Research On Parallel Control Method Of Grid-connected Inverter

With the continuous exploitation of oil,natural gas and other fuels,non-renewable energy is gradually depleted,solar energy,wind energy,tidal energy and other new energy power generation technology attract more and more people,grid inverter has been widely used.The parallel operation of grid-connected inverter has become a hotspot based on the development of new energy distributed grid-connected operation and the high reliability,large capacity and modularity of power supply system.Three-phase grid-connected inverter operation can greatly improve the system capacity,reduce the size of the power system and the current stress of switching device,thereby improving system reliability and reducing costs.It has important research significance and application value.This paper first briefly summarizes the inverter mathematical model,SVPWM control technology and current control technology.Since a single inverter requires good control performance,an improved repetitive control method is proposed to reduce the current harmonics of a single inverter.The harmonic suppression characteristics of the repeated control method is are analyzed and verified by simulation.A single grid-connected inverter is extended to a parallel system.The topology of parallel connection of grid-connected inverter is analyzed and the equivalent mathematical model of the parallel system is established.The operation principle and control method are analyzed based on the mathematical model of the parallel system.The direct current control method is used to design the parallel system.The responsed speed of system current is fast,but there is a certain circulation between the modules,Its current sharing characteristics is not good.In order to solve the circulation and current sharing of the parallel system,the paper analyzes the formation cause and suppression method of the system circulation.The zero vector control method is used to reduce the circulation of the system.The current sharing control technology of the inverter parallel connection is analyzed.The maximum current sharing method is used to realize the current sharing of the system.The parallel control method is simulated and verified based on the theoretical analysis.Finally,the experiment platform of grid-connected inverter system is designed,and the experiments of single grid-connected inverter and inverter parallel system are carried out.The experimental results verify the feasibility of the repeated control and parallel operation method.The parallel system is stable and has good current sharing characteristics.