Research On Braking Energy Recovery Control Strategy For Electric Vehicle With Four In-Wheel-Motor

The popularity of traditional cars has led to the depletion of non-renewable energy such as fossil fuels since industrialization and environmental pollution has become increasingly serious.In recent years,energy conservation and emission reduction policies have risen to the national strategic level,the awareness of green transportation travel has won support among the people deeply.It is the general trend that the future development of automobile will turn to electrification and greenness.However,the speed of electric vehicles development is relatively slow due to the limited driving range,short battery life and high initial cost.The braking energy recovery technology can reduce the heat decay and loss of the vehicle system by reasonably distributing the braking force,it also can recover part of the energy in the braking process of the vehicle and improve the driving range of the vehicle.Electric vehicle with four in-wheel-motor is selected as the research object in this paper,which has advantages in dynamic control and energy flow transfer efficiency,it has a better capacity of braking energy recovery effect.This paper carries out a research on the related problems of braking energy control system in order to maximize the recovery of braking energy as the goal and ensure the stability and safety of vehicle braking as the premise.Firstly,this paper describes the basic theoretical knowledge of braking energy recovery system,carries out the selection and parameter matching design of the key components of four hub motor-driven electric vehicle power system,builds the vehicle model in cruise simulation software based on the vehicle dynamics theory,completes the mechanical connection and bus signal connection,verifies the vehicle power performance and driving range performance through the simulation task.Secondly,referring to the advantages and disadvantages of classical front and rear axle braking force distribution strategy,this paper proposes an improved control strategy based on ECE regulation curve and ideal braking force distribution curve in order to ensure good braking performance and energy recovery.Two kinds of regenerative braking force distribution control strategies are designed: Taking the battery SOC value,vehicle speed v and braking strength z as the input and the regenerative braking force distribution coefficient as the output after being adjusted by fuzzy controller to control the distribution of motor regenerative braking torque and friction mechanical torque;taking the peak voltage,peak current,internal resistance of power battery and wheel motor speed and other related parameters to calculate the maximum motor braking force power,set the controller to distribute motor braking torque and brake braking torque,determine the vehicle braking energy recovery control strategy.Finally,utilizing the designed braking energy recovery control strategy to establish the corresponding model in MATLAB/Simulink software,and the vehicle model built in cruise software is co simulated.The simulation results show that the maximum motor braking force control strategy is more effective than the fuzzy control strategy in the three different urban cycles such as NEDC,FTP72 and FTP75,it has higher contribution rate of battery SOC value and braking energy recovery effect;the vehicle has better braking performance and braking energy recovery efficiency when using the maximum motor braking force control strategy under constant braking strength working condition and constant initial braking speed working condition in the simulation of typical braking conditions.