A microgrid is a small network of electricity users with a local source of supply that is usually attached to a larger grid but can function independently. The interconnection of small scale generating units, such as PV and wind turbines, and energy storage systems, such as batteries, to a low voltage distribution grid involves three major challenges: variability, scalability, and stability. It must keep delivering reliable and stable power also when changing, or repairing, any component, or under varying wind and solar conditions.