Auxiliary Coil Based Square Coupler for Wireless Power Transfer System

The transfer of energy with higher efficiency is the primary requirement in wireless power transfer systems. In this article, a single-sided flux-generated coupler structure suitable for loosely coupled wireless power transfer systems is introduced. Here, the achievable efficiency is decided by the coupling factor and mutual inductance between the transmitter and receiving coils. In this article, an auxiliary coil of a few turns is employed to enhance the mutual inductance with an improved coupling factor. The auxiliary coil is connected in series with the main coil in both the transmitter and receiver. The electrical and geometrical design considerations are brought out for the proposed auxiliary coil-assisted structure. Finite-element method (FEM) electromagnetic field simulations are carried out in the Ansys-Maxwell platform. The proposed auxiliary coil assisted coupler's efficacy is compared with the existing coil structures (circular, square, double DD) in terms of coupling factor, mutual inductance, and self-inductance through FEM simulations. With the proposed work, an improvement in flux density distribution toward the receiver together with higher mutual inductance and coupling factor is achieved. These improvements are verified through field simulations and experiment. Detailed design steps for the proposed coupler are given. For concept demonstration, a prototype WPT system with a power output close to 150 W is constructed. An input dc supply voltage is 48 V and the inverter is switching at 100 kHz. Enhanced features (improved mutual inductance profile together with the coefficient of coupling) of the proposed coupler are demonstrated through experimental measurements. The effect of different distances on power transfer and efficiency of the system is also measured. Measurement observations are in close agreement with analytical predictions.