Modeling of Litz Wire Winding AC Resistance Based on Improved Segmented Equivalent Circuit

Litz wire is a promising solution for reducing winding loss in high-frequency magnetics, but modeling its ac resistance remains a challenge. This article proposes the improved segmented circuit method (iSEC) for modeling the ac resistance of concentric and composite litz wires. The method approximates the twisting effect of litz wire by using segmented parallel strands that are cascaded into segmented circuits. The segmented circuit is then simplified to a matrix calculation based on the twisting characteristics, reducing computational consumption while maintaining accuracy. The impedance matrix is calculated using the one-dimensional field and the proposed modified coefficient. Consequently, iSEC can fully analytically calculate the ac resistance of concentric and composite wires. The method is validated in the 2 MHz range using transformer samples with various configurations, and the average error in the studied cases is 11.1%.