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. © 2020 IEEE.