I O exp Vp  RsI  / a  1  C P 
 dt
I  F (V p )  C P  C P



dV p
dt
On the far right of Equation, the equation is rewritten to show the
two components of I, a function of voltage F(V P) and the current in
the parasitic capacitance. Using this notation, the incremental
conductance of the array gp can be defined as dF(Vp)/dVp and the
instantaneous conductance of the array, gL can be defined as –F(Vp)
=Vp. The MPP is located at the point where dP/dVp= 0. Multiplying
Equation by the array voltage Vp to obtain array power and
differentiating the result, the equation for the array power at the MPP
is obtained.
 dF (V p ) 
 dV d 2V  F VP 

 

C

0


P
dV
V
V
V


P
P


The three terms in Equation represent the instantaneous
conductance, the incremental conductance, and the induced ripple
from the parasitic capacitance. The first and second derivatives of the
array voltage take into account the AC ripple components generated
by the converter. The reader will note that if CP is equal to zero, this
equation simplifies to that used for the incremental conductance
algorithm. Since the parasitic capacitance is modelled as a capacitor
13-14 May 2011
In other words:
VMPP
1
VOC
The constant voltage algorithm can be implemented using the
flowchart shown in Figure The solar array is temporarily isolated
from the MPPT, and a VOC measurement is taken. Next, the MPPT
calculates the correct operating point using Equation and the preset
value of K, and adjusts the array‘s voltage until the calculated VMPP
is reached. This operation is repeated periodically to track the
position of the MPP. Constant voltage control can be easily
implemented with analog hardware.
However, its MPPT tracking efficiency is low relative to
those of other algorithms. Reasons for this include the
aforementioned error in the value of K, and the fact that measuring
the open-circuit voltage requires a momentary interruption of PV
power. It is possible to dynamically adjust the value of K, but that
requires a search algorithm and essentially ends up being the same as
P&O.
4) INCREMENTAL CONDUCTANCE METHOD
The incremental conductance method consists in using the
slope of the derivative of the current with respect to the voltage in
order to reach the maximum power point. To obtain this point, dV/ dI
must be equal to –I/V as shown in Figure [5] & [7].
For any solar panel, the output power is function of the
temperature and the sunshine values of the site where the panel is
placed. This power can decrease or increase as result of any
temperature and/or shining variations.
In Solar panels, output power is not constant. To maximize
this power and maintain it constant at high values, it is necessary to
define the Maximum Power Point Tracking (MPPT) methods, and
apply these methods to controlled dc-dc converters (choppers).
Now, let see the incremental conductance & solar panel modulation
Modelling of a solar panel In the obscurity, a semiconductor presents
a high resistance. When it is strongly illuminated, its resistance
decreases. If the energy of the photons that constitutes the luminous
ray is sufficient, these photons will be able to excite the electrons
blocked in the valence layer to jump to the conduction layer. It is the
phenomenon of photo conductibility. The expression of the diode
current is described by the following equation:
B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology

 eV  
I P  I CC  I d  I CC  I S  Exp  P   1
 kT  

with:

Ip and Vp are the current and voltage of this photovoltaic
cell,

Is is the saturation current,

ICC and Id are the short-circuit and the direct currents,

k is the Boltzmann constant (equal to 8,62.10- 5eV/°K),

T is the absolute temperature,

e is the electron charge
This equation corresponds to a current generator, which models the
sunshine, and a diode in parallel, which represents the PN junction.
The equivalent circuit of the ideal photovoltaic is given in figure.
Figure 4 Flow Chart of Incremental conductance method [6]
Figure 3: Ideal photovoltaic [5]
To draw the real model of photovoltaic cell shown in fig. 3,
it is necessary to take in account the losses due to the manufacture.
Therefore, two resistances should be added to the ideal model, one
placed in series and the other in parallel. In fact, the resistance Rs
represents the losses dues to the contacts and the connections. The
parallel resistance Rsh represents the leakage currents in the diode.
The characteristic equation becomes then:
V 
I P  I CC  I d  

 Rsh 
In fact, applying a variation on the voltage toward the
biggest or the smallest value, its influence appears on the power
value. If the power increases, one continues varying the voltage in
the same direction, if not, one continues in the inverse direction. The
simplified flow chart of this method is discussed in chapter 1. In
addition, by using the power formula P=V.I, its derivative by
dP = V dI + I.dV
The duty cycle (αn) of the used chopper (dc-dc converter)
is calculated by the following expression,
αn = αn−1 ± ∆α
Where ∆α is the duty cycle step
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The parasitic capacitance algorithm is similar to
incremental conductance shown in fig. 4, except that the effect of the
solar cells‘ parasitic junction capacitance CP, which models charge
storage in the p–n junctions of the solar cells, is included. By adding
this capacitance to the lighted diode equation, Equation, and
representing the capacitance using
 dV 
i (t )  C 

 dt 
On the far right of Equation, the equation is rewritten to show the
two components of I, a function of voltage F(V P) and the current in
the parasitic capacitance. Using this notation, the incremental
conductance of the array gp can be defined as dF(Vp)/dVp and the
instantaneous conductance of the array, gL can be defined as –F(Vp)
=Vp. The MPP is located at the point where dP/dVp= 0. Multiplying
Equation by the array voltage Vp to obtain array power and
differentiating the result, the equation for the array power at the MPP
is obtained.
 dF (VP ) 
 dV d 2V  F (VP )



C

0
P


V 
VP
V
 dVP 
The three terms in Equation represent the instantaneous
conductance, the incremental conductance, and the induced ripple
from the parasitic capacitance. The first and second derivatives of the
array voltage take into account the AC ripple components generated
by the converter. The reader will note that if CP is equal to zero, this
equation simplifies to that used for the incremental conductance
algorithm. Since the parasitic capacitance is modelled as a capacitor
connected in parallel with the individual solar cells, connecting the
cells in parallel will increase the effective capacitance seen by the
MPPT. From this, the difference in MPPT efficiency between the
parasitic capacitance and incremental conductance algorithms should
be at a maximum in a high-power solar array with many parallel
modules.
B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology
III. BOOST CONVERTER ANALYSIS
III. CHARACTERISTIC OF SOLAR ARRAY
Solar cell consists of semiconductor materials which is able to
convert solar irradiation into DC current using PV effect. The
characteristic equation for solar panel is given by
 
  
q
IRs 
  1  V 
I  I lg  Ios exp 
Rsh 
  AkT V  IRs    
where Ilg is the light generated current, IOS is the reverse saturation
current, q is the electronic charge, A is dimensionless factor, k is
Boltzmann constant, T is the temperature in K, Rs is series resistance
of the cell, and Rsh is the shunt resistance of the cell. The variation of
the output I-V characteristic of a solar panel is shown in Figure 2.
The maximum power point is located at the knee of the I-V output
characteristic. Figure 3 shows a typical output characteristic of a solar
panel under different temperature and irradiation level.
A simple boost converter consists of an inductor, a switch, a diode,
and a capacitor as shown in Figure. Boost converter circuit can be
divided into two modes. Mode 1 begins when the switch SW is
turned on at t = Ton as shown in Figure 5. The input current which
rises flows through inductor L and Switch SW. During this mode,
energy is stored in the inductor. Mode 2 begins when the switch is
turned off at t= Toff. The current that was flowing through the switch
would now flow through inductor L, diode D, capacitor C, and load
Energy stored in the inductor is then transferred to the load.
Therefore, the output voltage is greater than the input voltage and is
expressed as
1
Vout  [
]Vin
1 k
Where Vout is the output voltage, k is duty cycle, and Vin is input
voltage which in this case will be the solar panel voltage.
Fig 5: Typical solar panel I-V and P-V Characteristic
Fig 7: Circuit diagram of Boost-Converter during Ton
Fig 6: Typical output characteristic of solar panel based on insulation and
temperature changes
Fig 8: Circuit diagram of boost converter during Toff
Fig 9: Circuit diagram of open loop boost converter
13-14 May 2011
B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology
[1  k ]^ 2  k  R 
L min  

2 f


In order to operate the converter in continuous conduction
mode (CCM), the inductance is calculated such that the
inductor current IL flows continuously and never falls to
zero.
Fig 11: Waveform for discontinuous conduction mode
Where Lmin is the minimum inductance, k is duty cycle,
R is output resistance, and f is the switching frequency of
switch SW.
The output capacitance to give the desired output voltage
ripple is given by
k
------------------- (4)
C min 
f  R  Vr
Where Cmin is the minimum capacitance, k is
duty cycle, R is output resistance, f is switching frequency
of switch SW, and Vr is output voltage ripple factor. Vr can
be expressed as
Vr 
Vout
Vout
----------------- (5)
IV. Control Approach
Fig 10: Waveform during continuous conduction mode
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In this paper, the incremental conductance method is
treated [5]. This method consists in using the slope of the
derivative of the current with respect to the voltage in order
to reach the maximum power point. To obtain this point,
dI/ dV must be equal to –I/V. In fact, applying a variation
on the voltage toward the biggest or the smallest value, its
influence appears on the power value. If the power
increases, one continues varying the voltage in the same
direction, if not, one continues in the inverse direction. The
simplified flow chart of this method is given in figure 4.
B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology
Fig 13: Circuit diagram of close loop boost converter
V. SIMULATION RESULT
The studied system is shown in figure 10. With the
‗Incremental conductance‘ method, which is already
explained in the previous section, the curve of the output
power versus time is illustrated in figure. This figure shows
that the power value remains approximately constant, with
small ripples. Also, the time response is not negligible.
any disturbance at the input of solar panel. This converter has
advantages like reduced hardware and good output voltage
regulation as compare to other step-up converter.
VII. ACKNOWLEDGEMENTS
I take this opportunity to express my sincere thanks and heartful
gratitude to my project supervisor Asst. Prof. A. R. Patel, my
friend Asst. Prof. N. H. Adroja. It was their repeated
encouragement, supervision, and invaluable guidance that helped
me in completing this project. I am deeply indebted to him for
giving clarity of vision and thought which enabled me to complete
the paper.
I am deeply grateful to my husband, Jatin, for his
patience, understanding, and for being a constant source of
motivation throughout.
VIII. REFERENCES
[1] A & V. Olgyay, ‗‗Solar control and shading devices‘‘ Book,
Princeton (1976).
[2] V. Salas, E. Olias, A. Barrado & A. Lazaro, ‗‗Review of the
Fig 14: Power waveform by using incremental conductance MPPT
method
[3]
VI. CONCLUSION
[4]
It became apparent that all tests conducted have shown that the
Boost converter produced more power than the standard system
without the technology. Boost converter with incremental
conductance method able to transform unusable power into usable
power, which itself is a significant capability improvement to the
current technology as compare to previous technology. PSIM
models for open loop system of boost converter and close loop
boost converter are developed using the blocks of simulink and
the same are used for simulation studies. The open loop system is
not able to maintain the constant voltage. But using closed loop,
boost converter provides constant voltage without affecting by
13-14 May 2011
[5]
[6]
maximum power point tracking algorithms for stand-alone
photovoltaic systems‘‘, Elsevier, 2005.
Seoul, A stand alone photovoltaic (AC) scheme for village
electricity A.M.Sharaf', SM IEEE, A.R.N.M. Reaz UI Haque,
Jan. 2005, ISSN: 0160-8371, ISBN: 0-7803-8707-4
D. P. Hohm and M. E. Ropp, 2003. ―Comparative study of
maximum power point tracking algorithms,‖ in Prog.
Photovolt: Res. Appl. 2003, pp. 47-62. 10).
J. Kouta, A. El-Ali, N. Moubayed and R. Outbib, ―Improving
the incremental Conductance control method of a solar energy
conversion system‖, Department of Electrical Engineering Lebanese University, IEEE-2005.
European Journal of Scientific Research ―Development of
microcontroller based boost converter for photovoltaic system‖
ISSN 1450-216X Vol.41 NO. 1 (2010)
[7] http://www.renewables-info.com
[8] http://www.soton.ac.uk/~solar/intro/tech0.htm
[9] http://en.wikipedia.org/wiki/File:Fuel_Cell_Block_Diag
ram.svg
B.V.M. Engineering College, V.V.Nagar,Gujarat,India