Enhanced grid-current feedback active damping for LCL grid connected inverter using discretized band-pass filter with full delay compensation

• Proposal of a Band-Pass Filter (BPF) for grid-current feedback active damping. • Discretization via Tustin pre-warping introduces negative gain near Nyquist frequency. • Modified first-order digital filter (MFODF) used for full delay compensation. • Effective damping range extended from 0.333 f s to 0.455 f s with enhanced stability. • Experimental validation confirms improved damping and reduced high-frequency noise. This Grid Current Feedback Active Damping (GCF-AD) strategies based on high-pass filter HPF -either first order (FO) or second order (SO)- are widely used to suppress resonance in LCL grid-connected inverters. However, these methods suffer from high-frequency noise sensitivity due to their respective slopes of +20 dB/decade and +40 dB/decade. To address this limitation, a Band-Pass Filter (BPF) is proposed as the active damping feedback function. When discretized using the Tustin pre-warping method, the BPF introduces a negative gain near the Nyquist frequency, effectively attenuating high-frequency noise amplification. Nevertheless, the digital implementation of the BPF restricts the range of positive virtual resistance, and therefore the effective damping range to approximately 0.333 f s ( f s the sampling frequency). To overcome this limitation, a delay compensation block based on a Modified First-Order Digital Filter (MFODF) is cascaded with the BPF. The analysis demonstrates that this compensation significantly expands the effective damping range, reaching up to 0.455 f s , and contributes to improved closed-loop system stability. Furthermore, a comprehensive z-domain stability analysis of the closed-loop is conducted to evaluate the impact of key control parameters. The effectiveness of the proposed method is validated through laboratory experiments, confirming the improvements in both damping performance and closed-loop system stability.