Robust Fault-tolerant Control Research Articles

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.

Co-design between robust L 1 fault-tolerant control and discrete event-triggered communication scheme for networked control systems with transmission delay and quantisation

In order to take into account both the system performance and economical utilisation of network resources, under the discrete event-triggered communication scheme, the problems of the robust fault-tolerant control for a class of uncertain networked control systems with actuator fault constraint are investigated. In consideration with the imperfect networked environment with transmission delay and quantisation, a model of the error dependent networked closed-loop fault system is established. By constructing an appropriate delay-dependent Lyapunov–Krasovskii functional, the sufficient condition for the existence of robust fault-tolerant controller is obtained for an error dependent networked closed-loop fault system, and a co-design method for gaining the discrete event-triggered parameter and fault-tolerant controller is proposed in terms of linear matrix inequalities. Notice that the structure of Lyapunov–Krasovskii functional which considers the piecewise-linear sawtooth structure characteristic of transmission delay, a less conservative result is obtained. Finally, simulation examples are provided to illustrate the feasibility of the proposed method.

Robust qLPV Tracking Fault-Tolerant Control of a 3 DOF Mechanical Crane

The main aim of this paper is to propose a robust fault-tolerant control for a three degree of freedom (DOF) mechanical crane by using a convex quasi-Linear Parameter Varying (qLPV) approach for modeling the crane and a passive fault-tolerant scheme. The control objective is to minimize the load oscillations while the desired path is tracked. The convex qLPV model is obtained by considering the nonlinear sector approach, which can represent exactly the nonlinear system under the bounded nonlinear terms. To improve the system safety, tolerance to partial actuator faults is considered. Performance requirements of the tracking control system are specified in an H∞ criteria that guarantees robustness against measurement noise, and partial faults. As a result, a set of Linear Matrix Inequalities is derived to compute the controller gains. Numerical experiments on a realistic 3 DOF crane model confirm the applicability of the control scheme.

Observer based finite-time fault tolerant quadrotor attitude control with actuator faults

This paper investigates a nonlinear robust fault tolerant control method for rejecting wind disturbances and accommodating actuator faults in quadrotor attitude system. Actuator faults are modeled as a sudden loss of actuator effectiveness (LAE) in the rotor thrust. First, the lumped disturbances, including wind disturbances and LAE actuator faults, are estimated by a novel adaptive finite-time extended state observer (AFTESO). Additionally, a rigorous analysis for finite-time convergence of estimation errors is provided. Next, based on the estimated information from AFTESO, a continuous fast nonsingular terminal sliding mode controller (CFNTSMC) is proposed to achieve high-precision tracking and finite-time convergence. CFNTSMC provides faster convergence performance in both reaching and sliding phases. The proposed control scheme combines ESO-based and NTSM-based anti-disturbance mechanisms, which retains the advantages of the two control schemes and limits their drawbacks, thus achieving promising features, as finite-time convergence, fault tolerance and chattering suppression. The finite-time stability of the closed-loop system is supported by Lyapunov theory. Finally, extensive numerical simulations are carried out to demonstrate the effectiveness of the proposed method in different working regimes.

Fault tolerant control for linear parameter varying systems: An improved robust virtual actuator and sensor approach

This paper presents a robust Fault-Tolerant Control (FTC) methodology for the design of virtual sensors and virtual actuators for discrete-time Linear Parameter Varying (LPV) systems. Conditions based on Linear Matrix Inequalities (LMIs) are proposed for the synthesis of a reconfiguration block composed of a virtual actuator and a virtual sensor, guaranteeing input-to-state stability (ISS). The main contribution of the proposed FTC approach is to deal with LPV models where input and output matrices can be parameter-dependent. Moreover, differently from results found in the literature, a single reconfiguration block can be designed to be robust to different kinds and magnitudes of faults. Real-time level-control experiments illustrate the efficiency of the proposed procedure; the system used in the experiments consists of a nonlinear two coupled tanks with two inputs and two outputs, represented by an LPV model subject to sensor and actuator faults. Experimental results and comparisons with results in the literature indicate that the proposed approach is able to mitigate the fault effects with better performance indices than the literature approaches.

Robust fault estimation and fault tolerant control for three-motor web-winding systems

This paper studies the problems of fault estimation and fault tolerant control for three-motor web-winding systems in the presence of multiple disturbances and actuator faults. A disturbance compensation-based fault estimation observer is designed to estimate the system actuator faults. By setting the reference outputs, a method of obtaining equilibrium control inputs and equilibrium states is formulated to achieve the variation dynamic model at equilibrium points by Taylor expansion. Then, based on the estimated actuator faults, an effective fault tolerant control strategy is proposed by the methods of interval matrix and disturbance local compensation. Sufficient conditions of asymptotic stability of the estimation error system and the closed-loop system are derived based on the Lyapunov theory. Fault estimation observer and fault tolerant controller gain matrices are obtained by solving the linear matrix inequalities. Finally, simulations and analysis are performed to verify the effectiveness of the proposed method.

Fuzzy robust fault-tolerant control for offshore ship-mounted crane system

In this paper, a novel event-triggered fuzzy robust fault-tolerant control approach is designed to handle the offshore ship crane nonlinear system with actuator fault and external disturbance. The main objective of this study is to realize the tracking control ability of the outputs while saving the transmission resources, which is achieved by constructing the integrated adaptive sliding mode controller and event trigger mechanism. The fuzzy logic theory is used both in the observer and controller design processes to approximate the nonlinear unknown functions. First, the information of the crane system state, actuator fault, and lumped disturbance are acquired by designing a fuzzy composite observer. Then, a novel adaptive sliding mode controller is presented by using the estimated values. In the proposed control scheme, two adaptive parameters are contained to consider the disturbance elimination and to enhance the tracking performance. An adaptive law is also included to compensate for the fuzzy approximation error. Furthermore, a novel event-triggered controller is proposed to reduce the transmission load of the crane system while also maintaining the tracking ability of the crane system. The no Zeno phenomenon performance is analyzed and, finally, the application to the crane system is given to show the fault tolerance ability of the proposed method.

Velocity-based robust fault tolerant automatic steering control of autonomous ground vehicles via adaptive event triggered network communication

This paper proposes a velocity-based robust fault tolerant automatic steering control approach for autonomous ground vehicles via an adaptive event triggered network communication mechanism. Firstly, as the vehicle longitudinal velocity is not fixed but time-varying, a polytope with finite vertices is adopted to construct a linear parameter varying vehicle system model. Secondly, since network-induced delay and actuator fault inevitably occur in the control system, a novel Lyapunov function is formulated to guarantee the asymptotical stability of the closed-loop system. Moreover, an advanced event triggered communication scheme is proposed for the co-design of robust automatic steering controller, which is quite effective to reduce network communication burden and enhance resource utilization of the shared band-limited in-vehicle communication network. Finally, numerical simulations on two cases are carried out to evaluate and verify the effectiveness and robustness of the proposed controller. Compared with existing studies, the proposed controller contributes greatly to the economization of communication resource and improvement of path following performance and lateral stability.

Robust fault tolerant control based on adaptive observer for Takagi-Sugeno fuzzy systems with sensor and actuator faults: Application to single-link manipulator

In this work, we investigate the problem of control for nonlinear systems represented by Takagi-Sugeno (T-S) fuzzy models affected by both sensor and actuator faults subject to an unknown bounded disturbances (UBD). For this, we design an adaptive observer to estimate state, sensor and actuator fault vectors simultaneously despite the presence of external disturbances. Based on this observer, we develop a fault tolerant control (FTC) law not only to stabilize closed loop system, but also to compensate the fault effects. For the observer-based controller design, we propose less conservative conditions formulated in terms of linear matrix inequalities (LMIs). Moreover, both observer and controller gains are calculated via solving a set of LMIs only in single step. Finally, comparative results and an application to single-link flexible joint robot are afforded to prove the efficiency of the proposed design.

Robust Fault-Tolerant Control for Underactuated Takeoff and Landing UAVs

This article surveys the trajectory tracking issue of underactuated vertical takeoff and landing (VTOL) unmanned aerial vehicles (UAVs) subject to thrust and torque faults, i.e., loss of efficiency and actuator biases. In particular, a robust control algorithm against time-varying faults and disturbances is proposed. To exploit the underactuated nature of the VTOL UAV system, the control algorithm is developed based on a hierarchical framework, under which the position and attitude loops are studied in sequence. Specifically, by implementing a novel robust fault-tolerant control strategy, a force command is first synthesized for the position tracking to the desired trajectory, and then, a desired torque using an innovative sliding manifold is designed such that the nonsingular attitude tracking to an attitude command is achieved. This attitude command, as well as the desired thrust, is extracted from the synthesized force command. In terms of hierarchical system stability theory, it is shown that the overall closed-loop error system is asymptotically stable. Finally, simulation results validate and highlight the tracking performance of the proposed control algorithm.

Distributed fault-tolerant control of modular and reconfigurable robots with consideration of actuator saturation

A novel decomposition-based distributed robust fault-tolerant control method is proposed for modular and reconfigurable robots based on joint torque sensing. The designed robust controller compensates for both model uncertainties and a class of actuator faults. In addition, the proposed scheme does not require a fault detection and diagnosis module, avoiding time delay associated with it. Furthermore, a radial basis function neural network-based compensation scheme is proposed to deal with the actuator saturation problem, which is especially critical when actuator fault has to be tolerated by the control system. Simulation results have shown the effectiveness of the presented method.

Fault-Tolerant Prescribed Performance Attitude Tracking Control for Spacecraft Under Input Saturation

This brief examines the problem of attitude tracking control with prescribed performance guarantees for a spacecraft subjected to actuator faults and input saturation. To pursue this, the open-loop tracking error dynamics with certain designer-specified performance constraints is first transformed into an equivalent “state-constrained” one, via an error transformation; furthermore, the resulting dynamics is augmented with a dynamic system, which is tactfully constructed to ensure that the control input satisfies the magnitude limits. Subsequently, a robust fault-tolerant controller is developed by using a low-pass filter and an auxiliary system in conjunction with adaptive backstepping design. It is shown that the control algorithm developed not only achieves the stable attitude tracking with prescribed behavioral metrics but also guarantees the boundedness of all the closed-loop signals. Finally, simulation results are given to evaluate the efficacy of the proposed scheme.

Robust Fault Tolerant Control Design for Nonlinear Systems not Satisfying Matching and Minimum Phase Conditions

This paper proposes an adaptive sliding mode fault tolerant control design for lipschitz nonlinear system subject to simultaneous actuator and sensor faults. First, in order to estimate the system states, actuator and sensor faults, only one observer with an adaptive nonlinear gain is required where the minimum phase condition is relaxed to delectability and the matching condition is weakened to become a condition related to the system dimensions. Furthermore, our approach is applicable where there are faults greater than outputs. Next, a virtual sensor technique is developed to replace a failed, missing or corrupted sensor to provide a signal having the same effect of the nominal sensor. Then, this study provides an adaptive sliding mode fault tolerant control to achieve an optimal interaction between observer, virtual sensor and controller models. Thus, using the LMI technique with multiobjective optimization performance, sufficient conditions are derived to ensure the closed-loop Lipschitz nonlinear system stability and guarantee that the Lipschitz set of the adaptive sliding mode observer is a subset of the adaptive sliding mode control Lipschitz set. Two illustrative examples the first is the robotic manipulator model and the second is the longitudinal dynamics of the following vehicle system were performed to verify the effectiveness of the proposed approach.

Adaptive Fuzzy Integral Sliding-Mode Control for Robust Fault-Tolerant Control of Robot Manipulators With Disturbance Observer

This article develops a new strategy for robust fault-tolerant control (FTC) of robot manipulators using an adaptive fuzzy integral sliding-mode control (ISMC) and a disturbance observer (DO). First, an ISMC is developed for the FTC system. The major features of the approach are discussed. Then, to enhance the performance of the system, a fuzzy logic system approximation and a DO are introduced to approximate the unknown nonlinear terms, which include the model uncertainty and fault components, and to estimate the compounded disturbance and then are integrated into the ISMC. Next, a switching term based on an adaptive two-layer supertwisting algorithm is designed to compensate the disturbance estimated error and guarantee stability and convergence of the whole system. The nominal controller of the ISMC is reconstructed using a backstepping control technique to achieve the stability for the nominal system based on the Lyapunov criterion. The computer simulation results demonstrate the effectiveness of the proposed approach.

Robust fault tolerant tracking control for the multi-joint manipulator based on operator theory

Uncertainties and fault signals usually exist in the real systems and it is difficult to maintain stability and tracking performance for the real applications. Therefore, it is important to study the robust fault tolerant tracking control (RFTTC) for uncertain nonlinear feedback systems (NFS). Generally, the RFTTC schemes are designed for the uncertain NFS by using operator theory based robust right coprime factorization (ORRCF) method. In details, firstly, one novel RFTTC scheme is proposed for the uncertain NFS, wherein the fault tolerant controllers as well as the tracking one are designed based on the internal model. Secondly, the other new RFTTC scheme is proposed where the robust fault tolerant controllers are combined with the compensation operator and the tracking controller. By the proposed two design schemes, the impacts induced by the faults on the system is eliminated, and the entire nonlinear feedback system holds strong robustness and perfect tracking performance. Finally, simulation results of the multi-joint manipulator are used to indicate the validity of proposed two design schemes.

Optimal adaptive neural PI full-order sliding mode control for robust fault tolerant control of uncertain nonlinear system

This paper proposes a robust fault tolerant control scheme for a class of second-order uncertain nonlinear systems. First, a novel PI full-order sliding mode (PI-FOSM) control, which integrates a new PI-FOSM sliding surface and a continuous control law, is developed. The crucial parameters of the controller are optimally selected by Bat algorithm so that the nearly optimal performance of the controller can be achieved. In addition, the unknown system dynamics is approximated by using a radial basic function neural network (RBFNN) so that the proposed controller does not require an exact model of the system. Compared with other existing sliding mode controllers for fault tolerant control system, the proposed method provides very strong robustness, low oscillation, fast convergence and high precision. The superior performance of the proposed robust fault tolerant controller is proved through simulation results for attitude control of a spacecraft.

Incremental backstepping robust fault-tolerant control with improved IHSTD for RLVs

Aiming at unknown disturbances/uncertainties, partial effectiveness loss fault (PELF) and stuck failure (SF) of the actuator, a composite robust fault-tolerant control strategy based on incremental backstepping (IBS) is proposed for a reusable launch vehicle (RLV) during re-entry. By converting PELF to disturbances/uncertainties, this paper presents an incremental form of disturbance observer based on an improved inverse hyperbolic sine tracking differentiator (IHSTD) to compensate these interference terms originally ignored in the IBS design process. Furthermore, a failure symbol matrix is set to control the on-off states of the reaction control system of the RLV to make up for the missing torque of the actuator SF, which can strengthen the fault-tolerance capability of the control system. The simulation results show that the tracking effect of the proposed method on the attitude-angle commands is better than traditional backstepping with disturbance observer, and the presented control allocation strategy is capable of timely resolving the actuator SF problem to ensure stability of flight.

Incremental backstepping robust fault-tolerant control with improved IHSTD for RLVs

Incremental backstepping robust fault-tolerant control with improved IHSTD for RLVs

Fault tolerant tracking control for a class of linear parameter varying systems using reduced-order simultaneous estimator and optimal preview policy

This paper considers the reduced-order estimator based fault tolerant preview tracking control problem for a class of linear parameter varying (LPV) systems. The main research contents are composed of two aspects. First, a scheduling-parameter-dependent reduced-order simultaneous state/fault estimator is designed based on model transformation method, unknown input observer theory, estimator parameterisation, and robustness optimisation. Second, a novel robust fault tolerant preview tracking control policy is constructed by integrating fault signal compensation, state feedback, preview action of reference signals, and integral regulation of tracking errors. Compared with the relevant studies, the merits can be summarised in two aspects. On one hand, the proposed design method of reduced-order estimator can be applied to more general LPV models because it does not depend on the traditional constraint operations, such as decomposition of system output equation, separated estimations of actuator and sensor faults, or derivative of output equation. On the other hand, the optimal preview policy including preview action and integral regulation is introduced to increase the design degree of freedom, which contributes to the optimisation of fault tolerant tracking performance even under influences of fault estimation errors and disturbances. Finally, the effectiveness of the proposed method is verified by three case studies.

Event-based fault-tolerant control for networked control systems applied to aircraft engine system

This paper studies the observer-based fault-tolerant control (FTC) for a class of networked control systems (NCSs) subject to system fault and external disturbance. Firstly, in order to reduce the number of sampled data transmissions, an improved adaptive event-triggered mechanism (AETM) is proposed, which can not only reflect the whole real-time information of the addressed NCSs, but also help to enlarge the application areas. Then based on the triggered output signals, a combined observer is proposed to estimate the state and system fault, and the estimations are further utilized to design the fault-tolerant controller. By choosing an augmented Lyapunov–Kroasovskii functional (LKF), two sufficient conditions on co-designing the AETM, observer, and controller are presented in terms of linear matrix inequalities (LMIs). Moreover, we adopt the derived methods to tackle the robust FTC for networked aircraft engine model. Finally, two numerical examples are provided to demonstrate the effectiveness of our obtained results by some simulations and comparisons.