Accurate Method for Extracting the Coupling Coefficient of an LCC-Series Wireless Power Transfer System

This article proposes a method of extracting the coupling coefficient and the resonant frequency of the receiving (Rx) side of a wireless power transfer system with an LCC-series topology, using only information from the transmitting (Tx) side. The proposed method has three modes, which allow the Tx coil and the Rx coil inductance and the coupling coefficient to be extracted, respectively. The coupling coefficient can be calculated while considering the tolerance of the coils. The Rx side senses the frequency of the Rx coil current, which is equal to the operating frequency of the inverter. This indicates that which mode the system is in, and the circuit on the Rx side is then modified to fit each mode. Details of the proposed method were analyzed using calculations, and simulations and experiments confirmed the effectiveness of the proposed method. Results showed that the coupling coefficient of the WPT system can be extracted with an error of less than 8%. In addition, the resonant frequency of the Rx side was accurately predicted, and then used as the operating frequency of the WPT system. Up to a 4% increase in efficiency was confirmed in the 80-W-class WPT experiment.