Optimum and adjustable damping control of grid-connected inverter with an LCL filter

This paper proposes a simple and general active damping method with good suppression effects by the optimal control principle with the state feedback approach. It may reduce number of sensors by estimations with a state observer. The proposed method can enhance the damping effects by adjustment of control parameters which correspond to a sort of virtual resistors. Its general design method and examples are described. The regulated current error transfer-functions at the oscillation frequency of the Alter are suppressed effectively by validation through simulation by SABER and experiment by a DSP-based digital control system.