1.Key Laboratory of the Ministry of Education on Smart Power Grids (Tianjin University), Tianjin 300072, China;2.Tianjin Key Laboratory of Power System Simulation and Control (Tianjin University), Tianjin 300072 China;3.State Grid Jiangsu Electric Power Co., Ltd., Nanjing 210000, China;4.Electric Power Research Institute of State Grid Jiangsu Electric Power Co., Ltd., Nanjing 211000, China

With the development of power electronic technology, flexible DC distribution system has gradually become a research hotspot. Single-pole grounding fault is the most common fault type in the DC distribution system. When the AC side is grounded through high resistance, the change of fault current is not obvious after the single-pole grounding fault occurs on DC side, so it is difficult to accurately locate the fault. Based on the coordination of control and protection, a single-pole grounding fault protection strategy is proposed for double-terminal DC distribution system. By detecting the current differential of the AC grounding branch on the spot to judge the occurrence of the fault, the small resistor in parallel on the AC grounding branch can be switched on quickly. Compared with traditional differential protection methods, the proposed method saves the communication time and effectively improves the rapidity of the protection. At the same time, according to the requirements of protection reliability, the resistance value of the parallel small resistor is optimized. Finally, the simulation analysis is carried out in PSCAD/EMTDC platform to verify the reliability and rapidity of the proposed protection strategy.