Adaptive consensus control of leader-following systems with transmission nonlinearities

In this paper, the leader-following consensus problem of multi-agent systems is studied. It is assumed that there exist gain and bias transmission nonlinearities in the links in the communication network. Two distributed adaptive control schemes, where the transmission nonlinearities are compensated, are designed to guarantee that the consensus problem is solved and synchronisation errors are cooperatively uniformly and ultimately bounded. By using Lyapunov stability theory, the stability of closed-loop system is proven. The effectiveness of the proposed control methods is demonstrated by simulation results.     

The leader-following attitude control of multiple rigid spacecraft systems

In this paper, we consider the leader-following consensus problem for a multiple rigid spacecraft system whose attitude is represented by the unit quaternion. Most results on this problem rely on the assumption that every follower can access the state of the leader and are obtained via a decentralized control manner. By developing a nonlinear distributed observer for the leader system, we can solve this problem via a distributed control scheme under the mild assumptions that the state of the leader can reach every follower through a path and that the communication between followers is bidirectional. Moreover, our result can accommodate a class of desired angular velocities generated by a marginally stable linear autonomous system.     

Leader-following consensus of multi-agent systems under directed communication topology via distributed adaptive nonlinear protocol

In this paper, we study the leader-following consensus problem of general linear multi-agent systems under directed communication topology. To avoid using any global information, an adaptive nonlinear protocol is proposed based only on the relative state information. It is proved that, for any directed communication graph that contains a spanning tree with the root node being the leader agent, the proposed control law solves the leader-following consensus problem. A numerical example is provided to illustrate the effectiveness of the theoretical results.     

Leader-following consensus of multi-agent systems with switching topologies and time-delays

This paper investigates the leader-following consensus problem of multi-agent systems where the leader is static and the controlling effect of each follower depends on its own state. The control protocols are proposed for two cases: i) for network with switching topologies and undirected information flow; ii) for network with directed information flow and communication time-delays. With the aid of several tools from algebraic graph, matrix theory and stability theory, the sufficient conditions guaranteeing leader-following consensus are obtained by constructing appropriate Lyapunov functions. Simulations are presented to demonstrate the effectiveness of our theoretical results.     

时延多智能体系统领导跟随一致性研究

为符合实际情形,针对不确定与随机发生非线性的多智能体系统,研究了有时延且网络拓扑切换时系统的领导跟随一致性。传统协议通常保守的假设邻接个体间通信时延与个体和领导者间通信时延大小相同,新协议中上述时延可以大小不同。相比于传统方法,新颖的将复杂网络同步问题研究领域对时延的处理方法引入到多智能体系统一致性问题的研究中,利用一类推广的Halanay不等式,给出系统实现领导跟随一致性需满足的两个与时延无关的充分条件,即时延在相关参数满足定理条件的前提下不影响系统最终实现一致性。相比其他方法得到的含有时延的判定条件,本研究结果保守性更低,实例仿真验证了新协议的可行性。     

Observer-based event-triggered leader-following control of a class of linear multi-agent systems

This paper addresses an observer-based consensus problem for leader-following control of a class of linear multi-agent systems (MASs) under a directed communication topology via event-triggered approaches. State observers are employed to tackle the scenario wherein inner information of the follower agents are not available for measurement. And then, an observer-based distributed leader-following control scheme is developed on the basis of event-triggered mechanisms. Further, to avoid continuous measurement information monitor, we present a technical approach for generation of the combinational information from their own neighbouring agents only at triggered instants. In theory, the stability of the resulting closed-loop system is rigorously investigated, and it is proven that all signals in the closed-loop system are bounded and Zeno behaviour is also excluded. Finally, simulation examples are presented for illustration of the theoretical claims.     

Consensus control of leader-following nonlinear multi-agent systems with distributed adaptive iterative learning control

This paper addresses the consensus problem of leader-following nonlinear multi-agent systems with iterative learning control. The assumption that only a small portion of following agents can receive the information of leader agent is considered. To approximate the nonlinear dynamics of a given system, the radial basis function neural network is introduced. Then, a distributed adaptive iterative learning control protocol with an auxiliary control term is designed, where the estimates of nonlinear dynamics are applied in control protocol design and three adaptive laws are presented. Furthermore, the convergence of the proposed control protocol is analysed by Lyapunov stability theory. Finally, a simulation example is provided to demonstrate the validity of theoretical results.     

Computation of the target state and feedback controls for time optimal consensus in multi-agent systems

N identical agents with bounded inputs aim to reach a common target state (consensus) in the minimum possible time. Algorithms for computing this time-optimal consensus point, the control law to be used by each agent and the time taken for the consensus to occur, are proposed. Two types of multi-agent systems are considered, namely (1) coupled single-integrator agents on a plane and, (2) double-integrator agents on a line. At the initial time instant, each agent is assumed to have access to the state information of all the other agents. An algorithm, using convexity of attainable sets and Helly's theorem, is proposed, to compute the final consensus target state and the minimum time to achieve this consensus. Further, parts of the computation are parallelised amongst the agents such that each agent has to perform computations of O(N²) run time complexity. Finally, local feedback time-optimal control laws are synthesised to drive each agent to the target point in minimum time. During this part of the operation, the controller for each agent uses measurements of only its own states and does not need to communicate with any neighbouring agents.     

Finite-time distributed consensus via binary control protocols

This paper investigates the finite-time distributed consensus problem for multi-agent systems using a binary consensus protocol and the pinning control scheme. Compared with other consensus algorithms which need the complete state or output information of neighbors, the proposed algorithm only requires sign information of the relative state measurements, that is, the differences between a node’s state and that of its neighbors. This corresponds to only requiring a single-bit quantization error relative to each neighbor. This signum protocol is realistic in terms of observed behavior in animal groups, where relative motion is determined not by full time-signal measurements, but by coarse estimates of relative heading differences between neighbors. The signum protocol does not require explicit measurement of time signals from neighbors, and hence has the potential to significantly reduce the requirements for both computation and sensing. Analysis of discontinuous dynamical systems is used, including the Filippov solutions and set-valued Lie derivative. Based on the second-order information on the evolution of Lyapunov functions, the conditions that guarantee the finite-time consensus for the systems are identified. Numerical examples are given to illustrate the theoretical results.     

Stochastic consensus of double-integrator leader-following multi-agent systems with measurement noises and time delays

This paper studies a leader-following consensus problem of continuous-time double-integrator multi-agent systems with measurement noises and time-varying communication delays under directed topology. By utilising the neighbour position and velocity information, which are delayed and disturbed by measurement noises whose intensities are considered a function related to the neighbour position and velocity of agents, a distributed consensus protocol is presented, sufficient conditions of the tracking consensus in the sense of mean square are derived. Finally, the effectiveness of the proposed consensus protocol is proved by some simulations.     

Robust discrete time dynamic average consensus

This paper deals with the problem of average consensus of a set of time-varying reference signals in a distributed manner. We propose a new class of discrete time algorithms that are able to track the average of the signals with an arbitrarily small steady-state error and with robustness to initialization errors. We provide bounds on the maximum step size allowed to ensure convergence to the consensus with error below the desired one. In addition, for certain classes of reference inputs, the proposed algorithms allow arbitrarily large step size, an important issue in real networks, where there are constraints in the communication rate between the nodes. The robustness to initialization errors is achieved by introducing a time-varying sequence of damping factors that mitigates past errors. Convergence properties are shown by the decomposition of the algorithms into sequences of static consensus processes. Finally, simulation results corroborate the theoretical contributions of the paper.     

Finite-time and fixed-time leader-following consensus for multi-agent systems with discontinuous inherent dynamics

This paper is concerned with finite-time and fixed-time consensus of multi-agent systems in a leader-following framework. Different from conventional leader-following tracking approaches where inherent dynamics satisfying the Lipschitz continuous condition is required, a more generalised case is investigated: discontinuous inherent dynamics. By nonsmooth techniques, a nonlinear protocol is first proposed to achieve the finite-time leader-following consensus. Then, based on fixed-time stability strategies, the fixed-time leader-following consensus problem is solved. An upper bound of settling time is obtained by using a new protocol, and such a bound is independent of initial states, thereby providing additional options for designers in practical scenarios where initial conditions are unavailable. Finally, numerical simulations are provided to demonstrate the effectiveness of the theoretical results.     

Observer-based leader-following tracking control under both fixed and switching topologies

This paper studies the tracking problem for a class of leader-follower multi-agent systems moving on the plane using observerbased cooperative control strategies. In our set-up, only a subset of the followers can obtain some relative information on the leader. We assume that the control input of the leader is not known to any of the followers while the system matrix is broadcast to all the followers. To track such a leader, an observer-based decentralized feedback controller is designed for each follower and detailed analysis for the convergence is presented for both fixed and switching interaction topologies between agents with the method of common Lyapunov function. We can also generalize the result to the higher dimension case for fixed topology and some special system matrices of the leader for switching topology.     

Guaranteed performance consensus in second-order multi-agent systems with hybrid impulsive control

This paper studies the problem of guaranteed performance consensus in second-order multi-agent systems. Taking advantage of impulsive control, a hybrid cooperative control is presented, and an index function is introduced to assess the performance of agents. It is shown that by synthesizing the coupling weights and the average impulsive intermittence, multi-agent systems can achieve guaranteed performance consensus. A numerical example is given to illustrate the theoretical results.     

二阶多智能体系统采样控制的一致性

研究在固定拓扑和切换拓扑下,二阶多智能体系统通过采样控制的一致性问题。首先,对于固定拓扑,给出了二阶多智能体系统通过采样控制达到一致性的充要条件;其次,对于切换拓扑,在所有联合切换拓扑有生成树的前提下,建立基于控制参数和采样周期使二阶系统实现一致性的充分条件。最后,用数值仿真验证所给结论的有效性。     

离散多智能体切换系统的二阶分组一致性研究

针对随机切换拓扑下离散多智能体系统的二阶分组一致性问题进行了研究。 设计了一种新颖的分组一致性协议,该协议不依赖于保守的假设条件,能全面反映系统中智能体在分组内与分组间的相互影响。引入马尔科夫链来模拟系统的随机拓扑变化, 基于矩阵理论和图论得到了在马尔科夫切换拓扑条件下,应用新协议使系统达到分组一致的充分条件。 在证明过程的结尾部分,使用线性不等式 (LMI) 工具给出了获取协议中控制参数的算法。最后,通过数字仿真实例证明了理论结果的有效性。     

Distributed consensus control of unicycle agents in the presence of external disturbances

In this paper, a distributed consensus control strategy is presented for a team of unicycle agents subject to external disturbances. Bounded disturbances with unknown dynamics on both translational and angular velocities are applied to the system. The key idea is to design the control inputs of each agent in such a way that, after a finite time, agents move with an acute angle with respect to a reference vector typically used for the consensus control of disturbance-free single-integrator agents. Convergence to consensus is then proved using Lyapunov theory. Simulation results confirm the efficacy of the proposed controller.     

Second-order consensus of multi-agent systems with noises via intermittent control

Second-order consensus of multi-agent systems with noises via intermittent control is investigated in this paper. First, we study the mean-square consensus problem with communication noises by intermittent control. In order to reach consensus, under the strong directed interacted topology, by using the tools of graph theory and Lyapunov method, a distributed control protocol is proposed based on the noises and periodical intermittent information. The upper bound of noise strength in the sense of matrix norm and the lower bound of communication time duration are obtained. Second, a class of coupled system models which include delay-terms in their nonlinearities in the noisy environment is discussed. Under the balanced strongly connected topology, the sufficient conditions to achieve the mean-square average-consensus are obtained. Finally, simulations are given to illustrate the effectiveness of our results.     

分布式事件触发多自主体领导跟随一致性研究

为了提高系统的通信效率和能源利用率,减少多自主体系统硬件资源的浪费,提出了只需要自主体自身及其最近邻居节点信息的分布式事件触发控制算法。研究了带有动态领导者的二阶多自主体系统领导跟随一致性问题。应用矩阵论和现代控制理论研究了在分布式事件触发机制下的二阶系统,得到了基于事件触发机制的多自主体系统协同运动的收敛条件。通过理论分析与计算表明,在此控制协议下不会存在芝诺行为,并且多自主体系统可以实现领导跟随一致性。最后,应用计算机仿真验证了本文所提控制协议的可靠性。     

Second-order consensus predictive control for 360MN extrusion machine

A new consensus predictive control protocol is proposed in this paper. It significantly speeds up the convergence rate comparing to traditional consensus mechanism and has been proved working well in simulation platform. A mathematical model is built by simplifying the hydraulic cylinders to single-DOF agents distributed evenly around 360MN extrusion machine׳s main table. With this model, a theoretical analysis of the mechanism is given and the validity of the consensus predictive control protocol for strong coupling multi-agent system on ADAMS–EASY5 simulation platform is illustrated. The machine׳s main table balance problem is well solved and the convergence rate is increased. These results are meaningful for increasing productivity.