Digital Transmitter Coil for Wireless Power Transfer Robust Against Variation of Distance and Lateral Misalignment

A digital transmitter (TX) coil consisting of several subcoils connected in parallel is proposed in wireless power transfer (WPT) systems robust against the variation of distance and lateral misalignment. According to the position of the receiver coil, the radius of the digital TX coil can be programed to its optimal value to achieve the maximum coil-to-coil efficiency. Moreover, targeting the wireless charging of mobile devices, we propose a practical design methodology for the digital TX coil. It is concluded that the digital TX coil consisting of two subcoils is an effective design and that the performance is not significantly improved by adding more subcoils. The optimal radius ratio of these two subcoils is 0.54. Furthermore, we implement the designed digital TX coil in a prototype WPT system, including a power amplifier and a rectifier. Experimental results show that within a space with a maximum distance and lateral misalignment of 100 mm, the system efficiency is improved by the digital TX coil and reaches a maximum value of 48%. Compared with using a conventional TX coil with a constant radius, the system efficiency shows an absolute improvement of up to 7%.