Research On The Control Strategy Of Single-phase Grid-connected Photovoltaic System

As energy shortage and environment pollution problems highlighted increasingly,more and more people pay attention to the development and utilization of solar energy,what's more photovoltaic(pv)grid power generation become the main tend in the use of solar energy.The pv grid inverter plays as the bridge between the pv system and the grid in the pv grid power generation system.It can improve the control strategy of the system.Nowadays the quasi-Z source inverter topology and control strategy has been one of the most popular researches.Quasi-Z source inverter has the advantages that the traditional inverter does not,simple structure,small output waveform distortion,allowing the inverter bridge has the direct state,etc.This article is to study and optimal the control strategy of pv grid power generation system which is based on the quasi-Z source inverter topology.Firstly,this paper analyzes the single phase of quasi-Z source inverter topology,the principle of work and booster deeply.The parameters of quasi-Z source network will be designed reasonablely,such as the inductance,capacitance and the output fiter inductance;in order to booster and buck,the simple booster and the single polarity SPWM method will be used with inserting the pass-through state.Secondly,the control strategy of quasi-Z source pv grid will be analyzed and the PI method will be used in the voltage and current double close loop.By adjusting the shoot-through duty ratio to realize the maximum power point tracking(MPPT),therefore,on the basis of comparing a variety of methods,the constant voltage combined with variable step incremental conductance method is proposed.The method owns short response time,small fluctuations,higher efficiency and so on,the efficiency of the system is improved.Finally,the active and passive island detections are analyzed and the periodic active frequency drift method is built to make the system own the island protection function.The mode of pv grid power generation system is established in Matlab/Simulink simulation environment and the mathematical model of solar panel,grid-connection control strategy,the maximum power point tracking control strategies are simulated to prove the correctness and feasibility of the control strategy of this paper.