Comparison of Spiral and Square Coil Configurations in Wireless Power Transfer System for Contactless Battery Charging

In the inductive contactless battery charging, the power transfer capability and efficiency are mainly depending on the coupling coefficient (k) between the inductively coupled coils. In this work, the spiral and square coil configurations were experimentally made from litz wire as well as another spiral copper coil. This study investigates the frequency characteristics of these coil configurations in order to analyze the frequency characteristics of the self-inductance and equivalent series resistance of each coil; as well as we measured coefficient k under different conditions based on the air-gap variation between the inductively coupled coils and the misalignment between them. Furthermore, we examined the interoperability between the spiral and square coils configurations. It has been found that the litz spiral coil achieved slightly higher self-inductance with compare to litz square coil and spiral copper coil. Likewise, the square litz coil has slightly high equivalent series resistance with compare to other coils. On the other hand, the copper spiral coil has achieved better k than the other coupling interfaces of the litz wire coils.