Distance-Insensitive Wireless Power Transfer Using Mixed Electric and Magnetic Coupling for Frequency Splitting Suppression

This paper presents a distance-insensitive wireless power transfer (WPT) system based on mixed electric and magnetic coupling between the transmitter and the receiver. By making use of the out-of-phase characteristic of the electric and magnetic coupling coefficients, the variation of the magnetic coupling strength can be offset by the electric one. In this way, magnetic overcoupling can be avoided in case of close distance between the transmitter and the receiver. Consequently, much more stable total coupling coefficients are realized at various transmission distances and frequency splitting is suppressed to realize stable output power. An equivalent circuit model is used to theoretically analyze the impact of mixed coupling on the transmission coefficients. The condition of electric and magnetic coupling for suppressing frequency splitting is derived. To realize the desired coupling strength, a new method is proposed to individually extract the electric and magnetic coupling coefficients and is then employed to guide the coupling strength control. For verification, the proposed WPT prototype is fabricated and measured. Within the operating distance ranging from 40 to 170 mm, it can achieve over 75% efficiency with a maximum of 93.8%. Compared with the conventional WPT, the operating distance is extended by about 60% and the efficiency at short distance is enhanced by about four times. The measured results are in good agreement with the theoretical and simulated ones.