Research On Layered Direct Yaw Moment Control Strategy Of In-wheel Electric Vehicle Based On Terminal Sliding Mode Theory

The energy crisis and environmental pollution caused by the traditional internal com-bustion vehicle make the electric vehicle become the current research hotspot,among which the in-wheel electric vehicle(IEV)is widely concerned because of its unique struc-ture and driving form,in order to improve the driving stability of the in-wheel electric ve-hicle under the limit condition,this paper proposes a direct yaw moment control(DYC)strategy based on the layered idea.Firstly,the influence of yaw rate on the driving stability of IEV is analyzed,and then a two degree of freedom(2DOF)vehicle model is established based on vehicle dynamics analysis to obtain the desired yaw rate,on this basis,the DYC control strategy based on hierarchical structure is designed.The control system is divided into upper control and lower control,the traditional terminal sliding mode(TSM)controller is used in the upper control to output the additional yaw moment needed for the stable driving of the vehicle,so as to ensure that the yaw rate is close to the ideal value as much as possible,and then the total longitudinal force of the vehicle is obtained by simple PI control.In the lower control,the additional yaw moment and longitudinal force obtained from the upper control are reasonably distributed to four in-wheel motors by using the moment distributor,in order to expand the range of vehicle stability under the action of DYC,when the IEV actuator operates without fault,the torque divider based on dynamic load distribution is used,when the IEV actuator fails,a reconfigurable distributor based on quadratic programming is used to redistribute the residual driving force optimally,and the torque applied by each wheel in-wheel motor to the corresponding wheel is obtained.Secondly,in order to suppress the system chattering caused by the excessive con-trol gain of the TSM controller to suppress the unknown interference of the system,an adaptive terminal sliding mode(ATSM)control method is proposed,the proposed ATSM controller is composed of adaptive law and terminal sliding mode technology,its feature is to make the controller automatically search for the minimum gain satisfying the sliding mode arrival condition,so that the gain of the TSM controller changes with the distur-bance to successfully suppress the system chattering.To further improve the robustness of DYC,a new type of nonlinear disturbance observer(NDOB)is proposed to estimate the internal and external disturbances of the system,the NDOB is combined with the above ATSM controller to form a composite direct yaw moment controller.Finally,a joint simulation test is carried out by using the vehicle dynamics software Carsim and the mathematical software Matlab,the closed-loop simulation test is carried out on the low adhesion road with different working conditions,when there is no fault in IEV actuator,two conditions of driver’s open-loop and closed-loop,and four working conditions are further distinguished whether there is side wind,in case of failure,single wheel failure and double wheel failure shall be considered,and the performance of each controller shall be comprehensively verified according to the above conditions.The sim-ulation results show that the proposed direct yaw moment control strategy can guarantee the driving stability of the vehicle before and after the failure of IEV actuator,in addi-tion,through the analysis and comparison of the control effect of DYC under the action of different controllers,it is found that the ATSM composite controller based on NDOB performs best in different working conditions,which not only can effectively suppress the system chattering,but also has higher tracking accuracy and anti-interference.