Robust Fault-tolerant Control Scheme Research Articles

A hybrid robust fault tolerant control based on adaptive joint unscented Kalman filter

In this paper, a new hybrid robust fault tolerant control scheme is proposed. A robust H∞ control law is used in non-faulty situation, while a Non-Singular Terminal Sliding Mode (NTSM) controller is activated as soon as an actuator fault is detected. Since a linear robust controller is designed, the system is first linearized through the feedback linearization method. To switch from one controller to the other, a fuzzy based switching system is used. An Adaptive Joint Unscented Kalman Filter (AJUKF) is used for fault detection and diagnosis. The proposed method is based on the simultaneous estimation of the system states and parameters. In order to show the efficiency of the proposed scheme, a simulated 3-DOF robotic manipulator is used.

Actuator fault-tolerant robust control of an uncertain networked control system with random time delays

In this paper, a novel robust fault-tolerant control scheme of networked flight control system against actuator faults with consideration of both norm-bounded uncertainties and time delays is proposed. Different from other research results on actuator fault-tolerant control methods, a complete fault model of actuators with partial failure is developed to represent the type and degree of actuator faults in an integrated parameterised way. Moreover, both of the time delays that are induced by avionic-bus and system uncertainties are considered to be described as mathematic parameters in complete fault model. By employing multiple parameter-dependent Lyapunov-Krasovskii functions, sufficient stability conditions of uncertain networked flight control systems with actuator faults are derived, and robust fault mode depended controllers are obtained in terms of linear matrix inequalities (LMIs), which is capable of accommodating uncertainties in the presence of actuator faults. Finally, examples are provided to illustrate the effectiveness of the proposed method.

Fault diagnosis and robust fault-tolerant control for linear over-actuated systems

This paper proposes a novel fault diagnosis and robust fault-tolerant control strategy for over-actuated systems which subject to actuator faults. Firstly, the considered fault is formulated into an additive term (which is referred to as virtual fault). Then an augmented state observer is used to estimate this virtual additive fault. To achieve fault isolation and estimation for the over-actuated system, which is more difficult than that of an ordinary system, this paper considers the actuator fault as a sparse signal and proposes a constrained sparse optimization approach to recover the actual multiplicative fault in the over-actuated system. Based on the fault diagnosis result, a robust fault-tolerant controller is designed by the virtual actuator approach, which aims to construct a reconfiguration block to force the output of the reconfigured faulty plant approximated the behavior of a nominal system. Finally, the proposed fault diagnosis and fault-tolerant scheme is applied to an ADMIRE model. Simulation results demonstrate the effectiveness of the proposed method.

Actuator fault-tolerant control (FTC) design with post-fault transient improvement for application to aircraft control

Summary A robust fault-tolerant control scheme is proposed for uncertain nonlinear systems with zero dynamics, affected by actuator faults and lock-in-place and float failures. The proposed controller utilizes an adaptive second-order sliding mode strategy integrated with the backstepping procedure, retaining the benefits of both the methodologies. A Lyapunov stability analysis has been conducted, which unfolds the advantages offered by the proposed methodology in the presence of inherent modeling errors and strong eventualities of faults and failures. Two modified adaptive laws have been formulated, to approximate the bounds of uncertainties due to modeling and to estimate the fault-induced parametric uncertainties. The proposed scheme ensures robustness towards linearly parameterized mismatched uncertainties, in addition to parametric and nonparametric matched perturbations. The proposed controller has been shown to yield an improved post-fault transient performance without any additional expense in the control energy spent. The proposed scheme is applied to the pitch control problem of a nonlinear longitudinal model of Boeing 747-100/200 aircraft. Simulation results support theoretical propositions and confirm that the proposed controller produces superior post-fault transient performance compared with already existing approaches designed for similar applications. Besides, the asymptotic stability of the overall controlled system is also established in the event of such faults and failures. Copyright © 2015 John Wiley & Sons, Ltd.

Robust fault-tolerant control for uncertain robot manipulators based on adaptive quasi-continuous high-order sliding mode and neural network

This paper investigates a robust fault-tolerant control scheme for uncertain robot manipulators. The proposed scheme is designed via active fault-tolerant control method by combining a fault estimation scheme with a novel robust adaptive quasi-continuous second-order sliding mode (AQC2S) controller, so as to accommodate not only system failures but also uncertainties. First, a neural network based fault estimation is designed to online approximate the unknown uncertainties and faults. The estimated uncertainty and fault information are then used to compensate in advance for the effects of uncertainties in fault-free operation and both uncertainties and faults in fault operation. To eliminate the neural network compensation error, QC2S with adaptation gain, named as adaptive QC2S (AQC2S), is proposed. By integrating the advantages of the neural network observer and the AQC2S controller, the integrated scheme has a good capability to accommodate both the uncertainties and faults with chattering-free, higher position tracking accuracy, and no requirement of prior knowledge of the fault information. The stability and convergence of the proposed fault-tolerant control system is proved theoretically. Simulation results for a PUMA560 robot demonstrate the effectiveness of the proposed algorithm.

Robust Adaptive Fault-Tolerant Tracking Control of Three-Phase Induction Motor

This paper deals with the problem of induction motor tracking control against actuator faults and external disturbances using the linear matrix inequalities (LMIs) method and the adaptive method. A direct adaptive fault-tolerant tracking controller design method is developed based on Lyapunov stability theory and a constructive algorithm based on linear matrix inequalities for online tuning of adaptive and state feedback gains to stabilize the closed-loop system in order to reduce the fault effect with disturbance attenuation. Simulation results reveal the merits of proposed robust adaptive fault-tolerant tracking control scheme on an induction motor subjected to actuator faults.

Influence Vectors Control for Robots Using Cellular-Like Binary Actuators

Robots using cellular-like redundant binary actuators could outmatch electric-gearmotor robotic systems in terms of reliability, force-to-weight ratio, and cost. This paper presents a robust fault-tolerant control scheme that is designed to meet the control challenges that are encountered by such robots, i.e., discrete actuator inputs, complex system modeling, and cross-coupling between actuators. In the proposed scheme, a desired vectorial system output, such as a position or a force, is commanded by recruiting actuators based on their influence vectors on the output. No analytical model of the system is needed; influence vectors are identified experimentally by sequentially activating each actuator. For position control tasks, the controller uses a probabilistic approach and a genetic algorithm to determine an optimal combination of actuators to recruit. For motion control tasks, the controller uses a sliding mode approach and independent recruiting decision for each actuator. Experimental results on a four degrees of freedom binary manipulator with 20 actuators confirm the method’s effectiveness and its ability to tolerate massive perturbations and numerous actuator failures.

Robust fault-tolerant control for flexible spacecraft against partial actuator failures

In this paper, we present a robust fault-tolerant control scheme to achieve attitude control of flexible spacecraft with disturbances and actuator failures. It is shown that the control algorithms are not only attenuate exogenous bounded disturbances with attenuation level, but also able to tolerate partial loss of actuator effectiveness. The proposed controller design is simple and can guarantee the faulty closed-loop system to be quadratically stable with a prescribed upper bound of the cost function. The design algorithms are obtained by combining free weighting matrices method with linear matrix inequality technique. The effectiveness of the proposed design method is demonstrated in a spacecraft attitude control system subject to loss of actuator effectiveness.

Set-based Fault-Tolerant Control of Convex Polytopic LPV Systems using a Bank of Virtual Actuators

We propose a robust actuator fault tolerant control strategy for systems with linear parameter varying (LPV) uncertainty model description. The scheme employs a set-based robust fault detection and identification (FDI) approach and a bank of virtual actuators (VA). An interesting feature is that the virtual actuators are used both for FDI and controller reconfiguration (CR) tasks. The robust FDI method is based on the separation of relevant sets defined for measurable residual signals, which are computed based on the virtual actuator signals and taking into account model uncertainty, noises and process disturbances. For CR, each VA is designed to operate adequately in combination with a nominal controller (designed for the fault-free plant) to achieve correct reconfiguration for a particular fault situation in a considered range of fault scenarios. The resulting robust fault tolerant control scheme ensures boundedness of the closed-loop system trajectories under a wide range of actuator fault scenarios. The performance of the scheme is illustrated through a simulation example.

Fault-tolerant control of systems with convex polytopic linear parameter varying model uncertainty using virtual-sensor-based controller reconfiguration

In this paper, a novel robust sensor fault tolerant control strategy for systems with linear parameter varying (LPV) uncertainty model description is proposed. The strategy combines a robust fault detection and identification (FDI) unit based on an invariant-set approach with controller reconfiguration based on the use of a virtual sensor. The robust FDI unit employs a bank of observers that can detect faulty and healthy situations based on the separation of relevant sets, whose computation takes into account system disturbances and model uncertainty. The closed-loop system is reconfigured by means of a virtual sensor which is adapted to the fault situation detected by the FDI unit. The FDI and virtual sensor modules are designed using polytopic LPV techniques and bilinear matrix inequalities. The resulting robust fault tolerant control scheme is guaranteed to preserve boundedness of the closed-loop system trajectories under a wide range of sensor fault scenarios. The performance of the proposed scheme is illustrated by a simulation example.

Fault tolerant autonomous rendezvous and docking architecture for spacecraft in presence of control actuator failures

PurposeThe purpose of this paper is to present novel robust fault tolerant control design architecture to detect and isolate spacecraft attitude control actuators and reconfigure to redundant backups to improve the practicality of actuator fault detection.Design/methodology/approachThe Robust Fault Tolerant Control is designed for spacecraft Autonomous Rendezvous and Docking (AR&D) using Lyapunov direct approach applied to non‐linear model. An extended Kalman observer is used to accurately estimate the state of the attitude control actuators. Actuators on all three axes (roll/pitch/yaw) sequentially fail one after another and the robust fault tolerant controller acts to reconfigure to redundant backups to stabilize the spacecrafts and complete the required maneuver.FindingsIn the simulations, the roll, pitch and yaw dynamics of the spacecraft are considered and the attitude control actuators failures are detected and isolated. Furthermore, by switching to redundant backups, the guarantee of overall stability performance is demonstrated.Research limitations/implicationsA real time actuator failure detection and reconfiguration process using robust fault tolerant control is applied for spacecraft AR&D maneuvers. Finding an appropriate Lyapunov function for the non‐linear dynamics is not easy and always challenging. Failure of actuators on all three axes at the same time is not considered. It is a very useful approach to solve self‐assembly problems in space, spacecraft proximity maneuvers as well as co‐operative control of planetary vehicles in presence of actuator failures.Originality/valueAn approach has been proposed to detect, isolate and reconfigure spacecraft actuator failures occurred in the spacecraft attitude control system. A Robust Fault Tolerant Control scheme has been developed for the nonlinear AR&D maneuver for two spacecrafts. Failures that affect the control performance characteristics are considered and overall performance is guaranteed even in presence of control actuator failures. The architecture is demonstrated through model‐based simulation.

Robust multisensor fault tolerant model-following MPC design for constrained systems

Robust multisensor fault tolerant model-following MPC design for constrained systemsIn this paper, a robust fault-tolerant control strategy for constrained multisensor linear systems, subject to sensor faults and in the presence of bounded state and output disturbances, is proposed. The scheme verifies that, for each sensors-estimator combination, suitable residual variables lie inside pre-computed sets and selects a more appropriate combination based on a chosen criterion. An active fault tolerant output feedback controller yields an MPC-based control law and, by means of the notion of a "tube" of trajectories, we ensure robust closed-loop exponential stability and good performance in the fault-free case and under the occurrence of abrupt sensor faults.

Fault-Tolerant Control of Convex Polytopic Linear Parameter Varying Systems Using Virtual-Sensor-Based Reconfiguration

In this paper, a novel robust sensor fault tolerant control strategy for systems with linear parameter varying (LPV) uncertainty model description is proposed. The strategy combines a robust fault detection and identification (FDI) unit based on an invariant-set approach with controller reconfiguration based on the use of a virtual sensor. The robust FDI unit employs a bank of observers that can detect faulty and healthy situations based on the separation of relevant sets, whose computation takes into account system disturbances and model uncertainty. The closed-loop system is reconfigured by means of a virtual sensor which is adapted to the fault situation detected by the FDI unit. The FDI and virtual sensor modules are designed using polytopic LPV techniques and bilinear matrix inequalities. The resulting robust fault tolerant control scheme is guaranteed to preserve boundedness of the closed-loop system trajectories under a wide range of sensor fault scenarios. The performance of the proposed scheme is illustrated by a simulation example.

Output feedback based adaptive robust fault-tolerant control for a class of uncertain nonlinear systems

An adaptive robust approach for actuator fault-tolerant control of a class of uncertain nonlinear systems is proposed. The two chief ways in which the system performance can de- grade following an actuator-fault are undesirable transients and unacceptably large steady-state tracking errors. Adaptive control based schemes can achieve good final tracking accuracy in spite of change in system parameters following an actuator fault, and robust control based designs can achieve guaranteed transient response. However, neither adaptive control nor robust control based fault-tolerant designs can address both the issues associ- ated with actuator faults. In the present work, an adaptive robust fault-tolerant control scheme is claimed to solve both the problems, as it seamlessly integrates adaptive and robust control design techniques. Comparative simulation studies are performed using a nonlinear hypersonic aircraft model to show the effectiveness of the proposed scheme over a robust adaptive control based fault- tolerant scheme.

A robust fault-tolerant control strategy for networked control systems

Networked control systems (NCS) are one type of distributed control systems where serial communication networks is used to exchange system information and control signals between various physical components of the systems that may be physically distributed. The existence of real-time network in the feedback control loop makes analysis and design of an NCS complex, and conventional control theories such as synchronized control and non-delayed sensing and actuation must be reevaluated prior to application to networked control systems. NCS is a kind of feedback control systems where the control loops are closed through real-time control network. The performance of the closed-loop system is not only determined by the characteristics of the control system, but also determined by the scheduling manner imposed by network. In this paper, adjustable deadbands are explored as a solution to reduce network traffic in networked control systems and we presented a new modeling method for networked control systems with random time delays and communication constraints based on quasi-T–S fuzzy models. The integrity design for the kind of networked control systems is analyzed based on robust fault-tolerant control theory and information scheduling. Parametric expression of controller is given based on feasible solution of linear matrix inequality (LMI). After detailed theoretical analysis, this paper also provides the simulation results, which further validate the proposed scheme.

The development of a fault-tolerant control approach and its implementation on a flexible arm robot

This article presents a robust sensor fault-tolerant control (FTC) scheme and its implementation on a flexible arm robot. Sensor faults affect the system's performance in the closed loop when the faulty sensor readings are used to generate the control input. In this article, the non-faulty sensors are used to reconstruct the faults on the potentially faulty sensors. The reconstruction is subtracted from the faulty sensors to generate a 'virtual sensor' which (instead of the normally used faulty sensor output) is then used to generate the control input. A design method is also presented in which the virtual sensor is made insensitive to any system uncertainties (which could corrupt the fault reconstruction) that cannot fit into the framework of the model used. Two fault conditions are tested: total failure and incipient faults. Then the scheme robustness is tested and evaluated through its implementation on two flexible arm systems, one with a flexible joint and the other with a flexible link. Excellent results have been obtained for both cases (joint and link); the FTC scheme produced system performance almost identical to the fault-free scenario, whilst providing an indication that a fault is present, even for simultaneous faults.

ON ROBUST FAULT-TOLERANT CONTROL OF MISSILE CONTROL SYSTEM

In order to avoid ballistic missile self-destruction because of sensor failures caused by element aging of long time storage, a reconstructed feedback robust fault-tolerant control scheme is presented. In our scheme, a fault detection method based on the adjacent coefficient of Mallat wavelet is proposed firstly so that the fault information, which is masked by several elastic oscillation signals with time-varying magnitudes and frequencies, can be extracted efficiently. As soon as a fault is detected, the switch control unit immediately isolates the failed sensor and switch from the original control model to the reconstructed one. To remain the stability of the system and control the tracking error in case of time-varying of missile parameters, a frequency domain robust stability control is designed, so that speed test feedback of engine swing angle and gain feedback of normal sensor are used to ensure the control stability and restrict the tracking error within a designed value. Finally, the effectiveness of our method is shown by an example of a Soviet missile flight simulation.

불확실성의 존재에서 관절 고장을 가지는 로봇 시스템에 대한 강인한 내고장 제어

This paper proposes a robust fault-tolerant control framework for robot manipulators to maintain the required performance and achieve task completion in the presence of both partial joint failures and complete joint failures and uncertainties. In the case of a complete joint failure or free-swinging joint failure causing the complete loss of torque on a joint, a fully-actuated robot manipulator can be viewed as an underactuated robot manipulator. To detect and identify a complete actuator failure, an on-line fault detection operation is also presented. The proposed fault-tolerant control system contains a robust adaptive controller overcoming partial joint failures based on robust adaptive control methodology, an on-line fault detector detecting and identifying complete joint failures, and a robust adaptive controller overcoming partial and complete joint failures, and so eventually it can face and overcome joint failures and uncertainties. Numerical simulations are conducted to validate the proposed robust fault-tolerant control scheme.

Hot isostatic pressing furnaces

A robust fault-tolerant model predictive control (MPC) scheme for the precise control of temperature in hot isostatic pressing (HIP) furnaces was designed based on a nonlinear state-space representation of the dynamics of the temperature in an HIP furnace. The model was developed and validated using the data collected from open-loop experiments. The MPC-based controller was then implemented and tested on a six-zone HIP furnace at Bodycote IMT, Inc. The robust fault-tolerant MPC was demonstrated to outperform the existing PID-based control system in the following aspects: 1) achievement of a heating rate of at least twice that achieved by the existing PID-based system; and 2) automatic detection of loss of power to a furnace zone and controller reconfiguration to achieve the desired process objectives, which with the current PID system would be impossible and would require operator intervention.