| Magnetically-coupled Resonant Wireless Power Transfer(MCRWPT)is a non-contact power transfer technology,which utilizes an invisible soft medium in magnetic field space.Because of the advantages of safety,reliability and flexible power supply,it has attracted widespread attention of scholars at home and abroad.In practical application,the resonant frequency of a system is changed with the changes of the system parameters change,resulting in frequency detuning of the system.The frequency detuning will greatly reduce the transmission efficiency and output power of the system.Therefore,in order to improve the transmission performance of MCR-WPT system,it is of great importance to study the frequency characteristics and the method of frequency tracking.The main research contents of this thesis are as follows:(1)Aiming at the problem that the variation law of the frequency characteristics is still unclear in the MCR-WPT system with different coil lateral misalignments,an equation for solving the resonant frequency is obtained,the multiple resonance frequencies corresponding to the peak efficiency point.At the same time,a formula for differentiating the output power with respect to frequency is also deduced,the multiple frequencies corresponding to the peak output power point are calculated.It is concluded that there is always a resonant frequency corresponding to the peak efficiency and a frequency corresponding to the peak output power,which are close to each other,and their frequency both change with the change of the coil lateral misalignments.The correctness of the variation law of the frequency characteristics is verified by formula calculation,simulation and experimental measurement results.(2)Aiming at the problem that how to increase efficiency and output power simultaneously in the MCR-WPT system with different coil lateral misalignments.A method of segmentation frequency tracking is proposed,the high efficiency and high output power can be obtained simultaneously with different lateral misalignment by the proposed method.The effectiveness of the method of segmented frequency tracking is verified by simulation and experimental measurement results.(3)Aiming at the problem that the overshoot of resonant frequency and unstable load voltage in the MCR-WPT system with coil lateral misalignments and load variations,a mixed-modulation method for adjusting frequency and voltage with a Fuzzy PI algorithm is proposed.The frequency tracking with Fuzzy PI algorithm can solve the overshoot of resonant tracking.In addition,the mixed-modulation method for adjusting frequency and voltage further adjust the duty cycle and the frequency respectively by utilizing the selection algorithm of the duty cycle and the phase-shifting angle calculation,it can maintain the voltage stability and the resonant state of the system.The effectiveness of proposed method is verified by the analysis of the formula calculation and simulation analysis. |
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