Simultaneous Actuator Faults Research Articles

Hierarchical Structure-Based Fault-Tolerant Tracking Control of Multiple 3-DOF Laboratory Helicopters

This study proposes a hierarchical structure-based fault-tolerant tracking control methodology for multiple 3-DOF helicopters in the presence of system nonlinearities, uncertainties and simultaneous actuator faults (partial loss of effectiveness, stuck, and saturation), and sensor faults (bias and drift). The hierarchical structure consists of the decentralized fault estimation hierarchy and distributed fault-tolerant tracking control hierarchy. The distributed constant gain-based, node-based, and edge-based adaptive fault-tolerant tracking control designs are developed to cope with bidirectional interactions and to guarantee the robust asymptotic stability and the good tracking property of multihelicopter systems, respectively. Simulation results validate the effectiveness of the proposed hierarchical structure-based tracking control algorithm.

Integrated fault estimation and tolerant control for discrete-time switched affine systems with mixed switching laws

This study is concerned with the issues of simultaneous actuator fault estimation and the design of observer-based fault-tolerant control for a class of discrete-time switched affine systems subject to a mixed switching scheme. A mixed switching law, which is composed of constant dwell-time and state-dependent switching logic, is introduced to avoid the chattering phenomenon of augmented error switched affine system, and a discretized Lyapunov function approach is used to ensure the asymptotic stability of error systems. Then, the simultaneous fault estimation and tolerant control based state observer are studied and the corresponding design problem is transformed into resolving a multi-objective optimization for augmented error systems with H∞ performance index. Moreover, the gains of fault estimator and tolerant controller are explicitly calculated via resolving the conditions of linear matrix inequalities. Finally, a practical application of DC motor/Buck–Boost converter is illustrated to verify the effectiveness and practicability of the developed approach.

Active fault tolerant tracking control of turbofan engine based on virtual actuator

In this paper, an active fault-tolerant tracking control scheme for the turbofan engine under dynamic and simultaneous actuator faults and sensor faults under disturbances is proposed. First, based on the linear parameter-varying model of the turbofan engine, an H∞ state feedback nominal controller is designed so as to achieve rotor speed tracking control with adaptive gain scheduling characteristics at different working conditions for the turbofan engine. Next, for the control system with simultaneous multiplicative actuator faults and additive sensor faults, a virtual actuator based active fault-tolerant tracking control strategy is developed to reconfigure the system such that it can obtain the similar behavior to the fault-free system without modifying the nominal controller. Specifically, in addition to handle the actuator fault by the virtual actuator, the reconfigured controller adopts a feedforward control signal to compensate for the sensor fault. Besides, in order to guarantee the reconfigured system, a sufficiency criterion is proposed. Finally, simulations have been conducted on a twin-spool turbofan engine to verify the effectiveness of the strategy.

Fault-tolerant control allocation of a flexible satellite with an infinite-dimensional model

Fault-tolerant control allocation (FTCA) strategy is proposed for attitude stabilization of a flexible satellite with actuator redundancy. The control scheme is based on the infinite-dimensional model of a flexible satellite with no discretization, so the spillover instability is eliminated. This is one of the important benefits of the proposed control scheme over the previous FTCA schemes that have been used for the flexible satellite. The proposed scheme contains two modules. The first module provides a virtual control law to meet stabilization and vibration control objectives in the presence of uncertainties and external disturbances. There is no need to implement in-domain actuators on panels to stabilize their vibration. In this module, the virtual control is designed using adaptive integral sliding mode approach where the sliding surface includes angular velocities, internal reaction torques, and nominal control for healthy system. The second module, based on fault/failure information and using a control allocation scheme, provides redistribution of the virtual control law among the available actuators. Due to simultaneous actuator faults and control constraints, there is an error between the actual virtual control and the designed control that affects the overall system stability. To eliminate this error, gain of the virtual control signal is adjusted by an adaptive updating law. The closed-loop system stability is guaranteed for small changes in a neighborhood of the sliding surface with simultaneous vibration damping. A numerical example illustrates the effectiveness of the proposed control strategy.

Fault-Tolerant Model Predictive Control Trajectory Tracking for a Quadcopter with 4 Faulty Actuators

Abstract In this paper, an active fault tolerant control (AFTC) framework is presented, with the ability to automatically estimate and compensate for the Loss Of Effectiveness (LOE) of all actuators of a quadcopter Unmanned Air Vehicle (UAV), while achieving trajectory tracking. The aforementioned AFTC framework consists of a reconfigurable controller based on Nonlinear Model Predictive Control (NMPC), and a fault detection and diagnosis (FDD) module based on a simple and computationally cheap nonlinear algebraic observer algorithm. The presented FDD module estimates the multiplicative faults in all quadcopter actuators simultaneously in an accurate and timely manner. A nonlinear simulation validates the proposed framework and proves a precise trajectory tracking performance in the presence of 4 simultaneous actuator faults. Furthermore, simulation results show that this framework is numerically tractable and real-time applicable, as the ratio of run-time to simulation time is much less than one.

Fault-tolerant Control for Linear System Under Sensor Saturation Constraint

An observer-based fault-tolerant control method is proposed for a linear system with sensor saturation constraint. Considering the linear system with simultaneous actuator faults and sensor faults, the sensor saturation would bring the output measurement error of the system, which would result in the estimation performance degradation. Firstly, the intermediate estimator is modified to estimate the system states and fault signals at the simultaneous time, and the fault-tolerant controller is designed based on the estimation to compensate the effect of actuator faults effectively. Through Lyapunov stability analysis, the sufficient conditions are obtained to ensure the states of closed-loop system to be uniformly ultimately bounded. The effect of sensor saturation error can be suppressed by adjusting some specified parameters directly without introducing any performance index. Finally, the effectiveness and superiority of the proposed method are verified by a simulation example.

Robust Fault Estimation and Fault-Tolerant Control Based on Sliding Mode Observer for Takagi–Sugeno Fuzzy Systems Subject to Actuator and Sensor Faults

In this paper, the problems of fault estimation and fault-tolerant control for Takagi-Sugeno fuzzy system affected by simultaneous actuator faults, sensor faults and external disturbances are investigated. Firstly, an adaptive fuzzy sliding-mode observer is designed to simultaneously estimate system states and both actuator and sensor faults. Then, based on the online estimation information, a static output feedback fault-tolerant controller is designed to compensate for the effect of faults and to stabilize the closed-loop system. Moreover, sufficient conditions for the existence of the proposed observer and controller with an H∞ performance are derived based on Lyapunov stability theory and expressed in terms of linear matrix inequalities. Finally, a nonlinear inverted pendulum with cart system application is given illustrate the validity of the proposed method.

A fault tolerant tracking control for a quadrotor UAV subject to simultaneous actuator faults and exogenous disturbances

ABSTRACTAn observer-based robust adaptive Fault Tolerant Control approach is proposed in this paper to tackle the problem of trajectory tracking for a quadrotor unmanned aerial vehicle (UAV) suffering simultaneous actuator faults, exogenous disturbances and actuator saturation limits. An adaptive fuzzy state observer is proposed to estimate the immeasurable states by using fuzzy logic systems to approximate the unknown nonlinear functions of the uncertain system model. Based on the estimates of the fuzzy observer, an Integral Terminal Sliding Mode Controller that guarantees finite time convergence of the states to a small neighbourhood of zero, even under impaired conditions, is developed. Stability analysis was carried over using the Lyapunov method. The proposed approach was implemented to a quadrotor UAV and its performance was assessed under nominal conditions, and by subjecting the quadrotor to disturbances, simultaneously occurring actuator faults and input saturation limits. Excellent tracking performance and robustness even under worst-case scenarios are among the positive features of the proposed approach.

Finite time estimation of actuator faults, states, and aerodynamic load of a realistic wind turbine

This paper provides finite time estimation of wind turbine actuator faults and unknown aerodynamic load. Furthermore, finite-time state estimation of drivetrain, generator, and pitch subsystems are addressed in the contrary of asymptotic state/fault estimation in previous works. A realistic wind turbine model, incorporating the aero-elastic FAST simulator, is considered as the simulation example. Generally, aerodynamic load is not measurable in real applications due to instrument limitations, then, it is considered as an unknown input in this study. A novel terminal sliding mode observer is introduced for finite-time estimation of generator/convertor states, faults, and unknown aerodynamic load. Pitch actuator hydraulic pressure drop is modelled as an additive fault, by introducing a fault indicator. Then, two cascaded sliding mode observers are exploited for each pitch subsystem, to provide finite time state and fault reconstructions. Sufficient number of design parameters helps to achieve desired accuracy and convergence time. Finally, simulation results authenticate finite time estimation of wind turbine states and simultaneous actuator faults. • This paper proposes a fault detection algorithm for generator and pitch actuator faults utilizing. • A novel terminal sliding mode observer is utilized for generator fault detection and reconstruction. • Hydraulic pressure drop fault of each pitch actuator, is reconstructed by two cascaded sliding mode observers. • The terminal sliding mode observer reconstructs the states, aerodynamic torque, and faults in finite time. • Numerical simulations are performed in FAST & MATLAB Simulink to a benchmark wind turbine model.

Fault‐tolerant sliding mode control for uncertain active suspension systems against simultaneous actuator and sensor faults via a novel sliding mode observer

SummaryIn this paper, the problem of fault estimation and fault‐tolerant control for half‐car active suspension system with simultaneous varying sprung and unsprung mass, actuator fault, and sensor fault is investigated. First, Takagi‐Sugeno fuzzy approach is used to describe the uncertain half‐car active suspension system with simultaneous actuator fault and sensor fault. Then, a novel augmented descriptor sliding mode observer is designed to estimate the state of system, actuator fault, and sensor fault with good precision. Based on the state and fault estimation, a fault‐tolerant sliding mode control scheme is designed to stabilize the resulting fault half‐car active suspension system. By utilizing Lyapunov stability theory, the existence condition for the proposed sliding mode observer and fault‐tolerant sliding mode controller is provided in terms of linear matrix inequalities (LMIs). In addition, it is shown that the reachability of the developed sliding surface can be ensured under the design control law. Finally, simulation results for uncertain half‐car active suspension systems are presented to demonstrate the effectiveness of the proposed design techniques.

An Adaptive Fault-Tolerant Sliding Mode Control Allocation Scheme for Multirotor Helicopter Subject to Simultaneous Actuator Faults

This paper proposes a novel adaptive sliding-mode-based control allocation scheme for accommodating simultaneous actuator faults. The proposed control scheme includes two separate control modules with virtual control part and control allocation part, respectively. As a low-level control module, the control allocation/reallocation scheme is used to distribute/redistribute virtual control signals among the available actuators under fault-free or faulty conditions, respectively. In the case of simultaneous actuator faults, the control allocation and reallocation module may fail to meet the required virtual control signal, which will degrade the overall system stability. The proposed online adaptive scheme can seamlessly adjust the control gains for the high-level sliding mode control module and reconfigure the distribution of control signals to eliminate the effect of the virtual control error and maintain the stability of the closed-loop system. In addition, with the help of the boundary layer for constructing the adaptation law, the overestimation of control gains is avoided, and the adaptation ceases once the sliding variable is within the boundary layer. A significant feature of this study is that the stability of the closed-loop system is guaranteed theoretically in the presence of simultaneous actuator faults. The effectiveness of the proposed control scheme is demonstrated by experimental results based on a modified unmanned multirotor helicopter under both single and simultaneous actuator faults conditions with comparison to a conventional sliding mode controller and a linear quadratic regulator scheme.

Fault-Tolerant Control for Physically Linked Two 2WD Mobile Robots with Actuator Faults

In this paper, a fault-tolerant control scheme for two physically linked two wheel drive (2WD) mobile robots with multiple and simultaneous actuator faults is proposed. The kinematic and dynamic models are first presented. A kinematic control law is designed, based on which, a dynamic control law is investigated. By applying the proposed dynamic control signal, the desired system stability and tracking properties are ensured. Simulation results are finally presented to verify the effectiveness of the developed fault-tolerant control scheme.

Distributed reconfigurable control strategies for switching topology networked multi-agent systems

In this paper, distributed control reconfiguration strategies for directed switching topology networked multi-agent systems are developed and investigated. The proposed control strategies are invoked when the agents are subject to actuator faults and while the available fault detection and isolation (FDI) modules provide inaccurate and unreliable information on the estimation of faults severities. Our proposed strategies will ensure that the agents reach a consensus while an upper bound on the team performance index is ensured and satisfied. Three types of actuator faults are considered, namely: the loss of effectiveness fault, the outage fault, and the stuck fault. By utilizing quadratic and convex hull (composite) Lyapunov functions, two cooperative and distributed recovery strategies are designed and provided to select the gains of the proposed control laws such that the team objectives are guaranteed. Our proposed reconfigurable control laws are applied to a team of autonomous underwater vehicles (AUVs) under directed switching topologies and subject to simultaneous actuator faults. Simulation results demonstrate the effectiveness of our proposed distributed reconfiguration control laws in compensating for the effects of sudden actuator faults and subject to fault diagnosis module uncertainties and unreliabilities.

Smart Investment for Redundancies Selection Integrated to Reconfigurable Fault-Tolerant Control Design

This paper presents a methodology for the optimal hardware redundancies selection in the context of reconfigurable fault-tolerant control design. Assuming that a nominal controller of reduced dimension has been successfully designed, the objective is to accommodate a presumed set of failures, including partial, total, and simultaneous actuator faults, preserving the system stability and maintaining an acceptable dynamic performance. The methodology is based on a multiobjective optimization framework to obtain a suitable trade-off between conflicting design objectives such as controllability and performance. The selection of additional hardware devices (not included in the nominal controller) is penalized to determine the minimum number of redundancies that should be installed. In addition, the redundancies selection is performed without explicitly considering the type of control structure. The effectiveness of the proposed approach is tested using the well-known Tennessee Eastman benchmark.