Robust Class E2 Wireless Power Transfer System Based on Parity–Time Symmetry

Thanks to the superiority of zero-voltage switching (ZVS), the Class E
²
topology has become a promising candidate in wireless power transfer (WPT) at medium and small power levels. However, in practical applications, it is a challenging and significant issue to maintain robust WPT under varying transfer distances, especially for the highly sensitive Class E power amplifier (PA). To solve this issue, the parity–time (PT) theory is initially developed into the Class E
²
WPT system. A general design procedure for the PT-symmetry-based Class E
²
WPT system is proposed, including the parameters of the Class E PA, resonant tank, and Class E rectifier. The power losses and efficiencies of the above-mentioned components are analytically derived as well. The ZVS operation is quantitatively described for the PT-symmetry-based Class E
²
WPT system, demonstrating that the maximum phase variation with coupling coefficient is rather small and independent of the natural resonant frequency, thereby achieving robust and highly efficient power transfer. Finally, the prototype with current feedback control to guarantee the PT mechanism and ZVS is built. The experimental results illustrate that under various coupling coefficients, robust and efficient power transfer is realized by a 165-W prototype with about 92.6% efficiency.