International Conference on Electrical, Electronics, and Optimization Techniques (ICEEOT) - 2016
Modified Maximum Power Point Tracking for PV
System Using Single Switch DC/DC Converter
Shahana P. S. and Rajin M. Linus
Dept. of Electrical and Electronics Engineering
MEA Engineering College
Perinthalmanna, Kerala, India
ps_shanu5@yahoo.in., rajinmlinusped@meaengg.in.
Abstract— This paper proposes maximum power point
tracking (MPPT) of photo voltaic (PV) system based on the
relation between optimum voltage and atmospheric temperature.
This method uses existing single switch DC-DC power converter
which is the integration of buck and buck-boost converter results
in single stage single switch converter (SSC). It reduces the power
losses. In this article, perturb and observe (P&O) algorithm with
the large step forward and small step reverse is considered for
the initial tracking of maximum power point (MPP). The
optimum voltages of PV systems are almost constant at the
different insolation level and assumed that which is inversely
proportional to the temperature variation with constant
irradiation. The proposed MPPT algorithm with the above
relation provides fast and accurate tracking for every
atmospheric condition. The performance of the proposed model
is validated by simulation in MATLAB/SIMULINK.
Keywords—Perturb and observe (P&O), maximum power point
tracking (MPPT), photovoltaic (PV) system, single switch converter
(SSC)
I. INTRODUCTION
In the recent times, there is a high degree of demand for
global energy. While analyzing the inescapable arises of
pollutions due to fossil fuel energy sources, solar energy
appears to be one of the best options available in the literature.
The use of solar energy offers ultra clean, natural and
justifiable source of energy with immense environmental and
financial paybacks. A standalone PV-battery system can be
used for various applications where the battery can be used for
supplying the power in the absence of insolation or at partial
shading condition. A suitable MPPT system assimilated in the
PV system provides the maximum power at different
environmental conditions with minimum losses.
The electronic power converter is one of the enabling
technologies required for utilizing renewable energy. SSC
topology proposed in [1] eliminates the cost, size and
components of the circuitry. Double stage converter can be
deducted into single stage single switch converter by replacing
the active switches by a single switch [2]. Hence, the number
of the control circuitry can be reduced. The combination of
buck and buck-boost converter results in the SSC topology.
Twofold control strategy on a single switch is adopted here
with load regulation by pulse width modulation (PWM)
technique as well as pulse frequency modulation (PFM) for
978-1-4673-9939-5/16/$31.00 ©2016 IEEE
input stage control. In order to achieve this control, the input
side of the converter (buck stage) is operating in discontinuous
conduction mode (DCM) and output side (buck-boost stage) is
in continuous conduction mode (CCM) [3]. The main
drawback of SSC topology is that there will be a high voltage
stress across the single switch and is rectified by providing a
stiff DC voltage using a battery as in [4].
The fractional open circuit voltage method in [3] is less
suitable for speedily changing atmospheric condition since it
is based on assumptions. Variable perturbation in frequency is
proposed in a center point iteration MPPT method [5] by
splitting the entire power-voltage (PV) characteristic into a
number of non-overlapping areas. In [6], variable frequency or
duty ratio control method is proposed with the incremental conductance method. P&O method with fixed and variable
step size along with its application is described in [7]. Both the
incremental conductance and conventional hill climb search
[8] (HCS) MPPT methods have steady state oscillation around
the MPP.
The article [9] proved that large step forward and small step
reverse tracking improves the tracking speed. Also, the linear
relation between wind velocity and optimum speed provides
the optimum point during changes in wind velocity in a wind
energy conversion system (WECS) This article adopts a
modified hill climb searching algorithm proposed in [8] with
large step forward and small step reverse tracking for initial
tracking. The maximum power point voltage is assumed to be
constant at the dissimilar irradiation level. As WECS and PV
system characteristics curve is a hill shaped curve, while
analyzing PV system characteristic, optimum voltage seems to
be inversely proportional to temperature variation with
constant irradiation. This article uses this relation to track the
optimum voltages for various temperatures after the optimum
voltage of a particular temperature is traced using the initial
tracking. This way of tracking provides better response in
MPPT. SSC with this modified MPPT method provide better
operation in PV system with minimal losses, fast tracking and
mitigates the number of control circuitry.
This paper is structured as follows: converter description is
given in section II. Section III describes the principle of
operation of the converter. The proposed system with
modified MPPT is detailed in section IV. Simulation results at
different temperature levels are given in section V and
conclusion is in section VI.
II. CONVERTER DESCRIPTION
Active switches in the double stage converter are
substituted by a single MOSFET switch as in Fig.1. Where,
buck converter is integrated into a buck-boost converter to
develop the SSC. The front stage buck converter is used for
MPPT and the load regulation is done by the second stage
buck-boost converter. The battery in the circuit is for giving
stiff DC-link voltage. Capacitor C1 across the battery removes
the ripple component of battery current. Inductors in buck
stage (L1) and buck-boost stage (L2) operates in DCM and
CCM respectively in order to attain the dual control in a single
switch.
During ON time power switch in the return path makes a
current path for the battery as well as the PV source. Positive
and negative currents of the battery flow through the diodes D1
to D3 during different operation periods. Diode D4 and
capacitor C2 sustain the output load. Battery is also helping to
shrink the voltage stress across the MOSFET.
III. PRINCIPLE OF OPERATION
As the dual control strategy is adopted in this paper, PV
input voltage is controlled by varying the switching frequency
using the modified HCS MPPT method.
A. Modes of Operation
Single switch converter has four steady state modes of
operation [3].
1) Mode 1: During this mode switch S is ON and only
diode D2 is conducting. Inductor L1 charges with inductor
current, as in (1)
I L1 =
V in − V B
L1
 dt
(1)
Current through the inductor L2 is the summation of the
inductor current in L1 and the battery current iBC, as in (2)
I L 1 = I L 2 + I BC
stored energy to the battery as well as the inductor L2
withstands the load. The discharging current of L1 and L2 is
given as in (3)-(4).
V
(3)
i = − B dt
L1
iL 2 = −
L1

Vo
L2
 dt
(4)
4) Mode 4: During this mode, switch S is OFF. Since
inductor L1 is in DCM, it resets. Inductor L2 operates in CCM.
Hence, it discharges to the load with current as in (4).
IV. PROPOSED SYSTEM CONFIGURATION
In this section the proposed modified MPPT technique with
PV characteristic is explained.
A. Mathematical Study of PV curve
PV characteristics at different insolation and temperature
level are given in Fig.2 and Fig.3 respectively. From Fig.3, it
is clear that temperature and optimum voltage (VMPP) are
inversely proportional. Hence, once the VMPP at a particular
temperature is determined, remaining optimum voltages at
different temperatures can be determined using the proposed
relation as in (5).
V MPP
− new
T
=  ref
 T new

V ref

(5)
Where, VMPP-new is the voltage which is to be determined at
any temperature level. Tref and Vref is the temperature and the
corresponding optimum voltage respectively. Tnew is the new
change in temperature in degree Celsius at which the VMPP-new
has to be determined.
(2)
2) Mode 2:In this mode, the extra energy from the PV
source is stored in the battery. This condition occurs when IL1
is greater than IL2. Both of the inductor currents reaches at
their peak at time T2.
3) Mode 3: This mode occurs in the time interval T2-T3,
during the switch S is turned OFF. Inductor L1 discharges its
Fig.1. Circuit description of single switch converter.
Fig. 2. Power-Voltage characteristics of PV system at different irradiation
levels.
Power (W)
Vref
(using Mode-1)
VMPP-new
(using Mode-2)
Fig. 3. Power-Voltage characteristics of PV system at different temperature
levels.
B. Proposed MPPT Technique
The proposed algorithm has two modes of operation. In
Mode-1, VMPP at the initial temperature is traced using large
step forward and small step reverse tracking which is shown in
Fig. 4. In Fig. 4 the forward large step size is ΔV1 and the
small step reverse ΔV2. Mode-2 is considered during changes
in temperature, which uses the relationship explained in
equation (5) and depicted in Fig. 5.
Voltage (V)
Fig. 5. Tracking of new optimum voltage in Mode-2 from Mode-1 in the
Power Vs Voltage curve of PV system.
Flow chart of the modified MPPT algorithm is depicted in
Fig.6. The algorithm checks the present and previous changes
in voltages ∆V(k) and ∆V(k-1) respectively before deciding
the initial optimum point. Then VMPP at initial temperature is
tracked and stored in memory. As the alteration in temperature
occurs, maximum power is chased according to Mode-2.
C. SSC with MPPT Technique
The proposed modified P&O algorithm provides the
optimum reference voltage to the control blocks of SSC
topology for tracking MPP for various atmospheric conditions.
The front stage converter tracks optimum voltage using the
proposed algorithm through variable frequency control.
Output load is regulated by normal PWM technique. MPPT
algorithm yields the VMPP fit for different environmental
conditions.
Fig. 4. Perturbation concepts in Mode 1 in the Power Vs Voltage curve of PV
system.
Fig. 6. Flow chart with Modified MPPT.
L1
Vo-PV
D4
VB
D1
C1
D2
Gate
Signal
R
C2
C3
L2
VO
D3
Relational
Operator
Vref1
Modified MPPT
HCS Algorithm
-
Vref2
+
PI
Controller
Ramp
Generator
PI
Controller
-
+
Reference Output
Voltage
Fig.7. Single switch converter with modified HCS MPPT algorithm.
P V p a n e l o u tp u t v o lta g e (V )
The consolidated closed loop block diagram is given in
Fig.7. Where,Vref1 is compared with the PV output voltage and
fed to the proportional integral (PI) controller for an enhanced
steady state performance. A variable frequency carrier signal
is generated in this part, where the frequency is agreeing to the
temperature variation. Buck-boost stage control is acquired by
varying the duty cycle. The normal PWM technique is adopted
here. Once the load regulation is obtained for a particular duty
ratio, by keeping that duty ratio fixed and then controls the
buck stage. The voltage across the load is measured and
compared with the reference value. This error signal is fed to
PI controller. Gate pulses are generated by merging the PFM
and PWM control.
60
40
T= 25°C
20
T= 25°C
T=55°C
T=55°C
0
0
0.1
0.2
0.3
0.4
0.5
Time (s)
0.6
0.7
0.8
0.9
1
Fig. 8. Output voltage of PV module at different temperature level.
2.5
2
T= 5°C
1.5
T= 25°C
T= 25°C
1
0.5
0
0
V. SIMULATION RESULTS
T=55°C
0.1
T=55°C
0.2
0.3
0.4
0.5
Time (s)
0.6
0.7
0.8
0.9
1
Fig. 9. Current through PV module at different temperature level.
P V m odule output pow er (W )
In Mode-1 (initial tracking), the forward and reverse
tracking step size is ΔV1= 2V and ΔV2 = 0.5V respectively. As
the temperature of 25°C the optimum voltage of PV system
VMPP = 16.8V. This value paved a way to track optimum
voltage during changes in temperature using the relation
optimum voltage is inversely proportional to changes in
temperature as in Mode-2. Fig.8 shows the changes in
optimum voltages at different temperature. The temperature
variation considered in this study is between 5°C and 55°C. It
shows that as the temperature decreases optimum voltage is
increasing and vice-versa. This finding is given in (5) as the
temperature and optimum voltage in a PV system is inversely
proportional.
T= 5°C
80
C urrent through P V m odule (A )
Consequently, corresponding variable frequency control is
possible with PFM technique. Finally the combination of three
operations as maximum power point tracking, charging and
discharging of the battery and power regulation of load is
carried out using SSC.
150
T= 5°C
100
50
T= 25°C
T= 25°C
T=55°C
T=55°C
0
0
0.1
0.2
0.3
0.4
0.5
Time (s)
0.6
0.7
0.8
Fig. 10. Output power of PV module at different temperature level.
0.9
1
References
O utput voltage (V )
20
[1]
15
[2]
10
5
[3]
0
0
0.1
0.2
0.3
0.4
0.5
Time (s)
0.6
0.7
0.8
0.9
1
Fig. 11. Regulated load voltage of SSC.
The corresponding changes in current and power at the
different temperature are shown in Fig.9 and Fig.10
respectively. Where, the output current and power are
increasing as the temperature is reduced and vice-versa. Fig.11
shows the regulated output voltage of SSC. Where, the output
voltage remains constant as 15V for different temperature
levels of PV system.
VI. CONCLUSION
The proposed modified MPPT method is simple and copeup with different environmental conditions. Single switch
converter topology eliminates the complexity and the number
of the control circuitry [3]. This proposed MPPT algorithm
adopted forward large step and reverse small step for initial
tracking which improves the tracking speed. The simulation
study proves that the optimum voltage is indirectly
proportional to the temperature variation.
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