The converters without the DC fault clearing capability limit the wide application and development of overhead lines in flexible DC transmission projects. The fault mechanism and DC fault currents transient characteristics of DC short-circuit faults on the DC side of flexible HVDC transmission systems are analyzed in detail. For the hybrid modular multilevel converter (MMC) based on half bridge submodule and full bridge submodule, the MMC-blocked DC fault ride-through strategy and MMC-non-blocked DC fault ride-through strategy after DC short circuit fault are analyzed comparatively. An MMC non-blocking DC fault ride-through control strategy which can improve the DC short-circuit fault clearing speed is proposed. Finally, a DC grid simulation model is built on the PSCAD/EMTDC platform to verify the effectiveness and feasibility of the proposed control strategy.

DC short-circuit faults, fault ride-through, Modular multilevel converter