A Modular Multilevel Converter (MMC) , comprising: multiple sub-modules connected in series with each other; and a controller for controlling on/off switching of the sub-modules , wherein: the multiple sub-modules include N sub-modules , which participate in operation of the MMC , and M redundant sub-modules , which participate in the operation in place of a failing sub-module when at least one of the N sub-modules fails; the controller switches on a sub-module if a carrier signal assigned thereto is higher than a preset reference signal , and switches off a sub-module if a carrier signal assigned thereto is lower than the preset reference signal , among the N+M sub-modules to which the carrier signals are assigned; each of the carrier signals of the N+M sub-modules is configured such that a range from a top to a rest position thereof is not balanced with a range from a bottom to the rest position thereof, such that when the reference signal oscillates within a top-to-bottom range from -A to +A, each of the carrier signals oscillates within a top-to-bottom range from -A to + (A × (N + M) / N) ; and N+M carrier signals are assigned to the N+M sub-modules , respectively, and N sub-modules , selected from among the N+M sub-modules , rotationally participate in the operation of the MMC . multiple sub-modules connected in series with each other; and a controller for controlling on/off switching of the sub-modules , wherein: the multiple sub-modules include N sub-modules , which participate in operation of the MMC , and M redundant sub-modules , which participate in the operation in place of a failing sub-module when at least one of the N sub-modules fails; the controller switches on a sub-module if a carrier signal assigned thereto is higher than a preset reference signal , and switches off a sub-module if a carrier signal assigned thereto is lower than the preset reference signal , among the N+M sub-modules to which the carrier signals are assigned; each of the carrier signals of the N+M sub-modules is configured such that a range from a top to a rest position thereof is not balanced with a range from a bottom to the rest position thereof, such that when the reference signal oscillates within a top-to-bottom range from -A to +A, each of the carrier signals oscillates within a top-to-bottom range from -A to + (A × (N + M) / N) ; and N+M carrier signals are assigned to the N+M sub-modules , respectively, and N sub-modules , selected from among the N+M sub-modules , rotationally participate in the operation of the MMC . the multiple sub-modules include N sub-modules , which participate in operation of the MMC , and M redundant sub-modules , which participate in the operation in place of a failing sub-module when at least one of the N sub-modules fails; the controller switches on a sub-module if a carrier signal assigned thereto is higher than a preset reference signal , and switches off a sub-module if a carrier signal assigned thereto is lower than the preset reference signal , among the N+M sub-modules to which the carrier signals are assigned; each of the carrier signals of the N+M sub-modules is configured such that a range from a top to a rest position thereof is not balanced with a range from a bottom to the rest position thereof, such that when the reference signal oscillates within a top-to-bottom range from -A to +A, each of the carrier signals oscillates within a top-to-bottom range from -A to + (A × (N + M) / N) ; and N+M carrier signals are assigned to the N+M sub-modules , respectively, and N sub-modules , selected from among the N+M sub-modules , rotationally participate in the operation of the MMC . <EOS>