Investigating the magnetic characteristics of unsymmetrical coil pair employing archimedean spiral for EV battery charging

The position of a magnetic null in the coupling profile of a charging pad decides the operating area over which power transfer can take place. For circular charging pads, employing an Archimedean spiral, a magnetic null occurs at a misalignment distance equal to about 40% of the pad diameter (or 70% of the coil's diameter) irrespective of the coil separation. However, this is true only for identically sized (symmetrical) coil pairs. In this paper, five different unsymmetrical coil-pairs were investigated to determine their magnetic characteristics. It was found that the position of magnetic null shifts with the changing air-gap for unsymmetrical coil-pairs. By operating the coils in an unsymmetrical coil-pair at a distinct separation, a relatively wider charging zone can be obtained as compared to the symmetrical coil-pair.