Research On VSG Control Strategy For Grid Voltage Failure

With energy security,climate change and environmental deterioration increasingly prominent,the development of new energy industry has been promoted vigorously.When new energy resources such as wind energy and solar energy are incorporated into the traditional power system in a high proportion to adjust the industrial structure,the voltage and frequency of the grid will fluctuate greatly,and the intermittency and instability existing in operation will directly affect the safe and stable operation of the power system.Symmetrical grid voltage sag and grid voltage imbalance in the non-ideal grid-connected operation state will cause overcurrent and power fluctuations in the virtual synchronous generator.,and excessive output current will directly burn power electronic devices and cause power safety accidents.Solving such failures and realizing the friendly grid connection of new energy power generation is a severe challenge facing the industry at present.The main circuit of the three-phase voltage source inverter is designed,and its mathematical model is derived from the main circuit.The control circuit adopts active-frequency control and reactive-voltage control,and then the overall control strategy of the virtual synchronous generator is obtained from the main circuit and the control circuit.Use the designed control strategy to simulate under sudden load conditions to verify the control effect of the virtual synchronous generator and the effectiveness of the proposed control strategy;analyze the dynamics of the virtual synchronous generator under symmetrical grid voltage sag conditions to obtain the factors affecting the output current of the inverter and improve the traditional virtual synchronous generator control strategy,and introduce voltage amplitude control and output active power control to achieve real-time detection of the grid-side voltage amplitude and solve power angle stability of virtual synchronization,so as to limit the fault current;for the grid voltage imbalance,analyze the impact of this fault on the virtual synchronous generator system,and obtain the factors that affect the inverter output current and power balance.Then correct the positive and negative sequence command values of its controlled current based on the instantaneous power model of the virtual synchronous generator and track the corrected current command values.Finally,analyze and verify the improved control strategy through Matlab/Simulink simulation software,and the improved control strategy can achieve different control goals such as inverter output current balance,output active power and output reactive power constant.