Performance analysis of a cooperative adaptive cruise controller subject to dynamic time headway

The current paper shows string stability of a platoon of vehicles when the spacing policy within the platoon is dynamic, i.e., it has time-varying parameters. This problem setup is to address the safety issues that arise due to malfunction of some redundant sensing/communicating devices installed on the vehicles. In such a faulty situation, the controller is still functional due to the redundancy of the sensing/communicating devices as well as estimating resources which provide the controller with the required information. However, the accuracy of the controller will be reduced. This loss of accuracy should be compensated by doing a more conservative design of safety important parameters such as the safe inter-vehicle distance, which is selected based on the string stability requirement. The decision of a change in the inter-vehicle distance, or equivalently the spacing policy, is made by a so called “safety checker” function which can be introduced into the loop of vehicle and controller. Here, it is shown that an adopted cooperative adaptive cruise controller renders the string of vehicles stable even if the spacing policy is time variant. The stability requirement of the closed-loop system is that the switching signal suggested by the safety checker unit being piecewise constant, i.e., the safe inter-vehicle distance policy does not change continuously.