Synthesis of Distributed Longitudinal Control Protocols for a Platoon of Autonomous Vehicles

We develop a framework for control protocol synthesis for a platoon of autonomous vehicles subject to temporal logic specifications. We describe the desired behavior of the platoon in a set of linear temporal logic formulas, such as collision avoidance, close spacing or comfortability. The problem of decomposing a global specification for the platoon into distributed specification for each pair of adjacent vehicles is hard to solve. We use the invariant specifications to tackle this problem and the decomposition is proved to be scalable.. Based on the specifications in Assumption/Guarantee form, we can construct a two-player game (between the vehicle and its closest leader) locally to automatically synthesize a controller protocol for each vehicle. Simulation example for a distributed vehicles control problem is also shown

Robust Distributed Control Protocols for Large Vehicular Platoons with Prescribed Transient and Steady State Performance

In this paper, we study the longitudinal control problem for a platoon of vehicles with unknown nonlinear dynamics under both the predecessor-following and the bidirectional control architectures. The proposed control protocols are fully distributed in the sense that each vehicle utilizes feedback from its relative position with respect to its preceding and following vehicles as well as its own velocity, which can all be easily obtained by onboard sensors. Moreover, no previous knowledge of model nonlinearities/disturbances is incorporated in the control design, enhancing in that way the robustness of the overall closed loop system against model imperfections. Additionally, certain designer-specified performance functions determine the transient and steady-state response, thus preventing connectivity breaks due to sensor limitations as well as inter-vehicular collisions. Finally, extensive simulation studies and a real-time experiment conducted with mobile robots clarify the proposed control protocols and verify their effectiveness.Comment: IEEE Transactions on Control Systems Technology, accepte

Cognitive Vehicle Platooning in the Era of Automated Electric Transportation

Vehicle platooning is an important innovation in the automotive industry that aims at improving safety, mileage, efficiency, and the time needed to travel. This research focuses on the various aspects of vehicle platooning, one of the important aspects being analysis of different control strategies that lead to a stable and robust platoon. Safety of passengers being a very important consideration, the control design should be such that the controller remains robust under uncertain environments. As a part of the Department of Energy (DOE) project, this research also tries to show a demonstration of vehicle platooning using robots. In an automated highway scenario, a vehicle platoon can be thought of as a string of vehicles, following one another as a platoon. Being equipped by wireless communication capabilities, these vehicles communicate with one another to maintain their formation as a platoon, hence are cognitive. Autonomous capable vehicles in tightly spaced, computer-controlled platoons will lead to savings in energy due to reduced aerodynamic forces, as well as increased passenger comfort since there will be no sudden accelerations or decelerations. Impacts in the occurrence of collisions, if any, will be very low. The greatest benefit obtained is, however, an increase in highway capacity, along with reduction in traffic congestion, pollution, and energy consumption. Another aspect of this project is the automated electric transportation (AET). This aims at providing energy directly to vehicles from electric highways, thus reducing their energy consumption and CO2 emission. By eliminating the use of overhead wires, infrastructure can be upgraded by electrifying highways and providing energy on demand and in real time to moving vehicles via a wireless energy transfer phenomenon known as wireless inductive coupling. The work done in this research will help to gain an insight into vehicle platooning and the control system related to maintaining the vehicles in this formation

Robust String Stability of Vehicle Platoons with Communication

This work investigates longitudinal spacing policies and vehicular communication strategies that can reduce inter-vehicular spacing between the vehicles of automated highway platoons, in the presence of parasitic actuation lags. Currently employed platooning technologies rely on the vehicle’s onboard sensors for information of the neighboring vehicles, due to this they may require large spacing between the vehicles to ensure string stability in the presence of uncertainties, such as parasitic actuation lags. More precisely, they require that the minimum employable time headway (hmin) must be lower bounded by 2τ₀ for string stability, where τ₀ is the maximum parasitic actuation lag. Recent studies have demonstrated that using vehicular communication one may be able to employ smaller spacing between vehicles while ensuring robustness to parasitic lags. However, precise results on the extent of such reduction are sparse in the literature. In this work, platoon string stability is used as a metric to study controllers that require vehicular communication, and find the amount of reduction in spacing such controllers can offer. First, the effects of multiple vehicle look ahead in vehicle platoons that employ a Constant Spacing Policy (CSP) based controller without lead vehicle information in the presence of parasitic lags is studied and string instability of such platoons is demonstrated. A robustly string stable CSP controller that employs information from the leader and the immediate predecessor is considered to determine an upper bound on the allowable parasitic lag; for this CSP controller, a design procedure for the selection of controller gains for a given parasitic lag is also provided. For a string of vehicles adopting a Constant Time Headway Policy (CTHP), it is demonstrated that the minimum employable time headway can be further decreased via vehicular communication in the following manner: (1) if the position, velocity and acceleration of the immediate predecessor vehicle is used, then the ii minimum employable time headway hmin can be reduced to τ₀; (2) if the position and velocity information of r immediately preceding vehicles is used, then hmin can be reduced to 4τ₀/(1 + r); (3) furthermore, if the acceleration of ‘r’ immediately preceding vehicles is used, then hmin can be reduced to 2τ₀/(1 + r); and (4) if the position, velocity and acceleration of the immediate and the r-th predecessors are used, then hmin = 2τ₀/(1 + r). Note that cases (3) and (4) provide the same lower bound on the minimum employable time headway; however, case (4) requires much less communicated information. Representative numerical simulations that are conducted to corroborate the above results are discussed. Vehicle formations employing ring structured communication strategies are also studied in this work and a combinatorial approach for developing ring graphs for vehicle formations is proposed. Stability properties of the platoons with ring graphs, limitations of using ring graphs in platoons, and methods to overcome such limitations are explored. In addition, with ring communication structure, it is possible to devise simple ways to recon- figure the graph when vehicles are added to or removed from the platoon or formation, which is also discussed in this work. Further, experimental results using mobile robots for platooning and two-dimensional formations using ring graphs are discussed