Three-Phase Four-Wire LCL Filter Active Damping Control Based on Common Mode Capacitor Current Feedback

LCL filters active damping methods of the three phase three-wire (3P3W) grid-connected inverter have been extensively studied, but no study has been done for the active damping control of the three-phase four-wire (3P4W) LCL filters. In this paper, the differential mode (DM) and common mode (CM) models of the 3P4W LCL filter are decoupled, and it is shown that a separate active damping control is needed for the CM circuits besides the DM circuits. The active damping of the CM circuit of LCL filter is realized by the proposed CM capacitor current proportional feedback. The proposed CM active damping control also features the new deterministic design method to obtain the proportional coefficient in one step, so that the maximum damping ratio is obtained. Finally, the proposed method is validated by simulation and experiment results.