Partial Interleaving: A Method to Reduce High Frequency Losses and to Tune the Leakage Inductance in High Current, High Frequency Transformer Foil Windings

The paper describes a method for reducing the winding losses and for tuning the leakage inductance of transformers with foil windings. A new way of interleaving foil windings called "partial interleaving" is used to adjust the profile of the magnetic field. This results in relatively low field intensity and hence low eddy current losses in the windings. The partial interleaving is mainly suitable for transformers with winding ratio close to 1. Together with the partial interleaving, a layer of magnetic polymer is used in the windings to enhance and to tune the value of the leakage inductance. The main design objectives are to keep windings simple and to achieve high power density. The partially interleaved design is compared with a foil winding without interleaving. The method is demonstrated for a 50 kW transformer where a clear improvement is observed. Using the method resulted in a transformer volume of less then 2 litres. The paper also discusses two analytical methods for calculating the winding losses of the partially interleaved windings. FEM simulation is used as the reference