Closed Loop Modified SEPIC Converter for Photovoltaic System
ABDEL-KARIM DAUD, SAMEER KHADER
Electrical Engineering Department
Palestine Polytechnic University
West Bank- Hebron, P.O.Box 198
PALESTINE
Abstract:- The high static gain modified single ended primary coil (MSEPIC) converter is presented in this
paper. The proposed converter presents low switch voltage and high efficiency for low input voltage and high
output voltage applications. The configuration of MSEPIC converter is presented and analyzed. Closed loop
feedback control with PID controller based on triggering system is developed for MSEPIC converter to
maintain constant output voltage. Furthermore, the model is integrated with Photovoltaic generator where the
input voltage and current depend on the solar irradiation rates. The proposed model is analyzed and simulated
in Matlab/Simulink and m-file code. Simulation model is developed with a maximum power at full sun equal to
315 W, which presents efficiency equal to 99.03%. The PID controller works as intended, as the output voltage
can approach the expected value. Furthermore, performance and robustness are tested by load variations and set
point variations.
Key-Words: - Renewable Energy, DC-DC Power Conversion, Modified SEPIC Converter, PID Controller.
Received: July 14, 2021. Revised: May 17, 2022. Accepted: June 14, 2022. Published: July 5, 2022.
1 Introduction
Traditional electrical sources suffer greatly from the
expected depletion, the fluctuations of the global
market, and the global political crises, or economic
consequential crises. As well-known alternative
sources of energy are inexhaustible, environmental
friendly and fulfill the world demand toward
minimizing the needs of reserve fossil fuels.
Photovoltaic solar energy presents one of the most
effectively used sources [1, 2, 3]. Power electronic
converters such as DC-DC converters are primarily
implemented to improve energy conversion
efficiency when extracting electric power .DC-DC
converters are circuits which typically supply a
constant output and convert DC voltage to a
different voltage level [4, 5, 6].
These converters have diverse applications in
electric traction, electric vehicles, and distributed-
DC systems like space applications, ships, and
airplanes [6, 7]. Solar photovoltaic and specialized
electrical machine drives are other areas where the
converters are useful [8, 9, 10, 11].
This paper focuses on the modified single-ended
primary-inductance DC-DC Converter (MSEPIC).
The MSEPIC converter is able to reduce or raise the
electrical potential (voltage) at the output and can be
considered as a buck/boost converter [5, 12, 13]. To
maintain the output voltage of MSEPIC, a feedback
closed loop control is necessary as shown in Fig. 1.
The voltage sensor is used to measure the voltage of
MSEPIC converter, which is comparing
continuously with a set reference voltage and a
desired control signal is produced and improved
with the help of PID Controller operation [12, 13,
14]. Controller corrects the error between measured
value and a required set point value that can adjust
the whole process accordingly by which dynamic
response can improve and also reduce the steady-
state error in the system [15, 16]. The output signal
generated by the PID controller is used as the input
signal to control the suitable range of duty cycle (D)
WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS
DOI: 10.37394/23201.2022.21.17
Abdel-Karim Daud, Sameer Khader
E-ISSN: 2224-266X
161
Volume 21, 2022
in a suitable range for the MSEPIC converter, and
the required output voltage is then obtained [17].
In dc-dc converter, the MOSFET switching are
done by PWM technique in which oscillator
frequency is constant and value of average voltage
provides to the given load to turn on and off quickly
by which controls the operation [18].
This paper has been focused on design of PV
system with the MSEPIC converter as using closed
loop feedback control. Simulation input and output
performance of converter such as voltage, current
and power, are compared and verified on MATLAB
software.
Fig. 1 Block diagram of closed loop MSEPIC
converter
2 Analysis and Design of the MSEPIC
The modified SEPIC converter is accomplished by
including of the diode - capacitor circuit in basic
SEPIC converter as shown in Fig. 2. The voltage
multiplier technique is used to increase the static
gain of single-phase boost dc–dc converters. Many
operational characteristics of the basic SEPIC
converter are changed with the proposed
modification. This converter comprises the main
switching device (S), three capacitors (C1, C2, and
Co), two diodes (D1 and D2) and two inductors (L1
and L2). The presence of the diode-capacitor circuit
is able to reduce switching voltage stress on
switching device.
The output voltage from Boost converter is used to
charges C2. Furthermore, the voltage of second
capacitor VC2 is applied to the L2 during the
conduction period of the switching device S. This
condition increases the voltage gain that is obtained
when compared to the conventional step-up
converters.
Fig.2 PV-Modified SEPIC converter
Each component parameter in MSEPIC converter is
calculated by formulas respectively stated in table 1
[5]. Each parameter of modified MSEPIC converter
is selected by default based on of formulas stated in
table1, and its obtained results are presented in table
2.
Table 1 MSEPIC Converter Formulas
Parameters
Formulas
Duty Cycle
Inductances
Capacitors
Static Gain
Capacitor Voltages
MSEPIC
Converter
Solar
PV
(DC
Input)
Load
Voltage
Sensor
Referen
ce
Voltage
Comparator
PI
Controller
Pulse
WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS
DOI: 10.37394/23201.2022.21.17
Abdel-Karim Daud, Sameer Khader
E-ISSN: 2224-266X
162
Volume 21, 2022
The consideration design parameters of MSEPIC
converter are explained for the converter duty cycle
of D=0.5, at which the current ripple becomes
maximum [19].The input (inductor) ripple current is
considered to be approximately 40% of the
maximum input current [20]. As the average input
current is higher than the average output current for
a step-up converter, the volume of 2nd inductor L2 is
lower than the volume of 1st inductor L1, meaning
that the value of L2=50% L1as stated in table 2 [5].
Table 2: MSEPIC Converter Parameters
Parameters
Value
Vin, V
Variable
Vo, V
Variable
D
0.1 – 0.9
L1, mH
1.98
L2, mH
0.99
C1, F
660
C2, F
660
Co, F
10
Ro, Ω
Variable
The maximum capacitor voltage ripple of C1 equals
to nearly 7% of the output voltage for traditional and
modified SEPIC converters [20, 21].The output
voltage ripple of the output filter capacitance Co is
considered equal to 1% of the average output
voltage.
The highest efficiency at constant duty cycle (D =
0.5) for modified MSEPIC is obtained by a
switching frequency (fs) of 50 kHz [5]. In [5], the
distinction of MSEPIC converter’s efficiency over
the other step-up converters is shown.
3 Photovoltaic Performance
For simulation issue, the SUNPOWER photovoltaic
panel type SPR-315E-WHT-D with 315 Watts peak
with conversion efficiency of 19.3% is used, where
the panel I-V and P-V performances are shown on
Fig. 3 for various irradiation rates [22, 23].
From Fig. 3, the main useful PV parameters
values (VMPP, IMPP and PMPP) are determined for
various irradiation rates at temperature of 25°C,
which are declared in Table 3.
Fig. 3 Panel I-V and P-V characteristics [17]
Table 3: Some important data specification for SPR-
315E-WHT-D at STC
Parameters
Irradiation
G (W/m2)
VMPP
(Vin)
(V)
IMPP
(Iin)
(A)
PMPP
(Pin)
(W)
100
51.75
0.575
29.75
250
53.26
1.443
76.86
500
54.32
2.881
156.50
750
54.60
4.324
236.10
1000
54.70
5.760
315.00
4 Simulation Results
The designed parameters of the modified SEPIC
system are given in table 2. The closed loop
Simulink model for the modified SEPIC converter
based solar system is shown in Fig. 4.
From Fig. 5, input voltage, current, and power
at full sun is 54.7 V, 5.817 A and 318.2 W
respectively. Similarly, from Fig. 6, output voltage,
current, and power is 152 V, 2.074 A and 315.1 W
respectively. Therefore, MSEPIC efficiency in % =
(Output Power / Input Power) ×100 = 99.03 %,
which is verified by [5].
WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS
DOI: 10.37394/23201.2022.21.17
Abdel-Karim Daud, Sameer Khader
E-ISSN: 2224-266X
163
Volume 21, 2022
Fig.4: The Closed Loop Simulink Model of the MSEPIC
Fig. 5 MSEPIC Inputs voltage, current, and power
versus time
Fig. 7 shows the output voltage stabilization at 60V,
90V, 120Vand 150V step voltage references at time
t=0, t=0.3, t=0.6 and t=0.9s respectively at constant
input voltage and constant input power (Pin 315
W).
Fig. 6 MSEPIC Outputs voltage, current, and power
versus time
Fig. 8 shows the input voltage, current and power
variation according to solar irradiation rates, where
it can be shown that:
- The input voltage which is corresponding to
MPPT values varies between 51.7V to 54.7
V at full sun.
WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS
DOI: 10.37394/23201.2022.21.17
Abdel-Karim Daud, Sameer Khader
E-ISSN: 2224-266X
164
Volume 21, 2022
- The input current varies between 0.57A to
5.7 A at full sun, and
- The input power varies between 29.7W to
315 W at full sun.
Fig. 7 Output voltage variation Waveforms of
MSEPIC at constant input voltage Vin = 54.7 V and
constant input power Pin = 315 W
Fig. 8 Input Voltage, current and power variation
waveform
While, figure 9 shows the output voltage, current
and power variation according to solar irradiation
rates, where it can be shown that:
- Irrespective of input voltage variation the
chopper maintains the output voltage at
constant value of 100V as a result of
applied PID controller.
- Voltage which is corresponding to MPPT
values varies between 51.7V to 54.7 V at
full sun.
- The load (output) current at varies
irradiation rates is determined mainly based
on the output voltage and load resistance
and cannot exceed the available input
current corresponding to instant irradiation.
For example, at full sun the input current is
5.7A, while the output current is 3.12 A
drawn by a load of Ro=31.2.
- At full sun the output power equals or a
little bit less than the input power with high
efficiency equal to 99.04%.
Fig. 9 Constant output Voltage with reference value
(Vref = 100 V) at various irradiation rates
WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS
DOI: 10.37394/23201.2022.21.17
Abdel-Karim Daud, Sameer Khader
E-ISSN: 2224-266X
165
Volume 21, 2022
Figure 10 shows the MPPT current and output load
current at various loading levels and irradiation rate,
where three loads are added t =0, 0.4 & 0.8 seconds
with values R1=140 , R2=30 , and R3=40 with
currents 0.71A, 3.33A, and 2.5A respectively.
It can be noticed that there is no limitation on the
output current while Iout ≤ Iinp at given irradiation,
while when Iout ≥ Iinp the load current is limited to
the input current value at given irradiation .
Fig. 10 Input current and output load current at
various loading levels and irradiation rate
6 Conclusions
Taking into account the built simulation model and
obtained results for MSEPIC converter the
following conclusions can be stated:
- MSEPIC converter allows wide range of
output voltage regulation at various MPPT
voltage according to available irradiation.
- The output voltage can be maintained
constant irrespective of input MPPT voltage
that varies according to available irradiation.
While the input voltage varies in the range
of 51.7 to 54.7, the output voltage can be
boosted till 150V and much more without
significant voltage stress across the
transistor switch and the load due to added
closed loop and PID controller.
- The input MPPT voltage variation becomes
significant when Photovoltaic panels are
connected in series forming strings, where
the closed loop system with added PID module
becomes important module in maintaining the
output voltage at fixed value irrespective of
irradiation rates.
- The drawnoutput current cannot exceed the
input current values, which in turns the
output power cannot exceed the available
input MPPT power at given irradiation,
where at full sun the maximum power that
can be extracted from the system is 315.1
W. In case of requesting additional power a
parallel and series connected panels that
forming solar arrays and strings can be
proposed.
References:
[1] S. S. Martin, A. Chebak and N. Barka,
"Development of renewable energy laboratory
based on integration of wind, solar and
biodiesel energies through a virtual and
physical environment," 2015 3rd International
Renewable and Sustainable Energy Conference,
Marrakech, 2015, pp. 1-
8.https://doi.org/10.1109/irsec.2015.7455086.
[2] G. M., Masters, ) Renewable and efficient
electric power systems, 2013, John Wiley &
Sons, Hoboken, New Jersey.
[3] Y. Mahmoud, W. Xiao, and H. H. Zeineldin,
“A simple approach to modeling and simulation
of photovoltaic modules,” IEEE Trans. Sustain.
Energy, vol. 3, no. 1, Jan. 2012, pp. 185–
186.https://doi.org/10.1109/tste.2011.2170776.
[4] S. Khader, A.K. Daud, “Boost chopper
behaviors in Solar photovoltaic system”, Smart
Grid and Renewable Energy, Volume 12,
March 2021, pp. 31-52, ISSN: 2151-481X,
https://doi.org/10.4236/sgre.2021.123003.
[5] A.K. Daud, S. Khader, "Comparison Analysis
between Various Boost Chopper
Configurations", International Journal of
Circuits and Electronics, Volume 7, February
2022, pp. 1-12, ISSN: 2367-8879.
[6] I. Alhamrouni, M. K. Rahmat, F. A. Ismail, M.
Salem, A. Jusoh, and T. Sutikno, "Design and
development of SEPIC DC-DC boost converter
for photovoltaic application", International
Journal of Power Electronics and Drive System,
vol. 10, no, 1, pp. 406-413, 2019.
WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS
DOI: 10.37394/23201.2022.21.17
Abdel-Karim Daud, Sameer Khader
E-ISSN: 2224-266X
166
Volume 21, 2022
[7] V. Samavatian and A. Radan, “Electrical Power
and Energy Systems”, 2014.
[8] M. Abu-Aligh, “Design of Photovoltaic Water
Pumping System and Compare it with Diesel
Powered Pump”, Jordan Journal of Mechanical
and Industrial Engineering, 2011, vol. 5, pp.
273-280.
[9] S. Khader, A.K. Daud, “PV-Grid Tie System
Energizing Water Pump”, Journal of Smart
Grid and Renewable Energy, 2013, vol. 4, pp.
409-418,
https://doi.org/10.4236/sgre.2013.45047.
[10] A.-K. Daud, M.M. Mahmoud, “Solar Powered
Induction Motor-Driven Water Pump Operating
on a Desert Well, Simulation and Field Tests”,
ELSEVIER, Renewable Energy 30 (2005), pp.
701–714,
https://doi.org/10.1016/j.renene.2004.02.016.
[11] A.-K. Daud, “Performance analysis of two
phase brushless DC motor for sensorless
operation”, WSEAS Transactions on Power
Systems, Issue 5, vol. 1, pp. 802-809, May
2006.
[12] K. Gangadharan, “A closed loop control of
modified SEPIC converter for renewable
applications”, IJREE-International journal of
research in electrical engineering, vol. 03, no.
02, pp. 7-12, 2016.
[13] S.J. Chiang et al.,“Modeling and Control of PV
Charger System With SEPIC Converter”, IEEE
Trans. Ind. Electron., vol. 56, no. 11, pp. 4344–
4353, Nov. 2009.
https://doi.org/10.1109/tie.2008.2005144.
[14] S. Kumar, R. Kumar, N. Singh, “Performance
of Closed Loop SEPIC Converter with DC-DC
Converter for Solar Energy System”,
Conference Paper, March 2017IEEE,
DOI:10.1109/ICPCES.2017.8117668.
[15] R. Arulmurugan, N. Suthanthira Vanitha,
“Optimal design of DC to DC boost converter
with closed loop control PID mechanism for
high voltage photovoltaic application”,
International Journal of Power Electronics and
Drive System, vol. 2, no. 4, pp. 434- 444,
December 2012.
[16] Y. Li, K. H. Ang, and G. C. Y. Chong, “PID
control system analysis and design”, IEEE
Control Syst. Mag., vol. 26, no. 1, pp. 32–41,
2006.
[17] J. E. Salazar-Duque, E. I. Ortiz-Rivera, and J.
Gonzalez-Llorente, “Analysis and non-linear
control of SEPIC dc-dc converter in
photovoltaic systems“, IEEE Workshop on
Power Electronics and Power Quality
Applications (PEPQA); 2015, pp.1–9.
[18] M. Vujacic, M. Hammam, M. Sandvik, and G.
Grand, “Analysis of DC-Link Voltage
Switching Ripple in Three-Phase PWM
Inverters”, Energies 2018, vol.11, no. 2; pp.
471-485. https://doi.org/10. 3390/en11020471.
[19] M. H. Rashid, Power Electronics, Devices,
Circuits, and Applications. 4th edition, Pearson
Education Limited 2014, ch.5, pp. 234-303.
ISBN97800-13-3125900.
[20] D. Zhang, “AN-1484 Designing A SEPIC
Converter” Texas Instruments, Application
Report, SNVA168E–May 2006–Revised April
2013, pp 1-10.
[21] K. Singh, A.N. Tiwari, K. P. Singh,
Performance Analysis of Modified SEPIC
Converter with Low Input Voltage, IJECT Vol.
3, Issue 1, Jan. - March 2012, International
Journal of Electronics & Communication
Technology, Pp: 21-25, ISSN : 2230-9543 .
[22] SUNPOWER Datasheet, SPR-315E-WHT-D.
http://www.solardesigntool.com/components/
module-panel-solar/Sunpower/21/SP-R-315E-
WHT-D/specification-data-sheet.html.
[23] Matlab and Simulink, The Mathworks, Inc.,
VersionR2016b, http://www.mathworks.com
WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS
DOI: 10.37394/23201.2022.21.17
Abdel-Karim Daud, Sameer Khader
E-ISSN: 2224-266X
167
Volume 21, 2022
Contribution of Individual Authors to the
Creation of a Scientific Article (Ghostwriting
Policy)
The authors equally contributed in the present
research, at all stages from the formulation of the
problem to the final findings and solution.
Conflict of Interest
The authors have no conflicts of interest to declare
that are relevant to the content of this article.
Creative Commons Attribution License 4.0
(Attribution 4.0 International, CC BY 4.0)
This article is published under the terms of the
Creative Commons Attribution License 4.0
https://creativecommons.org/licenses/by/4.0/deed.en
Sources of Funding for Research Presented in a
Scientific Article or Scientific Article Itself
No funding was received for conducting this study.
