1. Center for Advanced Power-conversion Technology and Equipment, Southeast University, Nanjing 210096, China;2. Nanjing Power Supply Company of State Grid Jiangsu Electric Power Co. Ltd., Nanjing 210008, China

With the rapid development of high voltage direct current(HVDC)transmission and the increasing complex structure of DC power grid, DC power-flow regulation and short circuit fault interruption have become more and more prominent. Based on the technology of interline direct current power flow controller and fault suppression, this paper proposes a novel unified device of power flow controlling circuit breaker(PFCCB)for DC power grid, which combines power flow controller and DC circuit breaker. The PFCCB can not only adjust the power flow flexibly between two lines, but also curb the short current and cut off the fault line in time. Its operating principles, control strategy and performance are analyzed in a three-terminal meshed grid with PFCCB. Simulation is also made with PLECS software and the results validate the feasibility and effectiveness of PFCCB.