Harmonic Stability Assessment for Multiparalleled, Grid-Connected Inverters

This paper investigates the harmonic interactions of current controllers in multiparalleled grid-connected inverters. Potential harmonic instability phenomenon, which features oscillations above the fundamental frequency, is evaluated by the impedance-based stability criterion. The possible reasons of the destabilized inverter with different types of grid impedances are explained by the passivity-based analysis and impedance-based stability criterion. Thereafter, case studies are provided, which shows how the nonpassive grid connected inverters interact with the varying grid impedance due to load changes or by the new connections of other grid-connected inverters. Time domain simulations in the PSCAD/EMTDC environment and experimental results show the corresponding harmonic interaction problems may exist in nowadays power system and the impedance-based stability analysis can be an effective tool to assess those problems.