Research Of Wireless Power Transfer System With Constant Voltage And Constant Current Output

With the background of " carbon neutrality and carbon emissions peak " and the support of government policies,renewable energy vehicles are in a stage of rapid development due to their energy saving and environmental protection characteristics.Wireless power transfer technology realizes the transmission of electric energy in a non-contact mode,which has the characteristics of safety,flexibility and convenience.So,it has broad application prospects in the field of electric vehicle charging.Aiming at the charging characteristics of lithium battery,this thesis focuses on the constant current and constant voltage output characteristics of wireless power transfer system.Firstly,this thesis introduces the background of related research,and details the research status of magnetic coupling wireless power transfer technology.The research status of wireless power transfer system structure,coil structure design,compensation topology and constant current/voltage control mode are analyzed and compared,and their advantages and disadvantages are summarized.Secondly,this thesis introduces a DC/DC wireless power transfer system which is based on pulse frequency modulation(PFM).The problem of system gain characteristics change caused by coil misalignment in the practical application of wireless power transfer system is studied.By deducing the conversion relationship between the two equivalent models of the coil,and based on the equivalent transformer model,the gain characteristics are analyzed by the fundamental wave equivalent method,and the relationship between the system parameters and the gain characteristics is obtained when the coil is aligning and misaligning.Through comparative study,it is found that the misalignment of coil will lead to non-monotonicity in the frequency modulation range.An asymmetric compensation capacitor design scheme is proposed to enhance the misalignment tolerance of the system with the PFM control strategy.According to the given system design index,the system parameters are designed under the condition of limiting current and voltage stress.The design scheme and control strategy are verified in the simulation platform.Then,this thesis introduces a single-stage AC/DC wireless power transfer system based on phase shift control.Aiming at the problem that the control strategy of power factor correction(PFC)scheme in wireless power transfer system is too complex,the existing control algorithm is simplified.By analyzing the principle of PFC and the working mode of the circuit,the modulation expression is derived.Compared with the traditional scheme,the modulation strategy does not require the AC side current control loop,which optimizes the control complexity.Then the vital parameter design is given,and the effect of PFC and the constant current/voltage output are verified in the simulation.Finally,a 1.2k W DC/DC experimental prototype and a 1.2k W single-stage AC/DC experimental prototype for wireless power transfer are designed respectively,and the test results of the prototype are given.The DC/DC experimental prototype based on PFM maintains stable operation when the coil shifts 75 mm in the X-axis direction and 100 mm in the Y-axis direction,and achieves the constant voltage and constant current output target.The maximum efficiency of the system is 93.56%.The functions of PFC and constant current/voltage output are achieved by the single-stage AC/DC experimental prototype based on phase shift control.At rated power,the PF and THD reach 0.999 and 4.05%,and the transmission efficiency is 95.7%.The experimental waveforms and data conform to the theoretical analysis.and the effectiveness and feasibility of the theoretical analysis and design in this thesis are verified.