A High-Frequency MMC for DC–DC Applications Using a Three-Winding Transformer With DC Flux Cancellation

In this article, a novel high-frequency isolated modular multilevel dc–dc converter is proposed for large step ratio, medium voltage dc–dc applications. The proposed converter is based on the recently introduced class of converters termed the current shaping modular multilevel dc–dc converter (CS-MMC). In the CS-MMC, no string inductors are required and only a fraction of the voltage source modules are switched in each fundamental ac period enabling high effective frequencies to be achieved. The proposed converter builds on this earlier work by introducing a new topology featuring galvanic isolation using only a low voltage, high-frequency, three-winding transformer, and imposing dc flux canceling within the transformer. This article describes the converter architecture, its operating principles, and a control design. Experimental results are provided from a 1250V to 145V, 50 kHz laboratory-scale prototype with a peak measured efficiency of 96.8% at 2.8 kW.