基于模糊预测的网络控制系统研究概述

从分析网络控制系统(NCS)的基本问题入手，探讨了基于模糊和预测控制思想解决网络延时、网络拥塞、队列管理等NCS问题的途径和方法。通过对新型网络控制算法的分析，指出将模糊和预测控制技术有机结合是解决NCS问题的有效方法之一，并给出了几个有价值的研究方向。     

Optimal codesign of industrial networked control systems with state‐dependent correlated fading channels

This paper examines a codesign problem in industrial networked control systems (NCS) whereby physical systems are controlled over wireless fading channels. The considered wireless channels are assumed to be stochastically dependent on the physical states of moving machineries in the industrial working space. In this paper, the moving machineries are modeled as Markov decision processes whereas the characteristics of the correlated fading channels are modeled as a binary random process whose probability measure depends on both the physical states of moving machineries and the transmission power of communication channels. Under such a state‐dependent fading channel model, sufficient conditions to ensure the stochastic safety of the NCS are first derived. Using the derived safety conditions, a codesign problem is then formulated as a constrained joint optimization problem that seeks for optimal control and transmission power policies which simultaneously minimize an infinite time cost on both communication resource and control effort. This paper shows that such optimal policies can be obtained in a computationally efficient manner using convex programming methods. Simulation results of an autonomous forklift truck and a networked DC motor system are presented to illustrate the advantage and efficacy of the proposed codesign framework for industrial NCS.     

Try-once-discard scheduling for stochastic networked control systems

In practical networked control systems (NCS), such as smart grids, cooperative robotics, and sensor networks, often multiple control applications share a communication infrastructure, requiring a smart and efficient scheduling mechanism to coordinate the access to the capacity-limited communication medium. In this article we consider the problem of event-based scheduling design for NCSs consisting of multiple control loops over a shared communication medium. We extend the notion of Try-Once-Discard (TOD), which is one of the basic deterministic event-based scheduling protocols for resource constrained NCSs, to the case of multiple stochastic control systems coupled via a shared communication medium subject to capacity limitation and stochastic packet delivery failure. Showing that the overall network-induced error is a homogeneous Markov chain in our stochastic set-up, we first study stability properties of such networked systems under the TOD scheduling scheme employing the concepts of stochastic stability. Then, we derive sufficient stability conditions under the TOD rule assuming that the communication channel is not ideal, i.e. a scheduled data packet for transmission might be lost in the communication channel with a non-zero probability. Furthermore, we derive analytic performance bounds by finding uniform upper-bounds for an average quadratic cost function. The numerical simulations are performed for variety of system parameters and NCS set-ups to strengthen our stability claim as well as illustrating performance bounds. Additionally, we show that the TOD scheduling rule outperforms the conventional time-triggered, and uniform and non-uniform random channel access arbitration mechanisms, in terms of efficient coordination of channel access in stochastic NCSs.     

一类网络控制系统的建模及分析

网络控制系统由于将通信网络引入控制系统的闭环反馈中,使得对其的分析、仿真和设计非常复杂。作为这些工作的基础,对网络控制系统如何建模以及建立合适的模型,意义尤显重要。在给出一定合理假设的条件下,对通信网络只存在于传感器和控制器之间的一类网络控制系统结构进行了分析,建立了其适当的数学模型。考虑到网络控制系统中通信网络的存在会导致多数据包传输的情况,因此在给出模型的基础上,又建立了多数据包传输的网络控制系统模型,并做了分析。     

Modelling and robust stability of networked control systems with packet reordering and long delay

In this article, modelling and robust stability of networked control systems (NCS) are discussed. Considering the existence of packet reordering and network-induced delay, a new mathematical model of NCS whose network-induced delay is longer than one sampling period is obtained, which can fully describe packet reordering and effectively eliminate the impact of packet reordering on the performance of NCS such that the newest control input can be executed by the actuator. Based on this model, the time-varying NCS is converted into an uncertain discrete linear system with multi-step delay in terms of matrix theory. Furthermore, a sufficient condition for robust stability of NCS is presented. Linear matrix inequality approach has been employed to solve the controller design problems. Numerical examples are compared with previous schemes to demonstrate the effectiveness of the proposed method.     

网络化控制系统中状态估计策略的进展

在网络化控制系统(Networked Control Systems,简记为NCSs)中,由于网络的介入使控制系统的规模和复杂性显著增加,且产生了各种新问题,为了使控制更加容易,需要设计合理的估计策略.主要从控制和通信2个角度出发,集中考虑了在量化影响、时延与丢包、不确定性等通信受限因素下状态估计策略的研究与进展.一直以来,状态估计都是诸如过程监控、故障诊断等控制领域中不可缺少的重要部分,当前已成为网络化控制系统研究的热点和准点,为抵消网络环境不确定性对闭环系统性能的影响,设计最优的状态估计策略必将成为不可缺少的因素之一.     

存在通信约束和时延的多输入多输出网络控制系统镇定研究

讨论了一类存在通信约束和时延的多输入多输出网络控制系统（NCS）的建模和控制问题.该NCS具有多个传感器和执行器，由于网络通信受限,在同一时刻只能允许部分传感器和执行器访问网络.传感器和执行器访问网络的过程可以用两个马尔可夫链来描述,并且在假设传感器—控制器时延和控制器—执行器时延均为短时延的情况下,将整个闭环NCS建模成一个具有两个模式的马尔可夫切换系统.基于LMI技术和李亚普诺夫方法,给出了闭环NCS随机稳定的充分条件,并给出了状态反馈控制器的设计方法.最后的数值算例验证了所提方法的有效性.     

Fault detection of networked control systems with limited communication

Fault detection (FD) of networked control systems (NCS) with limited communication is addressed in this article. In periodic communication sequence-based NCS, at each time instant only parts of the actuators and sensors are allowed to communicate with the central FD system, which leads to incomplete plant information at the central station. In this article, a parity space based multi-solution FD scheme is proposed based on different information structures of the incomplete plant information. In this multi-solution scheme, each solution is an independent residual generator and has different properties. It is proved that there is a tradeoff between fast FD and detection performance, i.e. the solution with a smaller FD delay has a poorer fault sensitivity and thus a larger miss detection rate, whereas the one with a higher fault sensitivity has a larger FD delay. The FD scheme can be realised by diagnostic observers as well, which have more design freedom. Simulation results are also given to illustrate the results obtained.     

基于网络控制系统的水下自主航行器制导系统结构

在现代控制系统中,网络控制系统可以用最小成本实现柔性系统,该柔性系统可以完成包括功能可重新配置的许多任务;网络控制系统采用公用的总线结构,使得系统具有更加有效的灵活功能、更好的资源共享、降低系统的维护成本,网络控制系统的最大问题是由于网络而产生的时延和数据包的丢失;研究了基于网络控制原理的水下自主航行器制导系统,详细分析了水下自主航行器网络控制系统的稳定性问题和基于时间触发的TTCAN高层协议;论文旨在通过对水下自主航行器网络控制系统结构的研究,指出其结构的意义和进一步的研究领域.     

基于同态加密的线性系统求解方案

在科学计算、统计分析以及机器学习领域,许多实际问题都可以归结到线性系统Ax=b的求解,如最小二乘估计和机器学习中的回归分析等.而实际中用于计算的数据往往由不同用户拥有且包含用户的敏感信息.当不同的数据拥有者想在合作求解一个模型的同时保护数据的隐私,同态加密可以作为解决方法之一.针对两个用户参与的场景,基于Cheon等提...     

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.     

Stabilization of linear discrete‐time networked control systems via protocol and controller co‐design

This paper investigates the stabilization problem for networked control systems (NCSs) with communication constraint and packet loss. The communication constraint considered is that only one network node is allowed to access a shared communication channel during one time‐slot, and a feedback control is performed with only partially available measurements and control inputs. By taking random packet loss into consideration, a stochastic switched system model is presented to describe the NCS. A sufficient condition is derived for the NCS to be mean‐square exponentially stable, and it is shown that the system performance specified by the exponential decay rate critically depends on the network accessing rates (NARs) of the network nodes and the packet loss probability. The state feedback controller and scheduling protocol, which allocates the NARs, are co‐designed such that the NCS achieves a minimal decay rate. Finally, an illustrative example is given to show the effectiveness of the proposed design approach. Copyright © 2014 John Wiley & Sons, Ltd.     

Signcryption with fast online signing and short signcryptext for secure and private mobile communication

Signcryption scheme is one of the useful tools for secure communication where authenticity and confidentiality are simultaneously required.Now,mobile devices are more and more widely used for communication,and thus it is desirable to design a scheme suitable to mobile applications.In this paper,we propose a signcryption scheme which is efficient enough to be implemented on mobile devices.In our scheme,we need only one multiplication in an online phase,and thus a signcryptor can generate a signcryptext very efficiently in the online phase.Moreover,the size of signcryptext is very short compared with exsiting schemes,and thus our scheme is very efficient in terms of communication overhead.The security of our signcryption scheme is proven in the random oracle model.     

Stabilizing bit-rates in networked control systems with decentralized event-triggered communication

In a decentralized event-triggered networked control system (NCS), an agent samples and transmits its local state information to the controller when some local event occurs. Such event-triggered NCSs were expected to be more efficient than traditional periodically sampled system in terms of communication channel usage. This paper studies the stability of decentralized event-triggered NCS in the presence of quantization and delays. We point out some potential issues in decentralized event-triggered design and propose an alternative decentralized event with a linear-affine threshold, which avoids infinitely fast data transmission. Conditions on quantizer and communication channel are derived, which, when satisfied, can guarantee stability of the resulting NCS. Based on these conditions, finite stabilizing bit-rates are provided.     

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.     

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.     

The design of distributed control computer systems

The top-down approach in the design of Distributed Control Computer Systems, DCCS, is presented. The starting point of the study is three statements: (i) the design approach should be production process control oriented; (ii) for real time process control applications, computer networks require an efficient communication subsystem, the most important features of which are high reliability and short message transmission times and (iii) recent research has shown that the tools and methodologies used in both computing and control should be complementary to each other in order to solve some of the distributed control computer system/distributed computer control system design problems. The paper contains the design problems of distributed control computer systems, the presentation of the methods and tools for the study and design of the DCCS, the top-down approach in the design of the DCCS, and examples of two design stages.     

一类线性网络控制系统鲁棒L1控制

研究一类网络控制系统(NCS)的L1控制问题.针对一类具有时延和丢包的网络控制系统,将其建模为线性时变时延系统,利用Lyapunov稳定性理论和线性矩阵不等式方法建立具有鲁棒L1性能约束的状态反馈控制器.首先给出闭环系统渐近稳定且具有峰—峰值性能约束的充分条件,然后给出网络控制系统状态反馈控制器L1控制率的设计方法,最...     

Output Feedback Stabilization of Networked Control Systems With Packet Dropouts

In this paper, we discuss the modeling and control of a class of networked control systems (NCSs) with packet dropouts. For the cases that there may be packet dropouts in both the backward and the forward channels in the communication network, and that the network-induced delays are shorter than one sampling period, the closed-loop NCS is modeled as a discrete-time switched system with four subsystems. By using the asynchronous dynamical systems approach and the average dwell-time method, sufficient conditions for the exponential stability of the closed-loop NCS are presented in terms of nonlinear matrix inequalities, and the relation between the packet dropout rate and the stability of the closed-loop NCS is explicitly established. A procedure involving an iterative algorithm is proposed to design the observer-based output feedback controllers. Lastly, an illustrative example is given to demonstrate the effectiveness of the proposed results.     

网络化控制系统的研究现状与展望

随着网络技术的发展,网络化控制系统日益成为人们关注的课题,特别是目前工业以太网所取得的进展引起人们广泛兴趣。介绍了网络化控制系统的发展过程,在综述网络化控制系统研究现状的基础上,对网络化控制系统的建模、状态估计、信息时延、调度算法、通信约束等方面进行了深入分析,并对其中的建模、网络信息调度的最优化、网络环境下控制理论研究、应用研究等方面的未来发展作了展望。