Fault-tolerant Control Technique Research Articles

Fault Diagnosis and Fault Tolerant Control of Wind Turbines: An Overview

Wind turbines are playing an increasingly important role in renewable power generation. Their complex and large-scale structure, however, and operation in remote locations with harsh environmental conditions and highly variable stochastic loads make fault occurrence inevitable. Early detection and location of faults are vital for maintaining a high degree of availability and reducing maintenance costs. Hence, the deployment of algorithms capable of continuously monitoring and diagnosing potential faults and mitigating their effects before they evolve into failures is crucial. Fault diagnosis and fault tolerant control designs have been the subject of intensive research in the past decades. Significant progress has been made and several methods and control algorithms have been proposed in the literature. This paper provides an overview of the most recent fault diagnosis and fault tolerant control techniques for wind turbines. Following a brief discussion of the typical faults, the most commonly used model-based, data-driven and signal-based approaches are discussed. Passive and active fault tolerant control approaches are also highlighted and relevant publications are discussed. Future development tendencies in fault diagnosis and fault tolerant control of wind turbines are also briefly stated. The paper is written in a tutorial manner to provide a comprehensive overview of this research topic.

Fault-tolerant control with high-order sliding mode for manipulator robot

<p>The safety of manipulators systems is receiving a lot of attention these days. Faults have the ability to carry out harmful activities that harm equipment, the environment, or persons. As a result, it is critical to detect and diagnose problems as soon as possible, as well as to incorporate fault tolerance to avoid performance deterioration and harmful circumstances. Robust sensor fault detection and isolation (FDI) as well as fault-tolerant control (FTC) for a robotic system are discussed in this work. The goal of this research is to create an FDI method that uses a super-twisting third-order sliding mode (STW-TOSM) observer to estimate residual signals. A suggested system based on a higher-order sliding mode (HOSM) observer/controller approaches is used to accomplish this. In comparison to an active FTC technique, the test results demonstrate high level of performance. Finally, simulation results illustrate the efficacy of the presented techniques.</p>

Seven-Phase PMSM Drives Operation Post Two Types of Faults

This research presents a seven-phase PMSM drive with a high degree of reliability. This enhancement in reliability is achieved by applying two new Fault Tolerant Control techniques (FTC) at the same time. The first FTC will maintain the operation of the seven-phase PMSM drive after the failure in one based on the minimum inverter current optimization technique. The implementation of this FTC technique is achieved through developing a novel Space Vector Pulse Width Modulation (SVPWM) to assure proper distribution of the currents in the remaining phases post failure. The second FTC technique keeps the operation of the faulty seven-phase PMSM drive post the failure in the speed sensor. This is created by developing a new algorithm to obtain the rotor position and speed of the faulty seven-phase PMSM drive based on the voltage excitation method. Simulation results are presented to demonstrate the enhancement in the reliability achieved by the FTCs developed in this paper for the seven-phase motor drive running post the failures in phase ‘A’ and the speed sensor at the same time.

A Dynamic Proportional-Integral Observer-Based Nonlinear Fault-Tolerant Controller Design for Nonlinear System With Partially Unknown Dynamic

For the nonlinear system with partially unknown dynamic, the problems of fault estimation and fault-tolerant control are considered. A novel adaptive observer is designed to reconstruct the system state, process fault, sensor fault, and the measurement disturbance, simultaneously. The designed observer can be treated as a dynamic proportional-integral observer, where both the output information and the derivative of the output are used, while the output derivative can be unmeasurable. Utilizing the estimation information obtained by the designed observer, a nonlinear fault-tolerant control technique is proposed to stabilize the system. At the end of this article, three examples are listed to verify the proposed method.

Novel Approach to Fault-Tolerant Control of Inter-Turn Short Circuits in Permanent Magnet Synchronous Motors for UAV Propellers

This paper deals with the development of a novel fault-tolerant control technique aiming at the diagnosis and accommodation of inter-turn short circuit faults in permanent magnet synchronous motors for lightweight UAV propulsion. The reference motor is driven by a four-leg converter, which can be reconfigured in case of a phase fault by enabling the control of the central point of the motor Y-connection. A crucial design point entails the development of fault detection and isolation (FDI) algorithms capable of minimizing the failure transients and avoiding the short circuit extension. The proposed fault-tolerant control is composed of two sections: the first one applies a novel FDI algorithm for short circuit faults based on the trajectory tracking of the motor current phasor in the Clarke plane; the second one implements the fault accommodation, by applying a reference frame transformation technique to the post-fault commands. The control effectiveness is assessed via nonlinear simulations by characterizing the FDI latency and the post-fault performances. The proposed technique demonstrates excellent potentialities: the FDI algorithm simultaneously detects and isolates the considered faults, even with very limited extensions, during both stationary and unsteady operating conditions. In addition, the proposed accommodation technique is very effective in minimizing the post-fault torque ripples.

A comprehensive review of fault diagnosis and fault-tolerant control techniques for modular multi-level converters.

Many faults occur in the modular multi-level converters (MMCs), including unbalancing capacitor voltage, lower and upper arm unbalancing, the line to line voltage unbalancing, sensors and actuators fault, system fault, and sub-modules fault in high as well as medium voltage applications. Several fault-tolerant approaches are presented to overcome these problems, such as active fault-tolerant control system (AFTCS), passive fault-tolerant control system (PFTCS), hybrid fault-tolerant control system (HFTCS), redundant system technique, special power circuit with the controller, and zero sequence voltage methods, which we will explain extensively in this article. This review emphasizes the types of faults in the MMCs and discusses the protection methods under failure conditions. The MMC is more popular in high voltage applications because it not only improves the quality of the grid but also has good harmonic performance in high power transmission. There is no need for any isolated dc sources to operate it. When faults are removed, the efficiency and reliability of the system will be increased. This extensive explanation of the current literature on MMC fault diagnosis and control techniques will conclude which methods provide a more valuable solution. Finally, this paper discusses the best approach to reduce MMC faults and provides a future research direction to the readers.

A Dynamic-State-Estimator-Based Tolerance Control Method Against Cyberattack and Erroneous Measured Data for Power Systems

Cyberattacks against measured variables and faulty metering devices are among the most important threats to modern systems that should be detected and isolated, and the control actions based on the measured variables should be appropriate in order to keep the power system security. This article proposes a dynamic-state-estimation-based cyberattack-tolerant control method for modern power systems. The proposed method involves two new schemes: one is for dynamically detecting the cyberattack and the other isolates the location of the attack. These schemes are based on dynamic observer designs that can eliminate the effects of unknown inputs. This article also proposes a fault-tolerant control technique using these observer-based detection and isolation schemes. The proposed method can accurately track dynamic states, detecting both cyberattack against measured variables and faulty measuring devices, and isolating the cyberattack and fault locations. The results verify its superiority in comparison with other techniques.

Reliable speed control of a separately excited DC motor using advanced modified triple modular redundancy scheme in H-bridges

The risk of danger in industries is increasing due to the unexpected shutdowns owing to the unwanted faults in the components. These faults can also lead to a complete failure of the system causing costly production losses and safety issues. Therefore, Fault-Tolerant Control (FTC) techniques are used for such systems to get better reliability, and safety to prevent faults. This paper presents a Modified Triple Modular Redundancy (MTMR) based fault-tolerant system for a separately excited Direct Current (DC) motor with a Fault Detection and Isolation (FDI) unit that can detect, isolate, and replace the faulty switch with the standby switches to prevent the unwanted shut down of the system and support the process continuity thereby increasing reliability. The proposed MTMR will still be able to provide output with only one healthy switch with the other two in the faulty conditions. MATLAB/Simulink software was used for the experimentation process to check the performance of the system. The presented work establishes that the MTMR-based fault-tolerant H-bridge with the FDI unit is a highly reliable solution for the speed control of a separately excited DC motor. The comparison of the proposed work with existing works also demonstrates its superior performance.

Fuzzy adaptive sliding mode fault estimation and fixed-time fault-tolerant control for coupled spacecraft based on SE(3)

The goal of this study is to develop fault estimation (FE) and fault tolerant control (FTC) techniques for rigidly coupled spacecraft. A fuzzy adaptive sliding mode fault estimation approach is proposed to address fault tolerance against a large scale of disturbances, including inertia parametric uncertainties, space disturbances, actuator faults and saturation constraints. Firstly, a six-degrees of freedom (6-DOF) fault tolerant control architecture is established on the Lie group SE(3), which combined rotation and translation coupling kinematics and dynamics together. Then, a nonlinear fault estimator is used to deal with controllability loss of the fault actuator and the fuzzy logic system (FLS) is presented to solve the lumped disturbance. Next, in order to reduce the number of control parameters, the exponential parameters of the fast double-power sliding mode surface and the reaching law are set to be the same, which are nested with the estimated value of actuator effectiveness and combined with the pseudo inverse control allocation method to form the control algorithm in this paper. Finally, the stability and fixed-time convergence of the proposed method are proved theoretically by Lyapunov function, and the effectiveness of the scheme is verified by numerical simulation.

Fault-Tolerant Operation of a Multimode Stacked Switch Rectifier Leg Through Built-In Circuit Redundancy

In this paper, the open-circuit fault-tolerant operation of a multi-mode stacked switch rectifier leg is presented and investigated. A fault-tolerant control technique is proposed through the built-in circuit redundancy operation of the presented multi-mode stacked switch rectifier leg. A bidirectional CLLC resonant DC-DC converter that employs the presented leg is used to demonstrate the features of the presented control scheme. The proposed control is able to allow post fault operation of the converter to continue to deliver the demanded load power with soft-switching operation in case any switch experiences an open-circuit fault. In addition, the built-in circuit redundancy of the leg allows the resonant converter to operate in different operating modes, resulting in an enhanced control in regulating the output voltage while avoiding the switching frequency to diverge far from the resonant frequency, leading to better performance and improved efficiency with the complete soft-switching operation before and after the fault. To highlight the merits of the proposed fault-tolerant control in the multi-mode stacked switch rectifier leg, experimental results are provided on a 300W resonant converter prototype with an input of 250V and an output voltage of 400V.

An Active Fault-Tolerant Control Strategy for Current Sensors Failure for Induction Motor Drives Using a Single Observer for Currents Estimation and Axes Transformation

This paper proposes a fault-tolerant control technique against current sensors failure in direct torque controlled induction motors drives, based on a new modification of Luenberger observer for currents estimation and axes transformation for vector rotation. Several important aspects are covered in the proposed algorithm, such as the detection of sensors failure, the isolation of faulty sensors, and the reconfiguration of the control system by a correct estimation. A logic circuit ensures fault detection by analyzing the residual signal between the measured and estimated quantities, while a single observer performs the task of estimating the line currents. In addition, a decision logic circuit isolates the erroneous signal and simultaneously selects the appropriate estimated current signal. An axes transformation ensures rotation from (a,b) to (α,β), which keeps a low-cost control using only two current sensors. The proposed scheme is tested on MATLAB/Simulink environment and experimentally validated in a laboratory prototype mainly containing a dS1104 card and 4 kW induction motor.

Design of an Improved Hybrid FTC for Faults in Aero-Engine Closed-Loop Control System

Due to the aero-engines in a high temperature, pressure, and spool speed environment, the concurrent faults in actuator/sensor combined with degradation of the aero-engine could arise the problem of closed-loop instability during the flight. For this purpose, an improved hybrid fault-tolerant control (FTC) technique has been studied in this paper to deal with simultaneous failure of actuators and sensors associated with health parameters of the typical components’ degradation in aero-engines. The improved hybrid FTC structure combined with the nonlinear thermodynamic component-level (NCL) model-based estimation method merges fault estimation of actuators/sensors and typical components’ degradation estimation process into the FTC process. A robust H ∞ state feedback controller under the disturbance of simultaneous actuator and sensor faults is designed in the proposed method, together with the switching algorithm serving for the fault estimation and improved hybrid FTC channels. In order to show the feasibility of the proposed method, several semiphysical experiments are engaged to illustrate that the improved hybrid FTC structure can save the tolerant-control time and improve performance of the control system.

Composite attitude fault tolerant tracking control for flexible satellite with time delay

This article deals with the problem of attitude tracking control for flexible satellite under flexible vibration disturbance, actuator fault and time delay. Based on disturbance observer and fault tolerant control techniques, the flexible vibration disturbance and actuator fault are effectively estimated by disturbance observer and fault estimation observer, respectively. Meanwhile, a delay-dependent attitude tracking feedback controller is designed to ensure that the reference attitude is stably tracked. To reduce the conservatism of the designed algorithm, a time delay correlative decomposition factor is introduced to make the flexible satellite have a better performance for attitude tracking control. Finally, the effectiveness of the proposed method is illustrated by numerical simulations.

Fault Tolerant Discrete Control Technique for PV Fed Stepper Motor Drive

This paper deals with the fault tolerant discrete control technique for the Photo Voltaic (PV) fed 3-phase stepper motor (SM). The operation of stepper motor is complex under high speed applications due to dificulty in locating the step-angle and there is a chance of missing the step-angle. A robust discrete sliding mode control (DSMC) algorithm is developed to overcome this problem along with the fault tolerant topology. The drive is powered by PV array and using perturb and observe (P&O) algorithm maximum power is retrieved from the source. The closed loop control of this drive is implemented using MATLAB/SIMULINK simulation software and the speed control of stepper motor is achieved by introducing stepped reference signal. The fault tolerance is verified by introducing open circuit (OC) and short circuit (SC) faults in the driver circuit and the speed response of the same is plotted. The robustness of the discrete controller is proved by introducing changes in the irradiance of PV array, changes in reference speed and faults in the driver circuit. The oveall system is cheap, compact, robust and reliable under all test conditions and suitable for very low and very high speed applications.

Model-Based Unified Framework for Detection and Mitigation of Cyclic Torque Imbalance in a Gasoline Engine

Abstract Torque produced by the internal combustion (IC) engine is desired to be of similar value for consecutive combustion cycles; nevertheless, difference occurs in the cyclic torque due to uncertainties in its generation. Variations between output work of successive combustion cycles are considered as the main cause of imbalance in the cyclic torque. Such variations are displayed in engine output torque and affect the engine performance. In this paper, a novel model-based unified framework is proposed for the detection and mitigation of cyclic torque imbalance in a gasoline engine by employing the first principle-based engine model (FPEM). Engine speed dynamics in the model are transformed to develop the direct relationship between engine speed dynamics and fuel input. Fault in fuel injection subsystem is induced to generate imbalance in the cyclic torque. FPEM-based uniform second-order sliding mode (USOSM) observer is applied for estimation of the unknown input, i.e., net piston force (fn) from engine speed dynamics to detect imbalance in the cyclic torque. Estimated net piston force (f⁁n) is utilized to design the control law for certainty equivalence super twisting algorithm (CESTA) based fault tolerant control (FTC) technique to mitigate the torque imbalance. The results of numerical simulation demonstrated that the desired objective is achieved by the proposed unified framework.

Simple current sensor fault‐tolerant control strategy for switched reluctance motors in high‐reliability applications

Switched reluctance motors (SRMs) are considered as a potential candidate in many high-reliability demanding applications, including electrical vehicles (EVs), hybrid EVs and more electric aircrafts. For precise and stable control performance, normally an SRM drive requires one current sensor for each phase winding. Failure of any of these sensors will inevitably degrade the system's performance. The behaviour of an SRM drive under current sensor failure is investigated and a fault-tolerant control technique is proposed by changing the current sensor installation scheme without adding extra current sensors. Moreover, through the analysis of the detected currents by the phase current sensors and the dc-link sensor, a diagnostic scheme for current sensors failure is presented. The excitation current in the faulty phase under postfault conditions is reconstructed through a simple calculation without injecting a high-frequency signal or modifying the switching signals, thereby reducing the current distortion and avoiding voltage penalty issues. Motor drive can operate with satisfactory control performance even when all the phase current sensors are in fault conditions. Detailed analysis under both steady state and dynamic conditions through thorough simulations and experiments has been carried out on a three-phase 12/8 SRM. The extensive results validate the effectiveness of the proposed technique.

Fault recoverability for nonlinear systems with application to fault tolerant control of UAVs

Unmanned Aerial Vehicles (UAVs) have received numerous attention since they can be used in many applications. Like other systems around us, UAVs are vulnerable to different faults. If a fault appears in UAVs, they should be able to perform their mission within an acceptable level. To ensure successful missions, fault tolerant control (FTC) algorithms need to be used for UAVs. By using FTC algorithms, the system can increase the level of autonomy that allows self-reconfiguration. Having a certain redundancy level in the system, is a prerequisite for the success of FTC techniques. In this paper, the fault recoverability measure for nonlinear systems is presented. The presented measure can be used to ensure that a sufficient redundancy level for the success of FTC exists in the system. It also gives insight into the ways to improve the redundancy level in the systems design process. To extend the notion of fault recoverability to nonlinear systems empirical gramians are used. The proposed method is used to calculate fault recoverability for multirotor UAVs to reveal its relation to redundant actuation possibilities in the model.

A Survey on Active Fault-Tolerant Control Systems

Faults and failures in the system components are two main reasons for the instability and the degradation in control performance. In recent decades, fault-tolerant control (FTC) approaches have been introduced to improve the resiliency of control systems against faults and failures. In general, FTC techniques are classified into active and passive approaches. This paper reviews fault and failure causes in control systems and discusses the latest solutions that are introduced to make the control system resilient.The recent achievements in fault detection and isolation (FDI) approaches and active FTC designs are investigated. Furthermore, a thorough comparison of several different aspects is conducted to understand the advantage and disadvantages of various FTC techniques to motivate researchers to further developing FTC and FDI approaches.

Fixed-Time Actuator Fault Accommodation Applied to Hypersonic Gliding Vehicles

This article presents a fixed-time accommodation strategy of actuator faults for hypersonic gliding vehicles (HGVs). The approach against actuator faults is incorporated by sliding mode control (SMC), bilimit homogeneity, and adaptive techniques, with consideration of practical constraints and model uncertainties. The resulting fault-tolerant attitude control law allows the fault compensation to be completed in a fixed time, in view of the limited time available for recovery of a faulty HGV. The effectiveness of the presented scheme is validated by comparing it to the finite-time fault accommodation scheme. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —Hypersonic vehicles have drawn significant interests due to the features of super-fast and flexible maneuverability. The use of advanced fault-tolerant control (FTC) techniques is expected to guarantee safety during hypersonic vehicle operation. A challenging problem is how to counteract actuator faults promptly and effectively in the presence of practical constraints and model uncertainties. This article presents a fixed-time FTC algorithm for a hypersonic gliding vehicle.

Fault-Diagnosis and Virtual Flux-Based Tolerant Control for Grid Connected PV System

This article presents easy and robust Measurement Fault Detection and Isolation (MFDI) and Fault Tolerant Control (FTC) technique against grid voltage measurement failure, where scaling and dc-offset errors are considered. The proposed MFDI method is based on grid voltages orientation, which enables to generate two residuals. It does not require an extra hardware and is insensitive to system parameters variation; therefore, the model knowledge is not necessary. FTC technique is applied to overcome the fault. It is focused on Virtual Flux using Second-Order Generalized Integrator with a Frequency Locked-Loop. The estimated quantity is injected into the system control instead of the erroneous measurement. Simulation results prove the effectiveness of the proposed MFDI and FTC methods against different magnitude and type of grid sensor faults, and well identify the occurrence fault in each phase. In addition, it is characterized by a lower software capacity compared with model-based methods. An experimental platform was used to validate the obtained results and to show the reliability of the proposed techniques.