An enhanced MMC topology with DC fault ride-through capability

Abstract

High-voltage direct current system using modular multilevel converter (MMC-HVDC) is a potential candidate for grid integration of renewable energy over long distances. The dc-link fault is an issue MMC-HVDC must deal with. This paper proposed an enhanced MMC topology with dc fault ride-through capability. By using diode clamp sub-modules, the freewheeling effect of diodes is eliminated and fault currents can be very rapidly extinguished. Since the tripping of circuit breakers is avoided, MMC can immediately restart power transmission for non-permanent faults. The required rated voltage of additional semiconductors is half the conventional semiconductors, resulting in low extra cost. Simulation results using PSCAD/EMTDC have verified the validity of the proposed protection scheme.