Research On Direct Yaw Moment Control For In-wheel Electric Vehicle(IEV) Based On Disturbance Observer And Sliding Mode Theory

In order to enhance vehicle stability in critical situations,In this paper,A direct yawmoment control(DYC)strategy is proposed for in-wheel electric vehicles by using sliding mode and nonlinear disturbance observer techniques.Firstly,the paper analyses the dynamics of in-wheel electric vehicles,and on this basis,considering the influence of the yaw rate and sideslip angle on the vehicle's yaw moment,then the ideal yaw rate and sideslip angle at the gravity are calculated by utilizing a two-degree of freedom(DOF)vehicle model,thereby the direct yaw-moment control strategy is determined.this strategy consists of a state observer of the sideslip angle,a direct yaw-moment controller and moment allocation controller:(1)by using a linear 2DOF vehicle model,the state observer is constructed base on second-order sliding model control(SMC)theory to identify and estimate the actual sideslip angle;(2)a traditional sliding mode direct yaw-moment controller is designed to guarantee that the actual sideslip angle and yaw rate will approach the ideal ones in a finite-time,and the additional yawing moment needed to maintain vehicle stability is also gotten by the yaw-moment controller.(3)dynamic load allocation method is utilized on the moment allocation controller,whose function is to distribute the additional moment computed by the direct yaw-moment to the four in-wheel motors.accordingly,the driving or braking forces exerted on the four wheels of vehicle are identified.Secondly,to tackle the chattering problem existing in the traditional sliding mode controller,a second-order sliding mode controller is designed by taking the derivative of the controller as the virtual control,which implies that although the virtual controller is discontinuous,the actual controller considered as an integration of the virtual control is continuous.In addition,to avoid the large gains in the derived controllers,by combining the nonlinear disturbance observer with the second-order sliding mode controller,the composite control scheme is further proposed.Finally,the CarSim is utilized to construct the vehicle model,and the DYC model is build up in MATLAB/Simulink,then combining CarSim with MATLAB/Simulink to carry on simulation test.In this paper,Considering the conditions with or without lateral wind disturbance,and the vehicle is running along the double lane-change track on the road of low adhesion coefficient.According to simulation results,it is obtained that the proposed DYC strategy is able to guarantee the vehicle operating stability effectively.Meanwhile,in comparison with the other three controllers,the proposed second-order sliding mode controller based on nonlinear disturbance observer not only tackles the chattering problem existing in the traditional sliding mode controller,but also shows a high robustness and precise.