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International Journal of Electrical, Electronics and Computer Systems (IJEECS)
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SIMULATION OF A SOLAR MPPT CHARGER USING CUK
CONVERTER FOR STANDALONE APPLICATION
1
Diva Catherine, 2Kavitha Bhaskar
1
M tech student, 2Assisstant Professor
Jyothi Engineering College, Thrissur
Email : [email protected], [email protected]
power control mechanisms called the Maximum Power
Point Tracking (MPPT) algorithms has led to the
increase in the efficiency of operation of the solar
modules and thus is effective in the field of utilization of
renewable sources of energy.
ABSTRACT: Standalone photovoltaic system requires a
proper battery charge controller. The main disadvantage
of photovoltaic system is its variations in output voltage.
Therefore to obtain a stable voltage from solar panels, DCDC converters are used. This paper explains the use of cuk
converter with MPPT technique in a photovoltaic system.
The MPPT is implemented by incremental conductance
algorithm with direct control method. This system
simplifies the conventional MPPT systems by eliminating
proportional integral control loop. The overall system is
designed,
developed
and
validated
by
using
MATLAB/SIMULINK.
The main challenge of the generation side of the PV
system is to generate as much power as it can. This is
related to the payback and efficiency of the system.
Thus in PV system efficient dc-dc converter is used to
control the load power and to ensure that system
operates in maximum power point.[15-16] In this paper
cuk converter is used in between the PV panel and
inverter. In Cuk converter the source and load side are
separated via a capacitor thus energy transfer from the
source side to load side occurs through capacitor which
leads to less current ripples at the source and load side.
The most common algorithms for Maximum Power
Point (MPP) are Perturb and Observe algorithm and
Incremental conductance method.
KEYWORDS: Renewable energy, Cuk Converter, Mppt
I. INTRODUCTION
One of the major concerns in the power sector is the
day-to-day increase in power demand but the
unavailability of enough resources to meet the power
demand. Demand has increased for renewable sources of
energy to be utilized along with non renewable energy
resources to meet the energy demand.[1-5] Renewable
energy sources like wind energy and solar energy are the
prime energy sources which are being utilized in this
regard.
In this paper cuk converter is used for maximum power
point tracking. The outline of the proposed system is
given in fig 1
Solar energy is abundantly available and that has made it
possible to harvest it and utilize it properly. A
photovoltaic system can be a standalone generating unit
or can be a grid connected generating unit. Thus
standalone system can be used to power rural areas
where the availability of grids is very low.[6]
Photovoltaics are semiconductor devices which convert
solar irradiation in the visible spectrum to generate
direct current.
In order to increase the efficiency of a solar panel
certain control methods used.[8-9]The use of the newest
Fig 1 Outline of the proposed system
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maximum power point tracking(MPPT).The output of
MPPT is given to dc-dc converter for extracting the
output
II. PV MODULE AND MPPT
The solar cell is the basic unit of a PV system. An
individual solar cell produces direct current and power
typically between 1 and 2 W, hardly enough to power
most applications. Solar Cell or Photovoltaic (PV) cell is
a device that is made up of semiconductor materials
such as silicon, gallium arsenide and cadmium telluride,
etc. that converts sunlight directly into electricity.
IV. SELECTION OF CONVERTER
Switch Mode Power Supply topologies follow a set of
rules. A very large number of converters have been
proposed, which however can be seen to be minor
variations of a group of basic DC- DC converters – built
on a set of rules.[8-9]Many consider the basic group to
consist of the three: BUCK, BOOST and BUCKBOOST converters. The CUK, essentially a BOOSTBUCK converter, may not be considered as basic
converter along with its variations: the SEPIC and the
zeta converters.[12],[18] The buck, boost and buckboost converters all transferred energy between input
and output using the inductor, analysis is based of
voltage balance across the inductor.[21] The CUK
converter uses capacitive energy transfer and analysis is
based on current balance of the capacitor. The circuit in
Fig.4 is derived from DUALITY principle on the buck boost converter.[22-23]
The voltage of a solar cell does not depend strongly on
the solar irradiance but depends primarily on the cell
temperature. PV modules can be designed to operate at
different voltages by connecting solar cells in series.
When solar cells absorb sunlight, free electrons and
holes are created at positive/negative junctions. If the
positive and negative junctions of solar cell are
connected to DC electrical equipment, current is
delivered to operate the electrical equipment. The
equivalent circuit of the PV cell is shown in figure 2.
Fig : 3 cuk converter
If we assume that the current through the inductors is
essentially ripple free we can examine the charge
balance for the capacitor C1. For the transistor ON the
circuit becomes
Fig 2 Equivalent circuit of PV
The panel is modelled by a Thevenin’s equivalent
circuit, fig 2 which consists of a voltage source Vg
connected in series with an output resistance Rg around
the MPP. Both and are subject to the level of insolation
and temperature. The input voltage and equivalent input
resistance of the converter are and, respectively. As the
input power to the tracker is equal to the output power of
the panel.
III. PARAMETERS OF PV
Module
Module used here is KC85T

Pmax=87w

Vmp=17.4v

Imp=5.02A

Voc=21.7V

Isc=5.34A
Fig :4 cuk converter on state
and the current in C1 is IL1. When the transistor is OFF,
the diode conducts and the current in C1 becomes IL2.
This is for 1000w/m^2 irradiance level In addressing
the poor efficiency of PV systems, some methods are
proposed, among which is a new concept called
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achieve maximum efficiency. The main objective of this
controller is to regulate the operating point of the system
in case of variations in environment conditions. The dcdc converter is connected with the solar-PV array to
regulate the operating point through a MPPT controller.
The output power of PV panel is varied due to change in
solar radiation and temperature conditions and under
consumer load variations. The cuk dc-dc converter is
used here as shown in Fig.3. Its output voltage Vc can
be regulated by controlling the duty cycle of the switch
S1. Duty cycle presents the ratio of the on and off
periods for a switch in one cycle. It also allows
regulation of the input voltage though controlling the
duty cycle. Different methods are proposed and
analyzed for tracking the MPP in a solar- PV system.
Here the modified incremental conductance (IC) method
is used as a MPPT approach. This tracking approach
uses a fix step size and it can be chosen by the tracking
speed requirements. This algorithm utilized the principle
of calculating the change in output power in the fixed
time period and from this it determines the duty ratio as
shown in Fig.5
Fig :4 cuk converter off state
Since the steady state assumes no net capacitor voltage
rise ,the net current is zero.
[24-25]The relations between output and input currents
and voltages are given in the following:
(Vo/Vin)= -(D/1-D)-----(3)
(Io/ I in)= -(D/1-D)-----(4)
D-duty cycle
Thus the voltage ratio is the same as the buck-boost
converter. The advantage of the CUK converter is that
the input and output inductors create a smooth current at
both sides of the converter while the buck, boost and
buck-boost have at least one side with pulsed current.
In this modified approach, two conditions loop is used
according to the change in radiation. First case is an
increase in radiation and second one is a decrease in
radiation. When the solar radiations increase then the
voltage and current both increase and thus the V/P and
I/P both are positive and when solar radiation decreases
then also V/P and I/P both become positive.
Some analyses of Cuk converter specifications are
provided in [23], and a comparative study on different
schemes of switching converters is presented in the
literature [8-9]
[14]In first case when the radiation decreases then, if
one takes only first loop of V/P, the voltage and power
reduce but the ratio of them becomes positive and it
increases the duty ratio which is incorrect in this case.
Therefore the second loop is used and in case of an
increase in radiation the controller follows the first loop
for determining the duty ratio. The modelling of this
approach is performed in Simulink and integrated into
the system as a subsystem.
The components for the Cuk converter used in
simulation and the hardware setup were selected as
follows:

Input inductor L1=5mH

Duty cycle=50%

Capacitor c1 (pv side )=47uF

Filter inductor L2 = 5mH

Switch : MOSFET –IRF540

Freewheeling diode

Capacitor c2 (filter side ) =1uF

Resistive load =10©

Switching frequency =10kHz

Pic processor
V. MPPT CONTROL
SCHEME
Performance of the solar-PV system not only depends
on the environment conditions but also the MPPT
approach holds a significant role. In case of high solar
radiation situation, the PV system generates the power
efficiently using an effective MPPT method.[14] A
MPPT is the approach which is used in the system to
Fig 5 algorithm [14]
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Voltage measurement is required at the point where the
PV module output is connected to the input of the Cuk
converter. The voltage at this point is the operating
voltage of the PV module. On the other hand, current
measurement is also necessary to indicate the generated
current of the PV module on each operating point. It is
particularly important to determinate the atmospheric
condition, which is vital in connection with the accuracy
of MPP tracking.
VI. DIRECT CONTROL
Method
Conventional MPPT systems have two independent
control loops to control the MPPT. The first control loop
contains the MPPT algorithm, and the second one is
usually a proportional (P) or P–integral (PI)
controller.[15] The IncCond method makes use of
instantaneous and IncCond to generate an error signal,
which is zero at the MPP; however, it is not zero at most
of the operating points. The main purpose of the second
control loop is to make the error from MPPs near to
zero. Simplicity of operation, ease of design,
inexpensive maintenance, and low cost made PI
controllers very popular in most linear systems.
However, the MPPT system of standalone PV is a
nonlinear control problem due to the nonlinearity nature
of PV and unpredictable environmental conditions, and
hence, PI controllers do not generally work well. In this
paper, the IncCond method with direct control is
selected. [16]The PI control loop is eliminated, and the
duty cycle is adjusted directly in the algorithm. The
control loop is simplified, and the computational time
for tuning controller gains is eliminated. To compensate
the lack of PI controller in the proposed system, a small
marginal error of 0.002 was allowed.
Fig 6 simulation of proposed system
In this paper the second control loopis eliminated and
shows that sophisticated MPPT methods do not
necessarily obtain the best results, but employing them
in a simple manner for complicated electronic subjects is
considered necessary [3]. The feasibility of the proposed
system is investigated with a dc–dc converter configured
as the MPPT. In, it was mentioned that the power
extracted from PV modules with analog circuitry can
only operate at the MPP in a predefined illumination
level.
VII. SIMULATION
The diagram of the closed-loop system designed in
MATLAB and Simulink is shown in Fig.6, which
includes the PV module electrical circuit, the Cuk
converter, and the MPPT algorithm. This block is
simulated using the Simulink blocks available in the
MATLAB library. The converter components are chosen
according to the values presented previous section. The
PV module is modeled using electrical characteristics to
provide the output current and voltage of the PV
module. The provided current and voltage are fed to the
converter and the controller simultaneously.
Fig 7 simulation of mppt algorithm
VIII. SIMULATION RESULT
The flowchart of the incremental conductance MPPT
algorithm has been implemented in Matlab/Simulink.
The figure 7 illustrated the modeling diagram for the
above algorithm. The simulation results of the ouput
power of the PV module and the MPPT pulse width
modulated output is shown in figure 8. The diagram of
figure 10 represents the whole PV system with MPPT
along with the cuk converter has been implemented in
the Matlab/ simulink.
The Output of PV panel is given to MPPT controller.
Triggering pulse of MPPT controller is given to IGBT
switch. Then the output is fed to the load.The entire
system has been modelled on MATLAB™ 2009a.The
PI control loop is eliminated, and the duty cycle is
adjusted directly in the algorithm. To compensate the
lack of PI controller in the proposed system, a small
marginal error of 0.002 is allowed.
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International Journal of Electrical, Electronics and Computer Systems (IJEECS)
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losses in the inductor and capacitor of the boost
converter. This can be seen from the plots of the
respective power curves. The results also indicate that
the proposed control system is capable of tracking the
PV array maximum power and thus improves the
efficiency of the PV system and reduces low power loss
and system cost.
IX. CONCLUSION
A low power stand-alone solar-PV energy generation
system with a cuk dc-dc converter has been designed
and the performance analysis of the system has been
presented using MATLAB simulation with the device
currents and voltages. The MPPT method simulated in
this paper is able to improve the dynamic and steady
state performance of the PV system simultaneously.
Through simulation it is observed that the system
completes the maximum power point tracking
successfully despite of fluctuations. When the external
environment changes suddenly the system can track the
maximum power point quickly.
Fig 8 Simulation of MPPT
X. REFERENCES
Fig 9 scope of generation of pulses
Fig 10 simulation of output voltage
The various waveforms were obtained by using the plot
mechanism in MATLAB. There is a small loss of power
from the solar panel side to the boost converter output
side. This can attributed to the switching losses and the
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