Comparison of Litz Wire and PCB Inductor Designs for Bidirectional Transformerless EV Charger with High Efficiency

Abstract

Inductor design can be a process of repetitive core searching and iterative turn and airgap calculation, where every decision to be made involves a trade-off in terms of power loss, cost and power density. This paper deeply discusses the inductor design for a transformerless DC EV battery charger where inductance and operating DC bias are required to be high ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{500}\ \ \mu \mathrm{H}$</tex> and 32 A). The design of the charger's filter is discussed to provide the values of the passive components and to motivate the inductor design. Two commonly used but seldom compared winding options, Litz wire and printed circuit board, are both designed and examined with respect to power loss and difficulty of the fabrication. Through tuning of the trace width and copper weight, the PCB design can provide similar performance to the Litz wire configuration, at higher cost and increased manufacturing complexity. In order to verify the text-colorblacktheoretical calculations, high-fidelity 3D finite element analysis is performed for both inductor types. After comparison, the Litz wire implementation was chosen for its reduction in power losses, cost and manufacturing complexity. The Litz wire inductor is assembled and tested on a transformerless DC charger platform with ≥ 99% efficiency at 11 kW and ≥98% efficiency at up to 22 kW.