A Front-End Monitoring Method for Coupling Coefficient and Receiver Resonant Frequency in the SS-Compensated Wireless Power Transfer Systems With Unknown Receiver Parameters

In this article, a front-end monitoring method is proposed to estimate the coupling coefficient and receiver resonant frequency in the series–series compensated wireless power transfer systems. The proposal requires no prior knowledge of the receiver circuit parameters, such as the self-inductance of the coil, compensated capacitor, load resistance, and resonant frequency. Hence, it is suitable for the development of universal wireless charging systems and is immune against parameter tolerances and aging effects. It uses a sensing coil, which is decoupled from the transmitter coil but coupled with the receiver coil, to detect the phase information of the current on the receiver side. Only one zero-crossing sensor is required to detect the voltage information in the sensing coil. Two frequency sweeping processes are included to find the frequency points where the ac output voltage is in phase or out of phase with the ac input voltage. In the experiment, the estimation errors are less than 4.91% for the coupling coefficients and 1.33% for the receiver resonant frequencies. In addition, the estimation is extremely fast. The estimation time is within 5–9 ms.