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.     

Distributed consensus over digital networks with limited bandwidth and time-varying topologies

In this paper, we consider discrete-time distributed average-consensus with limited communication data-rate and time-varying communication topologies. We design a distributed encoding-decoding scheme based on quantization of scaled innovations and a control protocol based on a symmetric compensation method. We develop an adaptive scheme to select the numbers of quantization levels according to whether the associated channel is active or not. We prove that if the network is jointly connected, then under the protocol designed, average-consensus can be asymptotically achieved, and the convergence rate is quantified. Especially, if the duration of any link failure in the network is bounded, then the control gain and the scaling function can be selected properly such that 5-level quantizers suffice for asymptotic average-consensus with an exponential convergence rate.     

Consensus of linear multi-agent systems with communication delays by using the information of second-order neighbours under intermittent communication topology

This paper investigates the consensus of identical linear multi-agent systems with aperiodic intermittent communication topology by using the information of second-order neighbours (two-hop neighbourhood). The protocols based on two-hop neighbourhood information and intermittent communication topology are designed, under which consensus is reached. If the communication rate is larger than the corresponding threshold value, the networks will accelerate consensus by using two-hop neighbourhood information. By means of switching systems theory and Lyapunov–Razumikhin theorem, consensus of multi-agent systems with communication delays and intermittent communication topology is reached by two-hop neighbourhood information. Finally, simulation examples are provided to show the effectiveness of the theoretical results.     

Leader-following consensus of second-order agents with multiple time-varying delays

In this paper, a leader-following consensus problem of second-order multi-agent systems with fixed and switching topologies as well as non-uniform time-varying delays is considered. For the case of fixed topology, a necessary and sufficient condition is obtained. For the case of switching topology, a sufficient condition is obtained under the assumption that the total period over which the leader is globally reachable is sufficiently large. We not only prove that a consensus is reachable asymptotically but also give an estimation of the convergence rate. An example with simulation is presented to illustrate the 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.     

Event-based consensus of multi-agent systems with general linear models

In this paper, the event-based consensus problem of general linear multi-agent systems is considered. Two sufficient conditions with or without continuous communication between neighboring agents are presented to guarantee the consensus. The advantage of the event-based strategy is the significant decrease of the number of controller updates for cooperative tasks of multi-agent systems involving embedded microprocessors with limited on-board resources. The controller updates of each agent are driven by properly defined events, which depend on the measurement error, the states of its neighboring agents and an arbitrarily small threshold. It is shown that the controller updates for each agent only trigger at its own event time instants. A simulation example is presented to illustrate the theoretical results.     

切换拓扑一阶积分器网络量化趋同控制

针对数字信道中传输的是经过量化和编码后的数据,研究了切换拓扑情况下连续时间一阶积分器网络中的量化趋同问题.通过均匀量化器,每个智能体将量化后的状态传输给邻居,并利用所得信息设计协议,实现量化趋同.在所提出的量化趋同协议下,所有状态将在有限时间内进入包含状态均值的量化层中.特别地,对于通信拓扑是时不变的情况,给出了实现量化趋同所需时间的上界.仿真结果验证了所提出算法的有效性.     

多智能体系统在分布式采样控制下的动力学行为

本文运用图论、矩阵分析和现代控制理论等工具, 研究信息网络传输下多智能体系统的协调控制和动力学行为. 假设每个智能体通过数字化网络传感器获得其邻近智能体的位置状态,而且多智能体系统采取分布式线性控制协议. 每个智能体被描述为一个简单的采样系统,多智能体系统转化为混合动力学系统. 研究结果表明,多智能体系统所呈现的渐近聚集、周期振荡和发散动力学行为不仅和网络结构的代数特征有关, 而且和每个智能体的动力学方程、采样周期有关. 本文给出了具体精确的代数判据. 仿真例子进一步验证了本文结果的有效性.     

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 for multi-agent systems with delays and noises in transmission channels

This paper studies the distributed consensus problem for linear discrete-time multi-agent systems with delays and noises in transmission channels. Due to the presence of noises and delays, existing techniques such as the lifting technique and the stochastic Lyapunov theory are no longer applicable to the analysis of consensus. In this paper, a novel technique is introduced to overcome the difficulties induced by the delays and noises. A consensus protocol with decaying gains satisfying persistence condition is adopted. Necessary and sufficient conditions for strong consensus and mean square consensus are respectively given for non-leader–follower and leader–follower cases under a fixed topology. Under dynamically switching topologies and randomly switching topologies, sufficient conditions for strong consensus and mean square consensus are also obtained. Numerical examples are given to demonstrate the effectiveness of the proposed protocols.     

有向图中网络Euler-Lagrange系统无需相对速度信息的群一致性

在非对称有向图中,研究网络Euler-Lagrange系统的群一致性问题.每组内的智能体均为合作关系,而组间智能体则可以为合作关系或竞争关系.为了实现群一致性,假设组与组之间是无环连接的且系统有向图满足入度平衡条件.考虑到智能体间相对速度信息难以精确测量的实际情形,设计无需相对速度信息的分布式自适应控制算法,实现网络Euler-Lagrange系统的群一致性.最后通过仿真分析验证所设计算法的有效性.     

Global consensus for discrete-time multi-agent systems with input saturation constraints

In this paper, we consider the global consensus problem for discrete-time multi-agent systems with input saturation constraints under fixed undirected topologies. We first give necessary conditions for achieving global consensus via a distributed protocol based on relative state measurements of the agent itself and its neighboring agents. We then focus on two special cases, where the agent model is either neutrally stable or a double integrator. For the neutrally stable case, any linear protocol of a particular form, which solves the consensus problem for the case without input saturation constraints, also solves the global consensus problem for the case with input saturation constraints. For the double integrator case, we show that a subset of linear protocols, which solve the consensus problem for the case without saturation constraints, also solve the global consensus problem for the case with input saturation constraints. The results are illustrated by numerical simulations.