Frequency Tracking Notch Filter for LCL Filter in Grid Connected Inverter

Unlike L filter, LCL filter has a resonance problem in grid-connected inverter. To prevent the resonance of LCL filter, several damping methods exist such as passive and active damping techniques. Among active damping, using a notch filter (band stop filter) is being actively researched. However, the resonant frequency can be change; thus, notch frequency and the resonant frequency are not matched. To prevent the resonance problem, the notch frequency should be changed to match changed resonant frequency. This study proposes a frequency tracking notch filter. The proposed technique detects the resonant frequency only through the current sensor used for current control without any additional sensors.