Effective Coupling Factors for Series and Parallel Tuned Secondaries in IPT Systems Using Bipolar Primary Pads

Inductive power transfer is a method of delivering power from a source to a load by resonating inductive coils in proximity with each other. Two main pad topologies exist: one that can generate nonpolarized and one that can generate polarized fields. Multicoil pads such as bipolar pads (BPPs) have been proposed as a pad topology that is interoperable with both polarized and nonpolarized pads. BPPs comprise two ideally overlapped mutually decoupled coils, which can be driven in any relative magnitude or phase. A polarized pad structure, such as a double d pad, is not equivalent to a BPP, and the polarized pad is a subset of the multicoil pad. It also shows that the effective coupling factor (keff) between the BPP primary and the secondary depends on the coupling factors that exist between each primary coil and the secondary coil, the reflected impedances, and the relative magnitude and phase of currents between the primary coils. An equation that describes keff is proposed and considers all these factors to show how each coil in a BPP can be energized to control VA transfer.