Nonlinear Resonant Circuits for Coupling-Insensitive Wireless Power Transfer Circuits

Wireless power transfer (WPT) technology is expected to significantly impact many applications ranging from charging of electric vehicles to mobile devices. A major limitation of current WPT technology is its power transfer efficiency (PTE) dependence on the relative position between the transmitter (TX) and receiver (RX). In this paper, a specific class of nonlinear resonant circuits is introduced for the design of coupling-insensitive WPT circuits. Such circuits maintain constant PTE while the coupling factor (k) varies at a fixed operating frequency. A self-adaptive nonlinear WPT circuit is designed using passive nonlinear devices without tuning the operating frequency or employing any active feedback and control circuitry. The presented WPT circuit prototype is capable of transferring 60 W at 2.25 MHz while maintaining a constant PTE of 85% from 5 cm to 25 cm. Compared to conventional WPT circuits, the transmission range is significantly extended by at least 200 % while PTE at the shortest transmission distance is improved by approximately 400%.

I. Introduction

Near-field WPT is an emerging technology that enables seamless and contactless electrical power transmission. This technology utilizes time-varying electromagnetic fields to transfer energy between the transmitter and receiver [1]. The typical block diagram of an inductively-coupled WPT system is shown in Fig. 1(a). In such a system, the power source drives the transmit coil, while the secondary coil in the receiver captures the RF energy transmitted through time-varying magnetic fields. Subsequently, the received RF is converted to DC via a rectifier and regulated using a power management unit before it is delivered to a load which is often a rechargeable battery.