Adaptive frequency measurement in magnetic resonance coupling based WPT system

Resonance frequency is a key factor for improving transfer efficiency in a Wireless Power Transfer (WPT) system which has a wide application because the wired media is eliminated. In this paper, an adaptive frequency measurement method is presented and the influence on the transfer efficiency in the WPT system is explored. The LC circuit is adaptively excited by a pulse exciter to generate damped oscillation. The frequency signal of LC circuit is shaped to a rectangle pulse before measurement. In the proposed digital frequency measurement, a direct pulse counting technique is employed in which the pulse width is computed with the counter pulse. The pulse counting is implemented by a constant time window for reducing measurement error in the resonance frequency signal. The frequency measuring method is demonstrated by an experimental study based on coupled magnetic resonances. The experimental results show that the WPT efficiency and the peak power when driven at real resonant frequency are about 2.1% and 2.3%, respectively, higher than that of theoretical values, which indicated a better performance of resonance frequency measurement.