A Survey of Fault Diagnosis and Fault-Tolerant Techniques—Part I: Fault Diagnosis With Model-Based and Signal-Based Approaches <s> D. Fault Diagnosis for Networked and Distributed Systems <s> We introduce a novel control network protocol, try-once-discard (TOD), for multiple-input-multiple-output (MIMO) networked control systems (NCSs), and provide an analytic proof of global exponential stability for both the new protocol and the more commonly used (statically scheduled) access methods. Our approach is to first design the controller using established techniques and considering the network transparency, and then analyze the effect of the network on closed-loop system performance. When implemented, an NCS consists of multiple independent sensors and actuators competing for an access to the network, with no universal clock available to synchronize their actions. Since the nodes act asynchronously, we allow access to the network at anytime, but assume each access occurs before a prescribed deadline, known as the maximum allowable transfer interval. Only one node may access the network at a time. This communication constraint imposed by the network is the main focus of the paper. The performance of the new TOD protocol and the statically scheduled protocols are examined in simulations of an automotive gas turbine and an unstable batch reactor. <s> BIB001 </s> A Survey of Fault Diagnosis and Fault-Tolerant Techniques—Part I: Fault Diagnosis With Model-Based and Signal-Based Approaches <s> D. Fault Diagnosis for Networked and Distributed Systems <s> Abstract In this paper a new algorithm for discrete-time overlapping decentralized state estimation of large scale systems is proposed in the form of a multi-agent network based on a combination of local Kalman filters and a dynamic consensus strategy, assuming intermittent observations and communication faults. Conditions are derived for the algorithm to provide, under general conditions concerning the agent resources and the network topology, asymptotic stability in the sense of bounded mean-square estimation error. It is also demonstrated how the consensus gains can be chosen by minimizing the total steady-state mean-square estimation error. Numerical examples illustrate some properties of the proposed algorithm. <s> BIB002 </s> A Survey of Fault Diagnosis and Fault-Tolerant Techniques—Part I: Fault Diagnosis With Model-Based and Signal-Based Approaches <s> D. Fault Diagnosis for Networked and Distributed Systems <s> In this paper, the robust fault detection problem is investigated for a class of discrete-time networked systems with unknown input and multiple state delays. A novel measurement model is utilized to represent both the random measurement delays and the stochastic data missing phenomenon, which typically result from the limited capacity of the communication networks. The network status is assumed to vary in a Markovian fashion and its transition probability matrix is uncertain but resides in a known convex set of a polytopic type. The main purpose of this paper is to design a robust fault detection filter such that, for all unknown inputs, possible parameter uncertainties and incomplete measurements, the error between the residual signal and the fault signal is made as small as possible. By casting the addressed robust fault detection problem into an auxiliary robust H"~ filtering problem of a certain Markovian jumping system, a sufficient condition for the existence of the desired robust fault detection filter is established in terms of linear matrix inequalities. A numerical example is provided to illustrate the effectiveness and applicability of the proposed technique. <s> BIB003 </s> A Survey of Fault Diagnosis and Fault-Tolerant Techniques—Part I: Fault Diagnosis With Model-Based and Signal-Based Approaches <s> D. Fault Diagnosis for Networked and Distributed Systems <s> We propose a decentralized non-abrupt fault detection (DNaFD) scheme for leader-to-follower formations of unmanned airships. Non-abrupt faults are those that result in slow performance degradation and in undesirable drift, which can propagate from one vehicle to another, and therefore can adversely affect mission integrity, potentially destabilizing multivehicle formations, while being difficult to detect. As opposed to model-based fault detectors, which are typically insensitive to non-abrupt faults, the proposed signal-based DNaFD enables the detection of slowly degrading vehicle performance by performing a statistical test on heading angle trajectories. Here, the formation of unmanned airships is assumed stabilized by a distributed formation guidance scheme that uses neighboring vehicle information. High-fidelity, nonlinear 6-degrees-of-freedom (DOF) simulations of formation flying airships show that the proposed DNaFD scheme combined with a simple guidance adaptation technique enable detection of a class of non-abrupt faults and formation recovery, despite mild winds and parametric uncertainties, while preserving a requirement on formation geometry. <s> BIB004 </s> A Survey of Fault Diagnosis and Fault-Tolerant Techniques—Part I: Fault Diagnosis With Model-Based and Signal-Based Approaches <s> D. Fault Diagnosis for Networked and Distributed Systems <s> We investigate the design of a second order sliding mode observer for detecting anomalies in TCP networks. More precisely, based on a fluid model of TCP network, we aim at designing an observer, whose state variables reconstruct some external signals which perturb the nominal behavior of TCP. The proposed methodology is validated via NS-2 simulations. Finally, an experimental setup is proposed to show the effectiveness of our approach. <s> BIB005 </s> A Survey of Fault Diagnosis and Fault-Tolerant Techniques—Part I: Fault Diagnosis With Model-Based and Signal-Based Approaches <s> D. Fault Diagnosis for Networked and Distributed Systems <s> The penetration of distributed generation (DG) in distribution power system would affect the traditional fault current level and characteristics. Consequently, the traditional protection arrangements developed in distribution utilities are difficult in coordination. Also, the reclosing scheme would be affected. With the rapid developments in distribution system automation and communication technology, the protection coordination and reclosing scheme based on information exchange for distribution power system can be realized flexibly. This paper proposes a multi-agent based scheme for fault diagnosis in power distribution networks with distributed generators. The relay agents are located such that the distribution network is divided into several sections. The relay agents measure the bus currents at which they are located such that it can detect and classify the fault, and determine the fault location. The proposed technique uses the entropy of wavelet coefficients of the measured bus currents. The performance of the proposed protection scheme is tested through simulation of two systems. The first system is a benchmark medium voltage (MV) distribution system and the second system is practical 66 kV system of the city of Alexandria. <s> BIB006 </s> A Survey of Fault Diagnosis and Fault-Tolerant Techniques—Part I: Fault Diagnosis With Model-Based and Signal-Based Approaches <s> D. Fault Diagnosis for Networked and Distributed Systems <s> This paper investigates the leakage fault diagnosis problem for a physical Internet-based three-tank system (ITTS). Data from different devices locating at different places communicate with each other via Internet and, due to the limited bandwidth of communication channel, data suffer from delay and/or dropout phenomenon during the transmission. The resulting incomplete signals are utilized for the control and diagnosis purpose, giving rise to a networked control system (NCS). After linearization and discretization of the mathematical model of the three-tank system (TTS), the original nonlinear fault diagnosis problem is converted into a robust leakage fault detection and isolation problem for a linear system with uncertain parameters. The detection problem is then solved by using the robust H_ filter technique and the leakage faults of different tanks are isolated by using the idea of residual contributing degree (RCD). Experimental results are provided to show the effectiveness and applicability of the proposed techniques. <s> BIB007 </s> A Survey of Fault Diagnosis and Fault-Tolerant Techniques—Part I: Fault Diagnosis With Model-Based and Signal-Based Approaches <s> D. Fault Diagnosis for Networked and Distributed Systems <s> In this paper, the problems of fault detection, isolation, and estimation are considered for a class of discrete time-varying networked sensing systems with incomplete measurements. A unified measurement model is utilized to simultaneously characterize both the phenomena of multiple communication delays and data missing. A least-squares filter that minimizes the estimation variance is first designed for the addressed time-varying networked sensing systems, and then a novel residual matching (RM) approach is developed to isolate and estimate the fault once it is detected. The RM strategy is implemented via a series of Kalman filters, where each filter is designed to estimate the augmented signal composed of the system state and a specific fault signal. The design scheme for each filter is proposed in a recursive way. The main idea for the fault detection and estimation is that the Kalman filter with least residual value is regarded as corresponding to the right fault signal, and its estimation is utilized to represent the actual occurred fault. The effectiveness of our proposed method is demonstrated via simulation experiments on a real Internet-based three-tank system. <s> BIB008 </s> A Survey of Fault Diagnosis and Fault-Tolerant Techniques—Part I: Fault Diagnosis With Model-Based and Signal-Based Approaches <s> D. Fault Diagnosis for Networked and Distributed Systems <s> This paper addresses the problem of fault detection (FD) in nonlinear stable systems, which are monitored via communications networks. An FD based on the system data provided by the communications network is called networked fault detection (NFD) or over network FD in the literature. A residual signal is generated, which gives a satisfactory estimation of the fault. A sufficient condition is derived, which minimizes the estimation error in the presence of packet drops, quantization error, and unwanted exogenous inputs such as disturbance and noise. A linear matrix inequality is obtained for the design of the FD filter parameters. In order to produce appropriate fault alarms, two widely used residual signal evaluation methodologies, based on the signals' peak and average values, are presented and compared together. Finally, the effectiveness of the proposed NFD technique is extensively assessed by using an experimental testbed that was built for performance evaluation of such systems with the use of IEEE 802.15.4 wireless sensor networks (WSNs) technology. In particular, this paper describes the issue of floating point calculus when connecting the WSNs to the engineering design softwares, such as MATLAB, and a possible solution is presented. <s> BIB009 </s> A Survey of Fault Diagnosis and Fault-Tolerant Techniques—Part I: Fault Diagnosis With Model-Based and Signal-Based Approaches <s> D. Fault Diagnosis for Networked and Distributed Systems <s> Anomaly detection has been an active open problem in the networks community for several years. In this brief, we aim at detecting such abnormal signals by control theory techniques. Several classes of sliding mode observers are proposed for a fluid flow model of the transmission control protocol (TCP)/internet protocol network. Comparative simulations via network simulator NS-2 show the enhancement brought by a higher order sliding mode observer. The efficiency of this observer opens the way toward observing traffics with real TCP flow characteristics. To achieve this end, trace replay techniques for TCP traffic traces are presented. Finally, experiments lead to successful anomaly estimation under real traffic conditions. <s> BIB010 </s> A Survey of Fault Diagnosis and Fault-Tolerant Techniques—Part I: Fault Diagnosis With Model-Based and Signal-Based Approaches <s> D. Fault Diagnosis for Networked and Distributed Systems <s> This paper develops a filtering approach for distributed fault detection of a class of interconnected continuous-time nonlinear systems with modeling uncertainties, disturbances and measurement noise. A distributed fault detection scheme and the corresponding adaptive thresholds are designed based on filtering certain signals so that the effect of the measurement noise and of the disturbances is attenuated, allowing for the design of less conservative thresholds. A key novelty of the proposed work is that a general class of filters can be embedded into the design of the residual and threshold signals in a way that takes advantage of the filtering noise suppression properties. The analysis of the proposed distributed fault detection scheme shows that the derived thresholds guarantee that there are no false alarms and characterizes quantitatively the class of detectable faults. Further rigorous detectability analysis provides results regarding the magnitude of the detectable faults, an upper bound on the detection time and the relation of the detection time with respect to the order and pole locations of the filters used. Simulation results illustrate the proposed distributed fault filtering approach. <s> BIB011 </s> A Survey of Fault Diagnosis and Fault-Tolerant Techniques—Part I: Fault Diagnosis With Model-Based and Signal-Based Approaches <s> D. Fault Diagnosis for Networked and Distributed Systems <s> Monitoring the reliability of an industrial network has become more and more important due to the complexity of the networked systems and the costs associated with the system downtimes. Among the numerous factors that affect the reliability of networks, intermittent connection (IC), a situation where communication lines suffer from short random disconnections because of various reasons, is a frequent and hard troubleshooting problem. It leads to both quality drawback issues and threat to personal safety. Hence, early detection of ICs is a necessary and challenging task for maintenance of the networked systems. In this paper, a novel model-based IC detection method is proposed based on a generalized zero-inflated Poisson model. A maximum-likelihood-estimation-based model parameter estimation method and optimization of the ranked probability control chart are applied for monitoring the IC events. Characteristics including minimum sampling size and confidence interval of estimated parameters are also studied for model interpretation and IC error detection. A test bed is constructed, and a computer-controlled emulation system is developed. A case study is conducted to demonstrate the modeling and control chart design procedure, as well as the effectiveness of the proposed methodology on IC error detection and monitoring. <s> BIB012 </s> A Survey of Fault Diagnosis and Fault-Tolerant Techniques—Part I: Fault Diagnosis With Model-Based and Signal-Based Approaches <s> D. Fault Diagnosis for Networked and Distributed Systems <s> A controller area network (CAN)-based distributed system may develop faults at run-time. These faults need to be detected and diagnosed. This paper proposes a new algorithm named adaptive fault diagnosis algorithm for CAN (AFDCAN). It is designed for low-cost resource-constrained distributed embedded systems. The proposed algorithm detects all faulty nodes on the CAN. It allows new node entry and reentry of repaired faulty nodes during a diagnostic cycle. AFDCAN is found to provide high fault tolerance and to ensure reliable communication. It uses single-channel communication deploying the bus-based standard CAN protocol. A hardware implementation of the proposed algorithm has been used to obtain the results. The results show that the proposed algorithm diagnoses all faults in the system. Analysis of the proposed algorithm proves that the algorithm uses a definite and bounded number of testing rounds and messages to complete one diagnostic cycle. <s> BIB013 </s> A Survey of Fault Diagnosis and Fault-Tolerant Techniques—Part I: Fault Diagnosis With Model-Based and Signal-Based Approaches <s> D. Fault Diagnosis for Networked and Distributed Systems <s> In this technical note, a robust fault estimation method, based on sliding mode observers, is proposed for a collection of agents undertaking a shared task and exchanging only relative information over a communication network. Since the `system of systems' formed by the agents is not observable with respect to relative sensing information, by appropriate transformations and scalings of the inputs and outputs of the actual system, a meaningful observable subsystem is created. For this new subsystem, after modal decomposition based on the associated Laplacian, decoupled sliding mode observers, depending only on the individual node level dynamics of the network, can be created exploiting an existing design philosophy. These collectively form a centralized fault estimation scheme for the original system. <s> BIB014
The rapid developments in network technologies have much stimulated the real-time control and monitoring via communication channels, which is called networked control and monitoring, which have valuable advantages such as cost effectiveness, less weight and power requirements, easier installation and maintenance, and resources sharing BIB001 . It is noted that the introduction of limited-capacity network cables or wireless sensors into control and monitoring loops has unavoidably brought some unanticipated problems such as random communication delays, data dropout, and scheduling confusion, which make the network-based monitoring and fault diagnosis more challenging compared with conventional point-to-point control and monitoring systems. Therefore, in the network-based fault diagnosis, the residual or fault estimation error should be robust not only against modeling errors, process disturbance, and measurement noises but also against transmission delays, data dropouts, and incomplete measurements caused by the limit capacity of communication channels BIB007 . Recently, a variety of fault diagnosis techniques have been developed for various networked systems. For instance, fault detection filters were developed in BIB003 for systems subjected to communication delays and missing data, where the network status is assumed to vary in a Markovian fashion. In BIB008 , least square filters and Kalman filters were integrated for fault detection, isolation, and estimation for network sensing systems. In BIB009 , a networked-based fault diagnosis technique was addressed for nonlinear systems, which was assessed by an experimental test system with the use of IEEE 802.15.4 wireless sensor networks. In addition, it is also of interest to detect the anomaly of a communication network itself, which may affect the performance of network control systems. In order to monitor the guaranteed quality of service of the router and the whole topology, sliding mode observer techniques were employed in BIB005 and BIB010 for anomaly detection in the transmission control protocol. Very recently, model-based detection and monitoring approaches have been addressed in BIB012 and BIB013 for monitoring potential intermittent connections or faulty nodes for controller area networks. Complex industrial systems can be modeled as an interconnection of subsystems, and each subsystem has a decision marker (intelligent agent), which might have access to local measurements, subsystem models, local estimators/controllers, and constrained communication channels between the agent and its neighbors BIB002 . This kind of decentralized or distributed structure has become the mainstream in complex industrial processes owing to its less use of network resources, cost effectiveness, and convenience for expansion. On the other hand, real-time monitoring and fault diagnosis for distributed systems is much challenging due to the constrained information redundancy and limited communication capacity. A general idea of the distributed fault diagnosis is to design local estimators or fault detection filters by intelligent agents according to the local sensing and computing resources, and a consensus strategy is utilized to ensure the whole detection or estimation performance of all the agents in the network. Recent developments on distributed fault detection BIB011 and distributed fault estimation BIB014 have developed respectively by using adaptive thresholds and sliding modes techniques to improve the robustness against noises and modeling errors. Moreover, applications on unmanned airships BIB004 and power networks BIB006 are reported as well.