Analytical Models for HF-Losses of Litz Wire in Inductors With Arbitrary Winding and Gap Arrangements

Dueto 2D fields in the core window of inductors (e.g. the fringing field caused by core gaps) large errors can occur in the winding loss calculation, when the assumptions, that the $H$-field is parallel to the winding layers and constant along the field line, used for transformers are applied. Numerical methods, e.g. FEM, are accurate but are very time consuming for calculating the losses of litz wire windings and therefore cannot be integrated in converter optimisation routines, which require a fast execution due to the large number of evaluations. To overcome this limitation, this paper proposes a fast and accurate loss model for litz wire winding in inductors with arbitrary winding and gap arrangements. The application range of the proposed model covers inductors using cores with single and discrete gaps, and iron powder cores with distributed gaps. The proposed method is numerically and experimentally validated to be more accurate than state-of-the-art methods as e.g. the mirror image method and up to 1000 times faster than the semi-numerical method i.e. the square-field-derivative method with better or equivalent accuracy.