Abstract: The present invention relates to a micro-power source for successfully implementing a microgrid and to a control method for realizing smooth reconnection between the microgrid and an upper electric power system and smooth switching between the control modes of the micro-power source. A micro-power source sectionalizes an electric power system into an upper electric power system and a lower electric power system, and enables the lower electric power system to be independently operated in an island mode and to smoothly switch between a grid-connected mode and the island mode. As a result, a hierarchical microgrid is implemented with sectionalized sub-microgrids. One of the merits of the hierarchical microgrid is that each consumer group can be supplied with high quality power regardless of the power quality of the other consumer groups, and various types of services independently.