Information Flow Topology Research Articles

Developing a Distributed Consensus-Based Cooperative Adaptive Cruise Control System for Heterogeneous Vehicles with Predecessor Following Topology

Connected and automated vehicle (CAV) has become an increasingly popular topic recently. As an application, Cooperative Adaptive Cruise Control (CACC) systems are of high interest, allowing CAVs to communicate with each other and coordinating their maneuvers to form platoons, where one vehicle follows another with a constant velocity and/or time headway. In this study, we propose a novel CACC system, where distributed consensus algorithm and protocol are designed for platoon formation, merging maneuvers, and splitting maneuvers. Predecessor following information flow topology is adopted for the system, where each vehicle only communicates with its following vehicle to reach consensus of the whole platoon, making the vehicle-to-vehicle (V2V) communication fast and accurate. Moreover, different from most studies assuming the type and dynamics of all the vehicles in a platoon to be homogenous, we take into account the length, location of GPS antenna on vehicle, and braking performance of different vehicles. A simulation study has been conducted under scenarios including normal platoon formation, platoon restoration from disturbances, and merging and splitting maneuvers. We have also carried out a sensitivity analysis on the distributed consensus algorithm, investigating the effect of the damping gain on convergence rate, driving comfort, and driving safety of the system.

Stability Margin Improvement of Vehicular Platoon Considering Undirected Topology and Asymmetric Control

The platooning of autonomous vehicles has the potential to significantly improve traffic capacity, enhance highway safety, and reduce fuel consumption. This paper studies the scalability limitations of large-scale vehicular platoons moving in rigid formation, and proposes two basic ways to improve stability margins, i.e., enlarging information topology and employing asymmetric control. A vehicular platoon is considered as a combination of four components: 1) node dynamics; 2) decentralized controller; 3) information flow topology; and 4) formation geometry. Tools, such as the algebraic graph theory and matrix factorization technique, are employed to model and analyze scalability limitations. The major findings include: 1) under linear identical decentralized controllers, the stability thresholds of control gains are explicitly established for platoons under undirected topologies. It is proved that the stability margins decay to zero as the platoon size increases unless there is a large number of following vehicles pinned to the leader and 2) the stability margins of vehicular platoons under bidirectional topologies using asymmetric controllers are always bounded away from zero and independent of the platoon size. Simulations with a platoon of passenger cars are used to demonstrate the findings.

Stability and Scalability of Homogeneous Vehicular Platoon: Study on the Influence of Information Flow Topologies

In addition to decentralized controllers, the information flow among vehicles can significantly affect the dynamics of a platoon. This paper studies the influence of information flow topology on the internal stability and scalability of homogeneous vehicular platoons moving in a rigid formation. A linearized vehicle longitudinal dynamic model is derived using the exact feedback linearization technique, which accommodates the inertial delay of powertrain dynamics. Directed graphs are adopted to describe different types of allowable information flow interconnecting vehicles, including both radar-based sensors and vehicle-to-vehicle (V2V) communications. Under linear feedback controllers, a unified internal stability theorem is proved by using the algebraic graph theory and Routh–Hurwitz stability criterion. The theorem explicitly establishes the stabilizing thresholds of linear controller gains for platoons, under a large class of different information flow topologies. Using matrix eigenvalue analysis, the scalability is investigated for platoons under two typical information flow topologies, i.e., 1) the stability margin of platoon decays to zero as $0(\mbox{1}/N^{2})$ for bidirectional topology; and 2) the stability margin is always bounded and independent of the platoon size for bidirectional-leader topology. Numerical simulations are used to illustrate the results.

Consensus-based reconfigurable controller design for unmanned aerial vehicle formation flight

This article presents a distributed controller design methodology with a failure detection logic for formation flight of unmanned aerial vehicles (UAVs). An output feedback linearization method with a consensus protocol is used to maintain a specified time-varying geometric configuration of multiple UAVs. In this approach, any explicit leader does not exist in the team, and the control strategy requires only the local neighbour-to-neighbour information between the vehicles. A graph Laplacian matrix is used to define the information flow topologies between the vehicles. The Failure detection algorithm is also proposed in order to detect a communication loss or an aircraft system fault and to isolate the failed one. The detection logic proposed in this study considers the case in which one of the vehicles totally broke down. Once the failure is detected, the failed vehicle is isolated. Reforming the interconnection topology using the failure detection logic can guarantee the stable formation flight with the proposed controller. Numerical simulations are performed to validate the performance of the proposed controller with which the formation geometry is dynamically reconfigured using failure detection information.

Synchronization of networked Lagrangian systems with input constraints

AbstractThis paper addresses the synchronization problem of systems modeled by Euler-Lagrange equations and subject to input saturations. First, a new control design strategy, based on virtual systems, is proposed. This approach allows to generate control inputs that are a priori bounded in the presence of communication time-delays, regardless of the information flow topology between systems in the network. Second, we remove the requirement of the generalized velocities, leading to a velocity-free synchronization scheme with a priori bounded inputs. The effectiveness of the proposed control schemes is demonstrated through simulation examples on a network of four robot manipulator arms.

H ∞ control of networked multi-agent systems

This paper concerns the disturbance rejection problem arising in the coordination control of a group of autonomous agents subject to external disturbances. The agent network is said to possess a desired level of disturbance rejection, if the H∞ norm of its transfer function matrix from the disturbance to the controlled output is satisfactorily small. Undirected graph is used to represent the information flow topology among agents. It is shown that the disturbance rejection problem of an agent network can be solved by analyzing the H∞ control problem of a set of independent systems whose dimensions are equal to that of a single node. An interesting result is that the disturbance rejection ability of the whole agent network coupled via feedback of merely relative measurements between agents will never be better than that of an isolated agent. To improve this, local feedback injections are applied to a small fraction of the agents in the network. Some criteria for possible performance improvement are derived in terms of linear matrix inequalities. Finally, extensions to the case when communication time delays exist are also discussed.

리더가 없는 방식의 다수 무인기 편대비행 제어와 안정성 해석

본 논문에서는 궤환선형화를 이용한 일치기법을 사용하여 다수 무인기의 편대비행 제어기를 설계하였다. 제안한 기법은 한 대의 리더기를 중심으로 하는 집중형 방식이 아닌 분산형 방식으로, 각 개체의 제어입력은 인접한 개체만의 정보만을 이용하여 설계된다. 라플라시안 행렬을 이용하여 개체 간의 정보 교류를 정의한 후, 궤환선형화 과정을 거친 비행체에 적용하였다. 또한, 본 논문에서 제안한 제어기의 안정성 해석을 수행하였다. 또한 제안한 제어기의 성능을 검증하기 위해서 회전익 무인기 비행체 모델에 대한 수치 시뮬레이션을 수행하였다. A consensus-based feedback linearization method is proposed to maintain a specified time-varying geometric configuration for formation flying of multiple autonomous vehicles. In this approach, there exists no explicit leader in the team, and the proposed control strategy requires only the local neighbor-to-neighbor information between vehicles. The information flow topology between the vehicles is defined by Graph Laplacian matrix, and the formation flying can be achieved by the proposed feedback linearization with consensus algorithm. The stability analysis of the proposed controller is also performed via eigenvalue analysis for the closed-looop system. Numerical simulation is performed for rotary-wing type micro aerial vehicles to validate the performance of the proposed controller.

INFORMATION FLOW AND COOPERATIVE CONTROL OF VEHICLE FORMATIONS

Vehicles in formation often lack global information regarding the state of all the vehicles, a deficiency which can lead to instability and poor performance. In this paper, we demonstrate how exchange of minimal amounts of information between vehicles can be designed to realize a dynamical system which supplies each vehicle with a shared reference trajectory. When the information flow law is placed in the control loop, a separation principle is proven which guarantees stability of the formation and convergence of the information flow law regardless of the information flow topology.