A microgrid is a decentralized group of electricity sources and loads that normally operates connected to and synchronous with the traditional wide area synchronous grid (macrogrid), but can also disconnect to "island mode" and function autonomously as physical or economic conditions dictate. Microgrids are best served by local energy sources where power transmission and distribution from a major centralized energy source is too far and costly to execute. In this case the microgrid is also called an autonomous, stand-alone or isolated microgrid.In this way, microgrids improve the security of supply within the microgrid cell, and can supply emergency power, changing between island and connected modes. They also offer an option for rural electrification in remote areas and on smaller geographical islands. As a controllable entity, a microgrid can effectively integrate various sources of distributed generation (DG), especially renewable energy sources (RES).Control and protection are difficulties to microgrids, as all ancillary services for system stabilization must be generated within the microgrid and low short-circuit levels can be challenging for selective operation of the protection systems. A very important feature is also to provide multiple end-use needs simultaneously, such as heating, cooling, and electricity, since this allows energy carrier substitution and increased energy efficiency due to waste heat utilization for heating, domestic hot water, and cooling purposes (cross sectoral energy usage).