Decentralised Formation Control and Stability Analysis for Multi-vehicle Cooperative Manoeuvre

Multi-vehicle cooperative formation control problem is an important and typical topic of research on multi-agent system. This paper presents a formation stability conjecture to conceive a new methodology for solving the decentralised multivehicle formation control problem. It employs the "extensiondecomposition-aggregation" scheme to transform the complex multi-agent control problem into a group of sub-problems which is able to be solved conveniently. Based on this methodology, it is proved that if all the individual augmented subsystems can be stabilised by using any approach, the overall formation system is not only asymptotically but also exponentially stable in the sense of Lyapunov within a neighbourhood of the desired formation. Simulation study on 6-DOF aerial vehicles (Aerosonde UAVs) has been performed to verify the achieved formation stability result. The proposed multi-vehicle formation control strategy can be conveniently extended to other cooperative control problems of multi-agent systems.      

有向切换通信拓扑下多无人机分布式编队控制

本文对多无人机分布式时变编队控制问题进行了研究. 无人机之间的通信拓扑假定是有向和切换的. 基于 自身状态与邻居状态的相对局部信息构建了分布式编队控制器. 通过引入一个恰当的编队误差向量, 将有向切换 通信拓扑下的多无人机编队问题转化为一个切换系统的镇定问题. 基于Lyapunov稳定性分析方法得到了达成编队 的充分性条件. 仿真实验结果验证了结论的有效性.     

Consensus of multiple second-order vehicles with a time-varying reference signal under directed topology

This paper investigates two kinds of different consensus strategies for multi-vehicle systems with a time-varying reference velocity under directed communication topology, where the systems are modeled by double-integrator dynamics. For the fixed communication topology case, we provide a necessary and sufficient condition for all the vehicles with reference velocity to reach consensus by the use of a new graphic methodology. We then extend this method to deal with the general case, that is, both the communication topologies and weighting factors are dynamically changing. In particular, it is shown that all the vehicles can reach consensus even though the dynamically changing interaction topology may not have a globally reachable node.     

An output feedback nonlinear decentralized controller for unmanned vehicle co‐ordination

This paper presents vision‐based control strategies for decentralized stabilization of unmanned vehicle formations. Three leader–follower formation control algorithms, which ensure asymptotic co‐ordinated motion, are described and compared. The first algorithm is a full state feedback nonlinear controller that requires full knowledge of the leader's velocities and accelerations. The second algorithm is a robust state feedback nonlinear controller that requires knowledge of the rate of change of the relative position error. Finally, the third algorithm is an output feedback approach that uses a high‐gain observer to estimate the derivative of the unmanned vehicles' relative position. Thus, this algorithm only requires knowledge of the leader–follower relative distance and bearing angle. Both data are computed using measurements from a single camera, eliminating sensitivity to information flow between vehicles. Lyapunov's stability theory‐based analysis and numerical simulations in a realistic 3D environment show the stability properties of the control methodologies. Copyright © 2007 John Wiley & Sons, Ltd.     

Formation control of VTOL UAV vehicles under switching-directed interaction topologies with disturbance rejection

This paper addresses the adaptive formation control of a group of vertical take-off and landing (VTOL) unmanned aerial vehicles (UAV) with switching-directed interaction topologies. In addition, to tackle the adverse effect of disturbances, a couple of smooth bounded estimators are involved in the procedure design. Exploiting an extraction algorithm, we take advantage of the fully actuated rotational dynamics, to control the translational dynamics of each vehicle. We propose a distributed control scheme such that all vehicles track a desired reference velocity signal while keeping a desired prespecified formation. In this framework, the underlying topology of the agents may switch among several directed graphs, each having a spanning tree. The stability of the overall closed-loop system is proved through Lyapunov function. Finally, simulation results are given to better highlight the effectiveness of the proposed control scheme.     

Distributed control of angle-constrained cyclic formations using bearing-only measurements

This paper studies distributed control of multi-vehicle formations with angle constraints using bearing-only measurements. It is assumed that each vehicle can only measure the local bearings of their neighbors and there are no wireless communications among the vehicles. The desired formation is a cyclic one, whose underlying information flow is described by an undirected cycle graph. We propose a distributed bearing-only formation control law that ensures local exponential or finite-time stability. Collision avoidance between any vehicles can be locally guaranteed in the absence of inter-vehicle distance measurements.     

Time-varying formation control for double-integrator multi-agent systems with jointly connected topologies

Time-varying formation analysis and design problems for double-integrator multi-agent systems with jointly connected topologies are investigated. Different from the previous work on formation control, in this paper, the formation is specified by time-varying piecewise continuously differentiable vectors and the topology can be disconnected at any time instant. First, a distributed formation control protocol is constructed using local neighbour-to-neighbour information. In the case where the switching topology is jointly connected, necessary and sufficient conditions for double-integrator multi-agent systems to achieve time-varying formations are proposed, where the formation feasibility constraint is also derived. To describe the macroscopic movement of the whole formation, explicit expressions of the formation reference are presented, the motion modes of which can be partially assigned. Moreover, an approach to design the formation control protocol is given, which is fully distributed and requires no global information about the topology. Finally, the obtained theoretical results are applied to deal with the time-varying formation control problems of multi-vehicle systems.     

Time‐varying output formation control for linear multi‐agent systems with switching topologies

Time‐varying output formation control problems for linear multi‐agent systems with switching topologies are studied, where two types of switching topologies are considered: (1) the topology is undirected and jointly connected, and 2) each topology is directed and has a spanning tree. An output formation protocol under switching topologies is constructed using the outputs of neighboring agents via dynamic output feedback. Two algorithms are proposed to design the dynamic protocols under both jointly connected topologies and switching directed topologies. Time‐varying output formation feasibility conditions are given to describe the compatible relationship among the desired time‐varying output formation, the dynamics of each agent, and the switching topologies. The stability of the closed‐loop multi‐agent systems under the proposed two algorithms is investigated based on the common Lyapunov functional theory and the piecewise Lyapunov functional theory, respectively. In the case where the topologies are jointly connected, time‐varying output formation can be achieved for multi‐agent systems using the designed protocol if the given time‐varying output formation satisfies the feasible constraint. For the case where the switching topologies are directed and have a spanning tree, the time‐varying output formation can be realized if the output formation feasibility constraint is satisfied and the dwell time is larger than a positive threshold. Moreover, approaches to determine the output formation references are provided to describe the macroscopic movement of the time‐varying output formation. Finally, numerical simulation results are presented to demonstrate the effectiveness of the theoretical results. Copyright © 2016 John Wiley & Sons, Ltd.     

A Scalable Adaptive Approach to Multi-Vehicle Formation Control with Obstacle Avoidance

This paper deals with the problem of distributed formation tracking control and obstacle avoidance of multi-vehicle systems (MVSs) in complex obstacle-laden environments. The MVS under consideration consists of a leader vehicle with an unknown control input and a group of follower vehicles, connected via a directed interaction topology, subject to simultaneous unknown heterogeneous nonlinearities and external disturbances. The central aim is to achieve effective and collision-free formation tracking control for the nonlinear and uncertain MVS with obstacles encountered in formation maneuvering, while not demanding global information of the interaction topology. Toward this goal, a radial basis function neural network is used to model the unknown nonlinearity of vehicle dynamics in each vehicle and repulsive potentials are employed for obstacle avoidance. Furthermore, a scalable distributed adaptive formation tracking control protocol with a built-in obstacle avoidance mechanism is developed. It is proved that, with the proposed protocol, the resulting formation tracking errors are uniformly ultimately bounded and obstacle collision avoidance is guaranteed. Comprehensive simulation results are elaborated to substantiate the effectiveness and the promising collision avoidance performance of the proposed scalable adaptive formation control approach.      

Robust formation control of thrust-propelled vehicles under deterministic and stochastic topology

ABSTRACT

Formation control of multiple thrust-propelled vehicles (TPVs) under deterministic and stochastic switching topologies and communication delay is addressed. Introducing a new version of variable structure control and based upon sliding mode technique, adaptive control and projection operator, we effectively handle the impact of uncertainties on the mass and inertia matrix and a set of time-varying disturbances affecting the translational and rotational dynamics. Global stability of the whole closed-loop system is guaranteed through Lyapunov stability theory. For the deterministic topology, sufficient condition in terms of LMIs is derived to achieve formation in the presence of jointly connected switching topology. In the case of stochastic topology, based on the concept of super-martingales, it is shown that if the probability of existing a connected topology is not zero, under some conditions, formation is almost surely solved in the network. Finally, numerical simulations verify the effectiveness of the proposed control framework.     

基于图与势场法的多车道编队控制

多车协同驾驶能显著提高交通安全和效率,是未来5G网联自动驾驶技术的重要应用场景之一.传统上,多车协同驾驶的主要形式为单一车道上的无人车队列,其队列稳定性受队列长度、通信距离及延迟的限制.本文提出一种无人车编队方法,将单车道队列扩展为多车道护航编队.针对不同场景下的需求设计多车道编队调整策略,结合基于图的分布式控制,完成任意预定义的编队结构;同时,利用势场法对行车环境建立势场模型,实现无人车的避障轨迹规划,提高编队的避障能力;最后,结合纵横向控制器,实现无人车多车道护航编队控制.仿真实验表明,本文提出的无人车多车道护航编队方法,能适应不同交通场景,如道路变化、障碍车运动等,完成自动变换编队结构,实现安全、高效通行.     

Fault-tolerant shortest connection topology design for formation control

This paper studies the fault tolerant formation keeping problem of multi-agent systems with consideration of shortest connection topology. This is motivated by the requirement of low communication cost which largely depends on the communication length. Given a formation shape, a connection topology design method and its reconfiguration strategy are proposed in the sense that the whole connection path is shortest despite of communication faults. A control framework that combines the individual formation controller of each agent and connection topology is further presented. The stability of the whole system process is analyzed by switched system theories. Simulation results of unmanned aerial vehicles (UAVs) show the effectiveness of the proposed strategy.     

Centralized and decentralized distributed control of longitudinal vehicular platoons with non‐uniform communication topology

In this paper, the distributed control of a longitudinal platoon of vehicles with non‐uniform communication topology is studied. In the case of non‐uniform communication topology, some eigenvalues of the network's matrix may be complex which complicates the stability analysis of the platoon. Most previous studies on vehicular platooning focus mainly on uniform topologies such as uni‐directional, bi‐directional, and multi predecessors following. Since all eigenvalues of these topologies are real, the stability analysis can be performed in a straightforward manner. A third‐order linear differential model is employed to describe the upper‐level dynamics of each vehicle. The 3 N‐order closed‐loop dynamics of the platoon are decoupled to individual third‐order dynamics by presenting a new approach. Two new centralized and decentralized control protocols are introduced to perform the stability analysis of the closed‐loop dynamics. A constant time headway strategy is employed to adjust the inter‐vehicle spacing. Simulation results with different scenarios are presented to illustrate the effectiveness of the proposed approaches.     

Stabilization of sets with application to multi-vehicle coordinated motion

In this paper, we develop stability and control design framework for time-varying and time-invariant sets of nonlinear dynamical systems using vector Lyapunov functions. Several Lyapunov functions arise naturally in multi-agent systems, where each agent can be associated with a generalized energy function which further becomes a component of a vector Lyapunov function. We apply the developed control framework to the problem of multi-vehicle coordinated motion to design distributed controllers for individual vehicles moving in a specified formation. The main idea of our approach is that a moving formation of vehicles can be characterized by a time-varying set in the state space, and hence, the problem of distributed control design for multi-vehicle coordinated motion is equivalent to the design of stabilizing controllers for time-varying sets of nonlinear dynamical systems. The control framework is shown to ensure global exponential stabilization of multi-vehicle formations. Finally, we implement the feedback stabilizing controllers for time-invariant sets to achieve global exponential stabilization of static formations of multiple vehicles.     

Distributed Three‐Dimensional Formation Containment Control of Multiple Unmanned Aerial Vehicle Systems

This paper concentrates the distributed formation containment problems for multiple unmanned aerial vehicle (UAV) systems under both fixed directed and switching directed topologies. The objective is to introduce the formation control into the containment control research, where master UAVs should exchange information with each other to achieve and maintain a desired formation. Then, two different control protocols are proposed for the master UAVs and slave UAVs, respectively. Utilizing the algebraic graph theory and stability theory, some sufficient conditions are derived to guarantee the master UAVs complete a prespecified formation, while the states of the slave UAVs converge to a convex hull formed by those of the master UAVs. Finally, some numerical simulations are provided to verify the effectiveness of the theoretical results.     

Relative attitude formation control of multi‐agent systems

This paper investigates the relative attitude formation control problem for a group of rigid‐body agents using relative attitude information on SO(3). On the basis of the gradient of a potential function, a family of distributed angular velocity control laws, which differ in the sense of a geodesic distance dependent function, is proposed. With directed and switching interaction topologies, the desired relative attitude formation is showed to be achieved asymptotically provided that the topology is jointly quasi‐strongly connected. Moreover, several sufficient conditions for the desired formation to be achieved exponentially and almost globally are given. Additionally, numerical examples are provided to illustrate the effectiveness of the proposed distributed control laws. Copyright © 2017 John Wiley & Sons, Ltd.     

Distributed adaptive control for time-varying formation of general linear multi-agent systems

An adaptive gain scheduling technique is investigated to discuss distributed time-varying formation (TVF) control problems for general linear time-invariant multi-agent systems (LTI-MASs), where two types of topologies are considered: (1) the interaction topology is undirected and connected, and (2) the interaction topology is directed. Two fully distributed adaptive TVF control protocols are, respectively proposed, which both assign a time-varying coupling weight to each node in the interaction topology. Two algorithms to design the constructed protocols are presented under the undirected and directed interaction topologies, respectively. A feasible TVF set is provided. The stabilities of two algorithms are, respectively proved based on the Lyapunov functional theory. For both undirected and directed interaction topologies, general LTI-MASs can achieve the given TVF using the designed fully distributed adaptive formation protocol without any global information about the interaction topology when the TVF satisfies the feasible set. Finally, theoretical results are illustrated with numerical simulation examples.     

A shortly connected mesh topology for high performance and energy efficient network-on-chip architectures

Network-on-chip-based communication schemes represent a promising solution to the increasing complexity of system-on-chip problems. In this paper, we propose a new mesh-like topology called the shortly connected mesh technology (ScMesh), which is based on the traditional mesh topology, to exploit the graph symmetry properties of interconnection networks. This proposed topology not only enhances network performance by reducing the network diameter, but also provides a lower area/energy solution for interconnection network scenarios. This study analyzes and compares the performance of ScMesh to some newly improved topologies, including the WK-recursive, extended-butterfly fat tree, and diametrical mesh topologies. The experiment results indicate that ScMesh outperforms the other topologies, with throughput increases of 47.71, 33.45, and 18.64 % as well as latency decreases of 45.71, 35.84, and 14.58 % compared to the extended-butterfly fat tree, WK-recursive and diametrical mesh topologies, respectively. In addition, ScMesh achieves 41.22, 32.23, and 15.01 % lower energy consumption and 38.96, 27.43, and 18.21 % lower area overhead than the extended-butterfly fat tree, WK-recursive, and diametrical mesh topologies, respectively.     

Trajectory Tracking Controller Design for Unmanned Vehicles: A New Methodology

A major issue in the automatic guidance of vehicles is the design of control laws dedicated to the specific mobile platform used. Thus, if the model associated with the mobile platform or its constraints change, a new control law must be designed. In this paper, the problem of designing trajectory tracking controllers for unmanned vehicles is addressed. The methodology proposed here is an algebraic approach for obtaining optimum and stable trajectory tracking controllers for nonholonomic vehicles. Such an algebraic formulation makes the proposal suitable for embedded applications. The stability and optimality of the proposed controllers design method is theoretically proven for both bicycle‐type and unicycle‐type mobile robots, although the methodology can be extended to other types of unmanned vehicles. Four tests were carried out in this work in order to show the advantages of the proposal: the step discontinuity test, the curvature test, the real world test, and navigation under disturbances in the control actions. The results obtained were compared with four trajectory tracking controllers previously published in the literature. Additionally, an agricultural application is included in order to show the performance of the proposed controller when applied to a service unit within an agricultural environment. Field experiments demonstrating the capabilities of our proposal are also reported and discussed.