Analysis of Square and Circular Planar Spiral Coils in Wireless Power Transfer System for Electric Vehicles

Nowadays, wireless power transfer (WPT) has attracted great attention from researchers because it is a safe, convenient, and reliable way to recharge electric vehicles. Square and circular coils are most commonly used in WPT systems. However, there are few analyses of comparing these two geometry windings in detail. In this paper, two analytical models of both square and circular planar spiral coils between two semi-infinite substrates are developed based on Fourier-Bessel transformation and dual Fourier transformation. An analytical calculation of the self-and mutual inductance can be carried out with respect to the main parameters of the WPT systems such as the line spacing, the number of turns of the coils and the properties of the substrate. The analytical models can be used to investigate the different tendencies of self-and mutual inductance of square and circular coils, which is helpful for speeding up the design process. Finally, to compare the lateral misalignment tolerance between square and circular coils, a 600 mm x 600 mm with a nominal 200-mm-gap prototype has been built and tested.