Research On A Frequency Tracking Magnetically Coupled Wireless Charging System

Compared with traditional charging technology,wireless power transmission(WPT)system has a bright future in the field of electric vehicle charging due to its features of convenience,safety and elegant appearance.Based on magnetic coupling resonance technology,a frequency tracking wireless charging system is developed for electric vehicle charging.The system can realize constant voltage output under the condition of simultaneous change of coupling coefficient and load.In this thesis,we firstly give the electric magnetic coupling theory and present the frequency bifurcation phenomenon induced by changes of the load and coupling coefficient of the system with the series-series type of resonance topology.With Matlab,the output voltage changes and the decline of system efficiency caused by frequency bifurcation are verified.Secondly,In order to improve the stability of the system,with the analysis of the relationship of voltage gain and impedance phase angle to the switch frequency under the changes of the load and the coupling coefficient,we find that there exists a unity-gain frequency point when the coupling coefficient changes within a certain range,which can be tracked by the system impedance phase angle feedback,so that the output voltage is not affected by the load and coupling coefficient,the frequency bifurcation phenomenon can be avoided in the system and the soft switching operation of the switch tube can be realized.Thirdly,in the proposed control system,since the coupling coefficient changes within a certain range,when the coupling coefficient is too low,the coil leakage inductance increases and the radiation energy to the outside increases to cause the problems that the efficiency and stability of the system decrease.In order to improve the stability and efficiency of the system and solve the problems of electromagnetic radiation,Ansys Maxwell software is employed to design and optimize the coupling coils via the shape,size,and ferrite core.Finally,in order to verify the correctness of the proposed system,a 500 W experimental platform has been built,and the efficiency,frequency control accuracy and stability of the system are comprehensively tested.The results show that the proposed scheme has strong practicability.