Vehicle Stability Control Considering Uncertainties

The vehicle active safety system can effectively maintain the stability of the vehicle,which can also prevent the vehicle from slipping,rolling,collision,and plays a major role in protecting the safety of the driver and passengers.In the development of assisted driving and autonomous driving technology,the stability of vehicle is an important part of it.During the running of vehicle,the actual mass and moment of inertia of the vehicle can not be accurately obtained,which leads to the existence of system uncertainty.It is necessary to design a robust controller considering the parametric uncertainties to maintain the stability of vehicle.In this paper,the hierarchical control structure is adopted.The high-level controller is used to obtain the expected value of the resultant force(moment)of the vehicle,and the low-level controller assigns the expected value to the wheels in an equivalent and optimal manner.The main content of this thesis is vehicle stability control considering uncertainties,including the following parts:Firstly,a seven-degree-of-freedom vehicle model is established.The direct feedback linearization method is applied to partially cancel the nonlinearity in the vehicle model.Then a linear model with uncompensated dynamics is obtained.Analysis the uncertainties of mass and moment of inertia,thus,a nonlinear vehicle system considering parameter uncertainty is represented as a linear uncertain system with uncompensated dynamics.Second,design a robust controller.Since there is an uncompensated residual value in the linearization process of the model,the controller gain will have a certain perturbation,so the robust non-fragile guaranteed cost controller is designed.Select the linear two-degree-of-freedom model as the reference model,the deviation between the seven-degree-of-freedom vehicle model and the reference model longitudinal velocity,lateral velocity,and yaw angular velocity is used as the state variable.The Lyapunov stability theorem is used to solve the linear matrix inequality condition of the controller gain matrix,and then the final upper-level stability controller is solved.By analyzing the response curve of the vehicle's seven-degree-of-freedom model under the same input,the controller solved by the vehicle full-load condition is used as the final highlevel controller,and the resultant force(moment)for maintaining the stability of the vehicle is obtained.The resultant force(moment)solved by the high-level controller is a virtual control quantity.The real realization of the stability control of the vehicle needs to distribute the resultant force(moment)to the component forces of each wheel through low-level distribution controller and convert it into individual wheels torque.The vehicle's control distribution system is an overdrive control system with redundant actuators.The quadratic function is selected as the optimized performance indicator,the force of each tire is used to satisfy the resultant force(moment)expected by the high-level controller,the frictional ellipse constraint with adhesion and the physical constraint of the actuator itself are used as inequality constraints.The expected values of the longitudinal resultant force,the lateral resultant force and the yaw moment are optimally distributed to the longitudinal forces of the individual tires.The force and torque are then converted according to the tire kinematics model to obtain the torque command executable by the actuator.Finally,the feasibility and control effect of the overall control scheme under different vehicle mass and moment of inertia are verified by Matlab/Simulink and AMESim co-simulation.It shows that the control scheme is robust to the change of vehicle mass and moment of inertia.