Design and optimization of cancellation coil topologies for a ferrite-less wireless EV charging pad

Abstract

Ferrite cores are widely used in conventional wireless EV charging pads to reduce stray EMF emissions, but they can be brittle, heavy, and expensive. This work furthers the development of ferrite-less wireless charging pads by comparing an active and two distinct passive cancellation coil topologies as candidates to replace the ferrite. Using the software packages FEMM and MATLAB, each topology is optimized to find the best winding positions and radii to minimize leakage at a specified position under the side of the vehicle. The optimized designs are compared for shielding effectiveness, induced current, and efficiency. All three topologies are able to sufficiently reduce the leakage field below the ICNIRP limit of $27\ \mu\mathrm{T}_{\text{rms}}$ with just one turn. Interestingly, we find that an array of simple passive cancellation loops performs similar to the more widely studied passive cancellation coil.