Protection coordination of meshed MMC-MTDC transmission systems under DC faults

Modular multilevel converter (MMC) is very convenient to construct the multi-terminal DC transmission systems (MTDC). The MTDC is most vulnerable to a DC fault, so it is necessary to have the detailed study of the fault characteristics in order to design the corresponding protection schemes. The MMC topology and its working principles are introduced and corresponding steady-state control strategy for MMC-HVDC is analyzed. The DC line-to-ground fault, pole-to-pole fault and the open circuit fault were simulated in PSCAD/EMTDC. On the basis of the work mentioned above, a six-terminal DC connected transmission system model is built. The DC fault characteristics are analyzed on this model and corresponding protection schemes are proposed.