Vehicle Platoon Control Research Articles

Cooperative Platoon Control of Heterogeneous Vehicles Under a Novel Event-Triggered Communication Strategy

This paper investigates the cooperative platoon control problem of heterogeneous vehicles. Under a leader and predecessor following communication structure, each following vehicle tracks the state of the leader while maintaining a constant spacing between successive vehicles. To reduce the utilization of communication resources, a new event-triggered communication strategy (ETCS) is proposed, where the current data of the following vehicle is transmitted to its direct successor only when the difference between the current data and the last transmitted data exceeds a state-dependent threshold. By properly designing the threshold, the number of data transmissions near the steady state is greatly reduced. The tracking errors of all vehicles are shown to be bounded while Zeno behavior can be avoided under the ETCS. The advantages of the proposed ETCS are discussed by comparing with the existing strategies. Moreover, to deal with the heterogeneity of the vehicles' dynamics, a decentralized and computationally efficient method is presented to solve the non-identical control gains of all the vehicles. The numerical simulations have been conducted to illustrate the effectiveness of the proposed approach.

Networked Model for Cooperative Adaptive Cruise Control

This paper proposes a cooperative adaptive cruise control model, adding a communication network structure to an existing model that has been shown to capture real commercial adaptive cruise control vehicle behavior. The proposed model is interesting because it only requires minimal information sharing, facilitating the creation of platoons comprised of vehicles from different manufacturers. We prove the stability of the model and discuss string stability. Algorithms for estimating the velocity of the vehicles locally and for estimating the velocities of all the vehicles in the platoon are presented. We simulate vehicle platoon control with the lead vehicle following an experimentally collected trajectory, showing that adding communication can cause a string unstable platoon to become stable.

Neural Adaptive Sliding-Mode Control of a Bidirectional Vehicle Platoon with Velocity Constraints and Input Saturation

This paper investigates the vehicle platoon control problems with both velocity constraints and input saturation. Firstly, radial basis function neural networks (RBF NNs) are employed to approximate the unknown driving resistance of a vehicle’s dynamic model. Then, a bidirectional topology, where vehicles can only communicate with their direct preceding and following neighbors, is used to depict the relationship among the vehicles in the platoon. On this basis, a neural adaptive sliding-mode control algorithm with an anti-windup compensation technique is proposed to maintain the vehicle platoon with desired distance. Moreover, the string stability and the strong string stability of the whole vehicle platoon are proven through the stability theorem. Finally, numerical simulations verify the feasibility and effectiveness of the proposed control method.

Cooperative look‐ahead control of vehicle platoon travelling on a road with varying slopes

In the current literature, little research has been done in the eco-driving of vehicle platoon. To increase the fuel efficiency of vehicle platoon and ensure vehicle safety, this study proposes a switching control strategy for vehicle platoon travelling on a road with varying slopes, where the platooning and eco-driving technologies are used. To improve the fuel efficiency of vehicle platoon, the cooperative look-ahead controller is proposed by formulating a cooperative look-ahead control problem of vehicle platoon based on distributed model predictive control (CLCbDMPC), which is a constrained nonlinear non-convex multi-objective optimisation problem. To solve the CLCbDMPC problem quickly, after the minimum fuel consumption table and its corresponding optimal reduction gear ratio table are constructed and calculated off-line, the improved particle swarm optimisation algorithm with multiple dynamic populations is presented. Furthermore, the safety controller acting as the emergency brake to guarantee vehicle safety is also designed. The switch between the look-ahead controller and the safety controller forms the switching control strategy of vehicle platoon. Simulation results demonstrate, compared with benchmarks, the proposed strategy can significantly save up to 21.88% of fuel for vehicle platoon, and vehicle safety can also be guaranteed.

Integrated Longitudinal and Lateral Networked Control System Design for Vehicle Platooning.

This paper investigates platoon control of vehicles via the wireless communication network. An integrated longitudinal and lateral control approaches for vehicle platooning within a designated lane is proposed. Firstly, the longitudinal control aims to regulate the speed of the follower vehicle on the leading vehicle while maintaining the inter-distance to the desired value which may be chosen proportional to the vehicle speed. Thus, based on Lyapunov candidate function, sufficient stability conditions formulated in BMIs terms are proposed. For the general objective of string stability and robust platoon control to be achieved simultaneously, the obtained controller is complemented by additional conditions established for guaranteeing string stability. Furthermore, constraints such as actuator saturation, and controller constrained information are also considered in control design. Secondly, a multi-model fuzzy controller is developed to handle the vehicle lateral control. Its objective is to maintain the vehicle within the road through steering. The design conditions are strictly expressed in terms of LMIs which can be efficiently solved with available numerical solvers. The effectiveness of the proposed control method is validated under the CarSim software package.

Nonlinear finite-time consensus-based connected vehicle platoon control under fixed and switching communication topologies

This paper proposes nonlinear consensus-based control strategies for a connected vehicle (CV) platoon under different communication topologies. In particular, pinning control based consensus protocols are proposed by incorporating the car-following interactions between CVs under fixed and switching communication topologies. The finite-time stability and consensus of the proposed protocols are rigorously analyzed using the LaSalle’s invariance principle and Lyapunov technique. The theoretical analyses investigate the impacts of communication topology on convergence and stability of CV platoon. This study conducts numerical experiments for a CV platoon under four scenarios: (i) Fixed communication topology with time-invariant leader, (ii) fixed communication topology with time-variant leader, (iii) switching communication topology with time-invariant leader, and (iv) switching communication topology with time-variant leader. Simulations results illustrate the effectiveness of the proposed protocols in terms of convergence time and stability with respect to position and velocity profiles.

Retrofit control: Localization of controller design and implementation

In this paper, we propose a retrofit control method for stable network systems. The proposed approach is a control method that, rather than an entire system model, requires a model of the subsystem of interest for controller design. To design the retrofit controller, we use a novel approach based on hierarchical state-space expansion that generates a higher-dimensional cascade realization of a given network system. The upstream dynamics of the cascade realization corresponds to an isolated model of the subsystem of interest, which is stabilized by a local controller. The downstream dynamics can be seen as a dynamical model representing the propagation of interference signals among subsystems, the stability of which is equivalent to that of the original system. This cascade structure enables a systematic analysis of both the stability and control performance of the resultant closed-loop system. The resultant retrofit controller is formed as a cascade interconnection of the local controller and an output rectifier that rectifies an output signal of the subsystem of interest so as to conform to an output signal of the isolated subsystem model while acquiring complementary signals neglected in the local controller design, such as interconnection signals from neighboring subsystems. Finally, the efficiency of the retrofit control method is demonstrated through numerical examples of power systems control and vehicle platoon control.

Tradeoff between Quality of Control (QoC) and Quality of Service (QoS) for Networked Vehicles Cruise Control

In this paper, we present a vehicle platoon control over network. We focus on cruise control problem with network delay. Here, we study the stability of the vehicle platoon under network constraints and based on the stability criterion, we trade-off between quality of service (QoS) and quality of control (QoC). A controller is designed for speed regulation. We present the condition for maximum allowable delay bound, by using LMI, which can be tolerated by the close loop platoon system. The relation between maximum allowable transfer interval (MATI) and maximum allowable delay bound (MADB) under try once discard (TOD) scheduling algorithm is shown. Some of the existing networked technologies are studied and compared.

Event-triggered cooperative control of vehicle platoons in vehicular ad hoc networks

This paper deals with the problem of event-triggered cooperative control of vehicle platoons with actuator delays caused by fueling and braking. An event-triggered communication scheme (ECS) is introduced, where an event-triggered condition with tunable threshold parameters is designed. Under the ECS, the sampled velocities and accelerations of each follower vehicle are transmitted among neighbors via vehicular ad hoc networks (VANETs) only when the event-triggered condition is violated. Based on the ECS and a platoon model transformation, the problem of event-triggered cooperative control of the vehicle platoons is transformed into a stabilization problem of a vehicle tracking error system with a time-varying delay. Then, the Lyapunov–Krasovskii functional method is employed to formulate some sufficient conditions on stability of the tracking error system with time-varying delay. Based on these conditions, suitable event-triggered feedback controllers can be designed in terms of solutions to a set of linear matrix inequality. A numerical example is given to show effectiveness of the proposed theoretical results.

Arterial Intersection Improvement by Using Vehicle Platooning and Coordinated Start

Intersections are the bottlenecks of the urban arterial causing the reduction of its capacity. In order to maximize the efficiency of existing transportation systems capacity with urban congestion reduction, intelligent transportation systems are employed. In this paper, such a solution is presented using the cooperative adaptive cruise control (CACC) of vehicle platoons waiting at a red traffic signal which enables thus to begin accelerating in a coordinated manner once the traffic signal turns green. This coordinated start could allow more vehicles to pass through an intersection on a green cycle than manual driving and thus increasing the urban arterial capacity. To design and evaluate the CACC system, a novel simulator for connected vehicle applications is developed. The simulation results show that the proposed CACC approach offers significant mobility.

Cooperative Look-Ahead Control of Vehicle Platoon for Maximizing Fuel Efficiency Under System Constraints

The fuel consumption and greenhouse gas emissions can be reduced by organizing a group of vehicles into a platoon at a short inter-vehicular distance. Additionally, the eco-driving technology has the potential to further increase fuel efficiency by optimizing the speed trajectories of vehicles. However, little research has been done into the eco-driving of a vehicle platoon. This paper proposes a cooperative look-ahead control strategy for maximizing the fuel efficiency of vehicle platoon travelling on a road with varying slopes. In this paper, the aerodynamic drag, nonlinear engine fuel consumption model, discrete gear ratios, and three engine operating modes are considered in the control strategy; under system constraints, a cooperative optimal fuel consumption problem of vehicle platoon based on distributed model predictive control is formulated; to obtain the optimal solution of the formulated nonlinear optimization problem, after the minimum fuel consumption table and the corresponding optimal control variable tables are obtained, the nonlinear optimization problem with discrete control variables is transformed into a 0–1 binary mixed linear programming problem. Simulation results show that, compared with benchmarks, the proposed control strategy can significantly improve fuel efficiency under different passenger comfort requirements, allowed speed ranges, and predictive control horizons.

Cooperative Spacing Control for Interconnected Vehicle Systems With Input Delays

Time delay is an inevitably negative factor to real-time vehicle control. This paper investigates cooperative spacing control of vehicle platoons with input delays under no communication between vehicles (including the lead vehicle). The spacing control strategy is based solely on self information and onboard measurement of the immediate neighbor vehicles (preceding and succeeding vehicles). Considering the delay constraints, sufficient stability conditions are derived for the vehicle system with input delays. To avoid transient spacing errors to amplify along the string of vehicles, we give conditions that guarantee string stability of the vehicular platoon, by which the upper bound of tolerable delays are derived in terms of controller parameters and the model parameters. An algorithm is then given to determine the controller parameters using the stability and string stability conditions simultaneously. Simulations illustrate the effectiveness and the advantages of the proposed control methodology.

Convergence Analysis of Cooperative Braking Control for Interconnected Vehicle Systems

Cooperative braking control is a very important operation in vehicle platoon control for developing intelligent transportation systems, which can effectively increase road capacity, decrease safety hazard, and avoid serial rear-end collisions. This paper focuses on cooperative braking control of autonomous vehicles, the objectives of which are to ensure intervehicles keep within the safe spacing range and rapidly, smoothly, and accurately stop at the desired target stopping positions with zero velocity. To achieve these goals, a three-vehicle platoon framework is presented and the corresponding dynamic model is established based on only information about front-end and rear-end sensors of vehicles, so communication is not needed. The explicit solutions on the three-vehicle platoon are derived by rigorous convergent analysis and detailed proof, such that intrinsic characteristic of the interconnected vehicles is revealed. The resulting convergent conditions and convergent rate are obtained under three cases including: 1) considering internal virtual forces; 2) considering external braking forces; and 3) considering both the internal virtual forces and external braking forces simultaneously. Moreover, an example is further provided to verify that the derived convergence conditions are effective and sufficient under the different controller parameter selection. These results can provide a solution for a wide class of interconnected systems and a guide for controller design to select control parameters in real engineering applications. Simulation results demonstrate the validity of the proposed control approaches.

String Stability and a Delay-Based Spacing Policy for Vehicle Platoons Subject to Disturbances

A novel delay-based spacing policy for the control of vehicle platoons is introduced together with a notion of disturbance string stability. The delay-based spacing policy specifies the desired intervehicular distance between vehicles and guarantees that all vehicles track the same spatially varying reference velocity profile, as is for example required for heavy-duty vehicles driving over hilly terrain. Disturbance string stability is a notion of string stability of vehicle platoons subject to external disturbances on all vehicles that guarantees that perturbations do not grow unbounded as they propagate through the platoon. Specifically, a control design approach in the spatial domain is presented that achieves tracking of the desired spacing policy and guarantees disturbance string stability with respect to a spatially varying reference velocity. The results are illustrated by means of simulations.

Safety-Critical Driver Assistance Over LTE: Toward Centralized ACC

Cooperative advanced driver assistance systems (ADAS) have the potential to increase traffic efficiency and safety beyond the level of sensor-based systems. Further development toward centralized cooperative systems is motivated by the improving performance of cellular technologies. However, the suitability of cellular communication, up to now, remains an unresolved topic in current research due to high system requirements (on, e.g., latency). In a centralized system design, the control algorithm is located at a central unit and the system input, as well as the measured output, is transmitted over the cellular network. This paper addresses the technical feasibility and practicability of centralized longitudinal control of vehicles and vehicle platoons with communication over long-term evolution (LTE). The focus is laid on the investigation of the system in disturbed situations, as well as on the evaluation and optimization of the required LTE resources. Therefore, a novel design of a centralized adaptive cruise control is developed, which satisfies required stability properties and optimizes the resource usage. The evaluation is based on simulation studies since it requires a large number of devices, as well as deep data logging within LTE. In summary, system safety can be achieved with moderate requirements on the cellular technology in the case of high localization accuracy. Considering the objectives of LTE, the communication requirements should be satisfied in areas with gapless coverage and with dedicated resources in the case of saturated channel conditions.

Distributed receding horizon control for fuel-efficient and safe vehicle platooning

This paper investigates the problem of fuel-efficient and safe control of autonomous vehicle platoons. We present a two-part hierarchical control method that can guarantee platoon stability with minimal fuel consumption. The first part vehicle controller is derived in the context of receding horizon optimal control by constructing and solving an optimization problem of overall fuel consumption. The Second part platoon controller is a complementation of the first part, which is given on the basis of platoon stability analysis. The effectiveness of the presented platoon control method is demonstrated by both numerical simulations and experiments with laboratory-scale Arduino cars.

Event-triggered platoon control of vehicles with time-varying delay and probabilistic faults

This paper investigates event-triggered platoon control of vehicles with probabilistic faults (i.e., sensor and actuator) and time-varying communication delay. A novel platoon model is established, in which the effect of time-varying delay, event-triggered scheme and probabilistic faults are involved. Based on the new model, criteria for the exponential stability and criteria for co-designing both the output feedback and the trigger parameters are derived by using Lyapunov functional. The obtained controller is complemented by additional conditions established for guaranteeing string stability and zero steady state velocity errors, yielding a useful string stable platoon control method. The effectiveness and advantage of the presented methodology are demonstrated by both numerical simulations and experiments with laboratory scale Arduino cars.

Robust static output feedback synthesis for platoons under leader and predecessor feedback

SummaryA multi‐objective static output feedback synthesis problem is considered for the control of vehicle platoons under leader and predecessor feedback. Sufficient linear matrix inequality conditions are derived for the solvability of the problem in a way to facilitate static feed‐forward as well. A novel velocity‐dependent spacing policy is integrated into the control scheme together with a platoon model in which the emphasis on the predecessor information can be adjusted by a normalized scalar weight. It is shown that the string stability of the spacing errors and the acceleration signals can always be guaranteed by choosing this weight sufficiently small. Moreover, provided that the time headway is chosen sufficiently large, the synthesis can be performed in a way to avoid the amplification of acceleration energies if compared with the leader. As a particularly convenient feature, the target spacing between the vehicles becomes smaller when moving backward along the platoon. The total increase in the platoon length caused by the introduction of the velocity‐dependent scheme is shown to be bounded and decreasing with decreasing predecessor weight. It is also established that the predecessor weight can be adjusted smoothly over time without endangering the formation stability. In addition to the optimization of the parameters of common fixed‐structure controllers for general vehicle models, the proposed synthesis procedure provides various tools for improving robustness against measurement noise, communication delay, and model uncertainty. Copyright © 2016 John Wiley & Sons, Ltd.

Stability Analysis of a Predecessor-Following Platoon of Vehicles With Two Time Delays

The problem of controlling a platoon of vehicles moving in one dimension is considered so that they all follow a lead vehicle with constant spacing between successive vehicles. The stability and the string stability of a platoon of vehicles with two independent and uncertain delays, one in the inter-vehicle distance and the other in the relative velocity information channels, are considered. The main objectives of this paper are: (1) using a simplifying factorization procedure and deploying the cluster treatment of characteristic roots (CTCR) paradigm to obtain exact stability boundaries in the domain of the delays, and (2) for the purpose of disturbance attenuation, the string stability analysis is examined. Finally, a simulation example of multiple vehicle platoon control is used to demonstrate the effectiveness of the proposed method.

Exact stability of a platoon of vehicles by considering time delay and lag

The problem of controlling a string of vehicles moving in one dimension is considered so that they all follow a lead vehicle with constant time headway spacing between successive vehicles. Due to realistic design and execution, the negative effect of the tracking lag parameter and time delay is taken into account. By applying an acceleration feedforward, the distance error of each vehicle will be independent of the behavior of other vehicles. As a result, the vehicle is better able to track a desired trajectory, which improves the string stability. Cluster treatment of characteristic roots (CTCR) paradigm is utilized to reveal the stabilizing parametric regions in the domain of the time delay to render the stability of closed loop system. The string stability analysis is performed to evaluate the disturbance attenuation. Finally, an example of multiple vehicle platoon control is presented, which demonstrates the effectiveness of the proposed method.