An Anti-Misalignment Wireless Charging System for Low-Power Applications Based on Solenoid Coils Incorporated With Reverse Windings

Many consumer electronics employ wireless charging technology, but it is difficult to achieve free positioning wireless charging. Also, significant changes in the mutual inductance can happen when moving the device during charging, causing hazards to the devices. This paper proposes a solenoid coil that solves this problem by utilizing reverse windings to maximize average mutual inductance and stabilizing its variance. Firstly, the design principle of the reverse winding is explained, and then the flow chart of the optimal design is given. The optimal layer number of the outer winding of the solenoid is determined, and the reverse winding is placed in the innermost layer. The maximum average mutual inductance obtained under the condition of a limited mutual inductance fluctuation ratio is 13.866 \mu \text{H} . Compared with the results without the reverse winding, the mutual inductance fluctuation is reduced by nearly 2 times. In addition, placing the solenoid coils on the transmitter side in a hexagonal shape enables the receiver to cover a larger transmission area during movement. Finally, a low-power experimental prototype is designed, and the experimental results verify the effectiveness of the design method.