Design of MPPT Algorithm for Solar Charge Controller to Efficiency Improvement for PSC Condition

INTRODUCTION

Among all different sources of renewable energy i.e. solar, wind, geothermal, tidal etc. Solar tends as an important source of electricity generation. In this context, photovoltaic (PV) power generation has an important role to play due to the fact that it is a green source. Lifetime of solar after implementation is around 25 years, so it can produce more energy than their manufacturing. It can be installed in roofs, deserts, and at place which has no use at residence, and also produce energy from their remote locations also. Now a day‘s trends is to improve efficiency with the solar system and to track maximum power which of generated, so MPPT techniques serves purpose of it. This will directly improves efficiency at low cost. In the past years numerous MPPT algorithms have been published [1][2][10]. They differ in many aspects such as complexity, sensors required, cost or efficiency The objective of this paper is firstly to review best MPPT algorithms. Then the most popular, perturb and observe (P&O)[7], incremental conductance (InCond)[3][6][7][9], are analyzed in depth. After that, improvements to the P&O and the InCond algorithms are suggested to succeed in the MPP tracking under conditions of changing irradiance[7][10] by simulating it in PSIM and efficiency is compared. Finally it is concluded that Incremental Conductance is more efficient then Perturb and Observe.

MPPT algorithms are necessary in PV applications because the MPP of a solar panel varies with the irradiation and temperature, so the use of MPPT algorithms is required in order to obtain the maximum power from a solar array[2][4][6]. There are many different MPPT techniques, Among these techniques, the P&O and the InCond algorithms are the most popular and common to easy implementation[7][9]. Below shown is block diagram of MPPT system. Here now we see basic two MPPT-P&O and MPPT-IncCond algorithm

The first one is P&O algorithm, which used to track maximum power point. It can calculate the power at PV array by determining value of voltage and current. P&O link to determine variation in PV array voltage and current by linking present and past value of voltage and current periodically[7]. In this method, the sign of the last perturbation and the sign of the last increment in the power are used to decide what the next perturbation should be. As it can be seen in Figure 2, So on the left of the MPP incrementing the voltage to get to the Maximum power point whereas on the right of MPP decrementing the voltage to get to the Maximum power point which finally will increases the output power.

If there is an increment in the power, the perturbation should be kept in the same direction and if the power decreases, then the next perturbation should be in the opposite direction[7]. Based on these facts, the algorithm is implemented. The process is repeated until the MPP is reached. Then the operating point oscillates around the MPP. This problem is common also to the In Cond method, as was mention earlier. A scheme of the algorithm is shown in the figure 2.

The disadvantage of the perturb and observe method to track the peak power under fast varying atmospheric condition is overcome by IncCond method. The incremental conductance algorithm is based on the fact that the slope of the curve power vs. voltage (current) of the PV module is zero at the MPP, positive (negative) on the left of it and negative (positive) on the right[3][6][10], it can be written as. A scheme of the algorithm is shown in figure below.

The INC can determine that the MPPT has reached the MPP and stop perturbing the operating point. If this condition is not met, the direction in which the MPPT operating point must be perturbed can be calculated using the relationship between dl/dV and –I/V This relationship is derived from the fact that dP/dV is negative when the MPPT is to the right of the MPP and positive when it is to the left of the MPP[3][7], shown in Figure 5. This algorithm has advantages over P&O in that it can determine when the MPPT has reached the MPP, where P&O oscillates around the MPP. Also, incremental conductance can track rapidly increasing and decreasing irradiance conditions with higher accuracy than perturb and observe.

DC-DC Boost converter without MPPT for 25 W solar panel has been used in this simulation and all the output result was taken as per different radiation and temperature data for May 27, 2007 for Lucknow city. Shown fig 6 is circuit diagram of boost converter without MPPT system. Below table shows the efficiency of the system without MPPT.

A 30 KW panel is considered as consisting of 24,080 solar cells arranged in 344X70 combinations. The solar array consists of number of panels connected in series-parallel configuration and a panel consists of number of cells. The power characteristics of the solar cell are formulated using its equivalent circuit. The equivalent circuit of the cell is presented as a current source in parallel with diode and a parallel resistance with a series resistance.

The output current can be measured by subtracting the diode currents and current through resistance from the light generated current. From this circuit, the output current of the cell is expressed as, Where

For simplicity, it is initially supposed that the array under PSC is subjected to two different irradiance levels. Modules that receive high irradiance level (Hs) are called insolated modules and those which receive lower irradiance level (Ls) are named shaded modules. The insolated modules of a string drive the string current. Therefore, portion of the string current that is greater than the generated current of shaded modules passes through parallel resistance of the shaded modules and generates negative voltage across them. Thus, the shaded modules consume power instead of generating it. In this condition, not only the overall efficiency drops, but also the shaded the string pass through it. Consequently, the voltage across that module will be about and efficiency of the string will improve.

This paper presents a Solar PV energy system for standalone system. The standalone Solar PV System is consider under Partial Shading Condition for Maximum Power Tracking using MPPT. This Paper also highlights the future developments, which have the potential to increase the economic attractiveness of such systems and their acceptance by the user. This Paper also represents the modelling and Simulation of Solar PV System using MATLAB-SIMULINK software. The Simulation results show the ideal I-V and P-V characteristics of the solar PV system under Partial Shading Condition for Maximum Power Tracking using MPPT. The Simulation of Grid integration of proposed solar PV system with MPPT under PSC is successfully done.

REFERENCES

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PG Student, Electrical Department, MEC, BASNA, Visnagar, Gujarat, India