Resilient microgrid formation in unbalanced AC/DC hybrid distribution system considering DC interconnections

Microgrid formation (MF) is an essential method for enhancing distribution system resilience. Existing MF research focuses on AC distribution systems, where the formed microgrids must satisfy the radial operation constraints. However, with the increasing penetration of DC sources and loads, the distribution network is transitioning from an AC configuration to a hybrid AC/DC configuration that can operate in a ring structure. Thus, traditional MF methods achieve limited critical load restoration of these systems. To achieve the most efficient restoration of AC/DC hybrid systems, this paper developed a novel MF method leveraging DC line interconnections. First, an energization route-based analytical model is developed for the decision-making of an microgrid topology containing DC lines. The energization status of AC and DC lines is differentially modelled to enable flexible interconnection and energy transfer between microgrids. Then, a coordinated scheduling model for resilient hybrid distribution systems is established, with the goal of increasing critical load supply. To mitigate the unbalanced current from three-phase AC loads, the use of flexible voltage source converter power control is emphasized. Furthermore, the original nonlinear model is linearized for tractability. The simulation results validate the merits of proposed MF method for improving the resilience of AC/DC hybrid distribution systems.