Comparison of Circular and Double-D Coil Topologies for Automotive Inductive Charging Systems

In current proposals of SAE J2954, ISO 19363 and IEC 61980 for the standardization of automotive WPT systems, the circular and Double-D coil topologies are introduced. Only reference designs and coupling factor values are specified for both variants in the standardization documents. To compare and evaluate the topologies in terms of interoperability, this paper analyzes the coupling factor tolerance of the coil systems in the case of misalignment and defines a new parameter to compare the systems. In a second step, the quality factors of the coils are determined by measurements to calculate the achievable efficiency as further comparative value. These investigations are conducted for the two systems with identical coil topologies on both sides as well as for the two cross-systems with mixed coil topologies. Based on the knowledge obtained from these investigations a comparison of these four systems for application in automotive WPT systems can be made.