Stability Analysis Method for Three-Phase Multi-Functional Grid-Connected Inverters With Unbalanced Local Loads Considering the Active Imbalance Compensation

This paper proposes a small-signal stability analysis method for the three-phase multi-functional grid-connected inverter (MFGCI) system with an unbalanced local load based on impedance modeling. To attenuate the imbalance introduced by the local load, a modified power quality-compensation algorithm for the MFGCI based on the conservative power theory is proposed and incorporated into the stability analysis. The impedance model of the three-phase system is developed by adopting the complex space vector method to simplify the stability analysis process in this paper. In addition, based on the proposed impedance model and stability analysis, it is proven that the unbalanced local load can affect the stability of the system when the grid-impedance is not negligible. Furthermore, the adoption of the active imbalance compensation can reshape the impedance characteristics of the unbalanced system and improve the stability. The accuracy of the proposed impedance model, and the stability analysis results are verified by the simulation and experimental results.