MIXED-MODULATION METHOD FOR ADJUSTING FREQUENCY AND VOLTAGE IN THE WPT SYSTEMS WITH MISALIGNMENTS AND LOAD VARIATIONS

Abstract

The resonant frequency will be changed, and the load voltage will be unstable with misalignments and load variations in wireless power transfer (WPT) systems. In this paper, the expression for solving the resonant frequency is obtained. The calculation result shows that the resonant frequency is changed with the changes of misalignment and load. First, a new control method of frequency tracking with a Fuzzy proportional-integral (PI) compound controller is proposed, which can eliminate the overshoot of resonant frequency and improve the speed of frequency tracking. Second, a mixed-modulation method for adjusting frequency and voltage is further proposed, which is mainly composed of the selection algorithm of the duty cycle, the phase-shifting angle calculation, and the method of frequency tracking based on the Fuzzy PI compound controller. The appropriate duty cycle is obtained by the selection algorithm of the duty cycle to adjust the load voltage. The phase-shifting angles of different duty cycles are obtained by the phase-shifting angle calculation, which play a role in adjusting the resonant frequency by combining the Fuzzy PI compound controller. The proposed method can not only make the system keep a resonant state, but also make the output voltage across the load stable. A WPT system via magnetically coupled resonance is designed. Calculation and simulation results validating the superiority of the proposed method are given.