Robust Active Damping for LCL-Type Grid-Connected Inverter with Capacitor Current Quasi-Integral Feedback

Considering the time delay introduced by the digital control, it turns out that capacitor current proportional feedback active damping (AD) is equivalent to a frequency-dependent virtual impedance in parallel with the filter capacitor. Unstable open-loop poles will arise due to the presence of virtual negative resistor, which causes that the system stability is highly sensitive to grid-impedance v...