Presence Of Unknown Actuator Faults Research Articles

Adaptive vibration control for constrained moving vehicle-mounted nonlinear 3D rigid-flexible manipulator system subject to actuator failures

This paper proposes an active adaptive fault-tolerant control scheme for position tracking and vibration suppression of a constrained moving rigid-flexible manipulator system (RFMS) in three-dimensional (3D) space. The investigated RFMS comprises four parts: a vehicle, a rotatable base, a rigid link, and a flexible link, which is first modeled using nonlinear partial differential equations (PDEs) in terms of Hamilton’s principle. The system may suffer from unknown actuator faults, and the proposed control strategy can compensate for the faults without knowing the fault type and information. The displacement constraint of the vehicle can be ensured by using the barrier Lyapunov function. In the presence of unknown actuator faults and the displacement constraint, the angular position tracking of rigid link, flexible link and rotatable base, and vehicle position tracking can be realized. At the same time, the vibration of the flexible link can be effectively suppressed. The closed-loop system is proven to be asymptotically stable via employing the extended LaSalle’s invariance. Numerical simulations are carried out to verify the effectiveness of the proposed control protocol.

Event-triggered adaptive fault-tolerant attitude synchronization and tracking control of multiple rigid bodies with finite-time convergence

This study investigates finite-time attitude synchronization and tracking control of multiple rigid bodies under event-triggered control strategy in presence of actuator faults and an external disturbance. The event-triggered implementation technique aims to reduce resource utilization in regard to control effort and communication burden. To achieve this aim, the adaptive sliding mode structure is used, and a novel triggering condition is proposed. In presence of unknown actuator faults and external disturbance, it is shown that the multiple rigid bodies track a time-varying attitude of a virtual leader synchronously in finite time under limited data communication. Moreover, a lower bound on the inter-event times has been derived to ensure that the Zeno behavior is avoided. The effectiveness of the proposed method is validated by numerical simulation along with comparison with another relevant research.

Event-driven adaptive fault-tolerant tracking control for uncertain mechanical systems with application to flexible spacecraft

An event-driven neural network–based fault-tolerant tracking control scheme is investigated for uncertain mechanical systems with performance guaranteed in the presence of unknown actuator faults and external disturbances. Compared with the existing works, the primary advantage is that the detections and identifications of actuator faults are not required, whereas the convergence rate and tracking accuracy can be guaranteed a priori by constructing an adaptive tracking controller with a few aperiodic updates. Moreover, by using the norm-bounding skill, only two adaptive parameters are needed to update online, which dramatically decreases the complexity of the corresponding adaptive schemes. Finally, applications to the attitude stabilization and tracking control of the flexible spacecraft are used to validate the effectiveness of the proposed control scheme.

Finite-Time Fault Estimator Based Fault-Tolerance Control for a Surface Vehicle With Input Saturations

In this article, in the presence of unknown actuator faults, input saturations, and complete unknowns including both internal dynamics and external disturbances, exact trajectory-tracking problem of a surface vehicle (SV) is solved by creating a finite-time fault estimator based fault-tolerance control (FFE-FTC) scheme. By virtue of input saturations, smoothly saturated controls are separated from input nonlinearities including unknown faults, thereby leaving faults-mixed unknowns be exactly observed by a finite-time fault estimator (FFE). By defining an integral sliding-mode (ISM) manifold and deriving affine controls with unknown gains from smooth saturations, Nussbaum technique is deployed to synthesize a uniformly adaptive finite-time controller working in a large range outside input saturations. Within the close range where saturations are removed, an ISM-based nonsmooth controller with finite-time auxiliary compensation dynamics is devised to finely stick tracking errors to the origin. Intuitively, large- and close-range control actions are triggered by measuring the ISM error, thereby contributing to the entire FFE-FTC scheme, which achieves exact fault-tolerance and unknown rejection under input saturations. Lyapunov and nonsmooth syntheses prove that the closed-loop FFE-FTC system is globally finite-time stable. Simulation results and comparisons on a prototype SV demonstrate remarkable performance in terms of feasibly saturated controls and exact trajectory-tracking, simultaneously.

Adaptive Backstepping Based Fault-tolerant Control for High-speed Trains with Actuator Faults

In this paper, the fault-tolerant control problem is addressed for high-speed trains with unknown time-varying system parameters, traction system actuator faults and disturbances. To represent the unknown time-varying system parameters in mathematical form, a new piecewise time-varying indicator including commonly used 0–1 case, is employed, which results in a piecewise time-varying nonlinear model with some unknown parameters and piecewise disturbances. For the healthy system with the time-varying indicator in the unknown forms and having known switching time instants, an adaptive backstepping controller is proposed to deal with the unknown system parameters and disturbances and achieve the position tracking. Further, the adaptive backstepping based fault-tolerant controller with adaptive laws is developed to guarantee the system states boundedness and the position tracking, in the presence of unknown actuator faults. Based on Lyapunov function, the stability of the closed-loop system is proved. Simulation studies on CRH2 (China Railway High-speed Train II) verify the performance of the proposed fault-tolerant control scheme.

Neural Adaptive Fault Tolerant Control of Nonlinear Fractional Order Systems Via Terminal Sliding Mode Approach

This article proposes an adaptive neural output tracking control scheme for a class of nonlinear fractional order (FO) systems in the presence of unknown actuator faults. By means of backstepping terminal sliding mode (SM) control technique, an adaptive fractional state-feedback control law is extracted to achieve finite time stability along with output tracking for an uncertain faulty FO system. The unknown nonlinear terms are approximated by radial-basis function neural network (RBFNN) with unknown approximation error upper bound. Using convergence in finite time and fractional Lyapunov stability theorems, the finite time stability and tracking achievement are proved. Finally, the proposed fault tolerant control (FTC) approach is validated with numerical simulations on two fractional models including fractional Genesio–Tesi and fractional Duffing's oscillator systems.

Indirect adaptive fuzzy fault-tolerant tracking control for MIMO nonlinear systems with actuator and sensor failures

In this paper, an active fuzzy fault tolerant tracking control (AFFTTC) scheme is developed for a class of multi-input multi-output (MIMO) unknown nonlinear systems in the presence of unknown actuator faults, sensor failures and external disturbance. The developed control scheme deals with four kinds of faults for both sensors and actuators. The bias, drift, and loss of accuracy additive faults are considered along with the loss of effectiveness multiplicative fault. A fuzzy adaptive controller based on back-stepping design is developed to deal with actuator failures and unknown system dynamics. However, an additional robust control term is added to deal with sensor faults, approximation errors, and external disturbances. Lyapunov theory is used to prove the stability of the closed loop system. Numerical simulations on a quadrotor are presented to show the effectiveness of the proposed approach.

RETRACTED ARTICLE: Immersion and invariance based fault tolerant adaptive spacecraft attitude control

In this paper, an immersion and invariance (I&I) adaptive fault tolerant satellite attitude tracking control scheme is proposed. The proposed controller is capable of track the desired trajectory in the presence of unknown actuator multiplicative faults and unknown inertial matrix. Also based on Lyapunov direct method, all closed loop signals are proven to be globally asymptotically stable. The main advantage of this controller is improving closed loop performance while maintaining stability in the presence of unknown actuator faults. This method does not rely on certainty equivalence principle so it can be used to control the transient response of overall closed loop system by means of controlling the parameter estimation behavior which is not possible in traditional adaptive control. Numerical simulations are performed to demonstrate the effectiveness of proposed control scheme.

Adaptive fault tolerant control using integral sliding mode strategy with application to flexible spacecraft

Adaptive-based integral sliding mode control scheme is developed to solve the actuator fault-tolerant compensation problem for linear time-invariant system in the presence of unknown actuator faults and external disturbances. A nonlinear integral-type sliding manifold is first presented that incorporates a virtual nominal control to achieve prescribed specifications of the perturbed system, and an adaptive sliding mode controller is constructed to automatically compensate for external disturbances and unknown time-invariant faults. It is shown that the proposed controller has the capability to guarantee that the resulting closed-loop system is asymptotically stable. Control design methodology is then extended to tackle with the unknown time-varying actuator faults. It is proved that any given level of gain attenuation from external disturbance/parametric estimation error to system output is achieved with the developed control law. The closed-loop performance of the new control solution derived here is evaluated extensively through numerical simulations in which the flexible spacecraft attitude control under both the external disturbances and actuator faults are considered.

Multiple model adaptive reconfiguration control of state delayed systems

In this paper, a new direct model reference adaptive control framework based on a multiple model approach is proposed. The main objective is to synthesize a fault-tolerant controller which reconfigures the faulty system with state delay. This approach provides stable adaptation for a class of linear systems with state delay in the presence of unknown actuator faults. The proof of stability is based on the Lyapunov−Krasovskii function, while appropriate switching of the multiple models ensures asymptotic tracking for the system outputs, and under the proposed algorithms, the tracking errors of the reconfigured system trend to zero rapidly. Simulation results are presented to illustrate the efficiency of the proposed method.