Fault-tolerant control system of flexible arm for sensor fault by using reaction force observer

In recent years, control system reliability has received much attention with increase of situations where computer-controlled systems such as robot control systems are used. In order to improve reliability, control systems need to have abilities to detect a fault (fault detection) and to maintain the stability and the control performance (fault tolerance). In this paper, we address the vibration suppression control of a one-link flexible arm robot. Vibration suppression is realized by an additional feedback of a strain gauge sensor attached to the arm besides motor position. However, a sensor fault (e.g., disconnection) may degrade the control performance and make the control system unstable at its worst. In this paper, we propose a fault-tolerant control system for strain gauge sensor fault. The proposed control system estimates a strain gauge sensor signal based on the reaction force observer and detects the fault by monitoring the estimation error. After fault detection, the proposed control system exchanges the faulty sensor signal for the estimated one and switches to a fault-mode controller so as to maintain the stability and the control performance. We apply the proposed control system to the vibration suppression control system of a one-link flexible arm robot and confirm the effectiveness of the proposed control system by some experiments.     

Robust Fault Estimation and Accommodation for a Class of T–S Fuzzy Systems with Local Nonlinear Models

This paper focuses on the problems of fault estimation and accommodation for a class of T–S fuzzy systems with local nonlinear models and having an external disturbance and sensor and actuator faults, simultaneously. A fuzzy robust fault estimation observer is designed to estimate the system state and sensor and actuator faults. Compared with existing results, the observer not only is robust to the disturbance but also has a wider application range and more freedom for design. To compensate for the effect of faults and to stabilize the closed-loop system, an observer-based fault-tolerant controller is proposed. The separate design of the observer and controller avoids coupling between them. Finally, a simulation is conducted to demonstrate the effectiveness of the proposed method.     

Fault-Tolerant Control for Markovian Jump Delay Systems with an Adaptive Observer Approach

This paper investigates the problem of fault estimation and fault-tolerant control for a class of Markovian jump systems with mode-dependent interval time-varying delay and Lipschitz nonlinearities. In this paper, a new adaptive fault observer is designed to solve the problem of fault estimation. The proposed observer can estimate the states and faults simultaneously, whether faults are of time-varying or constant characterization. Based on the fault estimation, a fault-tolerant controller is designed to stabilize the closed-loop system. Sufficient conditions for the existence of the observer gain and fault-tolerant controller gain are got by a set of linear matrix inequalities. Finally, a numerical example is presented to illustrate the effectiveness of the proposed fault-tolerant control method.     

A fault-tolerant strategy based on SMC for current-controlled converters

The sliding mode control (SMC) is used to control variable structure systems such as power electronics converters. This paper presents a fault-tolerant strategy based on the SMC for current-controlled AC–DC converters. The proposed SMC is based on three sliding surfaces for the three legs of the AC–DC converter. Two sliding surfaces are assigned to control the phase currents since the input three-phase currents are balanced. Hence, the third sliding surface is considered as an extra degree of freedom which is utilised to control the neutral voltage. This action is utilised to enhance the performance of the converter during open-switch faults. The proposed fault-tolerant strategy is based on allocating the sliding surface of the faulty leg to control the neutral voltage. Consequently, the current waveform is improved. The behaviour of the current-controlled converter during different types of open-switch faults is analysed. Double switch faults include three cases: two upper switch fault; upper and lower switch fault at different legs; and two switches of the same leg. The dynamic performance of the proposed system is evaluated during healthy and open-switch fault operations. Simulation results exhibit the various merits of the proposed SMC-based fault-tolerant strategy.     

A combined decision fusion and channel coding scheme for distributed fault-tolerant classification in wireless sensor networks

In this paper, we consider the distributed classification problem in wireless sensor networks. Local decisions made by local sensors, possibly in the presence of faults, are transmitted to a fusion center through fading channels. Classification performance could be degraded due to the errors caused by both sensor faults and fading channels. Integrating channel decoding into the distributed fault-tolerant classification fusion algorithm, we obtain a new fusion rule that combines both soft-decision decoding and local decision rules without introducing any redundancy. The soft decoding scheme is utilized to combat channel fading, while the distributed classification fusion structure using error correcting codes provides good sensor fault-tolerance capability. Asymptotic performance of the proposed approach is also investigated. Performance evaluation of the proposed approach with both sensor faults and fading channel impairments is carried out. These results show that the proposed approach outperforms the system employing the MAP fusion rule designed without regard to sensor faults and the multiclass equal gain combining fusion rule     

Adaptive Dynamic Sliding Mode Control for Near Space Vehicles Under Actuator Faults

A novel adaptive dynamic sliding mode (ADSM) fault-tolerant control (FTC) methodology is developed for near space vehicle attitude control systems with actuator faults in this paper. The proposed ADSM approach combines dynamic sliding mode with adaptive control strategies that can make the systems stable and accurately track the desired signals in the presence of external disturbances, model parameter uncertainties, and even actuator faults. Firstly, the attitude dynamic model of X-33 and its faulty model are introduced, then the ADSM control and fault-tolerant control laws are designed for outer-loop and inner-loop, respectively. Finally, in comparison with one existing approach, the simulation results are provided to show the effectiveness of the proposed FTC scheme.     

Robust and fault-tolerant linear parameter-varying control of wind turbines

High performance and reliability are required for wind turbines to be competitive within the energy market. To capture their nonlinear behavior, wind turbines are often modeled using parameter-varying models. In this paper we design and compare multiple linear parameter-varying (LPV) controllers, designed using a proposed method that allows the inclusion of both faults and uncertainties in the LPV controller design. We specifically consider a 4.8 MW, variable-speed, variable-pitch wind turbine model with a fault in the pitch system.We propose the design of a nominal controller (NC), handling the parameter variations along the nominal operating trajectory caused by nonlinear aerodynamics. To accommodate the fault in the pitch system, an active fault-tolerant controller (AFTC) and a passive fault-tolerant controller (PFTC) are designed. In addition to the nominal LPV controller, we also propose a robust controller (RC). This controller is able to take into account model uncertainties in the aerodynamic model.The controllers are based on output feedback and are scheduled on an estimated wind speed to manage the parameter-varying nature of the model. Furthermore, the AFTC relies on information from a fault diagnosis system.The optimization problems involved in designing the PFTC and RC are based on solving bilinear matrix inequalities (BMIs) instead of linear matrix inequalities (LMIs) due to unmeasured parameter variations. Consequently, they are more difficult to solve. The paper presents a procedure, where the BMIs are rewritten into two necessary LMI conditions, which are solved using a two-step procedure.Simulation results show the performance of the LPV controllers to be superior to that of a reference controller designed based on classical principles.     

State and Disturbance Estimator for Time-Delay Systems With Application to Fault Estimation and Signal Compensation

For a state-space time-delay system with linearly coupled input and output disturbances, a simultaneous state and disturbance estimation technique is developed. For a nonlinear state-space time-delay system with dependent input and output disturbances, a nonlinear estimator is also proposed to estimate system state and disturbance at the same time. The proposed estimator techniques are applied next to estimate system state and fault signal. Via actuator and/or sensor signal compensation, a simple and efficient fault-tolerant operation can be realized. In the developed design, no limitations and prior knowledge are required on the considered faults. Moreover, identical actuator and/or sensor switches and control gain reconstruction are not necessary. Therefore, the proposed estimation and fault-tolerant scheme is economical and convenient in practical applications. After that, the design techniques are extended to the case of systems with a class of uncoupled input and output faults. Examples and simulations given show excellent signal estimation and fault-tolerant performance.     

A fault-tolerant control architecture for induction motor drives in automotive applications

This paper describes a fault-tolerant control system for a high-performance induction motor drive that propels an electrical vehicle (EV) or hybrid electric vehicle (HEV). In the proposed control scheme, the developed system takes into account the controller transition smoothness in the event of sensor failure. Moreover, due to the EV or HEV requirements for sensorless operations, a practical sensorless control scheme is developed and used within the proposed fault-tolerant control system. This requires the presence of an adaptive flux observer. The speed estimator is based on the approximation of the magnetic characteristic slope of the induction motor to the mutual inductance value. Simulation results, in terms of speed and torque responses, show the effectiveness of the proposed approach.     

A Region-based Fault-Tolerant Routing Algorithmfor 2D Irregular Mesh Network-on-Chip

This paper presents a deadlock-free fault-tolerant routing algorithm for irregular mesh network-on-chips based on a region-based approach. In this approach, a set of rectangular faulty regions called faulty blocks is formed for faulty nodes and a detour path is defined for each faulty block to indicate how packets must detour thefaulty block. The most recent routing algorithm on this approach is Message-Route (Holsmark and Kumar J Inf Sci Eng 23:1649–1662, 2007) which does not have restrictions on the number of tolerable faulty nodes and its distribution. However, this algorithm has three crucial problems; (1) this algorithm fails to provide complete and deadlock-free routing, (2) many nonfaulty nodes are contained in faulty blocks and thus deactivated, and (3) complex routing functions are not feasible for hardware implementation. In this paper, we give a solution for each of the above three problems. We correct the errors of Message-Route to make it complete and deadlock-free. Then, we propose a deadlock-free fault-tolerant routing algorithm which can work under small-sized faulty blocks with a simple routing control. Experimental results show that the proposed algorithm significantly reduces the size of faulty blocks and improves communication latency for both random and cluster faults. Moreover, an FPGA implementation of the proposed algorithm is also discussed.     

Fault tolerance in multisensor networks

Replicating sensors is desirable, not only to tolerate sensor failures, but to increase the average accuracy of the ensemble of replicated sensors beyond that obtainable with a single sensor. Such replication is used in a multi-sensor environment or in a distributed-sensor network. Following Marzullo (1990), the authors have modeled a continuous valued sensor as an interval of real numbers containing the physical value of interest. Given n sensors of which at most f can suffer arbitrary failures, this paper presents an efficient O(n·log(n)) fault-tolerant algorithm (J/FTA) whose output is reliable (guaranteed to contain the correct value at all times) and is fairly accurate when f1/₂(n+1)). The output of J/FTA can be either a single-interval or a set-of-intervals, depending on the nature of the multi-sensor environment. J/FTA can be used not only to detect all possibly-faulty sensors but to detect all sets (combinations) of possibly-faulty sensors. This paper proves the following results pertaining to the possibly-faulty sensors identified by J/FTA: the number of sets each containing f possibly-faulty sensors is at most (f+1); the number of sets each containing f or fewer faulty sensors is at most (2f+1); and the number of possibly-faulty sensors identified by J/FTA is at most 2f. These results help to: narrow the search to detect faulty sensors; bound the number of intervals needed to construct an accurate and reliable abstract sensor; and identify at least one correct sensor     

A New Approach to Observer-Based Fault-Tolerant Controller Design for Takagi-Sugeno Fuzzy Systems with State Delay

This paper deals with the problem of active fault-tolerant control (FTC) for time-delay Takagi-Sugeno (T-S) fuzzy systems based on a fuzzy adaptive fault diagnosis observer (AFDO). A novel fuzzy fast adaptive fault estimation (FAFE) algorithm for T-S fuzzy models is proposed to enhance the performance of fault estimation, and sufficient conditions for the existence of the fault estimator are given in terms of linear matrix inequalities (LMIs). Using the obtained on-line fault estimation information, an observer-based fast active fault-tolerant controller is designed to compensate for the effect of faults by stabilizing the closed-loop system. Simulation results of a track trail system and a nonlinear numerical example are presented to illustrate the effectiveness of the proposed method.     

An improved fault detection crow search algorithm for wireless sensor network

In wireless sensor networks (WSNs), the collected data during monitoring environment can have some faulty data, and these faults can lead to the failure of a system. These faults may occur due to many factors such as environmental interference, low battery, and sensors aging etc. We need an efficient fault detection technique for preventing the failures of a WSN or an IoT system. To address this major issue, we have proposed a new nature-inspired approach for fault detection for WSNs called improved fault detection crow search algorithm (IFDCSA). IFDCSA is an improved version of the original crow search algorithm (CSA). The proposed algorithm first injects the faults into the datasets, and then the faults are classified using improved CSA and machine learning classifiers. The proposed work has been evaluated on the three real-world datasets, ie, Intel lab data, multihop labeled data, and SensorScope data, and predicts the faults with an average accuracy of 99.94%. The results of the proposed algorithm have been compared with the three different machine learning classifiers (random forest, k-nearest neighbors, and decision trees) and Zidi model. The proposed algorithm outperforms the other classifiers/models, thus generating higher accuracy and lower features without degrading the performance of the system. Index Terms—big data, crow search algorithm, IoT, machine learning, nature-inspired algorithm, wireless sensor network.     

Reaching Trusted Byzantine Agreement in a Cluster-Based Wireless Sensor Network

A wireless sensor network (WSN) consists of spatially distributed autonomous devices which use sensor nodes to monitor physical or environmental conditions cooperatively. Currently, WSNs are expected to be integrated into the internet of things (IoT), where sensor nodes join the internet dynamically and collaborate to accomplish their tasks. In the application of the IoT, WSNs can play an important role by collecting surrounding contextual and environmental information. However, ensuring a stable and reliable topology is an important issue with regard to WSNs. To cope with the influence of faulty components, it is essential to reach a common agreement in the presence of faults, before performing certain tasks. However, the Byzantine agreement (BA) problem is a fundamental issue in fault-tolerant distributed systems. To enhance the fault tolerance and reliability of the WSN, the BA problem in the cluster-based WSN (CWSN) is revisited in this study. The proposed protocol can achieve agreement on a common value among all functional nodes in a minimal number of message exchange rounds, and can tolerate a maximal number of allowable faulty components in the CWSN.     

Fault tolerant system based on IDDQ testing

Offline test is essential to ensure good manufacturing quality. However, for permanent or transient faults that occur during the use of the integrated circuit in an application, an online integrated test is needed as well. This procedure should ensure the detection and possibly the correction or the masking of these faults. This requirement of self-correction is sometimes necessary, especially in critical applications that require high security such as automotive, space or biomedical applications. We propose a fault-tolerant design for analogue and mixed-signal design complementary metal oxide (CMOS) circuits based on the quiescent current supply (IDDQ) testing. A defect can cause an increase in current consumption. IDDQ testing technique is based on the measurement of power supply current to distinguish between functional and failed circuits. The technique has been an effective testing method for detecting physical defects such as gate-oxide shorts, floating gates (open) and bridging defects in CMOS integrated circuits. An architecture called BICS (Built In Current Sensor) is used for monitoring the supply current (IDDQ) of the connected integrated circuit. If the measured current is not within the normal range, a defect is signalled and the system switches connection from the defective to a functional integrated circuit. The fault-tolerant technique is composed essentially by a double mirror built-in current sensor, allowing the detection of abnormal current consumption and blocks allowing the connection to redundant circuits, if a defect occurs. Spices simulations are performed to valid the proposed design.     

允许多处理机故障的实时任务容错调度算法

随着故障处理机个数增加,基于主/从版本技术的实时容错调度算法对处理机利用率迅速下降。论文提出了一种能够调度周期和非周期混合实时任务的容错调度算法,该算法允许多个处理机出现故障。把DS(Deferrable Server)算法扩展到多处理机系统,可在系统中设置多个DS服务器来处理非周期任务。当处理机出现故障时,通过在其他处理机上回卷执行故障任务,保证了系统的容错性能。实验结果表明,该算法能够使系统接收的所有实时任务满足截止期限并有效地减少了所需的处理机数。     

A scalable built-in self-recovery (BISR) VLSI architecture and design methodology for 2D-mesh based on-chip networks

On-Chip Networks (OCNs) have been proposed to solve the complex on-chip communication problems. In Very Deep-Submicron era, OCN will also be affected by faults in chip due to technologies shrinking. Many researches focused on fault detection and diagnosis in OCN systems. However, these approaches didn’t consider faulty OCN system recovery. This paper proposes a scalable built-in self-recovery (BISR) design methodology and corresponding Surrounding Test Ring (STR) architecture for 2D-mesh based OCNs to extend the work of diagnosis. The BISR design methodology consists of STR architecture generation, faulty system recovery, and system correctness maintenance. For an n×n mesh, STR architecture contains one controller and 4n test modules which are formed as a ring-like connection surrounding the OCN. Moreover, these test modules generate test patterns for fault diagnosis during warm-up time. According to these diagnosis results, the faulty system is recovered. Finally, this paper proposes a fault-tolerant routing algorithm, Through-Path Fault-Tolerant (TP-FT) routing, to maintain the correctness of this faulty system. In our experiments, the proposed approach can reduce 68.33∼79.31% unreachable packets and 4.86∼23.6% latency in comparison with traditional approach with 8.48∼13.3% area overhead.     

Advanced Fault-Tolerant Control of Induction-Motor Drives for EV/HEV Traction Applications: From Conventional to Modern and Intelligent Control Techniques

This paper describes active fault-tolerant control systems for a high-performance induction-motor drive that propels an electrical vehicle (EV) or a hybrid one (HEV). The proposed systems adaptively reorganize themselves in the event of sensor loss or sensor recovery to sustain the best control performance, given the complement of remaining sensors. Moreover, the developed systems take into account the controller-transition smoothness, in terms of speed and torque transients. The two proposed fault-tolerant control strategies have been simulated on a 4-kW induction-motor drive, and speed and torque responses have been carried to evaluate the consistency and the performance of the proposed approaches. Simulation results, in terms of speed and torque responses, show the global effectiveness of the proposed approaches, particularly the one based on modern and intelligent control techniques in terms of speed and torque smoothness     

Mobile-agent-based collaborative signal and information processing in sensor networks

In this paper, we develop an energy-efficient, fault-tolerant approach for collaborative signal and information processing (CSIP) among multiple sensor nodes using a mobile-agent-based computing model. In this model, instead of each sensor node sending local information to a processing center for integration, as is typical in client/server-based computing, the integration code is moved to the sensor nodes through mobile agents. The energy efficiency objective and the fault tolerance objective always conflict with each other and present unique challenge to the design of CSIP algorithms. In general, energy-efficient approaches try to limit the redundancy in the algorithm so that minimum amount of energy is required for fulfilling a certain task. On the other hand, redundancy is needed for providing fault tolerance since sensors might be faulty, malfunctioning, or even malicious. A balance has to be struck between these two objectives. We discuss the potential of mobile-agent-based collaborative processing in providing progressive accuracy while maintaining certain degree of fault tolerance. We evaluate its performance compared to the client/server-based collaboration from perspectives of energy consumption and execution time through both simulation and analytical study. Finally, we take collaborative target classification as an application example to show the effectiveness of the proposed approach.