The Electric Multipole Produced by an SAE J2954 Wireless Power Transfer System Employing DD Couplers

Vehicular wireless power transfer (WPT) systems conforming to the SAE J2954 standard are thought to operate as inductive WPT systems. As such, they should be able to be accurately represented by a magnetic multipole source. For example, the magnetic field of the “circular” coupler, which is described in the SAE standard, can be represented by a combination of a vertical, linear magnetic quadrupole and a horizontal magnetic dipole. However, it has been recently shown that a significant conservative electric field exists in such a WPT system due to the multiturn windings. This can lead to a significant electric multipole contribution, predominantly a vertical linear electric quadrupole for the circular coupler. In fact, the circular coupler electric field (not the magnetic field) is somewhat similar to that of a coaxial aperture. Here, we carry out a detailed analysis of the electric multipole representation of the “DD” coupler which is also described in the SAE standard. The analysis of the electric multipole of the DD coupler is more complex than that of the circular coupler. Because the DD coupler is composed of two side-by-side spiral windings, it is possible to obtain two different electric multipoles from configurations that produce nominally the same magnetic multipole and the same magnetic performance. Fortuitously, the configuration used in the DD coupler very nearly cancels the conservative electric field, the associated electric multipole, and the attendant emissions.