Protection issues and state of the art for microgrids with inverter-interfaced distributed generators

One of the most challenging topic related to practical implementation of innovative distribution network paradigms, such as microgrids, is fault protection. General solutions, guidelines and standards, somehow defined worldwide for traditional distribution systems, have not been found yet and perhaps even not possible for microgrids protection. It is still necessary to investigate different potential solutions and application contexts, especially for microgrid protection in presence of inverter-interfaced distributed generators (IIDGs), typical with renewable energy sources. The main aim of this work is pointing out the issues related to this complex problem, as well as presenting the state of the art about the protection schemes proposed during the last years. The focus will be on microgrids supplied by IIDGs, which pose additional problems on the difficult field of microgrids protection.