A Self-Adaptive Wireless Power Transfer System to Cancel the Reactance

This article presents a 6.78-MHz wireless power transfer (WPT) system, which is configured to automatically cancel the reactance in primary and secondary. In the WPT system, the detuning caused by the parameter variation, the implementation of the frequency control, and components tolerance will decrease a lot the system performance, especially in very low coupling (k = 0.06) and low power applications. The delivered power is sensitive to the reactance under low coupling and high-frequency conditions, accordingly, a novel self-adaptive WPT system to automatically retune the resonance is proposed. The proposed concept uses a synchronous series compensator (SSC) instead of a capacitor in series with the secondary to tune it, which can automatically cancel the reactance caused by the inductor, nonresistive load or frequency variation, hence increases the system performance in terms of delivered power and efficiency. A prototype has been built and tested experimentally to validate the feasibility of the proposed concept. A constant power of 1.8 W can be transmitted with 50% overall efficiency at a coil separation distance of 1.5 cm between the printed-circuit-board transmitter (3 × 3 cm 2 ) and receiver (1 × 2 cm 2 ) under wide detuning conditions, being 0.95 the ratio between distance and the equivalent diameter of receiver.