Decentralized optimal control of a vehicle platoon with guaranteed string stability

International audienceThis paper presents new decentralized optimal strategies for Cooperative Adaptive Cruise Control (CACC) of a car platoon under string-stability constraints. Two related scenarios are explored in the article: in the first one, a linear-quadratic regulator in the presence of measurable disturbances is synthesized, and the string-stability of the platoon is enforced over the controller's feedback and feedforward gains. In the second scenario, H2- and Hinf-performance criteria, respectively accounting for the desired group behavior and the string-stability of the platoon, are simultaneously achieved using the recently-proposed compensator blending method. An analytical study of the impact of actuation/communication delays and uncertain model parameters on the stability of the multi-vehicle system, is also conducted. The theory is illustrated via numerical simulations

Stability and String Stability Analysis of Formation Control Architectures for Platooning.

This thesis presents theoretical results for stability and string stability of formation control architectures for platooning. We consider three important interconnection topologies for vehicles travelling in a straight line as a string: leader following, cyclic and bidirectional. For the leader following topology we discuss modifications that allow reduced coordination requirements. In the first case we consider the use of the leader velocity as the state to be broadcast to the followers, rather than the standard use of the leader position. This selection yields a formation control architecture that achieves string stability even under time delays in the state broadcast, while reducing typical coordination requirements of leader following architectures. For the second modification we change the way in which the leader position is sent across the string to every follower. This technique keeps some of the good transient properties of the standard leader following architecture but eliminates most of the coordination requirements for the followers. However, we show that this technique does not provide string stability when time delays are present in the communication. The second topology that we discuss is a cyclic one, where the first member of the platoon is forced to track the last one. We discuss two strategies: one where the inter-vehicle spacings may follow a constanttime headway spacing policy and one where an independent leader broadcasts its position to every member of a cyclic platoon. For both strategies we obtain closed form expressions for the transfer functions from disturbances to inter-vehicle spacings. These expressions allow us to show that if the design parameters are not properly chosen, the vehicle platoon may become unstable when the string size is greater than a critical number. On the contrary, if the design parameters are well chosen, both architectures can be made stable and string stable for any size of the platoon. The final topology that we consider is bidirectional, where every member of the platoon, with the exception of the first and last, use measurements of the two nearest neighbours to control their position within the string. Although the derivations are more complex than in the two previous unidirectional cases, we obtain closed form epressions for the dynamics of the platoon. These expressions are in the form of simple transfer functions from disturbances to vehicles. They allow us to obtain stability results for any size of the platoon and understand the behaviour of the least stable pole location as the string size increases. All of the results obtained are illustrated by numerical examples and ad-hoc simulations

Stability and String Stability Analysis of Formation Control Architectures for Platooning.

This thesis presents theoretical results for stability and string stability of formation control architectures for platooning. We consider three important interconnection topologies for vehicles travelling in a straight line as a string: leader following, cyclic and bidirectional. For the leader following topology we discuss modifications that allow reduced coordination requirements. In the first case we consider the use of the leader velocity as the state to be broadcast to the followers, rather than the standard use of the leader position. This selection yields a formation control architecture that achieves string stability even under time delays in the state broadcast, while reducing typical coordination requirements of leader following architectures. For the second modification we change the way in which the leader position is sent across the string to every follower. This technique keeps some of the good transient properties of the standard leader following architecture but eliminates most of the coordination requirements for the followers. However, we show that this technique does not provide string stability when time delays are present in the communication. The second topology that we discuss is a cyclic one, where the first member of the platoon is forced to track the last one. We discuss two strategies: one where the inter-vehicle spacings may follow a constanttime headway spacing policy and one where an independent leader broadcasts its position to every member of a cyclic platoon. For both strategies we obtain closed form expressions for the transfer functions from disturbances to inter-vehicle spacings. These expressions allow us to show that if the design parameters are not properly chosen, the vehicle platoon may become unstable when the string size is greater than a critical number. On the contrary, if the design parameters are well chosen, both architectures can be made stable and string stable for any size of the platoon. The final topology that we consider is bidirectional, where every member of the platoon, with the exception of the first and last, use measurements of the two nearest neighbours to control their position within the string. Although the derivations are more complex than in the two previous unidirectional cases, we obtain closed form epressions for the dynamics of the platoon. These expressions are in the form of simple transfer functions from disturbances to vehicles. They allow us to obtain stability results for any size of the platoon and understand the behaviour of the least stable pole location as the string size increases. All of the results obtained are illustrated by numerical examples and ad-hoc simulations

Leveraging Connected Highway Vehicle Platooning Technology to Improve the Efficiency and Effectiveness of Train Fleeting Under Moving Blocks

Future advanced Positive Train Control systems may allow North American railroads to introduce moving blocks with shorter train headways. This research examines how closely following trains respond to different throttle and brake inputs. Using insights from connected automobile and truck platooning technology, six different following train control algorithms were developed, analyzed for stability, and evaluated with simulated fleets of freight trains. While moving blocks require additional train spacing beyond minimum safe braking distance to account for train control actions, certain following train algorithms can help minimize this distance and balance fuel efficiency and train headway by changing control parameters

A Dynamics-Based Adaptive String Stable Controller for Connected Heavy Road Vehicle Platoon Safety

This is the final version. Available on open access from IEEE via the DOI in this recordThis article presents a string stable controller for the autonomous operation of a platoon of Heavy Commercial Road Vehicles (HCRVs) in a connected environment. This study considers factors such as brake/powertrain actuator dynamics, resistive forces, tyre model and wheel dynamics, which are crucial during on-road operation of HCRVs. A nonlinear vehicle dynamic model encompassing all these factors has been considered. The dependency between aerodynamic drag and inter-vehicular distance in the platoon has also been taken into account. The aforementioned factors motivated the use of Sliding Mode Control (SMC), which is a nonlinear and robust control technique. A lower level Proportional Integral Derivative (PID) controller has been successfully integrated with SMC to compensate for pneumatic brake and powertrain system delay. The designed controller was evaluated for string stable platoon operation by considering various road conditions, load conditions and operating speeds. It was observed that the string stable controller performance is highly dependent on the operating conditions. To ensure string stable operation for different operating scenarios, an adaptive time-headway based enhancement has also been integrated in the controller design. The efficacy of the proposed adaptive time-headway policy over the existing constant time-headway policy has been methodically analysed and a performance comparison between them has also been presented. The aspect of communication delay during connected vehicular operation has also been studied and the maximum tolerable communication delay magnitude for maintaining string stable operation has also been presented.Ministry of Skill Development and Entrepreneurship, Government of Indi

The Feedback Control Strategy of the Takagi-Sugeno Fuzzy Car-Following Model with Two Delays

Considering the driver’s sensing the headway and velocity the different time-varying delays exist, respectively, and the sensitivity of drivers changes with headway and speed. Introducing the fuzzy control theory, a new fuzzy car-following model with two delays is presented, and the feedback control strategy of the new fuzzy car-following model is studied. Based on the Lyapunov function theory and linear matrix inequality (LMI) approach, the sufficient condition that the existence of the fuzzy controller is given making the closed-loop system is asymptotic, stable; namely, traffic congestion phenomenon can effectively be suppressed, and the controller gain matrix can be obtained via solving linear matrix inequality. Finally, the simulation examples verify that the method which suppresses traffic congestion and reduces fuel consumption and exhaust emissions is effective

Cooperative adaptive cruise control over unreliable networks: an observer-based approach to increase robustness to packet loss

International audienceCooperative Adaptive Cruise Control (CACC) is nowadays a promising technique to increase highway through-put, safety and comfort for vehicles. Enabled by wireless communication, CACC allows a platoon of vehicles to achieve better performance than Adaptive Cruise Control; however, since wireless is employed, problems related to unreliability arise. In this paper, we design a digital controller to achieve platoon stability, enhanced by an observer to increase robustness against packet losses. A preliminary set of simulation results is presented, which confirms the interest of using an observer in combination with a local and cooperative digital controller