Semi-Analytical AC Resistance Prediction Model for Litz Wire Winding in High-Frequency Transformer

The importance of the high-frequency transformer in power electronics devices cannot be overstated. Its compact design is made possible by operating in a high-frequency range, although winding losses increase due to eddy current effects. One solution to this problem is using litz wire, which has a small cross-sectional area and is less affected by eddy current effects at high frequencies. However, accurately predicting winding loss in litz wire is challenging due to efficiency and accuracy concerns as well as the impact of influencing factors. Prior articles have focused on the strand structure of litz wire conductors, often ignoring the impact of operating conditions and geometrical parameters on leakage field distribution and ac resistance. To address this gap, this article introduces a simple semi-analytical model with revised coefficient to enhance the accuracy of conventional ac resistance prediction models. The model considers the interplay between winding structure and core as well as the influence of operating conditions on the conductor. The article examines the winding loss of litz wire in a high-power transformer using this model. Experimental prototypes based on the resulting formulas confirm improved matching between calculation results and measurements.