Research On Efficiency Improvement And Optimal Control Of PV Module In The Presence Of Partial Shading

Energy issue is the focus of global attention in recent years,and the search for clean,sustainable new energy sources to replace traditional fossil fuels has become an important way to deal with the energy crisis.As a representative of new energy,solar energy has the advantages of abundant storage and pollution-free.Photovoltaic power generation is the most widely used technology for solar power generation,photovoltaic modules are monomers that make up the photovoltaic array,and photovoltaic modules are generally composed of several photovoltaic cells in series.In practice,the shadows caused by buildings,trees,clouds and so on will cause mismatch of the PV modules in series,it will lead to the decrease of photovoltaic modules power generation efficiency,and damage photovoltaic modules because of hot spot when the problem gets more serious.Therefore,increasing the efficiency of photovoltaic power generation in the presence of shading is always a hot point in studying.In allusion to the problem that mismatch cause to low efficiency of photovoltaic modules in series,advantages and disadvantages of existing control schemes at home and abroad are analyzed and summarized in the paper in methods: topology optimization,global maximum power point tracking,distributed maximum power point tracking and other new type mismatch optimization control technologies.A system scheme of “bus” structure is adopted,according to the principle of power redistribution,and voltage balance control method is used.The currents of normal photovoltaic sub-strings are assigned to photovoltaic sub-strings which are in shade to make sure that currents of substrings in series are equal,so that the output power of photovoltaic sub-strings are are matched,output power is maximized,and efficiency of photovoltaic module is improved.The research and design of the thesis are as follows:(1)Equivalent circuit model of photovoltaic module is built under normal and partial shading conditions.Engineering mathematical model is built with actual physical parameters of photovoltaic module to get the output characteristics of photovoltaic module in the two cases.Combining with the working principle of the bypass diode,the mismatch mechanism and the causes of mismatch of photovoltaic module in series under shading are analysed.(2)For the bus-based series-matching topology structure of PV module,a bidirectional Cúk converter is adopted as a circuit of energy bidirectional transferring,and mathematical model of converter is developed.The loss of converter circuit and device parameters of capacitors,inductors,and power switchs are analysed.(3)For the problem of power matching control of PV sub-strings,the optimal method based on linear programming algorithm and the power matching suboptimal method based on voltage balance are analyzed.The principle and realization process of optimal control are gived.Two control methods are comparatively analyzed.(4)Small signal model is built for the series-matching circuit based on bus structure of PV module,controller design is completed by the analytic method of frequency field,and system performance is improved.In conclusion,the paper combines series-matching topology of PV module based on bus and power matching suboptimal method based on voltage balance,the power matching optimal control of PV module is realized in the presence of partial shading.The simulation and the experimental results verify the validity of the method.