High Frequency Transformer Core Loss Analysis in Isolated Modular Multilevel DC-DC Converter for MVDC Application

An Isolated Modular Multilevel DC-DC Converter (iM2DC) operating with Phase Shifted - Square Wave Modulation (PS-SWM) featuring reduced passive components and low Total Device Rating (TDR) for MVDC applications is presented here, and the effect of the PS-SWM modulation scheme on high frequency (HF) transformer core loss is analyzed. A down-scaled iM2DC prototype is built with a 1:1 transformer and it is proved that the transformer losses are not affected by the staircase shaped voltage of the PS-SWM modulation. The transformer core loss is analytically found equal to the core loss obtained with pure square wave voltage excitation with 50% duty ratio. This simplifies the HF transformer design and optimization process for this application. The core loss is experimentally measured and validated.