Analytical model for effects of twisting on litz-wire losses

Abstract

Litz wire uses complex twisting to balance currents between strands. Most models assume that the twisting works perfectly to accomplish this balancing, and thus are not helpful in choosing the details of the twisting configuration. A complete model that explicitly models the effect of twisting on loss is introduced. Skin effect and proximity effect are each modeled at the level of the individual strands and at each level of the twisting construction. Comparisons with numerical simulations are used to verify the model. The results are useful for making design choices for the twisting configuration and the pitches of each twisting step. Windings with small numbers of turns are the most likely to have significant bundle-level effects that are not captured by conventional models, and are the most important to model and optimize with this approach.