Lateral Path Following Control of Automated Vehicle Platoons.
Nowadays, traffic congestion on highways is still an increasing problem, in the Netherlands and worldwide. Hence, there is an increasing societal demand for innovative solutions for this problem. Preferably, these solutions also contribute to the reduction of fuel consumption (and hence emissions) and higher traffic safety. This has raised the interest in the development of automated highway (platooning) systems. If vehicles would drive together in a platoon with small inter vehicle time gaps of well below one second, the road capacity of existing roads can be increased significantly. Moreover, due to the lower aerodynamic drag, especially for truck platoons, the emission can be reduced. Driving safely at very small inter vehicle time gaps, however, requires vehicle automation in both longitudinal and lateral direction, due to the limited reaction time of a human driver. Most research activities regarding automated vehicle platoons focus on the longitudinal control of a vehicle, and less research has been performed on the aspect of lateral automation. This is one of the main motivations for this work to focus on the development of a lateral controller for cooperative vehicle platoons. For the lateral control, a vehicle following control strategy is proposed, in which the design strategy is based on vehicle path following rather than direct vehicle following. The former approach shows better tracking performance based on numerous research studies. For the control design, a linear vehicle model is used and the error dynamics of a vehicle with respect to a reference path, generated by a preceding vehicle, are derived. A static output feedback control law is designed in combination with a feedforward controller based on the control input of the preceding vehicle which is obtained through wireless inter vehicle communication. As a result of the vehicle following control strategy, the lateral dynamics of the individual vehicles are coupled through the cooperative control law. Therefore, string stability in the lateral direction should be taken into account in the controller design, as well. In literature, lateral string stability has been achieved for direct vehicle following control methods, but this concept is not well developed in the scope of lateral control methods for vehicle path following, in the scope of platooning. In this work, a method has been developed to analyze the platoon dynamics in the frequency domain, where the lateral control of each individual vehicle is based on the proposed vehicle path following control method. Marginal lateral string stable behavior is obtained for the designed control strategy, evidenced both in the frequency domain and in time domain simulation. Finally, the control algorithm has been implemented and tested using two Toyota Prius III vehicles. Different lateral maneuvers, such as a lane change maneuver, are performed both at low and high speed. The experimental data validates the analytic results and shows that the lateral dynamics of automated vehicle platoons can successfully be controlled using the proposed vehicle path following control method.