| As we all know,electric motor has completely different working characteristics from gasoline engine,and pure electric vehicles have put forward new requirements for transmission applications.At present,the transmission systems matched by pure electric vehicles is mostly single-stage gearbox,and the Electric Mechanical Continuously Variable Transmissions(EMCVT)as a new type of power transmission device,equipped with pure electric vehicles in the driving process,EMCVT continuous change of the speed ratio adjustment will change the operating range of the motor.Because the power battery and motor are in the same circuit,the change of the motor operating rang will inevitably cause the change of the power battery working environment,and then have a certain impact on the power battery cycle life.Power battery as the only energy source of pure electric vehicle,its full life cycle life has an impact on the economy of the whole vehicle,and this paper takes a power battery equipped with EMCVT pure electric vehicle as the research object,and carries on the change of power battery cycle life in the course of vehicle driving,which has important practical value.The main research contents of this paper are as follows:(1)Introduced the characteristics and working principle of lithium-ion power battery,and focused on analyzed the impact of the main factors such as temperature,discharge rate and depth of discharge on the cycle life of power battery,and expounded the life decay mechanism of Li-ion battery from the positive side,negative side and electrolyte.(2)Analyzed Several commonly used battery models,and the second-order equivalent circuit model is established by using the module library in MATLAB/Simulink according to the modeling requirements of this paper.Using the Parameter Estimation toolbox to identify the necessary parameters of the model with the voltage and current curve obtained by the triple lithium battery single pulse charge and discharge test.The identification principle uses nonlinear least squares method,and after several iterations,the parameters of different SOC points in the direction of charge and discharge are obtained,these parameters are used for the establishment of power battery model.(3)Analyzed the power transmission system of the pure electric vehicle equipped with EMCVT,and the base on MATLAB/Simulink software to build the model of each component and integrate the condition simulation,the simulation results are with the actual vehicle test results.The comparison results are very similar and the accuracy of the built model is verified,and the foundation for the subsequent power battery system test dynamic current conditions to lay the foundation.(4)Using UDDS and US06 cycle conditions to represent the daily travel of electric vehicles and simulate them.,with a single-stage gearbox pure electric vehicle power battery discharge current for comparative analysis.The two cycle conditions as the target condition simulation to obtain the dynamic current of the power system test,according to this dynamic current power battery system cycle life test,record the capacity retention rate and the number of cycle strains corresponding data.The genetic algorithm is used to fit out the power battery system capacity decline mathematical model with EMCVT and single-stage gearbox,and to compare and analyze the principle of end-life of the capacity of the electric pool which is lower than the nominal capacity of 80%. |
