Feasibility Study of Nanocrystalline-Ribbon Cores for Polarized Inductive Power Transfer Pads

Abstract

MnZn-based ferrite materials like the EPCOS N87 or K2004 are commonly used as magnetic cores in inductive power transfer (IPT) applications. However, the performance and the reliability of IPT systems are limited by ferrite's intrinsic brittleness and low flux density saturation point. In this article, a study of nanocrystalline-ribbon-based magnetic cores for IPT applications is presented. Finite element method (FEM) simulations and experimental validations are used to compare both materials. The design of ultrathin laminated cores such as nanocrystalline ribbons for IPT systems is presented. Compared to ferrite, nanocrystalline ribbon is mechanically more robust; it has a higher magnetic permeability and a higher saturation point. Results show that nanocrystalline ribbon cores achieve more than a $\text{50}%$ volume reduction when used in IPT pads. This is due to nanocrystalline's high saturation point. However, a compromise arises as the total power loss increases due to the induced eddy currents in the core. The reduction of efficiency can be mitigated by special geometrical designs of the nanocrystalline ribbon cores. A 6.6-kW IPT system has been built for experimental validation of the design methodology.