Frequency Tracking Method for Wireless Power Transfer Based on Current Zero-crossing Comparison and Dynamic Time Delay

To solve the problem of frequency detuning caused by the parameters variations of the wireless power transfer system, the magnetic coupling equivalent model of power transmission was established to study the system frequency tracking control principle, and to reveal the influence of coupling coefficient and load parameters on the system voltage gain and transconductance gain. The realization conditions of the switching tube working in the state of zero voltage switch and the variation range of the switching frequency were obtained. On this basis, the control method of digital phase-locked loop and system impedance angle adjustment based on the digital signal processing technology of current zero-crossing comparison and dynamic time delay was proposed to realize the frequency and phase tracking of voltage and current, which was combined with the double closed-loop control of voltage outer loop and current inner loop to realize constant voltage or constant current output. Finally, an experimental platform was built to verify the feasibility and effectiveness of the proposed control method. The experimental results show that the frequency and phase tracking control of the voltage and current can be realized by changing the air gap distance. When the air gap distance is greater than a certain value, the transmission efficiency of the proposed method is more than 4% higher than that of fixed frequency control method, which verifies the effectiveness of the control method.