具有通信约束的网络化控制系统容错控制研究

Implementing a control system over a communication network induces inevitable time delays that may degrade performance and even cause instability. One of the most effective ways to reduce the negative effect of delays on the performance of networked control system (NCS) is to reduce network traffic. In this paper, adjustable deadbands are explored as a solution to reduce network traffic in NCS. A method of fault-tolerant control of networked control system is presented, which takes into account system response as well as network traffic. The integrity design for a kind of NCS with sensor failures and actuator failures is analyzed based on robust fault-tolerant control theory and information scheduling. After detailed theoretical analysis, the paper also provides the simulation results, which further validate the proposed scheme.     

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.     

Predictive control and scheduling codesign in network control systems

A codesign approach combining predictive control compensation and network scheduling is presented in this paper to overcome the adverse influences of stochastic time delays and packet losses encountered in network-based real-time control systems. The state estimation and control prediction compensation algorithms are used for the random network delays in the feedback and forward channels, and the stability criteria are analyzed. The proper sampling rate is given with network scheduling to meet the desired system performance, while the network-induced delay is tolerated. Simulations show that the codesign approach works well with the bounded network delay.     

网络传输迟延与丢包的补偿及系统稳定性分析

针对网络传输在控制系统中引发的问题,提出在控制器节点采用针对迟延和丢包的补偿估计器．以提高控制系统的性能。当迟延小于一个采样周期且数据包传输率已定时,将包含该补偿估计器的网络控制系统（CEDPNCS）,描述为具有两个事件的异步动态系统,并推导出保证系统稳定的时变双线性矩阵不等式．仿真结果表明．所提出的方法能有效提高控制系统的性能．     

MIMO网络控制系统的稳定性分析

推导了多输入多输出网络控制系统的时滞离散时间数学模型，此模型包括了控制网络的网络延时．提出了一种新的网络控制系统稳定性分析方法，得到了使系统稳定的各网络延时应满足的条件．只要系统的网络延时满足这些条件，网络控制系统的极点便分布在复平面内的一个圆形区域内．若此圆形区域在单位圆内，网络控制系统就是稳定的．仿真实验验证了所提理论的有效性．     

基于AR模型时延预测的改进GPC网络控制算法

针对网络随机时延等不确定因数导致网络控制系统的控制性能下降甚至不稳定,提出一种新的网络控制算法.首先建立网络时延的自动回归模型;然后采用参数自校正的最小均方算法对网络时延进行在线预测;最后采用一种考虑时延的改进广义预测控制算法对网络时延进行补偿.仿真实验结果表明,该方法对网络时延具有较好的补偿效果,且在线计算量小,有很好的实时性,同时对干扰和丢包等因素具有良好的鲁棒性.     

Switching networked attitude control of an unmanned quadrotor

In this article, a switching networked attitude controller for an unmanned quadrotor over a wireless sensor network is presented. To deal with the network induced time varying delays, the quadrotor is being modeled as a switching time varying linear system, while the applied switching output feedback control scheme, is calculated based on Linear Matrix Inequalities, and is able to guarantee the stability of the quadrotor under arbitrary changes in the time delays.     

基于模糊模型和神经网络的多时滞不确定非线性系统的鲁棒H∞控制

针对一类具有多时滞的不确定非线性系统,提出了一种基于模糊模型和神经网络的组 合控制方法.利用具有多时滞的模糊T-S模型对系统进行近似建模并给出基于线性矩阵不等式 (LMI)的模糊H∞控制律.提出完全自适应RBF神经网络控制方法,通过在线自适应调整RBF 神经网络的权重、函数中心和宽度,来对消系统的未知不确定性和模糊建模误差的影响,不要求 系统的不确定项和模糊建模误差满足任何匹配条件或约束,并证明了闭环系统的稳定性.最后, 将所提出的方法应用到一具有多时滞的非线性混沌系统,仿真结果表明了该方法的有效性.     

Stabilization of networked control systems with nonuniform random sampling periods

In this paper, a new linear delayed delta operator switched system model is proposed to describe networked control systems with packets dropout and network‐induced delays. The plant is a continuous‐time system, which is sampled by time‐varying random sampling periods. A general delta domain Lyapunov stability criterion is given for delta operator switched systems with time delays. Sufficient conditions for asymptotic stability of closed‐loop networked control systems with both packets dropout and network‐induced delays are presented in terms of linear matrix inequalities (LMIs). A verification theorem is given to show the solvability of the stabilization conditions by solving a class of finite LMIs. Both the case of data packets arrive instantly and the case of invariant sampling periods in delta operator systems are given, respectively. Three numerical examples are given to illustrate the effectiveness and potential of the developed techniques. Copyright © 2010 John Wiley & Sons, Ltd.     

网络延时对PID控制系统性能影响的分析

由于网络通讯延时的存在，传统PID控制算法在网络化控制系统中的控制性能将受到影响．使用一种代价函数作为性能评估标准，并通过仿真实验分析了各种网络延时对PID控制性能的影响．利用根轨迹法分析了网络延时和PID参数对控制系统稳定性和控制性能的影响；用NetCon控制器实现了各种网络延时下对一个实验系统的控制．实验结果证明了仿真分析的正确性和有效性．     

Experimental Comparison Study of Control Architectures for Bilateral Teleoperators

A detailed experimental comparison study of several published algorithms for motion and force control of bilateral teleoperators, with emphasis on Internet-based teleoperation, is presented. The study investigates the effects of data losses, communication delays, and environmental constraints on a teleoperation system for different control techniques, which are based on wave variables, Smith predictors, and recent algorithms on synchronization. The controllers are compared on stability, transparency, and complexity using two identical nonlinear robots coupled via a stochastic network model that allowed transmission round-trip delays and data-loss rates to range from 8 to 1088 ms and 0% to 50%, respectively. A total of 18 subjects, which were distributed among 26 experiments with the aims of regulating the effects of the operators learning process and dynamic properties, participated in this study. Overall, the comparison study reports a deteriorating effect in the performance (i.e., larger position errors and lower fidelity of contact information) from delays and data losses. Yet, the effect of data losses is less critical when compared with time delays. In addition, the preference for a particular control framework is shown to strongly depend on the operational conditions of the system, such as the characteristics of the coupling channel, the specifics of the remote task, and the computational capabilities of the manipulators.      

Adaptive passive control with varying time delay

This paper presents a passive control scheme for a force reflecting bilateral teleoperation system with a varying time communication delay. To improve the stability and performance of the system, the master and slave must be coupled dynamically via a transmission network through which the force and velocity are communicated bilaterally. However, the time delay caused by various factors, such as the transmission distance, network congestion, and communication bandwidth, is a long-standing impediment to bilateral control that can destabilize the system. In this study, we investigated how a varying time delay affects the stability of a teleoperation system. A new optimal adaptive approach based on a passive control scheme was designed bilaterally for both the master and slave sites. Extra variables were transmitted together with the wave variables in the scattering system. The proposed scheme achieved both passive control, and an acceptable tracking performance. The tracking performance was demonstrated using a computer simulation of varying time delays in a bilateral teleoperation system.     

大时延网络控制系统的研究方法与最新动态

近年来,网络控制系统得到越来越多的关注,其主要挑战之一在于控制环中的网络时延对其影响;网络时延会降低网络控制系统的性能,甚至使系统不稳定;目前,大多数学者只研究了网络时延小于采样周期时对控制系统的影响,而网络控制系统中的大时延更加复杂,同时也更加难以处理;文章论述了带有大时延的网络控制系统的现有的研究方法。并指出这种问题的其它可能的研究方法。     

多包传输网络控制系统的对象建模

由于将通讯网络的引入,不可避免地引起传输延时。网络传输延时的存在使网络控制系统的分析和设计更加复杂和困难,尤其是多包传输的网络控制系统。在分析网络多包传输原因的基础上,研究了多包传输网络控制系统的对象建模。系统中传感器采用时间驱动的方式,控制器和执行器采用事件驱动的方式。在考虑系统噪声和网络诱导延时大于一个采样周期的情况下,给出了多包传输的网络控制系统模型。此模型可以用来分析系统的性能。     

Tracking control for sampled‐data systems with uncertain time‐varying sampling intervals and delays

In this paper, a solution to the approximate tracking problem of sampled‐data systems with uncertain, time‐varying sampling intervals and delays is presented. Such time‐varying sampling intervals and delays can typically occur in the field of networked control systems. The uncertain, time‐varying sampling and network delays cause inexact feedforward, which induces a perturbation on the tracking error dynamics, for which a model is presented in this paper. Sufficient conditions for the input‐to‐state stability (ISS) of the tracking error dynamics with respect to this perturbation are given. Hereto, two analysis approaches are developed: a discrete‐time approach and an approach in terms of delay impulsive differential equations. These ISS results provide bounds on the steady‐state tracking error as a function of the plant properties, the control design and the network properties. Moreover, it is shown that feedforward preview can significantly improve the tracking performance and an online extremum seeking (nonlinear programming) algorithm is proposed to online estimate the optimal preview time. The results are illustrated on a mechanical motion control example showing the effectiveness of the proposed strategy and providing insight into the differences and commonalities between the two analysis approaches. Copyright © 2009 John Wiley & Sons, Ltd.     

An analytical approach to improving due-date and lead-time dynamics in production systems

A deterioration of due-date reliability is often attributed by planners to external causes rather than to their own planning behavior. Particularly, planners tend to underestimate the effects of time delays, and may not sufficiently take control actions into account that have been initiated but are not yet demonstrating any effects. Unfavorable dynamic behavior can result if planners react inappropriately to short-term decreases in due-date reliability and, for example, use their intuition to adjust planned lead times. A better understanding is needed of the impact of time delays and lead-time-related adjustments on resulting system behavior and of how often plans and associated work releases should be adjusted in practice.In this paper, two planning and control approaches are modeled and analyzed: First, a production system is modeled in which planned lead times and work input are adjusted periodically if the average lead time deviates from the planned lead time. Second, a production system is modeled in which regulation of lead time towards a planned lead time is accomplished by adjusting the work input. For both approaches, discrete (z-transform) equations are obtained that allow trends in dynamic behavior to be characterized as a function of delays in obtaining production information, and delays in making lead time adjustment decisions and implementing them. Industrial data from a steel-producing company are used to illustrate the potential effects of time delays and of averaging of lead time data, as well as to illustrate how analytical results can be used to guide selection of the adjustment period and of lead time regulation parameters. The analytical approach presented here can be used as a tool for quantifying and guiding improvements in the performance, the robustness, and the agility of production systems. This is of particular interest with respect to cyber-physical technologies such as autonomous data collection and embedded models that present significant future opportunities for reducing delays in decision making and decision implementation.     

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。     

Adaptive finite‐time control for bilateral teleoperation systems with jittering time delays

In this paper, we present a robust adaptive control algorithm for a class of bilateral teleoperation systems with system uncertainties and jittering time delays. The remarkable feature of jittering delays is that time delays change sharply and randomly. Conventional controllers would fail because jittering time delays introduce serious chattering. To address the jittering issue, a novel jittering‐free scheme is developed by relaxing and extending the frequently used constant upper bound. Moreover, an adaptive law was incorporated with the Chebyshev neural network to deal with the system uncertainties. To obtain finite‐time synchronization performance, a fast terminal sliding mode controller is proposed through the technique of “adding a power integrator.” With the proposed control scheme, the robust finite‐time convergence performance is guaranteed. The settling time can be further calculated with the controller parameters. The simulation and experiment results have demonstrated the effectiveness of the proposed method.     

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.