Optimisation of Magnetic Material Placement in IPT Pad for EV Charging

Ferrite is used in inductive power transfer (IPT) pads to improve magnetic coupling and reduce magnetic field leakage, but it is brittle and costly. A potential alternative to ferrites in IPT pads is soft-magnetic composites (SMCs). SMCs have lower relative magnetic permeability, but can be lower cost with better mechanical properties that enable longer IPT system lifetimes. This paper uses an optimisation approach to design Double-D (DD) pads which incorporate both ferrite and SMC, for the primary side of an EV charger IPT system. In this paper, the optimisation process converges on results that concentrate ferrite in the central, high-field regions of the DD pad as ferrite significantly shapes magnetic field distribution. The optimisation process places SMCs in the outer regions of the pad to shield the leakage magnetic field. A selected Ferrite-SMC Double-D (FSDD) design showed only 3% drop in coupling, despite extensive reductions in leakage and ferrite volume. This performance was verified by transferring 1kVA uncompensated apparent power to a FFDD secondary at 93% efficiency.