Wireless Power Transfer in Over-Coupled Region: Analysis on Frequency Splitting and Multi-Mode Frequency Selection Methods

Frequency splitting occurs when a wireless power transfer (WPT) system works in over-coupled region. Multireceiver systems are especially liable to this phenomenon, therefore suffering from efficiency deterioration, power capacity degradation and unstable operation. By taking a single-transmitter and two-receiver system as an example, this paper aims to analyze and optimize its performance. To describe the system, a simplified model neglecting the cross coupling among receivers (Rx) is developed. Seen from the transmitter port, it is found that a one-to-many system is essentially a one-to-one system with enhanced coupling strength. Then, for accuracy, a full model considering Rx-to-Rx coupling is established, which shows a good agreement with ANSYS simulated results. On this basis, three operation modes are proposed to improve system efficiency, power capacity or achieve a balance of these two indexes. The results indicate that the power loss is decreased by 2.27% under maximum efficiency mode, the charging speed is increased by 21.00% under maximum power mode, and the energy transmission capacity of the system reaches maximum under dual-purpose mode.