Influence of Winding Direction of Solenoid Coil or Spiral Coil on Power Transfer Efficiency in Wireless Power Transfer

In recent years, wireless power transfer (WPT) technology of magnetic resonance coupling system has been actively studied. However, many of these studies have loaded external capacitors into the coil to achieve magnetic resonance coupling. The use of external capacitors entails increased maintenance costs and risks of failure. In this paper, the power transfer efficiency with regard to the shape and winding direction of the self-resonant coil without capacitor is clarified by experiments. From the experimental results, it was found that in horizontal arrangement, the efficiency is higher if the coils wound in the same direction are arranged regardless of the shape of the coil. In addition, since the solenoid coil can keep the coupling coefficient higher than that of the spiral coil, it is suitable for horizontal arrangement. From these results, it can be concluded that when using a relay coil in WPT, a solenoid coil is more suitable than a spiral coil.