To solve the problem of flexible application of high voltage direct current(HVDC)systems in long distance bulk power overhead line transmission

based on modular multilevel converter(MMC)with double clamp sub-module topology and dual thyristor sub-module topology

a bipolar hybrid MMC based HVDC(MMC-HVDC)transmission system is designed not only to tackle the level of DC voltage

output capacity and DC fault suppression capability

but also to solve the great energy consumption or long DC link fault enduring issues. The equivalent circuit and fault blocking mechanism is analyzed under different DC link faults

and the system restart process is also designed. Finally

the hybrid HVDC is built in PSCAD/EMTDC simulation environment

and a variety of operating conditions and fault ride-through characteristics of the system are studied. Simulation results show that the bipolar hybrid system has not only flexible and diverse steady-state operation characteristics

but also DC fault ride-through and rapid recovery capabilities better suited to large capacity long distance overhead line transmission applications.