A Modular Multilevel Converter (MMC) includes multiple sub-modules connected in series with each other and a controller for controlling on/off switching of the sub-modules, in which the multiple sub-modules include N sub-modules that participate in the operation of the MMC and M redundant sub-modules for replacing at least one N sub-modules when the at least one N sub-modules fail, and the controller switches on a sub-module if a carrier signal assigned thereto is higher than a preset reference signal, and switches off the sub-module if the carrier signal assigned thereto is lower than the preset reference signal.