A Reconfigurable Resonant Coil for Range Adaptation Wireless Power Transfer

To widen the range of a magnetically coupled wireless power transfer system, we propose a novel reconfigurable resonant coil. This device consists of a series of subcoils that use switches to control the number of turned-on subcoils. With this design, both the coupling coefficient between coils and the quality factor of the proposed coil can be dynamically tuned when the distance between the transmit and receive coils changes. Thus, the proposed coil system increases the efficient power transfer range compared to a conventional resonant system. In this work, we replace the first coil in a four-coil system with the proposed coil. This coil uses six switches to change the number of series subcoils from six to one as the distance between the transmit and receive coils increases. A theoretical analysis demonstrates how to properly design and configure the proposed coil. Experimental results show the range at which the system achieves 70% efficiency or higher increases by 120% compared to the conventional system without the proposed method. The proposed system keeps high efficiency when the load varies from 40 to 300 Ω.