Accurate Calculation of Eddy Current Loss in Litz-Wired High-Frequency Transformer Windings

As the power capacity of high-frequency transformer increases, the requirement on transformer efficiency gets higher and higher. Due to the rapid increase of switching frequency, the eddy current loss of high-frequency transformer windings becomes more and more significant. The use of litz-wire can reduce the high-frequency loss to some extent. The two most well-known methods for calculating the high-frequency power loss in round wire windings are the Dowell and Ferreira methods. These two models, however, are inaccurate under some conditions, because of the assumptions made in the establishment of the models. This paper presents an accurate model to calculate the power loss in litz-wired windings, through analysis of the skin and proximity effects from a single conductor to the whole twisted litz-wire. To extend the model into a 3-D calculation model, the twist effect is considered. The new model has a good accuracy within a wide bandwidth of frequency, and can be used for the electromagnetic design of high-frequency devices.