International Journal of Research in Engineering and Applied Sciences
COMPARATIVE ANALYSIS OF THE
PERTURB-AND-OBSERVE AND INCREMENTAL
CONDUCTANCE MPPT METHODS
Pratik U. Mankar1 and 2R.M. Moharil
1
PG student, Department of Electrical Engineering, Y.C.C.E., Nagpur
2
Professor, Department of Electrical Engineering, Y.C.C.E., Nagpur
Email {1pratikmankar90@gmail.com}
Abstract
This paper presents a comparative study between two maximum power point tracking (MPPT) methods in Matlab/Simulink
program that are perturb-and-observe method and incremental conductance method. Starting from the implemented model of
the photovoltaic (PV) array together with MPPT controls have been simulated the PV systems with both MPPT algorithms at
different solar radiation and finally, presents the simulations result depending on irradiance.
Keyword - Photovoltaic systems, maximum power point tracking MPPT), Perturb-and-Observe (P&O), Incremental
Conductance (INC).
1.
Introduction
The ever-increasing demand for low-cost energy and
growing concern about environmental issues has generated
enormous interest in the utilization of nonconventional
energy sources such as the solar energy. The freely and
abundantly available solar energy can be easily converted
into electrical energy using photovoltaic (PV) cells. A PV
source has the advantage of low maintenance cost, absence
of moving/rotating parts, and pollution-free energy
conversion process. However, a major drawback of the PV
source is its ineffectiveness during the nights or low isolation
periods or during partially shaded conditions. High initial
capital cost has been another hurdle in the popularity of PV
systems. These drawbacks notwithstanding, the PV systems
have emerged as one of the most popular alternatives to
conventional energy, thanks to the advancement in
technology and favourable government policies in several
countries. A major challenge in the use of PV is posed by its
nonlinear Current–voltage (I–V) characteristics, which
result in a unique maximum power point (MPP) on its
power–voltage (P–V) curve. The matter is further
complicated due to the dependence of these characteristics
on solar irradiation and temperature. As these parameters
vary continuously, MPP also varies. Considering the high
initial capital cost of a PV source and its low energy
conversion efficiency, it is imperative to operate the PV
source at MPP so that maximum power can be extracted.
Tracking the maximum power point (MPP) of a photovoltaic
(PV) array is usually an essential part of a PV system. As
such, there are at least 19 different algorithms of MPPT
control with different ways on implementation and
performance [1]. The best known MPPT classic algorithms
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are Perturb-and-observe (P&O) and incremental
conductance (Inc. Cond.). These algorithms are based on the
same technology, regulating PV array voltage by adjusting
the optimal set point that represents the voltage at maxim
power point (MPP) many MPP tracking (MPPT) methods
have been developed and implemented. The methods vary in
complexity, sensors required, convergence speed, cost, range
of effectiveness, implementation hardware, popularity, and
in other respects. Several tracking schemes have been
proposed Among the popular tracking schemes are the
perturb and observe (P&O) or hill climbing, incremental
conductance, short circuit current , open-circuit voltage , and
ripple correlation approaches etc. [2]
This paper aims to implement in Matlab/Simulink® the
perturb-and-observe (P&O) and incremental conductance
Algorithms that are published in the literature. This
comparative analysis is designed to determine which of these
two methods are the most suitable for MPPT in order to
establish an optimal algorithm.
2.
MPPT Implementation
The objective of MPPT algorithm is to adjust the current
(Impp) and voltage (Vmpp) of the PV array at which maximum
output power (Pmpp) is obtained under a specific irradiation
and temperature.
As mentioned earlier the P&O and INC are the most popular
techniques for tracking of maximum power. In the next
sections these two methods are explained briefly.
© IJREAS, Vol. 02, Issue 02, July 2014
International Journal of Research in Engineering and Applied Sciences
2.1 Perturb and Observe MPPT Method
The P&O algorithms are widely used in control of MPPT
thanks to their simple structure and reduced number of
necessary measured parameters [6]. The flowchart
implementation of P&O method is given in figure 1.
As the name implies, the concept behind of this method is
based on observation of PV array output power and its
perturbation by changing the current or the voltage of PV
array operation. The algorithm increments or decrements
continuously the reference voltage or current based on the
previous value of power until reaches the MPP. When
dP/dV>0 and the operating voltage of PV array is perturbed
in a specific direction, it known that perturbation moves the
operating point of PV array to the MPP. P&O method will
then continue to perturb the PV voltage in the same direction.
When dP/dV<0, the perturbation moves the operating point
of PV array away from the MPP and the P&O method
reverses the direction of the perturbation. Although this
method can result in oscillation of power output. It is
referred to as a hill climbing method. Because, it depends on
the rise of power against voltage below MPP and above
MPP. [3]
Fig.2 Shows typical P-V curve at 800 W/m2. On the LHS of
the MPP there is linear increase in power with respect to
voltage (dP/dV>0). But on RHS of the MPP there is increase
voltage with decrease in power (dP/dV<0). So, this P&O
algorithm will try to maintain the maximum power point by
perturbing voltage with respective power. At MPP change in
power with respect to change in voltage is zero (dP/dV=0).
Table I shows the direction of perturbation of voltage with
respect to power. Table I shows that with same sign of ΔV
and ΔP results in direction of step size is positive i.e. + C. and
if either sign of ΔV and ΔP results in direction of step size is
negative i.e. – C. [4], [5]. From flowchart shown in Fig.1, dV
and dP is calculated based on the difference between present
values of voltage, power and previous samples of voltage
and power. Based on the sign of dV,dP the perturbation is
approached .Table I xxxShows the sign of perturbation size
(C) changing with respect to the sign of dV and dP. For the
same sign of dV and dP the perturbation of step size is
positive, alternate sign results in negative step size
perturbation.
This algorithm has the drawback that after reaching the
maximum power point its starts deviating on the maximum
power point continuously all the time results in the
substantial amount of power loss at maximum power point.
Although this algorithm is quite simple to implement and it
requires only one voltage sensor so, the cost of
implementation of this algorithm is low [6].
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Fig.1 Flowchart of P&O MPPT Algorithm
Fig.2 Typical P-V curve at 800 W/m2
2.2 Approaches for implementation of Perturb and
Observe algorithmThere are two common approaches for implementing the
P&O algorithm.

Reference voltage perturbation

Direct duty ratio perturbation
© IJREAS, Vol. 02, Issue 02, July 2014
International Journal of Research in Engineering and Applied Sciences
Table 1
Truth Table of the Conventional P&O MPPT Method
Sign of ΔV
Sign of ΔP
dI -I
left of MPP

dV V
dI -I
At MPP
=
dV V
Direction of next
step
+
+
+C
-
-
+C
-
+
-C
+
-
-C
(3)
This method based on the whether the array voltage is
greater than or less than peak power point voltage. Equation
(10) shows that maximum power point can be tracked by
comparing the instantaneous conductance to the incremental
conductance. Incremental conductance method overcomes
the drawback of Perturb and Observe method by using PV
arrays incremental conductance to compute the sign of
 dP dV  without perturbation. This helps to determine the
In direct duty ratio perturbation, the duty ratio of the MPPT
converter is used directly as the control parameter. the duty
ratio is perturbed directly eliminating the need for a PI
controller which in turn reduces the complexity and
enhances the stability of the system. This method also offers
better energy utilization and better stability characteristics at
a slower transient response and worse performance at rapidly
changing irradiance [7].
In this paper P&O algorithm is implemented with Reference
voltage perturbation. The algorithm is programmed in
Matlab/Simulink.
2.2 Incremental Conductance MPPT Algorithm
The incremental conductance method is based on the fact
that the slope of the PV array power curve is zero at the MPP,
positive on the left of the MPP, and negative on the right as
given by,
dP
 0 left of MPP
dV
dP
(1)
 0 right of MPP
dV
dP
 0 At MPP
dV
dP d  IV 
dI
dI

=I+V
 I+V
dV
dV
dV
dV
Equation (1) can be rewritten as,
Since,
(2)
dI -I
right of MPP

dV V
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Maximum power point technique has reached the maximum
power point and stop perturbing the operating point.
Although this method has the drawback is that it increases
the complexity compared to Perturb & Observe method,
requires more time for computation [8].
Fig.3 showing a typical PV curves with relationship between
instantaneous conductance and incremental conductance.
Equation (10) showing that at maximum power point both
instantaneous and incremental conductance has same value.
Thus maximum power point can be tracked. This method has
the advantage over the Perturb & Observe of not oscillating
around the maximum power point under rapidly varying
environmental conditions [9].
200
180
160
140
P `o w e r in w a tt
In Reference voltage perturbation, the PV array output
voltage reference is used as the control parameter in
conjunction with a controller (usually a PI controller) to
adjust the duty ratio of the MPPT power converter. The PI
controller gains are tuned while operating the system at a
constant voltage equal to the standard test condition (STC)
value of the MPP voltage. These gains are kept constant
while the reference voltage is controlled by the MPPT
algorithm.
120
100
80
60
40
20
0
0
5
10
15
20
25
30
35
Voltage in volt
Fig.3 Conductance showing Typical P-V curve
The disadvantage of the Perturb and observe method to track
the peak power under fast varying atmospheric condition is
overcome by INC method. The INC 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 using the relationship between dl/dV and –I/V
.This relationship is derived from the fact that dP/dV is
negative when the MPPT is to the right of the MPP and
positive when it is to the left of the MPP. This algorithm has
advantages over P&O in that it can determine when the
© IJREAS, Vol. 02, Issue 02, July 2014
International Journal of Research in Engineering and Applied Sciences
MPPT has reached the MPP, where P&O oscillates around
the MPP. Also, incremental conductance can track rapidly
increasing and decreasing irradiance conditions with higher
accuracy than perturb and observe. One disadvantage of this
algorithm is the increased complexity when compared to
P&O [10].
Fig.5 Basic circuit diagram of MPPT method
MPPT algorithm would be Perturb & Observe and
Incremental conductance. Thus, by executing the Perturb &
Observe and Incremental Conductance in Matlab/M-files
under the different irradiation and keeping the PV panel
temperature constant and obtained the output power.
4.
Fig.4 Flowchart of Incremental Conductance algorithm
Fig.4 showing the flowchart of Incremental conductance, in
which incremental conductance is compared with
instantaneous conductance and thus maximum power point
is tracked. Increment size determines the how fast maximum
power point is tracked. Fast tracking can be achieved with
bigger increments but the system might not operate exactly
at the maximum power point and oscillate about instead.
This method has complex circuitry; accuracy of the method
depends on the iteration size, which is usually fixed for the
conventional incremental conductance method [11].
3.
System under Study
The basic circuit diagram shown in Fig. 5 represents the
overall working of the MPPT method. It contains the current
source which represents the photocurrent (Ip) i.e. the value of
current when solar radiation falls on the panel and current
flowing through the diode i.e. (Id) which represents the diode
saturation current. It is the value of the current when solar
radiation absent on the solar panel. Fig. also shows the load
current value is kept at zero value. the output current flowing
through the panel (I) and output voltage across the panel (Voc)
is given as feedback signal to the MPPT algorithm.
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Results and Discussions
For the comparative analysis datasheet of KC200 GHT Solar
Panel is considered shown in Table 2. In which 54 cells are
connected in series. This section represents variation in
irradiation will be done for particular range of iteration and
thus tracking of power will be achieved. For the comparative
analysis, three tests will be carried out. The first three test
will be carried out for step size of (C=0.3 V) and later on,
another three test will be carried out for step size of (C=0.5
V)). It is assumed that the cell temperature remains
constant at T=300 K throughout the program. In the first
test, The solar irradiation will start at a relative low level at
200 W/m2 for first 50 iterations and then rises to 300 W/m2
over 51 to 100 iterations. In the second test, The solar
irradiation will start at a Relative low level at 200 W/m2 for
first 50 iterations and then rises to 600 W/m2 over 51 to 100
iterations. In the third test, a fluctuated solar irradiation is
applied in which each radiation level will last for less
iteration over a complete 100 iterations.
Fig.6 shows the result of test 1, in which P&O and INC
output power plotted w.r.t iterations. It is clear that, the
output power is almost same around 70 iterations of both the
method. But later on there is slight increase in power output
of P&O compared to INC for step size, C=0.3 V shown in
table 3. Fig.6 also shows that after 70th iterations the power
output of INC slightly gets fluctuated and gives less output at
the end of 100 iterations.
In the second test irradiation varies 200 to 600 W/m2. From
table 4, it clearly shows that for first 50 iterations power
tracked by both the method is same i.e. for 200 W/m2. On
51th iterations irradiation changes to 600 W/m2, during this
irradiation level same power tracked by INC method is
quicker slightly as compared with P&O method.
© IJREAS, Vol. 02, Issue 02, July 2014
International Journal of Research in Engineering and Applied Sciences
Table 2
Parameters of KC200GHT-2 Solar Panel
Constraints
Icon
Maximum Power
[W]
Tolerance
Maximum Power Voltage[V]
Maximum Power Current[A]
Open Circuit Voltage[V]
Short Circuit Current [A]
Temperature coefficient of
[V/˚C]
Temperature coefficient of
[A/˚C]
NOCT
[˚C]
%
Table 4
Showing output corresponding to irradiation
Structured
Values
200
+10/-5
26.3
7.61
32.9
8.21
1.23×10
Iterations
(i)
1-50
51-100
Irradiation
(W/m2)
200
600
MPP At
Iteration
Output Power
(W)
P&O
INC
P&O
INC
50
89
50
87
25.15
122.97
25.15
122.97
3.18×10
-
47
Test 1- Varying irradiation from 200 to 300 W/m2 over 100
iterations
Table 3
Showing output corresponding to irradiation
Iterations
(i)
1-50
51-100
Irradiation
(W/m2)
200
300
MPP At
Iteration
P&O INC
Output Power
(W)
P&O INC
50
87
25.17
59.34
50
84
Fig. 7 Power Vs Iterations
Test 3- Varying different irradiation over 100 iterations
25.15
57.54
Table 5
Showing output corresponding to irradiation
Iteration
s (i)
1-20
21-40
41-55
56-75
76-88
89-100
Irradiat
ion
(W/m2)
800
500
300
400
600
700
MPP At
Iteration
Output Power
(W)
P&O
INC
P&O
INC
20
40
55
61
79
95
20
40
53
57
78
92
41.41
48.08
38.44
70.09
120.44
145.63
41.41
48.08
38.44
70.09
120.44
145.63
Fig. 6 Power Vs Iterations
Test 2- Varying irradiation from 200 to 600 W/m2 over 100
iterations
Fig.7 shows the graph between powers tracked by the both
MPPT method and Iterations. From graph, it clearly
indicates that power tracked by P&O and INC is same. Due
to which curve of both the methods overlapped with each
other. But iterations required is slightly lesser by the INC
method compared to P&O method.
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Table 5 shows the power tracked by the both methods for
various irradiations level, from table it clearly shows that at
various irradiation level power tracked by both methods is
same but iterations required at each level of irradiation is less
of INC method as compared to P&O method.
Fig.8 shows the graph Power Vs Iterations, it clearly
indicates that power tracked of both the method is same,
curves of the both methods is exactly same. Hence curves
overlapped each other.
© IJREAS, Vol. 02, Issue 02, July 2014
International Journal of Research in Engineering and Applied Sciences
iterations
Table 7
Showing output corresponding to irradiation
Iterations
(i)
1-50
51-100
Fig. 8 Power Vs Iterations
From test 2 and 3,it is clear that the power output
performance of P&O and INC MPPT method is exactly the
same for step size, C=0.3 V.
Now, again three test will be carried out for Step size, C=0.5
V. In the first test, The solar irradiation will start at a
relative low level at 200 W/m2 for first 50 iterations and then
rises to 300 W/m2 over 51 to 100 iterations. In the second test,
The solar irradiation will start at a Relative low level at 200
W/m2 for first 50 iterations and then rises to 600 W/m2 over
51 to 100 iterations. In the third test, a fluctuated solar
irradiation is applied in which each radiation level will last
for less iteration over a complete 100 iterations.
From test 1 and 2 it can be seen that output power
performance of both the MPPT method is same. But, there is
slight curve after irradiation changes on 50th iterations
onwards of P&O method shown in Fig.9.
Test 1- Varying irradiation from 200 to 300 W/m2 over 100
iterations
Table 6
Showing output corresponding to irradiation
Iterations
(i)
1-50
51-100
Irradiation
(W/m2)
200
300
MPP At
Iteration
Output Power
(W)
P&O
INC
P&O
INC
50
57
50
54
36.92
57.64
36.90
57.64
Irradiation
(W/m2)
200
600
MPP At
Iteration
Output Power
(W)
P&O
INC
P&O
INC
48
59
47
57
36.92
123.00
36.94
123.00
Fig. 10 Power Vs Iterations
From table 6 and 7 clearly shows the for tracking the same
power INC method requires less iterations comparatively to
the P&O method. Fig.10 shows output power comparison for
irradiation changes from 200 to 600 W/m2 for step size of
C=0.5 V. it can be seen that, irradiation changes after 50th,
that results in continuous deviation in output power. Because,
the incremental (dI/dV) and instantaneous conductance (-I/V)
continuously more or less to each other. i.e. (dI/dV) > (-I/V)
or (dI/dV) < (-I/V). That results in continuous variation in
output power.
Fig.10 also shows the output power of P&O method. This
method also results in power variation after 50th iteration due
to the continuous change in voltage (dV) and change in
power (dP) less than or greater than zero.
Test 3- Varying different irradiation over 100 iterations
Test 3 shows the rapid variation in irradiation, results
dynamic variation of output power w.r.t iterations. From
Fig.11 it is clear that, due to less iteration for each irradiation
results in initial power w.r.t irradiation doesn’t reach to
maximum power. i.e. not reaches to saturated value. In
between 56-75 iterations the radiation level is 400 W/m2.
During this period of iterations, the output power of
incremental conductance is continuously fluctuated due to
the, the incremental (dI/dV) and instantaneous conductance
(-I/V) continuously more or less to each other. i.e. (dI/dV) >
(-I/V) or (dI/dV) < (-I/V).That results in continuous variation
in output power. 76th iterations onwards there is stable power
output of both the method w.r.t. irradiation.
Fig. 9 Power Vs Iterations
Test 2- Varying irradiation from 200 to 600 W/m2 over 100
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© IJREAS, Vol. 02, Issue 02, July 2014
International Journal of Research in Engineering and Applied Sciences
Table 8
Showing output corresponding to irradiation
Iterations
(i)
1-20
21-40
41-55
56-75
76-88
89-100
Irradiation
(W/m2)
800
500
300
400
600
700
MPP At
Iteration
Output Power
(Watt)
P&O
INC
P&O
INC
20
40
54
60
79
94
20
40
53
56
78
92
69.02
79.99
57.64
78.99
123.0
145.1
69.02
79.77
57.64
78.99
123.0
145.6
Fig. 11 Power Vs Iterations
5.
Conclusion
In this study, the comparative analysis is made between P&O
and INC. In the initial three tests step size (C=0.3 V) is kept
at small value. That results in the less power during initial
iterations w.r.t. irradiation. But later on gives the rated
maximum power. But due to small step size the power
tracked by the both the method in initial iterations is small
compared to step size (C=0.5 V). From table 3 to 8 it is clear
that the iterations required by the INC MPPT method is less
compared to P&O method. From that we can concluded that,
the tracking speed of INC method is faster compared to P&O
method. From different tests, it is clear that for different
irradiations, the output power level of the both method i.e.
P&O and INC w.r.t. irradiation is almost same. Although the
both the method have different way to track the maximum
power.
References
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Biographies
R. M. Moharil: born on 06th Oct. 1966 at Nagpur,
India. He has completed his B.E. (Electrical)
engineering in 1989, M.Tech. (integrated power
System) in 1998 and Ph.D. degree in 2009 on the
topic, “Design and Reliability Analysis of Solar
Photovoltaic and Wind Energy Generation
Systems”. He has published 9 papers in
international Journals, 7 National Journals, 25
International Conferences and 15 National
Conferences. Presently he is working as Professor
and Head of Department of Electrical Engineering
in Yeshwantrao Chavan College of Engg., Nagpur.
Pratik U. Mankar: born on 29th July 1990 at
Nagpur, India. He has completed his B.E.
(Electrical) engineering in 2012 and currently
pursuing M.Tech. (Integrated Power System) in
Yeshwantrao Chavan College of Engg., Nagpur.
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© IJREAS, Vol. 02, Issue 02, July 2014