Design and Optimization of Asymmetric and Reverse Series Coil Structure for Obtaining Quasi-Constant Mutual Inductance in Dynamic Wireless Charging System for Electric Vehicles

Lateral misalignment along the driving direction may achieve half the length of a transmission coil in a dynamic wireless charging system for electric vehicles, which is called limit misalignment. This limit misalignment may cause the dynamic wireless charging system to malfunction because of the large fluctuation in mutual inductance. In this paper, an asymmetric and reverse series coil (ARSC) structure is proposed. In the ARSC structure, the transmission coil is smaller than the receiving coil in size to smoothen the fluctuation in mutual inductance. The receiving coil consists of a large coil ($\boldsymbol{R}_{\mathrm {x1}}$) and a small coil ($\boldsymbol{R}_{\mathrm {x2}}$) and $\boldsymbol{R}_{\mathrm {x1}}$ is reversely connected to $\boldsymbol{R}_{\mathrm {x2}}$ in series. The purpose of this design is to further reduce the fluctuation in mutual inductance. A calculation method of mutual inductance is then proposed based on the vector potential to calculate the mutual inductance of the ARSC structure. The law of mutual inductance is analyzed by the proposed calculation method for the ARSC structure. Moreover, an optimization method of coil parameters is proposed to obtain quasi-constant mutual inductance. The ARSC structure and optimization method are not only simple but can also make the mutual inductance nearly constant. Calculation, simulation, and experimental results validating the proposed method and structure are shown.