Research On A High Efficiency Soft-switching Of SR DC-DC Converter Applied On EVs

In recent years,many countries take more and more serious to the environment pollution and energy shortage.The Electric Vehicles with advantages of energy saving and environmental protection,attract more and more attention.The high voltage battery and low voltage battery are the main energy storage elements of EVs,the vehicular DC-DC converter is the key module of energy transform and conduct.Vehicular DC-DC converter must be high power density,high efficiency and high reliability,due to the technological difficulties of battery and terrible car environment.So it has theoretical value and practical significance research on the key technique of vehicular DC-DC converter.As to improve the power density,efficiency and reliability of vehicular DC-DC converter,this article emphatically researches on the technique about high efficiency soft-switching DC-DC converter.The research status of the vehicular converter is reviewed,and the second stage SR of Full-bridge is designed and studied.The voltage ringing of SR in Full-bridge is concerned,it causes the voltage stress and power loss.A novel high efficiency active clamped soft-switching of SR is proposed and analyzed,the working principle is analyzed base on ringing mechanism.The residual energy of resonant inductor are absorbed by camping capacitance through the resonant of camping capacitance and resonant inductor,it effectively reduces the voltage stress of the synchronous rectification switches.Then the discharge circuit for the capacitor is provided by the auxiliary switch,and energy feedback to the converter,it achieves the characteristics of low power loss and high efficiency.The key parameters design is given,and its validity and feasibility are verified by simulation,prototype design and experimental prototype.Through analysis and comparison,a two-stage converter Buck + SR Full-bridge is selected to as the design scheme of vehicular DC-DC power supply in this paper.The small-signal model based on the Buck + SR Full-bridge is analyzed,and the nonideal ac small-signal model of two-stage circuit with parasitic parameters is built.In order to improve the performance of circuit,the loop optimization is given base on the amplitude-frequency characteristics and phase-frequency characteristics of the mathematical model.The vehicular DC-DC power supply is with low voltage and high current output,its efficiency is limited by its high power loss.In order to achieve the high efficiency,the power loss model is built base on Buck + SR Full-bridge,the distribution ratio of power loss are obtained by the power loss analysis of key components.According to the composition of power loss,the efficiency optimization analysis is given about main power loss components:SR of Full-bridge,transformer and power switch of Buck.The efficiency optimized by technology of soft-switching,planar transformer design and select of components,the power loss before and after is comparative analyzed,and it is verified by experiment.In order to further reduce the ripple and increase capacity of vehicular DC-DC converter,the paper researches on the multiphase Interleave-Buck.The characteristics of input and output analyzed by mathematical model and its function waveforms.The low input and output current ripple,low output voltage ripple and high efficiency of multiphase Interleave-Buck verified by computer simulation and experimental.The high efficiency soft-switching of SR DC-DC converter applied on EVs is developed and set up with the parameters of 250-450VDC input,14.2VDC output and 2000W power.The prototype achieves maximum efficiency with 95.21%at rated input 336VDC.And the prototype achieves the design specification by:line regulation less than 0.5%,load regulation less than 1.5%,voltage accuracy less than 1%,voltage accuracy less than 2%,ripple of output voltage less than 5%,overshoot voltage less than 10%,and efficiency greater than 94%at rated voltage input with full load.The experimental results verify effectiveness of this scheme 'a high efficiency soft-switching of SR DC-DC converter applied on EVs',it can meet the application requirements of vehicular DC-DC power supply.And the Interleaved-Buck can reduce the current ripple and improve efficiency.