I. Introduction
The research interests in power electronic systems are penetrating more and more extensive areas of application in energy transmission, industry, and mobility [1], [2], [3]. To fulfill requirements on power density and efficiency, power magnetic devices are often applied under high-frequency operation [4]. With high frequency, frequency-dependent losses come into focus for system design and optimization. Litz wire is widely utilized in power magnetic components that carry high-frequency alternating current (ac), such as the transformers and inductors of high-frequency resonant systems [5], [6], [7]. The decision to use litz wires over the equivalent solid wire in high-frequency magnetic components design comes down to the loss reduction offered.