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In this work, we conduct a study of modeling and simulation of a system in the context of renewable energy in general, and solar system “photovoltaic” in particular; also, the optimizing system adapted by DC-DC converters static. Then the influence of temperature and irradiance on the optimal parameters (Power of MPP, VMPP, ...) of a solar system is analyzed in a way to operate a PV generator at its maximum power. This system includes a photovoltaic generator, “Boost & Buck”, converter and a load. Modeling and simulation system (solar panel, DC-DC converter command and load) is obtained through Matlab-Simulink software.

The greater part of the energy consumed currently comes from the use of fossil fuels like oil, coal, natural gas or nuclear power. These resources become increasingly rare while the energy demands of the world amounted continuously. Since this form of energy covers a large part of the current energy production, it is necessary to find an alternative solution to take the relay. The constraint is to use a source of economic power and low emission as the protection of the environment has become an important point. Photovoltaic solar energy is the direct conversion of part of the solar radiation into electrical energy. This energy conversion is affected throughout photovoltaic cell based on a physical phenomenon called the photovoltaic effect, which is to produce a current when the surface of the cell is exposed to light. Science is naturally interested in the “renewable” resources. Photovoltaic solar energy is increasingly used in various terrestrial applications such as lighting and telecommunications [

The PV cell, also called solar cell, constitutes the basic element of the photovoltaic conversion. This is a semiconductor device that converts electric energy into light energy provided by an inexhaustible source of energy and the Sun. It exploits the properties of semiconductor materials used in the electronics industry: diodes, transistors and integrated circuits.

The photovoltaic effect is manifested when a photon is absorbed in a semiconductor material composed of doped p (positive) and n (negative), referred to as p-n junction (or n-p). Under the effect of doping, an electric field is present in the material permanently (like a magnet which has a permanent magnetic field) [

with

The characteristic curve of a PV cell represents the variation of the current which it produces as a function of the voltage at its terminals, since the short circuit (zero voltage corresponding to the maximum current product) till the open circuit (no current to a maximum voltage across the cell) [

The maximum power ^{2}, power ^{2} power

The optimum voltage ^{2} and around ambient temperature (25˚C): when the temperature varies from 10˚C, the voltage ranges from 4.2%. These results show that the voltage varies relatively little in the course of the day. Also, it is considered as a first approximation that the optimal operation of PV generator substantially corresponds to operation at constant optimum voltage

The coefficient of maximum power point MPP and the optimal voltage linking the measured quantities and optimal variables is not always accurately fixed and little vary with time as a function of aging. It depends in particular on temperature and sunlight as illustrated in

The chopper is a DC-DC converter for converting a DC power to a given level of voltage (or current) in a continuous energy to another level of voltage (or current). Use turns out necessary to store solar energy in batteries or to feed a continuous load equivalent circuit of the chopper is represented by

The boost converter is known by the name of voltage booster that can be represented by the circuit of

For the BOOST, the switch K1 is closed during the

From Equation (3), the conversion ratio of boost chopper is given in the following form:

And for the BUCK converter, the switch K1 is closed during the fraction

From Equation (6), the conversion ratio of buck chopper is given in the following form:

After resolution of equations by Matlab can be shown the

This is Equation (6) which shows that the buck converter is a step-down voltage because the output voltage of the converter equal to the input voltage by a coefficient which varies in the range [0,1] as illustrated in

Four demonstrate the role of converters Buck we used Matlab simulation software and we are taking (

After having the voltage input 300 V as shown in the

And to give several values of voltage as a function of duty cycle which shows the proportionality between the duty cycle and the input voltage and also to express the role of a Buck in

The output voltage of the chopper is not continuous but always be positive. When the time is quite low (frequency 100 - 1000 Hz) the load does not “see” the not slots, but the medium value of the voltage. We notice whatever the nature of the charge, we have

To show the role of converters boost we used Matlab software for the simulation and we take (

After the results in

We recall the definitions of the different yields and measurement conditions thereof. As a result, the overall yield of the conversion chain reflects all sources of losses over the entire PV chain.

The power received by a panel of area ^{2}) is equal to

We will take as a definition reflecting performance the maximum capacity of a GPV and quality of the electron-photon conversion of a solar panel noted

^{2}) is defined as the amount of solar electromagnetic energy incident on a surface per unit of time and area.

Duty Cycle | |||
---|---|---|---|

0.20 0.30 | 0.40 | 0.50 | |

62 89.1 | 118 | 148.5 | |

1.975 2.970 | 4.692 | 4.694 |

The power P effectively delivered by an PV generator depends more on the command used in the converter (MPPT voltage control, direct connection, ...). Performance of the operating point which place we note

P is the power available at the terminals of GPV.

And performance the converter noted

Unfortunately, more the converter is complex, plus its own performance noted

For these variables must be optimized solar system by intelligent controls (embedded system) to increase the efficiency and effectiveness of our system.

Called form factor FF, also called factor curve or fill factor, the ratio between the maximum power output P_{max} cell (I_{opt}, V_{opt}) and the product of the short-circuit current I_{sc} by the open circuit voltage Voc (that is to say the maximum power an ideal cell). The shape factor indicates the quality of the cell [

For our system after the simulation of the influence of meteorological parameters on FF and performance are illustrated in the following

When illumination increases the fill factor increases. The fill factor diminishes as the temperature of the device increased. The decrease in FF with the working temperature of the device outweighs the slight increase in the short circuit current. Finally for having a clearer idea of the origins of losses and yields of each part of a chain of power for a solar system, we presented the definitions of performance and form factor to extract performance against weather conditions. In all cases it is necessary to continuously monitor the output voltage of the converter, that is to say either the voltage of the battery charger or the DC bus voltage to an inverter. In addition it is also useful to monitor the battery charge, the battery current measure, then it is easier to maximize the power output of the generator set and the converter because it is this power that is useful and not the extracted panel.

Therefore to increase the efficiency of a solar system must integrate MPPT controls for example knowing that there are different types of algorithms performing the search of maximum power point MPP [

The performance of the PV generator is evaluated according to the standard conditions (STC): irradiance 1000 W/m^{2}, and Temperature 25˚C. The performance of a PV solar system highly depends on the weather conditions, such as solar radiation, temperature and light, so does the performance of the PV generator degrade with increasing temperature, the decrease in intensity and the illumination load variations. To provide energy continuously throughout the year, a PV system must be properly sized and led by intelligent command to monitor MPPT for extracting the maximum energy. And for the simulation of DC-DC converters, we have shown by simulation that the average value of the output voltage can be adjusted by varying the duty cycle value. In perspective, this work will be continued with a practical realization of MPPT command based microcontroller and a follower by an Arduino board for increasing the efficiency of a solar system to extract the maximum energy.