Fault‐Tolerant Control Allocation for Overactuated Nonlinear Systems

This paper addresses the problem of fault‐tolerant control allocation for input affine nonlinear systems. The proposed scheme is divided in three main tasks: fault detection and estimation using a nonlinear observer, fault isolation through a bank of unknown input observers with a resetting policy to reduce the effects of nonlinearities and control reconfiguration based on reduced order allocation. Analytical results regarding the isolability and reconfigurability of actuator faults are derived and a simulation example is used to illustrate the the proposed fault tolerant control methodology.     

Robust Actuator‐Fault‐Tolerant Control System Based on Sliding‐Mode Observer for Thrust‐Vectoring Aircrafts

In this paper, a robust actuator‐fault‐tolerant control (FTC) system is proposed for thrust‐vectoring aircraft (TVA) control. To this end, a TVA model with actuator fault dynamics, disturbances, and uncertain aerodynamic parameters is described, and a local fault detection and identification (FDI) mechanism is proposed to locate and identify faults, which utilizes an adaptive sliding‐mode observer (SMO) to detect actuator faults and two SMOs to identify and estimate their parameters. Finally, a fault‐tolerant controller is designed to compensate for these actuator faults, disturbances, and uncertain aerodynamic parameters; the approach combines back‐stepping control with fault parameters and a high‐order SMO. Furthermore, the stability of the entire control system is validated, and simulation results are given to demonstrate the effectiveness and potential for this robust FTC system.     

Integral Sliding Mode Fault‐Tolerant Control for Spacecraft With Uncertainties and Saturation

An integral sliding mode fault‐tolerant control method is proposed to deal with faults with matched uncertainties, unmatched uncertainties, and input saturation. Integral sliding mode, control allocation, and parameter identification are included in this method. The Lyapunov stability conditions of the integral sliding mode control for uncertainties and input saturation, respectively, are obtained, which denote the robustness extent of the controller. The direct method for control allocation is improved by adding a judgement before calculating for each facet. Finally, the fault‐tolerant scheme is applied to a six‐wheel spacecraft and simulations are given to show its effectiveness.     

Aero‐Engine DCS Fault‐Tolerant Control with Markov Time Delay Based On Augmented Adaptive Sliding Mode Observer

With a focus on aero‐engine distributed control systems (DCSs) with Markov time delay, unknown input disturbance, and sensor and actuator simultaneous faults, a combined fault tolerant algorithm based on the adaptive sliding mode observer is studied. First, an uncertain augmented model of distributed control system is established under the condition of simultaneous sensor and actuator faults, which also considers the influence of the output disturbances. Second, an augmented adaptive sliding mode observer is designed and the linear matrix inequality (LMI) form stability condition of the combined closed‐loop system is deduced. Third, a robust sliding mode fault tolerant controller is designed based on fault estimation of the sliding mode observer, where the theory of predictive control is adopted to suppress the influence of random time delay on system stability. Simulation results indicate that the proposed sliding mode fault tolerant controller can be very effective despite the existence of faults and output disturbances, and is suitable for the simultaneous sensor and actuator faults condition.     

Fault‐Tolerant Stabilization in Discrete‐Time Multiple‐Integrator Networks with General Information Sharing

The paper considers a network of agents with identical discrete‐time multiple‐integrator dynamics. The agents share information according to an arbitrary topology. The information is relative to the states corresponding to some of the highest integration levels. With reference to this setting, a decentralized stabilization problem is faced, under the further assumption that faults may occur in the communication apparatus of one or several of the agents. A necessary and sufficient solvability condition is presented for the problem, together with formulas for a class of least‐order regulators.     

Fault‐Tolerant Control for Flutter of Airfoil Subject to Input Saturation

In this paper, a fault tolerant control is studied for a two‐dimensional airfoil with input saturation and actuator fault. The dynamic equation of airfoil flutter is firstly established, in which the cubic hard spring nonlinearity of pitch stiffness is considered. Then, an adaptive sliding mode fault tolerant control is derived by using an on‐line updating law to estimate the bound of the actuator fault such that no information about the fault is needed. Furthermore, an auxiliary design system is introduced to resolve actuator saturation in control. Next, Lyapunov stability analysis is carried out to prove that the system is asymptotically stable. Finally, the effectiveness of the proposed controller is verified through numerical simulations. Simulation results indicate that the adaptive sliding mode fault tolerant controller is effective in suppressing airfoil flutter under partial loss of actuator effectiveness performance and input saturation.     

Robust Fault‐Tolerant Control of Launch Vehicle Via GPI Observer and Integral Sliding Mode Control

A robust fault‐tolerant attitude control scheme is proposed for a launch vehicle (LV) in the presence of unknown external disturbances, mismodeling dynamics, actuator faults, and actuator's constraints. The input‐output representation is employed to describe the rotational dynamics of LV rendering three independently decoupled second order single‐input‐single‐output (SISO) systems. In the differential algebraic framework, general proportional integral (GPI) observers are used for the estimations of the states and of the generalized disturbances, which include internal perturbations, external disturbances, and unknown actuator failures. In order to avoid the defects of the conventional sliding surface, a new nonlinear integral sliding manifold is introduced for the robust fault‐tolerant sliding mode controller design. The stability of the GPI observer and that of the closed‐loop system are guaranteed by Lyapunov's indirect and direct methods, respectively. The convincing numerical simulation results demonstrate the proposed control scheme is with high attitude tracking performance in the presence of various disturbances, actuator faults, and actuator constraints.     

Finite‐Time Fault‐Tolerant Control for a Class of Non‐Affine Nonlinear System Using Sliding Mode Disturbance Observer

This study investigates a finite‐time fault‐tolerant control scheme for a class of non‐affine nonlinear system with actuator faults and unknown disturbances. A global approximation method is applied to non‐affine nonlinear system to convert it into an affine‐like expression with accuracy. An adaptive terminal sliding mode disturbance observer is proposed to estimate unknown compound disturbances in finite time, including external disturbances and system uncertainties, which enhances system robustness. Controllers based on finite‐time Lyapunov theory are designed to force tracking errors to zero in finite time. Simulation results demonstrate the effectiveness of proposed method.     

Collaborative Fault Tolerant Control for Non‐Gaussian Stochastic Distribution Systems Based on Adaptive Control Strategy

This paper presents a new fault tolerant controller design method for a class of interconnected non‐Gaussian stochastic distribution system with boundary conditions. In order to obtain the fault estimation value, an observer based fault detection and fault diagnosis algorithms are presented at first, then a collaborative fault tolerant controller is designed based on the adaptive control strategy. Different from most of the existing fault tolerant controllers, when fault occurs the controller need to be reconstructed is for the healthy subsystem in this paper. That is to say, the fault is compensated not by the faulty subsystem itself but by the healthy one. The proposed method is used to a simulation example for demonstration, and the effectiveness is verified.     

Fault‐Tolerant Finite Frequency H∞ Control for Uncertain Mechanical System with Input Delay and Constraint

In this paper, a novel fault‐tolerant finite frequency H_∞ controller (FFHC) is developed for uncertain mechanical system with input delay and constraint. First, the mathematical model of uncertain mechanical system is derived, where the uncertainties occur in mass, damping and stiffness matrices, respectively. Then, in view of the fact that the dominant resonance energies are caused by low‐order vibration modes of mechanical system, the finite frequency control algorithm is investigated to suppress these low‐order resonances peaks. By virtue of Lyapunov‐Krasovskii functional (LKF) and generalized Kalman‐Yakubovich‐Popov (GKYP) lemma, the desirable fault‐tolerant controller can be obtained by convex optimization. Numerical simulations verify the improvements and advantages of proposed cotroller in disturbance rejection when compared with the classic entire frequency H_∞ controller (EFHC).     

Fault‐tolerant adaptive control allocation schemes for overactuated systems

This paper presents a fault‐tolerant adaptive control allocation scheme for overactuated systems subject to loss of effectiveness actuator faults. The main idea is to use an ‘ad hoc’ online parameters estimator, coupled with a control allocation algorithm, in order to perform online control reconfiguration whenever necessary. Time‐windowed and recursive versions of the algorithm are proposed for nonlinear discrete‐time systems and their properties analyzed. Two final examples have been considered to show the effectiveness of the proposed scheme. The first considers a simple linear system with redundant actuators and it is mainly used to exemplify the main properties and potentialities of the scheme. In the second, a realistic marine vessel scenario under propeller and thruster faults is treated in full details. Copyright © 2010 John Wiley & Sons, Ltd.     

Fault‐tolerant control of singularly perturbed systems with actuator faults and disturbances

The article proposes several fault‐tolerant control (FTC) laws for singularly perturbed systems (SPS) with actuator faults and disturbances. One of the main challenges in this context is that the fast‐slow decomposition is not available for actuator faults and disturbances. In view of this, some conditions for the asymptotic stability of the closed‐loop dynamics are investigated by amending the composite Lyapunov approach. On top of this, a closed‐form expression of the upper bound of singular perturbation parameter (SPP) is provided. Moreover, we design several SPP‐independent composite FTC laws, which can be applied when this parameter is unknown. Finally, the chattering phenomenon is eliminated by using the continuous approximation technique. We also emphasize that, for linear SPSs, the FTC design can be formulated as a set of linear matrix inequalities, while the SPP upper bound can be obtained by solving a convex optimization problem. Two numerical examples are given to illustrate the effectiveness of the proposed methodology.     

Observer‐Based Adaptive Output Feedback Fault Tolerant Control for Nonlinear Hydro‐Turbine Governing System with State Delay

This paper focuses on the problem of adaptive output feedback fault tolerant control for a nonlinear hydro‐turbine governing system. A dynamic mathematical model of the system is established, which aims to investigate the dynamic performance of the model under servomotor delay and actuator faults. Then, a fault estimation adaptive observer is proposed to achieve online real‐time diagnosis of system faults. Based on the online fault estimation information, an observer‐based adaptive output feedback fault tolerant controller is designed. Furthermore, under reasonable assumptions, the results demonstrate that the closed‐loop control system can achieve global asymptotic stability by Lyapunov function. Finally, the numerical simulation results are presented to indicate the satisfaction control effectiveness of the proposed scheme.     

Youla Parameterization Based Adaptive Controller Design for Fault Tolerant Control

A new adaptive controller for fault tolerant control (FTC) is proposed in this paper. It is realized by adapting the reconfigurable fault parameterized matrix with the estimated fault. The proposed approach is applied in a linear reduced order aircraft model, and simulation results show the effectiveness.     

Adaptive Fault‐Tolerant Control of Uncertain MIMO Systems with Reduced Requirement on Desired Trajectory Under Unknown Control Direction

This paper aims at investigating the tracking control problem for a class of multi‐input multi‐output (MIMO) nonlinear systems with non‐square control gain matrix subject to unknown control direction and uncertain desired trajectory. By using the artificial neural network (NN) reconstructs the target trajectory with actual disguised trajectory, we are able to design a practical and stable tracking control scheme without the need for the unavailable desired trajectory. Nussbaum‐type function is incorporated in the control law to handle the unknown control direction. The remarkable feature of the proposed scheme is that it is robust against modeling uncertainties and tolerant to actuation faults, yet guarantees that the closed‐loop system is stable in the sense of ultimately uniformly bounded (UUB). The effectiveness of the proposed control schemes are illustrated through simulation results.     

Novel MPC‐Based Fault Tolerant Tracking Control Against Sensor Faults

The problem of active fault‐tolerant tracking control with control input and system output constraints is studied for a class of discrete‐time systems subject to sensor faults. A time‐varying fault‐tolerant observer is first developed to estimate the real system state from the faulty sensor output and control input signals. Then by using the estimated state at each time step, a model predictive control (MPC)‐based fault‐tolerant tracking control scheme is presented to guarantee the desired tracking performance and the given input and output constraints on the faulty system. In comparison with many existing fault‐tolerant MPC methods, its main contribution is that the proposed state estimator is designed by the simple and online numerical computation to tolerate the possible sensor faults, so that the regular MPC algorithm without fault information can be adopted for the online calculation of fault‐tolerant control signal. The potential recursive infeasibility and computational complexity due to the faults are avoided in the scheme. Additionally, the closed‐loop stability of the post‐fault system is discussed. Simulative results of an electric throttle control system verify the effectiveness of the proposed method.     

Fault‐tolerant spacecraft attitude control under actuator saturation and without angular velocity

In this paper, a fault‐tolerant control scheme is proposed to control the attitude of a rigid spacecraft subject to external disturbances and multiple system uncertainties, as well as actuator faults and saturation. More challengingly, it is assumed that the angular velocity is unavailable. A super‐twisting observer with time‐varying gain is firstly designed to accurately estimate the angular velocity in finite time. The choice of the time‐varying gain is dependent on a state‐norm estimate. Then, using the information from the observer (estimate of angular velocity), a fault‐tolerant controller is proposed, where an adaptive law is introduced to address the unknown loss of effectiveness and neural networks are used to approximate the unknown nonlinear functions. It is proved that the attitude orientations converge to the desired values at a fixed time. Finally, a simulation example is utilized to verify the effectiveness of the proposed scheme.