Fault-tolerant Control Technique Research Articles

An Improved Open-Phase Fault-Tolerant DTC Technique for Five-Phase Induction Motor Drive Based on Virtual Vectors Assessment

The multiphase machine (MM) drives are best suitable for safety-critical applications due to its inherent fault-tolerant capability. The fault-tolerant operation of MM drives is challenging and necessary for applications such as off-shore ship propulsion, highway electric vehicles, and more electric aircraft. A two-level voltage source inverter fed five-phase induction motor (FPIM) drive has been considered for the postfault performance assessment. In this article, an improved fault-tolerant direct torque control (DTC) technique is proposed for the FPIM drive based on virtual vector (VV)s assessment under the open-phase fault condition. The theoretical analysis is carried out to investigate the impact of VVs on the change in torque as well as flux response at different speeds and loading conditions. Based on this analysis, a modified lookup table, flux, and torque hysteresis bands are designed to improve the functioning of the fault-tolerant DTC of FPIM drive. The FPIM drive performance is analyzed and tested experimentally with an open-phase fault. Studies have confirmed the reliability and superiority of the proposed DTC controller over existing postfault solutions. In addition, the robustness of the FPIM drive at steady-state and dynamic operating conditions is evaluated from the given results, including the transition from pre-to-post fault operation.

Fault Tolerant Control Based on an Observer on PI Servo Design for a High-Speed Automation Machine

The fault tolerant control (FTC) technique is widely used in many industries to provide tolerance to systems so that they can operate when a system fault occurs. This paper presents a technique for FTC based on the observer signal application, which is used for a high-speed auto core adhesion mounting machine. The utilization of the observer signal information of the linear encoder fault is employed to adjust the gain parameters to achieve the appropriate gain value while maintaining the required performance of the system. The dynamic modeling of the servo motor system design utilizing a pole placement technique was designed to support the proposed method. A scaling gain fault step size adjustment from −1% to 1% with increments of 0.2% is used to simulate the fault conditions of the linear encoder. The statistical mean value of the observer error signal is used to train the artificial neural network (ANN) model. The results showed that the control system design successfully tracked the dynamic response. Furthermore, the ANN model, with more than 98% confidence, was satisfactory in classifying the linear encoder fault condition. The gain compensation was successful in reducing position error by more than 95% compared with the system without compensated gain.

Experimental Study of Sensor Fault-Tolerant Control for an Electro-Hydraulic Actuator Based on a Robust Nonlinear Observer

Electro-hydraulic actuators (EHAs) have been widely used in modern industries. However, sensor faults and actuator faults in EHA systems can arise due to aging during operation, making the system unstable and unsafe. To solve these issues, fault-tolerant control (FTC) techniques for EHA systems have been studied intensively. In this paper, an FTC is proposed and developed for the mini motion package (MMP) EHA system. First, a mathematical model of the MMP system is formulated and improved to provide position tracking control using a well-known proportional-integral-derivative (PID) controller. Second, an unknown input observer (UIO) reconstruction is performed to estimate the states, disturbances, and sensor faults so that an asymptotically stable control error can be obtained by a linear matrix inequality (LMI) optimization algorithm through Lyapunov’s stability condition. Third, the FTC designed for the nonlinear discrete-time system is formed from fault compensation based on a residual logic signal to implement the fault compensation process and ensure stability and tracking performance with respect to minimizing impacts of disturbances and sensor faults. Here, residual is defined by the difference between state response and state estimation. Finally, numerical simulations and experiments of the MMP system are presented to illustrate the efficiency of the proposed FTC technique.

Fault‐tolerant control of a smart PV‐grid hybrid system

This study deals with a fault-tolerant control of a smart PV-grid plant. The small scale system is dedicated to a stationary alternative current load and it consists of a photovoltaic module, supported by a single-phase grid. To ensure a smart permutation between the two proposed operation modes, a fuzzy logic-based power management algorithm is designed and implemented. In case of a sub-system failure, a fault-tolerant control technique is adopted to maintain the service continuity. In this study, two scenarios are proposed. The first concerns a load current sensor failure, where a material redundancy is adopted through the use of two observers, selected via a voting algorithm. The second deals to sense the system ability to maintain the service continuity in the worst case, where a grid black-out (grid-off) is planned. In this scenario, an additional functioning mode is added to reconfigure the control strategy. To prove the effectiveness of the proposed algorithms, the obtained experimental results with a given load profile are presented and commented.

Hierarchical Fault-Tolerant Control using Model Predictive Control for Wind Turbine Pitch Actuator Faults

Wind energy is one of the fastest growing energy sources in the world. It is expected that by the end of 2022 the installed capacity will exceed 250 GW thanks to the supply of large scale wind turbines in Europe. However, there are still challenging problems with wind turbines. In particular, off-shore and large-scale wind turbines are required to tackle the issue of maintainability and availability because they are installed in harsh off-shore environments, which may also prevent engineers from accessing the site for immediate repair works. Fault-tolerant control techniques have been widely exploited to overcome this issue. This paper proposes a novel fault-tolerant control strategy for wind turbines. The proposed strategy has a hierarchical structure, consisting of a pitch controller and a wind turbine controller, with parameter estimations using the adaptive fading Kalman filter technique. The pitch controller compensates any fault with a pitching actuator, while the wind turbine controller computes the optimal reference command for pitching behavior so that the effect of the fault with a pitch actuator can be minimized. The performance of the proposed approach is demonstrated through a set of simulations with a wind turbine benchmark model.

Fault-Tolerant Field-Oriented Control of Three-Phase Induction Motor Based on Unified Feedforward Method

With the increasing proliferation of variable speed drive, the demand for the more reliable drive is also on the rise. Despite the growing interest on more advanced motors like permanent magnet and flux switching motors, three-phase induction motors (3ph-IMs) are still the main workhorse in the industry and hence the fault-tolerant control of these motor drives remains an interesting and important topic. In this paper, a simple fault-tolerant field-oriented control technique for 3ph-IMs is presented. It is shown that by injecting zero-sequence compensation voltage in a feedforward manner, open-circuit faults can be effectively tolerated. Compared to the previous feedforward fault-tolerant control methods, the proposed approach does not require the knowledge of the magnetizing inductance, which is tricky to be obtained in induction motors. Furthermore, the unified feedforward approach allows the same control structure to be used for different fault-tolerant 3ph-IMs drive topologies, with minor modifications to the feedforward terms. In addition, the effect of inverter non-idealities on the performance of the proposed control method is also highlighted and addressed. The effectiveness of the proposed controller is verified using MATLAB simulation and further validated using experimental tests. This paper is accompanied by a video demonstrating the experimental results.

Distributed-observer-based Fault Tolerant Control Design for Nonlinear Multi-agent Systems

The problem of distributed adaptive fault tolerant control is investigated for nonlinear multi-agent systems with sensor faults in this paper. By utilizing radial basis function neural networks to approximate the unknown continuous nonlinear functions, a distributed-observer-based adaptive neural networks scheme is proposed to estimate each node state, which is unmeasured in the system. Then, a kind of distributed adaptive controller is proposed for each follower based on the sliding mode design technique and fault tolerant control technique. Based on graph and Lyapunov stability theory, it is proved that the tracking errors converge to a small neighborhood of the origin with all signals in the closed-loop system being bounded. Finally, simulation results are given to demonstrate the effectiveness of the control scheme proposed in this paper.

Fuzzy Adaptive Finite Time Fault-tolerant Control for Multi-input and Multi-output Nonlinear Systems with Actuator Faults

This paper investigates the problem of fuzzy adaptive finite-time fault tolerant control (FTC) for a class of multi-input and multi-output (MIMO) nonlinear systems with actuator failure. In control design, the fuzzy logic systems (FLSs) are adopted to identify the unknown nonlinear functions and a state observer is constructed to estimate the unmeasurable states. By combining dynamic surface control (DSC) technique with backstepping design, a novel finite-time fuzzy adaptive FTC strategy is proposed based on fault-tolerant control technique to overcomes the “explosion of complexity” problem. The presented control method demonstrates that all signals of the closed-loop system are semi-global practical finite-time stability (SGPFS), and the tracking errors converge to a small neighborhood of zero in a finite time. Finally, a numerical example is provided to illustrate the effectiveness of the presented control method.

Mixed ICC/ℋ∞ control for systems with sensors aging

A faulty sensor may lead to degraded system performance, system instability or even a fatal accident. On the other hand, the increasing need for safety and reliability has motivated the development of fault-tolerant control techniques. In this work, the sensor performance degradation due to its aging is modelled by the increment of sensor measurement noise covariance. The main contribution of this paper is the characterisation of the control synthesis conditions using parametrised linear matrix inequalities (PLMIs) for a multi-objective gain-scheduled noisy output-feedback controller that minimises the output cost on performance with satisfactory system stability, performance and control input covariance constraints ( constraints on the control inputs) in the presence of sensor aging. The closed-loop system stability and performance, in terms of mixed / performances, relative improvement, numerical complexity, computation time, and initial conditions response, are studied, and a numerical example is used to illustrate the effectiveness of the proposed control scheme. The synthesised controller guarantees not only the stability but also the closed-loop mixed / performances, and it is feasible for real-time applications.

Advanced Adaptive Fault Diagnosis and Tolerant Control for Robot Manipulators

In this paper, an adaptive Takagi–Sugeno (T–S) fuzzy sliding mode extended autoregressive exogenous input (ARX)–Laguerre proportional integral (PI) observer is proposed. The proposed T–S fuzzy sliding mode extended-state ARX–Laguerre PI observer adaptively improves the reliability, robustness, estimation accuracy, and convergence of fault detection, estimation, and identification. For fault-tolerant control in the presence of uncertainties and unknown conditions, an adaptive fuzzy sliding mode estimation technique is introduced. The sliding surface slope gain is significant to improve the system’s stability, but the sliding mode technique increases high-frequency oscillation (chattering), which reduces the precision of the fault diagnosis and tolerant control. A fuzzy procedure using a sliding surface and actual output position as inputs can adaptively tune the sliding surface slope gain of the sliding mode fault-tolerant control technique. The proposed robust adaptive T–S fuzzy sliding mode estimation extended-state ARX–Laguerre PI observer was verified with six degrees of freedom (DOF) programmable universal manipulation arm (PUMA) 560 robot manipulator, proving qualified efficiency in detecting, isolating, identifying, and tolerant control for faults inherent in sensors and actuators. Experimental results showed that the proposed technique improves the reliability of the fault detection, estimation, identification, and tolerant control.

Mitigating Sensor Attacks Against Industrial Control Systems

This paper describes how to design and implement a mechanism that helps to mitigate sensor attacks on industrial control systems. The proposed architecture is based on concepts from fault-tolerant control techniques. This short note explains how a Kalman filter can be used simultaneously with optimal disturbance decoupling observers to improve the performance of the mitigation mechanism for sensor attacks in cyber-physical control systems. Our proposal mitigates attacks by generating a signal that compensates the change provoked by the attacker, while at the same time reducing the number of false alarms. We demonstrate the effectiveness of our proposal using a three tanks control simulation.

Adaptive fault tolerant control for time-varying delay system with actuator fault and mismatched disturbance

In this paper, the fault tolerant control (FTC) problem for a class of continuous Lipschitz nonlinear systems with actuator fault, mismatched disturbance, and time-varying delay is investigated. An adaptive integral sliding mode fault tolerant control (AISMFTC) technique is proposed. First, a composite observer is designed to estimate the states and disturbance simultaneously, by introducing a sliding mode observer, the actuator fault is reconstructed. Then, in accordance with the estimated information, an AISMFTC method is designed. In the AISMFTC scheme, two adaptive laws and compensators are contained to compensate the observer errors, deal with the effects of actuator fault and attenuate the disturbance. Furthermore, the H∞performance is considered for the robustness of the system. Finally, the effectiveness of the proposed method is illustrated by two examples.

Adaptive Fuzzy Robust Fault-Tolerant Optimal Control for Nonlinear Large-Scale Systems

The problem of adaptive fuzzy decentralized fault-tolerant optimal control is investigated for nonlinear large-scale systems with actuator faults in this paper. Fuzzy logic systems are utilized to approximate the unknown nonlinear functions and learn cost functions. Filtered signals are adopted to circumvent the problems of an algebraic loop on designing the decentralized controllers. Based on the backstepping technique and fault-tolerant control technique, a decentralized feedforward control strategy is designed. Based on the adaptive critic technique, a decentralized feedback optimal control strategy is designed. By combining the feedforward control strategy with the feedback optimal control strategy, a novel adaptive fuzzy decentralized fault-tolerant optimal control scheme is established. The stability of the closed-loop system is proved by using the Lyapunov stability theory. The effectiveness of the proposed decentralized control approach is confirmed via a simulation example.

Unified FDI and FTC Scheme for Air Path Actuators of a Diesel Engine Using ISM Extended with Adaptive Part

AbstractA unified fault detection and isolation (FDI) and fault tolerant control (FTC) strategy for the diesel engine's air management system has been formulated. Diesel engines need to comply with the strict emission requirements for which they are equipped with specialized sub‐systems for the purpose, such as the variable geometry turbo (VGT) charger and exhaust gas recirculation (EGR). Hardware‐based controls tend to make the system more complex and prone to structured and unstructured faults. This calls for an advanced FTC technique that can ensure desired level of emissions even in the presence of minor system malfunctions. The scheme proposed in this paper detects, isolates and estimates the structured faults and minimizes their effects by re‐positioning the actuators using integral sliding mode (ISM) control. Estimating the magnitude of structured faults help to reduce the ISM controller gains, eventually reducing the chattering. The stability of the system is analyzed using Lyapunov stability criterion. Simulations have been performed using fully validated industrial scale model of a diesel engine to elucidate the effectiveness of our scheme.

RSimplex

As the complexity of Cyber-Physical Systems (CPS) increases, it becomes increasingly challenging to ensure CPS reliability, especially in the presence of software and/or physical failures. The Simplex architecture is shown to be an efficient tool to address software failures in such systems. When physical failures exist, however, Simplex may not function correctly because physical failures could change system dynamics and the original Simplex design may not work for the new faulty system. To address concurrent software and physical failures, this article presents the RSimplex architecture, which integrates Robust Fault-Tolerant Control (RFTC) techniques into the Simplex architecture. It includes the uncertainty monitor, the High-Performance Controller (HPC), the Robust High-Assurance Controller (RHAC), and the decision logic that triggers the switch of the controllers. Based on the output of the uncertainty monitor, we introduce a monitor-based switching rule in the decision logic in addition to the traditional envelope-based rule. The RHAC is designed based on RFTCs. We show that RSimplex can efficiently handle a class of software and physical failures.

A Fault Tolerant Control Technique for Hybrid Modular Multi-Level Converters with Fault Detection Capability

A Fault Tolerant Control Technique for Hybrid Modular Multi-Level Converters with Fault Detection Capability

Fault-Tolerant Control Strategy for Neutral-Point-Clamped Three-Level Inverter

A fault-tolerant control technique is discussed for the Neutral-Point-Clamped (NPC) three-level inverter, which ensures that the NPC inverter operates normally even under device failures. A two-level leg is added to the NPC inverter; when the device open circuit fault occurs, the load of this faulty phase is connected to the neutral point of this two-level leg through the bidirectional thyristors. An improved Space Vector Pulse Width Modulation (SVPWM) strategy called “addition and subtraction substitution SVPWM” is proposed to effectively suppress fluctuation in capacitor neutral-point voltages by readjusting the sequence and action time of voltage vectors. The fault-tolerant topology in this paper has the advantages of fewer switching devices and lower circuit costs. Experimental results show that the proposed fault-tolerant system can operate in balance of capacitor neutral-point voltages at full output power and the reliability of the inverter is greatly enhanced.

Observer-Based Adaptive Fuzzy Fault-Tolerant Optimal Control for SISO Nonlinear Systems.

This paper investigates adaptive fuzzy output feedback fault-tolerant optimal control problem for a class of single-input and single-output nonlinear systems in strict feedback form. The considered nonlinear systems contain unknown nonaffine nonlinear faults and unmeasured states. Fuzzy logic systems are used to approximate cost function and unknown nonlinear functions, respectively. It is assumed that the states of the systems to be controlled are unmeasurable, thus an adaptive state observer is developed. To solve the nonaffine nonlinear fault control design problem, filtered signals are introduced into the adaptive backstepping control design procedures, and in the framework of adaptive critic technique and fault-tolerant control technique, a novel adaptive fuzzy fault-tolerant optimal control scheme is developed. The stability of the closed-loop system is proved by using Lyapunov stability theory. The simulation results verify the effectiveness of the proposed control strategy.

Robust Fault Tolerant Control for Discrete-Time Dynamic Systems With Applications to Aero Engineering Systems

Unexpected faults in actuators and sensors may degrade the reliability and safety of aero engineering systems. Therefore, there is motivation to develop integrated fault tolerant control techniques with applications to aero engineering systems. In this paper, discrete-time dynamic systems, in the presence of simultaneous actuator/sensor faults, partially decoupled unknown input disturbances, and sensor noises, are investigated. A jointly state/fault estimator is formulated by integrating an unknown input observer, augmented system approach, and optimization algorithm. Unknown input disturbances can be either decoupled by an unknown input observer, or attenuated by a linear matrix inequality optimization, enabling the estimation error to be input-to-state stable. Estimator-based signal compensation is then implemented to mitigate adverse effects from the unanticipated actuator and sensor faults. A pre-designed controller, which maintains normal system behaviors under a fault-free scenario, is allowed to work along with the presented fault tolerant mechanism of the signal compensations. The fault-tolerant closed-loop system can be ensured to mitigate the effects from the faults, guarantee the input-to-state stability, and satisfy the required robustness performance. The proposed fault estimation and fault tolerant control methods are developed for both discrete-time linear and discrete-time Lipschitz nonlinear systems. Finally, the proposed techniques are applied to a jet engine system and a flight control system for simulation validation.

Performance comparison of open-circuit fault-tolerant control strategies for multiphase permanent magnet machines for naval applications

Naval propulsion is facing mutations toward electrification of propulsion system. In naval propulsion applications, motors and drives are required to be highly fault tolerant. For reasons such as reliability, smooth torque and partition of power multiphase motors appears to good candidates for electrical marine propulsion. Permanent magnet machines are preferred over others because of their higher power densities and efficiencies, allowing a more compact and efficient propulsion system design. In this paper, a comparison between two open-circuit fault-tolerant control techniques for 5-phase permanent magnet machines (PMSM) with trapezoidal back EMF is presented. The first technique is an off-line one based on the instantaneous power balance and the Joule losses minimization theory. The second technique is an on-line one based on the minimization of copper losses, as this point appears to be particularly relevant for ship propulsion. The objective of these two techniques is to achieve ripple-free torque with minimum Joule losses. Firstly, the dynamic model of the 5-phase PMSM with trapezoidal back-EMF is given. Then detailed derivation of both control techniques and current reference extraction are presented. Finally, simulation and experimental results on a low-power laboratory test bench are presented and discussed.