Research On Current Sharing Control System Of Parallel DC/DC Converter In High Power Charging System

High power charging system is a very important link in the development of electric vehicles.The main method to realize high power charging system is to combine multiple small and medium-power switching power supply modules in parallel.Soft switching technology is also very advantageous in improving power supply power and efficiency.Therefore,It is very necessary to study the current sharing technology of parallel switching power supply in high-power charging system combined with soft switching technology.Based on the topology of lagging leg series diodes phase shift full bridge converter（LLCD-PSFB）and the three loop current sharing control strategy of voltage loop,current loop and current sharing loop,this dissertation realizes the overall design of parallel structure in high-power charging system.The working principle of the main circuit topology is analyzed in detail.The small signal AC equivalent model is established by the average switching model method,and the transfer function of the switching power supply is obtained.The small signal model of current sharing control strategy in parallel system is designed.According to the design requirements,this dissertation reasonably selects various components used in the parallel system,including the design of high-frequency transformer,explains the turns ratio,conductor selection and winding method,calculates and selects the output filter inductance and capacitance,and selects the switching devices such as power switch and rectifier diode.In addition,the drive circuit,isolation circuit and auxiliary power supply of DC / DC converter are designed.In this dissertation,TMS320F28335 main control chip is used to control the parallel DC / DC converter system.Using the functions of CAN communication module,ADC sampling module and PWM signal module in this chip,the main program,interrupt program,PI program of three loop current sharing control and four PWM signals are designed.In order to verify the comprehensive performance of LLSD-PSFB and the rationality of parameter design,this thesis first uses PSIM simulation software to simulate the single module LLSD-PSFB,and then uses Simulink simulation software to simulate and verify the current sharing effect of parallel LLSD-PSFB.Finally,a test prototype is built to verify the working performance of LLSD-PSFB and the current sharing effect of three loop current sharing control.Through comprehensive comparative analysis,the correctness of the design of this subject is verified.