DC Fault Transient Characteristics and Fault Ride-through Control Strategy Based on Hybrid MMC-HVDC

For the problem that converters without DC fault clearing capability limit the widespread application and development of overhead lines in flexible DC transmission, the fault mechanism and DC fault current transient characteristics of the DC short-circuit fault on the DC side of the flexible HVDC transmission system are analyzed in detail. For the hybrid modular multilevel converters based on half bridge submodules and full bridge submodules, the blocking converter DC short-circuit fault clearing strategy and the non-blocking converter DC short-circuit fault ride-through strategy after DC short-circuit fault are studied in contrast. A judgment condition for restart of non-blocked converter after clearance of DC short circuit fault is proposed. Finally, the simulation model of DC power grid is built on PSCAD/EMTDC platform to verify the effectiveness and feasibility of the proposed control strategy.