Longitudinal control for heterogeneous vehicle platooning with uncertain dynamics

Abstract

The work presented in this report focuses on longitudinal control of heterogeneous platoon. Firstly, merging maneuver is looked upon, considering heterogeneity in the vehicles i.e. considering different dynamics for the vehicles involved. Then heterogeneity in platoon, arising from the difference in potential limits of the vehicles is taken into account, which the current literature fails to address. The uncertain/heterogeneous dynamics are addressed through the difference in the engine driveline constant, which differs for different vehicles and keeps on changing during operation. The heterogeneity is tackled by using Adaptive control, which adapts to the changing dynamics and estimates the uncertainty to act accordingly. Adaptive strategies for formation keeping in platoons of automated vehicles have been recently proposed; while these strategies are able to cope with uncertain vehicle parameters, they have the drawback of handling only acyclic graphs (e.g. look-ahead topology). This prevents from enhancing formation keeping protocols with more complex platooning maneuvers such as synchronized merging/splitting. This work proposes an adaptive strategy for performing synchronized merging maneuvers in the presence of uncertain vehicle parameters: during these maneuvers, a cyclic communication graph is instantiated, which must be handled in a suitable way. The strategy is framed as a synchronization protocol with a set of adaptive control laws, designed via Lyapunov stability theory. A benchmark scenario in which two platoons formed in different lanes are required to merge, (e.g. due to a lane closure because of roadworks) is presented to show the effectiveness of the proposed strategy. The approach is proven to be scalable to platoons with arbitrary number of vehicles. In later part of the work, a method is proposed which takes the limits of the vehicles into consideration, to make the platooning realistic. An adaptive platooning strategy is used so as the vehicles can adaptively synchronize to desired reference dynamics. In order to handle engine limits, a mechanism is proposed based on making the reference dynamics `not too demanding', by properly saturating their control action. Such saturation action will allow all vehicles in the platoon to remain in their engine potential limits throughout. Another problem that affects the stability of the platoon is that, any perturbations or disturbance in the platoon leaves the vehicle scattered if the vehicles are already running at their potential limits. This work proposes an adaptive platooning method with bi-directional interaction and a mechanism coping with engine constraints. The bi-directional interaction allows the vehicle to not only look at the error in spacing from the preceding vehicle (vehicle in front) but also the succeeding vehicle, this makes the vehicle's control action (acceleration) depend on both front and back errors, the vehicle can thus slow down for the following vehicle if it lags behind. The bi-directional strategy developed is then proved string stable, which the literature struggles to establish with the already developed bi-directional strategies. Simulations are then conducted to validate the theoretical analysis and show the effectiveness of the method in retaining cohesiveness of the platoon. The simulations include a merging maneuver to check the effectiveness of merging with synchronized cyclic communication. For the engine potential limits, the firstly state of the art algorithm's simulation is run which is then compared to the performance of the proposed algorithm. Finally, to check the effectiveness of bi-directional CACC strategy simulations for a specific case is run for both uni-directional and bi-directional strategies proposed in the thesis and are then compared, showing the advantage of using bi-directional CACC strategy over uni-directional.