Space vector modulation method for modular multilevel converters

This paper presents a generalized space vector modulation (SVM) method for any modular multilevel converter (MMC). The proposed SVM method produces the maximum level number (i.e., 2n+1, where n is the number of submodules in the upper or lower arm of each phase) of the output phase voltages and a higher equivalent switching frequency than other modulation methods, which consequently leads to reduced harmonics in the output voltages and currents. Compared with earlier modulation methods for MMCs, the proposed SVM method provides two more degrees of freedom, i.e., the redundant switching sequences and the adjustable duty cycles, thus offering significant flexibility for optimizing the circulating current suppression and capacitor voltage balancing. This SVM method is a useful tool for further studies of MMCs, as it can be conveniently extended for any control objectives. The demonstrated results validate the analysis.