Medium-frequency transformer scaling laws: Derivation, verification, and critical analysis

Medium-frequency transformers (MFTs) are one of the fundamental building blocks of modern power electronic converters. The usage of increased frequencies leads to improved characteristics, i.e., efficiency and power density (volumetric and gravimetric) but also to design challenges and constraints. This paper reviews the analytical modeling of MFTs. More particularly, the mapping between the design space and the performance space is analyzed. It is found that wide regions of the design space are mapped to a narrow region in the performance space, i.e., the optimum is flat and designs with very different parameters features similar performances (design space diversity). Scaling laws are derived for optimal MFTs operated at different power ratings and power densities, which provide a comprehensive and general insight on the achievable performances. In a next step, the results obtained with the analytical model are compared to numerical simulations. It is concluded that the derived scaling laws capture qualitatively and quantitatively the behavior of MFTs, but should be used with caution for accurate design processes.