Abstract: The DC fault current calculation method of modular multilevel converter（MMC）is the key to study

the DC fault transient characteristics and isolate the fault point rapidly in VSC-HVDC grid. Firstly，aiming at two

typical MMC fault equivalent models，the topology and the capacitor voltage characteristics when the fault occurs

were compared and analyzed. Secondly，considering the submodules′capacitor voltage balancing mechanism of

each MMC arm，the average capacitance calculation method of MMC was proposed，and then the MMC DC fault

current calculation method based on average capacitance was proposed. Finally，the MMC-HVDC model was built

on PSCAD/EMTDC and the precision and applicability of the DC fault current calculation method was verified.

      Key words: modular multilevel converter（MMC）；DC fault current；fault equivalent model；average capacitance