A Reduced Order Model to Determine the Coupling Factor Between Magnetic Pads Used in Wireless Power Transfer

Inductive power transfer has become increasingly popular for various charging applications, including cellphone charging and electric vehicles (EVs). In order to design the magnetic pads for these applications, many individual simulations have to be performed to determine magnetic properties, including the inductances, coupling, and quality factors given these change with varying offsets and tolerances. Consequently, the magnetic design of such systems becomes increasingly complex, resulting in exponential increases in the number of required simulations, which are time and resource intensive. This paper focuses on the EV application and presents a simplified coupling function based on spiral coils which, for each known secondary design, can accurately predict the expected coupling over a range of primary pad sizes after performing a small number of simulations, or with measurement results of known primary areas. The proposed model is validated in practice and shown to be valid for all considered coil arrangements under both aligned and misaligned conditions.