A Combined Koopman-Subgraph Method for a Secure Power System Islanding

This paper proposes a new methodology for power system islanding based on Koopman modal coherency (KMC) combined with subgraph theory. Initial system partitioning is determined from the Koopman bus-angle coherency matrix. Then, the technique of subgraph is used to modulate the partitions, yielding to viable islands. Balancing subgraphs are constructed from the clusters pairwise neighboring areas. Overload subgraphs swap to connected over-generation subgraphs. Stable islands satisfy nonlinear dynamic coherency, and minimal power mismatch. The search algorithm substantiates the required bands specified in the frequency operating standards. Under severe disturbances, over-frequency generation shedding and under-frequency load shedding schemes are implemented. The proposed islanding methodology is demonstrated on a realistic 151-bus, 24-machines power system. Results show that the proposed scheme can reduce failure regions in faulted power systems.