Design of fault‐tolerant control for MTTF

Mean time to failure (MTTF) is an important reliability index of fault‐tolerant control systems, which is chosen as a design objective in this paper. However, it is usually evaluated from stochastic reliability models, and no analytical expression is available to relate MTTF to controller parameters. To overcome this difficulty, a two‐stage design scheme is proposed in this paper: A gradient‐based search is firstly carried out on probabilistic H_∞ performance characteristics for MTTF requirement; a sequential randomized algorithm with a weighted violation function is then developed for a controller design to satisfy the required H_∞ performance, and its convergence is guaranteed with probability 1. Two iterative algorithms are carried out alternately to implement this scheme, and a controller can be designed for MTTF requirement. Copyright © 2008 John Wiley & Sons, Ltd.     

Active fault‐tolerant consensus control of Lipschitz nonlinear multiagent systems

This article investigates the active fault‐tolerant consensus problem for Lipschitz nonlinear multiagent systems under detailed balanced directed graph and actuator faults. First, a fault detection filter for each agent is designed, and all agents can be divided into two categories: healthy agents and possibly faulty agents. Second, fully distributed adaptive fault‐tolerant consensus protocols for healthy and possibly faulty agents are proposed to achieve state consensus. Third, based on the fault detection method and fault‐tolerant consensus protocols, active fault‐tolerant consensus algorithms are given. Simulation examples are presented to verify the effectiveness of the proposed active fault‐tolerant algorithms.     

Adaptive fault‐tolerant formation control for quadrotors with actuator faults

In this paper, we investigate the fault‐tolerant formation control of a group of quadrotor aircrafts with a leader. Continuous fault‐tolerant formation control protocol is constructed by using adaptive updating mechanism and boundary layer theory to compensate actuator fault. Results show that the desired formation pattern and trajectory under actuator fault can be achieved using the proposed fault‐tolerant formation control. A simulation is conducted to illustrate the effectiveness of the method.     

Observer‐based fault‐tolerant control for a class of hybrid impulsive systems

This paper investigates the fault‐tolerant control (FTC) problem for a class of hybrid nonlinear impulsive systems. Two kinds of faults are considered: continuous faults that affect each mode and discrete faults that affect the impulsive switching. The FTC strategy is based on the trade‐off between the frequency of switching and the decreasing rate of Lyapunov functions along the solution of the system, which maintains the stability of overall hybrid impulsive systems in spite of these two kinds of faults. A switched reluctance motor example is taken to illustrate the applicability of the proposed method. Copyright © 2009 John Wiley & Sons, Ltd.     

Novel frameworks for the design of fault‐tolerant control using optimal sliding‐mode control

This paper describes 2 schemes for a fault‐tolerant control using a novel optimal sliding‐mode control, which can also be employed as actuator redundancy management for overactuated uncertain linear systems. By using the effectiveness level of the actuators in the performance indexes, 2 schemes for redistributing the control effort among the remaining (redundant or nonfaulty) set of actuators are constructed based on an ‐based optimal sliding‐mode control. In contrast to the current sliding‐mode fault‐tolerant control design methods, in these new schemes, the level of control effort required to maintain sliding is penalised. The proposed optimal sliding‐mode fault‐tolerant control design schemes are implemented in 2 stages. In the first stage, a state feedback gain is derived using an LMI‐based scheme that can assign a number of the closed‐loop eigenvalues to a known value whilst satisfying performance specifications. The sliding function matrix related to the particular state feedback derived in the first stage is obtained in the second stage. The difference between the 2 schemes proposed for the sliding‐mode fault‐tolerant control is that the second one includes a separate control allocation module, which makes it easier to apply actuator constraints to the problem. Moreover, it will be shown that, with the second scheme, we can deal with actuator faults or even failures without controller reconfiguration. We further discuss the advantages and disadvantages of the 2 schemes in more details. The effectiveness of the proposed schemes are illustrated with numerical examples.     

Distributed fault‐tolerant control design for spacecraft finite‐time attitude synchronization

This paper develops two distributed finite‐time fault‐tolerant control algorithms for attitude synchronization of multiple spacecraft with a dynamic virtual leader in the presence of modeling uncertainties, external disturbances, and actuator faults. The leader gives commands only to a subset of the followers, and the communication flow between followers is directed. By employing a novel distributed nonsingular fast terminal sliding mode and adaptive mechanism, a distributed finite‐time fault‐tolerant control law is proposed to guarantee all the follower spacecraft that finite‐time track a dynamic virtual leader. Then utilizing three distributed finite‐time sliding mode estimators, an estimator‐based distributed finite‐time fault‐tolerant control law is proposed using only the followers' estimates of the virtual leader. Both of them do not require online identification of the actuator faults and provide robustness, finite‐time convergence, fault‐tolerant, disturbance rejection, and high control precision. Finally, numerical simulations are presented to evaluate the theoretical results. Copyright © 2015 John Wiley & Sons, Ltd.     

Sliding‐mode fault‐tolerant control using the control allocation scheme

This paper is devoted to the design of a novel fault‐tolerant control (FTC) using the combination of a robust sliding‐mode control (SMC) strategy and a control allocation (CA) algorithm, referred to as a CA‐based sliding‐mode FTC (SMFTC). The proposed SMFTC can also be considered a modular‐design control strategy. In this approach, first, a high‐level SMC, designed without detailed knowledge of systems' actuators/effectors, commands a vector of virtual control signals to meet the overall control objectives. Then, a CA algorithm distributes the virtual control efforts among the healthy actuators/effectors using the real‐time information obtained from a fault detection and reconstruction mechanism. As the underlying system is not assumed to have a rank‐deficient input matrix, the control allocator module is visible to the SMC module resulting in an uncertainty. Hence, the virtual control, in this scheme, is designed to be robust against uncertainties emanating from the visibility of the control allocator to the controller and imperfections in the estimated effectiveness gain. The proposed CA‐based SMFTC scheme is a unified FTC, which does not need to reconfigure the control system in the case of actuator fault or failure. Additionally, to cope with actuator saturation limits, a novel redistributed pseudoinverse‐based CA mechanism is proposed. The effectiveness of the proposed schemes is discussed with a numerical example.     

Sensor fault‐tolerant control of a magnetic levitation system

In this paper, a fault‐tolerant switching control strategy is implemented on a magnetic levitation (MAGLEV) system. Two sensors are embedded in the MAGLEV system and their measurements used by two independent estimators. Each sensors–estimator combination, together with a feedback controller can levitate and stabilize a 1‐in steel ball at a desired position in the air. The paper focuses on the design and testing of a switching scheme which, at each instant of time, selects the sensors–estimator combination that provides the best closed loop performance based on a chosen criterion. Theoretical results on the system linearization around an operating point ensure local closed‐loop stability and good performance under the occurrence of an abrupt fault in one of the plant sensors. Experimental results are provided which confirm the fault‐tolerant capabilities of the strategy. Copyright © 2010 John Wiley & Sons, Ltd.     

Integral sliding mode fault‐tolerant control allocation for a class of affine nonlinear system

This paper develops novel fault‐tolerant integral sliding mode control allocation schemes for a class of an overactuated affine nonlinear system. The proposed schemes rely on an existing baseline controller, and the objective is to retain the nominal (fault‐free) closed‐loop performance in the face of actuator faults/failures by effectively utilizing actuator redundancy. The online control allocation reroutes the control effort to healthy actuators using the knowledge of actuator effectiveness level estimates. One of the proposed schemes is tested in simulation using a well‐known high‐fidelity model of a large civil transport aircraft (B747) from the literature. Good simulation results show the efficacy of the scheme.     

Adaptive fixed‐time fault‐tolerant control for rigid spacecraft using a double power reaching law

In this paper, an adaptive fixed‐time fault‐tolerant control scheme is presented for rigid spacecraft with inertia uncertainties and external disturbances. By using an inverse trigonometric function, a novel double power reaching law is constructed to speed up the state stabilization and reduce the chattering phenomenon simultaneously. Then, an adaptive fixed‐time fault‐tolerant controller is developed for the spacecraft with the actuator faults, such that the fixed‐time convergence of the attitude and angular velocity could be guaranteed, and no prior knowledge on the upper bound of the lumped uncertainties is required anymore in the controller design. Comparative simulations are provided to illustrate the effectiveness and superior performance of the proposed scheme.     

Integrated fault estimation and fault‐tolerant control for stochastic systems with Brownian motions

This paper presents an integrated robust fault estimation and fault‐tolerant control technique for stochastic systems subjected to Brownian parameter perturbations. The augmented system approach, unknown input observer method, and optimization technique are integrated to achieve robust simultaneous estimates of the system states and the means of faults concerned. Meanwhile, a robust fault‐tolerant control strategy is developed by using actuator and sensor signal compensation techniques. Stochastic linear time‐invariant systems, stochastic systems with Lipschitz nonlinear constraint, and stochastic systems with quadratic inner‐bounded nonlinear constraint are respectively investigated, and the corresponding fault‐tolerant control algorithms are addressed. Finally, the effectiveness of the proposed fault‐tolerant control techniques is demonstrated via the drivetrain system of a 4.8 MW benchmark wind turbine, a 3‐tank system, and a numerical nonlinear model.     

Third‐order sliding mode fault‐tolerant control for satellites based on iterative learning observer

The attitude fault‐tolerant control problem for a satellite with reaction‐wheel failures, uncertainties, and unknown external disturbances is investigated in this paper. Firstly, an iterative learning observer (ILO) is proposed to achieve fault detection, isolation, and estimation. Secondly, based on the ILO, a third‐order sliding mode controller is proposed to stabilize the satellite attitude rapidly under unknown external disturbances and reaction‐wheel faults. Thirdly, the asymptotically stability of the ILO and the third‐order sliding mode controller is proved by using the Lyapunov stability theory. Finally, simulation results demonstrate that the proposed control scheme is more effective and feasible by comparing with other fault‐tolerant control approach.     

Adaptive fault‐tolerant control for feedback linearizable systems with an aircraft application

This paper investigates fault‐tolerant control (FTC) for feedback linearizable systems (FLSs) and its applications. The dynamic effects caused by the actuator faults on the feedback linearized model are firstly analyzed, which reveals that under actuator faults, the control input in the linearized model is affected by uncertain terms. In the framework of model reference control, the first FTC strategy is proposed as a robust controller, which achieves asymptotic tracking control of the FLS under actuator faults. A disadvantage of this strategy is that it relies on explicit information about several parameters in the actuator faults. This requirement is later relaxed by combining the robust FTC strategy with an adaptive technique to generate the adaptive FTC law, which is then improved to alleviate possible chattering of the actuator and estimation drifting of the adaptive parameter. Finally, the proposed FTC strategies are evaluated by reference command tracking control of a pendulum and an air‐breathing hypersonic vehicle under actuator faults. Simulation results demonstrate good tracking performance, which confirms effectiveness of the proposed strategies. Copyright © 2014 John Wiley & Sons, Ltd.     

Adaptive fault‐tolerant control for a class of output‐constrained nonlinear systems

In this work, by incorporating a tan‐type barrier Lyapunov function into the Lyapunov function design, we present a novel adaptive fault‐tolerant control (FTC) scheme for a class of output‐constrained multi‐input single‐output nonlinear systems with actuator failures under the perturbation of both parametric and nonparametric system uncertainties. We show that under the proposed adaptive FTC scheme, exponential convergence of the output tracking error into a small set around zero is guaranteed, while the constraint requirement on the system output will not be violated during operation. In the end, two illustrative examples are presented to demonstrate the effectiveness of the proposed FTC scheme. Copyright © 2015 John Wiley & Sons, Ltd.     

Supervisory adaptive fault‐tolerant control against actuator failures with application to an aircraft

In this paper, a supervisory adaptive fault‐tolerant control scheme is proposed for a class of uncertain nonlinear systems with multiple inputs. The multiple inputs are the outputs of an actuator group that may act either on one control surface or on multiple control surfaces and may fail during operation. With some actuator groups as backups, the supervisory adaptive control includes 2 modes: the adaptive compensation mode and the switching mode. The former is used to compensate for the failure of an actuator group as long as at least one actuator of the group works normally, and the latter, to switch the controller from a failed group to a healthy one when the failure is detected by one of the monitoring functions that are constructed to supervise some variables related to system stability. It is shown that with the proposed scheme, all signals of the closed‐loop system are bounded, and prescribed transient and steady state performance of the tracking error can be guaranteed. An aircraft example is used to demonstrate the application of the proposed scheme.     

Adaptive multivariable finite‐time continuous fault‐tolerant control of rigid spacecraft

The problem of fault‐tolerant attitude tracking control for rigid spacecraft in the presence of inertia uncertainties, actuator faults, and external disturbances is investigated in this paper. A novel adaptive finite‐time continuous fault‐tolerant control strategy is developed by combining the fast nonsingular terminal sliding mode surface and the adaptive multivariable super‐twisting algorithm, which improves the robustness while preserving high accuracy and finite‐time convergence. The main features of the control strategy are the double‐layer adaptive algorithm based on equivalent control, which ensures nonoverestimation of the control gain and the continuous controller, which maintains better property of chattering reduction. Finally, the efficiency of the proposed controller is illustrated by numerical simulations.     

Robust multiactuator fault‐tolerant MPC design for constrained systems

In this paper, we present a robust actuator fault‐tolerant control strategy for constrained linear systems in the presence of bounded state and input disturbances. The scheme is based on a bank of state estimators that match different fault situations that can occur in the system. A fault detection and isolation unit verifies that suitable residual variables lie inside pre‐computed sets and selects the estimate that matches the current plant behaviour. A bank of robustly stabilizing tube‐based model predictive control laws is designed, each associated to a fault scenario, and the appropriate controller is selected among them by using the information provided by the fault detection and isolation module. By means of ‘tubes’ of trajectories, we ensure robust closed‐loop exponential stability of the constrained system and good performance in the fault‐free case and under the occurrence of abrupt actuator faults, including actuator outage and loss of effectiveness by an unknown amount. Copyright © 2012 John Wiley & Sons, Ltd.     

Actuator fault‐tolerant control of ocean surface vessels with input saturation

In this paper, an actuator robust fault‐tolerant control is proposed for ocean surface vessels with parametric uncertainties and unknown disturbances. Using the backstepping technique and Lyapunov synthesis method, the adaptive tracking control is first developed by incorporating the actuator configuration matrix and considering actuator saturation constraints. The changeable actuator configuration matrix caused by rotatable propulsion devices is considered. Next, the actuator fault‐tolerant control is developed for the case when faults occur in propulsion devices of the ocean surface vessel. Rigorous stability analysis is carried out to show that the proposed fault‐tolerant control can guarantee the stability of the closed‐loop system under certain actuator failure. Finally, simulation studies are given to illustrate the effectiveness of the proposed adaptive tracking control and fault‐tolerant control. Copyright © 2015 John Wiley & Sons, Ltd.     

Sliding mode fault‐tolerant control of uncertain system: A delta operator approach

This paper is concerned with the sliding mode control of uncertain nonlinear systems against actuator faults and external disturbances based on delta operator approach. The nonlinearity, actuator fault, and external disturbance are considered in this study, and the bounds of Euclidean norms of the nonlinearity and the specific lower and upper bounds of the actuator faults and the disturbances are unknown knowledge. Our attention is mainly focused on designing a sliding mode fault‐tolerant controller to compensate the effects from the nonlinearity, unknown actuator fault, and external disturbance. Based on Lyapunov stability theory, a novel‐adaptive fault‐tolerant sliding mode control law is deigned such that the resulting closed loop delta operator system is finite‐time convergence and the actuator faults can be tolerated, simultaneously. Finally, simulation results are provided to verify the effectiveness of the proposed control design scheme. Copyright © 2017 John Wiley & Sons, Ltd.