Distributed learning and cooperative control for multi-agent systems

This paper presents an algorithm and analysis of distributed learning and cooperative control for a multi-agent system so that a global goal of the overall system can be achieved by locally acting agents. We consider a resource-constrained multi-agent system, in which each agent has limited capabilities in terms of sensing, computation, and communication. The proposed algorithm is executed by each agent independently to estimate an unknown field of interest from noisy measurements and to coordinate multiple agents in a distributed manner to discover peaks of the unknown field. Each mobile agent maintains its own local estimate of the field and updates the estimate using collective measurements from itself and nearby agents. Each agent then moves towards peaks of the field using the gradient of its estimated field while avoiding collision and maintaining communication connectivity. The proposed algorithm is based on a recursive spatial estimation of an unknown field. We show that the closed-loop dynamics of the proposed multi-agent system can be transformed into a form of a stochastic approximation algorithm and prove its convergence using Ljung’s ordinary differential equation (ODE) approach. We also present extensive simulation results supporting our theoretical results.     

Observer design for wired linear networked control systems using matrix inequalities

We design an observer-protocol pair to asymptotically reconstruct the states of a linear time-invariant (LTI) plant under communication constraints induced by the network. We parameterize a class of observers and protocols, and for a given network transmission interval, we derive sufficient conditions in terms of matrix inequalities for the existence of an observer-protocol pair in the considered class that asymptotically reconstructs the plant states.     

Architectures and coder design for networked control systems

In networked control systems (NCSs) achievable performance is limited by the communication links employed to transmit signals in the loop. In the present work, we characterise LTI coding systems which optimise performance for various NCS architectures. We study NCSs where the communication link is situated between plant output and controller, and NCSs where the communication link is located between controller and actuator. Furthermore, we present a novel NCS architecture, which is based upon the Youla parameterisation. We show that, which of these architectures gives best performance depends, inter alia, upon characteristics of a related non-networked design, plant disturbances and reference signal. A key aspect of our work, resides in the utilisation of fixed signal-to-noise ratio channel models which give rise to parsimonious designs, where channel utilisation is kept low. The results are verified with simulations utilising bit-rate limited channels.     

网络控制系统补偿器设计及稳定性分析

为解决网络延时对网络化控制系统性能的影响, 从控制的角度提出基于系统模型的补偿器设计方案以解决网络延时问题. 通过对广义预测控制算法GPC状态空间形式的推导, 设计具有多步预测功能的网络控制器, 实现前向通道的延时补偿; 构造具有延时补偿功能的状态观测器以补偿反馈通道延时. 分析了使用上述延时补偿策略所构成的闭环网络控制系统的稳定性. 通过对不同网络延时补偿的仿真实验, 证实了该补偿算法能有效改善控制系统性能并保持系统的稳定.     

Fault tolerant cooperative control for a class of nonlinear multi-agent systems

This paper studies the target aggregation problem for a class of nonlinear multi-agent systems with the time varying interconnection topology. The general neighboring rule-based linear cooperative protocol is developed and a sufficient aggregation condition is derived. Moreover, it is shown that in the presence of agent faults, the target point is still reached by adjusting some weights of the cooperative protocol without changing the structure of the topology. An unmanned aerial vehicle team example illustrates the efficiency of the proposed approach.     

Homogeneous control law design for output synchronization of networked Lur'e‐type systems with disturbances

In this paper, the homogeneous distributed control law is proposed such that the outputs of the networked Lur'e systems with disturbances are synchronized. A novel adaptive distributed state‐based disturbance compensator technique is utilized such that the disturbances can be offset asymptotically. The design of the distributed compensator is constructive in that some particular functions of the states of the Lur'e systems are included. The functions always exist for the considered Lur'e‐type system. Moreover, a theorem of networked Lur'e systems subject to disturbances is first presented to show the boundedness of the states of the closed‐loop system. Then, the synchronization is shown by the incremental passivity theory and graph theory. Finally, the effectiveness of the current method is illustrated by the networked Van der Pol oscillators with disturbances.     

Unknown input observer design and analysis for networked control systems

The insertion of communication networks in the feedback loops of control systems is a defining feature of modern control systems. These systems are often subject to unknown inputs in a form of disturbances, perturbations, or attacks. The objective of this paper is to design and analyse an observer for networked dynamical systems with unknown inputs. The network effect can be viewed as either a perturbation or time-delay to the exchanged signals. In this paper, we (1) review an unknown input observer (UIO) design for a non-networked system, (2) derive the networked unknown input observer (N_etUIO) dynamics, (3) design a N_etUIO such that the effect of higher delay order terms are nullified and (4) establish stability-guaranteeing bounds on the networked-induced time-delay and perturbation. The formulation and results derived in this paper can be generalised to scenarios and applications where the signals are perturbed due to a different source of perturbation or delay.     

网络化切换控制系统故障检测与优化设计

研究存在未知短时延、丢包和系统不确定性的网络化切换控制系统故障检测与时域优化问题. 首先基 于观测器构建残差发生器, 结合Lyapunov 函数方法和平均驻留时间方法分析系统的稳定性, 并以线性矩阵不等式(LMI) 形式给出故障检测滤波器的求解方法; 然后为了改善故障检测系统的性能, 采用后置滤波器对残差信号进行时域优化, 并利用奇偶空间方法给出其最优解; 最后设计并推导出自适应阈值. 仿真结果验证了所提出方法的有效性.

     

Co-simulation platforms for co-design of networked control systems: An overview

This paper gives an overview of the existing co-simulation platforms for co-design of networked control systems (NCSs). NCSs contain coupled control and communication perspectives. However, the existing simulators focus either on control systems or communication networks. In order to analyse the coupling effect from both sides, co-simulation method is under consideration as one of the most promising solutions. This paper briefly introduces the commonly used individual control and communication simulators. Then the existing co-simulation platforms have been reviewed and discussed. Synchronization technique is the key point toward co-simulation, thus different synchronization methods have also been summarized. Two sample case studies with results are provided to show the beneficial of co-simulations.     

具有通信约束的网络控制系统动态调度与H∞控制协同设计

针对一类具有通信约束的随机时延网络控制系统,提出一种基于试一次丢弃(try-once-discard,TOD)动态调度策略与鲁棒H∞控制器协同设计的方法.考虑通信约束和随机时延的影响,将系统建模为一类具有参数不确定性的离散切换系统,并采用切换系统和Lyapunov稳定性理论,给出了TOD调度策略下使闭环系统渐近稳定的鲁棒H∞控制器设计方法.最后通过仿真验证了方法的有效性.     

Stability,positive invariance and design of constrained regulators for networked control systems

In this article, the stability analysis, the positive invariance of polyhedral sets and the design of state-feedback regulators for networked control systems (NCS) with bounded transmission delays, constant and unknown or time-varying, are investigated. The dynamics of the NCS is described by autoregressive-moving-average (ARMA) models. Contrary to former approaches based on quadratic Lyapunov functions, in this article polyhedral Lyapunov functions are used for both stability and positive invariance analysis and state-feedback synthesis. Then, based on the property that the exponential of a matrix can be expressed as a weighted sum of its constituent matrices, it is proven that the problems of determination of stability margins or the design of stabilising controllers can be reduced to linear programming optimisation problems. The use of ARMA models allows the development of methods for the design of state-feedback controllers satisfying state constraints or convergence rate specifications defined on the NCS state space and not on the state of an augmented state space representation.     

Combined and passivity control for networked control systems with random gain fluctuations and sojourn probabilities: A switched system approach

On the basis of the passivity theory, the problem of designing non‐fragile control for a class of networked control systems (NCSs) with the plant being a switched system is presented. The NCSs under consideration are modeled by considering the network‐induced imperfections like transmission delays and packet dropouts as a single time‐varying delay. The network status is assumed to vary on the basis of sojourn probabilities, and these probabilities are known a prior. The controller is designed including stochastic fluctuations in its gain matrix by considering the Bernoulli distributed white sequence along with time‐varying probability measures. The key steps in this method are to construct an improved Lyapunov–Krasovskii Functional and to utilize reciprocally convex technique. The sojourn probability‐dependent sufficient criteria are obtained to ensure the closed‐loop, mode‐dependent switched NCSs to be robustly stochastically stable on the basis of the combined and passivity performance. The effectiveness of the proposed method is illustrated through an example. Copyright © 2017 John Wiley & Sons, Ltd.     

New approach to stochastic stability and controller design for networked control systems

This paper addresses the random time-delays and packet losses issues of networked control systems （NCS） within the framework of jump linear systems with mode-dependent time-delays. A new delay-dependent condition on the stochastic stability is proposed by a new stochastic Lyapunov-Krasovskii functional. The condition is formulated as a set of coupled linear matrix inequalities （LMIs）. As an example to verify the proposed method, an inverted-pendulum system with network is considered. The simulation results demonstrate the effectiveness of the method.     

New approach to stochastic stability and controller design for networked control systems

This paper addresses the random time-delays and packet losses issues of networked control systems (NCS) within the framework of jump linear systems with mode-dependent time-delays.A new delay-dependent condition on the stochastic stability is proposed by a new stochastic Lyapunov-Krasovskii functional.The condition is formulated as a set of coupled linear matrix inequalities (LMIs).As an example to verify the proposed method,an inverted-pendulum system with network is considered.The simulation results demonstrate the effectiveness of the method.     

Observer-based controller design for networked control systems with sensor quantisation and random communication delay

This article addresses the study of observer-based controller design for network-based control systems in the presence of output quantisation and random communication delay simultaneously. In the communication channel, the output measurement are quantised before transmission, and two kinds of network-induced delays are taken into account simultaneously: (i) random delay from sensor to controller and (ii) random delay from controller to actuator. These two types of random delays are modelled as two independent Bernoulli distributed white sequences. The observer-based controller is synthesised to stabilise the networked closed-loop system in the sense of stochastic stability. Sufficient conditions for the existence of the controller are provided by stochastic Lyapunov method. An illustrative numerical example is employed to demonstrate the applicability and flexibility of the proposed design strategy.     

Protocol sequence and control co‐design for a collection of networked control systems

This paper is concerned with the simultaneous stabilization of a collection of plants shared by the wireless network with capacity limitation. We use most regular binary sequences (MRBS) to control the medium access status of the plants. The design procedure of the scheduling policy translates to determine two parameters of the MRBS. With the MRBS protocol, each plant is essentially a sampled‐data control system with time varying sampling intervals. We derive a sufficient condition for determining the MRBS protocol that guarantees the controllability, observability, and stability of each plant. Most importantly, we give a methodology for MRBS protocol and controller co‐design, in which the controller has switching gains that are piecewise constant and dependent on the sampling intervals yielded by the MRBS. The main results are established using piecewise Lyapunov functional and the average dwell time technique. It is shown that the method can guarantee simultaneous stabilization of the collection of plants robustly in situations where the controller gain does not match the sampling interval or the sampling interval violates the maximum allowable transmission interval criteria. A numerical example is given to demonstrate the effectiveness of the co‐design method. Copyright © 2015 John Wiley & Sons, Ltd.     

网络控制系统的时延相关状态反馈控制器设计

研究了具有时延、丢包和数据包时序错乱的网络控制系统镇定问题.为了有效提高系统的控制性能,本文根据网络控制系统的特点提出一种时延相关状态反馈控制方法,并将闭环网络控制系统建模为离散时间切换模型.在此基础上,通过构造依赖于参数的Lyapunov函数给出了闭环网络控制系统的稳定条件和镇定控制器设计方法.仿真结果和实验结果表明所提方法的有效性和可用性.     

Exponential stabilization of networked control systems and design of switching controller

This paper deals with the problem of switching between an open-loop estimator and a close-loop estimator for compensating transmission error and packet dropout of networked control systems. Switching impulse is considered in order to reduce the error between theory and application, a sufficient condition for exponential stabilization of networked control systems under a given switching rule is presented by multiple Lyapunov-like functions. These results are presented for both continuous-time and discrete-time domains. Controllers are designed by means of linear matrix inequalities. Sim- ulation results show the feasibility and efficiency of the proposed method.     

Exponential stabilization of networked control systems and design of switching controller

1 Introduction Networked control systems (NCS) are feedback control systems whose feedback paths are implemented by a real- time network. This type of systems has advantages of more ?exibility with respect to traditional control systems. It also allows for reduced wiring, as well as a lower installation cost. Examples of such systems can be seen in remote sur- vey [1], telerobotics [2], unmanned aerial vehicles [3] and remote control laboratory [4,5]. Most of the times, sensors will transmit…     

Integrated design of residual generation and evaluation for fault detection of networked control systems

In this paper, integrated design of residual generation and evaluation is proposed to fault detection (FD) of networked control systems. Both the imperfect network transmissions and the sampling effects are considered under the assumption that no stochastic network model is available. By deriving a linear discrete time‐varying system equivalent to the sampled plant, the continuous‐time behaviors of disturbances and faults during sampling intervals are captured. Moreover, the effects of unknown but bounded packet delays and dropouts in the controller‐to‐actuator link are described by uncertain input delays with finite number of possibilities. A parity relation‐based FD module with multiple residuals is constructed for the derived system model. For the constructed FD module, the set of undetectable faults is obtained from integrated analysis of residual generation and evaluation and then designed to achieve its worst‐case minimal geometrical size while guaranteeing zero false alarms. Simulation results on a networked three‐tank system are provided to show the merits of the proposed integrated design approach. Copyright © 2015 John Wiley & Sons, Ltd.