Passivity-Based Design of a Fractional-Order Virtual Capacitor for Active Damping of Multiparalleled Grid-Connected Current-Source Inverters

Current-source inverters (CSIs) have advantages, such as voltage boosting capability and direct current controllability, in high-power conversion applications with low switching frequency. However, inadequate damping of the passive $CL$ filter gives rise to low-order harmonic resonance. The recent research regarding active damping techniques generally focuses on resonance mitigation of single grid-connected inverters. However, multiple resonances that arise from dynamic interactions among paralleled grid-connected inverters compromise system stability and power quality. This article presents the delay-dependent passivity-based analysis and design of a lossless fractional-order virtual capacitor for resonance damping of multiparalleled grid-connected CSI-based systems. Fractional-order capacitors provide a higher degree of freedom that enhances the frequency behavior and robustness of the control. Simulation and experimental results demonstrate the effectiveness of the proposed active damping control even with variations in the grid impedance and the number of paralleled CSIs.