Fault-tolerant Mode Research Articles

Integrating workload balancing and fault tolerance in distributed stream processing system

Distributed Stream Processing Engine (DSPE) is designed for processing continuous streams so as to achieve the real-time performance with low latency guaranteed. To satisfy such requirement, the availability and efficiency are the main concern of the DSPE system, which can be achieved by a proper design of the fault tolerance module and the workload balancing module, respectively. However, the inherent characteristics of data streams, including persistence, dynamic and unpredictability, pose great challenges in satisfying both properties. As far as we know, most of the state-of-the-art DSPE systems take either fault tolerance or workload balancing as its single optimization goal, which in turn receives a higher resource overhead or longer recovery time. In this paper, we combine the fault tolerance and workload balancing mechanisms in the DSPE to reduce the overall resource consumption while keeping the system interactive, high-throughput, scalable and highly available. Based on our data-level replication strategy, our method can handle the dynamic data skewness and node failure scenario: during the distribution fluctuation of the incoming stream, we rebalance the workload by selectively inactivate the data in high-load nodes and activate their replicas on low-load nodes to minimize the migration overhead within the stateful operator; when a fault occurs in the process, the system activates the replicas of the data affected to ensure the correctness while keeping the workload balanced. Extensive experiments on various join workloads on both benchmark data and real data show our superior performance compared with baseline systems.

Investigation of a Fault-Tolerant Control Method for a Multiport Dual-Stator Doubly Salient Electromagnetic Machine Drive

A novel fault-tolerant inverter topology of the multiport dual-stator doubly salient electromagnetic machine (MDDSEM) drive is proposed in this paper for high reliability applications such as automotive and aerospace industries. The proposed topology adopts four diverter switches to reconnect the floating phase windings under the fault conditions and reconfigures the dual inverter to be a five-leg inverter; the output performance could be maintained after a single-phase open-circuit or short-circuit fault of the dual inverter. Compared with the traditional fault-tolerant method of the dual inverter for the MDDSEM, the lower cost and smaller volume of the proposed fault-tolerant system can be achieved. The operation principle and the optimized commutation method of the five-leg inverter for the MDDSEM are analyzed to eliminate the unexpected phase current drop so that the torque performance in the fault-tolerant mode could be improved. The effectiveness and feasibility of the proposed fault-tolerant topology and control strategies are verified by the simulation and experimental results of a 24/16-pole MDDSEM that includes both steady-state and dynamic processes with the standard angle control method and the advanced angle control method.

The Fractional Order PID Method with a Fault Tolerant Module for Road Feeling Control of Steer-by-Wire System

To improve the road feeling of the steer-by-wire (SBW) system, a fractional order PID (proportion-integral-derivative) method with a fault tolerant module is proposed in this paper. Firstly, the overall road feeling control strategy of the SBW system is introduced, and then the mathematical model of road feeling control is established. Secondly, a fractional order PID (FOPID) controller is designed to control torque of the road feeling motor. Furthermore, genetic algorithm (GA) is applied to tune the FOPID controller’s parameters. Thirdly, a fault tolerant module aiming at potential failures of the motor’s torque sensor is studied to improve the reliability of the system. Kalman Filter (KF) algorithm is utilized in the fault tolerant module so as to detect failures of the motor’s torque sensor, and then fault tolerant module reconfigures the motor’s torque estimated by KF as a substitute when the torque sensor fails. Finally, simulations based on MATLAB are performed with the proposed control strategy to identify its performance, and the results demonstrate that the proposed control method is feasible and accurate.

Fault diagnosis and its prediction in wireless sensor networks using regressional learning to achieve fault tolerance

SummaryDue to the wide range of critical applications and resource constraints, sensor node gives unexpected responses, which leads to various kind of faults in sensor node and failure in wireless sensor networks. Many research studies focus only on fault diagnosis, and comparatively limited studies have been conducted on fault diagnosis along with fault tolerance in sensor networks. This paper reports a complete study on both 2 aspects and presents a fault tolerance approach using regressional learning with fault diagnosis in wireless sensor networks. The proposed method diagnose the different types of faulty nodes such as hard permanent, soft permanent, intermittent, and transient faults with better detection accuracy. The proposed method follows a fault tolerance phase where faulty sensor node values would be predicted by using the data sensed by the fault free neighbors. The experimental evaluation of the fault tolerance module shows promising results with R2 of more than 0.99. For the periodic fault such as intermittent fault, the proposed method also predict the possible occurrence time and its duration of the faulty node, so that fault tolerance can be achieved at that particular time period for better performance of the network.

Fault-Tolerant Control of Medium-Voltage Modular Multilevel Converters With Minimum Performance Degradation Under Submodule Failures

As the state-of-the-art voltage-source topology, the modular multilevel converter (MMC) is attractive for various medium- or high-power applications. In MMC, reliability and uninterruptable operation are always seen as primary concerns, which requires the MMC can continue operating even though some of the submodules (SMs) are failed. In this paper, a novel fault-tolerant modulation and control strategy is proposed for MMC in medium voltage applications. Compared with previous works, the proposed strategy provides optimum performances under healthy conditions and minimum performance degradation after SM failures. During healthy conditions, the redundant SMs are fully utilized to decrease SM capacitor voltage for higher reliability and to reduce switching frequency for higher efficiency. While during fault-tolerant operation, by appropriate modification of the modulation and controllers, no extra healthy SMs need to be bypassed and the output voltage harmonics of MMC remain unchanged without causing voltage mismatches. Feasibility and effectiveness of the proposed strategy have been verified by simulations in MATLAB/Simulink software and experiments on a downscaled three-phase MMC prototype.

Fault-Tolerant Multilevel Topology Based on Three-Phase H-Bridge Inverters for Open-End Winding Induction Motor Drives

In this paper, a multilevel inverter based on three-phase H-bridge inverters for an open-end winding induction motor drive is presented and its fault-tolerance capability is investigated. The multilevel topology is obtained using three wye-connected three-phase H-bridge inverters to supply open-end winding induction motors. This topology has the ability to extend the maximum voltage applied to the motor windings up to two times the dc supply voltage of the three-phase inverters. For a given induction motor voltage, the topology allows the use of dc sources with a lower voltage rating. Consequently, faster power semiconductors can be used. This multilevel topology can be directly controlled by modifying known modulation concepts, such as sinusoidal pulse width modulation (PWM). In this study, two sinusoidal PWM modulation techniques will be implemented: the level-shifted carriers (phase disposition) and the phase-shifted modulator. Fault-tolerant operation under an open-switch fault without adding any extra components and without changing the modulation strategy is also proposed, adding fault-tolerant capability to the new topology. Experimental results of this multilevel inverter in normal operation and in fault tolerant mode are presented. The obtained results confirm the fault effectiveness of the proposed multilevel topology.

Suppression strategy for output unbalance of eight‐switch three‐phase inverter

The fluctuation of neutral-point potential (NPP) is an internal problem of three-level inverter. The fluctuation of NPP is investigated when the inverter, eight-switch three-phase inverter is working in fault tolerant mode. It is proved that the NPP fluctuation will cause output unbalance if the inverter is still controlled by the conventional space vector pulse-width modulation (SVPWM) strategy. Thus, a novel SVPWM considering NPP fluctuation is proposed to suppress the output unbalance. The effectiveness of the proposed method is demonstrated by the experimental results.

Two-way H∞ control method with a fault-tolerant module for steer-by-wire system

To improve the maneuverability, stability, and reliability of the steer-by-wire system, a two-way H∞ control method with a fault-tolerant module is proposed in this paper. First, a two-way H∞ control scheme is proposed. Two controllers are designed in this scheme: one is used as a feedback controller as a general practice to stabilize the system and detect the tracking error; the other is used as a feed forward controller to make the output of the system follow the driver’s steering intention rapidly and precisely. Second, a fault-tolerant module aiming at front wheel angle sensor which is an important feedback signal to the system is added to improve the reliability of the system. A revised Kalman filter is applied in the fault-tolerant module to reconfigure the front wheel angle as a reference value and a substitute when the sensor fails, thus replacing hardware redundancy by software redundancy in a cost-effective way. Lastly, simulations by Matlab/Simulink and CarSim software and hardware-in-the-loop experiments are conducted and effectiveness of the proposed control method is demonstrated by simulation and experimental results and numerical analyses.

Using Two Independent Channels With Gateway for FlexRay Static Segment Scheduling

The FlexRay bus is a communication standard used in the automotive industry. It offers a deterministic message transmission in the static segment following a time-triggered schedule. Even if its bandwidth is ten times higher than the bandwidth of CAN, its throughput limits are going to be reached in high-class car models soon. A solution that could postpone this problem is to use an efficient scheduling algorithm that exploits both channels of the FlexRay. The significant and often neglected feature that can theoretically double the bandwidth is the possibility to use two independent communication channels that can intercommunicate through the gateway. In this paper, we propose a heuristic algorithm that decomposes the scheduling problem to the ECU-to-channel assignment subproblem which decides which channel the ECUs (Electronic Control Units) should be connected to and the channel scheduling subproblem which creates static segment communication schedules for both channels. The algorithm is able to create a schedule for cases where channels are configured in the independent mode as well as in the fault-tolerant mode or in cases where just part of the signals are fault-tolerant. Finally, the algorithm is evaluated on real data and synthesized data, and the relation between the portion of fault-tolerant signals and the number of allocated slots is presented.

Fault-tolerant Mechanism for Cloud Storage System with Integrity Verification Mechanism

A self-adaption fault-tolerant mechanism based on access frequency (SFMAF) is proposed for the cloud storage platform, wherein this mechanism aims at adopting the approximate LRU (Least Recently Used) algorithm to maintain a file access frequency table in order to self-adaptively adjust the fault-tolerant mode. Specifically, the replica redundancy mechanism is adopted in SFMAF for the frequently accessed files and RS (Reed-Solomon) erasure code tolerant mechanism is adopted in SFMAF for the rarely accessed files. The experiment result shows: compared with the replica redundancy mechanism, SFMAF can reduce the transmission flow of the internal system data at the cost of increasing CPU and memory usage rates in an acceptable range, namely: the system storage space is reduced.

Independent Control of Two-PMSM Fed by Two SVPWM Inverters with Fault Tolerant Operation

This paper presents an implementation of anindependent control of two-mechanically coupled PermanentMagnet Synchronous Motor (PMSM) fed by two Space VectorPulse Width Modulation (SVPWM) inverters in a separate modeand in the event of failure one leg of one inverter, fault tolerantmode. In a fault tolerant mode, the two motors can operate in anindependent control strategy from one inverter with five legs tomaintain a constant output coupled torque. The Field OrientedControl (FOC) strategy is used to control the stator current of thetwo motors through two separate paths. Such application is usedin the field of a coupled torque produced by multi-motors such asin subway applications. The whole system is simulated in Matlab/Simulink and the simulated results show a stable and robustnessa system which can maintain a constant developed torque with avelocity reaches to the rated under fault tolerant operation.

English

Fault tolerance is a key factor of industrial computing systems design. But in practical terms, these systems, like every commercial product, are under great financial constraints and they have to remain in operational state as long as possible due to their commercial attractiveness. This work provides an analysis of the instantaneous failure rate of these systems at the end of their life-time period. On the basis of this analysis, we determine the effect of a critical increase in the system failure rate and the basic condition of its existence. The next step determines the maintenance scheduling which can help to avoid this effect and to extend the system life-time in fault-tolerant mode.

Rectifier Fault Diagnosis and Fault Tolerance of a Doubly Fed Brushless Starter Generator

This paper presents a rectifier fault diagnosis method with wavelet packet analysis to improve the fault tolerant four-phase doubly fed brushless starter generator (DFBLSG) system reliability. The system components and fault tolerant principle of the high reliable DFBLSG are given. And the common fault of the rectifier is analyzed. The process of wavelet packet transforms fault detection/identification algorithm is introduced in detail. The fault tolerant performance and output voltage experiments were done to gather the energy characteristics with a voltage sensor. The signal is analyzed with 5-layer wavelet packets, and the energy eigenvalue of each frequency band is obtained. Meanwhile, the energy-eigenvalue tolerance was introduced to improve the diagnostic accuracy. With the wavelet packet fault diagnosis, the fault tolerant four-phase DFBLSG can detect the usual open-circuit fault and operate in the fault tolerant mode if there is a fault. The results indicate that the fault analysis techniques in this paper are accurate and effective.

A real-time, practical sensor fault-tolerant module for robust EMG pattern recognition.

BackgroundUnreliability of surface EMG recordings over time is a challenge for applying the EMG pattern recognition (PR)-controlled prostheses in clinical practice. Our previous study proposed a sensor fault-tolerant module (SFTM) by utilizing redundant information in multiple EMG signals. The SFTM consists of multiple sensor fault detectors and a self-recovery mechanism that can identify anomaly in EMG signals and remove the recordings of the disturbed signals from the input of the pattern classifier to recover the PR performance. While the proposed SFTM has shown great promise, the previous design is impractical. A practical SFTM has to be fast enough, lightweight, automatic, and robust under different conditions with or without disturbances.MethodsThis paper presented a real-time, practical SFTM towards robust EMG PR. A novel fast LDA retraining algorithm and a fully automatic sensor fault detector based on outlier detection were developed, which allowed the SFTM to promptly detect disturbances and recover the PR performance immediately. These components of SFTM were then integrated with the EMG PR module and tested on five able-bodied subjects and a transradial amputee in real-time for classifying multiple hand and wrist motions under different conditions with different disturbance types and levels.ResultsThe proposed fast LDA retraining algorithm significantly shortened the retraining time from nearly 1 s to less than 4 ms when tested on the embedded system prototype, which demonstrated the feasibility of a nearly “zero-delay” SFTM that is imperceptible to the users. The results of the real-time tests suggested that the SFTM was able to handle different types of disturbances investigated in this study and significantly improve the classification performance when one or multiple EMG signals were disturbed. In addition, the SFTM could also maintain the system’s classification performance when there was no disturbance.ConclusionsThis paper presented a real-time, lightweight, and automatic SFTM, which paved the way for reliable and robust EMG PR for prosthesis control.

Control logic and strategy for emergency condition of piston type energy recovery device

Piston type energy recovery device (ERD) commonly depends upon the concerted actions of magnetic sensors and PLC controller to realize the energy recovery function. For ensuring operational stability and flexibility of the device, signal control mode is basically adopted in the standard PLC controller. However, as a typical emergency condition of the signal control mode, failure of the magnetic sensor may bring on function loss of the mode, which imperils the operational safety of the ERD and even the RO system. So in this paper, an optimized PLC control strategy with fault tolerance module is developed to resolve the possible control problem of piston-type ERD. The experimental results indicate that the optimized PLC control strategy can maintain reliable under simulated emergency condition of magnetic sensor failure.

Phase Open Fault Tolerant Control of High Reliability Doubly-Salient Wound-Field Machine

Doubly Salient Wound-Field Machine (DSWFM) can be employed on aeronautics starter-generator because it has good performance on both power generation and starting. To improve the system reliability, a three-phase four bridge legs converter which has fault tolerant capability is proposed to solve one phase open-circuit fault problem of the DSWFM. And the advantage of the proposed converter to the full-bridge converter fault-tolerant mode is analyzed. With the study of DSWFM theory and torque equation, a constant torque fault-tolerant strategy is proposed to keep the performance and reduce the torque ripple. The drive system after fault identification can be reconstructed by the proposed method, and the machine performance can recover quickly. Simulations confirm the feasibility of the proposed fault tolerant system.

A Fault-Tolerant Permanent-Magnet Traction Module for Subway Applications

A fault-tolerant permanent-magnet traction module is proposed for subway application, which has three different operation modes: normal, isolation, and fault-tolerant mode. In normal mode, 2 three-phase permanent-magnet synchronous machines (PMSMs) are controlled by 2 three-leg voltage-source inverters (VSIs), respectively. The proposed module can output maximum torque and reach the maximum velocity. When one leg fails, the corresponding PMSM is isolated from the fault VSI and the fault subway train operates in isolation mode, in which the traction effort is reduced but the maximum velocity can be maintained under light load. However, the fault subway train will stop if the load is heavy. To avoid the stop, the fault subway train is switched into fault-tolerant mode, in which the healthy VSI and fault VSI are reconfigured to 1 five-leg VSI by a fault-tolerant bridge. Due to lower phase-phase voltage apportionment ratio, the fault-tolerant mode is not used until the velocity is decreased to half of the maximum velocity. In fault-tolerant mode, the nonadjacent selection principle is proposed to prevent the common leg from overcurrent damage. The subway train equipped with the proposed module can maintain basic operation performances if any leg fails. The performances are analyzed and the effectiveness is verified by experimental results.

A Three-Phase Current Reconstruction Technique Using Single DC Current Sensor Based on TSPWM

Three-phase current reconstruction technique using dc current information in conventional two-level inverters can be used for the purpose of cost reduction and sensor fault tolerance. A novel phase current reconstruction scheme, with reduced immeasurable area and common mode voltage, is proposed in this paper. A tristate pulse-width modulation technique has been employed, in which three adjacent switching states are used to construct the reference voltage. The active switching states are arranged at the edge and the center of a PWM cycle. Fixed sampling and simultaneous three-phase currents can be easily achieved with very little hardware and software requirements. A detailed analysis of the effects of nonidealities leads to regional modifications of the switching sequence resulting in almost the whole hexagon as the feasible area. The usefulness of the proposed reconstruction algorithm has been verified by experimental results obtained from a 4-kW induction motor drive system. Smooth transitions between the redundant and fault-tolerant modes were observed.

Control and Fault Handling in a Modular Series-Connected Converter for a Transformerless 100 kV Low-Weight Offshore Wind Turbine

A transformerless wind power generator concept with the potential to achieve 100 kV dc output is proposed in this paper. In this paper, the modular ac/dc converter system suitable for such a high-voltage generator is analyzed for normal operation and fault-tolerant modes. The control synthesis is addressed, based on an assumption that the control can be designed modularly. Additionally, the investigated control system can facilitate fault-tolerant operation without changing the main structure. The robustness of the module control system is analyzed, and the limits for fault-tolerant operation are investigated. The theoretical studies are supported by transient analysis through simulations of the turbine in EMTDC/PSCAD. Finally, the generator/converter solution is verified experimentally. The laboratory results were obtained using a 45 kW prototype with three generator segments and three converter units in series.

English

Cloud computing is upcoming a mainstream feature of information technology. More progressively enterprises deploy their software systems in the cloud environment. The applications in cloud are usually large scale and containing a lot of distributed cloud components. Building cloud applications is highly reliable for challenging and critical research issues. Information processing systems has increased the significance of its correct and continuous operation even in the presence of faulty components. To address this issue, proposes a cloud framework to build fault-tolerant cloud applications. We first propose fault detection algorithms to identify significant components from the huge amount of cloud components. Then, we present an efficient fault-tolerance strategy selection algorithm to determine the most suitable fault-tolerance strategy for each significant component. Software fault tolerance is widely adopted to increase the overall system reliability in critical applications. System reliability can be enhanced by employing functionally equivalent components to tolerate component failures. Fault-tolerance strategies introduced a three well- known techniques are in the following with formulas for calculating the failure probabilities of the fault-tolerant modules. Our work will mainly be driven toward the implementation of the framework to measure the strength of fault tolerance service and to make an in-depth analysis of the cost benefits among all the stakeholders. An algorithm is proposed to automatically determine an efficient fault-tolerance strategy for the significant cloud components. Using real failure traces and model, we evaluate the proposed resource provisioning policies to determine their performance, cost as well as cost efficiency. The experimental results show that by tolerating faults of a small part of the most important components, the reliability of cloud applications can be highly improved.