Research On Fault-tolerant Control Of SBW Of Four-wheel Hub Motor Driven Electric Vehicle

Nowadays,environmental problems are increasingly serious,energy saving and emission reduction is urgent,because of the environmental protection and economy of electric vehicles,the utilization rate is increasing.However,because of the full-line control characteristics of electric vehicles,compared with the mechanical connection of traditional vehicles,its safety is lower.Therefore,in order to improve the driving safety of electric vehicles,this thesis focuses on the problem of steering failure and fault tolerance of four-wheel-drive electric vehicles.The main research contents are as follows:Firstly,a four-wheel hub motor-driven electric vehicle model was established using MATLAB/simulink.This model considers the lateral,yaw,longitudinal and wheel rotation of the car and the non-linear of the tire,and the simulation results of the model are compared with those of the car model in Carsim,which verifies the accuracy of the model built in this thesis.In addition,based on the artificial fault tree method,the qualitative and quantitative analysis of the steering failure of the steer-by-wire system is made,and the fault-tolerant control method of steering failure based on differential braking is determined.Secondly,in order to accurately obtain the input parameters of the fault-tolerant controller,the vehicle state observer is studied.The vehicle state observer based on UKF and EKF was built,and verified under the three working conditions of double shifting sine and angular step.Through the comparison and analysis of the estimation results,the accuracy of UKF state observer is verified,and the vehicle state observer in this thesis is determined to be the state observer based on UKF algorithm.Subsequently,the research on the steering failure-tolerant control strategy is carried out.Based on the design idea of the overdrive system controller,a layered control strategy is established: the upper layer uses sliding mode variable structure control to obtain the total driving force;the lower layer is the torque distribution control layer,which uses the adhesion elliptic function as the optimization objective to improve tire utilization,and calculate the driving force of each wheel based on the Lagrange Multiplier to reduce the computer solution time;at the same time,based on the single-point preview theory,establish a PID driver with driving speed and driving path following and lateral acceleration feedback Model,the model is built to form a real-time closed-loop simulation in the simulation process.Finally,the effectiveness that the fault-tolerant control strategy designed in this thesis is verified.In order to ensure the effectiveness of the observer,simulations are carried out under the same working conditions,and the simulation results of steering failure and steering failure tolerance are compared.It is proved that the fault-tolerant control strategy in this thesis can improve the driving safety of four-wheel hub motordriven electric vehicles.