Research On Frequency Tracking Technology For Wireless Charging System Of Magnetically Coupled Resonant Electric Vehicle

Wireless charging technology is developing fast,which provides a new way of charging or power supply for many kinds of electrical equipment.Especially for the battery charging of electric vehicles,wireless charging has unique advantages over traditional wired charging.At the same time,the application of this charging mode is also in line with the development direction of intelligent and unmanned electric vehicles.Efficiency is the core issue in the research of wireless charging technology,and it must be paid attention to in the application of wireless charging.Although wireless charging technology has the advantages of no wear,no contact spark,no plugging and no manual intervention,its efficiency is slightly lower than the traditional wired charging method,and the transmission efficiency is very vulnerable to external factors.This paper studies the charging efficiency of electromagnetic coupling resonance wireless charging system for electric vehicles.The interference factors that can affect the transmission efficiency of the system in practical applications are analyzed,such as load resistance,coil spacing and coil offset.The method of frequency tracking is proposed to improve the stability of the working frequency of the wireless charging system under the influence of the above factors and improve the transmission efficiency of the system.This paper studies the detuning theory of wireless charging system,establishes the equivalent circuit model,derives the relationship between the main parameters of the system and the phase angle of the voltage and current of the transmitter coil,and further studies the efficiency characteristics of the system in detuning state.After the theoretical analysis of the system,a new frequency tracking method is proposed.Based on the scheme of combining software method with hardware method,phase identification and phase difference acquisition are carried out by CD4046 and CD4013 respectively.The frequency of the system is automatically adjusted by STM32F407 single chip computer to track and control the frequency of the system,so as to prevent the system from working in a detuning state and improve the efficiency of the system.In the overall design of the wireless charging system for EV with frequency tracking,this paper introduces the design schemes of the high frequency inversion part in detail,communication part,signal acquisition part,phase detection part and protection part.This paper also explains the selection of the control chip type,diode type,power switch type and other components parameters of the system.In this paper,the experimental data of efficiency characteristics are sorted out.The relative efficiency and phase difference formulas are programmed and calculated by MATLAB,and the curves drawn by comparing the calculated results are compared.Finally,the system is equipped with a frequency tracking device.The oscilloscope is used to test the power waveform and transmission efficiency of the system,and the efficiency characteristics of the wireless charging system without a frequency tracking device are compared to verify the effectiveness of frequency tracking to improve the transmission efficiency of the system.