Resonance Analysis and Coordinated Active Damping of Multiparallel Grid-Connected Converters Under Filter-Inductance Attenuation and Grid-Strength Variation

Abstract

Parallel converter operation enables flexible capacity expansion of energy-storage power conversion systems. However, parallel converter interactions, filter-inductor saturation, and grid-strength variations increase the risk of resonance instability. The measured current-inductance characteristic is incorporated into an operating-point-dependent closed-loop Norton model. The grid current of an individual converter is decomposed into self-reference, parallel converter coupling, and grid-voltage-disturbance responses. It reveals that converter-side inductance attenuation shifts the internal and parallel resonances to higher frequencies and increases resonance-instability risk, whereas converter number and grid impedance primarily reshape the parallel resonance. A coordinated active-damping method is then developed: PCC voltage feedforward weakens common-network interaction, and capacitor-voltage feedback increases local LCL-filter damping. Simulation and experimental results validate the feasibility and effectiveness of the proposed control method. Experiments with two parallel converters validated the proposed control method. Stable transient current responses were achieved during a simultaneous current-reference step from 50 to 120 A, while the grid-current THD and power-sharing deviation remained below 3% and 5%, respectively.