Longitudinal And Lateral Control Of Vehicles In Automated Highway System

Automated Highway System (AHS) is an uppermost subsystem of Intelligent Transport System (ITS). The system includes vehicle automatic navigation and control, traffic management automation and traffic accident treatment automation. It will significantly increase the throughput on the highways and enhance driving safety. A key factor in AHS deployment is the synthesis and design longitudinal and lateral control laws for vehicle automated driving. In this dissertation, from constructing dynamic model of vehicle, based on the stability analysis for interconnected nonlinear systems, the longitudinal control for vehicle following, and lateral control for lane keeping and lane changing in AHS were studied.The important factors affecting vehicle driving performance, and the coupling effects between longitudinal vehicle dynamics and lateral vehicle dynamics were investigated. Based on the analysis of vehicle dynamics, by using some of dynamics theorems, the longitudinal dynamic model, lateral dynamic model, and coupled dynamic model considering the coupling effects were constructed by taking the longitudinal velocity, lateral velocity, and yaw rate as the states.The stability of two classes of infinite-dimensional nonlinear interconnected systems was studied. Under the assumption that the systems are globally Lipschitz, from the conditions of stability of isolated subsystems decomposed from the interconnected nonlinear systems, by applying vector Lyapunov function method and comparison principle, the sufficient conditions of exponential string stability for these interconnected systems were obtained.The longitudinal control for vehicle following in AHS was studied. By employing "look ahead" and "look both ahead and behind" approach for control systems design, respectively, based on longitudinal dynamic model of vehicles and constant spacing policy, the dynamical equation for spacing errors of the string vehicles was constructed, assuming that each controlled vehicle in the platoon has full access to information on the position, velocity and acceleration of lead vehicle and vehicle in front and behind of it, by sliding mode control method, the longitudinal control laws for vehicle following were designed by taking the propulsive/braking effort as the control input. The stability of the longitudinal following control system was analyzed by the stability criteria of nonlinear interconnected systems. In the presence of parametric uncertainty (time varying or unknown), the decentralized adaptive algorithm to compensate for parametric variations was investigated and the robust variable structure control laws for each vehicle in the platoon were designed.The lateral control for lane keeping in AHS was studied. Applying the look-ahead scheme and vehicle lateral dynamic mode, the vehicle lateral dynamics about the lateral displacement error and yaw angle error at the look-ahead distance were modeled. Assuming the data of the lateral offset from the centerline of the lane and the angle between the tangent to the road and the vehicle orientation at the look-ahead distance can be measured with on-board sensors, applying terminal sliding mode and finite time sliding mode reaching law, the variable structure control law for lane keeping was designed taking the steering angle as the control input. In the presence of parametric uncertainty, the robust variable structure control laws were designed, the adaptive algorithm to compensate for parametric variations was investigated by the Lyapunov function method.The lateral control for lane changing in AHS was studied. Applying trapezoidal acceleration trajectory, considering the curvature varying from starting lane to target lane, a virtual trajectory for lane changing on curved road was presented. Applying the predetermined trajectory, the desired yaw angle and yaw rate for lane changing were generated. Assuming that the information on yaw rate of vehicle can be measured with on-board sensors, based on the lateral dynamical model of vehicle, by the finite time sliding mode reaching law, the lane changing variable structure control law was designed. The lateral velocity was estimated by the Lyapunov function method.The coupled longitudinal and lateral control in AHS was studied. Based on coupled longitudinal and lateral model of vehicle in a platoon, by the design method of finite time sliding mode reaching law, the coupled control laws for vehicle following with lane keeping, and vehicle following with lane changing were designed, respectively. The stability of control systems was analyzed using Lyapunov function method.The control for vehicle split from a platoon and join a platoon was studied based on inter-vehicle communication. The control algorithm for vehicle split from a platoon and join a platoon was designed by applying the longitudinal and lateral control laws for vehicle following, lane keeping and lane changing in AHS.The simulation was done applying Matlab toolbox. Simulation results indicate that the longitudinal and lateral control performance was good by using the control laws designed for vehicle following, lane keeping, and lane changing in this dissertation. Simulations also verify the feasibility of the control algorithm for vehicle split from a platoon and join a platoon.