Fault-tolerant Control Technique Research Articles

ADP-Based Fault-Tolerant Control for Multiagent Systems With Semi-Markovian Jump Parameters.

This article analyzes and validates an approach of integration of adaptive dynamic programming (ADP) and adaptive fault-tolerant control (FTC) technique to address the consensus control problem for semi-Markovian jump multiagent systems having actuator bias faults. A semi-Markovian process, a more versatile stochastic process, is employed to characterize the parameter variations that arise from the intricacies of the environment. The reliance on accurate knowledge of system dynamics is overcome through the utilization of an actor-critic neural network structure within the ADP algorithm. A data-driven FTC scheme is introduced, which enables online adjustment and automatic compensation of actuator bias faults. It has been demonstrated that the signals generated by the controlled system exhibit uniform boundedness. Additionally, the followers' states can achieve and maintain consensus with that of the leader. Ultimately, the simulation results are given to demonstrate the efficacy of the designed theoretical findings.

Integrated Fault-Tolerant Control Design With Sampled-Output Measurements for Interval Type-2 Takagi-Sugeno Fuzzy Systems.

This article is concerned with the integrated design of fault estimation (FE) and fault-tolerant control (FTC) for uncertain nonlinear systems suffering from actuator faults and external disturbance. The uncertain nonlinear systems are characterized as the interval type-2 (IT2) Takagi-Sugeno (T-S) fuzzy model, and IT2 membership functions are employed to effectively handle uncertainties. A fuzzy observer, utilizing only sampled-output measurements, is applied to simultaneously estimate actuator faults and system states. Based on the estimation, the fault-tolerant controller is designed to ensure the system stability under a predefined H∞ performance. The sampling behavior complicates the system dynamics and makes the integrated FTC design more challenging. To confront this issue, the discontinuous Lyapunov functional technique is exploited to enhance stability results by considering the sampling characteristic, upon which FE and FTC units are co-designed in the linear matrix inequality (LMI) framework. To further relax stability criteria, the analysis process incorporates the bound information of membership functions through the membership-function-dependent (MFD) method. Additionally, the relationship of mismatched premise variables resulting from the sampling scheme is also taken into account. Moreover, considering the imperfect premise matching (IPM) framework, the proposed fault-tolerant controller provides greater flexibility in selecting the shapes of membership functions and number of fuzzy rules that can vary from the counterpart of the fuzzy system. Finally, the efficacy of the proposed FTC technique is validated through a detailed numerical example.

Fault tolerant motion planning for a quadrotor subject to complete rotor failure

Assuring safety of a quadrotor subject to rotor failure has been heavily investigated at the control level in view of fault tolerant control (FTC) approach. Yet, the existing FTCs are often concerned with tracking the reference motion even when that reference may not be safely trackable due to the physical constraints of the quadrotor. This paper tackles the faulty quadrotor safety at the planner level, proposing a fault tolerant motion planner. Starting from the formal backward reachability problem formulation, the proposed motion planner generates the time trajectory of the coupled rotational and translational motions that safely guide the faulty quadrotor. The generated trajectory is theoretically guaranteed to be tracked by the embedded FTC without violating the physical constraints. Further, the trajectory is prescribed as an analytical closed-form expression and thus suitable for real-time emergency maneuvers. The effectiveness of the proposed motion planner is numerically validated in conjunction with the different FTC techniques and compared to the existing planning method. The simulation results clearly signify that the proposed planner can successfully complement the fault tolerance of quadrotor. The supplements including code implementations are available on GitHub repository: https://github.com/HMCL-UNIST/Fault-tolerant-motion-planner.

Robust Fixed-Time Adaptive Fault-Tolerant Control for Dynamic Positioning of Ships with Thruster Faults

The ship dynamic positioning system has long been a subject of great interest due to the intricate and unpredictable nature of the maritime environment, which affects its dependability and timeliness. This study focuses on the issue of developing a robust, efficient, and adaptable fault-tolerant control system for ship dynamic positioning systems that experience thruster malfunctions. Firstly, we build the motion model of the ship’s dynamic positioning system with three degrees of freedom, as well as the model for faults in the thruster. A second-order fast fixed-time nonsingular sliding mode surface is formulated, and a robust adaptive control technique is introduced to counteract external environmental disturbances and model errors. The objective is to ensure rapid convergence of the system within a predetermined time frame. Simultaneously, combined with the fault-tolerant control technique, it is ensured that the dynamic positioning ship can still achieve system stability when thruster faults occur. In addition, the analysis of the Lyapunov stability criterion proves that the proposed fixed-time adaptive fault-tolerant control scheme can make the system tracking error converge within a fixed time. Finally, the effectiveness of the proposed control scheme is verified by numerical simulation results.

Adaptive fault-tolerant control for ascent HSV with wing damage and function constraints on states

In this article, a fault-tolerant tracking control technique is developed for the ascent of hypersonic vehicles (HSV) experiencing wing damage and time-varying state constraints. The difficulty of control problem lies in handling state constraints associated with both state and time, while determining the unknown control directions of the multi-input multi-output (MIMO) nonlinear system. The presence of constraints in both state and time complicates the design of the control algorithm. This paper proposes the construction of a novel state transition function to establish a new unconstrained system, thereby eliminating the conservative feasibility conditions of Barrier Lyapunov Function (BLF) and integral BLF methods when dealing with time-varying constraints. The fusion of time-varying scaling functions and Nussbaum-type functions not only resolves the issue of unknown control directions in the MIMO nonlinear system but also enhances the transient and steady-state performance of the closed-loop system. Neural Networks are employed to approximate the unknown nonlinear functions. Using Lyapunov stability theory, it is proven that state constraints are not violated, and all signals in the closed-loop system are bounded. Simulation results demonstrate the merits of the designed fault-tolerant control (FTC) algorithm.

Fault-Tolerant Control Based on Current Space Vectors against Total Sensor Failures.

This paper proposes a fault-tolerant control (FTC) strategy using the current space vectors to diagnose sensor failures and enhance the sustained operation of a field-oriented (FO) controlled induction motor drive (IMD). Three space vectors are established for the sensor fault diagnosis technique, including one converted from the measured currents and the other two calculated from the current estimation technique, respectively, measured and with reference speeds. A mixed mathematical model using three space vectors and their components is proposed to accurately determine the fault condition of each sensor in the motor drive. After determining the operating status of each sensor, if the sensor signal is in good condition, the feedback signal to the controller will be the measured signal; otherwise, the estimated signal will be used instead of the failed signal. Failure states of the various sensors were simulated to check the effectiveness of the proposed technique in the Matlab/Simulink environment. The simulation results are positive: the IMD system applying the proposed FTC technique accurately detected the failed sensor and maintained stability during the operation.

Improved solar photovoltaic performance in standalone low‐voltage direct current microgrids using sensor fault tolerant control

AbstractThe advancement of renewable energy technology has been significantly aided by solar photovoltaics (PV). Since solar PV is a weather‐dependent source, it cannot be dispatched. To ensure that the solar PV system can harvest the maximum amount of electricity for the available irradiance level, maximum power point tracking (MPPT) algorithms are used. For standalone low‐voltage DC (LVDC) microgrids to utilize the energy storage system as efficiently as possible, maximum power extraction is essential. The sensed PV voltage and current are essential for these MPPT algorithms to ensure that the maximum power point of the panel is captured. This work proposes an effective fault‐tolerant control (FTC) scheme for the solar PV subsystem in the LVDC microgrid that can seamlessly extract the maximum power despite the PV voltage sensor being faulty. The proposed FTC scheme uses a sliding mode observer (SMO)‐based method to detect and isolate PV voltage sensor faults in the standalone LVDC microgrid. The efficacy of the proposed FTC is assessed in a range of circumstances involving load disturbance, irradiance change, and various sensor fault scenarios. The performance of the proposed FTC is validated using experimental analysis on the LVDC microgrid testbed and MATLAB simulations. Given a faulty PV voltage sensor, at a given operating condition of the microgrid, the proposed FTC scheme is successful in reducing the additional power burden on the battery storage by at least two times. Consequently, the additional discharge in terms of SoC is also seen to be decreased by at least 9%. The proposed FTC technique outperforms the popular MPPT approaches for solar PV in terms of PV voltage sensor fault tolerance in the microgrid.

RETRACTED: Data–Driven Adaptive Fault–Tolerant Control for Floating Offshore Wind Turbines

Floating offshore wind turbines have increased in popularity owing to their adaptability for deep-water applications and high power generation efficiency. The control of floating offshore wind turbines, on the other hand, is very complex. The main challenges are the difficulty in precisely modelling floating offshore wind turbines and the higher failure rate of components. As a consequence, this study proposes a model-free adaptive fault-tolerant control system for blade root moment sensor failures. A model-free adaptive control approach is used to construct an individual pitch controller and a fault compensation to avoid mathematical modelling of floating offshore wind turbines. The proposed fault-tolerant control technique removes the need for fault detection and isolation by converting the fault dynamic compensation process into a real-time control issue for nonlinear systems. The fatigue, aerodynamics, structures, and turbulence code simulates and tests the proposed control strategy, and the results show that the proposed strategy can not only keep the wheel bearing load balanced but also reduce the movement of the floating platform and significantly reduce the bearing load of the floating offshore wind turbines. Furthermore, the output power is closer to the rated power, proving the strategy’s high fault tolerance in the face of repeated blade root moment sensor faults.

Fault Mode Analysis and Convex Optimization-Based Fault-Tolerant Control for New Type Dissimilar Redundant Actuation System of Near Space Vehicle

A new type dissimilar redundant actuation system (NT-DRAS), which is composed of an electro-hydrostatic actuator (EHA) and an electro-mechanical actuator (EMA), is applied in high value unmanned aerial vehicles such as the future near space vehicles to improve their reliability and performance index simultaneously. Further improvement in the flight safety is achieved with the fault-tolerant control (FTC) technique which deals with system faults. This paper proposes a novel convex optimization-based fault-tolerant control (CO-FTC) strategy for the NT-DRAS subject to gradual faults which are included in the state space representation of the system. A convex analysis-based treatment for system uncertainty caused by gradual faults is applied to determine the control gain matrix. The existence condition of the control gain matrix is optimized in the linear matrix inequality (LMI) form. Finally, the determined subsystems based on the novel technique is used to solve the modeled robust FTC problem. Case studies of NT-DRAS subject to different gradual faults have been accomplished to illustrate the FTC necessity for NT-DRAS. Furthermore, the effectiveness of the proposed CO-FTC strategy is validated by comparative analysis of the simulation results.

Control of 7-phase permanent magnet synchronous motor drive post three failures

<span lang="EN-US">The article is introducing a new control technique for the 7-phase permanent magnet synchronous motor (PMSM) drive to enhance its robustness against the failure of phases ‘a’ and ‘c’ in addition to the failure of the encoder occurring simultaneously. The article is firstly developing a new multi-dimension space vector pulse width modulation (SVPWM) technique as a part of the fault-tolerant control technique (FTC) to control the magnitudes and angles of the motor’s current after the failures of phases ‘a’ and ‘c’. Moreover, the paper is developing another FTC to obtain a sensorless operation of the 7-phase motor after the failure in the encoder while the phase ‘a’ and ‘c’ are faulted based on the tracking of the saturation saliency. Simulation results prove that the ripple in the speed post the three failures was maintained to be less than 10 rpm compared to 2 rpm when the 7-phase drive is running without faults. In addition to that, the results demonstrated that the motor responded to instant changes in speeds and loads with a dynamic response very close to that obtained when the 7-phase motor ran under healthy operating conditions.</span>

Event-based fault-tolerant [formula omitted] synchronization for inertial neural networks via a semi-Markov jump approach

In this paper, the synchronization problem of semi-Markov jump neural networks with inertial terms is studied. The semi-Markov jump (s-MJ) process is used to describe the random jump parameters in the system, so Weibull distribution is used to replace the exponential distribution of Markov jump process for the sojourn-time (ST) of each mode in the system. First, a second-order differential system is transformed into a first-order differential system by an appropriate vector substitution. Then, by applying passive fault-tolerant control techniques, the master and slave systems can be synchronized even when the controller fails. In addition, in order to reduce the waste of bandwidth, an event-triggered strategy is designed to determine whether the data needs to be transmitted. Then, by constructing a suitable Lyapunov function and using the characteristics of the cumulative distribution function, the sufficient conditions are established to ensure the stochastic stability of the closed-loop system and meet the specified H∞ performance when the controller fails. Finally, a numerical example and an image processing example are given to verify the effectiveness of the proposed method.

Observer-Based Fault Estimation Applied to a Point Absorber Wave Energy Converter

The economic viability of wave energy conversion systems is one of the open points among the research community. To lower the energy cost, the devices in charge of extracting the wave power, called wave energy converters (WEC), are often controlled by means of optimal control (OC) strategies. Such OC systems, which have proven their effectiveness in wave energy applications, often rely on a mathematical model of the device (and, in some cases, on the wave excitation force) to optimize the control action provided to the system. Nevertheless, the marine environment results hostile for general device safe operations, potentially triggering a variety of faults in the WEC system. Such condition (for example, a sensor failure or additional friction inside a gearing) directly affects the system dynamics. If this deviation is not considered by the control algorithm, the energy production performance can degrade considerably, or the control action itself can cause a more serious fault. A possible solution is that of designing an algorithm capable of compensating for eventual faults in the system, while still respecting the initial design performance or, when not possible, preserving the main device functionalities. Such a control strategies belong to the family of Fault Tolerant Control (FTC) techniques, which can be divided into two macro-categories: Passive (PFTC) and active (AFTC) algorithms. While PFTC systems are designed offline and can account only for a predefined set of system faults, AFTC algorithms are more suitable to tackle significant system deviations from the nominal model. For this purpose, such algorithms may require some routine to detect, isolate and eventually estimate the specific fault. This task is accomplished by Fault Detection and Identification (FDI) routines. According to the AFTC algorithm, the FDI module must accomplish different tasks. Furthermore, the FDI module accuracy plays a crucial role in some AFTC strategies, since the poor estimation of a faulty signal can induce the controller to behave incorrectly. This paper presents an FDI algorithm applied to a point-absorber wave energy converter (WEC). The proposed structure consists of an observer-based strategy in charge of detecting, isolating, and tracking effectively faulty signals occurring in numerical simulations. The results demonstrate the proposed observer effectiveness for a predefined set of actuator and sensor faults, both in the case of independent, and simultaneous fault occurrence.

Fault-Tolerant Control for Uncertain Nonstrict-Feedback Stochastic Nonlinear Systems With Output Constraints

This article investigates the problem of fault-tolerant control (FTC) for nonstrict-feedback (NSF) stochastic nonlinear systems subject to actuator faults and output constraints. Most of the existing backstepping-based FTC techniques have been developed for strict-feedback systems, which may cause algebraic loop problems when applied directly to NSF systems. In this work, unknown nonlinear functions are approximated by neural networks (NNs). Based on the properties of NN basis functions and a barrier Lyapunov function, a novel adaptive FTC strategy for an NSF system is proposed to achieve tracking control without violating the output constraint. Adaptive fault accommodation terms are constructed to compensate for the faults without a priori information to achieve online fault tolerance. The designed controller guarantees the fault-tolerant tracking performance while ensuring that all signals are bounded in probability and that the output is within the specified constraint. The performance of the proposed FTC strategy is illustrated by simulation studies.

A simple fault-tolerant control method for open-phase three-phase induction motor drives

Fault-Tolerant Control (FTC) strategies for Three-Phase Induction Motors (TPIMs) against an open-phase fault have attracted considerable interest in safety-critical applications. In the available literature, open-phase FTC methods for TPIMs are typically implemented using suitable Current Transformation (CT) and Voltage Transformation (VT) matrices. However, the controller design becomes complicated due to different transformations. In addition, the model based on CT and VT suffers from slow dynamics due to several Proportional–Integral (PI) controllers. This paper proposes an open-phase FTC technique for TPIM drives with proof of its asymptotic stability. It is designed based on a new CT for stator current components. Using this CT, the traditional vector control method can be used for Open-Phase TPIMs (OPTPIMs). Furthermore, considering that parameters of the PI controller have an important effect on the OPTPIM drive performance, a design technique is presented to achieve the best values of PI controller parameters. Additionally, an open-phase fault detection technique is presented based on the third-difference operator. The proposed FTC has a simple structure and fast dynamic responses. Matlab simulation and experimental results using DSP/TMS320F28335 approve the ability and good performance of the introduced FTC technique for TPIM drive systems under different conditions.

Prescribed-time extended state observer and prescribed performance control of quadrotor UAVs against actuator faults

The detection and accommodation of actuator faults in control systems have received considerable attention. However, the existing fault-tolerant control techniques typically require complex and computationally intensive algorithms, and the settling time cannot be pre-assigned offline, which limits the practical applicability of these techniques. To address these problems, this paper proposes a prescribed-time fault-tolerant tracking control scheme for accommodating actuator failures in quadrotor unmanned aerial vehicles. First, a prescribed-time nominal controller is developed to precisely track the desired position in the absence of actuator faults. Subsequently, an extended state observer is developed to precisely estimate the uncertainties derived from actuator failures. Using the estimated values, a prescribed-time tracking control scheme is designed for the position subsystem, based on the prescribed performance control technique. In addition to having a simple structure, the proposed controller relaxes the limits that both the settling time and desired transient- and steady-state performances cannot be pre-assigned. Similarly, an observer-based prescribed-time tracking control scheme is established for the attitude subsystem under actuator failures. Numerical simulations are performed to validate the effectiveness and robustness of the proposed control method.

Adaptive finite-time fault-tolerant control for switched nonlinear systems with actuator fault and dead-zone via prescribed performance

In this work, an adaptive finite-time fault-tolerant control (FTC) technique for a class of switched nonlinear systems in strict-feedback form is presented. The switched nonlinear systems are considered under the influence of actuator fault, input-dead zone, and external disturbances. A prescribed performance function is used to ensure transient and steady-state control performance. To approximate unknown functions and minimize the negative effect of faults, radial basis function neural networks (RBFNNs) are used. With the help of neural networks and the backstepping method, an adaptive finite-time tracking controller is constructed. For the stability analysis of the proposed approach, the common Lyapunov function (CLF) is employed. Based on the Lyapunov function method, it has been shown that all the signals in the closed-loop system are semi-globally practically finite-time (SGPF)-stable. Also, the tracking error converges to a small residual set with the prescribed performance bounds. Finally, two simulation examples show the effectiveness of the presented control method, one of which is an application to a continuous stirred tank reactor (CSTR).

Fault-Tolerant Control for Multiphase Induction Machines With Torque Ripple Reduction Considering Harmonic Injection

Open-circuit fault is one of the common faults of multiphase motors. After fault occurrence, the control strategy needs to be modified in order to maintain smooth and uninterrupted operation. However, existing strategies with harmonic injection are unable to achieve effective decoupling of multiple planes. This letter proposes a novel fault-tolerant strategy with harmonic injection for the purpose of torque ripple reduction while enhancing torque operation range compared with state-of-the-art method. Since the higher order harmonic plane has less effect on torque ripple generation, the proposed strategy introduces harmonics into the higher order plane, thereby reducing its coupling to the fundamental plane. A seven-phase induction motor is utilized as the prototype to verify the effectiveness of the proposed fault-tolerant control technique. Furthermore, the design principles of the proposed strategy in this letter can easily be extended to multiphase motors with higher phase numbers.

Fault-tolerant tracking control for nonlinear observer-extended high-order fully-actuated systems

In the paper, a fault-tolerant tracking control strategy is proposed for a class of nonlinear high-order fully-actuated systems (HOFASs) with multiplicative and additive actuator faults. Different from general state space methods, HOFAS approaches can achieve global stability through specific nonlinear control laws, and maintain the fully-actuated and uncoupled characteristics of most physical objects. Starting from the HOFAS tracking error dynamics, a tracking differentiator is designed to solve the reference signal and its derivatives numerically. Furthermore, a specific extended state observer is firstly embedded into the HOFAS, which expands the application scenarios of the HOFAS theory. Based on Lyapunov stability theory, a fully-actuated fault-tolerant control technique is presented to ensure the uniformly ultimately bounded stability of the tracking error. A numerical comparative experiment fully illustrates the effectiveness of the proposed strategy.

Fault estimation and fault tolerant control for interval type-2 Takagi–Sugeno fuzzy systems via membership-function-dependent approach

This paper investigates the fault estimation (FE)-based fault tolerant control (FTC) technique to achieve the desired control performance for the nonlinear systems suffering from uncertainties, external disturbance and actuator faults using the interval type-2 (IT2) Takagi–Sugeno (T–S) fuzzy model. In this work, an IT2 fuzzy observer is built to simultaneously estimate both the system states and actuator faults, upon which a fault tolerant controller is proposed to guarantee the asymptotical stability of the closed-loop system with a prescribed H_{infty } performance level. Considering the bidirectional robustness interactions between the observer and FTC system, an integrated design technique is developed to address observer and FTC units together in one step to realize the required robustness within the whole closed-loop FTC system. By utilizing Lyapunov stability theory combined with the matrix inequality convexification techniques, a membership-function-dependent (MFD) FTC strategy is proposed where the information of membership functions is taken into account in the analysis for relaxation of the stability conditions. Additionally, to offer greater design flexibility and lower implementation cost to the fault tolerant controller, the imperfect premise matching (IPM) scheme is adopted, such that the premise membership functions of the fault tolerant controller can be chosen differently from those of IT2 fuzzy model. Finally, simulation results are provided to validate the effectiveness of the proposed FTC strategy.

Fault-Tolerant Sequential MPC for Vertical Switch Open-Circuit Fault and ZSCC Suppression for Parallel T-Type Converters

A fault-tolerant control (FTC) is proposed for enhancing the reliability of power electronic systems. The software-based FTC of parallel-connected three-level T-type converters (3LT <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> Cs) for suppressing zero-sequence circulating current (ZSCC) induced by a vertical switch open-circuit fault is investigated. A simplified sequential model predictive control (SSMPC)-based FTC technique is developed. Parallel-3LT <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> Cs and their prediction models are introduced, followed by an SSMPC for the no-fault condition. The model inaccuracies under vertical switch faults are elaborated. For the faulty 3LT <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> C, two fault-tolerant SSMPC (FT-SSMPC) methods are provided by creating a sequential predictive controller that considers ZSCC suppression and grid current tracking. The control policies for the ZSCC are changed from the standard feedback-free to feedback-based cost function (CF) optimization using the unimproved FT-SSMPC. Furthermore, an improved FT-SSMPC is proposed using a phase-deficient CF, which increases the accuracy of the mathematical relation of the fault condition. After fault diagnosis, the proposed method achieves neutral-point voltage balance and excellent point-of-common-coupling current, effectively suppresses the ZSCC, and increases the control reliability. Finally, experiments demonstrate the effectiveness of the proposed FT-SSMPC under various conditions.