Design on nonfragile fuzzy filter for nonlinear time-delay systems

This article studies the problem of nonfragile filtering for delayed nonlinear systems, which are represented by Takagi-Sugeno (T-S) affine-fuzzy model. By employing a reciprocally convex matrix inequality, auxiliary function-based summation inequalities, S-procedure, and some decoupled techniques, an improved fuzzy filter design method is proposed. In the design process, uncertainties in filter gains are taken into account, making a contribution to enhancing the robustness of the designed fuzzy filter. This is the first study to propose a nonfragile H_∞ filtering method for T-S affine-fuzzy systems with time delays. The obtained results enrich the theoretical research of nonlinear systems and provide theoretical guidance for practical applications. Three examples are given to reveal the merits and applicability of the new design techniques.     

Hybrid-triggered fault detection filter design for networked Takagi–Sugeno fuzzy systems subject to persistent heavy noise disturbance

In the network environment, the single time-triggered scheme wastes limited bandwidth resources due to all the sampled data are transmitted to the networks, and the single event-triggered scheme may increase system error because of ignoring factors such as changes in network utilization. To reduce the design conservatism, this paper is concerned with the hybrid-triggered L₁ fault detection filter design for a class of nonlinear networked control systems (NCSs) described by Takagi–Sugeno (T-S) fuzzy model. Taking the effects of time-triggered scheme and event-triggered scheme into consideration simultaneously, we construct a fuzzy fault detection system. New results on stability and L₁ performance are proposed for fuzzy fault detection system by exploiting the Lyapunov–Krasovskii functional and by means of the integral inequality method. Specially, attention is focused on the design of fault detection filter that guarantees a prescribed L₁ noise attenuation level . Finally, two examples are presented to demonstrate the effectiveness of the proposed method.     

Hybrid-driven-based fuzzy secure filtering for nonlinear parabolic partial differential equation systems with cyber attacks

The problem of hybrid-driven fuzzy filtering for nonlinear semi-linear parabolic partial differential equation systems with dual cyber attacks is investigated. First, a Takagi-Sugeno (T-S) fuzzy model is employed to reconstruct the original nonlinear systems. Second, a hybrid-driven mechanism is applied for filter design to balance the systems' performance and the limited network resource consumption under dual cyber attacks composed of deception and denial of service attacks. Based on the Lyapunov direct method, sufficient conditions to guarantee the stability of the augmented system are obtained, and the parameters of the designed filter are earned with explicit form. Finally, a simulation example with robust analysis and comparative analysis is provided to illustrate the effectiveness of the proposed method.     

Memory-based dynamic event-triggered control for networked interval type-2 fuzzy systems subject to DoS attacks

In this article, the memory-based dynamic event-triggered controller design issue is investigated for networked interval type-2 (IT2) fuzzy systems under non-periodic denial-of-service (DoS) attacks. For saving limited network bandwidth, a novel memory-based dynamic event-triggered mechanism (DETM) is proposed to schedule data communication. Unlike existing event-triggered generators, the developed memory-based DETM can utilize a series of newly released signals and further save network resources by introducing interval dynamic variables. Moreover, to improve design flexibility, an IT2 fuzzy controller with freely selectable fuzzy rule number and premise membership functions (MFs) is synthesized. Then, a new switched time-delay system with imperfectly matched MFs is established under the consideration of memory-based DETM and DoS attacks simultaneously. Besides, based on the property of MFs, the boundary information of membership grades and slack matrices are introduced in the stability analysis. Furthermore, by using a piecewise Lyapunov–Krasovskii method, membership-functions-dependent criteria are deduced to ensure the asymptotic stability of built fuzzy switched systems. Finally, the effectiveness of proposed control strategies is demonstrated by simulation examples.     

Fault detection for a class of network‐based nonlinear systems with communication constraints and random packet dropouts

This paper is dealt with the fault detection (FD) problem for a class of network‐based nonlinear systems with communication constraints and random packet dropouts. The plant is described by a Takagi–Sugeno fuzzy time‐delay model, it has multiple sensors and only one of them is actually communicated with the FD filter at each transmission instant, and the packet dropouts occur randomly. The goal is to design a FD filter such that, for all unknown inputs, control inputs, time delays and incomplete data conditions, the estimation error between the residual and ‘fault’ (or, more generally, the weighted fault) is minimized. By casting the addressed FD problem into an auxiliary H_∞ filtering problem of a stochastic switched fuzzy time‐delay system, a sufficient condition for the existence of the desired FD filter is established in terms of linear matrix inequalities. A numerical example is provided to illustrate the effectiveness and applicability of the proposed technique. Copyright © 2011 John Wiley & Sons, Ltd.     

Delay‐dependent robust L2–L∞ filtering of T‐S fuzzy systems with time‐varying delays

This paper considers the problem of robust delay‐dependent L₂–L_∞ filtering for a class of Takagi–Sugeno fuzzy systems with time‐varying delays. The purpose is to design a fuzzy filter such that both the robust stability and a prescribed L₂–L_∞ performance level of the filtering error system are guaranteed. A delay‐dependent sufficient condition for the solvability of the problem is obtained and a linear matrix inequality (LMI) approach is developed. A desired filter can be constructed by solving a set of LMIs. Copyright © 2009 John Wiley & Sons, Ltd.     

Robust H∞ filtering for uncertain Markovian jump systems with mode‐dependent distributed delays

This paper deals with the problem of robust H_∞ filter design for Markovian jump systems with norm‐bounded time‐varying parameter uncertainties and mode‐dependent distributed delays. Both the state and the measurement equations are assumed to be with distributed delays. Sufficient conditions for the existence of robust H_∞ filters are obtained. Via solving a set of linear matrix inequalities, a desired filter can be constructed. The developed theory is illustrated by a simulation example. Copyright © 2009 John Wiley & Sons, Ltd.     

Distributed stubborn-set-membership filtering with a dynamic event-based scheme: The Takagi-Sugeno fuzzy framework

The article develops a novel stubborn set-membership filtering with the dynamic event-triggered scheme for discrete-time nonlinear systems with the state-delays, unknown-but-bounded noises as well as abnormal measurements. First, in comparison with traditional event schemes, a dynamic event-triggered scheme with a time-varying auxiliary offset variable in the threshold is employed to schedule the access token with the purpose of mitigating the communication burden. A novel fuzzy stubborn filter in a distributed way is then constructed to obtain the ellipsoid set including the real state while constraining the direct influence of abnormal measurements, which could come from outliers or a malicious modification by attackers. An algorithm with the form of recursive linear matrix inequalities is presented to determine the desired ellipsoids as well as the distributed filter gains, where the operation of the algorithm do not depend on the global information of network topology. Finally, the validity of the proposed scheme is illustrated via an inverted pendulum system.     

Sampled-data filter design for large-scale interconnected systems with sensor fault and missing measurements

This article focuses on a decentralized sampled-data filter design for a class of large-scale interconnected systems. Precisely in the addressed system, the inevitable factors such as missing measurements, time-varying delays, randomly occurring uncertainties, and impulsive effects are taken into consideration. Also, we incorporated the gain perturbations and sensor faults in the proposed filter design. Furthermore, a new set of sufficient criterion has been derived by choosing an appropriate Lyapunov-Krasovskii functional that ensures the asymptotic stability of the resulting augmented filtering error system with the prescribed mixed H_∞ and passive performance index. Specifically, the corresponding filter gain matrices are derived by solving the developed sufficient criterion formulated in terms of linear matrix inequalities. The effectiveness of the proposed filter design technique are then exemplified by two numerical examples with simulations.     

Reliable H∞ filtering for discrete time‐delay Markovian jump systems with partly unknown transition probabilities

In this paper, the reliable H_∞ filtering problem is studied for a class of discrete nonlinear Markovian jump systems with sensor failures and time delays. The transition probabilities of the jumping process are assumed to be partly unknown. The failures of sensors are quantified by a variable taking values in a given interval. The time‐varying delay is unknown with given lower and upper bounds. The purpose of the addressed reliable H_∞ filtering problem is to design a mode‐dependent filter such that the filtering error dynamics is asymptotically mean‐square stable and also achieves a prescribed H_∞ performance level. By using a new Lyapunov–Krasovskii functional and delay‐partitioning technique, sufficient delay‐dependent conditions for the existence of such a filter are obtained. The filter gains are characterized in terms of the solution to a convex optimization problem that can be easily solved by using the semi‐definite programme method. A numerical example is provided to demonstrate the effectiveness of the proposed design approach. Copyright © 2011 John Wiley & Sons, Ltd.     

Adaptive sliding mode control for fuzzy singular systems with time delay and input nonlinearity

This paper addresses the sliding mode control problem for a class of uncertain Takagi‐Sugeno fuzzy singular systems with state delay and subject to input nonlinearity. Our purpose is focused on designing an adaptive sliding mode controller for such a complex system. First, a new fuzzy integral‐type sliding function is designed. Then, an adaptive sliding mode control scheme is established such that the resulting closed‐loop system is insensitive to all admissible uncertainties and satisfies the reaching condition. Moreover, delay‐dependent sufficient conditions are derived such that the admissibility and the L₂‐L_∞ performance requirement of the sliding mode dynamics can be guaranteed in the presence of time delays, external disturbances, and sector nonlinearity input. Finally, the validity and applicability of the proposed theory are illustrated by a numerical example.     

A unified filter for singular Markovian jump systems with mixed delays based on an extended free-matrix-based inequality approach

In this article, the problem of unified filters design including H_∞ , L₂ − L_∞ , passive, dissipative filters and their reduced-order ones is addressed for continuous-time singular Markovian jump systems with discrete and distributed delays. Unlike some existing works, the mixed delays can be fully captured by proposing an extended free-matrix-based integral inequality. By considering two cases of distributed delays, two novel criteria are presented to ensure the filtering error system to be stochastically admissible and extended dissipative. Some numerical examples are provided to illustrate the effectiveness of the unified filter design methods.     

Quantized H∞ filtering for state‐delayed systems with finite frequency specifications

This paper presents a novel design approach for the finite frequency (FF) H_∞ filtering problem for discrete‐time state‐delayed systems with quantized measurements. The system state and output are assumed affected by FF external noises. Attention is focused on the design of a stable filter that guarantees the stability and a prescribed ?₂ gain performance level for the filtering error system in the FF domain of input noises. Sufficient conditions for the solvability of this problem are developed by choosing an appropriate Lyapunov‐Krasovskii functional based on the delay partitioning technique and using the FF ?₂ gain definition combined with the generalized S‐procedure. Then, by means of Finsler's lemma, the derived conditions are linearized and additional slack variables are further introduced to more flexible result. Final filter design conditions are consequently established in terms of linear matrix inequalities in three different frequency ranges, ie, low‐, middle‐ and high‐frequency range. Finally, a simulation example is presented to illustrate the effectiveness and the merits of the proposed approach.     

Network‐based fault detection for discrete‐time state‐delay systems: A new measurement model

In this paper, the fault detection problem is studied for a class of discrete‐time networked systems with multiple state delays and unknown input. A new measurement model is proposed to account for both the random measurement delays and the stochastic data missing (package dropout) phenomenon, which are typically resulted from the limited capacity of the communication networks. At any time point, one of the following cases (random events) occurs: measurement missing case, no time‐delay case, one‐step delay case, two‐step delay case, …, q‐step delay case. The probabilistic switching between different cases is assumed to obey a homogeneous Markovian chain. We aim to design a fault detection filter such that, for all unknown input and incomplete measurements, the error between the residual and weighted faults is made as small as possible. The addressed fault detection problem is first converted into an auxiliary H_∞ filtering problem for a certain Markovian jumping system (MJS). Then, with the help of the bounded real lemma of MJSs, a sufficient condition for the existence of the desired fault detection filter is established in terms of a set of linear matrix inequalities (LMIs). A simulation example is provided to illustrate the effectiveness and applicability of the proposed techniques. Copyright © 2007 John Wiley & Sons, Ltd.     

Detecting deception attacks in cyber-physical linear parameter varying systems with packet loss

The increased connectivity of cyber-physical systems (CPS) to enterprise networks raises challenging security concerns. Detecting attacks on CPS is a vital step to improving their security. Most of the existing attack detectors are for CPS with linear dynamics. In this study, an investigation is made for designing a detector of deception attacks in a cyber-physical linear parameter varying (LPV) system in the presence of packet loss. A model-based attack detector is designed to detect deception attacks on output measurements, actuators, or schedule variables. With an unreliable network, the LPV attack detector enhances detection capacity and attenuates disturbances on the detector module to improve detection accuracy. During communication, packet loss results in network unreliability, which is modeled by the Bernoulli process. Stochastic stability is used to determine LPV attack detector parameters. A residual signal is built by comparing the detector's output and the actual sensor measurement and provides the deception attack's essential data. However, the packet loss causes some impulse signals in the residual signal, resulting in false alarms. Therefore, the detector module is equipped with a median filter to suppress packet loss's effect on evaluating the residual signal. Tests and validations of the proposed approach are performed on a two-tank system and a continuous stirred tank reactor. According to evaluation results conducted on two testbeds, the proposed method accurately detects deception attacks even when there is packet loss.     

Stabilization of controlled positive discrete‐time T‐S fuzzy systems by state feedback control

This paper deals with sufficient conditions of asymptotic stability and stabilization for nonlinear discrete‐time systems represented by a Takagi–Sugeno‐type fuzzy model whose state variables take only nonnegative values at all times t for any nonnegative initial state. This class of systems is called positive systems. The conditions of stabilizability are obtained with state feedback control. This work is based on multiple Lyapunov functions. The results are presented in linear matrix inequalities form. A real plant is studied to illustrate this technique. Copyright © 2010 John Wiley & Sons, Ltd.     

计及网络攻击影响的安全稳定控制系统风险评估方法

安全稳定控制系统(稳控系统)是保证电网可靠运行的重要防线,针对稳控系统的网络攻击会造成严重的物理后果。为了量化评估稳控系统遭受网络攻击的影响,解决现有风险评估方法未充分考虑网络攻击易发性的问题,文中提出一种计及网络攻击影响的稳控系统风险评估方法。文中首先分析了稳控系统的层次结构;然后,从攻击对象、攻击方式、攻击后果3个角度分析了稳控装置本体与稳控装置站间通信的网络攻击风险点;其次,基于模糊层次分析法对网络攻击易发性进行量化,并结合由Petri网建立的网络攻击防护单元模型建立针对稳控系统的网络攻击成功概率模型;最后,结合物理后果和攻击成功概率,对标准系统和实际系统进行风险评估,计算了正常运行和网络攻击2种情况下的风险值,验证了所提模型的有效性。     

H∞ filtering of discrete-time switched singular systems with time-varying delays

In this article, the analysis and design problems of H_∞ filtering for a class of discrete-time switched singular systems with time-varying delay under an arbitrary switching signal are investigated. The main attention is focused on the design of a linear mode-dependent filter guaranteeing the regularity, causality, and asymptotic stability of the resulting filtering error system with a prescribed H_∞ performance bound. By using a multiple Lyapunov-Krasovskii functional, and utilizing the linearization technique, novel sufficient conditions for the solvability of H_∞ problem are derived in terms of linear matrix inequalities. Solving that, the desired filter gains can be determined. Any model transformation of system, which often leads the large computational burden is involved. The free weighting matrix technique is introduced to provide additional degree of freedom, which improves the conservativeness of the developed method. Finally, numerical examples are given to demonstrate the effectiveness and the merit of the proposed approach and to compare the obtained results with some previous works in the literature.     

Investigation of the influence of network‐induced time delays on the activated sludge process behavior in the networked wastewater distributed systems

This paper examines the effects of networked induced time delays on the dissolved oxygen (DO) concentration in the activated sludge process (ASP) of a networked wastewater treatment plant (WWTP). This is a situation in which the controller and the wastewater plant are separated by wide geographical distance. This is a new type of WWTP control that allows two or more WWTPs to be controlled by a single controller placed in a remote location. The objective is to achieve flexibility of control and to reduce its cost. The communication medium between the controller and the WWTPs introduces communication drawbacks into the control system. The influences of network‐induced time delays [controller to actuator delay (τ_ca) and the sensor to controller delay (τ_sc)] over the behavior of the DO process controlled by both nonlinear linearizing and proportional‐integral controllers are investigated for constant and random delays. Investigation of the DO process under random delays was also performed with varying linear controller parameters [proportional gain (K_p) and integral time (T_I)]. Simulation results reveal that large network‐induced time delays in the closed‐loop DO process leads to depletion of the amount of oxygen available for microorganism metabolism, leading to inefficiency of the ASP. The critical delay during which the DO process becomes unstable due to communication drawbacks was also determined for constant and random delays. These values are found to vary depending on the delay type (constant/random), delay magnitude, and the linear controller parameters K_p and T_I. The results of this study would provide useful information for process performance and form the basis for the design of a robust networked control for the DO process capable of mitigating communication drawbacks in a networked wastewater distributed systems. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.