A New Active Damping Control Strategy for LCL Converter in Hybrid Coordinate System

Compared with L filter, LCL filter is favored because of its advantages of volume and low cost. LCL filter suffers from resonance problem. In this paper, the active damping strategy using only grid current is further studied. Firstly, it is pointed out that the reason for the resonance problem is the absence of the characteristic equation corresponding to the transfer function of the output current $i_{g}$ to the input voltage u
inv
. The model analysis of LCL part proves that the system is strongly coupled in dq synchronous rotating frame, and the highest coupling term is second differential term, which makes decoupling difficult. Then the active damping strategy in hybrid coordinate system is proposed. The closed-loop control of dc-link voltage and grid-connected current is finished in dq synchronous rotating frame and the active damping control strategy is finished in ${a} \beta $ stationary frame. In the discrete ${z}$-domain, the root locus method is used to design the parameters of the controller and the active damper, and the effectiveness of the proposed strategy is proved by using MATLAB/Simulink.