A LCC and MMC hybrid HVDC topology with DC line fault clearance capability

• A LCC and MMC hybrid HVDC topology suitable for bulk power transmission is proposed.
• The start-up process of the topology is implemented in two stages.
• The LCC blocks itself to ride through dc faults.
• High power diodes are installed in the overhead line near MMCs to clear dc faults.
• A hybrid three terminal HVDC system is modeled in PSCAD/EMTDC.

This paper proposes a LCC and MMC hybrid HVDC topology with dc line fault clearance capability suitable for bulk power transmission, in which the rectifier adopts a line commutated converter (LCC) and the inverters adopt two modular multilevel converters (MMCs). Resiliency to dc line faults can be achieved by alpha-retard of the LCC and the high power diodes installed in the overhead line close to the inverters. The start-up process is implemented in two stages. A hybrid HVDC system is modeled in PSCAD/EMTDC to demonstrate the effectiveness of the control system and the start-up scheme. Moreover, simulation results of a dc line fault confirm the feasibility that the fault current paths can be blocked by alpha-retard of the LCC and the installed high power diodes, and the whole system is able to restart after clearance of the transient dc line fault.