Abstract Modular multilevel converter (MMC) with half-bridge sub-modules (SMs) is the most promising technology for high voltage direct current (HVDC) grids, but it lacks DC-fault clearance capability.Aiming at the frequent transient DC faults in flexible HVDC, the paper proposes a way of DC fault isolation based on hybrid bypass in MMC-HVDC. When DC-fault occurs, get the bypass thyristor connected, then remove the residual current of the bridge arm by virtue of arrester and isolate the DC line by a fast mechanical switch. Hybrid bypass DC-fault isolation scheme can isolate immediately the MMC and DC transmission line, and the MMC is capable of operating in STATCOM mode after fault isolation. A model of a two-terminal monopolar HVDC grid is developed in PSCAD/EMTDC.
2017, Vol. 18 
