ABSTRACT

A microgrid can contain different types of distributed energy resources (DERs), such as distributed generators (DGs) (which are also called microsources in a microgrid) and energy storage systems. As a microgrid can normally operate either in grid-connected or islanded mode, a reliable, seamless transition between these two modes should be achieved. In an islanded microgrid that adopts master-slave control, one distributed generation (or energy storage system) adopts constant voltage and frequency control that provides a reference voltage and frequency to other DGs, while the other DGs adopt PQ control. There are two basic droop control methods: controlling the output power via the frequency and magnitude of the voltage, and controlling the frequency and magnitude of the voltage based on the output power. The chapter also discusses the impact of downstream faults of microgrid MG on downstream and upstream protections.