An Improved Active Damping Method with Grid-Side Current Feedback to Maximize Damping Ratio for LCL-Type Grid-Connected Inverter

LCL-type grid-connected inverter is largely utilized in renewable generation system due to high harmonic suppression. In order to tackle the resonance issue induced by LCL-type filters, grid-side current feedback active damping method (GCFADM) without extra sensors has been extensively investigated. However, the damping characteristic under GCFADM has not been fully evaluated. In this paper, an improved GCFADM based on proportional derivative algorithm is proposed to maximize damping ratio which can enlarge the existence steady region. By utilizing root locus analysis method, the maximal damping ratio (MDR) is obtained in classification of the control delay time and the ratio of resonance frequency to sampling frequency respectively. Based on MDR, stability regions of the proposed method are identified. By comparing with different stability regions, the optimized proportional derivative GCFADM can be obtained intuitively as well as the corresponding control parameters. To verify the analyses, simulation and experiment platform are both set up. Simulation and experimental results show that the proposed method can not only achieve the best damping performance, but also manifest strong robust against main circuit variations.