A study of three-coil magnetically coupled resonators for wireless power transfer

With the development of electric vehicle and consumer electronics, the wireless power transfer (WPT) becomes a popular technology. Magnetic resonant coupling is considered to be the most effective and attractive WPT approach in recent years. Two-coil structure is widely used, where optimal load value and distance are critical to achieve maximum efficiency. In this paper, a three-coil structure is proposed, analyzed and compared with two-coil structure. With the proposed structure, the efficiency stiffness of the system is improved, therefore, a wider range of load and distance variation can be tolerated. Additionally, with the proposed structure, the electromagnetic field (EMF) emission caused by coils misalignment is significantly reduced. The comparisons of two-coil and three-coil WPT systems are evaluated and verified with simulation and experimental results.