Influence of inner skin- and proximity effects on conduction in litz wires

For inductive components such as coils, inductors or transformers, litz wires with isolated strands are used to decrease conduction losses in applications with higher operating frequencies. Depending on the inner structure of these wires, the frequency dependent losses differ extremely. Until now simulations have not sufficiently matched experimental measurements. The usual simulation approach has been to assume the initial current values in all strands in the litz wire to be the same. In this paper, a 3-D simulation of the connector allows the determination of the current values depending on the position of the strands in the wire. This current distribution is transferred to a 2-D rotationally symmetric simulation of the system (windings, coils, etc.). The current values are permuted between different strands to simulate the twisting of strands inside the litz wire. With this new method a very good agreement with measured losses was achieved and demonstrates how simulation allows one to improve the performance of litz wires.