New Active Damping Method for LCL Filter Resonance Based on Two Feedback System

Two feedback active damping technique for LCL filter resonance is proposed using the capacitor voltage and the grid current. The proposed method is derived in continuous time domain with discussion for its discrete implementation. Based on the proposed method, excitation of un-stable open loop pools, which implies non-minimum phase behavior, can be avoided over a wide range of resonant frequencies; Co-design procedures for both the active damping loops along with the fundamental current regulator are presented. Numerical example and simulation work are presented to confirm the performance of the proposed method at different resonant frequencies.