A Modular Multilevel DC-DC Converter With Flying Capacitor Converter Like Properties

This article proposes a novel modular multilevel dc-dc converter with high power-density potential based on a cascaded string of voltage source submodules (VSMs) merged with a current source submodule (CSM) that is configured to rapidly invert the polarity of the current in the VSM string. The proposed hybrid converter combines the modularity advantages of the modular multilevel converter (MMC) and the high effective frequency advantages of the flying capacitor converter. Unlike other hybrid nonisolated MMC structures the proposed converter features a novel CSM stage enabling a near 50% reduction in string current, and the input source and output load to be commonly grounded. In addition, the proposed operational approach enables self-balancing of the VSMs and a simple overall control structure. This article introduces the main operating principles of this novel topology termed the current shaping modular multilevel forward converter along with a proposed control design. A peak efficiency of 97.1% is measured from a laboratory-scale prototype at 950-137V and 1.45 kW.