Trends in the protection of inverter-based microgrids

The study reviews the current trends in the protection of inverter-based microgrids. This topic is currently given significant attention, as the inverter-interfaced distributed generation is likely to become dominant in microgrids. Since low fault current is a well-known signature of microgrids, the emphasis is on the complicated fault characteristics in inverter-based microgrids, bearing in mind that low-magnitude fault current and complicated fault responses are inter-related. The fault characteristics are rooted in the inverter controllers that can control inverter voltages and currents during the fault period such that they are completely different from the conventional fault characteristics. Given that these differences could impact conventional protection schemes, challenges to different elements of fault identification, i.e. fault detection, fault polarisation, and faulted phase selection in microgrids are separately addressed in detail. The existing preliminary solutions that define the current trends are discussed and gaps are identified accordingly. The review classifies techniques into three categories: modified classical techniques, heuristic techniques, and differential-based techniques. The explanations are supported by simulation case studies to provide clarification. The purpose is to provide the current status of microgrid protection and assist in developing new effective solutions to protect these grids.