Triangulated Transmitter Coils With High Design Freedom for Free-Positioning and Omnidirectional Wireless Power Transfer System

This article presents a novel framework for designing planar transmitter (Tx) coils to mitigate coil misalignment issues in wireless power transfer (WPT) systems. The proposed triangulated Tx coils, composed of multiple triangular unit cells, offer high design freedom in terms of size and shape. Moreover, with the proposed stitched winding technique, the current direction within each coil segment can be altered, enabling precise manipulation of the resultant magnetic field. However, this flexibility comes with the challenge of introducing new coil segments that have the potential to reduce and interfere with the magnetic field. Therefore, a robust modeling approach is developed to accurately and rapidly predict the magnetic field generated by arbitrary coil configurations in the presence of shielding structures. Then, a two-objective optimization is performed to find the optimal current directions and excitation strategy, concerning both receiving stability and intensity. The theoretical analysis and simulation results show that the proposed Tx coils can obtain 3-D rotating magnetic fields within the whole charging area, where a planar single-axis coil is sufficient to realize free-positioning omnidirectional WPT. The experimental results validate that over 94% uniformity can be achieved in terms of both angular and lateral misalignment. When using one receiver coil, a dc–dc power efficiency of 2.137% can be achieved.