Resonance Interaction of Multi-Parallel Grid-Connected Inverters with LCL Filter

This letter investigates the resonance characteristics and stability problem caused by the interactions of multiparallel LCL-filtered inverters. Compared to single grid-connected inverter, the multiinverter system presents a more challenging resonance issue, where the inverter interactions may excite multiple resonances at various frequencies. This letter proposes a modeling and analysis method based on the current separation scheme. It reveals that an interactive resonant current that circulates between the paralleled three-phase inverters may arise, depending on the current distribution and the system resonance characteristics. This is different from the common resonant current injected into the grid and has yet been discussed before. The analysis with the root loci in the discrete z-domain are carried out with two stability constraints identified, which correspond to the conditions of triggering the interactive resonant current and common resonant current, respectively. Simulations and experimental results verify the theoretical analysis.