Phase Synchronization Method Based on Self-Oscillation Mode for Bidirectional EC-WPT System

Bidirectional electric-field coupled wireless power transfer (EC-WPT) technology with bilateral physical isolation enables energy interaction between electrical devices. Phase desynchronization of the output voltages generated by the primary and secondary converters causes issues such as periodic variations in the relative phase difference and continuous oscillations in the output power. Therefore, this article proposes a phase synchronization method based on self-oscillation mode that can tolerate misalignment of coupling plates in the bidirectional EC-WPT system. The method analyzes the effect of coupling capacitances variation on the soft-switching operating points by establishing a stroboscopic mapping model of the system, and provides a stable resonant frequency operating at the maximum amplitude-frequency gain. Based on the principle of self-oscillation, the system autonomously drives the bilateral converters by tracking the zero-crossing points of the resonant currents and ultimately operates at a stable resonant frequency for precise phase synchronization. It operates without the need for complicated computation, additional complex analog circuits, and is not affected by the variation of coupling capacitances. The experimental results show good agreement with the simulation results, validating that the effectiveness of the proposed phase synchronization method for the bidirectional EC-WPT system.