Novel Active Damping Design Based on a Biquad Filter for an LLCL Grid-Tied Inverter

LLCL filters for grid-tied inverters have been adopted to get better performance the harmonics near switching frequency than commonly used LCL filters. However, resonant peak caused by a pair of unstable resonance poles is introduced and makes system become unstable. In this paper, biquad filter composed notch resonator restrain peak. method, point are placed at appointed frequency, transferred stable area phase transformation, so that does not cross −180° This method higher control bandwidth stronger robustness even in weak power grid. Meanwhile, proportional-integral multiresonant repetitive controller low-frequency current improve steady-state dynamic system. Furthermore, based on active damping filter, stability criterion under grid given. Finally, accuracy analysis effectiveness verified simulations.