Active Fault Tolerant Control System Research Articles

A Novel Approach to Real-Time Fault Accommodation in NREL's 5-MW Wind Turbine Systems

This paper presents a real-time mechanism to tolerate faults occurring in a wind turbine (WT) system. This system is a FAST coded simulator designed by the U.S. National Renewable Energy Laboratory's (NREL's) National Wind Turbine Center. The demonstrated mechanism lies under the taxonomy of active fault-tolerant control (AFTC) systems, namely the projection-based approach. In the proposed approach, we do not use any a priori information about the model of the turbine in real-time. In fact, we use the online measurements generated by WT. Based on the given control objectives, and the observed measurements, an occurring fault is accommodated by reconfiguring the controller such that the turbine generates the rated power even under faulty conditions. Second, no use of an explicit fault-diagnosis module is seen in this approach. Therefore, the fault accommodation delay in the proposed AFTC structure is smaller than the delay as experienced in the traditional structure of AFTC systems.

Fuzzy gain-scheduled active fault-tolerant control of a wind turbine

Advanced fault detection and accommodation schemes are required for ensuring efficient and reliable operation of modern wind turbines. This paper presents a novel approach in designing a fault detection and diagnosis (FDD) and fault-tolerant control (FTC) scheme for a wind turbine using fuzzy modeling, identification and control techniques. First, an improved gain-scheduled proportional-integral (PI) control system based on fuzzy gain scheduling (FGS) technique for multi-input and multi-output wind turbine system is designed. Then, to accommodate sensor faults and based on a signal correction algorithm, an active fault-tolerant control system (AFTCS) is developed as an extension of the gain-scheduled PI control system. The AFTCS exploits the fault information from a model-based FDD scheme developed using fuzzy modeling and identification method. The proposed schemes are evaluated by a series of simulations on a well-known large off-shore wind turbine benchmark in the presence of wind turbulences, measurement noises, and different realistic fault scenarios. All results indicate high effectiveness and robustness of the designed control systems in both fault-free and faulty operations of the wind turbine.

Active fault tolerant control systems by the semi‐Markov model approach

SUMMARYThis paper investigates the active fault tolerant control problem via the H ∞ state feedback controller. Because of the limitations of Markov processes, we apply semi‐Markov process in the system modeling. Two random processes are involved in the system: the failure process and the fault detection process. Therefore, two corresponding semi‐Markov processes are integrated in the closed‐loop system model. This framework can generally accommodate different types of system faults, including the randomly happening sensor faults and actuator faults. A controller is designed to guarantee the closed‐loop system stability with a prescribed noise/disturbance attenuation level. The controller can be readily solved by using convex optimization techniques. A vertical take‐off and landing vehicle example with actuation faults is used to demonstrate the effectiveness of the proposed technique. Copyright © 2013 John Wiley & Sons, Ltd.

OPTIMAL CHOICE WITHIN A FAULT TOLERANT FLIGHT CONTROL SYSTEM

Safety of aircraft during the flight is one of the most important problems that concerns of all aviation. Failures/faults main elements automatic control system and damages to the external contour of the aircraft by foreign objects always lead to a change the characteristics of the aircraft, direct and indirect economic costs and sometimes to injury or death of passengers and crew. Real-time active fault tolerant control system makes it possible to warn or prevent emergency situations and thus improve safety.

A Control Reconfiguration Strategy for Post-Sensor FTC in Induction Motor-Based EVs

This paper deals with experimental validation of a reconfiguration strategy for sensor fault-tolerant control (FTC) in induction-motor-based electric vehicles (EVs). The proposed active FTC system is illustrated using two control techniques: indirect field-oriented control (IFOC) in the case of healthy sensors and speed control with slip regulation (SCSR) in the case of failed current sensors. The main objective behind the reconfiguration strategy is to achieve a short and smooth transition when switching from a controller using a healthy sensor to another sensorless controller in the case of a sensor failure. The proposed FTC approach performances are experimentally evaluated on a 7.5-kW induction motor drive.

Hybrid Fault-Tolerant Flight Control System Design Against Partial Actuator Failures

A model to represent loss of control effectiveness in an aircraft is developed by analyzing physical faults in the hydraulically-driven control surfaces. A hybrid fault-tolerant control system (FTCS) that combines the merits of passive and active FTCSs is proposed to accommodate this kind of partial actuator failures. The hybrid FTCS is able to first slow down the rate of fault induced system deterioration with minimal fault information so that the fault detection and diagnosis (FDD) schemes can have additional time to achieve more accurate fault diagnosis. Once the correct fault information is obtained, the hybrid FTCS can counteract the faults effectively through an optimal reconfigurable controller. Depending on the availability of actuator redundancies, the passive FTCS and the reconfigurable controller are designed in the framework of linear matrix inequality (LMI) approach. Case studies of an aircraft subject to different degree of loss of control effectiveness have been carried out to prove the effectiveness of this new approach to FTCS.

Active fault tolerant control for a class of linear time-delay systems in finite frequency domain

This article deals with the problem of active fault tolerant control (AFTC) for a class of linear time-delay systems in a finite frequency domain. A new ℋ∞ controller in generalised internal model control architecture with an observer-based fault estimator is proposed for the AFTC system. Based on online fault estimation and accommodation, the closed-loop system stability and ℋ∞ performance for both fault free and faulty cases are guaranteed. With the aid of the generalised Kalman–Yakubovich–Popov lemma for time-delay systems, sufficient conditions on the existence of such an AFTC system ensuring simultaneous finite frequency estimation and control performance are derived. The calculation procedure of the parameter matrices of the fault estimator and ℋ∞ controller is also proposed. Finally, a numerical example is given to illustrate the effectiveness of the proposed method.

Postgraduate Education on Fault Diagnosis and Control Reconfiguration in Aerospace

The computer-aided teaching process has increased the interaction between students and professors thus improving the learning process. The goal of courses for graduate students is to teach both a higher level of theoretical and methodological matters and how to design systems. This goal needs a project-based education that is an education performed while implementing a project. In the present paper, our project-based education deals with the implementation of an AFTCS (Active Fault Tolerant Control System) for a UAS (Unmanned Aerial System). The activity to be dealt with is twofold: one is of a methodological type and the other of a technical applicative type.

Fault-Tolerant Flight Control System Design Against Control Surface Impairments

An active fault-tolerant flight control system design technique against control surface impairments is proposed here. The aircraft control surface impairments are modeled as a polytopic linear parameter varying (LPV) system. Relying on the existing control surface redundancy of the aircraft, both state feedback and static output feedback controllers are synthesized against various degrees of control surface impairments. Simulation examples of an aircraft subject to inner elevon impairments have been used to illustrate the design process and to demonstrate the effectiveness of the proposed method.

Active FTC for Non-linear Aircraft based on Feedback Linearization and Robust Estimation

The current work concerns the development of a novel approach to robust fault estimation to achieve active Fault Tolerant Control (FTC) for a nonlinear aircraft system. The novelty lies in the combination of a feedback linearization controller, with a state/fault estimator. The active FTC system combines these to compensate for the faults acting in the control system. The paper focuses on the development of an active FTC scheme applied to a nonlinear unmanned airborne vehicle (UAV) system with different faults acting on three actuators and with wind turbulence affecting the vertical force. The aircraft dynamics are approximately linearized on-line using a dynamic inversion controller based on differential geometry theory. For the linearized system with bounded input disturbance, a robust state-space observer is designed to simultaneously estimate system states and actuator faults by solving a Lyapunov equation. The FTC scheme is achieved via a linear matrix inequality (LMI) approach, based on the estimated states/faults. The simulation results demonstrate the efficiency and robustness of the proposed design.

Active Fault Tolerant Control for a Class of Discrete-time Switched Linear Systems

This paper deals with the active fault tolerant control (AFTC) problem for a class of discrete-time linear switched systems under arbitrary switching through the residual feedback control structure. The design of the AFTC system is implemented in two steps. First, for residual generation, an optimal FDF is proposed by maximizing H_/H∞ or H∞/H∞ performance index based on a coupled Riccati equation. Then, a residual feedback control law is given for compensating the influence of fault and the parameter matrices of the controller are obtained by solving a non-convex optimization problem using linear matrix inequality (LMI) technique. A numerical example is given to demonstrate the effectiveness of the proposed method.

Fault-tolerant Compensation Control Incorporating Actuator Criticality

In this paper, actuator criticality analysis is integrated in the design of active fault-tolerant control systems. The main objective consists in the fault-tolerant controller synthesis which guarantees a highest overall system reliability while still maintaining immediate stability and tracking performance of reconfigured system. To achieve this task, an actuator criticality indicator is defined and incorporated in the fault-tolerant controller design. Such metric is implemented to manage the control inputs in order to improve the system dependability both in normal operation and in the presence of faults. Actuator criticality analysis of systems modeled by a state space representation is proposed. A design of the fault-tolerant compensation controller is reformulated as a linear matrix inequality problem.

Performance evaluation based fault tolerant control with actuator saturation avoidance

Performance evaluation based fault tolerant control with actuator saturation avoidanceIn this paper, a new approach regarding a reconfigured system is proposed to improve the performance of an active fault tolerant control system. The system performance is evaluated with an intelligent index of performance. The reconfiguration mechanism is based on a model predictive controller and reference trajectory management techniques. When an actuator fault occurs in the system, a new degraded reference trajectory is generated and the controller calculates new admissible controls. A constraint set and cost function are established to avoid actuator saturation and reduce the control energy spent in closed loop dynamics. The effectiveness of the proposed method is illustrated using a hydrothermal system subject to actuator faults and constraints on actuator dynamic ranges.

Fault Tolerant Model Predictive Control of Quad-Rotor Helicopters with Actuator Fault Estimation

AbstractModel predictive control (MPC) at each time step minimizes a cost function subject to dynamical constraints to obtain a stabilizing control signal. Further, MPC is one of the few methodologies that can be used to design feedback control for nonlinear dynamical systems taking into consideration of actuator saturations. It can thus serve as a suitable fault tolerant control approach for quad-rotor helicopter governed by nonlinear dynamics. However, MPC needs a relatively accurate model of the post-failure system to calculate a stabilizing control signal. The problem becomes more critical where the system dynamics is described by a nonlinear model, because there exist few effective nonlinear parameter estimators with reasonable online computation time. To address this issue, for online actuator fault estimation, this paper investigates Moving Horizon Estimation (MHE) and Unscented Kalman Filter (UKF) as two methods for nonlinear parameter estimation. A framework is then formulated for integrating MHE/UKF based fault estimator with MPC to form an active fault tolerant control system for systems with nonlinear constrained dynamics. Performance and computation requirement of both algorithms are also investigated.

H∞ stabilisation of non-linear stochastic active fault-tolerant control systems: fuzzy-interpolation approach

This study addresses the H ∞ control design problem systematically for a class of non-linear stochastic active fault-tolerant control systems with Markovian parameters. A sufficient condition for the non-linear stochastic fault-tolerant H ∞ control u 1 (x(t), η t ) is given in terms of a set of coupled Hamilton-Jacobi inequalities (HJIs). Then, a fuzzy-interpolation approach is developed to conquer the difficulty in solving the coupled HJIs, which sustains a fault-tolerant H ∞ fuzzy control u 2 (x(t), η t ) by solving linear matrix inequalities, instead of HJIs. A simulation example is presented to illustrate the effectiveness of the proposed design method.

Virtual sensors design for active fault tolerant control system applied to a winding machine

This paper presents a method for designing a virtual sensor in the case of Fault Tolerant Control. The whole approach, described in the paper, is applied to a winding machine. The process is modelled by a Linear Time Varying (LTV) model. The control of the web tension is based on the estimated or virtual measurements as feedback variables. The main contribution concerns the design of an accurate bank of observers able to both isolate and estimate sensor faults while preserving the system’s integrity in terms of structure and performances. The objective of Active Fault Tolerant Control System, is to maintain current performances close to desirable ones and preserve stability conditions when faults occur. The presented method allows one to isolate and to estimate sensor faults. The effectiveness and performances of the strategy are illustrated on the winding machine in the case of a complete loss of sensor.

Active Fault Tolerant Control System for a High Accuracy Planet—Image and Stellar—Pointing Satellite

AbstractThis paper focuses on the problem of nonlinear fault detection, diagnosis, and fault tolerant control for a satellite model through the construction of disturbance decoupled adaptive filters designed via the nonlinear geometric approach. Each filter of the bank is sensitive to all but one fault, and decoupled from aerodynamic disturbances. In order to fulfil the requirements of the proposed mission, the disturbance decoupling represents the key point, since the aerodynamic model is often uncertain. To the authors' knowledge, this is the first work presenting the solution of the aerodynamic disturbance decoupling problem. The controller reconfiguration logic exploits a further control loop depending on the on-line estimate of the fault signals. Simulations results for the case of a nonlinear satellite model with aerodynamic, gravitational, magnetic, and solar pressure disturbances are presented with reference to a pointing mission. The suggested approach allows to achieve better performances with respect to control schemes simply designed to be robust with respect to the considered disturbance contributions.

A solution for management of fault diagnosis and fault tolerance performances in active FTC schemes

AbstractThe general context of this paper is the design of active Fault Tolerant Control (FTC) strategies for Linear Time Invariant (LTI) uncertain systems. Active FTC systems work in such a way that when a fault is diagnosed by a Fault Detection and Isolation (FDI) unit, the control law is reconfigured to compensate the effect of fault. FDI and FTC performances are thus highly connected. In this paper, a procedure based on the structured singular value μ and its generalization μg is proposed to manage, for a given application, the interaction between the set of FDI and FTC units. It is shown that asymptotic stability is guaranteed and that global performance can be reached by means of the used μ/μg criteria. The HiMAT aircraft benchmark is used to illustrate the main steps of the method. Copyright © 2010 IFAC

Stochastic asymptotic stability of Markovian jumping neural networks with Markov mode estimation and mode-dependent delays

In a previous work [Z.D. Wang, Y.R. Liu, L. Yu, X.H. Liu, Phys. Lett. A 356 (2006) 346] an exponential stability analysis for a class of Markovian jumping neural networks (MJNNs) was presented. In this Letter we employ the same technique to extend the results for MJNNs with time-varying delays and mode estimation, appropriate for active fault-tolerant control systems.

Active fault-tolerant fuzzy control design of nonlinear model tracking with application to chaotic systems

The active fault-tolerant control (FTC) design problem for nonlinear model tracking based on the Takagi and Sugeno (T-S) fuzzy model is dealt with. For a nonlinear active FTC system, two random processes with Markovian transition characteristics are introduced to model the system component failure process and the fault detection and isolation (FDI) decision process used to reconfigure the control law, respectively. The random behaviour of the FDI process is conditioned on the failure process state. First, the T-S fuzzy model is employed to exactly represent the FTC system and the nonlinear reference model. A fuzzy controller is used to generate the FDI-decision-dependent control signal. As a result, an error fuzzy system with two Markovian jump parameters is obtained. Then, based on a stochastic Lyapunov function, a linear matrix inequality approach to the fuzzy control design is developed such that the error system is exponentially stable in the mean square and an H infin model-tracking performance is guaranteed. Finally, the proposed design method is successfully applied to the chaotic model-tracking control between Lorenz system and Rossler system.