Control Strategy Design and Dynamic Analysis of Grid-Connected Inverter Based on Virtual Synchronous Generator

In order to solve the shortcoming that the distributed generators cannot provide inertia for the power system and participate in the grid voltage regulation and frequency regulation when connecting to the grid by the grid-connected inverters, this paper designs a grid-connected inverter control strategy for simulating the characteristics of synchronous generators. Firstly, considering the corresponding relationship between the main circuit of grid-connected inverter and the equivalent circuit of synchronous generator, this paper proposes a virtual synchronous generator (VSG) outer loop controller for simulating synchronous machine rotor motion equation, active- frequency drooping characteristics and reactive-voltage droop characteristics. The virtual impedance controller is introduced in the strategy to simulate the electrical characteristics of the stator of the synchronous generator, which, combined with the inner loop controller based on the proportional integral (PI) controller forms the VSG control strategy for the grid-connected inverter. Then, the dynamic small-signal model of VSG power control is established, and the dynamic model of VSG participating in grid frequency regulation and voltage regulation is deduced. Moreover, the output active/reactive power characteristics of VSG are analyzed under the grid frequency/voltage fluctuations. Finally, the effectiveness of the VSG control strategy and the validity of the dynamic model of participating in the grid frequency regulation and voltage regulation are verified by the results of hardware-in-loop (HIL) experiments.