网络控制系统中的时戳预测函数控制

传统预测函数控制算法不能有效处理网络控制系统中的随机延迟,为此提出了时戳预测函数控制算法.该算法使用时间戳来估计由网络引入的控制延迟,在预测系统未来输出时明确考虑了该延迟,然后借鉴传统预测函数控制算法的基本策略,得到了适用于网络控制系统的控制规律.进一步由TrueT im e工具箱搭建了网络控制系统仿真平台,对比了时戳预测函数控制算法和传统预测函数控制算法.仿真结果表明随着网络引入延迟的增大,时戳预测函数控制算法给出控制品质明显优越于传统预测函数控制算法.     

基于网络模型的综合多速率采样预测控制器

针对网络控制系统(NCS)中存在的网络延迟和数据丢包问题以及网络控制系统的多采样率特性,将预测控制器和网络延迟补偿器相结合,提出一种基于网络模型的综合多速率采样预测控制器.预测控制器利用多步预测、滚动优化、反馈校正控制策略补偿了传感器-控制器传输延迟,网络延迟补偿器补偿了控制器-执行器传输时延和一些未知网络延迟.仿真试验表明,该算法对网络延迟和数据丢包具有一定的补偿作用,提高了网络资源利用率并且保证闭环网络控制系统渐近稳定.     

ADAPTIVE DYNAMIC MATRIX CONTROL FOR NETWORK‐BASED CONTROL SYSTEMS WITH RANDOM DELAYS

Random transfer delays in network‐based control systems (NCSs) degrade the control performance and can even destabilize the control system. To address this problem, the adaptive dynamic matrix control (DMC) algorithm is proposed. The control algorithm is derived by applying the philosophy behind DMC to a discrete time‐delay model. A method to estimate the network‐induced delays is also presented to facilitate implementation of the control algorithm. Finally, an NCS platform based on the TrueTime simulator is constructed. With it, the adaptive DMC algorithm is compared with the conventional DMC algorithm under different network conditions. Simulation results show that the proposed adaptive DMC algorithm can respond to various network conditions adaptively and achieve better control performance for NCSs with random transfer delays.     

Modelling and optimal controller design of networked control systems with multiple delays

In this paper we discuss the modelling and control of networked control systems (NCS) where sensors, actuators and controllers are distributed and interconnected by a common communication network. Multiple distributed communication delays as well as multiple inputs and multiple outputs (MIMO) are considered in the modelling algorithm. In addition, the asynchronous sampling mechanisms of distributed sensors are characterized to obtain the actual time delays between sensors and the controller. Due to the characteristics of a network architecture, piecewise constant plant inputs are assumed and discrete-time models of plant and controller dynamics are adopted to analyse the stability and performance of a closed-loop NCS. The analysis result is used to verify the stability and performance of an NCS without considering the impact of multiple time delays in the controller design. In addition, the proposed NCS model is used as a foundation for optimal controller design. The proposed control algorithm utilizes the information of delayed signals and improves the control performance of a control system encountering distributed communication delays. Several simulation studies are provided to verify the control performance of the proposed controller design.     

网络控制系统Smith Fuzzy PID控制器的设计

针对网络控制系统中普遍存在的时延问题,提出了一种将模糊自适应算法和Smith预估补偿算法与常规PID控制器相结合的智能控制策略。该方法充分利用了Smith预估控制算法对带时延系统的良好控制能力,同时利用模糊推理算法实现对PID参数的在线自整定,进一步改善PID控制器的性能。仿真结果表明,基于该智能控制器的网络控制系统克服了传统PID控制超调量大及常规Smith预估补偿过分依赖于被控对象精确数学模型的缺陷,可以有效降低时延对系统性能的不利影响,使被控对象具有良好的动、静态特性。     

网络化控制系统两种时延预测算法及其比较

针对网络化控制系统（NCS）中的随机时变时延,提出了两种时延预测算法——自适应最小均方差（LMS）算法和在线最小二乘支持向量机（LS-SVM）算法，对其进行预测，并用实际测试得到的网络时延数据，对两种算法的时延预测效果进行了详细分析比较，指出了各自的特点和适用范围。     

网络控制系统的滑模多步预估控制

针对网络控制系统中出现的长时滞、网络诱导噪声和数据包丢失,提出了的滑模多步预估控制器的设计方法.首先对提出的控制器进行了描述,它利用滑模控制的强鲁棒性来克服网络诱导噪声,采用多步预估的办法来处理网络中的时滞和数据包丢失.进而对导出的闭环网络控制系统的稳定性进行了分析.最后对通过网络控制的直流电机,采用所提出的方法设计了控制器,仿真结果验证了方法的有效性.     

LQG control of networked control systems with access constraints and delays

We explore the LQG control of a networked control system (NCS) in which a linear plant is controlled remotely over a network or other shared communication medium. The medium provides a limited number of simultaneous connections, so that only a subset of the plant's sensors and actuators may communicate with the controller at any one time, subject to known transmission delays. Instead of insisting on jointly optimal control and medium access policies, we reduce the infinity of possible access sequences down to those which preserve the stabilisability and detectability of the underlying plant, and are periodic. Our choice of communication and NCS model effect a kind of ‘decoupling’ of the LQG problem, in the sense that the medium access policy can be selected independently of the controller. This guarantees the existence of a stabilising LQG controller which is optimal for the communication policy of choice, and which is then combined with a delay compensator. We include simulations that illustrate our approach.     

基于带有随机时滞的多通信通道的网络控制系统镇定

基于带有随机时滞的多通信通道,建立了离散时间网络控制系统模型．利用缓存对丢包进行补偿,并设计了状态反馈控制器,使系统达到随机稳定．采用锥型补偿线性化（ＣＣＬ）算法得到了控制器增益的全局最优解．最后通过倒立摆系统的仿真例子验证了所提出方法的可行性．     

Adaptive mechanism-based congestion control for networked systems

In order to assure the communication quality in network systems with heavy traffic and limited bandwidth, a new ATRED (adaptive thresholds random early detection) congestion control algorithm is proposed for the congestion avoidance and resource management of network systems. Different to the traditional AQM (active queue management) algorithms, the control parameters of ATRED are not configured statically, but dynamically adjusted by the adaptive mechanism. By integrating with the adaptive strategy, ATRED alleviates the tuning difficulty of RED (random early detection) and shows a better control on the queue management, and achieve a more robust performance than RED under varying network conditions. Furthermore, a dynamic transmission control protocol–AQM control system using ATRED controller is introduced for the systematic analysis. It is proved that the stability of the network system can be guaranteed when the adaptive mechanism is finely designed. Simulation studies show the proposed ATRED algorithm achieves a good performance in varying network environments, which is superior to the RED and Gentle-RED algorithm, and providing more reliable service under varying network conditions.     

Stability validation of a constrained model predictive networked control system with future input buffering

This paper addresses the stability of a newly-developed control strategy for networked control systems (NCS). This control strategy hones the potential of constrained model predictive control (MPC) by buffering the predicted control sequence at the actuator in anticipation of typical data transmission errors associated with NCS. Closed-loop stability in the sense of Lyapunov is guaranteed for the controller in the linear case, by bounding the projected receding horizon costs by lower- and upper-bounding terms using a predetermined terminal cost. A stability theorem is developed, which provides a suboptimal measure for the controller in real time, and is sufficient to estimate the worst-case transmission delay that can be handled by the developed control buffering strategy. The stability conditions, as governed by the theorem, are validated through real-time implementation on an electro-hydraulic servo system of an industrial processing machine, through an Ethernet network.     

Model‐based event‐triggered predictive control for networked systems with communication delays compensation

This paper addresses the model‐based event‐triggered predictive control problem for networked control systems (NCSs). Firstly, we propose a discrete event‐triggered transmission scheme on the sensor node by introducing a quadratic event‐triggering function. Then, on the basis of the aforementioned scheme, a novel class of model‐based event‐triggered predictive control algorithms on the controller node is designed for compensating for the communication delays actively and achieving the desired control performance while using less network resources. Two cases, that is, the value of the communication delay of the first event‐triggered state is less or bigger than the sampling period, are considered separately for certain NCSs, regardless of the communication delays of the subsequent event‐triggered states. The codesign problems of the controller and event‐triggering parameter for the two cases are discussed by using the linear matrix inequality approach and the (switching) Lyapunov functional method. Furthermore, we extended our results to the NCSs with systems uncertainties. Finally, a practical ball and beam system is studied numerically to demonstrate the compensation effect for the communication delays with the proposed novel model‐based event‐triggered predictive control scheme. Copyright © 2014 John Wiley & Sons, Ltd.     

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.     

Structural Properties,LQG Control and Scheduling of a Networked Control System with Bandwidth Limitations and Transmission Delays

The problem of simultaneous LQG control and scheduling of a Networked Control System (NCS) with constant network induced delays at input and output and bandwidth limitations is investigated. Delays are considered at plant as well as controller side. Sufficient conditions for controllability, stabilizability, reconstructibility and detectability of the underlying networked control system are drawn. The proposed conditions extend previous works on structural properties of NCS by capturing both plant and controller side delays together with bandwidth limitations. A framework for computing the optimal LQG controller for the NCS with a fixed scheduling is provided. The proposed modeling approach facilitates use of LQG as well as other control methods for NCSs with delays and bandwidth limitations. In order to optimize performance, a semi-online scheduling procedure is proposed based on an offline look up table. The look up table assigns an optimal schedule with associated optimal LQG controller to initial conditions. The proposed scheme improves previous results by online deployment of schedule and LQG control with stability guarantees and very low computational overhead. A simulation example with communication delays, packet losses and bandwidth limitations in both sensor and actuator sides is included. Static optimal periodic communication sequence, Optimal Pointer Placement (OPP) approach proposed in previous works, a random access scheduling method representing contention based access policies and the proposed method are simulated and compared.      

SCHEDULING AND CONTROL CO‐DESIGN FOR DELAY COMPENSATION IN THE NETWORKED CONTROL SYSTEM

The networked control system (NCS) is currently receiving increasing attention from researchers. Researches on this subject, however, have not considered the co‐design of network quality of service (QoS) and control quality of performance (QoP). This paper proposes a novel NCS design framework based on scheduling and control co‐design to compensate for random network‐induced delays. In the framework, a scheduling algorithm used to find the optimal sampling regions of control loops performs rough adjustment and guarantees the network QoS, while a novel adaptive fuzzy PID controller is designed to perform accurate adjustment to guarantee the control QoP. Practical application results obtained with a multi‐loop NCS show that the framework can ensure satisfactory performance due to its robustness against network uncertainty.     

一类具有随机时延的网络化控制系统的广义预测控制

网络化控制系统中,各种恒定、时变或者随机的网络时延会导致系统控制性能的下降甚至不稳定。针对基于交换式以太网所造成的随机网络时延问题,结合对系统结构及时延特征的分析,给出了一种基于广义预测控制的控制方法,该方法采用网络时间戳机制和模型的在线辨识,能够准确地测量系统输出并及时对预测值进行在线修正,实现对随机时延的网络化控制系统的有效控制。最后通过仿真验证了该方法的有效性。     

基于GPC算法的网络控制系统研究

针对具有随机时延的一类网络控制系统(NCS),文章设计了一种基于时延补偿和广义预测控制(GPC)算法的控制器。该控制器根据数据包的时间戳计算传感器-控制器时延,通过时延补偿得到被控对象当前的状态和输出,采用GPC算法计算控制量。仿真结果证实了该控制器的有效性。     

Robust partially mode delay dependent ℋ ∞ control of discrete-time networked control systems

This article proposes a methodology for designing a partially mode delay dependent ?_∞ controller design for discrete-time systems with random communication delays. Communication delays between sensors and controller are modelled by a finite state Markov chain where the transition probability matrix is partially known. Stability criteria are obtained based on Lyapunov–Krasovskii functional and a novel methodology for designing a partially mode delay dependent state feedback controller has been proposed. The controller is obtained by solving linear matrix inequality optimisation problems using cone complimentarity linearisation algorithm. A numerical example is provided to illustrate the effectiveness of the proposed controller.     

网络化控制系统中的延时问题:分析与展望

网络诱导延时是引起网络化控制系统性能下降甚至不稳定的主要因素之一,如何减小延时或降低其不确定性以克服延时的不利影响,一直是网络化控制系统研究领域的一个关键问题.对此,从控制和通讯网络两方面出发,对目前关于延时问题的研究结果进行了详细的论述和总结;通过系统地分析和对比,指出现有理论成果中存在的问题和不足;最后,指出该领域今后的主要任务和发展方向,并给出了一些有益的建议.     

含状态和输入时滞的网络控制系统镇定

研究含有更广泛被控对象的网络控制系统镇定问题．假定被控对象含有时变状态和输入时滞，采用Lyapunov-Krasovskii泛函方法分析了系统的稳定性．所提出的方法可转化为线性矩阵不等式的形式，因而可较为容易地求得控制器和广义最大允许时延．仿真结果说明了所提出方法的有效性．