A microgrid is a group of interconnected loads and distributed energy resources within clearly defined electrical boundaries that is able to operate in both grid-connected and islanded modes. This ability to continue to supply electrical power to loads within the microgrid when the normal grid supply is unavailable provides an increased level of reliability. Microgrids can use a wide variety of energy sources for generation and can operate at low voltage or at medium voltage. The ability of microgrids to change between grid-connected operation and islanded operation gives rise to a number of issues that need to be addressed in their design. This includes reliably detecting when the normal supply has been lost and changing the control within the microgrid so as to maintain voltage and frequency within acceptable limits. The decrease in fault levels between grid-connected and islanded modes means additional or more sophisticated protection methods might need to be used to adequately detect and clear faults when in islanded mode. Consideration also needs to be given to earthing arrangements in medium voltage microgrids. Microgrids require control systems that perform a number of different functions, ranging from embedded control of items of equipment such as inverters through to energy management systems which can incorporate sophisticated control and forecasting algorithms to maximize the available energy and/or the economic return of the DER within the microgrid.