Active variable reactance rectifier — A new approach to compensating for coupling variations in wireless power transfer systems

This paper introduces a new approach to compensating for coupling variations in wireless power transfer (WPT) systems using an active variable reactance (AVR) rectifier. The AVR rectifier incorporates a lossless resonant network and two actively-controlled bridge rectifiers, which are interfaced with the output of the WPT system using dc-dc converters. The input reactance of the AVR rectifier can be continuously varied by changing the relative voltages at its two outputs while maintaining soft-switching of the rectifier transistors, enabling the rectifier to compensate for coupler misalignments while achieving high efficiency at high switching frequencies. The AVR rectifier also ensures that the output power of the WPT system is maintained at a fixed level even during coupler misalignments. A prototype AVR rectifier is designed, built and tested with a 6.78-MHz 20-W capacitive WPT system for tablet charging applications. The system is able to fully compensate, i.e., maintain a fixed output power level, for up to 50% lateral misalignments in the capacitive coupler, while maintaining high efficiency.