Impedance-Matched Wireless Power Transfer Systems Using an Arbitrary Number of Coils With Flexible Coil Positioning

This letter presents a new analytic design method for impedance-matched wireless power transfer (WPT) systems using an arbitrary number of coils. For deriving the impedance matching condition, we have used an equivalent circuit of the WPT system. It allows us to avoid solving voltage-current equations for the actual circuit. For verifying the proposed design method, an impedance-matched WPT system with one repeater coil has been designed and fabricated. This letter also shows that the distances between the coils can be varied maintaining the impedance-matching performance, and the distances can be determined analytically using the presented design method. Application of the presented design method can be found in designing WPT systems that require flexible coil positioning.

I. Introduction

The Electromagnetic resonant coupling technique has been widely adopted for designing wireless power transfer (WPT) systems [1]–[8]. Compared to the other techniques, electromagnetic induction [9], [10] and microwave radiative power transfer [11], it has been reported to be more suitable for midrange power transfer. For designing the WPT systems, the voltage–current equations for the sending and receiving coils have been established and solved for the circuit models [6], [7]. This analysis method has led to a set of lengthy equations, and they become more complicated when more coils are employed in WPT systems.