Effects Of Actuator Faults Research Articles

Adaptive optimal fault-tolerant control scheme for a class of strict-feedback nonlinear systems

An active optimal fault-tolerant control (FTC) scheme for a class of nonlinear systems in strict-feedback form in the presence of partial loss of actuator effectiveness faults is proposed, using backstepping design technique and adaptive dynamic programming (ADP) algorithm to compensate the effects of failure. The proposed FTC scheme consists of feedforward controller that achieve the objective of fault-tolerant and feedback optimal controller, which can guarantee the performance index function is minimized. Since fault estimation and control law parameters are updated online, the control system has an adaptive failure compensation capability so as to reconfigure the control law in real time in response to failure indications. Based on Lyapunov stability theory, the whole closed-loop system is guaranteed to be ultimately uniformly bounded. Finally, the effectiveness of the proposed method is demonstrated by simulation.

Prescribed performance adaptive fault-tolerant tracking control for nonlinear time-delay systems with input quantization and unknown control directions

Abstract This paper addresses the adaptive prescribed performance tracking control problem for a class of nonlinear time-delay systems with actuator fault, input quantization, unknown control directions and disturbances. Neural networks (NNs) are employed to approximate the unknown nonlinear functions and the Nussbaum function is used to deal with the unknown control directions. Then, a novel adaptive prescribed performance controller is designed to reduce the effects of actuator fault, input quantization, NNs approximation errors and disturbances. Compared with the existing results, a new error transformation method is presented, and the knowledge of the quantization parameters and the control directions are unknown in the control design. Furthermore, the proposed control scheme can guarantee the semi-global boundedness of all the closed-loop signals and the prescribed time-varying tracking performance. Finally, simulation results are given to demonstrate the effectiveness of the proposed control method.

Adaptive fault-tolerant control for continuous-time Markovian jump systems with signal quantization

This paper investigates the adaptive fault-tolerant control problem for a class of continuous-time Markovian jump systems with digital communication constraints, parameter uncertainty, disturbance and actuator faults. In this study, the exact information for actuator fault, disturbance and the unparametrisable time-varying stuck fault are totally unknown. The dynamical uniform quantizer is utilized to perform the design work and the mismatched initializations at the coder and decoder sides are also considered. In this paper, a novel quantized adaptive fault-tolerant control design method is proposed to eliminate the effects of actuator fault, parameter uncertainty and disturbance. Moreover, it can be proved that the solutions of the overall closed-loop system are uniformly bounded, which is asymptotically stable almost surely. Finally, numerical examples are provided to verify the effectiveness of the new methodology.

Adaptive Fault-Tolerant Attitude Tracking Control of Spacecraft With Prescribed Performance

The science objectives of a spacecraft mission place stringent performance requirements on the spacecraft attitude control system. However, it remains an open problem how to guarantee consistent control performance necessary to meet these requirements, especially in the event of actuator faults and input saturation. Motivated by this fact, in this paper, we address the problem of attitude tracking control with prescribed performance guarantees for a rigid spacecraft subject to unknown but constant inertia parameters, unexpected disturbances, actuator faults, and input saturation. First, certain performance functions specified a priori by the designer are adopted to impose desired performance metrics on the attitude tracking errors. Then, the original attitude tracking error dynamics with performance constraints is transformed into an equivalent “state-constrained” one whose robust stabilization is shown to be sufficient to solve the stated problem via a novel error transformation. Subsequently, based on the transformed system, an adaptive fault-tolerant controller is derived by incorporating backstepping control, the barrier Lyapunov function, and Nussbaum gains. It is proved that the designed controller is able to guarantee the satisfaction of the prespecified constraints on the transformed errors, as well as the boundedness of all other closed-loop signals, without resorting to a judicious selection of the control parameters. Finally, the effectiveness of the proposed control scheme is evaluated by means of simulation experiments carried out on a microsatellite.

Chattering-Free Sliding Mode Control for Diesel Engine Air Path System with Actuator Faults

In this paper, a chattering-free sliding mode control law is constructed for the diesel engine air path system with consideration of partial loss of actuator effectiveness and additive fault. Firstly, sliding mode method and adaptive technique are employed to develop a fault-tolerant controller. With the adaptation update law, there is no requirement of the priori knowledge of the upper bounds of the actuator faults. Then, to attenuate the chattering behavior and improve system performance, the boundary layer is introduced to modify the sliding mode control method. Rigorous theoretical analysis is presented based on Lyapunov stability theory, which demonstrates that the system trajectories converge to a small neighborhood around the origin. Finally, numerical simulation results are carried out to show the effectiveness and validness of the proposed algorithms.

Actuator Fault Tolerant Control Proposal for PI Controlled SISO Systems

In this work, we develop a control structure which can be added to an existing closed loop in order to mitigate the effect of actuator faults. We analyze the initial performance of the closed loop in terms of robustness and time response under references, faults and measurement noises. In the design of the proposed active fault tolerant control structure, we keep the initial robustness and time response to references. At the same time, we try to improve some performance indices under faults at the cost of a higher control action activity caused by the measurement noises that affect the system. The design of the controller depends on a unique parameter so it can be easily understood. We show that although the response under step faults becomes oscillatory, the active fault tolerant structure reduces the integral of the absolute value of the tracking error under step faults and it attenuates the effect of ramp faults in steady state. Several examples show the goodness and drawbacks of the approach and show some aspects to be considered in the design.

Retrofit fault‐tolerant tracking control design of an unmanned quadrotor helicopter considering actuator dynamics

SummaryThis paper presents a retrofit fault‐tolerant tracking control (FTTC) design method with application to an unmanned quadrotor helicopter (UQH). The proposed retrofit fault‐tolerant tracking controller is developed to accommodate loss‐of‐effectiveness faults in the actuators of UQH. First, a state feedback tracking controller acting as the normal controller is designed to guarantee the stability and satisfactory performance of UQH in the absence of actuator faults, while actuator dynamics of UQH are also considered in the controller design. Then, a retrofit control mechanism with integration of an adaptive fault estimator and an adaptive fault compensator is devised against the adverse effects of actuator faults. Next, the proposed retrofit FTTC strategy, which is synthesized by the normal controller and an additional reconfigurable fault compensating mechanism, takes over the control of the faulty UQH to asymptotically stabilize the closed‐loop system with an acceptable performance degradation in the presence of actuator faults. Finally, both numerical simulations and practical experiments are conducted in order to demonstrate the effectiveness of the proposed FTTC methodology on the asymptotic convergence of tracking error for several combinations of loss‐of‐effectiveness faults in actuators.

Iterative learning control for output‐constrained nonlinear systems with input quantization and actuator faults

SummaryIn this work, we propose a novel iterative learning control algorithm to deal with a class of nonlinear systems with system output constraint requirements and quantization effects on the system control input. Actuator faults have also been considered, which include multiplicative, additive, and stuck actuator faults. To the best of our knowledge, this is the first reported work in the iterative learning control literature to deal with quantization effects for the control input of nonlinear systems under the effects of actuator faults and system output constraints. Under the proposed scheme, using backstepping design and composite energy function approaches in the analysis, we show that uniform convergence of the state tracking errors can be guaranteed over the iteration domain, and the constraint requirement on the system output will not be violated at all time. In the end, a simulation study on a single‐link robot model is presented to demonstrate the effectiveness of the proposed scheme.

Robust adaptive fault-tolerant control for leader-follower flocking of uncertain multi-agent systems with actuator failure

In this work, we study the flocking problem of multi-agent systems with uncertain dynamics subject to actuator failure and external disturbances. By considering some standard assumptions, we propose a robust adaptive fault tolerant protocol for compensating of the actuator bias fault, the partial loss of actuator effectiveness fault, the model uncertainties, and external disturbances. Under the designed protocol, velocity convergence of agents to that of virtual leader is guaranteed while the connectivity preservation of network and collision avoidance among agents are ensured as well.

Adaptive Neural-Fuzzy Sliding-Mode Fault-Tolerant Control for Uncertain Nonlinear Systems

This paper proposes an adaptive neural-fuzzy sliding-mode control method for uncertain nonlinear systems with actuator effectiveness faults and input saturation. The parameter dependence of the control scheme is removed from the bound of actuator faults by updating online. A neural-fuzzy model is developed to approximate the uncertain nonlinear terms and a sliding-mode online-updating controller is developed to estimate the bound of the actuator with no prior knowledge of the fault. The asymptotic stability is verified via the Lyapunov method in the presence of actuator faults and saturation. Furthermore, the adaptive neural-fuzzy control method is extended to the uncertain faulty nonlinear systems with integral sliding-mode manifold as well as other popular sliding-mode surfaces. A numerical example is presented to demonstrate the effectiveness of the derived results.

Nonlinear PD Fault-Tolerant Control for Dynamic Positioning of Ships With Actuator Constraints

This paper addresses the asymptotic dynamic positioning of ships in the presence of actuator constraints and partial loss of actuator effectiveness faults. A simple saturated proportional-derivative controller is proposed. Lyapunov direct method is employed to prove asymptotic stability. Explicit conditions on control gains for ensuring asymptotic stability are presented. Advantages of the proposed controller include simple and intuitive structure, high computation efficiency, and absence of modeling parameter and fault detection and isolation mechanism in the control law formulation, and thus it is ready to implement. An additive appealing feature is that the proposed controller has the abilities to protect the actuator from control effort saturation and compensate the partial loss of actuator effectiveness faults. An illustrative example is presented to demonstrate the effectiveness of the proposed approach.

Attitude stabilization of a rigid spacecraft with actuator delay and fault

Time delays and actuator faults are phenomena which are frequently encountered in practical control systems and are found to have significant effects on the performance of operation and control. It is shown that even a very small delay may destabilize the spacecraft system. Therefore, besides considering the effects of modelling uncertainties and external disturbances, time delay and actuator fault effects should be properly handled in the spacecraft to achieve reliable and accurate control. This paper describes a simple and effective method to attitude stabilize a spacecraft. The proposed method works by augmenting a backstepping controller with a modified extended state observer-based feedforward control law. The backstepping control is used to compensate for an unknown delay in the inputs, while the feedforward term attenuates the effects of modelling uncertainties, external disturbances and actuator faults. In particular, actuator faults, modelling uncertainties and external disturbances are viewed as unknown nonlinear functions of the measurable state variables, estimated using a modified extended state observer, and then compensated for. The effectiveness of the proposed control algorithm is analytically authenticated and verified via simulation studies.

Adaptive Fuzzy Decentralized Control for a Class of Large-Scale Nonlinear Systems With Actuator Faults and Unknown Dead Zones

This paper studies the fault-tolerant control problem for a class of uncertain large-scale nonlinear systems with unknown dead zones and actuator failures, including outage, loss of effectiveness, and stuck. It is assumed that the lower and upper bounds of actuator efficiency factor, the unparametrizable time-varying stuck fault, the system coefficient, and the uncertain functions of our considered systems are unknown. By introducing a smooth function, fuzzy logic systems and a bound estimation approach, a decentralized backstepping design method of fault-tolerant tracking controller is developed for the systems under consideration. The proposed controller can compensate the effects of actuator faults and dead zones completely. It is proved that all the signals in the closed-loop systems are ultimately bounded, and the tracking control performance can be achieved by the proposed controller. In comparing with the existing results, the restrictions on the number of failures are removed and the stuck fault is allowed to be time-varying. Finally, simulation results show the efficiency of the proposed control scheme.

Constrained Robust Control for Spacecraft Attitude Stabilization Under Actuator Delays and Faults

This paper deals with the attitude stabilizing control problem for a rigid spacecraft in the presence of model uncertainties, external disturbances, and actuator faults when delay effects and control input constraints are taken into consideration. First, a backstepping method is introduced in the control design for compensating unknown delays in inputs. Then, a disturbance observer is investigated for estimating model uncertainties, external disturbances, and actuator fault effects. The backstepping controller is augmented with the reconstructed information provided by the disturbance observer to make the closed-loop system insensitive to disturbances and faults. Next, the proposed observer–controller structure is redesigned to deal with control constraints. Rigorous proofs show that the developed control under simple sufficient conditions can render the system globally input-to-state stable (ISS). Numerical simulations are presented to illustrate the effectiveness of the proposed controllers.

Iterative Learning Fault-Tolerant Control for Networked Batch Processes with Multirate Sampling and Quantization Effects

The fault-tolerant control problem is investigated for a class of networked batch processes with actuator faults and external disturbances. A two-dimensional Fornasini-Marchesini (2D-FM) system with multirate sampling and quantization effects is introduced to model the networked batch processes, which may reflect the reality more closely. The aim of this paper is to design a dynamic output feedback controller such that the closed-loop system can achieve fault tolerance with the effect of actuator faults and satisfy the H∞ performance constraint for unknown external disturbances. By employing a combination of the Lyapunov stability analysis theory, lifting technique, and logarithmic quantization method, a networked iterative learning fault-tolerant control (NILFTC) scheme is first proposed, and some sufficient conditions are established for the existence of the desired dynamic output feedback controller. Finally, an example is exploited to illustrate the effectiveness of the developed method.

Finite‐time robust fault‐tolerant control against actuator faults and saturations

The finite-time robust fault-tolerant control problem is addressed for a class of perturbed linear systems with actuator faults and input amplitude saturations. A compensation control strategy is proposed to eliminate the effects of actuator faults and non-linear disturbance-like inputs within a finite-time, as well as to ensure the control inputs be limited within a desired constraint. Based on Lyapunov stability theory, it is shown that system states can converge to a small region in the cases of actuator faults and saturations by choosing suitable control parameters. Some relationships among convergence bounds, actuator faults and amplitude limits, as well as the control parameters are studied deeply and illustrated explicitly with formulas. Simulations of a linearised F-18 longitudinal dynamical control model are given to verify the effectiveness of the proposed method.

Sliding Mode Observers Based-Simultaneous Actuator and Sensor Faults Estimation for Linear Parameter Varying Systems

This paper proposes a scheme to estimate actuator and sensor faults simultaneously for a class of linear parameter varying system expressed in polytopic structure where its parameters evolve in the hypercube domain. Transformed coordinate system design is adopted to decouple faults in actuators and sensors during the course of the system’s operation coincidentally, and then two polytopic subsystems are constructed. The first subsystem includes the effect of actuator faults but is free from sensor faults and the second one is affected only by sensor faults. The main contribution is to conceive two polytopic sliding mode observers in order to estimate the system states and actuator and sensor faults at the same time. Meanwhile, in linear matrix inequality optimization formalism, sufficient conditions are derived withH∞performances to guarantee the stability of estimation error and to minimize the effect of disturbances. Therefore, all parameters of observers can be designed by solving these conditions. Finally, simulation results are given to illustrate the effectiveness of the proposed simultaneous actuator and sensor faults estimation.

An advanced robust fault-tolerant tracking control for a doubly fed induction generator with actuator faults

Fault-tolerant controller (FTC) designs for doubly fed induction generators (DFIGs) with actuator faults have recently gained considerable attention due to their important role in maintaining the safety and reliability of DFIG-based wind turbines via configured redundancy. The objective of this paper is to propose a novel active fault-tolerant tracking control strategy for a DFIG subject to actuator faults. The proposed strategy consists of first designing a proportional integral observer (PIO) for simultaneous system states and fault estimation and then secondly the FTC, which depends on the estimated states and faults. The objective of such a controller is to drive the state of the system to track a reference state generated by a reference fault-free model (nominal system). In addition, the main results for stability are demonstrated through a quadratic Lyapunov function, formulated in terms of linear matrix inequalities (LMIs) in order to guarantee the stability of the whole closed-loop system and to reduce the actuator fault effects with noise attenuation. Furthermore, the gain matrices of the FTC and the PIO are computed by solving a set of LMIs using the YALMIP toolbox with the SeDuMi solver. Finally, the simulation results under constant and time-varying actuator faults are provided to show the effectiveness of the developed FTC scheme.

Distributed attitude control for multiple flexible spacecraft under actuator failures and saturation

This paper solves the problem of attitude consensus for flexible spacecraft formation under actuator failures and saturation constraints. Three insightful distributed consensus control laws are designed based on the Lyapunov’s stability theory and graph theory. The induced oscillations of the spacecraft’s flexible appendages are compensated online with adaptive update parameters. Attitude consensus for the multiple spacecraft system can be achieved with limited information transfer. The modal variables of the flexible appendages are avoided in the distributed controllers in order to reduce the payload of the spacecraft. In addition, the issue of actuator saturation is rejected by applying a switching control scheme. Numerical simulations are performed to demonstrate that the proposed controller can guarantee attitude consensus despite the presence of modeling uncertainties, external disturbances, and simultaneous loss of actuator effectiveness faults and additive faults.

Adaptive Fault Tolerant Control for Liquid Tank Process

Level control of liquids in coupled tanks is a basic requirement in many industrial processes. Liquid levels in tanks must be controlled accurately regardless of environmental circumstances. Minor faults in sensors, actuators or other system components that take place in processes where liquid level control is required can result in catastrophic consequences. In this case, a fault tolerant control system is needed. The controller must be either robust (passive) or in reconfigurable (active) type in order to compensate for the effect of actuator faults and maintain system reliability and performance. In this study, a water tank level control system and possible valve actuator faults are modelled. By designing different controllers and using modelled failures a simulation is constructed. To test the reconfigurable type controller performance against faults/failures, a model reference adaptive control system is implemented and compared with PI-controlled system.