Research On Control Strategy Of Grid-connected Photovoltaic Power Generation Based On Virtual Synchronous Generator

Recent years, photovoltaic(PV) generation system gains more share in power system. But because of its fluctuation and discontinuity, it will bring about serious impact on grid stability when large-scale PV generation system connected to the grid. Distributed power is usually connected to the grid through power electronic inverters. And troop control strategy that is mostly used can realize load power distribution between parallel inverters, but these inverters don’t have the advantage of large inertia and large output impendence as synchronous generators do. To solve these problems above, a kind of virtual synchronous generator(VSG) control strategy is promoted, i.e., by using appropriate control algorithm, inverter based on VSG is equivalent to a synchronous generator in external characteristics, which means it will have the similar frequency and voltage regulation characteristics of synchronous generator.In this paper, building of VSG model is introduced, and controller is designed. Then structure of PV grid-connected generation system and control strategies adopted by each part are introduced, including MPPT control and grid-inverter’s control. VSG control strategy in this paper can be divided into three stages. Firstly, in off-grid mode, single DC power using VSG control strategy provide power to the load directly, which aims to verify the correctness of VSG model. Secondly, verify grid regulation characteristics of inverters based on VSG. Thirdly, add PV generation cells, make it into an equivalent VSG together with storage batteries(DC power supply).Simulation is done in Matlab/Simulink platform. Simulation results shows that VSG reflects characteristics of synchronous generator on the grid, can maintain system frequency and voltage stability and improve the network performance of PV cells effectively. By using hardware devices in laboratory, an experimental platform of inverter providing power to load based on VSG is built and situation of low power is verified experimentally. Experimental results are consistent to the simulation conclusion, which verified the feasibility of VSG control strategy.