Research On Parallel Control Strategy Of Three Phase LCL Grid-connected Inverter

With the development of renewable-energy generating and micro grid,grid-connected inverter has become a crucial part of the photovoltaic power generation system,at the same time,the LCL filter has been widely used in the grid-connected inverter because of its good filtering effect.And in the applications of high-power grid-connected inverter,single grid-connected inverter costs due to current stress on the power device and factors such as volume increases,which makes the parallel inverter technology has become an effective solution to solve the problem of the expansion of the inverter.But the parallel operation of the inverters will produce circulating current,which will lead to the instability of the system.Firstly,the mathematical model of three-phase grid-connected inverter with LCL filter is established,and the filtering characteristics of the LCL filter and the closed-loop stability of the three-phase LCL grid connected inverter are analyzed.Then,the generation of parallel circulation and its influencing factors are analyzed,and the circulating current suppression method of parallel system is summarized.Then,the zero sequence current suppression algorithm and improved master slave control strategy is designed.And the effect of the zero sequence current suppressor and the advantages of the improved master-slave control strategy are verified in the Matlab/simulink simulation model.Next,the hardware and software of the parallel system are designed,and the experimental platform of the parallel grid-connected inverter is built.Through a series of experiments,it is verified that the designed three-phase LCL grid-connected inverter system has a good effect onrestraining the circulation and reducing the THD of the grid current.