A PCB Integrated Winding Using a Litz Structure for a Wireless Charging Coil

The market of electric vehicles has experienced a rapid growth in the recent time due to global warming, increasing oil prices and pollution regulations. Wireless charging has gained recent attention through the increased customer convenience and the higher robustness compared to conventional charging systems. A key design factor for the vehicular coil is the limited space - thus, high power density is mandatory. This paper presents a novel planar secondary coil design. The utilization of PCBs interconnected by soldering pins results in a very cheap design while having a low height. To overcome high conductions losses, the PCB utilizes litz wires designed using FEM analysis. A three-step design procedure is described. In a first step, different litz wire geometries are compared. In a second step, the PCB's height is optimized to minimize losses for the chosen geometry. Finally, the strand width is chosen according to a loss optimization. The produced prototype shows a significant reduction of the winding losses by more than 50% compared to the non-litz design.