Optimization of stranded-wire windings and comparison with litz wire on the basis of cost and loss

Stranded wire with uninsulated strands has been proposed as a low-cost alternative to litz wire. In this paper, we develop a method to optimize stranded-wire designs on the basis of cost and loss, and compare the results to optimized litz-wire designs. A simply calculated parameter is shown to be useful to predict when each type of wire is preferred. A method to extend both loss prediction and optimization for arbitrary geometries and waveforms is also introduced. Deliberate oxidation of strands is proposed as a method to improve performance of stranded wire, and to increase its range of applicability. Experimental measurements with approximately 0.15 /spl mu/m oxide show dramatic increases in interstrand resistivity, indicating that this approach could be very effective.