Resonant feed forward control for LCL-type grid-tied inverters in weak grid condition

Weak grid is commonly seen as a voltage source which contains the gird impedance and background harmonics. The grid current closed-loop control and the grid voltage feed forward control are coupled with each other because of the grid impedance. The proportion feed forward control strategy introduces a positive feedback loop, which affects the grid current quality and the system stability. This paper establishes the model of LCL-type grid-tied inverter, and elaborates the formation mechanism of resonant current under weak grid condition. The resonant feed forward control (RFC) is proposed to attenuate the response of grid impedance during the resonant frequency band, and also to improve the phase margin and decrease the injected current steady state error. A 3kW singlephase grid-tied inverter prototype is designed in the lab, and the proposed RFC strategy is verified by experiments.