978-1-4673-0455-9/12/$31.00 ©2012 IEEE MPPT Techniques for Photovoltaic System under Uniform Insolation and Partial Shading Conditions Aseem Sayal, Student Member, IEEE. Abstract-- The photovoltaic energy is one of the renewable energies that has attracted the attention of researchers in the recent decades. The photovoltaic generators exhibit nonlinear I- V and P-V characteristics. The maximum power produced varies with solar insolation and temperature. It requires maximum power point tracking (MPPT) control techniques to extract the maximum available power from PV arrays. Due to partial shading condition, the characteristics of a PV system considerably change and often exhibit several local maxima with one global maxima. Conventional Maximum Power Point Tracking techniques can easily be trapped at local maxima under partial shading. This significantly reduced the energy yield of the PV systems. In this paper, various MPPT algorithms for uniform insolation and partial shading conditions are reviewed with their merits and demerits. Also, some new algorithms are proposed which are shown to be more efficient than the existing ones. Index Terms-- Fuzzy Logic Controller, Incremental Conductance, Maximum Power Point Tracking, Partial Shading, Perturb & Observe, Photovoltaic cell. I. INTRODUCTION N recent decades, the continuous growth of energy demand from all around the world has urged the society to seek for alternative energies due to the depletion of conventional energy resources and their undesirable impact on environment. Among the available alternative energies, photovoltaic (PV) energy is one of the most promising renewable energies. PV energy is clean, inexhaustible and free to harvest [1]. However, there are two main drawbacks of PV system, namely the high installation cost and the low conversion efficiency of PV modules which is only in the range of 9-17% [1]. Besides that, PV characteristics are nonlinear and weather dependent. Fig.1, 2 show the I-V and P-V characteristics of a typical PV module for a series of temperatures and solar irradiance levels [2],[3]. It can be seen from the P-V characteristic curve that there is only one operating point at which the power output is maximum, which is named as the maximum power point (MPP), say operating voltage. The MPPT control techniques are essential to extract the maximum available power from PV array in order to maximize the utilization efficiency of a PV array. As such, many MPP tracking (MPPT) methods have been developed and implemented in the literature. The methods vary in complexity, number of sensors required, convergence speed, Aseem Sayal is with the Department of Electrical Engineering, Delhi Technological University, New Delhi -110042, India (e-mail: aseem.sayal@gmail.com ). cost, and range of effectiveness, implementation hardware and in other respects. They range from the almost obvious (but not necessarily ineffective) to the most creative (not necessarily most effective). Under Partial Shading conditions, the multi- peak and wrong-tracking under quickly changed atmosphere are the main problems to achieve a high performance MPPT are. The study revealed that as if 10 percent of the photovoltaic arrays were covered, the entire photovoltaic system would lose at least 50 percent of the electricity. Therefore, it is necessary to improve the efficiency of solar power through tracking global maximum power point (GMPPT) under the partial shadows environment. In this paper, 8 MPPT techniques taken from the literature are discussed and analyzed in terms of their merits and demerits. In addition to this, 4 MPPT techniques are proposed. The proposed methods are more efficient than existing ones. II. MATHEMATICAL MODEL OF PV GENERATOR The building block of PV arrays is the solar cell, which is basically a p-n junction semiconductor, shown in Fig. 3. The V-I characteristics of a solar array is given by (1) [4], which considers the effect of shunt resistance R sh. . ( ) ( ) exp 1 s s SC o c sh qV RI V RI I I I nkT R ⎧ ⎫ + + ⎡ ⎤ ⎪ ⎪ = - - - ⎨ ⎬ ⎢ ⎥ ⎪ ⎪ ⎣ ⎦ ⎩ ⎭ (1) where V and I represent the output voltage and current of the PV array, respectively; R s and R sh are the series and shunt resistance of the cell; q is the charge of electron; I sc is the short circuit current; I o is the reverse saturation current; n is number of cells connected in parallel ; k is the Boltzmann constant and T c is the temperature in K 0 . Thermal voltage for standard temperature Tc:[3] c T nkT V q = (2) I PV Array Voltage (V) PV Array Current (A) PV Array Voltage (V) PV Array Power (W) Fig. 2. P-V Characteristics. Fig. 1. I-V Characteristics.