Irradiation and Temperature effects on Modified SEPIC Converter
Performance for PV Systems
ABDEL-KARIM DAUD, SAMEER KHADER
Department of Electrical Engineering
Palestine Polytechnic University (PPU)
P.O. Box 198, Hebron
PALESTINE
Abstract: - The changing position and nature of the sun due to changes in ambient temperature and irradiance
level throughout the day is the main difficulty with photovoltaic (PV) systems. This leads to fluctuations in
power levels. Therefore, maximum power point tracking (MPPT) under these conditions is the main challenge.
This paper proposes a new approach for directly operating at the maximum power point (MPP) at any value of
solar irradiation and cell temperature without applying further mathematical processing to operate at that point.
This technique is applied to a PV system containing a high-static-gain modified single-ended primary coil
MSEPIC converter, which is characterized by high efficiency and high gain voltage. The performance of this
converter is obtained with respect to load and output voltage variation under different climatic conditions in
Hebron, Palestine. Solar panel type LG450N2W-E6 is selected as the PV generator in this system with 450 W
at 41.1 V at MPP. The proposed model is analyzed and simulated in Matlab/Simulink, and m-file code.
Key-Words: - Modified SEPIC Converter, PID Controller, Photovoltaic Source, PWM, MPPT.
Received: August 17, 2022. Revised: August 6, 2023. Accepted: September 9, 2023. Published: October 4, 2023.
1 Introduction
Renewable energy (RE) resources are being
progressively integrated into power systems to
support a continuous increase in power generation
due to the limitation of fossil fuel supply and to
reduce negative environmental impacts [1]. Among
the RE resources, the energy from the solar
photovoltaic (PV) effect can be considered the most
necessary and sustainable resource due to its
ubiquity, large quantity, and sustainability [2].
This PV system consists of solar panels, a DC
chopper, a smoothing unit, and a power
management unit for operating the generator at
maximum extracted power, called the Maximum
Power Point Tracker (MPPT) [3, 4]. Usually,
photovoltaic systems operate at a point near the
point of maximum power, known as MPP, in order
to obtain maximum system efficiency.
Therefore, the need for an MPPT system is an
essential stage in the energy conversion procedure
to obtain maximum energy with reduced switching
losses of the chopper and minimized overall system
losses at high efficiency. There are several MPPT
techniques used to track the maximum power of the
PV system, such as Perturb and Observation (P&O),
Incremental Conductance (IC), and Fuzzy Logic
Control (FLC) [5, 6]. The P&O method uses
iteration procedures for reaching maximum power at
the knee of power performance. The IC method uses
a similar iteration process that uses the change in
current rather than the change in power with respect
to the voltage, while the FLC method with artificial
intelligence implementation is used very
successfully when applied for MPP searching and
the sliding mode control.
The P&O approach is the one that is most
frequently utilized among the others because it is so
straightforward. Despite this, this approach
performs well in conditions when the sun's
irradiance and temperature change slowly over time.
It takes a long time and cannot follow the MPP
rapidly, which results in power loss before
achieving the MPP value due to oscillation and
iteration, as well as voltage stress being generated
across the chopper switch as a result of duty cycle
change.
In this paper, the simulation model is built for
direct detection of the maximum power at any value
of solar irradiation and temperature during the
daytime without oscillation around the MPP for a
modified single-ended primary-inductance DC-DC
Converter (MSEPIC), as shown in Fig. 1 [7-9].
Closed-loop feedback control with a PID controller
based on a triggering system is developed for the
MSEPIC converter to maintain a constant output
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DOI: 10.37394/232016.2023.18.16
Abdel-Karim Daud, Sameer Khader
E-ISSN: 2224-350X
152
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voltage, as shown in Fig. 2. The proposed model is
analyzed and simulated in Matlab/Simulink, and m-
file code.
Fig. 1: Modified SEPIC Converter [14]
Fig. 2: Block diagram of closed loop MSEPIC
converter
2 Mathematical Modelling
For the simulation issue, the solar panel type
LG450N2W-E6 with 450 watts peak and a
conversion efficiency of 20.5% is used, and the
panel I-V and P-V performances are shown on Fig.
3 for various irradiation rates [10]. From Fig. 3, the
main useful PV parameter values (VMPP, IMPP and
PMPP) are determined for various irradiation rates at
25 °C, which are declared in Table 1 [11].
Table 1. PV data at MPP for LG450N2W-E6
G(W/m2)
Para-
meters
1000
750
500
250
100
VMPP, V
41.8
41.70
41.52
40.68
39.16
IMPP, A
10.79
8.07
5.37
2.69
1.08
PMPP, Watt
451
336.4
223
109.4
42.29
a)
b)
Fig. 3: Characteristics solar panel type LG450N2W-
E6: a) I-V and b) P-V characteristics
However, this I-V curve of the PV array relies on
irradiance and temperature conditions. When the
irradiance increases with constant temperature, the
PV current also increases in direct proportion, with
negligible effect on the PV voltage. Similarly, if the
temperature increases with constant irradiance, the
PV voltage decreases substantially while the PV
current increases slightly. Hence, a tracking
algorithm known as MPPT is needed to regulate the
PV panel output, which varies non-linearly with
irradiance, temperature, and load.
2.1 Voltage and Power Equations
Let’s start with the data specification related to
the solar panel type LG450N2W-E6, where the
voltage is displayed in Fig. 4a with an interpolated
equation stated in (1), while the power performance
versus irradiation has a linear change and is
presented as a first-order equation (2) as shown in
Fig. 4b. It’s shown that the MPP voltage shows a
slight change when the irradiation varies from weak
to full sun. The interpolated voltage equation is
presented as follows:
(1)
where
and
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.
While the power equation can be stated as follows:
(2)
2.2 Solar Irradiation Calculation
In order to determine the maximum power at a
given irradiation, it is necessary to determine the
daily solar irradiation at any time of the year [4, 12,
13] as follows:
(3)
where tsr, tss, Td are the sunrise time, sunset time,
and day duration, respectively. These parameters are
briefly described in [12–14]. Gmax is the solar
radiation at noon.
2.3 Effect of temperature
For a given daily temperature change at any time
of the year, with discrete values or an interpolated
equation, and taking into account the effect of
irradiation changes according to (3), the general
equations of the MPP voltage and power are
expressed as follows:
(4)
(5)
where
VMPP (STC) and PMPP (STC) are the rated panel
voltage and power at full sun and standard test
conditions. The obtained results related to voltage
and powers at MPP are displayed in Fig. 4 for
various irradiations of the LG450N2W-E6 solar
panel type.
a) Voltage at MPP
b) Power at MPP
Fig. 4: Voltage and power at MPP for various
irradiations of solar panel type LG450N2W-E6
3 Simulation Results and
Discussion
The derived equations for solar irradiation,
power, and duty cycle at MPP are simulated using
the MATLAB/SIMULINK platform for MSEPIC,
as shown in Fig. 1. The built-in simulation program
is illustrated in Fig. 5.
The proposed MPP approach is now applied to real
measured data taken from a weather station installed
over the roof top of the university buildings, where
the irradiation rate for May 23, 2022, is shown in
Fig. 6, while the real temperature measured for the
same date is shown in Fig. 7 [15].
The generated equations for irradiation (GT) and
temperature (Tt) are stated in (12) and (13) as
follows:
(6)
(7)
where
,
and
.
Fig.6: Measured real irradiation
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Fig. 5: Matlab/ Simulink Model
Fig.7: Measured real temperature
After generating approximated equations for both
irradiation and temperature, the MPP voltage and
power [9] are calculated according to (4) and (5)
and displayed on Fig. 8, taking into account the
effect of temperature change for performance test
conditions.
It can be noticed that the MPP voltage is higher
than that of STC because the maximum temperature
for that day (May 23rd, 2022) was detected at
around 20°C at noon time. The MSEPIC chopper
duty cycle is expressed according to (8) in order to
generate PWM pulses capable of regulating and
boosting up the MPP voltage according to the
reference values [9]:
Fig. 8 MPP voltage at various irradiation &
temperature
(8)
Figure 9 shows the continuous character of solar
irradiation and temperature changes on May 23,
2022, taken from the weather station installed over
one of our university buildings. A duty cycle is
generated, and MPP power is treated as input to the
chopper parameters, while the output parameters are
reference voltage, load voltage, current, and output
power under various loading rates.
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Fig.9: Main Input -output performances of the
proposed system
4 Conclusion
The proposed new approach presents a simple
and fast-responding method to determine the MPP
voltage and power at continuous changes in
irradiation and temperature, while till now, proposed
MPPT methods did not take into consideration the
continuous change in temperature during irradiation
changes.
Furthermore, applying such an approach reduces
the voltage stresses and oscillations across the
chopper elements, leading to better efficiency and
voltage stability.
The proposed approach used the PV key
specification provided by the panel’s manufacturer
at different irradiation rates, where a continuous
power function was derived for MPP points without
running any kind of iteration procedure.
The proposed model validation was verified based
on the real measured data for solar irradiation and
panel temperature.
For future research, a hardware prototype model
should be built and experimentally implemented in
order to practically validate the discussed analytical
and simulation results. This should be the main
objective of the upcoming article.
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DOI: 10.37394/232016.2023.18.16
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Contribution of Individual Authors to the
Creation of a Scientific Article (Ghostwriting
Policy)
Abdel-Karim Daud has performed the literature
review, carried out the mathematical model,
analyzed the numerical results, discussed the results,
drawn a conclusion, and finalized the paper.
Sameer Khader implemented the SIMULINK model
and presented building performances, conclusions,
and paper preparation.
Sources of Funding for Research Presented in a
Scientific Article or Scientific Article Itself
No funding was received for conducting this study.
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
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