Performance optimization of the wireless power transfer system with unbalanced resonator

Conventionally, in wireless power transfer (WPT) system, all resonators are set at exactly the same resonant frequency, which is considered as the optimal operation condition to achieve resonant coupling. However, at over-coupled region, frequency split issue occurs, as a result, the frequency for the maximum power is not coincident with the frequency for the maximum efficiency. This deteriorates the performance of the system. In this paper, an unbalanced resonator is introduced to solve this problem. Unbalanced resonator is defined as a LC resonator, whose frequency is slightly away from the original resonant frequency. Detailed theoretical analysis of the unbalanced resonator has been done, and a novel circuit model is developed for electromagnetic research study, along with a simplified circuit for engineering design. Also, simulation is implemented to verify the proposed idea. By adopting the unbalanced resonator, with same efficiency, the transferring power is increased by 38%. This method is further extended to apply in the WPT system with repeaters; experiments has been done and the results strongly agree with our proposal technology.