Networked Predictive Control of Systems With Random Network Delays in Both Forward and Feedback Channels

The design problem of networked control systems (NCS) with constant and random network delay in the forward and feedback channels, respectively, is considered in this paper. A novel networked predictive control (NPC) scheme is proposed to overcome the effects of network delay and data dropout. Stability criteria of closed-loop NPC systems are presented. The necessary and sufficient conditions for the stability of closed-loop NCS with constant time delay are given. Furthermore, it is shown that a closed-loop NPC system with bounded random network delay is stable if its corresponding switched system is stable. Both simulation study and practical experiments show the effectiveness of the control scheme     

Guaranteed Cost Networked Control for T–S Fuzzy Systems With Time Delays

This paper develops a guaranteed cost networked control (GCNC) method for Takagi-Sugeno (T-S) fuzzy systems with time delays. The state feedback controller is designed via the networked control system (NCS) theory. The stability of the overall fuzzy system using GCNC is also established. Network-induced delay in network transmission and packet dropout are analyzed. Some deductions are also extended to uncertain systems. Simulation results show the validity of the present control scheme     

具有时延和丢包的不确定性NCS的稳定性

研究了同时具有网络时延和数据丢包的不确定网络化控制系统的稳定性.将数据丢失看成一种特殊的时延,利用动态反馈控制器设计提高系统的动态性能,得到了总时滞(包括传感器与控制器之间的时滞,控制器与执行器之间的时滞)的表达式,建立了不确定网络化控制系统模型.通过构造李亚普诺夫函数,采用线性矩阵不等式技巧,给出了系统稳定的判定定理.仿真结果表明了该方法的有效性.     

Design and Stability Criteria of Networked Predictive Control Systems With Random Network Delay in the Feedback Channel

This paper is concerned with the design of networked control systems (NCSs) with random network delay in the feedback channel and gives stability criteria of closed-loop networked predictive control systems. The principle of predictive control is adopted to overcome the effects of network time delay. The necessary and sufficient conditions on the stability of the closed-loop NCS are derived, which provides useful analytical stability criteria. The closed-loop networked predictive control system with bounded random network delay is stable if the corresponding switched system is stable. Simulation and real-time results give an illustration of the proposed control strategies     

Stability of Nonlinear Networked Control System with Uncertainties

The problems of signal transmission delay, actuator data packet dropout, and measurement quantization in nonlinear networked control systems are investigated in this paper. First, a nonlinear system is represented as a series of linear systems through T–S fuzzy modeling, then the problem of actuator data packet dropout is solved through the introduction of a diagonal matrix; second, the problem of maintaining order is solved through the ZOH, and the problem of limited bandwidth is solved through the measurement quantization; and finally, the controller is designed to compensate the actuator data packet dropout.     

Improvement of State Feedback Controller Design for Networked Control Systems

A new method is proposed to improve the state feedback controller design for networked control systems (NCSs) taking both network-induced time delay and packet dropout into account in this paper. An appropriate Lyapunov functional is introduced to establish the improved sufficient stabilizability conditions for NCSs with memoryless state feedback controller by considering an additional useful term when estimating the upper bound of the derivative of Lyapunov functional and introducing new free weight matrices. Based on this less conservative existence condition, a networked controller design method is derived, which is equivalent to the solvability of a set of linear matrix inequalities. Numerical example is given to demonstrate the effectiveness and benefits of the proposed method.     

Control and Communication Challenges in Networked Real-Time Systems

A current survey of the emerging field of networked control systems is provided. The aim is to introduce the fundamental issues involved in designing successful networked control systems, to provide a snapshot assessment of the current state of research in the field, to suggest useful future research directions, and to provide a broad perspective on recent fundamental results. Reflecting the goals of the Special Issue itself, this paper surveys relevant work from the areas of systems and control, signal processing, detection and estimation, data fusion, and distributed systems. We discuss appropriate network architectures, topics such as coding for robustly stable control in the presence of time-varying channel capacity, channels with fixed versus adaptively variable data width, issues in data rate problems in nonlinear feedback problems, and problems in routing for stability and performance. In surveying current research on networked control systems, we find that recent theoretical advances and target applications are intimately intertwined. The common goal of papers in the Special Issue which follows is to describe key aspects of this relationship. We also aim to provide a bridge between networked control systems and closely related contemporary work dealing with sensor networks and wireless communication protocols     

State feedback controller design of networked control systems

This paper is concerned with the controller design of networked control systems (NCS). A new model of the NCSs is provided under consideration of both the network-induced delay and the data packet dropout in the transmission. In terms of the given model, a controller design method is proposed based on a delay-dependent approach. The feedback gain of a memoryless controller and the maximum allowable value of the network-induced delay can be derived by solving a set of linear matrix inequalities. Two examples are given to show the effectiveness of our method.     

Control over unreliable networks affected by packet erasures and variable transmission delays

This paper describes a novel control strategy aimed at achieving good performance over an unreliable communication network affected by packet loss and variable transmission delays. The key ingredient in the method described here is to use the large data packet frame size of typical modern communication protocols to transmit control sequences which cover multiple data-dropout and delay scenarios. Stability and performance of the resultant scheme are addressed under nominal networked conditions. Simulations verify that the strategy performs exceptionally well under realistic conditions with noise and unmeasured disturbances.     

An Integrated Control and Scheduling Optimization Method of Networked Control Systems

Modern computer and communication network technology has made it convenient to construct networked control systems. Feedback control systems wherein the control loops are closed through a real-time network are called networked control systems (NCSs)[1]. NCSs exhibit the characteristics of high reliability, simple installation, low maintenance, good diagnostic capability, and low cost. Recently, theWhen control and feedback signals transmit through the network, the network delay emerges unavo…     

Gain scheduler middleware: a methodology to enable existing controllers for networked control and teleoperation - part I: networked control

Conventionally, in order to control an application over a data network, a specific networked control or teleoperation algorithm to compensate network delay effects is usually required for controller design. Therefore, an existing controller has to be redesigned or replaced by a new controller system. This replacement process is usually costly, inconvenient, and time consuming. In this paper, a novel methodology to enable existing controllers for networked control and teleoperation by middleware is introduced. The proposed methodology uses middleware to modify the output of an existing controller based on a gain scheduling algorithm with respect to the current network traffic conditions. Since the existing controller can still be utilized, this approach could save much time and investment cost. Two examples of the middleware applied for networked control and teleoperation with IP network delays are given in these two companion papers. Part I of these two companion papers introduces the concept of the proposed middleware approach. Formulation, delay modeling, and optimal gain finding based on a cost function for a case study on DC motor speed control with a proportional-integral (PI) controller are also described. Simulation results of the PI controller shows that, with the existence of IP network delays, the middleware can effectively maintain the networked control system performance and stabilize the system. Part II of this paper will cover the use of the proposed middleware concept for a mobile robot teleoperation.     

Quantized Observer-Based Sliding Mode Control for Networked Control Systems Via the Time-Delay Approach

This paper investigates the sliding mode control problem for networked control systems, which are influenced by the non-ideal network environment, such as network-induced delays, packet dropouts and quantization errors. The states of the system are assumed to be unavailable, and an observer is designed to estimate the state of the system, based on which a sliding mode controller is given to guarantee the closed-loop system to be stable. Furthermore, it is shown that the proposed control scheme ensures the reachability of the sliding surfaces in both the state estimate space and the estimation error space. Finally, a numerical example is given to illustrated the effectiveness of the proposed methodology.     

QoS-based remote control of networked control systems via Profibus token passing protocol

This paper focuses on a quality-of-service (QoS)-based remote control scheme for networked control systems via the Profibus token passing protocol. Typically, token passing experiences random network delay due to uncertainties in token circulation, but the protocol has in-built upper and lower bounds of network delay. Thus, to ensure the control performance of networked control systems via the Profibus token passing protocol, the network delay should be maintained below the allowable delay level. As the network delay is affected by protocol parameters, such as target rotation time, we present here an algorithm for selection of target rotation time using a genetic algorithm to ensure QoS of control information. We also discuss the performance of the QoS-based remote control scheme under conditions of controlled network delay. To evaluate its feasibility, a networked control system for a feedback control system using a servo motor was implemented on a Profibus-FMS network.     

NCS中数据包丢失自适应补偿方法的研究

针对不确定性时延转化为固定时延的数据包丢失模型,改进补偿数据包丢失的方法.将时延大于一个采样周期的数据描述为数据包丢包,采用自适应线性预测方法对丢失的数据进行补偿,仿真结果表明所提到的补偿方法是有效的.     

基于TrueTime的无线网络控制系统仿真研究

无线网络控制系统（WiNCS,Wireless Networked Control Systems）是基于无线网络的分布式控制系统,融合了计算机、通信、网络与控制技术,具有无需布线、组网和维护方便、易于扩展以及良好的可移动性等优点。为了研究影响WiNCS控制性能的因素,利用WiNCS惯用的仿真工具Truetime,建立仿真系统,对网络时延、干扰、采样周期、传输速率、功率控制、节点间距离等因素进行了仿真研究,给出了仿真结果及相应的结论,对进一步研究无线网络控制系统有一定的帮助。     

Efficient De-Jitter Control for Voice Applications over Wireless Ad Hoc Networks

Voice over IP applications require a playout buffer at the receiver side to smooth network delay variations. Unfortunately, existing algorithms for dynamic playout adjustment designed for wireline networks do not operate correctly in wireless ad hoc networks. These algorithms estimate the end-to-end delay on the set of previous received audio packets. Indeed, such a delay estimation based on past history is not appropriate due to mobility which leads to random changes of the network topology. In this paper, we highlight this delay estimation problem. We show that route request AODV control messages provide more accurate delay estimation. Then, we propose a new algorithm for playout delay adjustment based on these control messages. The performance evaluation is performed by simulation using ns-2. We show that this algorithm outperforms existing playout delay adjustment algorithms. Performance criteria are loss late percentage (reliability criterion), averaged playout delay (interactivity criterion) and playout delay variation (stability criterion).     

Networked Predictive Control Systems Based on the Hammerstein Model

In this paper, a novel predictive control-based approach is proposed for a networked control system with random delays containing an input nonlinear process based on a Hammerstein model. The method uses a time-delay two-step generalized predictive control scheme, which consists of two parts: one is to deal with the input nonlinearity of the Hammerstein model and the other is to compensate for the network-induced delay in the networked control system. A theoretical result using the Popov criterion is presented for the closed-loop stability of the system in the case of a constant delay. Simulation examples illustrating the validity of the approach are also presented.     

Networked Control for Singular Systems Over Unreliable Channel with Limited Capacity

This paper addresses networked control problem for discrete-time linear singular systems over unreliable channel. It is assumed that the controller can only receive the transmitted sequence of finite coded signals via unreliable channels, which may be lost due to the limited communication capacity and transmission errors. By introducing compensation terms at every update instant and auxiliary systems in each sampling interval, both state- and output-based coder–decoder–controller procedures are proposed. Then, a uniform sufficient feedback stabilization condition involving the size of coding alphabet, the sampling period and data packet dropout rate is obtained. Finally, an example is given to illustrate the design procedures and effectiveness of the proposed results.     

基于DDE和Socket技术的网络控制系统仿真平台

文章从控制系统与实际网络相结合构成网络控制系统出发,应用动态数据交换（DDE,Dynamic Data Exchange）协议和Socket网络通信技术,构建了基于Matlab／Simulink的网络控制系统仿真平台。以起重机为网络远程被控对象,通过仿真平台将实际网络引入起重机控制系统,揭示了网络延迟对该系统的影响。     

HMM based estimation of NCS network load and its application in switching control

The analysis and design of the Networked Control System (NCS) are more challenging due to the random time delays brought by the network. And modeling the uncertain time delays has been becoming a significant focus of research. This paper modeled the network delays with Hidden Markov Model (HMM), and then on the basis of Viterbi algorithm, proposed a method to estimate the network’s current load state using random time delay sequence. In further simulation we first designed PID controllers corresponding to the network’s different load states respectively, and applied the proposed method to guide switching control of the networked closed-loop system. The results showed the effectiveness of HMM in network state estimation and switching control.