Design and electric field analysis of novel winding structures with fillets for medium frequency transformers

The medium frequency transformer (MFT) has a significant role in large‐capacity DC–DC convertors, whereas the design of insulation under compact structures remains a critical challenge. Generally, the electric field strength near the winding edges is much larger than other positions. To fulfil insulation requirements, the distance between windings and the magnetic core needs to be enlarged, which also expands the window area of the core and the total volume of the MFT. A series of winding structures with fillets is proposed, including constructing winding fillets with reshaped foil and adopting different techniques to fillet the foil. The finite‐element method is used to analyse the insulation effects of various winding structures with fillets, conducted under diverse voltage levels and insulation materials commonly used in MFTs. The structures can substantially reduce the local electric field strength, further compressing the volume of the MFT.