Optimum Design of Decoupled Concentric Coils for Operation in Double-Receiver Wireless Power Transfer Systems

Wireless power transfer is becoming ubiquitous in consumer electronics and electrified transportation, providing a convenient method to supply power or charge various devices, such as cell phones, watches, laptops, electric vehicles, and so on. Delivering power from one transmitter unit to more than one receiver can save space and reduce the cost of the overall system. For applications where the sizes of transmitter and receiver units are commeasurable, a frequently used design is the one with carefully overlapped D-shaped coils (also named bipolar pad) to achieve decoupling between coils. In this paper, an alternative optimized design of two concentric decoupled coils is proposed. The design allows the receiver coils to operate at close proximity, collecting power from a shared magnetic field generated by a single transmitter pad. The design methodology is based on a bucking coil layout where the coils' decoupling is achieved by means of flux cancellation caused by alternating the winding direction of turns in one of the coils. Apart from eliminating coupling between the two receivers, the proposed design maximizes the coupling between the transmitter and the second receiver coil and consequently increases the power transfer capability, offering the equivalent coupling coefficient similar to or better than a pair of bipolar DD coils. Finally, the number and space between turns are selected to improve the quality factor of the proposed receiver. The proposed solution is designable analytically and the second receiver can be added even after the first receiver is already built. Moreover, the proposed design demonstrates superior misalignment tolerance, particularly in the lateral direction, compared to other decoupled coil designs. The proposed methodology is validated through simulations and experimental tests and has proved to be accurate and easy for implementation.