Unified control strategy of islanding and grid-connected operations for DC microgrid

DC microgrids are gaining an increasing interest because more and more DC load and DC power generation are used in renewable energy applications. In this paper, an autonomous control scheme based on DC bus voltage levels was proposed in a low-voltage single type DC bus microgrid system. The design ideas of control scheme combined both grid-connected and islanding operating conditions. In the system, distributed power generation units and battery energy storage system operating in constant voltage control can achieve power sharing by added droop control. The design method of droop gain was presented. A power cut-back control strategy for non-critical loads converter was proposed. The simulation results demonstrated the proposed scheme during various operating conditions. The system can automatically skip to islanding mode from grid-connected mode in case of AC grid failure. Non-critical loads converter can switch to power-reducing mode when the energy in the system is deficient and improves the system available operating range. © 2015 Chin. Soc. for Elec. Eng.