A review of coordination strategies and protection schemes for microgrids

Distributed generation (DG) using renewable energy resources, is intended to reduce the impact of power generation from fossil fuels on climate change. Microgrids (MGs) represent a method of interconnecting several low voltage (LV) renewable energy sources and loads to the distribution system. Multi-microgrids (MMGs) integrate distributed generators (DGs) and MGs with medium voltage (MV) distribution systems. Protection system design for MGs pose significant challenges due to bi-directional flow from DGs as well as lower fault current levels due to the inverter connected DG sources in islanded MGs. This paper reviews the coordination strategies and protection schemes that have been proposed for MGs to address these challenges. The protection coordination strategies based on communication and time grading including their relative performance are described. The advantages and limitations of existing MG protection schemes are discussed. As most of these protection schemes apply to relatively small MGs, they may need to be extended for larger MG configurations in practical power systems. Some future directions for research in the protection system design for both MGs and MMGs are also outlined in this paper.