Utilization of MOSFET transistor as an electronic load to trace I-V and P-V curve of a solar panel

To understand the electrical behavior of a photovoltaic panel, it is necessary to know the characteristic Ipv = f(Vpv). The best way to obtainthis I-V curve is to use a variable resistor. This paper proposes a new and simple technique based on a MOSFET transistor as a variable load, which whose gate voltage is controlled by an RC filter from the Arduino. A comparison under standard temperature and illumination conditions between the manufacturer's datasheet with the simulation by MATLAB/Simulink on the one hand, and on the other hand between the manufacturer's datasheet with the experimental data for the evaluation of this technique that has been performed. Nomenclature a0 Temperature correction coefficient for current (°C). b0 Temperature correction coefficient for voltage (°C). G Solar irradiance on module plane (W/m). Iph Photo-generated current (A). Ipv Solar cell terminal current (A). ISC Short circuit current (A). I0 Reverse saturation current (A). I0i Reverse saturation current of diode in conventional model (A). n1 First diode ideality factor NS Cells number connected in series. Nsh Cells number connected in shunt. PV Photovoltaic. RS Series resistance (W). Rsh Shunt resistance (W). STC Standard Test Conditions (G0 = 1000 W/m,T0 = 25 °Cand AM = 1.5). T Cell or Module operating temperature (°C). Ta Ambient temperature (°C). ∆T Temperaturedifference : =T T0 (°C). VOC Solar cell open-circuit voltage (V). Vpv Solar cell output voltage (V). _______________________________ * Corresponding author:a.asbayou@gmail.com © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). E3S Web of Conferences 229, 01021 (2021) https://doi.org/10.1051/e3sconf/202122901021 ICCSRE’2020

Abstract. To understand the electrical behavior of a photovoltaic panel, it is necessary to know the characteristic I pv = f(V pv ). The best way to obtainthis I-V curve is to use a variable resistor. This paper proposes a new and simple technique based on a MOSFET transistor as a variable load, which whose gate voltage is controlled by an RC filter from the Arduino. A comparison under standard temperature and illumination conditions between the manufacturer's datasheet with the simulation by MATLAB/Simulink on the one hand, and on the other hand between the manufacturer's datasheet with the experimental data for the evaluation of this technique that has been performed.

Introduction
There is a lot of research on the measurement of the I-V characteristic of PV modules under different operating conditions with a variety of methods [1].The most and easy one is by using a variable resistor in series with the PV generator as a load.
Another way to plot the I-V curve of a PV generator, is the capacitive load. Some authors [2][3][4] have used capacitors as an automatic variable load to change the voltage V pv and the current I pv during the capacitor charging operation, which allowed them to obtain the I-V characteristic of the PV generator.
Kuai and al. [5] proposed a device based on an electronically variable load using the APL501J MOSFET transistor, which covers the full range of the I-V characteristic of PV panels in a very short time.
This paper proposes the design of a bench for tracing the I-V and P-V characteristics of PV panels based on a MOSFET(IRF740) transistor controlled by Arduino via a DC signal, which is injected into a simple RC filter to vary the V GS control voltage in a progressive way (figure 1). The system is analyzed and experimentally tested under standard temperature and lighting conditions using an SX330J solar panel.
This paper is divided into 5 sections: The first one gives the introduction of methods used to obtain the I-V characteristic of a PV panel. Then in section 2, we expose a brief description of the MOSFET by presenting the electrical behavior I D =f(V DS , V GS ). Then, section 3 gives details on the measurement bench, and section 4 summarizes and discusses the results obtained. We will conclude this article with a conclusion and the perspectives of this work.

Theoretical background of MOSFET as an electronic load
The MOSFET is a device that function as an electronically controlled load that change the operating point of a PV generator over the full range of the I-V characteristic [6]. When a control voltage is applied to its grid, it generates a fast and variable PV output current from 0 to I sc (A),and a variable output voltage from V oc to 0 (V).
The speed of the scan is made as fast as possible to reduce the effect of variation in illuminance and temperature fluctuations caused by cloud movement or other weather changes [7]. In this way, all points drawn on the I-V curve are captured under the same weather conditions in a very short time. The fast scanning also protects the MOSFET from superheating [8]. Figure 1 shows the variations of the I D current as a function of the V DS voltage and the value of the control voltage V GS . The three operating regimes of the MOSFET that describe the relationship between I D as a function of V GS and V DS are [5]: Blocking mode if : Ohmic mode if: Where K is the constant of the device and V th is the transistor control threshold voltage. By changing the value of V GS in an appropriate range, the measurement points can scan between I SC and V OC. . According to Figure 2: (4) I pv The electrical current of the PV panel according to the 1-diode model (Figure 2), Therefore: By application of the mesh law, the I sh current in the shunt resistor is expressed by: (8) The diode current I di is given by And: is the thermal voltage of the module.
I 01 are the saturation current of the one diode. n 1 are the ideality factors. So, the current supplied by the solar cell in 1 diode model is given by the following relation [11]: 1 (11) 3 Materials and methods A basic circuit with a MOSFET as electronic charge is shown in Figure 3  Arduino generates a continuous signal through pin3, then this signal is injected to an RC filter, to vary the control voltage of the V GS MOSFET in a progressive way, which also requires the R DS resistor to change progressively (figure 1).
The proposed test bench for real-time characterization of the PV panel is realized using an Arduino UNO board as a data acquisition control, and transfer unit (I PV and V PV ) to a computer via the PLX-DAQ tool [12].
The values of current intensity I pv and voltage V pv of the PV panel are measured using Arduino compatible current and voltage sensors, the temperature of the PV panel is measured using a thermocouple, while the irradiance is evaluated by using the FI 109SM Solar Meter [13], the panel used in this characterization is of polycrystalline type SX 330J, the electrical characteristics of which are summarized in Tables 1. is a technique used to control an analog circuit via the digital output, using two functions, either analogWrite or digitalWrite. A PWM (Pulse Width Modulation) signal is an electrical voltage with a maximum amplitude of 5V, a variable duty cycle and a constant frequency [15].
In this circuit (Figure 3), the signal delivered to control the MOSFET(IRF740) is amplified by a DC/DC booster, shown in Figure 4.  [16] The signal at the output of DC/DC Boost Converter, is injected into a RC filter, which R=110 ± 5.5 Ω [17], and capacitor C = 4.7 ± 0.94 mF [17], connected in series to change the control of the MOSFET, and finally plotted the I-V and P-V characteristic of the solar panel.
According to Figure 5, the expression of the V GS (t) command voltage of MOSFET is given by: . 1 (12)  In this manipulation the signal delivered by Arduino with duty cycleα=100%, we can observe that for high R and C values the time required to plot the I-V characteristic increases, for R=220Ωand C=2.2mF the time of the trace is 0.18sec, while R=440ΩandC=4.7mF tracing time is 0.69sec, but on the other hand when R and C increases the number of points displayed by the Macro-Excel PLX-DAQ increases.

I-V and P-V characteristics of the PV module
Using the electronic circuit described in Section 3 (Figure 3), the I-V and P-Vcurves were traced for the SX 330J polysilicon solar panel, a comparison between the datasheet of the manufacturer's with the simulation by MATLAB/Simulink on the one hand was made, and on the other hand between the datasheet of the manufacturer's with the experimental data. The small deviation observed between the experimental results and the datasheet of the SX 330J polycrystalline panel is caused by several factors; such as the fluctuations of the illuminance G, of the resistor R with temperature variations but also, the effect of the ohmic contacts between the cells of the PV panel and the rest of the mounting circuit.

Conclusion and perspectives
In this paper, we have proposed and realized a simple low-cost instrumentation solution to provide the I-V and P-V characteristics of the PV panel based on a MOSFET(IRF740) transistor controlled by Arduino via a DC signal. The whole system is composed of simple components, less complicated, less expensive and above all widely used in laboratories. The acquisition is realized through low-cost current and voltage sensors in communication with an Arduino type electronic board. The data is then reported in the Excel spreadsheet in real time using the Macro-Excel PLX-DAQ Spreadsheet interface. Experimental tests on a PV module type SX330J were performed under real operating conditions. The experimental results agree with the theoretical analysis carried out for the development of this