The present invention relates to an MMC converter system which can quickly cut off fault current by installing a plurality of disconnecting switch units on a line connected between two MMC converter devices. The MMC converter system comprises: a first MMC converter device including a plurality of serially connected sub modules; a second MMC converter device including a plurality of serially connected sub modules; a first disconnecting switch unit installed on a line between the first and second MMC converter devices; and a second disconnecting switch unit connected in series to the first disconnecting switch unit on the line, wherein each of the first and second disconnecting switch units comprises a mechanical switch installed on the line so as to open and close the line and a diode connected in parallel to the mechanical switch, and the two diodes are installed in opposite directions to each other.