Analysis and Utilization of the Frequency Splitting Phenomenon in Wireless Power Transfer Systems

The frequency splitting phenomenon (FSP) is a critical issue in wireless power transfer (WPT) systems. When the FSP exists, the load power will sharply increase and can be dozens of times of the power obtained at the resonant frequency if the driving frequency varies from the resonant frequency, which seriously affects the system safety. This article studies the impacts caused by the FSP in detail and then proposes a system control method by utilizing the advantages of the FSP to realize constant power output and zero voltage switching (ZVS) of the dc-ac inverter simultaneously. The splitting frequencies are tracked and the driving frequency is precisely adjusted together with the dc-link voltage. The specific implementation method is given in this article to minimize the impacts on the power transfer performance. An 85 kHz, 3.3 kW WPT system is built up to validate the proposed method. The experimental results show that when the FSP occurs at 150 mm coil-to-coil distance and 5 Ω load resistance, the load power can be hold at 3.3 kW with the dc-link voltage reduced from 327 to 160 V. Meanwhile, ZVS of the inverter is realized and the inverter efficiency is improved from 95% to 97%.