A Dual-Frequency Tuning Method for Estimating Coupling Coefficient and Output Voltage by Measuring Transmitter Current of IPT System

A dual-frequency tuning method of inductive power transfer (IPT) system is proposed to estimate the coupling coefficient and output voltage from the transmitter (Tx) during power transfer without using an additional communication channel. The Tx is designed to resonate at both the fundamental and seventh-order frequencies of a square wave voltage. The power receiver (Rx) coil is also tuned to maintain resonance at the fundamental frequency, but it is approximately short-circuited at the seventh-order frequency by a parallel LC tuning branch. The Tx coil current is measured during power transfer, and its fundamental and seventh-order components are extracted to estimate the coupling coefficient and output voltage. A practical prototype is built, and experimental results show that the coupling coefficient and output voltage can be accurately estimated, and the output voltage can be closely regulated to the reference value despite variations in the coupling coefficient (0.3 to 0.7) and the load resistance (1.5 to 60 Ω).