A Unipolar Coil Arrangement Method for Improving the Coupling Coefficient without Ferrite Material in Wireless Power Transfer Systems

In recent years, wireless power transfer (WPT) is extensively researched because it is a reliable and safest way of electric vehicle charging. Generally, rectangular-, square-, and circular-shaped unipolar coils are used in the static and dynamic WPT systems. However, these unipolar coils suffer from reduced coupling coefficient ( k ) due to large leakage flux, which decreases power transfer and transmission efficiency. In this context, this article proposes a unipolar coil arrangement method (UCAM) for improving k in WPT systems compared with conventional coils having the same self-inductances and outer dimensions. Furthermore, an analytical model is developed and used to calculate k of the coil structures (having different coil parameters) obtained using the proposed UCAM. For the rectangular geometry of 400 mm times300 mm, 6.78%-27.04% improvement in k is achieved at the 150-mm air gap for the case 3 coil system compared with the different conventional coil systems. The interoperability between the proposed and conventional coils is also studied. Moreover, this article examines the impact of increased k on power transfer capability and transmission efficiency. Prototypes of various coil systems are built. Experimental results confirm improvement in k , even for different misalignments between the transmitter and the receiver coils, of the designed coil system using the proposed UCAM.