Adaptive Frequency Tracking Notch Filter for Active Damping of Grid-Connected Inverter with LCL Filter

An LCL filter has higher harmonic attenuation and smaller size than an L filter, but the stability problem due to resonance is a critical issue. Various passive or active damping methods have been introduced to address this issue. Among various damping methods, the notch filter (also known as a band-stop filter) is one of the most commonly used due to its simple principle. However, the resonant frequency can drift because of grid inductance or deterioration of the filter capacitor, resulting in the notch and the resonant frequency not matching. In this case, the system may become unstable due to poor resonance suppression. Accordingly, notch and resonant frequency should be matched. In this article, a novel adaptive (self-tuned) frequency tracking notch filter algorithm is proposed. The proposed scheme detects the resonant frequency through a synchronous frame phase-locked-loop algorithm. The effectiveness of the proposed scheme is verified through both theoretical analysis and experimentation.