Data-Based Zero-Phase Angle Frequency Tracking for Series–Series Compensated WPT Systems

The zero phase angle (ZPA) operation is a widely used strategy in wireless power transfer (WPT) systems to improve the system efficiency. However, the ZPA frequency could vary in application scenarios such as ship-to-shore power systems, where the transfer distance is disturbed by waves, which could force the self- and mutual inductance of the coupled coils to change. Meanwhile, frequency bifurcation often occurs in tightly coupled WPT systems, leading to multiple ZPA frequencies. In this article, a data-based method is proposed to track one of the ZPA frequencies for a magnetic coupling WPT system with series–series compensation. The proposed method first tracks in real time the waveform of the inverter output current, i.e., amplitude and frequency, from sampled data; then, based on these quantities, align the output voltage and current of the inverter to achieve the ZPA operation. Moreover, convergence of the operation frequency is analyzed, and guidelines to suppress frequency hopping are suggested. The implementation of the proposed method in a digital signal processor with the help of a pulse width modulation module has also been discussed. The effectiveness of the proposed method is verified by experiments.