Dynamic Complex Impedance Tuning Method Using a Multiple-Input DC/DC Converter for Wireless Power Transfer

The performance of a wireless power transfer (WPT) system is highly dependent on the complex impedance of the receiver (RX). Therefore, dynamic complex impedance tuning methods are critical pieces for gaining sufficient control over WPT systems. However, prior methods cannot achieve the following three requirements simultaneously: high-frequency $(i.e.\ \mathrm{MHz},\ \mathrm{GHz})$ operation, continuous complex impedance tuning, and few additional components. To overcome these challenges, we present a dynamic complex impedance tuning method based on multiple-input $\mathrm{D}\mathrm{C}/\mathrm{D}\mathrm{C}$ converters andLC filters. The active operations used in our method are closed in the low-frequency (i.e. after-rectification) region of the circuit; it has the promise of achieving the three above-mentioned requirements. The proposed method was evaluated through theoretical analysis and SPICE simulations assuming a 6.78 MHz near-field WPT system. It was shown that the complex impedance can be tuned in a wide range in the complex plane; by using our method, the fluctuation of power factor can be suppressed to 1%, whereas prior methods show 12%.