Design And Research Of Unit Parallel Photovoltaic Grid-connected Inverter

As a green renewable energy,PV generation industry has attracted attention around the world.With the development of photovoltaic grid-connected generation technology,PV grid-connected inverter is widely used in the field.In this paper,the topology of PV grid-connected inverter,the grid-connected control strategy of the inverter,the potential leakage current and the current circulation problem of the inverter are studied and analyzed.Finally,on the basis of theoretical research,this paper designs a parallel-connected 500 k W photovoltaic grid-connected inverter.The main contents and contributions are as follows:(1)This paper studies the topologies of grid-connected inverters,analyzes the structural characteristics of inverter unit and the working principle and work process of the inverter unit,and then presents an integrated topological structure,which is the inverter unit parallel and IGBT cross-parallel combination of the topology.(2)The control strategy of grid-connected inverter is researched in this paper.Then,the SVPWM,phase-locked loop and loop control technology are analyzed and studied by establishing the mathematical model of the inverter unit.Finally,the control strategy of grid-connected control is verified by experiments.(3)In this paper,we study the possible circulation and leakage current problems,from the two aspects of the harm and the mechanism of the problem to analyze the causes and current flow path.A method of using common mode inductor and inter-cell synchronization signal is proposed to suppress the circulation and leakage current problems.(4)In this paper,a parallel-connected 500 k W photovoltaic grid-connected inverter prototype is developed.The hardware design includes: the selection of key devices,the main control circuit,drive circuit and protection circuit design.Software design part includes: system cycle main program,sampling program,SVPWM control and double closed-loop control and other parts.At last,a full power experimental platform is built to simulate the operation of photovoltaic power generation system.The theoretical research contents of t his paper are verified and the performance of grid-connected inverter prototype is tested.