DC fault analysis and protection design in shunt modular multilevel-based MTDC system

Abstract

Modular multilevel converters (MMC) are ideal next-generation multilevel converters well-suited for the high-voltage direct current (HVDC) transmission for multiterminal DC systems. However, the accidental DC faults in the cable or overhead lines, could give rise to safety concerns on transmission lines and converter stations. A protection design based on three-terminal voltage margin control method is proposed incorporating bypass thyristor and IGBT circuit breakers (IGBT-CBs) at DC side. In addition, IGBT-CBs isolate the DC line in case of a permanent fault utilizing the principle of handshaking method, making normal operation of the remaining system possible. This protection scheme is validated by the simulation studies on PSCAD/EMTDC, thereby demonstrating an improved DC fault reverse blocking capability of MMC-MTDC system.