Modeling of a Litz Wire with Perfect Strand Pattern

The paper deals with a novel modelling procedure for characterizing the AC resistance of Litz wires. These wires are composed by many twisted conductive strands which are individually insulated to reduce the skin and proximity effects. Litz wires are widely used in many applications, like transformers, induction heating or wireless power transfer (WPT) systems. The prediction of the AC resistance is not very easy and requires heavy 3D numerical calculations. Here a novel procedure is presented where the Litz wire strands have been assumed to be a uniform multiconductor transmission line (MTL). A simplified assumption is then made considering an ideal Litz wire where all the strands have a perfect transposition. It means that all the strands are assumed to have the same path, impedance and current. The results in terms of AC resistance obtained with the proposed method is compared with measured values revealing very good accuracy.