| As the rapid development of economy and increases of energy demand, nowadays, the problem of energy shortage is very serious in the global world. This is an opportunity for the development of new energy industry including wind, biomass and solar. Among them, more attention has been paid in solar energy for its speciality, such as low environmental pollution, flexible installation and strong complementary with the other energy.Several maximum power point tracking (MPPT) algorithms of photovoltaic grid connected system are analyzed. The traditional MPPT method has disadvantages in being influenced by environment factor, has the more power loss or the breakdown of DC bus voltage. According to the shortage of the other MPPT methods, fuzzy control method is introduced for MPPT algorithms, a MPPT using variable step fuzzy control strategy is proposed. The main content are as follows.Firstly, the solar cell mathematical model and output characteristics were analyzed, the influence to output characteristic for illumination intensity and the outside temperature were analyzed in this thesis. The solar cell simulation model was established in PSCAD platform by analyzed the mathematical model of the solar cell array.Secondly, according to the output characteristic of solar cell, after several MPPT controlling strategy are analyzed, in order to enhance efficiency of solar cells, a MPPT using variable step fuzzy control strategy is proposed. Then, the simulation models were designed by the perturb and observe method, the incremental conductance method and the variable step fuzzy control method separately, and compared the three methods.Finally, the experiment of solar cells array MPPT control is performed based on the experimental platform of grid-connected photovoltaic generation system. The result show that, the method can track the changes of the external weather, the photovoltaic grid-connected system can run in maximum power point with good dynamic and static performance. |
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