F2008-01-014
Control Concepts for Safe Vehicle Platooning
1. Introduction
The scope of the project KONVOI is to realize heavy-duty truck platoons of variable lengths allowing drivers to merge with a platoon and being guided autonomously in longitudinal and lateral direction with an inter-vehicular distance of 10m. A wireless inter-vehicular communication system supports each truck with all drivers’ demands and the dynamic states of all platoon members. Due to this it is possible to organize the trucks among each other, to decrease longitudinal control errors and to follow the leading vehicle's lateral position on the track. In order to realize safe operation for such close following the authors use new approaches for longitudinal and lateral control design to meet the strict safety requirements.
For close following operation the drivers' reaction is too slow and thus all maneuvers must be organized by a management system - only demands (like coupling to another truck) should be initialized by drivers using a visual action and feedback interface. For both longitudinal and lateral dynamics upper bounds on errors to the reference distances have to be maintained. Since the platoon operation concerns a vast range of operating velocities that strongly affect the truck’s dynamics enough robustness with respect to changing operation points needs to be established.
2. Control methods for safe operation
The control concept for both longitudinal and lateral guidance consists of the fusion of sensor-data, state estimation and state-feedback to control the steering actuator and engine respectively. Due to the different type of dynamic coupling the control methods for longitudinal and lateral control differ though. Since the lateral position of the leading vehicle can be transmitted via the communication system the front vehicle’s information can be exploited to generate future reference values. A lateral reference trajectory is generated for each vehicle and used for a model-based predictive control applied to the following vehicles to minimize tracking errors. Opposed to that, the longitudinal dynamics of the leading vehicle is directly coupled to the distances of all following vehicles and thus no future information is available here. Nevertheless, upper bounds on distance errors can be achieved by optimizing the transfer functions relating the leading vehicle's acceleration to the followers' errors. The authors use the formulation of linear matrix inequalities to express the minimization of the H-infinity norm for the corresponding transfer functions. This results in a convex optimization problem that can be solved efficiently from the numerical perspective.
3. Results
The project's goal is to realize platoon operation with surrounding traffic on highways by the end of 2008. All four test trucks are equipped with the necessary actuation, sensor and communication system already. The control algorithms are tested in simulations for all relevant maneuvers with a maximum number of four trucks. Especially upper bounds on longitudinal and lateral errors are shown to meet the safety conditions and robustness with respect to a vast region of operation points is investigated.
Poster presentation: Mobility concepts