Three-dimensional semi-finite element based proximity loss calculation for Litz wires in a high frequency transformer

Litz wires can be used to effectively reduce the skin effect loss while the proximity loss can be still significant considering the possible high flux densities produced by neighboring strands. This paper proposes a three-dimensional semi-finite element (semi-FE) based proximity loss calculation approach for Litz wires in a high frequency transformer. A set of analytical equations which are dedicated to the semi-FE approach for proximity loss calculations are derived. Compared to the existing semi-FE methods, the proposed method calculates proximity loss with volumetric factors in each element and hence can eliminate the error caused by the possible nonuniform mesh in winding regions. Experimental measurements show that compared to the conventional method, the proposed semi-FE method can predict closer proximity loss to measured results.