Improvement of equivalent magnetic coupling coefficient of wireless power transfer system with multiwinding transmission coil

This article proposes a novel method of improving the overall coupling coefficient of a wireless power transfer system by using a four-winding transformer of which two pairs of windings each are connected in parallel in the primary side and secondary side. By weakening the coupling coefficients k(c) between the parallel windings, the overall magnetic coupling between the primary side and secondary side of the transformer is improved. In order to confirm the validity of the proposed method, a conventional high-k(c) four-winding transmission coil and the proposed low-k(c) four-winding transmission coil are experimentally assessed. Then, the coils are introduced into a nonresonant inductive power transfer system utilizing a dual active bridge converter in order to confirm the correction of the input power factor. As a result, the overall magnetic coupling of the proposed four-winding coils was found to be improved by 17% compared with the overall magnetic coupling of the conventional coil. Moreover, the input power factor for the entire load is corrected with the proposed four-winding coil. Therefore, a low k(c) is effective in improving the overall magnetic coupling.