Modified VOC Using Three Symmetrical Components for Grid-Supporting Operation During Unbalanced Grid Voltages and Grid-Forming Operation in Hybrid Single-Phase/Three-Phase Microgrid

Abstract

Virtual Oscillator (VO) control is the most advanced time-domain based control strategy for grid-supporting and grid-forming inverters. VO Controllers (VOCs) provide better dynamic performance than droop controllers and virtual synchronous machine controllers. However, the existing VOCs can only provide synchronization with the positive sequence voltages of a connected electrical network. As a result, the existing VOCs cannot operate in an electrical network with unbalanced voltages. This paper has introduced the Instantaneous Symmetrical component based VOC (S-VOC), which can provide continuous synchronization simultaneously with the positive, negative, and zero sequence voltages of a connected electrical network. The proposed S-VOC enables two very important and relevant functionalities for grid-supporting and grid-forming inverters. The functionalities are the grid-supporting operation in the presence of unbalanced grid voltages and the accurate load-sharing in grid-forming mode when single-phase and three-phase sources are integrated into the same hybrid microgrid architecture. At the same time, the proposed S-VOC preserves the superior dynamic performance of the existing VOC. Furthermore, the proposed S-VOC can replace the existing VOC without any extra sensor. The systematic design procedure and mathematical analysis of the proposed S-VOC are presented in this article. Simulation studies and hardware experiments are conducted for validation.