40220130405018 2

International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING &
ISSN 0976 – 6553(Online) Volume 4, Issue 5, September – October (2013), © IAEME
TECHNOLOGY (IJEET)

ISSN 0976 – 6545(Print)
ISSN 0976 – 6553(Online)
Volume 4, Issue 5, September – October (2013), pp. 173-183
© IAEME: www.iaeme.com/ijeet.asp
Journal Impact Factor (2013): 5.5028 (Calculated by GISI)
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IJEET
©IAEME

THE AUTOMATIC VOLTAGE CONTROL DEVELOPED FOR THE
MAXIMUM POWER POINT TRACKING OF A PV SYSTEM
Mohammed SEDDIK1, S. Zouggar1, F.Z.Kadda1,
1

A. Aziz1,

M.L.Ahafyani1,

R.Aboutni1

Higher Institute of Technology EEML-BP. 473 Hay El Qods-60000 - Oujda, Morocco

ABSTRACT
The output power of the Photovoltaic generator is influenced by the climate changes, Such as
the temperature and the illumination. So, a maximum power point tracking is required to optimize
the performance of the PV system. Several MPPT techniques have been proposed in the literature,
among them we find the voltage control technology (the optimal output voltage of the PV generator
is weakly depending on the illumination), which has a major drawback; it neglects the effect of the
temperature on the PV generator. In this article, we present the Automatic Voltage Control
developed (AVCD) that takes into account the changes in the temperature. The PV model integrating
the AVCD and the Power Interface DC-DC Boost are implanted in the environment ORCAD /
PSPIC. The simulation and experimental results obtained are in very good agreement and show
excellent performance.
Keywords: Hybrid System, Photovoltaic System, Automatic voltage control, Boost Converter.
1.

INTRODUCTION

This work is a part of the energy management and the optimization of a hybrid system (HS),
that combines a photovoltaic generation system (PV) and wind turbine which are coupled via a DC
bus associated with a battery bank (figure1) [1]-[12]. With the HS, we can ensure the permanent
energy required by the load, by overseeing the power produced by the hybrid system (PV & Wind
Energy) and the level of charge and discharge of the battery. Generally, the optimization of a hybrid
system involves the optimization of the PV system and the wind turbine. So the final goal is to
provide a control laws to optimize the elements constituting the hybrid system.

173


Fig.1. Photovoltaic & Wind Hybrid System
In this work, we are particularly interested in the photovoltaic system to operate it under the
optimal conditions.
The PV power has non-linear characteristics; these characteristics have a Maximum Power
Point (MPP) depending on the illumination and the temperature. So, it is imperative to track the
maximum power of the PV. This tracking is usually done using adapters that are interposed between
the generator and the receiver. This adapter is a static converter controlled using laws which are
known by the name MPPT. Several MPPT techniques of PV systems have been proposed as the
perturbation and observation (P & O) [1, 2, 3], the incremental conductance (IncCond) [4,5], the
method of short circuit current (Isc ) [6], the method of open circuit voltage (Voc) [7], and the
subservience control voltage technique of PV generator [8], It maintains the terminal voltage of the
PV generator at its maximum value because the optimum voltage depends very little of the
illumination, therefore the output power is then maintained to the optimum one. This command was
attractive because of its simplicity of implementation and its lower cost. But, it has a major
drawback; it neglects the effect of the temperature on the PV generator, knowing that the temperature
is an important parameter in the behavior of the photovoltaic panel.
Indeed, if the temperature increases, the maximum power decreases, the MPPT point moves
to the left and the open circuit voltage (Voc) decreases, as shown in figure 2.

Fig.2. Evolution of the characteristic P (V) of the PV according to the temperature
In this article, we present theAutomatic Voltage Control developed (SCV,) which takes into
account the temperature changes. To do this, we have added a digital potentiometer to the SCV,
which tracks the maximum power point even if the temperature varies. The simulation results
(ORCAD / PSPICE) obtained show that CDAT has good results and that the controller is effective
and robust.
174


2.

THE CHARACTERISTICS OF THE SOLAR PANEL

The Mitsubishi UD180MF5 commercial PV module installed in our laboratory LGEM was
selected in this study [9, 12]. The characteristics of the PV module given by the manufacturer to the
temperature 25 C shown in Table 1 plus the model of the solar cell were used in the simulations to
obtain the output characteristics of the solar panel [10, 11].
Parameter

Value

Number of cells

50in series

Maximum power rating

80Wp

Open circuit voltage (Voc)

30.4V

Short circuit current (Isc)

8.03A

Maximum power voltage (Vmp)

24.2V

Maximum power current (Imp)

7.45A

TABLE 1: Electrical Characteristics of the mitsubishi UD180MF5 PV module [9]
The electrical characteristics of the PV module are represented generally by the current in
function of the voltage (I-V) and the power according to the voltage (P-V). The curves of Figures 3
and 4 show the characteristics of the PV module for different intensities of solar illumination. It
should be noted that each curve has a maximum power point which is the optimal point for the
effective use of the panel. This depends on the values of the temperature and the illumination.
10A

200W

8A

150W

6A
100W

4A
50W

2A
0A

0W
0V

10V
20V
W(V1)
V_V1

0V

30V

10V
20V
I(V1)
V_V1

30V

a) Characteristic P-V
b) Characteristic I-V
Fig.3. Characteristics of the PV module referenced by UD180MF5
In Figure 4 we represent the influence of the temperature on the characteristic of the PV for
an illumination of 1000W/ m² and deferent temperature values (60 °C, 25 °C, 0 °C).

175


Fig.4. Characteristics P-V of the PV module referenced by UD180MF5
3.

DESCRIPTION OF THE PROPOSED SYSTEM

The Figure 5 shows the block diagram of a photovoltaic chain that feeds a resistive load
(Rs).which is formed by the following elements: a photovoltaic generator (PVG), a quadripole
adaptation which is an energy converter of type booster (boost) and a tracking device (the Automatic
Voltage Control developed (MPPT)) [8]. Boost converter has the role of raising the voltage at the
output and regulating the voltage at the terminals of the PVG at a fixed value, by adjusting the duty
ratio. The most important function of the MPPT which represents the main objective of the present
work is to adjust the output voltage of the panel at a constant value (24.2V), so that the panel
provides the maximum power to the load.

Fig.5. Chain of a photovoltaic conversion system with CS controlled by a control voltage
4.

DC-DC CONVERTER (BOOST)
The basic circuit topology of the Boost DC-DC is shown in Figure 6.

Fig.6. Boost Circuit

176


The specifications is set for a voltage across the load less than 100 V and with a residual
ripple in the output voltage does not exceed 10 mV and the input does not exceed 100 mV.
The chopping frequency is set at 20 KHz. The duty cycle (eq 1) is defined as the ratio
between the duration of the high period of the signal (ton) and its period T= ton+toff.
D=

t on
t
= on
t on + t off T

(1)

Equation 2 of the duty ratio gives the control law which is produced by the MPPT system to
operate the PV at its maximum power point for a given load, illumination and temperature.
ܸ‫ ݏ‬ൌ
5.

ܸ‫ݒ݌‬
1െߙ

ሺ2ሻ

THE PROPOSED MPPT CONTROL

The diagram of the figures 7 and 8 shows the topology of the Automatic Voltage Control
developed. The latter generally includes: a temperature sensor, a digital potentiometer which varies
the picked voltage value of the PV, a differential amplifier which calculates the error between the
voltage taken from the PV and the reference voltage, an inverting operational amplifier 10 for
amplifying the error, a PI corrector, an integrator RC, and a comparator which compares the voltage
to a triangular wave signal to generate a pulse width modulated signal (PWM) (figure 8). To measure
the temperature, we used the open circuit voltage which gives a picture of the temperature. The
digital potentiometer used contained generally the integrated circuit CD4051 which is an analog
switch of type 1 position among eight (figure 7). In our case, we have used a bridge resistor divider
at several points, consisting of nine resistors placed in series. Then, the temperature of the analog
switch is used for connecting to an intermediate point of the resistor network. Finally, we have the
equivalent of a potentiometer. The resistance values are fixed to vary the value of the terminal
voltage of the PV from 19.1V to 26.2 by one steps (1V).
PV

CD4051B

1
5
2
4

11
10
9
6

0

I/O2
I/O3
I/O4
I/O5
I/O6

A
B
C
INH

Temperature
Sensor

Fig.7. Digital Potentiometer

177

O/I

I/O7

V
EE

12

I/O1

V
DD

15

I/O0

7

14

16

13

3

AVC


Fig.8. Synoptic Diagram of the AVC
6.

SIMULATION RESULTS

6.1.

Without Digital Potentiometer
A first simulation of the PV system was conducted by varying the temperature from 25 ° C to
60 ° C. the figure 9 illustrates the variation of the output power and The terminal voltage of the PV.
Indeed, up to t = 1.5s, the temperature is 25 ° C, the input voltage fluctuates around 24V (fig.9.b) and
the power supplied by the PV oscillates around its optimal value (180W) (fig.9.a). At time t = 1.5s,
the temperature change (60 ° C-Voc = 27.1), the input voltage of the chopper still oscillates about
24V and the power delivered by the PV fluctuates around 130W (fig 9.a). Knowing that the optimum
power that corresponds to the temperature 60°C is 150W and the optimum voltage is 21.1V as shown
in the figure 4, it is noted that there is a loss of power of 20W.
250W

42V
36V

195W
30V
24V
130W
18V
12V

65W

6V
0W

0V
0s

0.5s

1.0s

0s

I(L2)*V(V_PV)

0.5s

1.0s

V(V_PV)
Time

Time

a) Power
b) voltage
Fig.9. : Power supplied by the PV and the terminal voltage of the PV with a temperature
variation of (25 ° C-60 ° C) for the illumination of 1KW / m²
6.2.

With digital potentiometer
The second simulation was performed for a MPPT controller containing the digital
potentiometer and for a temperature range from 25 °C to 60 °C and then at 0 °C. The figure 10 shows
the power produced by the PV and the terminal voltage of the PV. As we can see, up to time t = 1.5s,
the temperature is 25 °C, the voltage across the PV oscillates around 24V (fig 10.b) and the power
178


supplied by the PV reaches its optimum value (180W) (fig 10 a). As at time t = 1.52s the temperature
is set to 60 °C, and we note that the input voltage of the chopper fluctuates around 21.3V (fig 10.b)
and the provided power from the PV is 150W (fig 10.a). At time t = 1.5s, the temperature reaches 0
°C, we observe that the output voltage of the PV oscillates around 27.2V (fig 10.b) and the power
supplied by the PV is 200W (fig 10.a). Consequently, the command tracks the maximum power point
even if the temperature varies.
250W

35V
30V

200W
25V
150W

20V

100W

15V
10V

50W
5V
0W

0V
0s

Fig.10.

7.

0.5s
1.0s
V(V_PV)*I(I_pv)
Time

1.5s

0s

0.5s

1.0s

1.5s

V(V_PV)
Time

a)Power
b)Voltage
The power delivered by the PV and the terminal voltage of the PV with a
temperature change (25 °C / 60 °C / 0 °C)

EXPERIMENTAL RESULTS

In order to validate the simulation results we have realized the system of figure 5.the Figures
11 and 12 show the PV panels (UD180MF5) used and the tester bank. The different blocks of
photovoltaic (converter, AVCD control) were performed on test models as recorded in Figure 13.

Fig.11. PV installed in our laboratory [9]

179


Fig.12. Photovoltaic system used for experimentation

Fig.13. Boost converter with the CATD
We set the parameters of the MPPT control for regulating the voltage of the PVG to the
desired optimum value which varies from 19.1V to 26.3V. In this sites the optimal voltage of the PV
range from 19.1V (Voc = 25.1) to 24.1V (Voc = 30.1V) which corresponds to a variation of the open
circuit voltage (Voc) of 25.1V to 30.1 V. The different measurements are performed during a day
where the open circuit voltage is 27.4V (fig 14.c). This value corresponds to the optimal voltage
21.1V (fig 4). On figures 14, 15, 16, we reproduce the voltage and the current measurements at the
output and the input of the boost converter, as well as the signals controlling the switch of the
converter for a load of 20 . We can see that the AVCD command instantaneously converges the
photovoltaic system to the optimal conditions and all the electrical values oscillate around the
optimal values. We can see that the AVCD command instantaneously photovoltaic system converges
to the optimal conditions and that all electrical values oscillate around the optimal values. The input
voltage (output) of the converter oscillates around 21.13V (fig 14.a) and the output is 44.9V
(fig 14.b), and the duty cycle value oscillates around the value 0.5236 (fig16).

180


a)The voltage across the terminals of thePV

b)The output voltage of the converter

c) The open circuit voltage of the PV
Fig.14. The input (Vin) and the output voltage (Vout) of the converter and The open
circuit voltage of the PV

a)input
b) output
Fig.15.
The Current at the input and at the output of the converter

181


Fig.16.

Signal controlling the BOOST switch

From these results we can deduce the power delivered by the PV (Pe) and the power
consumed by the load (Ps). The calculated results are:
Pe= 123.39W

Ps=104.617W

On this test, the yield measured according to Equation 3 is 84.78% with a power supplied by
the PVG of 123.39W.
ηൌ

8.

Ps
Pe

CONCLUSION

In this paper, we validated in simulation and experimentally that the automatic voltage
control developed (AVCD) can follow the maximum power point of the PV generator even if the
temperature varies. It regulates the power delivered by the PV generator at its optimum value. The
different experimental results presented show a very good agreement with those simulated in
Orcad-Pspice. These results demonstrate the robustness and reliability of the proposed system.
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