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In the last decade, the research and development of photovoltaic (PV) system technology has been accelerated due to its free of pollution, silent operation, long life time and low maintenance cost and the improvement of solar cell technologies and the increasing demand for PV systems have led to a reduction of the price of PV module, the costs of PV systems are still too high. Therefore, it is an important to design the PV systems which can maximize energy production from Sun through solar modules. The output power of solar module is a function of solar radiance, temperature and operating point because of its nonlinear current-voltage (I-V) relationship. Therefore, the maximum power point tracker (MPPT) is widely used to maximize the power output of the solar module. As such, many MPPT techniques have been developed and implemented. The techniques used generally are Hill Climbing, Perturb and Observe (P&O), Incremental Conductance (INC), Factional Open-Circuit Voltage and Fractional Short-Circuit Current. The past results show that P&O and Incremental Conductance are in general the most efficient techniques. For these two techniques, the derivatives of voltage and power measured from the solar module are still required.
Bisection Search Method: Now a novel MPPT technique based on bisection search theorem (BST) is proposed without the necessity of derivative computation. Thus, the new technique is even simpler in computation, cheaper in implementation and faster in tracking. The experimental results from solar array simulator in the laboratory show that the proposed technique can track maximum power point very fast within a few steps. The Feasibility of the proposed technique is also verified under real solar modules at the presence of natural environmental conditions. Thus, it is expected to be widely used to replace conventional MPPT techniques in PV systems. This technique is very efficient for maximum power point tracking of the solar PV array. The schematic diagram is as given below in the figure.
Bisection Search Theorem: The bisection search theorem is one of the bracketing methods for finding roots of equations. Assume that function y= f(x) and an interval [a, b] which contains a root x* of f(x) that lies somewhere in the interval such that f(c)= 0. The BST systematically moves the end points of the interval closer and closer together in the pace of halving interval for each step until an interval of arbitrarily small width that brackets the zero is obtained. The decision step for this process is first to choose the midpoint c =(a+b) / 2 and then to analyze the three possibilities that might rise. If f (a) and f (b) have opposite signs, a zero lies in [a, c]. If f (a) and f (b) have opposite signs, a zero lies in [c, b]. If f (c)=0, then the zero is c. If either case (1) or (2) occurs, an interval half as wide as the original interval that contains the root.
Maximum Power Point Tracking Using Bisection Search Method: In order to apply the BST into the MPPT technique in PV systems, the function of y= f(x) and the variable x should be chosen carefully. Fig. 2 shows a power-voltage (P -V) curve. From the (P -V) curve, it can be observed that the change in power with respect to voltage approaches zero at the maximum power point. Obviously, the powers at short circuit voltage (0 V) and open circuit voltage (Voc ) are zero, so maximum power should not happen in these two particular points even though the changes in power at these two points are also zero, which is caused by the small powers around these two points. Thus, tracking the maximum power point is essential to find the root in the function dP by regulating the voltage of solar module or solar array. As a result, the function y= f(x) can be regarded as the change in power dP, where the variable x is the voltage of solar module or solar array.