Comparative Evaluation of Different Cables for Magnetic Couplers in Inductive Power Transfer Systems

Copper litz wires are widely used in wireless charging stations of light-duty electric vehicles. This type of cable is specifically mentioned in the SAE J2954 standard. However, details as the number and diameter of strands, or the material of conductors are not mentioned in the standard, which makes room to address some research and innovations. In this work, several alternatives to the traditional copper-litz wires are analyzed. Specifically, aluminum litz wire, copper-clad aluminum litz wire, and copper tubes are considered as alternatives to standard litz wire for the mentioned application. Potential benefits of the considered alternatives could include weight and cost savings. However, these advantages could not be enough to justify a wiring change if the resistance of the power pads increases and, equivalently, the efficiency of the electromagnetic power transfer decreases. For this reason, a model of the parasitic resistance of windings is proposed by combining the analytical ac resistance of two-layered round strands and finite element simulations. This model is used to obtain a figure of merit related with the efficiency of the electromagnetic energy transfer which is used to compare the different cables. Apart from efficiency, thermal behavior, cost and weight are also considered for comparison purposes. As a result, some conclusions about the suitability of each cable with respect to the operating frequency range are extracted.