A Hybrid Wireless PLL for Phase Shift Control Based Maximum Efficiency Point Tracking in Resonant Wireless Power Transmission Systems

The application of Wireless Power Transfer (WPT) systems is primarily limited by its energy transfer efficiency. For modern WPT that utilises Strongly Coupled Magnetic Resonances (SCMR), which transfers energy by using the mutual inductance between coils, a higher efficiency can be achieved compared with a conventional air-core transformer module. An SCMR normally works at a desired frequency which is typically the self-resonant frequency of the receiver. However, this frequency varies during system operation where a changing environment, moving coil positions and variable loads may occur. In this paper, a hybrid wireless Phase Lock Loop (PLL) is proposed to lock the phase difference between the WPT's transmitting current and receiving voltage, at which point the system achieves maximum efficiency. A prototype WPT system is built verifying that the proposed wireless PLL effectively controls the wireless power system and operates at optimal frequencies under varying conditions.