Control strategy of unintentional islanding transition with high adaptability for three/single-phase hybrid multimicrogrids

Abstract

A seamless islanding transition from the grid-connected mode to the island mode can reduce system voltage and frequency drop and is the key technology for ensuring the safe and stable operation of a three/single-phase hybrid multimicrogrid (MMG). A three-phase unbalance problem and power shortage problem will occur during the unintentional islanding transition of a three/single-phase hybrid MMG. First, aiming to solve the three-phase unbalance problem caused by single-phase loads during the unintentional islanding period, a virtual combination method (VCM) of single-phase loads based on insertion sorting is proposed. Second, for the problem of power shortages during the unintentional islanding period, a load shedding control strategy based on a deep Q-learning network with prioritized experience replay (DQNPER) is proposed. The strategy not only eliminates the power shortage quickly but also considers the influence of the load level, frequency regulation factor, and three-phase unbalance factor on load shedding. Finally, a three/single-phase hybrid MMG with an IEEE 37-bus system is built to verify the effectiveness of the proposed strategy. The test results show that the proposed load shedding strategy has better adaptability than the model-based strategy in the unintentional islanding transition process. The proposed strategy can reduce the three-phase unbalance factor and frequency fluctuation range in the load shedding process and improve the power supply reliability.