Research On The Design Of Stand-alone And Grid-connected Photovoltaic Power Generation System

With the development of economy, the demand for energy is increasing, while the traditional non-renewable energy sources are depleted day by day, and serious environmental pollution is caused in the application process, so green energy comes into being.With the development of photovoltaic(PV) technologies, applications of photovoltaic have grown rapidly, indicating that the photovoltaic are attractive to produce environmentally benign electricity for diversified purposes. This thesis focuses on stand-alone and grid-connected photovoltaic power generation system, which includes modeling of PV systems, maximum power point tracking(MPPT) methods for PV arrays, steady state operation control strategy and Seamless switching control strategy.The modeling of PV arrays is the base of research on PV systems. This thesis presents simulation model of PV arrays based on the output characteristics formulas. It can be directly applied in circuit simulation and system analysis. Maximum Power Point Tracking(MPPT) method is an important means to improve the system efficiency of PV power generation system. MPPT theory and various MPPT algorithms are introduced in the literature. Based on those researches, this thesis proposes a novel implementation of a variable step P&O algorithm. In steady state, the variable step P&O can ensure the accuracy of the algorithm.This thesis analyzes the performances of three kinds of filter used commonly, then selects the LCL filter for grid-connected mode, and for stand-alone mode converts LCL to LC filter. The filter can both work well for grid-connected and stand-alone modes. According to the characteristics of photovoltaic inverter for dual modes, respectively expounds the design principle of stand-alone and grid-connected control system. Design the parameters PI regulator considering both the stability and dynamic response ability of the system, and finally get the output characteristics of dual mode inverter at the different operating conditions through the simulation.The switching sequence are studied. Analyze measures to reduce the the impact of grid, and in view of the transition mode in the process of switching, an improved seamless switch control method is put forward. The seamless switching control strategy, mode switching process using MATLAB/Simulink, and the simulation results are given.The simulation results verify that the variable step P&O the novel MPPT algorithm can track PV array’s MPP efficient; the design of the stand-alone and grid-connected control system can meet the requirement of dual mode; Using seamless switching control strategy, load voltage and grid current don’t have big impact, so the system stability is guaranteed.