Study Of MPPT Control Strategy For Photovoltaic Power Generation System

Facing the problem of increasingly serious global energy crisis，The solar energy resources is very richon earth，and green clean solar energy will not harm our environment，so it has been widely used by human.Photovoltaic power generation is one of the main ways of using solar energy, and it has been continuouslyapplied and development. For the sake of improve the conversion efficiency of PV system, the systemneeds to make a maximum power point tracking.Based on know the current background and status of photovoltaic technology, and make thephotovoltaic power generation system a brief overview. It points out two important factors that restrict thedevelopment of PV industry, the high cost and low conversion efficiency. Therefore, we need to find asuitable MPPT algorithm, which can improve the system’s output power effectively，and reduce the cost ofproduction per unit area. However, the burning large amounts of fossil energy brings a series ofenvironmental problems to the global word, causing the environment changes worse, and also affectedthe photovoltaic power generation system’s effective and stable operation in certain extent.In this situation, the paper from the working principle of photovoltaic cell, establishing themathematical model. Analysising the output characteristics of PV cells under illumination uniformity andpartial shade, putting forward two kinds of MPPT control algorithms, making the system track themaximum power point, and output the maximum power.1. Under illumination uniformity conditionsFor improve the maximum output power of the photovoltaic power generation system, throughanalysis the P-U curve of photovoltaic cells, and the mathematical modeling of PV array. On the basis ofthe incremental conductance method, propose a new maximum power point tracking control algorithm，infinitesimal step size adaptive incremental conductance method. Which needs to introduce a variable stepsize control factor, make the system track the maximum power point with infinitesimal step size adaptively.By Matlab/Simulink environment simulation, when external environment changes, the new algorithmreduces the time of maximum power tracking, and effectively suppress the oscillation of the system in themaximum power point (MPP), make the system has high tracking speed and accuracy. 2. Under partial shade conditionsIn order to prevent the hot spot effect which is caused by the local shadow to damage the photovoltaiccell, the photovoltaic cells need some bypass diodes in parallel. However, due to the addition of bypassdiodes, the P-U characteristic curve of the system output shows multiple peak, traditional single peakMPPT algorithm can fall into local peak so that it can not track the real maximum power point. Byanalyzing the mathematical model of photovoltaic cells under partial shade, propose the gather peakscanning discrimination method. The algorithm can control the system from both ends to the middle onpower curve to sequentially scanning every power value, through comparison and analysis, if the twoextreme point’s power is equal, then this point is the maximum power point. After the simulation test, thealgorithm can effectively resist the effects of partial shade, avoid the interference of local peak point, andtrack the real maximum power point, improves the syetem’s output power obviously.