Optimal Finite Element Modelling and 3-D Parametric Analysis of Strong Coupled Resonant Coils for Bidirectional Wireless Power Transfer

Abstract

Resonant coils can be utilised for the wireless transfer of power between a supply grid and an electric vehicle. In order to achieve an affordable and optimal resonant coil design, the coupling factor becomes a significant parameter. The coupling factor (k) indicates the percentage of the total magnetic flux responsible for the transfer of electrical power from the transmitter to the receiver. A higher value of k will increase the magnitude of real power transferred between coils as well as reduce in the proportion of reactive power circulating in the system. For optimal and efficient bidirectional Wireless Power Transfer (WPT) operation, the primary and secondary coils must be designed to achieve a high Quality factor (Q) and high coupling factor. Using the same length of copper wire and volume of ferrite core, three simple resonant coils using finite element modelling (FEM) designs are proposed: circular, rectangular and double-sided winding coils. The physical length (D) of the coils is restricted to be no more than 600 mm due to the physical diameter of most electric cars as well as regulations governing electromagnetic radiations. Magnetostatic performance analyses of the coil designs to confirm mutual inductances, coupling factors, the maximum magnetic flux density (B) distributions and maximum saturation current tolerances for the magnetic core over an airgap of 150 mm were carried out. Likewise, parametric performance evaluations of the different resonant coil designs in three-dimensional space comprising of airgap variation, longitudinal and lateral misalignment were undertaken. From the FEA and Parametric performance results, the model of an optimal design was evaluated through simulation and was found to achieve a strong magnetic coupling factor of more than 0.5 across an airgap of 170 mm.