A Primary-Side Monitoring Method for Coupling Coefficient and Receiver Resonant Frequency in SS-Compensated Wireless Charging Systems with Relay Coil

Abstract

A primary-side monitoring approach is proposed to estimate the coupling coefficient and receiver resonant frequency in a series-series compensated wireless power transfer (WPT) system in which the coupling coefficient and receiver's resonator parameters can be unknown. A relay coil, coupled with the receiver coil but decoupled from the transmitter coil, is designed to obtain the phase information of the receiver current. Two frequency sweeping processes are included to find the frequency points where the output voltage is in phase or out of phase with the input voltage. Only one zero-crossing detector is required in the process. A detailed analysis of the proposed approach is conducted. In the experiment, the estimation errors are less than 6% for the coupling coefficient and 1% for the receiver resonant frequency. Real-time implementation of the proposed method confirms that the estimation process is extremely fast. The whole estimation process only takes around ten milliseconds.