Microgrids: Operation and Control

A microgrid is a group of interconnected loads and distributed energy resources within clearly defined electrical boundaries that acts as a single controllable entity with respect to the grid and that connects and disconnects from such a grid to enable it to operate in both grid‐connected and island mode. There are four classes of microgrids: single facility microgrids, multiple facility microgrids, feeder microgrids, and substation microgrids. Distributed energy resources (DERs) are divided into two groups based on the type of interface with the microgrid. The first group includes conventional (rotary) units based on synchronous or induction generators that are interfaced directly to the microgrid. The second group are interfaced to the microgrid through power electronic converters which introduce novel control concepts. Frequency stability is a problem faced by islanded microgrids where any individual generator output forms a substantial portion of the total demand.