A Misalignment Tolerant Winding Pattern with AC Resistance Reduction Capability for Inductive Power Transfer Application

Litz wire planar coils are widely used in inductive power transfer systems due to the low profile and high efficiency in medium frequency operation. In high frequency region, the ac resistance of litz wire planar coils increases significantly, which leads to efficiency-drop and temperature-rise problems. Meanwhile, misalignment occurs during the daily operation and causes unstable power supply. In this work, we propose a novel winding pattern for reducing the ac resistance, thermal stress and misalignment sensitivity. From experimental result, the proposed winding pattern reduces the ac resistance maximally by 78\% at 1 MHz, and 263\% at 20 MHz compared with the conventional winding pattern under the same geometry and wire length. The total efficiency is improved by 2\% and misalignment tolerance is maximally improved by 46\% in terms of the output power, and 5\% in terms of the efficiency with the proposed winding pattern.