Research On LLC Resonant Converter Of Electric Vehicle Charging Pile

Compared with the fuel engine with combustion efficiency less than 50%,the energy conversion efficiency of the motor is far more than 50%.These advantages can effectively alleviate energy depletion and environmental degradation.As an important component,the performance of charger affects the safety and cost of electric vehicle.Therefore,the charger has also become one of the hotspots of current research.The development of high-performance electric vehicle charging equipment with high efficiency,high power density,high reliability and small volume is of great significance to the healthy development of electric vehicle industry and the sustainable utilization of energy.Full bridge LLC resonant converter is widely used in the post stage DC / DC module of charging equipment because it can realize zero voltage on(ZVS)of primary switch and zero current off(ZCS)of secondary rectifier diode.Taking the full bridge LLC resonant converter as the research object,this thesis studies its high-efficiency operation under full load.Firstly,the basic topology,working principle and working process of the full bridge LLC resonant converter are described.The equivalent model of the converter is obtained by the first harmonic approximation,and the DC gain function of the converter is deduced.Based on the DC gain function,the effects of inductance ratio and quality factor on DC gain are studied.The working area of the converter is divided by analyzing the characteristic impedance,Finally,according to the input impedance,the necessary conditions for the converter to realize the zero voltage conduction(ZVS)of the primary switch are deduced.The switching point of hybrid control is selected,and the implementation method of hybrid control is designed.Then,aiming at the problem that the overall efficiency is reduced due to the reduced efficiency of charge control during voltage reduction and light load operation,the causes of the problem are analyzed.The hybrid control composed of charge control and burst control is used to improve the overall efficiency.Four burst controls are compared,and the optimal trajectory burst control is selected as the control strategy for light load operation.Aiming at the problem that the optimal trajectory burst control needs real-time calculation,the charge type burst control is designed by combining the charge control and the optimal trajectory burst control,which solves the problem that the first pulse needs real-time calculation.To solve the problem of output voltage drift of step-down and light load,the method of calculating capacitance value according to voltage variation is adopted to limit the variation of output voltage,and the calculation formula is obtained.Finally,the simulation of hybrid control is realized in PSIM simulation software,and the feasibility of hybrid control is proved by analyzing the simulation results.Thirdly,the resonant parameters of LLC resonant converter are designed through the principle of Chapter 2 and the design requirements.According to the relevant literature,the physical parameters of transformer and inductance are designed,and the parameters and models of power devices are selected.On this basis,combined with the control strategy,the hardware power circuit,MOSFET driving circuit,current and voltage sampling circuit are designed,and TMS320F28335 is selected as the CPU,In the software part,the main program of hybrid control,PWM regulation subroutine,ADC sampling subroutine and digital PID program are designed.Finally,an experimental prototype of full bridge LLC resonant converter with rated power of 100 W is completed.The proposed hybrid control is tested on this prototype,and the experimental data are analyzed in detail.Experiments show that the hybrid control can effectively improve the overall efficiency of LLC resonant converter by 1.5%,which verifies the feasibility and effectiveness of the proposed hybrid control.Figure [58] Table [3] Reference [62]...