Research On Yaw Stability Control For Steer-by-wire Vehicles Via Sliding Mode Control Theory And Extreme Learning Machine

With the rapid development of vehicle industry and electronic information technology,the Steer-by-Wire(SBW)system has gradually come into the public’s view.Many intelligent vehicles tend to employ SBW system for its control flexibility since the mechanical structure of traditional steering system is replaced by electrical signals in SBW system.Considering the yaw stability of vehicles is also an important topic of the vehicle research,active front steering(AFS)control strategy for SBW vehicles has shown its reliability in improving vehicle stability in recent years.Thus,in this dissertation,a novel AFS control strategy based on sliding mode control(SMC)theory and extreme learning machine(ELM)is further studied for the purpose of improving the yaw stability and maneuverability of SBW vehicles.In this dissertation,the working principle and mechanical structure of the SBW system are firstly introduced.Then,the vehicle dynamics and mathematical model of SBW system are established by considering the system perturbation and external disturbances.Next,a conventional sliding mode control and adaptive recursive integral terminal sliding mode control(ARITSMC)are adopted in the upper controller for guaranteeing the convergence performance of both the actual sideslip angle and the yaw rate with strong robustness and fast convergence rate.And a fast nonsingular terminal sliding mode control(FNTSMC)with extreme learning machine(ELM)estimator to estimate its equivalent control is designed in the lower controller to track the desired front wheel steering angle calculated from the upper controller for driving the sideslip angle and the yaw rate to converge ideal value.The two upper controllers are designed to track the vehicle sideslip angle and yaw rate to ensure the yaw stability of SBW vehicles.Compared with the conventional sliding mode controller,the ARITSMC has better performance and its features are as follows: 1)Due to the introduction of an integral element in the proposed ARITSMC,not only can the reaching time be reduced,but also the chattering phenomenon can be decreased further.2)The tracking error can converge to zero in a finite time by designing the terminal sliding surface,and by combining the sideslip angle and yaw rate as the control objective,better stability performance can be obtained when compared with the case of using only one of these values alone.3)The switch gain in the upper controller can be estimated successfully in the sense of Lyapunov by using the adaptive law which relaxes prior knowledge of the system uncertainty required for conventional sliding mode controller design and enhances the system robustness.The lower FNTSMC based on ELM is implemented to guarantee the actual front wheel steering angle can track the desired one calculated from the upper controller.The features of this control scheme are as follows: 1)Compared the conventional sliding mode control,the proposed FNTSMC can guarantee the faster convergence rate and the error dynamics converge to the equilibrium points in a finite time rather than asymptotically.2)A novel estimator via the ELM is proposed to adaptively estimate the equivalent control component such that the dependence of system dynamics can be nicely alleviated.Finally,four simulation cases are designed to simulate the real steering behaviour according to the actual driving conditions,and two comparison control strategies are introduced to compare the performance of proposed controller by utilizing MATLAB/Simulink and Car Sim software.From the simulation results,it can be seen that the proposed control strategy obtains the most excellent performance compared the two other controllers.Furthermore,the yaw stability and maneuverability for SBW vehicles can be well maintained with the proposed controller when encountering strong external disturbances.