Design Of Fault-tolerant Systems Research Articles

Promoting the Maneuverability and Fault-Tolerant Control Capabilities of Dual-System/Hybrid VTOL UAVs

This paper presents an active fault-tolerant flight control system (FCS) design for the dual-system/hybrid VTOL UAV configuration that maximally exploits its inherent over-actuation abilities to provide higher levels of fault-tolerance and reliability compared to that of the other VTOL UAVs configurations up to this point. The significance of this study is to convert the main drawback of having the vertical rotors as dead weights during the cruise to a key advantage where all the UAV's controls are kept active during all the flight phases raising the UAV's fault-tolerance and maneuverability abilities. The FCS proposed elaborates on a new architecture for the hierarchical automatic control loops using the dynamic inversion control to design the trajectory tracking virtual commands and employing optimal dynamic control allocation to optimally resolve the controls redundancy. Regarding fault-tolerance, the presented FCS handles simultaneous failures and jamming of all the control surfaces during flight where the control commands to the healthy controls (vertical rotors) were automatically adapted such that the trimming and trajectory tracking were successfully maintained till the mission end. Additionally, this paper addresses for the first time the employment of the controls redundancy to enhance the VTOL UAV's maneuverability in fault-free cases, where we present a study of reducing the minimum turn radius of the UAV when the vertical rotors are employed with the control surfaces during the maneuver. A reduction of 38% in the coordinated steady-level minimum turn radius turn at 35 m/sec flight speed was achieved.

Methodological approach to recovery correct functioning of embedded systems at the level of programmable element base

The article proposes a methodical approach to restoring the proper functioning of specialized microprocessor control systems at the level of the programmable element base. This approach includes two stages. At the first stage, the main task of technical diagnostics is solved, namely the recognition of the state of a specialized microprocessor system, which includes: assessment of the technical state, forecasting, detection and localization of malfunctions. This task is solved by detecting errors in the operation of a specialized microprocessor control system, which are caused by the failure and failure of digital devices, errors in software, or other reasons, using existing control methods, as well as localization of malfunctions of a specialized microprocessor control system, using methods of test and functional diagnostics digital devices that are part of the system under consideration. At the second stage, the correct functioning of the specialized microprocessor control system is restored by reconfiguring its internal structure at the level of logical elements. At the same time, the reconfiguration of the internal structure is based on the position of the prescriptive theory, which considers the issue of purposeful management of objects of various nature, which are in a state of "conflict" with other objects. The implementation of the proposed approach in the future can be the basis for the design of active fault-tolerant systems that will be able to counteract failures a hardware and software nature as a result of internal or external adverse actions.

Design of hybrid fault-tolerant control system for air-fuel ratio control of internal combustion engines using artificial neural network and sliding mode control against sensor faults

This paper proposes a novel hybrid fault-tolerant control system (HFTCS) with dedicated non-linear controllers: artificial neural network (ANN) and sliding mode control (SMC) for active and passive parts, respectively. The proposed system can provide both desirable properties of stability to unexpected fast disturbances and post-fault optimal performance. In the active fault tolerant control system (AFTCS) part, the fault detection and isolation (FDI) unit is designed through the use of ANN for the estimation of faulty sensor values in the observer model. In the passive fault-tolerant system (PFTCS) part, the air-fuel ratio (AFR) controller is designed using a robust SMC that allows systems to manage faults in predefined limits without estimation. In the proposed system, SMC will form the passive part to react instantly to faults while ANN will optimize post-fault performance with active compensation. Moreover, Lyapunov stability analysis was also performed to make sure that the system remains stable in both normal and faulty conditions. The simulation results in the Matlab/Simulink environment show that the designed controller is robust to faults in normal and noisy measurements of the sensors. A comparison with the existing works also demonstrates the superior performance of the proposed hybrid algorithm.

Design of Active Fault-Tolerant Control System for Air-Fuel Ratio control of Internal Combustion engine using nonlinear regression-based observer model.

Internal Combustion (IC) engines are prevalent in the process sector, and maintaining sufficient Air-Fuel Ratio (AFR) regulation in their fuel system is crucial for enhanced engine performance, fuel economy, and environmental safety. Faults in the AFR system's sensors cause the engine to shut down, hence, fault tolerance is essential. In order to avoid engine shutdown, this paper offers a novel Active Fault-Tolerant Control System (AFTCS) for air-fuel ratio control of an Internal Combustion (IC) engine in a process plant. In the Fault Detection and Isolation (FDI) unit, the proposed AFTCS uses a nonlinear regression-based observer model for analytical redundancy. The suggested system was simulated in the MATLAB / Simulink environment. The proposed system was tested at two different speeds (300 r/min and 600 r/min) and the results show that the system's response is within the acceptable bound without compromising the stability. The findings also demonstrate the higher fault tolerance capability for sensor defects of the AFR control system, particularly for the MAP sensor (at 300 r/min) in terms of reduced oscillatory response in comparison to the current literature. Compared to the linear regression-based and Genetic Algorithm (GA) based model, the nonlinear regression-based model results in a more accurate estimation of the faulty sensors. The proposed model is also efficient in terms of computation power and response time.

Design of fault-tolerant control system for distributed energy resources based power network using Phasor Measurement Units

Distributed Energy Resources (DERs) play a significant role in reducing carbon emissions and improving the power system, nonetheless, maintaining the stability of the system parameters under faulty conditions is a major challenge. To minimize fault duration and maximize the system’s fault tolerance capability while maintaining affordability and being environment friendly, DERs supported by storage units are used in parallel with the main grid which offers promising results. This paper proposes the utilization of DERs as the primary source while the main grid shares the peak load. The paper also discusses the application of Phasor Measurement Units (PMUs) to record current and voltage values. PMUs are used to detect the fault in its early stage and communicate to the central controller to shift the load on storage units and isolate fault locations. The operation is controlled at two levels, that is at the load end and the junction point of the grid and DER. Any anomaly detected by PMUs is tested for the fault location, where faults are then controlled and minimized using the proposed method while keeping economic factors under consideration. The system is tested in light of results from mathematical modeling and design simulation which show very low latency time against demand response and quick isolation of fault location. A comparison with existing and previous works also shows the promising performance of the proposed fault-tolerant power system using PMUs.

Special Issue on Design of Fault-Tolerant Digital Circuits and Systems

As technology scales down, the speed and power efficiency of digital circuits become greatly enhanced [...]

A Comparative Study of Design of Active Fault-Tolerant Control System for Air–Fuel Ratio Control of Internal Combustion Engine Using Particle Swarm Optimization, Genetic Algorithm, and Nonlinear Regression-Based Observer Model

In this article, three distinct strategies for designing an Active Fault-Tolerant Control System (AFTCS) for Air-Fuel Ratio (AFR) control of an Internal Combustion (IC) engine in a process plant to avoid engine shutdown, are presented. The proposed AFTCS employs a Genetic Algorithm (GA), Particle Swarm Optimization (PSO), and a Nonlinear Regression (NLR)-based observer model in the Fault Detection and Isolation (FDI) unit for analytical redundancy. A comparison between these three proposed techniques is carried out to determine the least expensive and most accurate approach. The results show that the nonlinear regression produces highly accurate results by consuming very low computational power, and its response time is also very low as compared to GA and PSO. The results obtained show that NLR requires 99.6% and 93.1% less computational time for throttle and MAP estimation, respectively, by reducing the estimation error to as low as 0.01. The simulation of the proposed system is carried out in the MATLAB/Simulink environment. The results prove the superior fault tolerance performance for sensor faults of the AFR control system, especially for the Manifold Absolute Pressure (MAP) sensor in terms of less oscillatory response as compared to that reported in existing literature.

2-Odd Labeling of Graphs Using Certain Number Theoretic Concepts and Graph Operations

Graph theory plays a significant role in a variety of real-world systems. Graph concepts such as labeling and coloring are used to depict a variety of processes and relationships in material, social, biological, physical, and information systems. Specifically, graph labeling is used in communication network addressing, fault-tolerant system design, automatic channel allocation, etc. 2-odd labeling assigns distinct integers to the nodes of <img src=image/13427595_01.png> in such a manner, that the positive difference of adjacent nodes is either 2 or an odd integer, <img src=image/13427595_02.png>, <img src=image/13427595_03.png>. So, <img src=image/13427595_04.png> is a 2-odd graph if and only if it permits 2-odd labeling. Studying certain important modifications through various graph operations on a given graph is interesting and challenging. These operations mainly modify the underlying graph's structure, so understanding the complex operations that can be done over a graph or a set of graphs is inevitable. The motivation behind the development of this article is to apply the concept of 2-odd labeling on graphs generated by using various graph operations. Further, certain results on 2-odd labeling are also derived using some well-known number theoretic concepts such as the Twin prime conjecture and Goldbach's conjecture, besides recalling a few interesting applications of graph labeling and graph coloring.

The design of an affordable fault-tolerant control system of the brushless DC motor for an active waist exoskeleton

The design of an affordable fault-tolerant control system of the brushless DC motor for an active waist exoskeleton

A Low-cost Fault Tolerance Method for ARM and RISC-V Microprocessor-based Systems using Temporal Redundancy and Approximate Computing through Simplified Iterations

Approximate Computing techniques have been successfully used to reduce the overhead associated with redundancy in fault-tolerant system designs. This paper presents a fault tolerance method to reduce the execution time overhead of the well-known Time Redundancy technique by means of an improvement proposed for the Approximate Computing software-based technique known as loop perforation. Time Redundancy is a software-based fault tolerance technique that involves executing replicas of a task at different times. We propose to approximate the tasks to be executed using a new approximate computing technique based on loop perforation, i.e., simplified iterations. The novelty of this method is the combined use of the fault tolerance technique, temporal redundancy, jointly with the new proposed Approximate Computing technique, simplified iterations. The proposal is validated through simulation-based fault injection campaigns on several test programs for the ARM and RISC-V microprocessor architectures. Experimental results verified not only the applicability of the proposal in different architectures, but also its effectiveness, showing a good trade-off between reliability, error and overhead. Results showed that using the proposed method, a normalized mean work to failure (MWTF) up to 5.28× was obtained with approximation errors lower than those obtained using the traditional loop perforation technique.

Design of active fault-tolerant control system for Air-fuel ratio control of internal combustion engines using fuzzy logic controller.

Fault-Tolerant Control Systems (FTCS) are used in critical and safety applications to improve performance and stability despite failure modes. As a result, costly production losses related to unusual and unplanned shutdowns can be prevented by incorporating these systems in the critical process plant machines. The Internal Combustion (IC) engines are highly used process plant machines and faults in their sensors will cause their shutdown instigating the need to install FTCS in them. In this paper, an Active Fault-Tolerant Control System (AFTCS) based on a Fuzzy Logic Controller (FLC) is suggested to improve the reliability of the Air-Fuel Ratio (AFR) control system of an IC engine. For analytical redundancy, a nonlinear Fuzzy Logic (FL) based observer is implemented in the proposed system for the Fault Detection and Isolation (FDI) unit for nonlinear sensors of the AFR system. Lyapunov stability analysis was used for designing a stable system in both faulty and normal conditions. To evaluate its performance, this system was developed in the MATLAB/Simulink platform. The simulation results show that the developed system is robust under sensor fault conditions, retaining stability with a minimum decrease of AFR. This study's comparison with the existing literature demonstrates that the proposed system is effective for maintaining the AFR in IC engines during sensor faulty conditions thus reducing shutdown of engine and production loss for increased profits.

Fault-Tolerant System Design for Doubly Salient Electromagnetic Machine Under Loss of Excitation

Aiming at the problem that the traditional doubly salient electromagnetic machine (DSEM) cannot work when the excitation loss occurs, this article designs and analyzes a fault-tolerant DSEM for excitation loss, and the torque ripple suppression strategy under the fault-tolerant operation is studied. First, the characteristics of the output torque of DSEM before and after excitation-loss is analyzed, and a DSEM with a novel winding configuration is proposed to improve the fault tolerance. Second, under normal/excitation-loss conditions, the structure parameters of the fault-tolerant DSEM are analyzed to reveal the influence of the motor structure on its performance. Then, the steady-state torque of the fault-tolerant DSEM is compared with the traditional DSEM and the switched reluctance motor with the same size, which proves the effectiveness of the fault-tolerant design. By analyzing the inductance and torque characteristics, a torque ripple suppression strategy is proposed for the fault-tolerant DSEM without increasing the complexity of the system. Finally, a prototype is developed, and the experimental results verify the fault-tolerant capability of the prototype and the effectiveness of the proposed torque ripple suppression strategy. The research results of this article provide a specific implementation method for the fault-tolerant system design of DSEM under excitation loss.

Global fast terminal sliding mode based radial basis function neural network for accurate fault estimation in nonlinear systems

The problem of quick and accurate fault estimation in nonlinear systems is addressed in this article by combining the technique of radial basis function neural network (RBFNN) and global fast terminal sliding mode control (GFTSMC) concept. A new strategy to update the neural network weights, by using the global fast terminal sliding surface instead of conventional error back propagation method, is introduced to achieve real time, quick and accurate fault estimation which is critical for fault tolerant control system design. The combination of online learning ability of RBFNN, to approximate any nonlinear function, and finite time convergence property of GFTSMC ensures quick detection and accurate estimation of faults in real time. The effectiveness of the proposed strategy is demonstrated through simulations using a nonlinear model of a commercial aircraft and considering a wide range of sensors and actuators faults. The simulation results show that the proposed method is capable of quick and accurate online fault estimation in nonlinear systems and shows improved performance as compared to conventional RBFNN and other techniques existing in literature.

Design of Active Fault-Tolerant Control System for Multilevel Inverters to Achieve Greater Reliability With Improved Power Quality

Modern renewable energy systems mostly utilize multilevel converter applications for improved power quality and grid synchronization purposes. A multilevel converter is an electrical device that may offer several amounts of voltage levels at the output in order to make the output more comparable to a pure sine wave. The integrity of the multilevel converter depends on the reliability of individual switches such that the converter will collapse in case of faults in these switches. In this paper, a novel 7-level Fault-Tolerant Cascaded H-Bridge Multilevel Inverter (FT-CHB-MLI) has been proposed that offers high reliability with improved power quality. A dedicated Fault Detection and Isolation (FDI) unit has been built to diagnose the faulty switch and replace it with a standby redundant switch. Total harmonic distortion and the determination of a normalized output voltage factor are employed for fault diagnosis. The Phase Disposition Pulse Width Modulation (PD-PWM) technique has been utilized for switching due to its superior performance as compared to other conventional techniques. This early fault detection method not only identified the issues but also performed preventative actions to keep the system healthy and stable. The proposed system was tested on the MATLAB / Simulink environment to verify its performance. The simulation results demonstrated that the THD has been reduced to almost 18% with a significant increase in reliability with advanced fault-tolerant architecture consisting of FDI units. The reliability analysis was carried out using Markov chains that also showed its increased reliability. A comparison of the proposed work with literature was also carried out to demonstrate its superior performance with increased reliability.

Design of finite-time active fault tolerant control system with real-time fault estimation for a remotely operated vehicle

In this paper, a new approach is introduced for active fault tolerant control system of an underwater vehicle with unknown dynamics in the presence of thruster system faults and constraints. For this, a finite-time observer is proposed to estimate unknown system dynamics and the faults and failures of the thruster system simultaneously. In the observer, a novel unit based on acceleration feedforward is introduced into conventional extended-state observer so that real-time estimation of fault can be obtained regardless of uncertainties and disturbances. Stability analyses are carried out for the observer and it is proved that system states and uncertainties can be estimated in finite time and fault estimation error is proved to be globally uniformly ultimately bounded. In order to actively accommodate thruster system faults and failures, and to take saturation and rate limits into account, control allocation is utilized. To outline the advantages of the proposed control system, comparisons are made with previous works. The results show that the proposed observer has effectively estimated thruster system faults and failures. It is also shown that the post-failure/-fault behavior of the vehicle has significantly improved and despite keeping the position more accurately, the performance of the thruster system has considerably improved.

Evaluation of the applicability of asynchronous programming methods to the data consistency problem in a microservices environment

The paper considers the problem of an effective microservices interaction and its organization to support data consistency in fault tolerant and high load systems. The “Saga” microservices orchestration template was used for microservices management. The authors assessed the expediency of asynchronous programming principles usage for designing the Saga coordinator. The simulation of processes in the Saga coordinator was conducted; it considers different specifics of asynchronous and synchronous configurations of distributed transactions (Sagas) management. Synchronous configuration group includes a coordinator with a fixed pool of threads and a coordinator that generates a new thread for each new Saga. Asynchronous configuration group consists of a coroutines based coordinator and a coordinator that uses Linux core scheduler. The set of simulations with different numbers of Sagas and available coordinator processors was executed. It was shown that the use of asynchronous approaches significantly reduces the Saga’s execution duration up to 9.74 times and improves the processor time utilisation value up to 88 %. The obtained data proves the efficiency of asynchronous programming principles applied to the design of the Saga coordinator. The difference in efficiency between the asynchronous algorithms that were implemented in this paper was insignificant. Asynchronous programming principles used to build the Saga coordinator allow it to handle bigger load and to use processor resources in a more efficient way. The outcome of this research can be applied during the design of fault tolerant and high load systems. The paper might be interesting to IT-specialists and researchers focusing on distributed computing.

Adaptive Fixed-Time Nonsingular Terminal Sliding Mode Attitude Tracking Control for Spacecraft with Actuator Saturations and Faults

This paper focuses on the potential actuator failures of spacecraft in practical engineering applications. Aiming at the shortcomings and deficiencies in the existing attitude fault-tolerant control system design, combined with the current research status of attitude fault-tolerant control technology, we carry out high-precision, fast-convergent attitude tracking algorithms. Based on the adaptive nonsingular terminal sliding mode control theory, we design a kind of fixed-time convergence control method. This method solves the problems of actuator faults, actuator saturation, external disturbances, and inertia uncertainties. The control method includes control law design and controller design. The designed fixed-time adaptive nonsingular terminal sliding mode control law is applicable to the development of fixed-time fault-tolerant attitude tracking controller with multiple constraints. The designed controller considers the saturation of the actuator output torque so that the spacecraft can operate within the saturation magnitude without on-line fault estimation. Lyapunov stability analysis shows that under multiple constraints such as actuator saturation, external disturbances, and inertia uncertainties, the controller has fast convergence and has good fault tolerance to actuator fault. The numerical simulation shows that the controller has good performance and low-energy consumption in attitude tracking control.

Design of Active Fault Tolerant Control System for Air Fuel Ratio Control of Internal Combustion Engines Using Artificial Neural Networks

Fault tolerant control systems can be used in the process machines such as Internal Combustion (IC) engines to achieve greater reliability and stability in the fault conditions. Thus, costly loss of production due to the unusual and unexpected shutdown of these machines can be avoided. The Air Fuel Ratio (AFR) control system is an important system in IC engines and faults in the sensors of this system will cause its shutdown creating costly production loss, therefore, fault tolerance is necessary for them. In this paper, an Active Fault Tolerant Control System (AFTCS) based on Artificial Neural Networks (ANN) has been proposed for the AFR control system of a Spark Ignition (SI) IC engine to increase its reliability. In the proposed AFTCS, a nonlinear ANN-based observer is used in the Fault Detection and Isolation (FDI) unit for the highly nonlinear sensors of the AFR system for analytical redundancy. The Lyapunov stability analysis has been utilized to design a stable system in normal and faulty conditions. The system has been implemented in MATLAB/Simulink environment to test its performance. The simulation experimental results demonstrate that the suggested system stays reliable maintaining the stability well in the fault conditions of sensors with little degradation in AFR. A comparison with the existing works demonstrates the superior performance of the proposed AFTCS for the highly nonlinear sensors of the AFR control system. The technique suggested is very effective in terms of fault robustness and is more specifically based on the nonlinear behavior of the MAP sensor compared to the existing works.

Active Fault Tolerant Control System Design for Hydraulic Manipulator With Internal Leakage Faults Based on Disturbance Observer and Online Adaptive Identification

In this paper, an active fault-tolerant control (FTC) system design is proposed for an n-degree-of-freedom (n-DOF) hydraulic manipulator with internal leakage faults and mismatched/matched lumped disturbances. A pair of matched and mismatched disturbance observers (DOBs) is proposed to simultaneously estimate and compensate for the effects of matched/mismatched disturbances on the control system in healthy conditions. The fault detection is achieved when the estimated matched disturbance is larger than a threshold. After that, a novel control reconfiguration law is designed to switch from a normal controller to a fault-tolerant controller with an online identification algorithm based on an adaptive mechanism. The proposed active FTC guarantees the position tracking performance in not only single-fault but also simultaneous-faults conditions. Moreover, the problem of uniting disturbance-observer-based control for external disturbance and adaptive control for parametric uncertainty is solved in a novel approach. Simulation results are conducted in a two-degree-of-freedom hydraulic leg prototype, which verifies the effectiveness of the proposed method.

Software package for the implementation of bioinspired algorithms for the design of fault-tolerant control systems

The article considers a software package that allows you to form the composition of multiversion software for fault-tolerant control systems. The software implementation is based on a modified ant colony algorithm, which belongs to the class of bioinspired algorithms. The algorithm implements the search direction in order to minimize the cost of a program consisting of a set of modules. For each module, there are several versions of its implementation, developed within the framework of the multiversion programming methodology. The search direction is also implemented in order to maximize the reliability of the modular program in multiversion execution. The software implementation of the algorithm allows a number of experiments to be performed to obtain data that can be used to compare the performance of the standard and modified ant colony algorithms.