Dynamic interactions of DC and AC grids subject to DC faults

DC circuit breakers (DCCBs), AC circuit breakers (ACCBs) and Full-Bridge Modular Multi-Level Converters (FB-MMCs) can be used to block DC fault current in voltage source converter-based (VSC) multi-terminal high voltage direct current (MTDC) grids. However, the DC fault transient characteristics of AC/DC networks will be different depending on the type of devices used to protect the DC grid. In this paper, the DC fault clearance and post-fault restoration processes using DCCBs and ACCBs are analyzed. The transient response of the AC/DC system during DC faults is also assessed considering the analyzed approaches. The studies are conducted in PSCAD/EMTDC, where an integrated AC/DC transmission system has been modeled. Simulation results indicate that a different transient behavior arises when different fault isolation and post-fault restoration schemes are employed. The work of this paper provides an understanding of the dynamic behavior in AC/DC systems, in turn contributing to a deeper comprehension of system operation and control system design.