A Novel Hybrid Core Structure for 100kW Medium Frequency Transformers

Nanocrystalline has been a promising magnetic material for high power medium frequency transformers (MFT). However, the high conductivity and the laminated core structure make the leakage flux induced eddy current loss a major limitation for the nanocrystalline-based MFT at higher operation frequencies, especially when a certain amount of leakage inductance is needed by the topology. This paper proposes a novel nanocrystalline ferrite hybrid core that eliminates the local hot spots caused by the eddy current loss and reduces the overall core loss. Several different hybrid core structures are compared through finite element analysis (FEA) to show the superior performance of the proposed structure. The validity of the proposed structure is verified by experimental results, where a maximum temperature reduction of 39.9°C and almost 70% reduction in transformer loss is observed. This new hybrid core structure is therefore an important concept for better transformer design in applications such as the solid-state transformer (SST).