Fault-tolerant Control System Research Articles

Fault tolerant control for robotic manipulator using fractional-order backstepping fast terminal sliding mode control

In this paper, the problems of tracking control and finite-time stabilization of a high nonlinear system such as a robotic manipulator in the presence of actuator faults, uncertainties, and external disturbances are explored. In order to improve the performance of the system in the presence of actuator faults, uncertainties and external disturbances a novel fault tolerant control system based on fractional-order backstepping fast terminal sliding mode control is developed in this paper. The control system is developed by employing the results obtained from studies in the fields of fractional-order calculus, backstepping, sliding mode control, Mittag–Leffler stability, and finite-time Lyapunov stability. The performance of the suggested controller is then tested for a PUMA560 robot in which the first three joints are used. The simulation results validate the usefulness of the developed control approach in terms of accuracy of tracking, and convergence speed in the presence of disturbances, uncertainties and actuator faults. The trajectory tracking performance of the developed method is compared with other state of the art approaches such as conventional computed torque control, proportional integral derivative control and nonsingular fast terminal sliding mode control. The simulation results show that the proposed control approach performed better as compared to other control approaches in the presence of actuator faults, uncertainties, and disturbances.

Active fault-tolerant control system for a swash mass helicopter using back-stepping approach

In this article, an active fault-tolerant control system is designed and analyzed for a new model structure of unmanned aerial vehicles, which is referred to a swash mass helicopter. It consists of a double-blade coaxial shaft rotor for generating the necessary thrust and four masses that are located on the main body structure to maneuver the helicopter. The translational and rotational subsystems of the helicopter are highly coupled. Therefore, change of coordinate and feedback linearization methodologies are applied to address the problem and achieve the canonical form of the model. Next, actuator fault as a loss of effectiveness and bias faults are modeled for the dynamic. The main contribution of this article is to design an active fault-tolerant control system based on back-stepping and T-S fuzzy estimation methods for the swash mass helicopter which has never been designed in the last decades. T-S fuzzy methodology is responsible for obtaining the estimated value of the actuator faults during the flight. The Lyapunov theory illustrates that the proposed control strategy can stabilize the system despite the actuator’s fault. The simulation results show the effectiveness of the proposed scheme compared with another method.

Проблемы организации вычислений в многомашинных вычислительных системах с программно-управляемой сбое- и отказоустойчивостью. Часть I

This three-part paper analyzes existing approaches and methods of organizing failure- and fault-tolerant computing in distributed multicomputer systems (DMCS), identifies and provides rationale for a list of issues to be solved. We present the concept of fault tolerance proposed by A. Avizienis, explicate its dissimilarity from the modern concept and the reason for its inapplicability with regard to modern distributed multicomputer systems. We justify the necessity to refine the definition of fault tolerance approved by the State Standards, as well as the necessity to specify three input parameters to be taken into account in the DMCS design methods: permitted fault models, permitted multiplicity of faults, permitted fault sequence capabilities. We formulate the questions that must be answered in order to design a truly reliable, fault-tolerant system and consider the application areas of the failure- and fault-tolerant control systems for complex network and distributed objects. System, functional, and test diagnostics serve as the basis for building unattended failure- and fault-tolerant systems. The concept of self-managed degradation (with the DMCS eventually proceeding to a safe shutdown at a critical level of degradation) is a means to increase the DMCS active life. We consider the issues related to the diagnosis of multiple faults and present the main differences in ensuring fault tolerance between systems with broadcast communication channels and systems with point-to-point communication channels. The first part of the work mainly deals with the analysis of existing approaches and methods of organizing failure- and fault-tolerant computing in DMCS and the definition of the concept of fault-tolerance.

Development of a hardware-in-the-loop demonstrator for the validation of fault-tolerant control methods for a hybrid UAV

Many aircraft are inherently over-actuated with regard to their input variables. This can be particularly advantageous in the context of unmanned aerial vehicles (UAV), where actuator functions can fail in critical situations. In such cases, the redundant actuators can be used to further fulfil the control strategies used and thus increase the operational safety. Within such an active fault-tolerant control system, a fault detection and isolation (FDI) module is required. To evaluate such safety–critical systems, hardware-in-the-loop simulations (HIL) are a necessary step prior to real flight tests. These simulations can verify the correct implementation of the flight controller on the target hardware as well as the real-time capability of the algorithms used. Particularly in the context of active fault-tolerant control, investigations concerning the robustness of the used FDI module with regard to real, noisy sensor signals, which can be generated by a HIL demonstrator, are of utter importance. This paper presents the development of a HIL demonstrator for the validation of fault-tolerant control methods for a hybrid UAV. This includes a detailed description of the demonstrator’s design, control and interfacing between the integrated subsystems. As an application example, a hybrid UAV model will be shortly presented, which, in addition to the primary aerodynamic control surfaces, can also use four lift rotors to control the aircraft during cruise and is therefore inherently over-actuated. Finally, a closed-loop real-time simulation of the UAV model on the HIL demonstrator is presented on the basis of the exemplary simulation of an actuator failure and subsequent reconfiguration by the fault-tolerant flight control law.

Aircraft flight control system fault tolerance under structural and parametric uncertainties

The concept of an intelligent hybrid aircraft fault-tolerant flight control system operating under complete parametric and structural uncertainty is considered. Fault tolerance in the proposed system is ensured through the efficient integration of model-based and model-free health monitoring and reconfiguring methods.

Multiple Sensor Fault Detection Algorithm for Fault Tolerant Control of BLDC Motor

A direct redundancy-based fault tolerant control system (FTCS) is proposed for the operation of a brushless DC (BLDC) motor in the case of multiple sensor failures. The presented method expands on the previously published work that dealt with the failure of a single Hall-effect sensor. In this paper, a novel algorithm is developed along with the new experimental scheme and the FTCS can deal with the failure of up to two Hall-effect sensors. The fault tolerant control (FTC) algorithm is based on three conditions and is designed to deal with any scenario of the sensor faults. Simulation was performed and presented experimental results show effectiveness and validation of the method. The method can be implemented with ease, is fast and does not require high end processors.

Fault Diagnosis and Reconfigurable Control for Commercial Aircraft with Multiple Faults and Actuator Saturation

Active fault-tolerant control systems perform fault diagnosis and reconfigurable control. There is a bidirectional uncertainty between them, and an integrated scheme is proposed here to account for that. The system considers both actuator and sensor faults, as well as the external disturbance. The diagnostic module is designed using an unknown input observer, and the controller is constructed on the basis of an adaptive method. The integrated strategy is presented, and the stability of the overall system is analyzed. Moreover, different kinds of anti-windup techniques are utilized to modify the original controllers, because of the different controller structures. A simulation of the integrated anti-windup fault-tolerant control method is demonstrated using a numerical model of Boeing 747. The results show that it can guarantee the stability of the post-fault aircraft and increase the control performance for the overall faulty system.

Robust Passive Fault Tolerant Control for Air Fuel Ratio Control of Internal Combustion Gasoline Engine for Sensor and Actuator Faults

This paper presents a novel Passive Fault Tolerant Control System (PFTCS) for Air Fuel Ratio (AFR) control system of the Internal Combustion (IC) gasoline engine to prevent its shutdown. A Proportional plus Integral (PI) controller with high feedback gain is implemented to control AFR by introducing a fuel throttle valve in the fuel line of the engine. The salient feature of the proposed controller is its less complex structure due to the absence of Analytical Redundancy (AR). Dual redundancy in the hardware is suggested for the sensors to prevent tripping in case of coincident faults in multiple sensors and for the actuator assembly to confiscate a single point of failure. The robustness of the proposed PFTCS is tested by introducing noise in the sensor measurements. MATLAB / Simulink environment simulation results demonstrate that the proposed PFTCS is robust to faults in normal as well as noisy conditions of the sensors without any degradation of AFR. The stability analysis of the proposed controller is performed by determining the poles of the closed-loop system. The reliability analysis of the proposed controller has been performed by calculating the probabilistic reliability function of the model. The comparison of the proposed model with the existing models has also been carried out to elaborate its effectiveness.

Accelerated Landweber iteration based control allocation for fault tolerant control of reusable launch vehicle

This paper presents a novel Fault Tolerant Control (FTC) scheme based on accelerated Landweber iteration and redistribution mechanism for a horizontal takeoff horizontal landing reusable launch vehicle (RLV). First, an adaptive law based on fixed-time non-singular fast terminal sliding mode control (NFTSMC), which focuses on the attitude tracking controller design for RLV in the presence of model couplings, parameter uncertainties and external disturbances, is proposed to produce virtual control command. On this basis, a novel Control Allocation (CA) based on accelerated Landwber iteration is presented to realize proportional allocation of virtual control command among the actuators according to the effective gain as well as the distance from the current position of actuator to corresponding saturation limit. Meanwhile a novel redistribution mechanism is introduced to redistribute oversaturated command among healthy actuators (non-faulty or redundant). The proposed method can be applied to a real-time FTC system so that the controller reconfiguring is not required in case of actuator faults. Finally, the effectiveness of the proposed method is demonstrated by numerical simulations.

Adaptive Fixed-Time Nonsingular Terminal Sliding Mode Attitude Tracking Control for Spacecraft with Actuator Saturations and Faults

This paper focuses on the potential actuator failures of spacecraft in practical engineering applications. Aiming at the shortcomings and deficiencies in the existing attitude fault-tolerant control system design, combined with the current research status of attitude fault-tolerant control technology, we carry out high-precision, fast-convergent attitude tracking algorithms. Based on the adaptive nonsingular terminal sliding mode control theory, we design a kind of fixed-time convergence control method. This method solves the problems of actuator faults, actuator saturation, external disturbances, and inertia uncertainties. The control method includes control law design and controller design. The designed fixed-time adaptive nonsingular terminal sliding mode control law is applicable to the development of fixed-time fault-tolerant attitude tracking controller with multiple constraints. The designed controller considers the saturation of the actuator output torque so that the spacecraft can operate within the saturation magnitude without on-line fault estimation. Lyapunov stability analysis shows that under multiple constraints such as actuator saturation, external disturbances, and inertia uncertainties, the controller has fast convergence and has good fault tolerance to actuator fault. The numerical simulation shows that the controller has good performance and low-energy consumption in attitude tracking control.

Robust fault accommodation strategy of the reentry vehicle: a disturbance estimate-triggered approach

This study proposes a novel fault accommodation scheme for the strong coupled attitude system of the hypersonic reentry vehicle (HRV) with both actuator drift and loss of efficiency. A general coupling/fault/uncertainty effect-triggered control concept is first introduced for the HRV attitude tracking system to improve its robustness and dynamic performance, which can be derived easily via Lyapunov stability. The design of such a control approach is based on an improved adaptive disturbance observer (ADO) to estimate the lumped uncertainties and actuator faults. The proposed scheme can achieve graceful degradation in tracking performance for the fault-tolerant control system by eliminating the detrimental uncertainty and actuator fault while keeping the beneficial uncertainty and actuator fault. A detailed design procedure has been presented with consideration of the implementation problem. Simulation results obtained on the HRV have demonstrated the effectiveness of the approach proposed.

Speed sensorless fault-tolerant control of induction motor drives against current sensor fault

Current sensors are needed in conventional field-oriented control (FOC) in 3-phase induction motor (3-PIM) drives. Nevertheless, these sensors are exposed to different faults which reduce the reliability of drive systems. To solve this problem, a current sensor fault-tolerant control (FTC) for 3-PIM drives without speed measurement is proposed in this paper. In the proposed scheme, a sensorless FOC strategy based on open-loop speed estimator is utilized for normal condition. A third-difference operator performs the task of fault detection and isolation (FDI). After FDI, a sensorless FOC strategy based on extended Kalman filter (EKF) is used for the faulty condition. In this paper, the EKF is used for stator currents and speed estimation during post-fault operation. Such scheme is appropriate for sensorless 3-PIM drives to increase safety and reliability of the system, in the case of current sensor fault. The proposed FTC scheme is experimented for a 1HP 3-PIM drive system through a DSP/TMS320F28335. The experimental results show that the proposed FTC system can accurately and effectively control the 3-PIM during both healthy and faulty conditions.

Design of Active Fault Tolerant Control System for Air Fuel Ratio Control of Internal Combustion Engines Using Artificial Neural Networks

Fault tolerant control systems can be used in the process machines such as Internal Combustion (IC) engines to achieve greater reliability and stability in the fault conditions. Thus, costly loss of production due to the unusual and unexpected shutdown of these machines can be avoided. The Air Fuel Ratio (AFR) control system is an important system in IC engines and faults in the sensors of this system will cause its shutdown creating costly production loss, therefore, fault tolerance is necessary for them. In this paper, an Active Fault Tolerant Control System (AFTCS) based on Artificial Neural Networks (ANN) has been proposed for the AFR control system of a Spark Ignition (SI) IC engine to increase its reliability. In the proposed AFTCS, a nonlinear ANN-based observer is used in the Fault Detection and Isolation (FDI) unit for the highly nonlinear sensors of the AFR system for analytical redundancy. The Lyapunov stability analysis has been utilized to design a stable system in normal and faulty conditions. The system has been implemented in MATLAB/Simulink environment to test its performance. The simulation experimental results demonstrate that the suggested system stays reliable maintaining the stability well in the fault conditions of sensors with little degradation in AFR. A comparison with the existing works demonstrates the superior performance of the proposed AFTCS for the highly nonlinear sensors of the AFR control system. The technique suggested is very effective in terms of fault robustness and is more specifically based on the nonlinear behavior of the MAP sensor compared to the existing works.

Active Fault Tolerant Control System Design for Hydraulic Manipulator With Internal Leakage Faults Based on Disturbance Observer and Online Adaptive Identification

In this paper, an active fault-tolerant control (FTC) system design is proposed for an n-degree-of-freedom (n-DOF) hydraulic manipulator with internal leakage faults and mismatched/matched lumped disturbances. A pair of matched and mismatched disturbance observers (DOBs) is proposed to simultaneously estimate and compensate for the effects of matched/mismatched disturbances on the control system in healthy conditions. The fault detection is achieved when the estimated matched disturbance is larger than a threshold. After that, a novel control reconfiguration law is designed to switch from a normal controller to a fault-tolerant controller with an online identification algorithm based on an adaptive mechanism. The proposed active FTC guarantees the position tracking performance in not only single-fault but also simultaneous-faults conditions. Moreover, the problem of uniting disturbance-observer-based control for external disturbance and adaptive control for parametric uncertainty is solved in a novel approach. Simulation results are conducted in a two-degree-of-freedom hydraulic leg prototype, which verifies the effectiveness of the proposed method.

CNN-Based Intelligent Fault-Tolerant Control Design for Turbofan Engines With Actuator Faults

In this paper, the problem of fault-tolerant control is investigated for turbofan engines with actuator faults. The controller involvement has repressed the effects of actuator faults on the controlled outputs of turbofan engines, making fault-tolerant control difficult. To solve this problem, the internal gas-path data of turbofan engines is introduced to provide conducive fault information. Besides, the useful property of the convolution neural network (CNN) is explored and utilized in fault-tolerant control. Based on the analysis of actuator faults, by using the Lyapunov stability and $L_{2}$ -gain like theorems, a novel CNN-based intelligent fault-tolerant control system for turbofan engines is proposed, including a CNN-based fault diagnosis module and a nonlinear fault-tolerant control with corresponding reconfiguration unit. The CNN-based intelligent fault-tolerant control system has the advantages of reducing the accuracy requirements of the mathematical description of turbofan engines. Furthermore, the proposed system can diagnose actuator faults and reduce the adverse effects of actuator faults on turbofan engines. Finally, simulation results are presented to demonstrate the efficiency of the designed method.

Design and Implementation of a Fault-Tolerant Magnetic Bearing Control System Combined With a Novel Fault-Diagnosis of Actuators

Although magnetic bearings are generally reliable, an important concern for machine applications is fault tolerance. The fault-tolerant operation of a magnetic bearing system can be realized through the identification and isolation of fault actuators and subsequent support reconstruction via residual actuators. In this study, a novel fault-diagnosis algorithm for electromagnetic actuators (EMAs) is proposed. The equivalent slope of the load current is defined as a fault-diagnosis threshold by theoretically analyzing the variation characteristics of the current in the modulation. The synchronous sampling of the current and its processing algorithm are designed. By combining these algorithms with the generalized bias current linearization theory reported previously, a fault-tolerant control (FTC) system for magnetic bearings is developed, and control of multi-position and multi-current loops is realized by using two digital signal processors (DSP). The FTC of the rotor motion and the fault-diagnosis of actuators are executed in parallel. The proposed control system is verified by the experiments, and experimental results demonstrate that the proposed system can cope with EMA fault in an extremely short time of less than 5 ms. Thus, the support can be reconstructed by employing the FTC to maintain rotor stability.

Detection of negative sequence components in diagnosing and tolerating open‐gate fault for a voltage‐source inverter in an induction motor drive

Power converter faults represent about 12% of electrical system faults. More than 31% of these converter faults are caused by the transistors in the converters. These transistor failures are classified into open-gate and short-gate faults. A fault diagnostic and tolerant control system is proposed in this study for an open-gate fault of a three-phase voltage-source inverter (VSI). The system under study is an induction motor fed by a VSI. The diagnostic technique uses a detection method of positive and negative sequence components, which requires only the measurement of motor currents. The diagnostic signals are derived from the negative sequence components of the motor currents. These signals are then compared using logic functions to trigger the tolerant control. In the case of an open-gate fault, the tolerant system converts the inverter topology from six switches to four switches where the faulty inverter leg is disconnected. The proposed control method was evaluated under steady-state and transient conditions through simulation and experiments. The results confirm an effective and reliable performance of the motor under an open-gate fault.

A novel active fault-tolerant control for spacecrafts with full state constraints and input saturation

This paper proposes an active fault-tolerant control (AFTC) system for spacecrafts subject to model uncertainty, external disturbance and actuator fault simultaneously. Fault diagnosis is implemented by a robust fault observer with a simple structure. The observer can separately estimate the fault in the existence of disturbance and uncertainty. The influence on observation performance from disturbance and uncertainty is attenuated by linear matrix inequality (LMI) optimization. For the fault-tolerant controller, asymmetric barrier Lyapunov function and backstepping method are used to constrain all the states. Meanwhile, the control input is restricted by a saturation function. Validation and comparative simulations are implemented to demonstrate the proposed AFTC method.

Active fault tolerant control of turbofan engines with actuator faults under disturbances

Abstract In this paper, an active fault-tolerant control (FTC) scheme for turbofan engines subject to simultaneous multiplicative and additive actuator faults under disturbances is proposed. First, a state error feedback controller is designed based on interval observer as the nominal controller in order to achieve the model reference rotary speed tracking control for the fault-free turbofan engine under disturbances. Subsequently, a virtual actuator based reconfiguration block is developed aiming at preserving the consistent performance in spite of the occurrence of the simultaneous multiplicative and additive actuator faults. Moreover, to improve the performance of the FTC system, the interval observer is slightly modified without reconstruction of the state error feedback controller. And a theoretical sufficiency criterion is provided to ensure the stability of the proposed active FTC system. Simulation results on a turbofan engine indicate that the proposed active FCT scheme is effective despite of the existence of actuator faults and disturbances.

Active fault tolerant control of turbofan engines with actuator faults under disturbances

Abstract In this paper, an active fault-tolerant control (FTC) scheme for turbofan engines subject to simultaneous multiplicative and additive actuator faults under disturbances is proposed. First, a state error feedback controller is designed based on interval observer as the nominal controller in order to achieve the model reference rotary speed tracking control for the fault-free turbofan engine under disturbances. Subsequently, a virtual actuator based reconfiguration block is developed aiming at preserving the consistent performance in spite of the occurrence of the simultaneous multiplicative and additive actuator faults. Moreover, to improve the performance of the FTC system, the interval observer is slightly modified without reconstruction of the state error feedback controller. And a theoretical sufficiency criterion is provided to ensure the stability of the proposed active FTC system. Simulation results on a turbofan engine indicate that the proposed active FCT scheme is effective despite of the existence of actuator faults and disturbances.