Optimized Unsymmetrical Per-phase Droop for Soft Line Switching of Reconfigurable Unbalanced Inverter-Based Islanded Microgrid

The legacy of power distribution systems is evolving towards more flexible and dynamically reconfigurable microgrids, which substantially increases line-switching actions. This may introduce undesirable transients, poor reliability, deteriorated power quality, and significant wear and tear in switching devices. Frequent line switching is significant in unbalanced inverter-based islanded microgrids (UIBIM). This paper proposes an optimized unsymmetrical per-phase droop-controlled approach to mitigate the influence of line switching during UIBIM reconfiguration and partitioning. To determine the unsymmetrical per-phase Optimal Transitional Droop Settings (OTDS), a new mathematical formulation is modeled to minimize power flow at the switching location(s). Given the unbalanced nature of the system, the proposed unsymmetrical droop will be optimized for each phase independently. The activation start and end instants of the OTDS are selected to reduce the UIBIM dynamics due to the transition between the states due to switching. The superiority and effectiveness of applying the proposed unsymmetrical OTDS are assessed via Matlab/Simulink, utilizing case studies implemented on a 6-bus and an IEEE 34-bus unbalanced systems. The simulation results reveal that the proposed approach can independently minimize the current flow in each phase during the switching process by nearly 98%. Furthermore, the transient voltage during the switching process is significantly reduced.