Adaptive notch filter-based active damping technique for grid-connected inverters with LCL filter under resonance drift conditions

Abstract LCL filters are commonly used in grid-connected inverters but suffer from resonance, which may compromise stability. Active damping with a notch filter is effective, yet its performance is sensitive to variations in grid inductance and load conditions, leading to misalignment between the notch and actual resonance frequency. To address this issue, this paper proposes an adaptive notch filter that tracks the resonant frequency in real time using a synchronous-reference-frame phase-locked loop (SRF-PLL). The proposed method enables automatic frequency alignment without additional sensors or complex estimation algorithms. Both theoretical analysis and experimental validation demonstrate that the approach ensures stable current control under varying grid conditions.