Presence Of Actuator Faults Research Articles

Chattering-free Fault-tolerant Attitude Control with Fast Fixed-time Convergence for Flexible Spacecraft

This paper is mainly dedicated to the challenging issue of fixed-time attitude control for a flexible spacecraft in the presence of actuator faults, external disturbances and coupling effect of flexible modes. The attitude controller is developed by employing a fixed-time nonsingular terminal sliding mode under which the convergence time is bounded and independent of the initial states. This robust attitude controller is able to provide superior properties such as fast fixed-time attitude manoeuvring with high pointing accuracy, singularity avoidance and chattering free. More specifically, a new reaching law is employed to provide convergence rate improvement as well as chattering alleviating simultaneously. The actuator fault problem is also considered and the attitude control is achieved even when the actuators experience severe faults. The proposed controller ensures that the closed-loop attitude system is stable in the sense of fixed-time stability concept. Furthermore, since the upper bound of external disturbances and flexible vibrations acting on the spacecraft is not available, an adaptation mechanism is presented. Numerical simulations demonstrate that the proposed controller is able to successfully accomplish attitude control with high attitude pointing accuracy and stability in spite of the actuator faults, flexible structures vibrations and external disturbances.

Robust fault tolerant control of continuous-time switched systems: An LMI approach

The present paper proposes a new robust fault tolerant control (RFTC) design for continuous-time switched systems. The main objective is to design in an integrated way the couple (controller, observer) that allows to stabilize switched systems even in the presence of actuator faults. A state/fault estimation observer is designed to simultaneously estimate system state and actuator faults. Based on this observer, a fault tolerant controller is developed to stabilize the system and accommodate the actuator faults automatically. The RFTC problem is formalized in the form of linear matrix inequalities (LMI) rather than bilinear matrix inequalities (BMI), to avoid the difficulty of solving BMIs. Finally, a numerical example composed of unstable subsystems is studied to show the applicability and efficiency of the obtained results.

Adaptive Fault-Tolerant Compensation Control for T–S Fuzzy Systems With Mismatched Parameter Uncertainties

This paper is concerned with the adaptive fault-tolerant compensation control problem for a class of Takagi–Sugeno (T–S) fuzzy systems with mismatched parameter uncertainties and actuator faults. A matrix transformation technique is introduced to relax the restriction regarding the input matrices of T–S fuzzy systems considered in the existing results. Moreover, by combining backstepping-like technique and adaptive control method, a new adaptive fault-tolerant control scheme with compensation mechanism is proposed to achieve the desirable control performance. In addition, it is proved that the states of the resulting closed-loop fuzzy system converge to zero asymptotically even in the presence of actuator faults and mismatched parameter uncertainties. Finally, two simulation examples are given to verify the effectiveness of the presented control scheme.

Performance-Guaranteed Fault-Tolerant Control for Uncertain Nonlinear Systems via Learning-Based Switching Scheme.

This article is concerned with the challenge of guaranteeing output constraints for fault-tolerant control (FTC) of a class of unknown multi-input single-output (MISO) nonlinear systems in the presence of actuator faults. Most industrial systems are equipped with redundant actuators and a fault detection-isolation mechanism for accommodating unexpected actuator faults. To simplify the system design and reduce the risk of false alarm or missed detection brought by the detection unit, a learning-based switching function scheme is proposed to automatically activate different sets of actuators in a rotational manner without human intervention. By this means, no explicit fault detection mechanism is needed. An additional step has been made to guarantee that the system output remains in user-defined time-varying asymmetric output constraints all the time during the occurrence of failures by utilizing error transformation techniques. The stability of the transformed system can equivalently deliver the result that the original system output stays in the required bounds. Hence, system crash or further catastrophic outcomes can be avoided. A neural network is integrated to embody the adaptive FTC design for dealing with unknown system dynamics. The dynamic surface control (DSC) technique is also invoked to decrease complexity. Furthermore, the stability analysis is carried out by the standard Lyapunov approach to guarantee that all the signals of the closed-loop system are semiglobally uniformly ultimately bounded. Finally, the simulation results are provided to verify the effectiveness of the proposed scheme.

Distributed Resilient Observer-Based Fault-Tolerant Control for Heterogeneous Multiagent Systems Under Actuator Faults and DoS Attacks

In this article, we investigate the distributed resilient observer-based fault-tolerant control problem for heterogeneous linear multiagent systems in the presence of actuator faults and denial-of-service (DoS) attacks. In order to estimate the system matrix and the state of the exosystem, novel resilient adaptive distributed observers are proposed. By using the dwell time technique and the Lyapunov stability theory, the observer error system is shown to be exponentially stable even under the influence of DoS attacks. Then, an algorithm is proposed to determine observer parameters with the aim of maximizing the ability to resist attacks. Besides, a novel fault-tolerant controller without causing chattering behaviors is designed to compensate for actuator faults. Moreover, it is proved that the developed controller solves the cooperative fault-tolerant output regulation problem by using a newly derived lemma. Finally, an illustrative example is provided to verify the effectiveness of the proposed method.

Simultaneous actuator fault estimation and fault-tolerant tracking control for multi-agent systems: a sliding-mode observer-based approach

This study is concerned with the design of a distributed simultaneous fault estimation and fault-tolerant control scheme for linear multi-agent systems subject to actuator faults. For each agent, a sliding-mode observer-based estimator/controller module is proposed that uses the available local relative output measurements and the information transmitted from the neighbouring agents. By considering the performance index and using the linear matrix inequality technique, the parameters of the observers are designed such that the fault estimation is robust against disturbances and at the same time, a robust leader-following mission in the presence of actuator fault is guaranteed. As the fault estimator and fault tolerant controller are integrated in the proposed strategy, there is no need for separate design of these units. Moreover, the proposed method improves the existing fault estimation techniques in terms of both complexity and performance. Two simulation examples are presented to illustrate the effectiveness of the proposed methodology.

Robust neural event-triggered control for dynamic positioning ships with actuator faults

This paper presents a novel robust neural event-triggered control algorithm to achieve the dynamic positioning operation of marine surface ships in the presence of actuator faults. In the algorithm, the model uncertainty and the “explosion of complexity” are addressed by fusion of the robust neural damping and dynamic surface control techniques. The gain related adaptive law is constructed to compensate the gain uncertainties and the unknown actuator faults, which improved the stability of the ship dynamic loop system. Furthermore, the event-triggered mechanism is introduced to reduce the communication load between the controller and actuator. For merits of the aforementioned design, the proposed algorithm is with the advantages of concise form and easy to be implemented in practical ocean engineering. Based on the Lyapunov theory, rigorous analysis is proved to guarantee the semi-global uniform ultimate boundedness (SGUUB) of the closed-loop system. Finally, numerical simulations are conducted to demonstrate the validity and feasibility of the proposed algorithm.

Robust fault tolerant control scheme for descriptor systems using fixed control allocation

This paper investigates the design problem of fixed control allocation (CA) scheme for the multi-input multi-output (MIMO) linear time invariant (LTI) uncertain descriptor system (DS) to achieve fault tolerant control (FTC) where the control strategy is designed based on integral sliding mode. The CA technique used here has the capability to redistribute the control actions to the remaining redundant actuators in the face of faults/ failures without reconfiguring the structure of the controller. The control allocation scheme uses the information of actuator effectiveness matrix to redistribute the control actions therefore it doesn’t require any information about the actuator faults/ failures. The proposed scheme has the capability to handle actuator faults as well as total failure of certain actuators, provided that there is enough redundancy in the system. Unlike traditional integral sliding mode control (ISMC), the discontinuous control part of ISMC is replaced by a multivariable super-twisting sliding mode control. Under this modification, the control signal become continuous while retaining the nominal system’s performance in the face of actuator faults/ failures and external disturbances. The integral switching surface is designed in the context of descriptor system in such a way that this strategy will guarantee the robustness almost from the initial time of the system response. The rigorous stability analysis is performed to find the condition for stability to ensure robust closed loop stability of the uncertain descriptor systems in the presence of actuator faults and failures. Finally, in the simulation section, various situations related to fault/ failure cases are considered for a numerical example of descriptor system, to verify the effectiveness of the proposed design.

Adaptive fault tolerant control for a class of uncertain fractional‐order systems based on disturbance observer

SummaryIn this paper, a class of fractional‐order nonlinear systems are considered in the presence of actuator faults. A novel fault tolerant control scheme based on disturbance observer has been presented, where the actuator faults are considered as the system disturbance and can be approximated by the proposed disturbance observer. The developed fault tolerant control guarantees the convergence of the closed‐loop system and the output tracking performance. Finally, a simulation example is presented to verify the effectiveness of the new method.

Fixed-time velocity-free sliding mode tracking control for marine surface vessels with uncertainties and unknown actuator faults

In this paper, a novel fixed-time fault-tolerant control scheme is proposed for trajectory tracking of marine surface vessels (MSVs). A fixed-time extended state observer (FXESO) is developed to enhance the robustness. In conjunction with the FXESO, a fixed-time sliding mode control (FXSMC) law is applied to trajectory tracking control. The designed tracking control system can be stabilized to the origin in fixed time in the presence of actuator faults (AF), unmodelled dynamics, unmeasurable system states and exogenous disturbances. Specially, the convergence time of the system is independent of the initial states of an MSV. Meanwhile, a complete proof of closed-loop fixed-time stability is given. Finally, comparative simulations manifest the performance and advantage of the developed fixed-time control method.

Fault-tolerant formation control of stochastic nonlinear multi-agent systems with time-varying weighted topology

In this paper, the fault-tolerant formation control of nonlinear stochastic multi-agent systems in the presence of actuator faults, disturbances, and time-varying weighted topology is considered. While most traditional fault-tolerant control methods in the literature use fixed weights on the topology edges, in this study these weights are considered time-varying using a pre-designed function, which allows formulating the system more realistically. Moreover, in contrast with previous works on fault-tolerant multi-agent systems, in this study, the model of the agents is considered to be stochastic in general. Furthermore, the actuators of the agents are considered to have a time-varying fault of additive and multiplicative types. A passive and an active fault-tolerant controllers are designed based on the back-stepping sliding-mode approach. In the passive method, a constant robust controller is proposed using an upper bound of the faults while, in the active controller, the additive and multiplicative faults are estimated using adaptive laws. The active and passive fault-tolerant controllers guarantee that the formation errors converge to a bounded region near the origin in a mean-square sense and all of the existing signals in the closed-loop system remain bounded in probability. The results of the formation control are extended to consensus control as well. Finally, a stochastic multi-aircraft model and an RLC circuit with stochastic part are used as two case studies to illustrate the effectiveness of the proposed design method.

Robust Finite-Time Tracking for Uncertain Linear Systems with Actuator Faults

In this paper, a robust finite-time fault-tolerant control (FTC) scheme is developed for uncertain linear systems in the presence of actuator faults. Since the system uncertainties and actuator faults are unknown, the controller parameters are updated online by the adaptive laws without the need for fault detection and isolation. It is proved that the proposed state-feedback model reference adaptive finite-time FTC scheme can guarantee that the tracking error converges to a small neighborhood of the origin in finite time. An application example for an aircraft lateral-directional dynamic system is presented to show the effectiveness of the proposed control scheme.

Fault-tolerant control with state and disturbance observers for vehicle active suspension systems

This paper deals with the design of a fault-tolerant control scheme of active suspension systems for vehicle ride comfort. Unknown actuator failures from a variety of reasons cause performance deterioration of the active suspension controller. The proposed fault-tolerant control algorithm consists of two parts: a compensation for actuator failure and a fault mode selector. The main function of the fault compensation strategy is to estimate and compensate for the loss of effectiveness of the actuators. A suspension state observer and a disturbance observer operate simultaneously to determine the feedback control input. The controller and observer have been developed based on a reduced full-car dynamic model that contains only the vehicle body dynamics. The main advantage of the proposed observer is that an easily accessible and inexpensive measurement is only required and the effect of unknown road disturbance on the estimation error is completely removed. To cope with complete failure cases, the fault mode selector is also designed to redistribute the control input to the remaining healthy actuators. Tracking of the loss of effectiveness of the actuators is used for the fault model identification. The performance of the proposed approach has been evaluated via simulation studies. It is shown that the vehicle ride comfort in the presence of actuator faults can be improved by the proposed combined strategy of the fault compensation method and the fault mode selector.

Distributed adaptive fractional‐order fault‐tolerant cooperative control of networked unmanned aerial vehicles via fuzzy neural networks

This study presents a distributed fault-tolerant cooperative control (FTCC) strategy to achieve the attitude synchronisation tracking control of networked unmanned aerial vehicles (UAVs) in the presence of actuator faults and model uncertainties. By utilising the fuzzy neural networks (FNNs), the unknown non-linear terms induced by actuator faults and model uncertainties are estimated as lumped uncertainties. A set of distributed sliding-mode estimators (DSMEs) is then employed to estimate the leader UAV's attitudes for the follower UAVs via a distributed communication network. Based on the estimated knowledge from FNNs and DSMEs, a group of distributed FTCC laws is developed for all follower UAVs by using the fractional-order calculus. It is proven that with the proposed control scheme, all follower UAVs can track the attitudes of the leader UAV and the tracking errors are uniformly ultimately bounded even when a portion of networked UAVs encounters multiple actuator faults. Comparative simulation results are presented to demonstrate the effectiveness of the proposed approach.

Distributed Fault-Tolerant Cooperative Control for Multi-UAVs Under Actuator Fault and Input Saturation

This paper investigates a difficult problem of distributed fault-tolerant cooperative control for multiple unmanned aerial vehicles (UAVs) in the presence of actuator faults and input saturation. To eliminate the “explosion of complexity” in the traditional backstepping architecture, the dynamic surface control is utilized to construct the distributed fault-tolerant control scheme. Moreover, by using the disturbance observer technique, actuator faults and external disturbances are estimated as lumped uncertainties. Furthermore, to reduce the adverse influence caused by the control input saturation of UAVs, auxiliary dynamic systems are introduced to regulate the control signals when the input signals are saturated for a long time. The key feature is that the proposed fault-tolerant cooperative controller is designed based on the local information of neighboring UAVs and the factors including actuator faults, input saturation, and external disturbances are simultaneously addressed. It is shown by Lyapunov approach and graph theory that the synchronization tracking stability can be guaranteed and all follower UAVs can track the leader UAV. The effectiveness of the proposed control scheme is further validated by numerical simulation results.

Fault-tolerant output-constrained control of unknown Euler–Lagrange systems with prescribed tracking accuracy

This paper explores the output-constrained tracking control problem for unknown Euler–Lagrange systems subject to actuator faults, in the case where the reference trajectory is unknown in advance. The presence of actuator faults may lead to the loss of strong controllability of the system assumed in the existing literature on robust control of multi-input multi-output nonlinear systems. The lack of a priori knowledge on the reference trajectory renders the current constraint-handling techniques to achieve prescribed tracking accuracy infeasible. To conquer the above obstacles, a novel fault compensation scheme is designed in this paper, and a new-type error boundary is introduced to the control design. It is proved that the proposed approach guarantees output tracking with prescribed accuracy and constraint satisfactions simultaneously, even if actuator faults occur. A comparative simulation on a robot manipulator is conducted to further illustrate the established theoretical findings.

Robust Hybrid Control Design for Stochastic Markovian Jump System via Fault Alarm Approach

In this brief, the fault alarm-based hybrid control is developed for a class of stochastic Markovian jump systems subject to actuator faults, disturbances and time-varying delay. The main objective of this brief is to design a reliable state feedback controller such that the resulting closed-loop system is stochastically stable under a prescribed $H_{\infty }$ performance level $\gamma > 0$ in the presence of actuator faults. More precisely, an alarm signal is considered by designing suitable threshold to avoid false alarm, (i.e.,) to invoke the reliable controller and remove the estimated value of actuator failure. Based on the Lyapunov stability theory and the extended Wirtinger-based single integral inequality, a novel set of sufficient criteria is constructed in the form of linear matrix inequality (LMI) constraints to ensure the stochastic stability of the addressed system. Further, the control design parameters are calculated by solving the developed LMI constraints. Finally, two numerical examples including RLC series circuit with simulation results is provided to illustrate the effectiveness of the proposed control scheme.

Fault-tolerant control for fuzzy switched singular systems with persistent dwell-time subject to actuator fault

This paper investigates the problem of fault-tolerant state feedback fuzzy control for discrete-time nonlinear switched singular systems subject to the actuator fault. The typical Takagi-Sugeno model is utilized to process the nonlinearity of the systems. For the purpose of describing the intermittent occurrence of fast and slow switching among subsystems, a switching signal complying with persistent dwell-time switching regularity is introduced for the first time into the analysis of nonlinear switched singular systems. The primary objective is focused on constructing a fault-tolerant controller which can ensure that the closed-loop system is exponentially admissible with a prescribed l2 -gain performance in the presence of actuator fault. By using mode-dependent Lyapunov function and employing an improved matrix decoupling method, sufficient conditions with less conservatism for the existence of the desired controller are established and the explicit form of the controller gains is presented. For explaining the effectiveness of the proposed method, two illustrative examples are given finally.

Adaptive Fixed-Time Attitude Tracking Control for Rigid Spacecraft With Actuator Faults

This paper investigates fixed-time attitude tracking maneuver of rigid spacecraft in the presence of actuator faults, external disturbances, and inertia uncertainties. First, a fast finite-time stable system is investigated in the sense of fixed-time concept. Then, a nonlinear observer is designed to estimate the information of the lumped uncertainties, and this observer, integral sliding mode and geometric homogeneity are used to formulate one attitude controller, which can guarantee attitude tracking errors can be stabilized to the origin. Second, another adaptive controller is presented to steer attitude tracking errors to the equilibrium point. Lyapunov techniques are implemented to ensure the fixed-time stability of the closed-loop system. Finally, numerical simulations are carried out to demonstrate the performance of the proposed controllers.

Distributed Finite-Time Fault-Tolerant Containment Control for Multiple Unmanned Aerial Vehicles.

This paper investigates the distributed finite-time fault-tolerant containment control problem for multiple unmanned aerial vehicles (multi-UAVs) in the presence of actuator faults and input saturation. The distributed finite-time sliding-mode observer (SMO) is first developed to estimate the reference for each follower UAV. Then, based on the estimated knowledge, the distributed finite-time fault-tolerant controller is recursively designed to guide all follower UAVs into the convex hull spanned by the trajectories of leader UAVs with the help of a new set of error variables. Moreover, the unknown nonlinearities inherent in the multi-UAVs system, computational burden, and input saturation are simultaneously handled by utilizing neural network (NN), minimum parameter learning of NN (MPLNN), first-order sliding-mode differentiator (FOSMD) techniques, and a group of auxiliary systems. Furthermore, the graph theory and Lyapunov stability analysis methods are adopted to guarantee that all follower UAVs can converge to the convex hull spanned by the leader UAVs even in the event of actuator faults. Finally, extensive comparative simulations have been conducted to demonstrate the effectiveness of the proposed control scheme.