Research On Two-stage Single-Phase Grid-Connected Photovoltaic Inverter

With global energy demand growing,energy crisis and environmental pollution problem caused by the fast consumption of traditional energy could not be ignored any more.So much attention has been paid on the development and utilization of renewable energy.Among them,solar energy is getting more and more praise as a sort of resource-rich,renewable and nuisanceless natural energy.In recent years,the rapid development of power electronic technology makes photovoltaic power plants gradually with the value of large-scale promotional.Undoubtedly Photovoltaic(PV)grid generation will become an important approach for the solar energy utilization.Therefore,the research and design on the grid-connected photovoltaic system has practical significance.Single-phase grid system is the main research object in this thesis.The analysis and research of this system is carried out in detail from following aspects:the topology of grid system,the parameter selection,the maximum power point tracking,and the control strategy of the combination of the single-phase grid inverter and the active filter.Firstly,considering the characteristics of low power single-phase gird-connected system,a kind of small size,low cost,easy to control DC-DC circuit and a bridge type DC-AC inverter circuit is adopted in this thesis.In order to obtain the accurate main circuit components,the parameters in main circuit are calculated and the hardware circuit also has been designed.Secondly,the photovoltaic cell simulation model is seated up by using MATLAB/Simulink.To demonstrate feasibility of the maximum power point tracking(MPPT),the influence of output characteristics of PV cell when changing ambient temperature and light intensity condition is analyzed.On the basis above,several commonly used maximum power points tracking method is researched.Through the comparison of these methods,the traditional tracking method has been improved and the probability of a mistake of judgment in the optimization process has been reduced.Then,this thesis introduces the principle of islanding and the equivalent model of the island detection system is established.Several island detection methods in common use are illustrated.Based on that,the thesis puts forward a new method for disturbance,two-way disturbance frequency shift method.Meanwhile,through the simulation analysis with other methods,the advancements of two-way disturbance frequency shift method are verified.Finally,by deep analysis and research,the design of the hardware and software of the whole system is introduced in detail,including the design of the main circuit of the system and its parameters,the design of the control circuit,the assign of the hardware resource and the flow chart of the software of the system.