MPPT oscillations minimization in PV system by controlling non-linear dynamics in SEPIC DC-DC converter

International Journal of Electrical and Computer Engineering (IJECE)
Vol. 10, No. 6, December 2020, pp. 6268~6275
ISSN: 2088-8708, DOI: 10.11591/ijece.v10i6.pp6268-6275  6268
Journal homepage: http://ijece.iaescore.com/index.php/IJECE
MPPT oscillations minimization in PV system by controlling
non-linear dynamics in SEPIC DC-DC converter
M. Vaigundamoorthi1
, R. Ramesh2
, V. Vasan Prabhu3
, K. Arul Kumar4
1,4
Department of Electrical and Electronics Engineering, Madanapalle Institute of Technology & Science, India
2
Department of Electrical and Electronics Engineering, CEG, Anna University, India
3
Department of Electrical and Electronics Engineering, St. Joseph’s College of Engineering, India
Article Info ABSTRACT
Article history:
Received Feb 27, 2019
Revised May 2, 2020
Accepted Jun 17, 2020
Solar PV power generation has achieved rapid growth in developing countries
which has many merits such as absence of noise, longer life, no pollution, less
time for installation, and ease of grid interface. A maximum power point
tracking circuit (MPPT) consists of DC-DC power electronics converters that
are used to improve the energy attainment from solar PV array. This paper
presents a detailed analysis to control of chaos, a non-linear dynamic in SEPIC
DC-DC converter interfaced solar PV system, to minimize the oscillations near
to MPP. In SEPIC DC-DC converter, the input inductor current is continuous
and capable of sweeping the whole I-V curve of a PV module from open circuit
voltage (Voc) to short circuit current (Isc) operating points. To trace the true
maximum power point and to nullify the oscillations near to MPP, the yield
output voltage needs to ensure period-1 operation.
Keywords:
Adaptive controller
Chaos
MPPT
SEPIC converter
Solar PV module Copyright © 2020 Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
M. Vaigundamoorthi,
Department of Electrical and Electronics Engineering,
Madanapalle Institute of Technology & Science,
Madanapalle, Andhra Pradesh-517325, India.
Email: bacyavaigo2000@gmail.com; drvaigundamoorthim@mits.ac.in
1. INTRODUCTION
Solar power is a Green energy sources that employs DC-DC converter to harvest maximum power.
The efficiency of the energy conversion process is declined due to climate variable temperature, partial shading,
and atmospheric irradiation change and load conditions. The PV current changes with irradiation greatly and
the atmospheric temperature affects PV voltage [1-4]. The MPP is detected by Adaptive perturb and observer
MPPT algorithm which is embedded in Microcontroller, generate gate pulse which is applied to the DC-DC
converter switches [5-8].
The various types of DC-DC converters [9-12] such as buck, boost, buck boost, Cuk and SEPIC are
implemented in PV system by considering suitability factors such as cost, efficiency, maximum power flow,
ease of drive system, Positive output voltage, system stability and concluded that SEPIC converter is commonly
used in PV system to track maximum power from PV panel. Higher order converter such as SEPIC and Cuk
are widely used for MPPT charge controller because of their excellent steady state performance, isolation, over
current limit protection [13-21]. Quamruzzaman [17] has argued that the PV current with less ripple and
improved dynamic response can be achieved by SEPIC converter also proved that high input current ripple
content of the converter reduces the average value of current which may leads to wrong true MPP tracking.
Non-linear dynamics in power electronics circuits was put forward in [22-24] undergo sub-harmonics,
quasi-periodic oscillations, and chaotic mode of operation. The chaos is experienced in DC-DC converters and
its control methods are conducted in power electronics circuits. This abnormal operation would affect converter
tracking efficiency since the period -1 operation need to be ensured for MPP tracking in order to minimize
oscillations near to MPP. Several studies [25-27] have suggested many control methods that are mitigated to

Int J Elec & Comp Eng ISSN: 2088-8708 
Oscillations minimization at MPP by controlling non-linear dynamics in ... (M. Vaigundamoorthi)
6269
supress chaos. Also, The PID controller and sliding mode controllers are also experimented to nullify the effect
of chaos in DC-DC converters.
This paper explores that SEPIC DC-DC converter interfaced solar PV system may enter into chaotic-
aperiodic mode during maximum power tracking process. The analysis and suppression of chaos in a voltage
mode-controlled SEPIC converter-based solar PV system has been mitigated and the use of adaptive sliding
control method is experimented to nullify the chaos effect and that control has been examined to minimize
the oscillations near to MPP.
2. SEPIC CONVERTER BASED SOLAR PV SYSTEM
2.1. System description
Figure 1 and Figure 2 show the block diagram and hardware setup of sliding mode controlled SEPIC
DC-DC converter interfaced solar PV system. The power circuit has an inductors L1, L2, capacitors C1, C2,
a Power switch S, a load resistance, a solar PV module (L1235-37Wp) shown in Figure 3.
Figure 1. Block diagram Figure 2. Experimental setup
Figure 3. SEPIC DC-DC converter
2.2. Design of SEPIC converter
The SEPIC DC-DC converter has advantages such as non-pulsating nature of load current and positive
load voltage and has high efficiency than Buck-Boost converter. The positive output voltage is obtained based
on the following two modes of operation in one switching period. 1) MOSFET is ON and the diode is not
operated. The input inductor, L1, is charged from the PV input voltage. The output inductor L2 finds energy
from the first capacitor, and the output capacitor C2 is left to provide the load current. The fact is that both L1
and L2 are disconnected from the load when the switch S, is turned on. In mode 2), The MOSFET is turned off
and diode is operated, the input inductor L1 charges the capacitor C1 and also provides current to the load.
The second inductor is also connected to the load during this time. The steady state output voltage equation is
given by

 ISSN: 2088-8708
Int J Elec & Comp Eng, Vol. 10, No. 6, December 2020 : 6268 - 6275
6270
VO
VIN
=
D
(1−D)
(1)
Also, the steady state current equation is
IIN
I0
=
D
(1−D)
(2)
The (3) shows the designed value of inductors
L1 =L2=L=
VIN(MIN)∗ DMAX
∆IL∗fS
(3)
The voltage specifications of capacitor C1 is selected as high as input voltage. The ripple voltage of
C1 is given by
∆Vc1=
I(OUT)∗ DMAX
C1∗fS
(4)
The SEPIC DC-DC converter is designed with inductors L1=L2 =500µH, Capacitors C1=C2= 220µF, switching
frequency=25 KHz, MOSFET-IRF510, and diode-MUR450 are selected for hardware implementation.
2.3. L1235-37Wp Solar PV module
The solar PV output power depends on insolation, atmospheric temperature and type of load
characteristic. From the equivalent circuit shown in Figure 4(a), the current and voltage equations are given
by (5) and (6) respectively.
Isc=ID +Ipv + (VD / R p) (5)
Vpv=VD - (Ipv*Rs) (6)
Where diode current is, ID=Io + ( e (V
D
/ V
T
)
- 1), Isc is the short circuit current, Vt=NsKT / q is
the thermal voltage with Ns cells connected in a series (K is the Boltzmann constant, q is the electron charge
and T is the temperature of the PV cells). Using the equations 5 and 6, solar PV is modelled and simulated in
MATLAB, has V-I charecteristics which is shown in Figure 4(b), The V-I characteristics depend on
the conductance of the load. If the conductance value is high, The PV cell behaves like a constant current
source region. If conductance value is low, the PV cell acts as a constant volatge source. The parameters of
L1235-37W solar PV module which is used for experimental validation are open circuit voltage (Voc)=21,
Voltage at MPP (Vm)=16.4, Short circuit current (Isc)=2.5 A, Current at MPP (Im)=2.25A,
Rated power=37Wp.
Figure 4. (a) Equivalent circuit of solar PV Figure 4. (b) Non-linear V-I characteristics of L1235-
37Wp solar module

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3. RESULTS AND ANALYSIS
The SEPIC DC-DC converter interfaced solar PV system is simulated in MATLAB/Simulink shown
in Figure 5, which comprises PV electric circuit subsystem (MATLAB model), SEPIC DC-DC converter and
a resistive load.
Figure 5. SEPIC converter based adaptive perturb and observer MPPT
The atmospheric constant temperature is considered at 25°C and the irradiation level is set as
1000W/m^2 and after 0.01sec, the irradiation (G) is suddenly changed to 500W/m2
in computer simulation to
test the effectiveness of the adaptive Perturb and Observer algorithm and it was implemented in ATMEGA16
microcontroller. The step size of MPPT algorithm is adjusted which in turn to vary the duty cycle of the switch
in order to harvest maximum power which are shown in Figure 6 and Figure 7. The output power is extracted
from solar PV module at irradiation of 1000 W/m2
and 500W/m2
are 36.74W and 17W respectively.
Figure 6. Change in duty cycle for various irradiation level

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Figure 7. Extracted power for various irradiation level
3.1. Bifurcation analysis of adaptive controlled SEPIC converter based MPPT
Under maximum power point tracked condition, to minimize oscillations near to MPP the non-linear
dynamic behavior of SEPIC DC-DC converter system is mitigated by adjusting reference voltage Vref.
The input voltage of the PV fed SEPIC converter is 16.4 V. The ripples of the tracked voltage are examined
and found that the fundamental period 1-waveform is repeated with Vref =5.68V. At this condition, SEPIC DC-
DC converter system has stable periodic operating behavior. The input voltage ripple of the period-1 operation
under this condition is given in Figure 8.
When the reference voltage (Vref) is adjusted and set as 5.2V and the ripples of input is examined.
Now, SEPIC DC-DC converter undergo an unstable periodic behaviour. The 1-periodic orbit loses its stable
operation, via flip bifurcation it experienced a 2-periodic waveform. The voltage ripple of the period-2
operation is shown in Figure 9.
Figure 8. Tracked voltage ripples-period-1 waveform when Vref =5.62V
Figure 9. Tracked voltage ripples-period-2 waveform when Vref=5.2V

6273
Further, if Vref is varied, the converter operation changed from a stable period-1 operation to an
unstable operation. The input voltage ripples of SEPIC converter-has unstable aperiodic behavior.
Chaotic waveform is observed for the Vref=4.6V as shown in Figure 10. The state change from periodic to
aperiodic when Vref is adjusted, be the main cause to near to MPP. The sliding mode controller is designed
for SEPIC DC-DC converter by sensing output voltage and input inductor current. The Vref is varied from
4.00V to 5.6 V and Iref is set as 0-2 A and it is proved from Figure 11 that the SEPIC DC-DC converter is
operated in period-1 stable region for parameter variation
The chaotic free tracked input voltage from solar PV string is shown in Figure 12. The oscillations are
nullified near to MPP by eliminating aperiodic-chaos in solar PV system. The Figure 13 shows the experimental
harvested non oscilating power of 36.5w from solar PV under standard test conditions.
Figure 10. Tracked voltage ripples – aperiodic waveform when Vref =4.6V
Figure 11. Tracked voltage ripples-period-1 waveform for 3V< Vref < 5.76V
Figure 12. Tracked Input voltage waveform of the converter

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Figure 13. Experimental harvested power from solar PV
4. CONCLUSION
The adaptive Perturb and Observer algorithm is implemented and harvested maximum power from
solar PV using SEPIC DC-DC converter. To nullify the oscillations near to MPP, aperiodic chaotic behavior
of DC-DC converter is exempted experimentally. The sliding mode controller is designed to ensure period
1-operation of the input voltage of SEPIC DC-DC converter.
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BIOGRAPHIES OF AUTHORS
Dr. M. Vaigundamoorthi, working as Professor in the department of Electrical and Electronics
Engineering, Madanapalle Institute of Technology and science, Madanapalle, Andhra Pradesh,
India. He received his B.E degree in Electrical and Electronics Engineering from Madurai
Kamaraj University, Tamilnadu, India in 2002. He received his Master of Engineering degree and
Ph.D. in the area of Power electronics and Drives from College of Engineering Guindy
(Established 1794- The First engineering college in India), Anna University, Chennai, India in
2007 &2013 respectively. He is having 16 years of teaching experience and has published 7
research articles in reputed international journals. His area of interest include Power Electronics
for Renewable Energy System, controller design, Nonlinear dynamics analysis analysis in solar
PV system.
Dr. R. Ramesh was born in Tamil Nadu, India. He received his B.E degree in Electrical and
Electronics Engineering from University of Madras, Chennai, India in 1999. He received his M.E
degree in Power Systems from Annamalai University, Chidambaram, India in 2002. He received
Ph.D from College of Engineering Guindy, Anna University, Chennai, India in 2008. Presently
he is working as a Professor in the Department of Electrical and Electronics Engineering, College
of Engineering Guindy, Anna University, Chennai, India. His research areas are Multi-area Power
Systems, Solar PV systems, Power Electronic Converters, Web and Embedded based systems.
Dr. V. Vasan Prabhu, associate professor in the department of Electrical and Electronics
Engineering in St. Joseph’s College of Engineering, Chennai has 11 years of teaching and research
experience. He received his BE and ME degrees in Electrical &Electronics Engineering
department from Anna University Chennai. He completed his research work in Switched
Reluctance Machine and its control. His area of interest lies in special electrical machines,
machine design, drives and control and artificial intelligence.
Dr. K. Arul Kumar has obtained B.E., (Electrical and Electronics) degree from Anna University,
Chennai in 2008 and M.Tech (Power Electronics) degree from Vel Tech Dr.RR & Dr.SR
Technical University, Chennai in 2011 and Ph.D. degree in the School of Electrical and Electronic
Engineering, VIT University, Vellore in 2017. His current area of research interests are Power
electronics in Renewable Energy Systems. He is currently working as Associate Professor in
Electrical department in Madanapalle institute of Technology &Science

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