ELECTRIC POWER SYSTEM AND SERVER

In switching of a microgrid from an isolated operation to an interconnected operation with a power grid, a CEMS server determines a first master DER and slaves based on a master plan and performs master-slave control. When the first master DER goes down, the CEMS server compares remaining capacities of power-storage-type DERs included in a DER group (S27). The CEMS server then determines a DER with the highest remaining capacity as a second master DER among the power-storage-type DERs included in the DER group (S29) and performs master-slave control (S31).