AC resistance calculation methods and practical design considerations when using litz wire

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 skin depth, which allows the approximation of litz wire AC 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.