Research On Lateral Stability And Torque Distribution Control Of An In-wheel-motored Electric Vehicle

Environment and safety have become two major problems in the sustainable development of the modern automobile industry,which are the commanding height for major automobile enterprises to compete for the core and key technologies.The in-wheel-motored electric vehicles(IWMEV)have the advantages of short drive chain,high transmission efficiency,compact structure,and accurate and controllable wheel torque in four-quadrant,and have become an important development form for electric vehicles in the future.The distributed drive architecture not only brings opportunities for vehicle dynamics control,but also challenges the reliability of the control system.In order to improve the lateral stability of the IWMEV under critical maneuvers,it is necessary to further improve the theory and method of the vehicle lateral stability control.Aiming at the problems of drive motor modeling,reliable control of lateral stability,accurate estimation of the vehicle states,and efficient torque distribution control in the vehicle dynamics control of the IWMEV,the key technologies of the lateral stability control system of the IWMEV e are studied.This paper are expected to improve the reliability of lateral stability control of the distributed drive electric vehicles,and have certain significance for improving the theory and method of vehicle dynamics control.The research works carried out in this paper are as follows:A dynamic model of an IWMEV was established.In particular,based on the vehicle power requirements,a method for determining the modeling parameters of the brushless DC motor(BLDCM)is proposed.Firstly,combined with the dynamic equation of electric vehicle,the motor power and torque satisfying the power requirements of electric vehicles are matched.Then,according to the voltage equation of the BLDCM and the rotor dynamics equation,the back EMF coefficient of the motor and the range of the winding inductance are derived.According to the influence of power supply voltage,back EMF coefficient,winding inductance and resistance on vehicle dynamics,a method for determining motor modeling parameters is proposed.The control strategy of lateral stability for the IWMEV based on the regional pole placement is proposed.Considering the uncertainty of vehicle parameters,a flexible representation method is adopted to introduce par ameter uncertainty into the design of control strategy.The weight matrices of the state variables and the control output are defined in the cost function to balance the state deviation and control output.The numerical simulation results show that the pro posed control strategy can not only improve the steering stability of the vehicle,but also possess strong robustness to the parameter uncertainties.An estimator of vehicle states based on the adaptive unscented Kalman filter(AUKF)for an IWMEV is proposed.Given the merits of an independent drive structure,the tire forces of the IWMEV can be directly calculated through vehicle dynamic model.Additionally,by means of the normalized innovation square,the validity of vehicle states estimation can be detected and the sliding window length can be adjusted adaptively,and thus,the steady-state error and the dynamic performance of the estimator are demonstrated to be simultaneously improved.Then,an adaptive adjustment strategy for the noise covariance matrices is introduced to overcome the impact of parameter uncertainties.The numerical simulation results prove that the proposed vehicle states estimator based on AUKF not only improves estimation accuracy but also possesses strong robustness against paramet er uncertainties.A regularized strategy of torque vector distribution control is proposed.The direct yaw moment is achieved by the driving force and braking force of the hub motor,combined with the driving model switching and the wheel slip ratio contr ol to minimize the tire workload usage.The performance analysis of the control system is carried out by hardware-in-the-loop simulation.The experimental results show that the regularized strategy of torque distribution control can reliably ensure torque distribution on the low adhesion road surface,and the tire slip ratio is close to the ideal slip ratio,thus the lateral stability performance of the vehicle is greatly improved.