Fault-tolerant Control Architecture Research Articles

Fault-tolerant control based on adaptive dynamic programming for reentry vehicles subjected to state-dependent actuator fault

The paper addresses the problem of fault tolerant control (FTC) for reentry vehicles (RV) subject to actuator fault and perturbation. In contrast to the majority of papers assuming bounded and exogenous actuator fault effect, the adaptive dynamic programming (ADP) control algorithm has been considered here to tackle with the dependence of closed-loop states induced by the setup of an active FTC strategy. By this way, the FTC problem formulation takes theoretically into account the fact that an actuator fault can destabilize a closed-loop. First, the FTC problem in attitude tracking is transformed into an error-optimal control problem. Next, a cost function based on zero-sum game theory is considered to achieve tracking under the joint influence of state-dependent actuator faults and perturbations. Lyapunov theory has been next used to prove the stability of FTC architecture and the network weight convergence. Benefits of proposed ADP-FTC algorithm is finally highlighted on a numerical benchmark of RV.

Robust control scheme based on an uncertainty and disturbance estimator for a quadrotor with motor failures

AbstractThis paper proposes a new robust fault tolerant control architecture based on a disturbance observer. The control architecture is composed of a nominal controller and a rotor's fault observer capable to identify and estimate motors' degradation performance. Besides, is designed for a quadrotor vehicle and validated in critical and noncritical motors' failures. For both failure cases, each motor performance is analyzed to counteracted the failure and restore the system stability. If the practical stability is not recovered (critical case) a control reconfiguration is performed for safe landing. Experimental tests are carried out in real time to illustrate the effectiveness of the proposed architecture when confronting the stability of the system with aggressive disturbances or uncertainties.

End-to-End Deep Fault-Tolerant Control

PUBLISHED ON IEEE/ASME TRANSACTIONS ON MECHATRONICS, DOI: 10.1109/TMECH.2021.3100150. Ideally, accurate sensor measurements are needed to achieve a good performance in the closed-loop control of mechatronic systems. As a consequence, sensor faults will prevent the system from working correctly, unless a fault-tolerant control (FTC) architecture is adopted. As model-based FTC algorithms for nonlinear systems are often challenging to design, this paper focuses on a new method for FTC in the presence of sensor faults, based on deep learning. The considered approach replaces the phases of fault detection and isolation and controller design with a single recurrent neural network, which has the value of past sensor measurements in a given time window as input, and the current values of the control variables as output. This end-to-end deep FTC method is applied to a mechatronic system composed of a spherical inverted pendulum, whose configuration is changed via reaction wheels, in turn actuated by electric motors. The simulation and experimental results show that the proposed method can handle abrupt faults occurring in link position/velocity sensors. The provided supplementary material includes a video of real-world experiments and the software source code.

Fuzzy adaptive sliding mode fault estimation and fixed-time fault-tolerant control for coupled spacecraft based on SE(3)

The goal of this study is to develop fault estimation (FE) and fault tolerant control (FTC) techniques for rigidly coupled spacecraft. A fuzzy adaptive sliding mode fault estimation approach is proposed to address fault tolerance against a large scale of disturbances, including inertia parametric uncertainties, space disturbances, actuator faults and saturation constraints. Firstly, a six-degrees of freedom (6-DOF) fault tolerant control architecture is established on the Lie group SE(3), which combined rotation and translation coupling kinematics and dynamics together. Then, a nonlinear fault estimator is used to deal with controllability loss of the fault actuator and the fuzzy logic system (FLS) is presented to solve the lumped disturbance. Next, in order to reduce the number of control parameters, the exponential parameters of the fast double-power sliding mode surface and the reaching law are set to be the same, which are nested with the estimated value of actuator effectiveness and combined with the pseudo inverse control allocation method to form the control algorithm in this paper. Finally, the stability and fixed-time convergence of the proposed method are proved theoretically by Lyapunov function, and the effectiveness of the scheme is verified by numerical simulation.

Small-signal Stability Analysis of Paralleled Converter System under Power Quality Control Strategy for Microgrid

In order to enhance the output voltage stability of converter system under non-linear and unbalanced load conditions, the power quality control strategy based on fault-tolerant control architecture is adopted. By analyzing the principle of power quality control strategy, a mathematical model of parallel converter system is established. The mathematical model of the paralleled converter system is linearized at the steady-state operating point, and the corresponding small-signal mathematical model is established. The small-signal stability of the paralleled converter system under the power quality control strategy is analyzed. The results show that under the power quality control strategy, the output voltage stability of the converter system is improved, and the small interference stability of the parallel converter system is guaranteed.

Integrated Anti-Windup Fault-Tolerant Control Architecture for Optimized Satellite Attitude Stabilization

This article presents the development of an anti-windup (AW) compensator architecture for nanosatellite systems. The design addresses the problem of fault-tolerant control (FTC) for attitude stabilization subject to actuator saturation, actuator faults, and multiple disturbances. In many practical applications, certain physical limitations in the actuator design often mean that actuator saturation is mostly unaccounted for. Based on the ESTCube-2 nanosatellite model with reaction wheels (RWs), an integrated AW–FTC architecture is designed for an optimized attitude control system. The AW compensator is formulated using the linear matrix inequality (LMI) and computed to generate an augmented solution that is appended to the linear control system. The AW compensator in the architecture is designed with suitable parameters and effective controller gain values. The AW–FTC acts on the RW momentum as control input with the observed torque response, thereby ensuring an asymptotically stable system. Simulation results are presented to demonstrate the effectiveness of this approach with finite-time stabilization under actuator faults and saturation conditions.

A 6-DOF sliding mode fault tolerant control solution for in-orbit autonomous rendezvous

The goal pursued by this article, is to evaluate the potential of sliding-mode control and estimation techniques, to address fault tolerance against a large class of actuator faults, including loss of controllability of the faulty actuator, for autonomous rendezvous between a chaser spacecraft and a passive spacecraft on a circular orbit. The proposed solution is based on the dual quaternion formalism, to describe in a single equation, rotational and translational spacecraft dynamics, solar array flexible modes, propellant sloshing, the most dimensioning space disturbances, and their coupling. Such a modelling formalism enables to propose a six degree-of-freedom fault tolerant control architecture, which relies on the generalized super-twisting control algorithm nested with a nonlinear fault estimator. An anti-windup strategy based on polytope algebra is applied to the control algorithm, to prevent instability due to actuator saturation when faults occur. Asymptotic stability of the proposed fault-tolerant control scheme is formally proved with respect to a wide variety of faults, providing that the first derivatives of the fault estimation error versus time and the sliding surface, are bounded. Intensive simulations from a functional engineering simulator that accurately simulates the rendezvous mission, are presented in the paper, as well as capture-oriented criteria. The presented results demonstrate that the proposed fault-tolerant solution is able to cover any kind of thruster faults, including total loss of controllability of the faulty thruster, as well as solar array flexible modes, propellant sloshing, gravity gradient, the second zonal harmonic, atmospheric drag and magnetic disturbances.

Stable Inversion Based Fault-tolerant Trajectory Tracking Control of Civil Aircrafts Autolanding

This paper deals with aircraft autoland control in the presence of wind disturbances and actuator faults. To solve this problem, a fault-tolerant trajectory tracking controller is presented to autoland a commercial aircraft. Firstly, the dynamics models of the aircraft with faults and winds are built. Secondly, the stable inversion based fault-tolerant autolanding control architecture is proposed. The stable inversion control is used to improve output tracking precision. The H_∞ control is applied for robust stability against uncertainties caused by wind disturbances and the faults. Compare with common fault-tolerant autolanding control, the stable inversion based fault-tolerant autolanding control has more robust capability including stabilizing the non-minimum phase system. Finally, two scenario simulations are carried out for automatic landing control of a large civil aircraft under winds and elevator failures. The results indicate that the proposed stable inversion based fault-tolerant autolanding controller has better tracking performances than those of the stable inversion control and fault-tolerant autolanding control, even in control surface faults and large winds.

Actuator Fault-Tolerant Control Architecture for Multirotor Vehicles in Presence of Disturbances

In this article we present an actuator fault-tolerant control architecture for the attitude and altitude tracking problem of multirotor aircrafts, under the effects of unknown drag coefficients and external wind. The tracking problem is faced by splitting it into two sub-problems, namely control law and control allocation. The control law is designed in terms of desired forces and moments which should act on the system, it does permit to exploit possible estimations of the disturbances acting on the vehicle and does not depend on the multirotor configuration. The control allocation, instead, optimally solves the redistribution of the control efforts among the motors according to the specific multirotor configuration, moreover it can actively cope with actuator faults whenever their estimations are available. Numerical simulations based on realistic scenarios confirm that the control architecture permits to solve the attitude and altitude tracking problem, despite the effects of faults and disturbances on the system.

Tracking Fault Tolerant Control for Hybrid System: Two-Link Human Arm Application

This paper proposes a novel fault tolerant control (FTC) scheme for a class of hybrid dynamical system (HDS) subject to sensor faults. The corresponding FTC architecture is designed around a reconfiguration mechanism. It aims to compensate the effects of the sensors degradation and maintain satisfactory performances including continuous stability. Moreover, by using the linear matrix inequalities (LMI) approach, a fault estimation algorithm is fulfilled and the compromise between robustness to disturbances and sensitivity to fault is guaranteed. For the sake of trajectory tracking, a combined robust state feedback and proportional-integral-derivative control system is proposed herein. Finally, extensive simulation results conducted on two-link arm system are included to illustrate the efficiency of the designed FTC scheme.

Fault-tolerant Control of a Cyber-physical System

Cyber-physical systems represent a new emerging field in automatic control. The fault system is a key component, because modern, large scale processes must meet high standards of performance, reliability and safety. Fault propagation in large scale chemical processes can lead to loss of production, energy, raw materials and even environmental hazard. The present paper develops a multi-agent fault-tolerant control architecture using robust fractional order controllers for a (13C) cryogenic separation column cascade. The JADE (Java Agent DEvelopment Framework) platform was used to implement the multi-agent fault tolerant control system while the operational model of the process was implemented in Matlab/SIMULINK environment. MACSimJX (Multiagent Control Using Simulink with Jade Extension) toolbox was used to link the control system and the process model. In order to verify the performance and to prove the feasibility of the proposed control architecture several fault simulation scenarios were performed.

Fault‐tolerant control of non‐linear systems based on adaptive virtual actuator

A new adaptive fault-tolerant control architecture for Lipschitz non-linear systems is developed. Specifically, the proposed approach involves a novel adaptive virtual actuator which is inserted between the faulty plant and the nominal controller to hide faults and disturbances from the nominal controller. The envisaged adaptive virtual actuator does not require any information about the nominal controller nor does it require a separate fault detection, isolation and identification unit. Moreover, it can tackle loss of effectiveness and time-varying additive actuator faults as well as an external disturbance, and in addition to the stability of the closed-loop system, it also guarantees that the difference between the states of the nominal and the faulty systems tend to zero. Simulation results corresponding to the lateral directional dynamics of an aircraft demonstrate and illustrate the effectiveness of the proposed adaptive virtual actuator.

Fault detection and fault-tolerant control of actuators and sensors in distributed parameter systems

This paper proposes the architecture for fault detection and fault-tolerant control for distributed parameter systems with control actuators and measurement sensors. In the development of this architecture, it is assumed that the system contains multiple actuators and sensors with only one actuator and partial sensors are activated while keeping the remaining actuators and sensors dormant. For the approximate finite-dimensional model, a detection observer with a time-varying threshold is proposed to ensure the actuator faults can be detected. An actuator switching policy is used to arrange switching from faulty actuators to healthy ones based on performance enhancement arguments. To facilitate actuator fault diagnosis, an adaptive observer that accommodates actuator fault is designed. Residuals are defined so as to detect the sensor fault. Then, an integrated fault detection and fault-tolerant control architecture of actuators and sensors is taken into account in the implementation of the infinite-dimensional system on the basis of the singular perturbation formulation. Finally, the proposed theoretical results are verified through an example of chemical reaction.

Nonfragile Fault-Tolerant Fuzzy Observer-Based Controller Design for Nonlinear Systems

The problem of actuator fault estimation and fault-tolerant control for a class of uncertain nonlinear systems using Takagi–Sugeno fuzzy models is investigated. A design procedure for nonfragile proportional-integral (PI) observer is proposed to estimate the states of the nonlinear system and reconstruct the abrupt (modeled as step-like faults) and incipient fault signals. Subsequently, a nonfragile fault-tolerant controller is constructed, which is informed by the PI observer. Sufficient conditions of the existence of the PI observer and the fault-tolerant controller are provided in the form of linear matrix inequalities. The proposed fault-tolerant control architecture is tested on two numerical examples.

Modeling and fault tolerant control of an electro-hydraulic actuator

In the modern industry, electro-hydraulic actuators (EHAs) have been applied to various applications for precise position pressure/ force control tasks. However, operating EHAs under sensor faults is one of the critical challenges for the control engineers. For its enormous nonlinear characteristics, sensor fault could lead the catastrophic failure to the overall system or even put human life in danger. Thus in this paper, a study on mathematical modeling and fault tolerant control (FTC) of a typical EHA for tracking control under sensor-fault conditions has been carried out. In the proposed FTC system, the extended Kalman-Bucy unknown input observer (EKBUIO) -based robust sensor fault detection and identification (FDI) module estimates the system states and the time domain fault information. Once a fault is detected, the controller feedback is switched from the faulty sensor to the estimated output from the EKBUIO owing to mask the sensor fault swiftly and retains the system stability. Additionally, considering the tracking accuracy of the EHA system, an efficient brain emotional learning based intelligent controller (BELBIC) is suggested as the main control unit. Effectiveness of the proposed FTC architecture has been investigated by experimenting on a test bed using an EHA in sensor failure conditions.

Fault-tolerant multi-agent control architecture for autonomous mobile manipulators: Simulation results

This paper presents our ongoing efforts toward the development of a multi-agent distributed framework for autonomous control of mobile manipulators. The proposed scheme assigns a reactive agent to control each degree-of-freedom of the manipulator(s), a hybrid agent to control the mobile base, and a supervisory agent to coordinate and synchronize the work of the control agents. Each control agent implements a Simulation-Verification technique to optimize, locally and independently from the other agents, a predefined objective function. The final goal consists of bringing the end-effector as close as possible to imposed operational targets (reaching tasks).Different simulation scenarios are described and carried out for the case of RobuTER/ULM robot, with and without considering failures of some articulations of the manipulator or the mobile base. Results show that the main advantage of the proposed approach is that the system pledges a fault-tolerant response to some breakdowns without needing any specific additional treatment.

Active Fault Tolerant Control for Ultrasonic Piezoelectric Motor

Active Fault Tolerant Control for Ultrasonic Piezoelectric MotorUltrasonic piezoelectric motor technology is an important system component in integrated mechatronics devices working on extreme operating conditions. Due to these constraints, robustness and performance of the control interfaces should be taken into account in the motor design. In this paper, we apply a new architecture for a fault tolerant control using Youla parameterization for an ultrasonic piezoelectric motor. The distinguished feature of proposed controller architecture is that it shows structurally how the controller design for performance and robustness may be done separately which has the potential to overcome the conflict between performance and robustness in the traditional feedback framework. A fault tolerant control architecture includes two parts: one part for performance and the other part for robustness. The controller design works in such a way that the feedback control system will be solely controlled by the proportional plus double-integralPI2 performance controller for a nominal model without disturbances andH∞robustification controller will only be activated in the presence of the uncertainties or an external disturbances. The simulation results demonstrate the effectiveness of the proposed fault tolerant control architecture.

Data-Driven Design of Fault-Tolerant Control Systems

In this paper, a scheme for the design of a fault-tolerant control architecture using process data is proposed, whose core is an observer-based realization of the Youla parameterization of all stabilization controllers. The realization of a fault-tolerant control scheme based on the proposed architecture is demonstrated on a benchmark process.

A Fault-Tolerant Control Architecture for Different Battery Topologies in Electrified Vehicles

In this paper a variety of battery configuration topologies for electrified vehicles are investigated with regard to reliability and expected lifetime along with the possibility of applying active fault detection to provide early warnings for the driver. Different configurations are investigated ranging from a simple single serial string of battery cells providing only the lowest level of fault tolerance, to a highly elaborate and still practically relevant triple string configuration providing fault detection and reconfiguration possibilities as well as repair. All configurations are analyzed with regard to the associated reliability profile assuming non-ageing cell failure model. A novel method for active early fault detection is presented based on encoding faults into a parametric dynamic cell model, where parameters are continuously estimated under the influence of an auxiliary test signal designed to optimize parametric sensitivity. Finally reliability profiles for all investigated configurations are compared mutually and with standard requirements on the basis of mean time to failure statistics.

Model-Based Fault Detection and Fault-Tolerant Control of Process Systems with Sampled and Delayed Measurements

AbstractThis paper presents a model-based framework for actuator fault detection and reconfiguration in process systems with discretely-sampled and delayed output measurements. An observer-based output feedback controller that enforces closed-loop stability in the absence of faults is initially designed. To compensate for the lack of continuous measurements, an inter-sample model predictor is included within the control system to provide the observer with an estimate of the output when measurements are not available from the sensors. Measurement delays are compensated for by means of a propagation unit that uses the plant model and the past values of the control input to calculate an estimate of the current output from the received delayed measurements. This estimate is then used to update the inter-sample model predictor which, together with the controller, generates the control signal for the process. By formulating the closed-loop system as a combined discrete-continuous system, an explicit characterization of the minimum allowable sampling rate that guarantees stability in the absence of faults is obtained in terms of the plant-model mismatch, the controller and observer design parameters, the size of the measurement delay, and the choice of the control configuration. The characteristic fault-free closed-loop behavior is used as the basis for deriving (1) a time-varying alarm threshold on the residual of the fault detection filter, and (2) a controller reconfiguration law that determines the feasible fall-back control configurations that preserve closed-loop stability. Finally, the design and implementation of the integrated monitoring and fault-tolerant control architecture are demonstrated using a chemical process example.