Research On The Application Of Z-Source Inverter In Photovoltaic Grid-Connected Power Supply System

In recent years,photovoltaic(PV)power generation technology in solar energy has been developed rapidly because of its small geographical impact.As the core of PV grid-connected power generation system,the performance of grid connected inverter directly determines the quality of output power and the safe and reliable operation of PV grid-connected system.Therefore,it is of great practical significance to study the topology and control strategy of the inverter.The topology of the Z source inverter has been widely concerned because of its unique impedance network can boost or buck voltage arbitrarily.In order to better meet the higher requirements for the boost capacity and input current of PV power generation system,this paper firstly aims at the shortcomings of Z source inverter,such as input current is discontinuous,boost capacity is limited and capacitor voltage stress is large,and so on.The working principle of three improved Z-source inverter topologies: quasi-Z source inverter,switched-inductor quasi-Z-source inverter and improved switched-inductor quasi-Z-source inverter are analyzed in detail.And the simulation results show that the improved switched-inductor quasi-Z-source inverter with higher boosting capacity under the premise of comparing the boosting capacity,component capacity and cost,and application background is more suitable for applications such as PV where the input voltage varies widely.Secondly,the control strategy of PV grid-connected system based on Z source inverter is analyzed and studied.Under the premise of satisfying the grid-connected power quality and ensuring the safe and reliable operation of the system,the system's maximum power tracking control,Z-source capacitor voltage control,and grid-connected current control are designed and analyzed.The PV grid-connected control system of Z source inverter is simulated by Matlab/Simulink.The simulation results show that the PV grid-connected control method of Z-source inverter has better output power quality,better dynamic performance and better steady-state performance.Finally,aiming at the islanding effect in photovoltaic grid-connected system,the islanding protection to the system is carried on.Based on the analysis of the mechanism of islanding,a simulation model based on active frequency drift islanding detection is built,and it is proved that active frequency drift islanding detection method can detect the island and prevent the occurrence of island quickly and effectively.