Research On The Variable Voltage Power Supply System Of Pure Electric Vehicle

Due to the demand of energy exhaustion and ecological environment and the rapid development of intelligent network transportation,the three-power technology of electric vehicles has attracted the attention of academia and countries.We are facing a reflection on the ecological civilization of human transportation.Countries are committed to improving mileage anxiety and optimizing control strategies.In this paper,through the design and optimization of battery connection mode,the voltage change and speed and speed control of the power supply system of EV,the reliability and stability of the design structure are analyzed and simulated.In order to achieve the optimal energy transfer conversion between the power supply system and the motor,the efficiency and safety of EV are improved.Based on the power supply system,the following analysis is carried out in this paper.(1)In order to meet the requirements of high-speed,high-voltage,low-speed and low-voltage for electric vehicles,a power supply voltage-transforming circuit system is designed to realize the motor speed conversion under variable voltage.According to the theory of maximizing similarity of specifications,three-element single batteries are designed to form six battery pack modules in series and parallel.Six battery pack modules are converted in series and parallel by relay-type integrated intelligent switch.They are composed of 307V80Ah high-voltage battery pack module,153V160Ah medium-voltage battery pack module,51V480Ah battery pack parking module and other battery pack modules.To improve the parking safety at low voltage,the motor works near the rated speed of the corresponding motor at different voltage,which improves the driving efficiency of the motor,thus making the electric vehicle more economical,efficient and safe.Under the condition of low speed and constant torque,according to the characteristic of constant current,it is proposed that the battery capacity of low voltage mode is larger than that of high voltage mode,which can reduce the discharge rate(rate C=current/capacity),i.e.C rate.Small rate charging and discharging mode is beneficial to prolong the mileage life of power supply system.(2)Design the voltage switch circuit of relay type integrated intelligent conversion transformer and complete the simulation and verification of MATLAB/Simscape circuit.The switch aims at ensuring the optimal consistency of the battery pack.The battery pack module is connected in interlocking,intelligent,timely parallel conduction and disconnection mode.The high voltage battery pack module is connected in parallel when discharging to voltage balance.Each battery pack unit can only discharge and not be charged under the switch control.Relay-type intelligent switch executes control instructions sent by BMS to prevent charging from high energy to low energy.For high voltage energy battery pack module,it ensures that the required battery pack units are connected first.When high voltage discharges to voltage balance,the required battery pack units are connected in parallel to ensure consistency maximization and battery balance.To a certain extent,it is also an extension of effective consumption of passive equalization.The correctness of the switch circuit is verified by MATLAB/Simscape,and the parallel consistency simulation based on the second-order RC battery model is completed.(3)Anti-vibration and arc extinguishing design of relay.Based on the advantages of no-conduction voltage and cost-effective ratio,relay switch is selected.Because the breakdown voltage of relay switch is up to kilovolt,the unavoidable vibration condition of vehicle will inevitably cause the vibration arc problem of relay.This paper analyses the characteristics of three arc extinguishing optimization modes:magnetic blowing drive arc,RC parallel circuit arc extinguishing and optimizing contact material,and compares and chooses RC protection circuit based on RC.Countermeasure and anti-vibration structure are designed to restrain the shortcomings of high peak breakdown voltage and stability of vibration failure when relay is turned off.Zero-input response,zero-state response and full-response simulation of RC circuit are established in MATLAB,and the steady-state of circuit is analyzed to meet the arc-extinguishing conditions.(4)Regenerative braking and electromagnetic ABS under switch.When the vehicle decelerates,the intelligent switch is adjusted to the mode of high speed and low gear.The motor generates electricity to charge the battery,realizes regenerative braking function and has electromagnetic ABS function.When the vehicle decelerates,the switch generates control information through sampling speed signal and central processing system.The driving module controls the intelligent switch to the corresponding gear position,i.e.low-grade and high-speed operation mode.The induced electromotive force of the motor winding is higher than the battery voltage.The motor generates electricity to charge the battery,realizes regenerative braking function and increases the braking torque.Acting on the wheel and decelerating,the wheel does not lock,to achieve energy recovery and has electromagnetic ABS function.The regenerative braking energy recovery efficiency of electric vehicles with speeds of 110 km/h,80 km/h and 50 km/h is calculated in different periods.The regenerative braking energy recovery rate is about 23%by the ratio of electromagnetic braking force to total braking force.(5)EC3-C10HB-C03 vehicle refitting test and result analysis.The maximum speed,acceleration time of 0-50km/h and economic evaluation parameters of the vehicle are 112.3km/h,4.91s and 11.3kwh/100km respectively.The driving mileage is 246km.The results meet the design requirements...