An Active Damping Method With Improved Capacitor Current Feedback

Capacitor-Current Feedback Active Damping (CCFAD) is widely employed in LCL grid-tied inverters. However, the delay introduced by digital control can alter the traditional active damping characteristics, with the equivalent virtual resistance having a positive/negative crossover frequency of f_s/6. The LCL filter’s resonant frequency may change due to the extensive variation in grid impedance under weak grid conditions. When the resonant frequency of the LCL filter exceeds f_s/6, the stability of the system is severely compromised. A better approach is to add a lead compensation element to the current feedback branch of traditional CCFAD in response to these issues. This compensates for the phase lag caused by control delay, effectively extending the active damping region to (0, f_R), f_R ∈ (f_s/3, f_s/2), thereby enhancing system stability and robustness. The proposed method’s effectiveness has been confirmed by theoretical analysis and simulation on the MATLAB/Simulink platform, which utilizes a single-phase LCL grid-tied inverter model.