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The study targets uncertain coupling faults in robotic arm actuators and proposes a new fault-tolerant visual servo control strategy. Specifically, it considers both multiplicative and additive actuator faults within the dynamic of the robotic arm, treating the coupling faults and time-varying disturbances as an aggregate of concentrated uncertainties. A radial basis function neural network-based state observer is introduced to online approximate these concentrated uncertainties, which include fault information, eliminating the need for prior knowledge of faults. Furthermore, a fault-tolerant controller based on a non-singular fast terminal sliding mode is proposed, which separately decouples the nominal quantities and concentrated uncertainties and develops individual adaptive control laws for each. This effectively reduces the detrimental impact of coupled faults and disturbances on the system's performance, facilitating image feature trajectory tracking control with minimal jitter, high precision, and strong transient response capabilities. The stability of the state observer and the fault-tolerant controller has been substantiated through Lyapunov's theory. Lastly, numerical simulations validate the efficacy and robustness of the proposed fault-tolerant visual servo control approach. [ABSTRACT FROM AUTHOR]

This article studies the control ideas of the optimal backstepping technique, proposing an event-triggered optimal tracking control scheme for a class of strict-feedback nonlinear systems with non-affine and nonlinear faults. A simplified identifier-critic-actor framework is employed in the reinforcement learning algorithm to achieve optimal control. The identifier estimates the unknown dynamic functions, the critic evaluates the system performance, and the actor implements control actions, enabling modeling and control of anonymous systems for achieving optimal control performance. In this paper, a simplified reinforcement learning algorithm is designed by deriving update rules from the negative gradient of a simple positive function related to the Hamilton-Jacobi-Bellman equation, and it also releases the stringent persistent excitation condition. Then, a fault-tolerant control method is developed by applying filtered signals for controller design. Additionally, to address communication resource reduction, an event-triggered mechanism is employed for designing the actual controller. Finally, the proposed scheme's feasibility is validated through theoretical analysis and simulation. [ABSTRACT FROM AUTHOR]

This paper investigates hall sensor signal unbalancing faults in sensored Brushless Direct Current (BLDC) motor drives and presents a fault effect minimization scheme for implementation in motor controller without any modification in system architecture, or core commutation method. In the proposed scheme detection, classification, and estimation of fault extent are carried out separately at the start of controller itself for subsequent corrections without involving issue of repetitive error estimation and finding valid reference signal separately for correcting inverter switching mistiming, as required in classical methods. The categorization part of scheme maps the faults with corresponding hall sensors. The proposed scheme is validated in MATLAB/Simulink model. It is tested on experimental test bench of controller and 1 kW BLDC motor of an electric rickshaw, along with another technique based on least square method (LSM) for performance comparison. Results show reduction of peak-to-peak value by 30% and ripple content by 50% in phase currents, and peak-to-peak reduction of 47% with 29% lesser ripple content in DC link current by using the presented scheme. The observed increment in efficiency is 0.8% and 2% in nominal torque/ampere at 30% load. At 100% load, increase of 2.2% efficiency and 9% nominal torque/ampere are observed. The increased memory loading of controller is estimated to be 1.25 times as compared to normal run without any correction scheme. Approximately 24% of this additional loading is utilized for repetitive calculations as compared to 63% in the other LSM based scheme, resulting in lesser run time loading of controller. The transient response with sudden load change shows better response with implementation of the proposed scheme in controller. [ABSTRACT FROM AUTHOR]

Manufacturing systems are becoming more sophisticated and expensive, particularly with the development of the intelligent industry. The complexity of the architecture and concept of Smart Manufacturing (SM) makes it vulnerable to several faults and failures that impact the entire behavior of the manufacturing system. It is crucial to find and detect any potential anomalies and faults as soon as possible because of the low tolerance for performance deterioration, productivity decline, and safety issues. To overcome these issues, a variety of approaches exist in the literature. However, the multitude of techniques make it difficult to choose the appropriate method in relation to a given context. This paper proposes a new architecture for a conceptual model of intelligent fault diagnosis and self-healing for smart manufacturing systems. Based on this architecture, a review method for the different approaches, sub-approaches and methods used to develop a Fault Detection and Diagnosis (FDD) and Self-Healing-Fault-Tolerant (SH-FT) strategy dedicated to smart manufacturing is defined. Moreover, this paper reviews and analyzes more than 256 scientific articles on fault diagnosis and self-healing approaches and their applications in SM in the last decade. Finally, promising research directions in the field of resilient smart manufacturing are highlighted. [ABSTRACT FROM AUTHOR]

A fault-tolerant control approach is proposed, for a pumping airborne wind energy system (AWES) comprising a tethered fixed-wing aircraft with integrated propellers for vertical take-off and landing (VTOL). First, the flight control design for the traction phase of the system, when the tethered aircraft has to fly in loops using the rudder, is presented. Then, the presence of the propellers, that are normally not used in the traction phase, is exploited to obtain a fault tolerant controller in case of rudder malfunctioning. The approach detects a possible discrete control surface fault and compensates for the loss in actuation by using the VTOL system. A sophisticated model of the system is used to analyse the performance of the proposed technique. The main finding is that the approach is able to handle abrupt rudder faults with high tolerance. [ABSTRACT FROM AUTHOR]

This paper puts forward a novel multi-rate sampled-data fault-tolerant control strategy for quadrotor unmanned aerial vehicle. By constructing a loop-based Lyapunov functional, stability criteria of the system under aperiodic sampled-data framework is given. Fixing the sampled-data period under velocity and position control, this paper obtains a larger sampled-data period under attitude control than existing literature. An adaptive fault-tolerant control scheme is introduced to ensure steady-state operation in the presence of actuator faults. Furthermore, a multi-rate sampled-data controller solution method is proposed to address the actuator fault problem, enabling the stability of the system under the controllers with normal and uncertain gains. Simulation results using a quadrotor model validate the reliability of the planned fault-tolerant control scheme, ensuring stability even at very low sampled-data frequencies. Through comparative analysis, it is proved that the designed controller enables precise hovering at the desired position, regardless of the presence or absence of actuator faults. [ABSTRACT FROM AUTHOR]

This paper proposes a new fault-diagnosis method and fault-tolerance control (FTC) strategy applied to the field-oriented control (FOC) of induction motor drives. The proposed diagnosis method for open-switch faults (OSFs) relies solely on measured current behavior. The diagnostic variables are extracted from the average absolute values of the normalized phase currents. The simulation results show that the diagnosis method can detect the OSFs in less than 36% of the fundamental phase current period without additional sensors. A total of nine types of OSFs can be diagnosed accurately and quickly. In addition, the obtained results demonstrate the method's robustness against load-transient conditions. Compared with existing diagnosis methods, this technique relies on two diagnostic variables and an adaptive detection threshold. To improve the drive's reliability against OSF effects, a fault-tolerant control scheme is developed based on reconfiguring the voltage source inverter (VSI) topology. In this case, the faulty VSI phase is connected to the DC-link midpoint through bidirectional power switches. Most FTC systems reported in the literature require a change in the drive's control algorithm. Hence, this paper presents a low-cost FTC scheme without changing the FOC algorithm. Simulation results are carried out in MATLAB-Simulink to validate the effectiveness of the proposed fault diagnosis method and the FTC strategy. [ABSTRACT FROM AUTHOR]

This article investigates a heterogeneous vehicular platoon control problem, in which prescribed tracking performance can be achieved, it is assumed that the vehicle subjects to asymmetric nonlinear actuator saturation, dead-zone nonlinearity and actuator faults. Based on improved exponential spacing policy, an adaptive fault-tolerant sliding-mode control scheme is proposed to guarantee individual vehicle stability, string stability and traffic flow stability. The hypothesis that the spacing errors at initial time are zero is removed by employing the novel exponential spacing policy. Furthermore, to attenuate the harmful effects of actuator faults, saturation and dead-zone nonlinearity, a compensation system based on radial basis neural network (RBFNN) is established. Finally, the effectiveness of the proposed control scheme is verified by simulation results. [ABSTRACT FROM AUTHOR]

In the paper, a dynamic surface-based adaptive fuzzy fixed-time fault-tolerant control scheme is developed for nonstrict feedback nonlinear systems with non-affine faults. Firstly, the computational complexity is reduced by adopting dynamic surface control technique, and unknown nonlinear functions are approximated with the help of fuzzy logic systems. Secondly, non-affine faults involving system states and controller output are taken into account and treated by transforming it into nonlinear in the unknown parameters. Then, under the framework of fixed-time stability, a novel adaptive fuzzy fault-tolerant control strategy is designed so that the closed-loop system is semi-globally practically fixed-time stable. Finally, a numerical simulation and a model simulation are given to demonstrate the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

It is always problematic that the initial value of the trajectory tracking error must be inside the area included in the prescribed performance constraint function. To overcome this problem, a novel fault-tolerant control strategy is designed for a second-order multi-input and multi-output nonlinear system (MIMO-NLS) with unknown initial states, actuator faults, and control saturation. Firstly, a predefined time convergence (PTC) stability criterion is theoretically proven. Then, an error conversion function is introduced to convert the trajectory tracking error to a new error variable with an initial value of zero, and an adaptive fuzzy system is designed to approximate the compound interference composed of actuator fault, parameter perturbation, control saturated overamplitude, and external disturbance. Based on the backstepping control method, prescribed performance control method, and predefined time convergence stability theory, an adaptive fuzzy fault-tolerant controller for the new error variable is designed and theoretically proven for the predefined time convergence of the closed-loop system. The numerical simulation results of the guaranteed performance trajectory tracking control for industrial robots with actuator faults demonstrate that the adaptive fuzzy fault-tolerant control algorithm has strong fault tolerance to actuator faults and anti-interference capabilities. The convergence time and performance of trajectory tracking errors can be preset in advance, and the parameter settings of the prescribed performance constraint function are not affected by the initial state values. [ABSTRACT FROM AUTHOR]

This study addresses the problem of cooperative control design for a group of car-like vehicles encountering fading channels, actuator faults, and external disturbances. It is presumed that certain followers lack direct access to the states of the leader via a directed graph. This arises challenges in maintaining synchronization and coordination within the network. The proposed control strategy utilizes non-singular fast terminal sliding mode control to accelerate consensus tracking and enhance the convergence of the overall system. This controller is designed to mitigate the impact of actuator faults in the presence of fading channels in the communication network. The effects of such issues on team performance are rigorously analyzed. Based on the Lyapunov stability principle, it has been demonstrated that the controller is capable of providing satisfactory performance for the entire system despite these challenges. Moreover, vehicle synchronization can be effectively maintained. Numerical simulations are conducted to verify the theoretical findings. [ABSTRACT FROM AUTHOR]

This paper presents an active fault-tolerant flight control system (FCS) design for the dual-system/hybrid VTOL UAV configuration that maximally exploits its inherent over-actuation abilities to provide higher levels of fault-tolerance and reliability compared to that of the other VTOL UAVs configurations up to this point. The significance of this study is to convert the main drawback of having the vertical rotors as dead weights during the cruise to a key advantage where all the UAV's controls are kept active during all the flight phases raising the UAV's fault-tolerance and maneuverability abilities. The FCS proposed elaborates on a new architecture for the hierarchical automatic control loops using the dynamic inversion control to design the trajectory tracking virtual commands and employing optimal dynamic control allocation to optimally resolve the controls redundancy. Regarding fault-tolerance, the presented FCS handles simultaneous failures and jamming of all the control surfaces during flight where the control commands to the healthy controls (vertical rotors) were automatically adapted such that the trimming and trajectory tracking were successfully maintained till the mission end. Additionally, this paper addresses for the first time the employment of the controls redundancy to enhance the VTOL UAV's maneuverability in fault-free cases, where we present a study of reducing the minimum turn radius of the UAV when the vertical rotors are employed with the control surfaces during the maneuver. A reduction of 38% in the coordinated steady-level minimum turn radius turn at 35 m/sec flight speed was achieved. [ABSTRACT FROM AUTHOR]

In this article, a robust fault-tolerant sliding mode controller is proposed for a class of non-homogeneous Euler–Bernoulli beams which contains controller time-varying fault, external unknown spatiotemporally varying disturbance, and parametric uncertainties. Furthermore, to reduce the number of correspondence between the controller and the actuator, two event-triggered mechanisms are incorporated into the controller design. The sliding surface designed ensures that the system is uniformly ultimately bounded and robust to the parameter uncertainties in model. In addition, the Euler–Bernoulli beam can be used as a model for the flexible wind turbine tower. Numerical simulations are shown to illustrate the validity and effectiveness of the proposed control method. The simulation results show that in the presence of unknown faults and parametric uncertainties, the proposed controller can still effectively suppress the vibration of the tower, while the event-triggered mechanism significantly reduces the communications burden. [ABSTRACT FROM AUTHOR]

This article introduces a new fault-tolerant control method based on type-2 fuzzy systems with PID fast terminal sliding mode control. By integrating the advantages of proportional-integral-derivative (PID) control with fast terminal sliding mode (FTSM) control, a novel proportional-integral-derivative fast terminal sliding mode (PID-FTSM) is developed to accelerate convergence and decrease steady-state error. To provide outstanding fault tolerant control performance and approximation of system uncertainties, a type-2 fuzzy logical switching approach law eliminates the chattering phenomenon and reduce the need of prior knowledge without affecting the system's robustness. The overall stability of the system is verified using the Lyapunov function. Finally, several experiments demonstrate that the suggested technique outperforms alternatives. [ABSTRACT FROM AUTHOR]

The distributed adaptive fuzzy coordination control (DAFCC) method for the leader-following for non-affine nonlinear (NAN) multi-agent systems (MASs) with actuator failures (including partial failures and actuator bias failures) under the unreliable switching communication environments is proposed in this article. First, based on the neighborhood state information, a group of distributed reference observer (DRO) is constructed so that all followers can easily estimate the leader's information. Second, the implicit function theorem and the mean value theorem are utilized to convert the non-affine term into the corresponding affine term in order to solve the non-affine term in the NAN system. Third, to achieve global synchronization, we design an adaptive fuzzy coordination fault-tolerant controller with local estimation. Besides, the DAFCC method presented in this paper solves the cooperative control problem when switching undirected networks with intermittent communications. Finally, simulation is used to validate the effectiveness of the algorithm. [ABSTRACT FROM AUTHOR]

This paper proposes a new fault-tolerant control approach for gas turbines, based on fuzzy techniques that allow real-time observation of their behavior. The approach consists of detecting and locating faults, and then determining the appropriate control action to keep the turbine in stable operation. This improves the efficiency and lifespan of the turbine, and reduces maintenance costs with optimal planning. The state space model of the turbine is subjected to a diagnostic procedure based on Type-1 and Type-2 fuzzy models, using the operational data of the different operating points studied. The Luenberger observer is used in the fault detection mechanism, to characterize turbine component malfunctions by comparing the observed real behaviors and the fuzzy models. The results show that the fault-tolerant fuzzy control has ensured the stability and availability of the turbine during fault occurrence, with good performance in detection, isolation and reconfiguration. [ABSTRACT FROM AUTHOR]

This paper focuses on the trajectory tracking problem of nth-order uncertain nonlinear systems with sensor faults. The proposed approach utilizes a fuzzy observer to estimate the unmeasurable states in the systems. Moreover, the finite-time control strategy and the command filtered technique are added in the controller design. The former aims to enhance the systems' response speed, and the latter is to mitigate the "differential explosion" problem. Meanwhile, the adaptive technique is incorporated to compensate for sensor faults. The boundedness of all the signals within the closed-loop systems is confirmed through stability analysis. Finally, the effectiveness of the proposed approach is verified through two simulation examples. [ABSTRACT FROM AUTHOR]

T-type three-level inverters (T23LIs) are widely used in the electric drive system of new energy vehicles. However, the open-circuit (OC) faults of their switching devices will cause serious damage to the entire system operation. To mitigate the impact of switching faults, this paper proposes an OC fault diagnosis method based on the variations of common-mode voltage in small sectors of T23LI. Firstly, the normal characteristics of T23LI under SVPWM control algorithm are analyzed, and the correspondence between the space voltage vectors and the values of common-mode voltage is established. Then, the common-mode voltage variations under fault conditions are analyzed, and a fault diagnosis method based on these variations is proposed. The faults of the four switching devices in one phase is divided into two groups through the qualitative analysis of common-mode voltage variations, and the specific location of the faulty switch is located by further quantitative analysis. Finally, by analyzing the changes in the three-phase bridge output voltages after faults, the accurate location of the faults in the 12 switches of the three phases is located. Simulation and experimental results verify that the proposed method can accurately and quickly diagnose the single-switch OC faults of all switches, and it effectively accelerates the diagnosis speed and reduces costs by only requiring the collection of a single voltage signal. [ABSTRACT FROM AUTHOR]

The problem of adaptive fault-tolerant fixed-time control is studied for a class of strict-feedback nonlinear systems with multiple faults and multiple disturbances. We incorporate the tuning functions and the command filter technique into the controller design. Note that the former reduces the order of the controller, and the latter simplifies the derivation and calculation process and avoids the high calculation cost and differential explosion. In addition, since our proposed strategy is based on fixed-time control, it can ensure that the closed-loop system keeps the practically fixed-time stable, and the tracking error converges to a small neighborhood near the origin within fixed-time. As for the unknown items in the systems, fuzzy logic systems are used to approximate them. The simulation results show that the proposed control strategy is effective even if there exist actuator faults and multiple disturbances. [ABSTRACT FROM AUTHOR]

This paper gives a fault-tolerant control scheme concerning with the optimal and near-optimal system performance for a class of nonlinear systems with time-varying actuator faults, time-varying disturbances, and identification errors of the neural network-based identifier. In this paper, the adaptive dynamic programming method is directly used to design the optimal sliding surface, so that the designer can design the target dynamics of the sliding mode in advance. In addition, the barrier function-based sliding-mode control is used to cope with the bounded but boundary-unknown estimation errors of the identifier, and the method ensures that the sliding-mode variable converges to the designer's predefined neighborhood of zero in finite time and the control gain is not overestimated. Specifically, first, by adaptive dynamic programming, near-optimal sliding surface is designed in the sense of the quadratic optimal criterion. Second, a neural network identifier is designed to model the lumped uncertainties including actuator faults and disturbances. Third, a barrier function-based adaptive sliding-mode control is used to cope with the identification errors of the neural network identifier and has no control gain overestimation, which can guarantee to confine the sliding variable to a predefined vicinity of the proposed sliding surface. For this system with faults and disturbances, it is shown that near-optimal property is achieved by this scheme, the chattering phenomenon is effectively suppressed, and the reconstruction error of the neural network identifier with unknown boundary is effectively handled by the adaptive sliding-mode control based on the barrier function. The proof of stability is given by Lyapunov's direct method and the effectiveness of this control scheme is verified by applying it to the spacecraft attitude system. [ABSTRACT FROM AUTHOR]

This work presents an event-triggered mechanism-based distributed fractional-order fault-tolerant control (FTC) paradigm for multiple unmanned aerial vehicles (multi-UAVs) subject to full-state constraints. Distinct from the existing control solutions for multi-UAVs with constant constraints and symmetric constraints, the time-varying asymmetric constraints considered in this paper are more suitable for practical requirements. Neural networks are exploited to cope with uncertainties arising from unknown nonlinear dynamics. By cleverly combining speed functions with nonlinear state-dependent functions, a novel distributed FTC protocol is established to drive the system states into the boundary functions within a predetermined finite time. Simultaneously, fractional-order calculus is introduced to provide additional adjustment of control parameters, and an event-triggered mechanism is derived to reduce the update frequency of the control signal. It is testified that all signals of each follower UAV are semi-globally uniformly ultimately bounded, and all follower UAVs can follow the attitudes of the leader UAV. In the end, case studies are reported to corroborate the outperformance of the proposed methodology. [ABSTRACT FROM AUTHOR]

In this article, the cooperative control for nonlinear multi-agent systems (NMSs) subject to non-affine faults is investigated under directed graphs. A new distributed fixed-time event-triggered control protocol is proposed based on the leader–follower communication architecture, which saves network resources effectively and avoids Zeno behavior. A novel dynamic switching event-triggered mechanism (DSEM) is presented for each follower to ensure the smooth switching of two dynamic threshold strategies, and a dynamic internal trigger variable is designed based on the control input signals and errors, which can dynamically adjust the update frequency of the controller to reduce the number of system triggers. A new DSEM fixed-time distributed controller is designed based on local information to guarantee that all signals of the closed-loop system are fixed-time bounded. It is also proved that the consensus tracking errors of NMSs can converge to an explicitly given bound independent of the initial state in a fixed time. Finally, the validity of the presented control strategy is illustrated by two simulation examples. [ABSTRACT FROM AUTHOR]

In this paper, a class of nonlinear systems with sensor faults and uncertainty problem are considered. The proposed control scheme is designed based on backstepping procedure. Additionally, three classes of filters are introduced, a serious of K-filters and an auxiliary filter are used to deal with the unmeasurable system states, and the command filters are adopted to avoid the "differential explosion" problem in backstepping design. Furthermore, the bound estimation method is adopted to estimate the unknown system parameters, partial loss fault of sensor and the upper bound of unknown nonlinear functions. Meanwhile, the proposed scheme reduces the amount of calculations in the controller design and and plays a certain role in saving network resources. Even when the sensor fails, the proposed scheme can ensure that all the signals in the closed-loop system are uniformly and ultimately bounded. Finally, a single-link robot arm example is simulated to show the feasibility of the proposed scheme. [ABSTRACT FROM AUTHOR]

To improve the performance of a class of nonlinear system with actuator fault and external disturbance, a fault-tolerant control method with finite-time prescribed performance is proposed based on the super-twisting disturbance observer in this paper. First, the actuator bias fault and external disturbance of the system are regarded as a lumped disturbance, and it is estimated by the designed super-twisting disturbance observer in finite time. Second, a finite-time prescribed performance fault-tolerant controller under full state constraints is designed by combining the backstepping method, the modified barrier Lyapunov function (MBLF) method and the improved prescribed performance function (IPPF) method. Moreover, the "explosion of complexity" problem in the controller design is solved by the command filters with error compensation. Theoretical analysis shows that the closed-loop system can converge to the neighborhood near the equilibrium point in finite time, and all states are always within the constraint boundaries. Finally, the effectiveness and feasibility of the proposed method are verified by the comparisons of simulations and experiments based on a permanent magnet synchronous motor (PMSM) position system. [ABSTRACT FROM AUTHOR]

This paper studies the adaptive fault-tolerant control problem for biological systems with the invasion of alien species. Firstly, to overcome the difficulty of dealing with nonlinear terms in the system, the T-S fuzzy method is applied to obtain the T-S fuzzy biological systems. Then, an augmented matrix is developed for the T-S fuzzy system, and a sliding mode observer is constructed to estimate the state vector, sensor faults, sensor failure and external disturbances. In addition, an observer-based adaptive sliding-mode control law is designed to ensure the stability of the closed-loop biological system. Finally, a simulation example is presented to illustrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper expresses a novel adaptive fault-tolerant control (FTC) method for a robotic manipulator with dead zones and actuator faults in the task space. To specify, the actuator faults are the partial loss of effectiveness of actuators. The partial loss of effectiveness and the break-points of dead zone are estimated by the novel adaptive laws. Establishing an anti-singularity terminal sliding surface ensures the finite time convergence of the tracking errors to zero. The correctness of this method is proved by the Lyapunov criterion. Despite the fact that the proposed adaptive FTC method belongs to the passive group, it does not require any robust component which makes large-magnitude chattering phenomena to deal with the actuator faults. Instead, they are handled by a unique technique. The comparative simulation results illustrate the merit and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, a low-computation adaptive fault-tolerant control (FTC) scheme is proposed for a class of strict-feedback nonlinear systems with unmatched disturbances. In contrast to existing FTC schemes, a method called delayed actuator replacement is taken into account, that is, the backup actuator cannot be connected to the system immediately after failure detection. In order to restore the tracking error to the prescribed performance within a specified time, a set of shifting functions is established to derive new error variables. In addition, by introducing two novel error transformation functions, the designed low-computation adaptive control method overcomes the complexity explosion problem and simplifies the design process. Furthermore, a self-triggered mechanism is designed to improve the transmission efficiency of the whole system. The validity of our control scheme is demonstrated through a simulation example. [ABSTRACT FROM AUTHOR]

In this paper, the fault-tolerant capability of the existing stator-flux-oriented decoupling control (SFOC) for the DTP-PM motor is investigated, and a simple fault-tolerant SFOC is further designed to enhance fault tolerance. Firstly, the mathematical model of the DTP-PM motor in the stator-flux-oriented rotating coordinate system is analyzed. An SFOC is proposed to guarantee healthy operation performance, considering torque, flux linkage, and harmonic currents. Secondly, the coupling relationship under open-phase conditions is assessed. The assessed result shows that the coupling relationship between the harmonic and fundamental components results in conflicts and poor post-fault operation. Thirdly, the proposed SFOC includes an automatic deactivation module to detect conflicts with a variable threshold. The conflicted harmonic current controllers can be excluded automatically. Hence, fault-tolerant control can be remedied without diagnosing the specific fault scenario, and excellent fault-tolerant capability can be achieved. Finally, experiments on a DTP-PM motor are carried out to verify the feasibility and effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

In this article, for a class of stochastic pure-feedback nonlinear systems with simultaneous actuator and sensor faults, the problem of adaptive fault-tolerant control is examined. The stochastic pure-feedback nonlinear system is first converted into a strict-feedback by applying the mean value theorem and radial basis function neural networks are used to approximate the unknown functions. Only one adaptive parameter needs to be calculated online rather than the actual weight vector elements by determining the greatest value of the norm of the neural network weight vector. With the help of regrouping and parameter separation methods, the unavailability of state variables caused by sensor faults is addressed. The Lyapunov function methods and the backstepping recursive design technique are used to design an adaptive fault-tolerant controller. It is shown that by choosing proper the design parameters, the tracking errors converge to a small region of the origin, and all the signals in the closed-loop system are bounded in probability. The performance of the proposed controller is illustrated using a numerical example and a real-world example of a rigid robot manipulator system. [ABSTRACT FROM AUTHOR]

In this paper, the distributed fuzzy resilient tracking problem for a class of second-order nonlinear multi-agent systems (MASs) under denial-of-service (DoS) attacks is addressed. Compared with the existing distributed fuzzy tracking results, a more general class of second-order MASs with DoS attacks under combined output observable situation are considered in this paper. Under DoS attacks, the second-order derivative of the traditional distributed observer does not exist, while this signal is necessary to solve the distributed fuzzy tracking problem for second-order MASs when using the backstepping method. To solve the problem, a hierarchical control method that consists of a cooperative resilient observer and a distributed controller is proposed. Specifically, a new distributed resilient observer state with a second-order derivative and also the function of defending network attacks is designed based on a combined output observable condition. By using the backstepping technique, decentralized fuzzy adaptive resilient controllers are designed to achieve distributed tracking under DoS attacks. It is shown that the distributed fuzzy resilient tracking problem can be solved under our designed method. Finally, second-order nonlinear MASs are provided to verify the effectiveness of our method. [ABSTRACT FROM AUTHOR]

The fault-tolerant control problem associated with limited communication is addressed in this paper for coupled spacecraft in the presence of internal uncertainties, external disturbances, actuator uncertainties including failures, magnitude deviation and misalignment, and actuator saturation constraint. Firstly, considering the configuration and installation deviation of the thrusters, a six degree of freedom (6-DOF) kinematics and dynamics coupling model of the spacecraft is established and derived on the Lie group SE (3). Then, the lumped disturbance is estimated by using a fixed-time convergent sliding mode surface combined with a disturbance observer. Next, the dynamic event-triggered fault-tolerant controller is proposed for the first time to compensate for the lumped disturbance. Finally, both theoretical analysis and numerical simulation results verify that the method proposed in this paper can not only achieve fast and high-precision tracking control goal, moreover, through comparative analysis, but the data transmission frequency between the controller and the actuator are also effectively reduced, thereby significantly reducing the communication burden of the spacecraft. [ABSTRACT FROM AUTHOR]

The article concentrates on the finite-time fault-tolerant control for a class of nonstrict-feedback nonlinear systems subject to uncertain control gains and multiple actuator faults. First, neural networks are employed to approximate system uncertainties. By means of a vital structural attribute of neural networks, algebraic loop problem in standard backstepping control design is excluded. Then, a sliding manifold with exponential monotonic attenuation is introduced to ensure chattering-free response and robust performance. Besides, the lumped uncertainty of multiple faulty actuators is handled via applying Nussbaum gain technique and a modified Nussbaum boundedness criterion. To circumvent the issue of "complexity explosion", a second-order command filter is introduced in every step of recursive control design. Through the proposed adaptive finite-time fault-tolerant control scheme, the influence of actuator faults can be compensated effectively, and the tracking error converges into an arbitrarily small residuum in finite time. Meanwhile, the disc domain of convergent error as well as the upper bound of settling time can be estimated. Finally, two simulations concerned with practical models are discussed. It is expounded that the proposed scheme has more efficiency and less conservatism via comparing it with other existing methods. [ABSTRACT FROM AUTHOR]

In this paper, a fixed-time prescribed performance fault-tolerant control scheme is presented for the n-link flexible joint robot with actuator failures. Firstly, a modified prescribed performance control method is proposed to enhance the robustness of the system against input perturbations and to ensure that the tracking error converges in a predetermined time, and the constrained system is transferred into an unconstrained system. Secondly, an adaptive-based passive fault-tolerant controller is constructed to counteract the actuator failures in the system. Then, the uncertainty problem in the flexible-joint robot system is solved by incorporating the radial basis function neural networks and adaptive techniques into the fixed-time backstepping framework. After that, the "complexity explosion" issue is well handled by creating the fixed-time second-order filter, in which the filtering errors are eliminated by the devised compensation mechanism. The stability analysis proves that the closed-loop system is fixed-time stable, and the tracking error is limited to the predefined range. Finally, simulations have been performed on a two-link FJR and a three-link flexible joint robot, respectively. Via the three conditions: actuators operating normally, actuators losing 50% of effectiveness instantaneously, and actuators losing 50% of effectiveness gradually, the results show that the tracking error of each joint of the system is less than 0.2 rad, and the tracking time is limited to the specified time (0.8 s), which proves the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

In our study, an adaptive sliding mode fault-tolerant control scheme is proposed for attitude tracking of spacecraft with actuator faults. Two-power reaching laws are used for sliding mode control, which are designed not only to solve the chattering problem of the sliding mode variables near the sliding mode surface, but also to directly obtain more accurate convergence time expression of the sliding mode variables. At the same time, a redundant actuator configuration of spacecraft is considered especially, and it improves the fault tolerance of the system. Moreover, for unknown items in the system, an adaptive control technique is introduced to approximate them. Our proposed control strategy can ensure that the attitude error and the angular velocity error of spacecraft converge to a small area near zero even when some actuators fail completely. Finally, the effectiveness of our proposed approach is verified by a numerical simulation example. [ABSTRACT FROM AUTHOR]

To enhance system position estimation reliability when a single-phase open-circuit fault occurs, this study provides a sensorless control strategy based on a medium and high-speed super-twisting sliding mode observer (ST-SMO) for a five-phase permanent magnet synchronous motor, in which the space vector pulse width modulation (SVPWM) control strategy is adopted. In this method, a super-twisting sliding mode observer is developed to achieve any two-healthy phase back electromotive force (EMFs) estimation, during normal and open-circuit fault operations, irrespective of parameter variations and external disturbances. Then a phase-locked loop (PLL) is presented to extract the position and the speed of the rotor directly from the estimated two phase back-EMFs. The proposed ST-SMO algorithm achieves strong robustness to various external variations, suppresses system chattering, and enhances the estimation accuracy in the medium and high-speed range. Simulation and experimental results are provided to verify the effectiveness of the proposed method under different load conditions over medium to high-speed ranges. [ABSTRACT FROM AUTHOR]

To improve control performance in robotic systems with faults and unknown uncertainties, a fault-tolerant control (FTC) system based on a wavelet type-2 fuzzy brain emotional learning controller (WT2FBC) is developed in this research. Type-2 fuzzy logic systems can handle uncertainties better than type-1 fuzzy logic systems, so they can solve some uncertain complex problems more accurate. Given its fast learning and problem-solving capabilities, the proposed WT2FBC is an important fuzzy neural network. The next step is to investigate how a WT2FBC-based FTC system can help solve the puzzles that plague the robotic systems. To achieve FTC, a control system with a computed torque controller and the WT2FBC estimator is provided. If the robotic system ever exhibits faults, it can consult an online fault estimator built on WT2FBC, and then compensates the faults. For more efficient, the total number of fuzzy rules of WT2FBC can be dynamically adjusted using a self-organizing algorithm based on the technique for order of preference by similarity to ideal solution. Simulations of a biped robot and a two-link manipulator robot have demonstrated the effectiveness of the proposed control algorithm. [ABSTRACT FROM AUTHOR]

An adaptive tracking control problem of high-order nonlinear strict-feedback system (SFS) with non-affine nonlinear faults is considered in this paper. Based on high-order fully actuated (HOFA) systems theory, dynamic surface control technique and universal approximation of fuzzy logic systems, a novel adaptive fuzzy fault-tolerant tracking controllers are directly constructed, it does not need to convert the high-order system into first-order one. By using Lyapunov function theory, the proposed controller design approach can guarantee that the closed-loop system is stable; at the same time, the tracking error can converge to a compact neighborhood with respect to zero. The simulation example has been verified the feasibility and effectiveness of the control approach in this paper. [ABSTRACT FROM AUTHOR]

This research is devoted to devising a fault-tolerant control system to resolve the challenge of multi-fault automatic repair in variable-structure flight conditions of fighters. In the classical fighter system, the increment of the state parameter is used to represent the variable structure parameter. To illustrate the broad applicability of the following technique, Rudder and Sensor Gain Loss and Bias Faults are constructed. The Extended Observer is designed to simultaneously gauge faults, states, and disturbances. Furthermore, the harmonic functions is designed to quickly adapt to fighter configuration changes, time-varying disturbances, and to estimate all failures. Similar harmonic functions also appear in the design of fault self-healing algorithms, i.e., adaptive fault-tolerant controllers with variable-structure harmonic functions, simultaneously repairing gain loss and bias faults of rudder and sensors. Verification of the method's effectiveness is achieved through semi-physical simulations, while the Lyapunov function function demonstrates the system's stability. [ABSTRACT FROM AUTHOR]

This article investigates adaptive fuzzy fixed-time fault-tolerant control for strict-feedback nonlinear systems with unknown nonaffine nonlinear faults. To address the nonaffine nonlinear fault, Butterworth filter signal is introduced into the adaptive backstepping control design procedures. The "explosion of complexity" is avoided by adopting command filter method, and the filter errors can be eliminated by introducing compensating signals. Fuzzy logic system as an approximator that is employed to estimate the unknown term in the system. Lyapunov stability analysis testifies that the closed loop system is semiglobally fixed-time stable, and the tracking error can converge to a small neighborhood of zero in a fixed time that the convergence time is not affected by the initial conditions of the system. The simulation consequences illustrate the effectiveness of the proposed control method. [ABSTRACT FROM AUTHOR]

In real-world applications, faults and delays can occur in all system variables such as inputs and/or states and/or outputs. The challenge of designing Takagi-Sugeno (T–S) fuzzy controllers for faulty and fully delayed systems is addressed. In contrast to most existing works, the system states are assumed to be unavailable for measurement, and no prior information about the system delays and faults as well as their boundaries is required. Furthermore, the time delays are multiple, unknown, and different in each distinct input and/or state and/or output. Because the system states, delays, and faults are unavailable and unknown, the T–S fuzzy controller premise variables become immeasurable. Thus, the design of fuzzy state observers and fuzzy controllers under the presence of all previous uncertainties to ensure overall system stability has become a big challenge. This challenge is solved in two stages. First, a new model for a fully delayed system with different delays in each distinct input, and/or state, and/or output is obtained, which is realized by transforming the fully delayed system into a general delayed model with delayed states and inputs as well as the biasing uncertainties in the sensors. Subsequently, the T–S fuzzy-descriptor systems are investigated, and simultaneous fault-tolerant T–S fuzzy observers–controllers are proposed. The overall stabilities are ensured using the Lyapunov–Krasovskii functional method. Three simulated examples are presented to prove the applicability and advantages of the proposed approach. [ABSTRACT FROM AUTHOR]

The electro-hydraulic servo system (EHSS) usually faces multiple sensor faults and disturbances, which is difficult to achieve good tracking control, reliability, and stability control. In this article, an advanced fault-tolerant controller is proposed for an EHSS to deal with the above challenge. The three fault observers, called nonlinear unknown input observers (NUIOs), are developed to effectively estimate the position, velocity, pressure sensor faults and the system states. The fault detection, estimation, and isolation are then presented as effective for multiple sensors failure at a time. The first NUIO for position sensor fault is utilized for the tracking control, while the other NUIOs are used for alarm proposal. The adverse effects caused by the matched and unmatched disturbances are eliminated by two extended state observers (ESOs). In addition, to avoid the "explosion of complexity" when computing the derivatives of virtual control laws, the dynamic surface control is applied to design the fault-tolerant control (FTC) scheme. The Lyapunov principle ensures system stability under lumped disturbance and faulty conditions. Finally, simulation studies and evaluation results are performed to demonstrate the validity of the proposed FTC algorithm. [ABSTRACT FROM AUTHOR]

In this paper, a robust control algorithm is designed to achieve a finite-time vehicle height and posture control through electronically controlled air suspension (ECAS) system subject to actuator faults, uncertainties under non-stationary condition. To achieve simultaneous position control of four corners of vehicle, synchronization errors between corners are taken to form a synchronization control strategy. Furthermore, to improve the system convergence speed and robustness, finite-time stability constrain is applied and H ∞ index is designed strategically in order to develop a novel robust finite-time controller. Since the solenoid valves in the ECAS system may degrade with the frequent switching, actuator fault and uncertain parameters are considered in this study to design the proposed fault-tolerant control methodology. Meanwhile, road disturbance is applied to the vehicle with the ECAS system to provide a non-stationary condition. Several software-in-the-loop tests and hardware-in-the-loop test are conducted to illustrate the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

Standalone low-voltage DC (LVDC) microgrids have emerged as potential alternatives in the context of effective rural electrification. The factors of reduction in conversion costs, paradigm shift in voltage levels of domestic loads made LVDC Microgrids more preferable. Being driven by intermittent renewable sources and dynamic loading, the voltage control is quite crucial and challenging to ensure a stable LVDC microgrid. Furthermore, delivering the control objectives becomes very difficult in the presence of sensor faults. In order to address this issue of sensor faults, this work proposes an Extended Luenberger Observer-based Active Sensor Fault-Tolerant Control (ELO-ASFTC) scheme. The proposed control scheme consists of the aspects of fault detection and isolation (FDI), and control reconfiguration. The proposed control scheme achieved the voltage tracking objective of the LVDC microgrid even under the presence of a faulty DC bus voltage sensor. The performance of the proposed scheme is observed in handling different sensor fault scenarios, loading conditions and irradiance changes. The effectiveness of the proposed control scheme is studied analytically, through the simulation studies in MATLAB, and hardware experimentation on the in house LVDC microgrid test bed. [ABSTRACT FROM AUTHOR]

This paper investigates the actuator fault detection and tolerant control problem for vehicle platoons with partial loss of effectiveness and bias faults. Considering the inherent coupling between the control input and the nonlinear term in the actuator, a decoupled observer based fault detection algorithm with time-varying threshold is developed to decide whether the actuator fault occurs in the platoon. Then, by employing radial basis function neural networks (RBF NNs) and backstepping control method, an adaptive robust fault-tolerant control (FTC) scheme is proposed, which is proved to be capable of achieving the safety, stability and tracking performance of vehicle platoons in the presence of actuator fault. Simulation studies illustrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Cable-driven parallel robots (CDPRs) are a class of parallel robots where the cables are used as the arms of the robot in a redundant kinematic architecture. Such an architecture allows manipulation in a considerably large working area and also operation at high speed and acceleration. However, as cables only support tensile force, the controller should generate positive control effort, which leads to a complex constrained control problem. The positive tension distribution in redundant CDPR is generally maintained via redundancy resolution (RR) methods, which are originally optimization-based. The RR methods are prone to kinematic uncertainty, which brings complexity to the control apart from the original effects of kinematic uncertainty. The constrained control of CDPRs gets more complex in the faulty mode of the actuators. The combined effects of faulty actuators along with the kinematic uncertainty limit the application of RR in practice. To address this, a robust fault-tolerant constrained control scheme is proposed to generate an unidirectional control signal for maintaining positive tension in cables in the presence of actuator fault and model uncertainties, taking advantage of an adaptive finite-time sliding mode control along with a nonlinear adaptive observer. The proposed observer estimates the model uncertainties and the actuator fault, while the controller ensures the convergence of the state variables and compensates for the observer estimation error. The H ∞ asymptotic stability of the proposed observer is ensured through sufficient conditions using linear matrix inequality. Furthermore, Lyapunov's second method is employed to prove the finite-time stability of the system. The performance of the proposed scheme is experimentally validated using a planar CDPR in the presence of actuator fault and model uncertainties. [ABSTRACT FROM AUTHOR]

In this paper, a fault-tolerant control method for an input-series output-parallel modular grid-tied pulse-width modulation (PWM) current source inverter is proposed to address the most commonly seen single symmetrical gate-commutated thyristor (SGCT) open-circuit fault problems. This method actively offsets the neutral point of the current space vector to ensure a sinusoidal output of the grid current, and it can achieve the upper limit power of the inverter under the condition of a single SGCT open-circuit fault. In addition, an active damping control method based on grid harmonic current feedback is proposed after analyzing the influence of the transformer ferromagnetic resonance caused by the neutral point offset on the power quality of the grid current. It has been demonstrated that the proposed method effectively suppresses the resonance caused by the transformer and the modified modulation, improving the grid current's power quality. [ABSTRACT FROM AUTHOR]

In this paper, Barrier function based adaptive global sliding mode fault-tolerant control and its application in quad-rotor UAV system are studied. Firstly, the global sliding mode surface is combined with Barrier function based adaptive sliding mode control, which omits the approach process of phase I of traditional Barrier adaptive sliding mode motion, thus improving the rapidity and accuracy of the algorithm. Secondly, the Barrier function adaptive law is used to adjust the gain of the switching term, so that the controller gain can change with the amplitude of the total disturbance in a timely and accurate manner, avoiding the overestimation problem and thus reducing the chattering of the control signal. Finally, the experimental results on the fault-tolerant control platform for multi-rotor UAVs prove the effectiveness and superiority of the proposed algorithm. [ABSTRACT FROM AUTHOR]

This paper investigates the design issue of the fault-tolerant tracking controller for uncertain nonlinear systems with input delay and actuator faults. Fuzzy logic systems are employed to approximate the uncertainties of the nonlinear systems. A state observer and a disturbance observer are designed to estimate the unmeasurable states and external disturbances, respectively. Moreover, an auxiliary system is applied to make up for the impact of the input delay. Furthermore, with the aid of the backstepping technology and the dynamic surface control method, a disturbance observer-based adaptive fuzzy fault-tolerant tracking controller is designed, which can guarantee that the output signal can track the reference signal greatly, and the other signals are bounded in the closed-loop system in case of input delay and actuator faults. Finally, a practical simulation example is supplied to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper develops a new fault-tolerant control (FTC) of wireless sensor network in vehicle that aims to solve three problems in engineering practice: lack of data in sensor failure state, high system complexity and multiple sensors concurrent failure. In the new FTC framework, a new belief rule base expert system for concurrent events is developed to aggregate the data and knowledge and handle the concurrent events. In the FTC framework, fault detection and diagnosis (FDD) part is firstly conducted, and then, the output of the failure sensors is reconstructed based on the output reconstruction strategy by the observation information from the available sensors. In the FDD model, the fault diagnosis strategy of proximity classification based on distance is applied in the FDD model. To further improve the performance of the FTC framework, a new optimization model is proposed. A case study is conducted to illustrate the effectiveness of the proposed framework. [ABSTRACT FROM AUTHOR]

To improve the fault redundancy capability for the high reliability requirement of a brushless doubly-fed generation system applied to large offshore wind farms, the control winding of a brushless doubly-fed reluctance generator is designed as an open-winding structure. Consequently, the two ends of the control winding are connected via dual three-phase converters for the emerging open-winding structure. Therefore, a novel fault-tolerant control strategy based on the direct power control scheme is brought to focus in this paper. Based on the direct power control (DPC) strategy, the post-fault voltage vector selection method is explained in detail according to the fault types of the dual converters. The fault-tolerant control strategy proposed enables the open-winding brushless doubly-fed reluctance generator (BDFRG) system to operate normally in one, two, or three switches fault of the converter, simultaneously achieving power tracking control. The presented results verify the feasibility and validity of the scheme proposed. [ABSTRACT FROM AUTHOR]