| In this thesis the so-called "spacing distance control." problem (in contrast with the "headway control" problem) of a platoon of identical vehicles is studied. It is initially shown that (i) if a platoon of vehicles is controlled by decentralized controllers, then the resulting closed loop system is always string unstable with respect to velocity, and (ii) if a platoon of vehicles is controlled by identical decentralized controllers, then the resultant closed loop system will also be string unstable with respect to spacing distance. Because of this negative result, the case when vehicles in a platoon are controlled by decentralized non-identical controllers is then investigated. In this problem, it is desired to achieve asymptotic error regulation in the spacing of the vehicles, independent of any constant velocity (assumed unmeasurable) which the lead vehicle may take, such that (i) the control signals and states of the vehicles in the platoon remain bounded, and (ii) there exists a vehicle indexed N¯ by which the system is string stable with respect to spacing distance for all vehicles with index n ≥ N¯ + 1. This latter property (ii) of a system is called "eventual string stability". In particular, a new decentralized platoon controller is proposed which has the property that if the decentralized controller parameters are tuned appropriately, then all inputs and states of the platoon remain bounded, while at the same time ensuring asymptotic spacing regulation and eventual string stability of the spacing distance. A number of simulation studies are made to illustrate the results for the case of a platoon consisting of a large number of vehicles (up to 2000 vehicles). The results obtained are then extended to a two-dimensional platoon of vehicles which are assumed to have both acceleration/deceleration and steering inputs. |
