MPPT

1. ECAI 2016 - International Conference – 8th Edition
Electronics, Computers and Artificial Intelligence
30 June -02 July, 2016, Ploiesti, ROMÂNIA
Maximum Power Point Tracking Quadratic
Boost Converter for Photovoltaic Systems
Necmi Altin, Ertan Ozturk
Department of Electrical & Electronics Engineering, Faculty of Technology
Gazi University
Ankara, Turkey
naltin@gazi.edu.tr, erozturk@gazi.edu.tr
Abstract – Providing maximum utilization of the
photovoltaic system is one of the significant challenges.
Therefore, converter technologies and maximum power
point tracking algorithms are important research topics.
In this study, a quadratic boost converter with high
conversion ratio is proposed. The proposed quadratic
converter not only steps up the PV voltage which is
commonly low, it also tracks the maximum power point of
the PV system under varying operation conditions. The
incremental conductance method is used as maximum
power point tracking algorithm. Thus, productivity of the
PV system is increased. It is seen from simulation results
that, proposed system has fast tracking capability even
under fast irradiation changes and less oscillation besides
the features of high voltage conversion gain.
Keywords – Quadratic Boost Converter; MPPT;
Incremental Conductance; PV
I. INTRODUCTION
Increasing world power demand, depletion of
fossil fuels and increasing awareness on green word
concept make renewable energy resources (RESs)
popular, and therefore number of researches on RESs
has been exponentially increased in last two decades.
However, stochastic natures of RESs and variable
power generation characteristics of these source makes
power converter topologies important. Several DC-
DC, AC-DC and DC-AC converter topologies have
been proposed for renewable energy systems [1].
Output voltage of the photovoltaic (PV) modules
which are one of the most promising green energy
sources varies with load level and natural conditions
such as ambient temperature and solar irradiation.
Same condition is also valid for fuel cells (FCs).
Therefore, PV systems and FC systems require a DC-
DC converter for regulating their output voltage. The
output voltage of the PV module and the FC stack are
usually low and require to step-up. The conventional
boost converters are commonly used to regulate and
step-up the PV or the FC supplied DC voltage.
However, step-up ability of the conventional DC-DC
converter is related with the duty ratio, and to obtain
high step-up ability, high duty ratios are required.
Therefore, the practical voltage conversion gain of the
conventional boost converter is limited [2-3]. Hence,
different topologies have been investigated to obtain
high step-up ability [3-5]. Initial studies have
considered the cascaded connection of conventional
DC-DC converters. However, number of the power
processing stages and power switches are equal to
number of cascaded converters and this increases the
power losses and decreases the efficiency [6-7].
Recently, different DC-DC converter topologies
with high voltage step-up ability have been proposed
including conventional boost converter combined with
switched capacitors [8], voltage multipliers and
coupled inductors [9-10]. The quadratic boost
converter (QBC) which is structurally similar to
cascaded two boost converters has been proposed to
provide high voltage conversion ratio. The QBC
converter circuit is given in Figure 1. The output
voltage of the QBC is given as a quadratic function of
the duty cycle of switching signal [11]. The QBC has
only one active switch, driver circuit requirement is
removed and converter efficiency is improved.
Therefore, the QBC is used in several applications
where high voltage conversion ratio is required such as
power factor correction applications and PV
applications [12-13].
One of the important application of DC-DC
converter in PV systems is regulating output voltage
and power level to get maximum available power from
PV modules. This action is called maximum power
point tracking (MPPT). There is a nonlinear relation
between the PV voltage and the PV current. Because
of this nonlinear characteristic, there is a single point
on the P-V curve of a PV module that the PV module
power gets its maximum value. This operation point is
called as Maximum Power Point (MPP) [14]. The
MPP of the PV module changes with load level and
environmental conditions such as irradiation and
temperature, and therefore it should be tracked during
the operation to obtain maximum power and
maximum energy conversion efficiency for any
operation conditions. Several methods have been
proposed to track the MPP of the PV system. These
methods can be analysis in two groups: directs
methods and indirect methods. Indirect methods are
usually easy to implement and provide fast response,
but since the PV parameters such as voltage, current or
solar irradiance are not measured online, the real
maximum power point cannot be tracked. Direct
methods are generally computational based methods,
and they try to compute the real MPP in each control
cycle. These methods can track the real MPPT but
they may cause an oscillation on output power. The
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2. Necmi ALTIN, Ertan OZTURK
pilot cell, the constant voltage, the constant current,
the look-up table can be refereed as indirect methods,
and the perturb and observe (P&O), the incremental
conductance (IC), the fuzzy logic, the neural network
based methods are common and well-known direct
MPPT methods [15-18]. Among them, the IC method
has some advantages such as being a direct control
method, it can adjust fast changing atmospheric
conditions and there is less oscillation around MPP
than the other direct methods [17-18].
In this study, a QBC with MPPT capability for PV
systems is proposed. The low voltage generated by the
PV system is step-up with a QBC which has high
voltage conversion ratio, and required voltage level for
inverters or other DC applications is obtained. In
addition, the MPP of PV system is tracked with IC
based MPPT method, and maximum energy is
extracted from PV system in any operation conditions.
The results obtained from MATLAB/Simulink
simulations show that, proposed system has quadratic
voltage conversion ratio and tracks the MPP of the PV
system for different operation conditions.
Figure 1. The QBC circuit
II. MODELLING OF THE QBC
The QBC shown in Figure 1 has only one active
switch and analysis of the converter is performed
according to switch condition. When the switch is ON,
D2 diode is forward biases and D1 and D3 diodes are
reverse biased. L1 and L2 are charged by supply
voltage and C1 capacitor, respectively. When the
switch is OFF, D2 diode is reverse biased, and D1 and
D3 diodes are forward biased. C1 and C2 capacitors are
charged by the supply voltage and inductors (L1 and
L2). These operation conditions are shown in Figure 2.
By assuming that all components are ideal and
supply voltage is constant DC voltage, equations given
below can be written:
0)(
0
11 dttvV
ST
LL (1)
0)(
0
22 dttvV
ST
LL (2)
here, TS is switching period. By using (1) and (2)
expressions for each component voltage and current
can be derived as given below:
D
V
V in
C
1
1 (3)
(a)
(b)
Figure 2. The quadratic boost converter a) When switch is ON; b)
When switch is OFF
D
V
V in
C
1
1 (3)
220
1 D
V
VV in
C (4)
41
1 DR
V
I in
L (5)
32
1 DR
V
I in
L (6)
here D is duty ratio.
III. PROPOSED QBC WITH MPPT CAPABILITY
In this study, maximum power point tracking
quadratic boost converter for PV systems is designed.
The designed system is depicted in Figure 3. As it is
seen from figure, the system composes PV modules,
the quadratic boost converter and the IC based MPPT
algorithm.
Figure 3. Bock diagram of the proposed system
The IC algorithm is one of the common MPPT
methods. This method is more complex than the P&O
method, however, the continuous perturbation
requirement is removed and thus power and voltage
oscillations appeared on P&O method are removed
substantially. This method uses the slope of P-V curve
of the PV system as depicted in Figure 4. The slope of
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3. Maximum Power Point Tracking Quadratic Boost Converter for Photovoltaic Systems
the P-V curve is equal to zero when the operation point
is equal to the MPP. If the slope of the P-V curve is
negative, this represents that, operation point of the PV
system is at the left side of the MPP. Similarly, if the
slope of the P-V curve is positive, this represents that
operation point of the PV system is at the right side of
the MPP. This situation can be expressed analytically
as given below [18]:
dV
dI
VI
dV
dI
V
dV
dV
I
dV
IVd
dV
dP
(7)
Since the slope of P-V curve is equal to zero at the
MPP, (8) can be written:
V
I
dV
dI
dV
dP
0 (8)
Figure 4. Schematic representation of the operation principle of the
IC algorithm.
IV. SIMULATION RESULTS
The proposed QBC and IC based MPPT algorithm
are modeled and MATLAB/Simulink simulations are
carried out. Both design of the QBC and performance
of the MPPT method is investigated. Therefore, input-
output voltage relations of the converter, response of
the proposed system while the solar radiation and load
are changing are tested.
In Figure 5, input and output voltage of the
proposed QBC converter for different duty ratio values
such as 0.3 and 0.5 are given. It is seen that, while the
input voltage value is 100V, the output voltage of the
converter is equal to 200V and 400V for 0.3 and 0.5
duty ratio values, respectively. As one can easily see
that, there is a quadratic relationship between the duty
ratio and voltage conversion gain.
In addition, both input and output variations are
considered to check the performance of the proposed
the proposed MPPT algorithm and the converter. As it
is shown in Figure 6, step load changes are applied to
the system. At t=0.3 s, the load resistance value is
increased from 50 Ω to 100 Ω (load level of the
converter is reduced to 50%), and at t=0.6 s, the load
resistance value is reduced from 100 Ω to 50 Ω (load
level of the converter is increased to 100%). In fact,
50% step load is applied and removed. As it can be
easily seen from Figure 6 that, the proposed MPPT
quadratic boost converter system tracks the MPP of
the PV system and keeps the PV power at its
maximum point by regulating its output voltage and
power. The performance of the MPPT algorithm and
the QBC converter is tested for varying solar
irradiation conditions. As it is shown in Figure 7,
0.2 0.3 0.4 0.5 0.6 0.7 0.8
0
100
200
300
400
500
t (s)
V0 (V)
V0
Vin
D=0.3
(a)
0.2 0.3 0.4 0.5 0.6 0.7 0.8
0
100
200
300
400
500
t (s)
V0 (V)
V0
Vin
D=0.5
(b)
Figure 5. Input and output voltage waveforms of the proposed QBC
a) For D=0.3, b) For D=0.5
0
500
1000
Ir (W/m2
)
Ir (W/m2
)
V0 (V)
0
500
1000
PPV (W)
PPV (W)
0
100
200
300
V0 (V)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0
2
4
I0 (V)
I0 (V)
t (s)
Figure 6. Response of the proposed system for load changes a) The
solar radiation, b) The PV system power, c) The output voltage of
the proposed converter, d) The load current
a step change in solar radiation from 1000 W/m2 to
250 W/m2 and from 250 W/m2 to 1000 W/m2 is
applied at t=0.1 s and t=0.25 s, respectively. As seen
from the figure, the MPPT quadratic boost converter
tracks the variation in the operation conditions, and
regulates its operation point to get maximum available
power from the PV system. Furthermore, it is seen that
the proposed system has high tracking speed and less
oscillation. In addition, a ramp variation on the solar
radiation (both increasing and decreasing solar
irradiation conditions) is also applied and the
performance of the proposed system is tested. It is
seen that, the proposed MPPT quadratic boost
converter can track the rapid changes in operation
conditions. The proposed system with less oscillation,
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4. Necmi ALTIN, Ertan OZTURK
0
500
1000
Ir (W/m2
)
Ir
(W/m2
)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0
500
1000
PPV (W)
t (s)
PPV
(W)
Figure 7. Response of the proposed system under variable solar radiation, a) The solar radiation (W/m2
), b) The PV system power (W)
high tracking speed and accuracy has superior
performance in both transient conditions and steady
state conditions.
V. CONCLUSIONS
In this study, a maximum power point tracking
quadratic boost converter is proposed. Since there is a
quadratic function between the output voltage and the
duty ratio values of the converter, this converter is
very suitable for PV systems, where the voltage level
is usually low and is required to step-up. In addition,
the incremental conductance MPPT method is applied
in control of the proposed QBC. Thus, the proposed
system can track the MPP of the PV modules and
provides more efficient operation. It is seen from
MATLAB/Simulink simulation results that the
proposed system has higher voltage conversion gain
than the conventional boost converters. Moreover, the
proposed converter with IC algorithm has high
tracking speed and less oscillations, and it is suitable
for tracking MPP of PV system even under rapidly
changing atmospheric conditions.
ACKNOWLEDGMENT
This research has been supported by European
Union Ministry of Turkey, National Agency of Turkey
within the Project Code: 2015-1-TR01-KA203-
021342 entitled Innovative European Studies on
Renewable Energy Systems.
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