A cross-shape coil structure for use in wireless power applications

Abstract

This paper presents a novel coil structure employing two parallel-connected subunit rectangular coils. The structure is based on the fact that the rectangular coils are less sensitive to misalignment along its longer side. Therefore, two identical subunit rectangular coils are vertically-oriented to one another and connected in parallel to form a cross-shape coil. The cross-shape coils have the advantage of better misalignment tolerance as compared to circular and square coils with similar footprints at the cost of an increased wire usage. Electromagnetic simulations and experiments on various small-sized coils are performed to verify the advantages of the proposed coil structure. Based on the simulation and measurement results, cross-shape coils exhibit not only better tolerance to misalignment, but also smaller self-inductance values resulting in larger coupling coefficients as compared to square and circular coils. A large cross-shape coil pair consisting of 100 x 70 cm subunit rectangles are fabricated with copper tubes and utilized in a frequency-tuned wireless power transfer system. When coils are separated by 17 cm, a near constant efficiency of more than 89% up to 15 cm misalignment along x-or y-directions and 13 cm along diagonal direction is obtained in the frequency-tuned system.