New modular multilevel converter with power channels between upper- and lower arms suitable for MV drives

When a modular multilevel converter (MMC) is operated at low frequencies, the submodule (SM) capacitors will suffer from huge voltage fluctuations. This problem must be overcome before MMCs find wider applications in medium voltage (MV) drives that require a wide speed range. The established solution for suppressing the voltage fluctuation have been injecting high frequency common-mode voltage and circulating current into each phase leg. This inevitably increases current stress of the power devices, which is not welcome in high power applications. Based on the fact that the pulsating powers of the upper- and lower arms are in opposite phase, this paper aims to eliminate the voltage fluctuation via added power channels between the upper- and lower arms of each phase. These power channels can also be used for active power decoupling, which can greatly reduce the SM capacitance.