A Comprehensive Review of DC Microgrids: Controls, Topologies, Protection and Future Trends

Microgrids are important technologies for increasing the penetration of renewable energy sources (RESs). Compared with AC microgrids, DC microgrids avoid frequency regulation and reactive-power compensation. Moreover, many RES interfaces and energy storage systems (ESSs) are DC or DC-link based; therefore, they can be integrated into DC buses with fewer conversion stages, reducing conversion losses. Consequently, DC microgrids have attracted increasing attention. This paper reviews DC microgrid topologies, hierarchical control methods, and protection schemes. First, the representative topologies are compared from the perspectives of structural features, control implications, protection requirements, and application scenarios. Next, primary, secondary, and tertiary control strategies are analyzed, with emphasis on droop control, virtual impedance, virtual inertia, fractional-order control, communication delay, and energy management. Protection issues, including fault detection, fault interruption, and ground-fault protection, are then discussed with respect to topology–control interactions. Finally, future research trends and challenges for DC microgrids are summarized.