Frequency Splitting Suppressing of Hybrid Coupling WPT and Transfer Distance Extending by Rotating the Transmitter

Frequency splitting, a phenomenon causing transfer efficiency decreasing in wireless power transfer (WPT) systems when the coupling strength is too strong, can be suppressed by combining the magnetic and the electric couplings with out-of-phase polarities to constitute a hybrid WPT (HWPT) structure. In this paper, the exact critical coupling coefficient of the HWPT structure is obtained from the ridge equation of the analytical efficiency expression. It is found to approximate 1/Q (Q is the loaded quality factor of the resonators), which shows a similar property with the conventional inductively-coupled WPT system. In order to improve the efficiency after the critical coupling distance, the magnetic coupling only or the in-phase structures are proposed and realized by rotating the transmitter and adjusting the values of the electric coupling. In addition, for the applications requiring high efficiency over a long transfer distance, a design procedure of the resonator is given with the help of the analytical relationships between the electric parameters and geometrical parameters of the coupling structures. The electromagnetic simulations (ANSYS HFSS) and experiments show good agreement with the theory. The efficiency can hold above 70% within 40 ~ 260 mm transfer distance. Compared with the existing HWPT system, the operating distance range is extended from 130 mm to 220 mm, featuring an ~ 69% improvement.