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This paper reviews and compares two easily applicable methods used to calculate the AC resistance and an optimal strand diameter for a litz wire. The methods can be implemented in mathematical software, such as MATLAB, by using the equations and program listings given in this paper. The practical limitations of the litz wire are discussed based on the results of the methods. The AC to DC resistance ratios are plotted as a function of various strand diameters with respect to sk in d ep th , w h ic h a l lo w s th e a p p ro x im a t io n o f litz w ire A C resistance with a small calculation effort. The analysis and results presented in this paper are verified by measurements and FEM simulations with various litz wire configurations.

This paper discusses the accuracy of typical AC resistance calculation methods in gapped inductors. It is shown that despite the additional losses caused by fringing flux induced eddy currents, the calculated resistances can be overestimated considerably due to non-tangential field distribution and reduced winding proximity losses. However, this phenomenon is not so significant with windings having only a few winding layers; in such cases 1D calculation methods can be useful in predicting the winding resistances. It is also demonstrated how the fringing flux induced losses affect the calculated results and how they can be taken into account when using the 1D methods.

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