Improved Litz-Wire Designs for the MHz Range

Alternative litz wire configurations for cases in which the skin depth is smaller than the minimum practical strand diameter are analyzed. This is common for designs in the low MHz frequency range. A new modeling method allows for inclusion of bundle-level skin effect losses in wires with non-ideal construction. Three wire types are compared over a large simulation range: solid wire, standard litz wire, and a “hollow” litz wire structure in which strands are confined to the outer perimeter of a dielectric core. We show that the hollow litz structure is superior to standard litz for many high-frequency designs, and that both litz types have lower loss than solid wire at higher frequencies than indicated by previous models. Measurements of large-scale standard and hollow litz wire prototypes verify these findings.