Abstract. This paper proposes an improved generalized

physical model for PV cells, panels and arrays modelling taking into the

account the behaviour in the Direct and the reverse mode biasing. The Enhanced

model, named IDRM model, shows actually how the shot circuit current behaves

according to the variation of both temperature and irradiation. Due to its

easier implementation. This proposed model can be is useful power electronic

systems. Existing PV physical models were no problems for simulating influence

of irradiation changes on the short circuit current but for temperature changes

influences could not be visualized. The developed model was tested on a

marketed PV panel and it gives a satisfactory results compared with those shown

on the manufacturer datasheet.

Keywords.

Photovoltaic

cells, Photovoltaic panels, PV cell/panel simulations, Direct and reverse mode

modeling, IDRM Model, I-V characteristics, Solar Irradiation.

INTRODUCTION

The efficiency of photovoltaic panels depends on the health

of the basic element that is the PV cell. PV cell can operates in the first

quadrant of the I-V characteristics as generator or in the second one as

receiver. In this last operating mode the PV cell imposes its functioning

against the others PV cells in the same string. Shadow as example conducts the

PV cell when shaded acts as load, consumes power delivered from other cells and

its temperature rises allowing appearance of hot spot heating 1-6. Therefore,

the authors in 7 have proposed a DRM model which is able to produce I-V

characteristics in both direct and reverse operating mode according to the experiments

made on the reverse mode biasing of 60 polycrystalline silicon cells.

References 8-9 were proposed a model based on a transistor model.

These proposed models, except the DRM model; do not take

into account the reverse operating mode. DRM model reproduce practically the I-V behaviour of PV cells, PV panel and PV

array according to the irradiation and the temperature changes. But the

influence of the temperature variation is not visible on its I-V

characteristics. In this proposed physical model, we present an improved DRM

model for PV cells/panel/array modelling named IDRM.

The basic idea for thinking about a new proposal named DRM

model for PV modelling is coming from testing what about 60 polycrystalline PV

cells in the reverse mode biasing. Experimental results of current vs voltage

of these 60 PV cells reverse biased were shown in Fig .1.

FigURE 1. Experimental I-V curves of 60 polycrystalline

PV cells in the reverse mode biasing.

From this figure, it important is to note the presence of a

huge discrepancy in the behaviour of the PV cells. We note also the appearance

of two avalanche voltages on the reverse mode around -5V and -14V. These

results conduct the authors in 7 to propose the initial DRM model illustrated

in Fig .2 and which is implemented under Orcad/Pspice as shown in Fig .3.

FigURE 2. The DRM model proposed in 7.

Fig URE 3. The DRM model of 7 implemented under

orcad/pspice.

Improved DRM model for PV cells

modelling

Figure 4 show the layout of the improved DRM model for PV

cells modelling proposed in work. This model take into account simultaneously

of the variation of the photocurrent the short circuit current. The principle contribution

in this model is the adding of the diode (D384) to the previous model presented

in Fig .3. This added diode is able to reproduce perfectly the influence of

temperature variation on the photonic current on the I-V characteristics.

FigURE 4. Layout of the improved physical DRM for PV

cell modelling.

To test its effectiveness, this improved model has been applied to a PV cell modelling, with the

following step variation of temperature: -10, 0, 25, 50, 70, 85 and 100 °C. Fig

.5 shows the obtained simulation.

Figure 5. I-V characteristics of a PV

cell under influence of temperature changes by applying the improved DRM model.

From Fig .5, one can remark that the increasing of

temperature causes a decrease simultaneously on the open circuit voltage and

the maximum power of the PV cell and causes also an increasing of the short circuit current,

which represents the photonic current image. Due to the temperature increasing,

it is clear that the short circuit current changes from 1.5 to 1.6 amps for the

entire region that the PV cells behaves as a DC power current supply.

Application of the improved DRM

model on the shaded marketed PV panel

The BP solar module BP350J used in simulation is a 50W PV

panel composed by two parallel of 19 polycrystalline silicon PV cells strings

connected in series. The open voltage value

is 21.8v under STD operating conditions and produce a short current of

3A. The MPP is about (2.9A, 17.5v) and can produce 50 Watts. Only one terminal

by-pass diode mounted for its protection against hot spots. The I-V

characteristics, under temperature variations, as provided by manufacturer are

shown in Fig .6.

Figure 6. Influence of temperature variations on the

I-V characteristics of PV BP solar BP350J from manufacturer datasheet.

In order to show the influence of both shadow and

temperature changes, we have partially shaded the entire surface of one PV cell

in the panel and varied the temperature with the same manner as in Fig .5. The

model of the simulated PV panel implemented under Orcad/Pspice software was

built by associating the PV cell model according to its configuration presented

in its datasheet.

Simulated results of I-V and P-V curves due to the

temperature variations were presented in Figs .(7-8) respectively.

These figures show that the temperature diminution causes an

increase in the peak power and the shadow effect is visualized by the presence

of knees in the I-V curves and a local maxima in the P-V curves. The influence of

the temperature changes on the short circuit current and on the open voltage

circuit is also observed in Figs .(7-8) with a good reproduction of the values

indicated in Fig .6. In the simulated model, the temperature influence is

estimated by a value equal to: 0.04545 mA/°C. So, the photonic current is affected by a value

equal to: 0.045%/°C which is nearby of the value mentioned by the manufacturer

datasheet. This result proves that the new proposed IDRM model is correct.

Figure 7. Influence of the

temperature variations on the I-V characteristics of the shadowed PV BP solar

BP350J simulated with IDRM and accompanied with a zoom around the short circuit

current.

FIGURE 8. Displacement

of the MPP on the p-v characteristics of the BP solar BP350J panel under

partial shadow and temperature changes.

Conclusion

In this work, a new general improved physical model for PV

cells, panels and arrays operating in both direct and reverse biasing modes is

proposed. The new model, named IDRM, is based on the use of a conventional one

or two diodes model for PV modelling and experiments performed on

polycrystalline PV cells operate in the reverse biased mode. The IDRM model is

able to reproduce the influence of environmental variables (temperature and

irradiation) on the I-V and P-V characteristics in both the first and the second

quadrant of the operating modes. Really, the photonic current and as a result the

short circuit current are affected by the temperature variations. Noting that this

fact is taken in consideration in the proposed model. To prove the validity of

the proposed model, the degree of the temperature influence on the photonic

current is compared to the I-V curves of a marketed panel provided by a manufacturer.

Noting that, the shadow defect is considered in the IDRM model and applied to

the simulated marketed panel.