Robust adaptive active fault‐tolerant control of UAH with unknown disturbances and actuator faults

This paper proposes a robust active fault‐tolerant control (AFTC) approach for medium‐scale unmanned autonomous helicopter (UAH) with rotor flapping dynamics in the presence of unknown external disturbances and actuator faults. The robust items are adopted to improve the disturbance rejection capability of the UAH system. The adaptive fault observers are developed to estimate the fault parameters and the fault detection (FD) algorithms are presented to detect the actuator faults in different loops. In order to obtain satisfactory trajectory tracking performance, a backstepping‐based robust AFTC scheme is designed for the simplified 6‐degree‐of‐freedom (DOF) UAH nonlinear dynamics model and the global stability of the closed‐loop system is proved by using the Lyapunov method. Several groups of numerical simulation results are carried out to verify the effectiveness of the developed method.     

Robust actuator fault compensation accounting for uncertainty in the fault estimation

We propose a fault tolerant control scheme that compensates for actuator faults by adjusting the controller gain based on an estimate of the fault magnitude. The scheme consists of a plant in closed loop with an observer‐based feedback tracking controller, which is adapted to the fault situation diagnosed by a fault detection and isolation algorithm. We give conditions for correct fault detection and isolation and for robust closed‐loop stability accounting for possible errors in the fault estimation. Copyright © 2013 John Wiley & Sons, Ltd.     

Transient management of a supervisory fault‐tolerant control scheme based on dwell‐time conditions

The paper deals with the design of an active fault‐tolerant control strategy based on the supervisory control approach technique for linear time invariant MIMO systems affected by disturbances, measurement noise, and faults. From a bank of Luenberger observers that plays the role of a fault detection and isolation scheme, the supervisory algorithm aims at selecting the suitable fault‐tolerant controller by means of a hysteresis‐based switching mechanism. Based on dwell‐time conditions, Lyapunov global exponential stability is addressed, and it is shown how transient behaviors due to the inherent interactions between fault detection and isolation, fault‐tolerant control, and the reconfiguration mechanism can be improved. The main advantage with respect to existing solutions of open literature is relative to a simple parameterization of all controllers (possibly having different state dimensions, integral action, and/or unstable poles) in order to cope with bumps and undesirable transients when (possible multiple) switches occur. Moreover, it is shown that it is possible to improve (reduce) the dwell‐time value in some cases. The efficiency of the approach is demonstrated on the academic highly maneuverable technology benchmark. Copyright © 2014 John Wiley & Sons, Ltd.     

LMI‐based adaptive output feedback fault‐tolerant controller design for nonlinear systems

This paper presents 2‐novel linear matrix inequality (LMI)‐based adaptive output feedback fault‐tolerant control strategies for the class of nonlinear Lipschitz systems in the presence of bounded matched or mismatched disturbances and simultaneous occurrence of actuator faults, including failure, loss of effectiveness, and stuck. The constructive algorithms based on LMI with creatively using Lyapunov stability theory and without the need for an explicit information about mode of actuator faults or fault detection and isolation mechanism are developed for online tuning of adaptive and fixed output‐feedback gains to stabilize the closed‐loop control system asymptotically. The proposed controllers guarantee to compensate actuator faults effects and to attenuate disturbance effects. The resulting control methods have simpler structure, as compared with most existing recent methods and more suitable for practical systems. The merits of the proposed fault‐tolerant control scheme have been verified by the simulation on nonlinear Boeing 747 lateral motion dynamic model subjected to actuator faults.     

Active fault‐tolerant attitude control for flexible spacecraft with loss of actuator effectiveness

A theoretical framework for active fault‐tolerant attitude stabilization control is developed and applied to flexible spacecraft. The proposed scheme solves a difficult problem of fault‐tolerant controller design in the presence of severe partial loss of actuator effectiveness faults and external disturbances. This is accomplished by developing an observer‐based fault detection and diagnosis mechanism to reconstruct the actuator faults. Accordingly, a backstepping‐based fault‐tolerant control law is reconfigured using the reconstructed fault information. It is shown that the proposed design approach guarantees that all of the signals of the closed‐loop system are uniformly ultimately bounded. The closed‐loop performance of the proposed control strategy is evaluated extensively through numerical simulations. Copyright © 2012 John Wiley & Sons, Ltd.     

Active fault‐tolerant control for near space vehicles based on reference model adaptive sliding mode scheme

In this paper, an adaptive sliding mode (ASM) scheme is proposed for fault identification and fault‐tolerant control of near space vehicles (NSVs). First, the attitude dynamic model is introduced, and a baseline controller based on reference sliding mode scheme is designed in the case of no faults. Then fault parameterizations with actuator dynamics is presented for several classes of faults: lock‐in‐place, float, hard‐over, and loss of effectiveness. On the basis of adaptive observer design, fault parameters can be accurately estimated on‐line. Furthermore, an ASM fault‐tolerant controller is designed for both cases of actuator dynamic faults and control effector damage. Finally, simulation experiments show that the proposed ASM scheme is able to quickly and accurately identify faults and reconfigure the controller, resulting in excellent overall system performance. Copyright © 2012 John Wiley & Sons, Ltd.     

A model reference tracking based on an active fault tolerant control for LPV systems

This work deals with the problem of a model reference tracking based on the design of an active fault tolerant control for linear parameter‐varying systems affected by actuator faults and unknown inputs. Linear parameter‐varying systems are described by a polytopic representation with measurable gain scheduling functions. The main contribution is to design an active fault tolerant controller whose control law is described by an adaptive proportional integral structure. This one requires 3 types of online information, which are reference outputs, measured real outputs, and the fault estimation provided by a model reference, sensors, and an adaptive polytopic observer, respectively. These types of information are used to reconfigure the designed controller, which is able to compensate the fault effects and to make the closed‐loop system able to track reference outputs in spite of the presence of actuator faults and disturbances. The controller and the observer gains are obtained by solving a set of linear matrices inequalities. Performances of the proposed method are compared to another previous method to underline the relevant results.     

Comparisons of adaptive fault‐tolerant insensitive control methods for a class of linear systems

In this paper, the problem of fault‐tolerant insensitive control is addressed for a class of linear time‐invariant continuous‐time systems against bounded time‐varying actuator faults and controller gain variations. Adaptive mechanisms are developed to adjust controller gains in order to compensate for the detrimental effects of partial loss of control effectiveness and bias‐actuator faults. Variations of controller gains arise from time‐varying and bounded perturbations that are supposed to always exist in adaptive mechanisms. Based on the disturbed outputs of adaptive mechanisms, three different adaptive control strategies are constructed to achieve bounded stability results of the closed‐loop adaptive fault‐tolerant control systems in the presence of actuator faults and controller gain variations. Furthermore, comparisons of convergence boundaries of states and limits of control inputs among adaptive strategies are developed in this paper. The efficiency of the proposed adaptive control strategies and their comparisons are demonstrated by a rocket fairing structural‐acoustic model.     

Accommodation of unknown actuator faults using output feedback‐based adaptive robust control

In this paper, we solve the problem of output tracking for linear uncertain systems in the presence of unknown actuator failures using discontinuous projection‐based output feedback adaptive robust control (ARC). The faulty actuators are characterized as unknown inputs stuck at unknown values experiencing bounded disturbance and actuators losing effectiveness at unknown instants of time. Many existing techniques to solve this problem use model reference adaptive control (MRAC), which may not be well suited for handling various disturbances and modeling errors inherent to any realistic system model. Robust control‐based fault‐tolerant schemes have guaranteed transient performance and are capable of dealing with modeling errors to certain degrees. But, the steady‐state tracking accuracy of robust controllers, e.g. sliding mode controller, is limited. In comparison, the backstepping‐based output feedback adaptive robust fault‐tolerant control (ARFTC) strategy presented here can effectively deal with such uncertainties and overcome the drawbacks of individual adaptive and robust controls. Comparative simulation studies are performed on a linearized Boeing 747 model, which shows the effectiveness of the proposed scheme. Copyright © 2011 John Wiley & Sons, Ltd.     

Analysis and detection of incipient faults in post‐fault systems subject to adaptive fault‐tolerant control

This paper presents an effective scheme for detecting incipient faults in post‐fault systems (PFSs) subject to adaptive fault‐tolerant control (AFTC). Through a survey of existing techniques, it is shown that the adaptivity of the AFTC counteracts the effect of an incipient fault in the PFS. This makes some of the conventional fault‐detection strategies, such as Beard–Jones detection filters and adaptive observers, ineffective in this situation. It is shown that the unknown input observer (UIO) is an effective tool; hence, the UIO is designed to decouple the incipient fault from the AFTC such that the fault‐detection residual is sensitive only to the incipient fault. Extensive simulation study is presented using an aircraft example to test three fault‐detection approaches; it is demonstrated that the UIO is the most effective tool in detecting the incipient fault in a PFS subject to AFTC. Copyright © 2007 John Wiley & Sons, Ltd.     

Adaptive fault tolerant control for a class of multi‐input multi‐output nonlinear systems with both sensor and actuator faults

Compared with the fault diagnosis, detection, and isolation literature, very few results are available to discuss control algorithms directly for multi‐input multi‐output nonlinear systems with both sensor and actuator faults in the fault tolerant control literature. In this work, we present a fault tolerant control algorithm to address the system output stabilization problem for a class of multi‐input multi‐output nonlinear systems with both parametric and nonparametric uncertainties, subject to sensor and actuator faults that can be both multiplicative and additive. All elements of the sensor measurements and actuator components can be faulty. Besides, the control input gain function is not fully known. Backstepping method is used in the analysis and control design. We show that under the proposed control scheme, uniformly ultimate boundedness of the system output is guaranteed, while all closed‐loop system signals stay bounded. In the cases where the sensor faults are only multiplicative, exponential convergence of the system state variables into small neighbourhoods around zero is guaranteed. An illustrative example on a robot manipulator model is presented in the end to further demonstrate the effectiveness of the proposed control scheme.     

Adaptive fault tolerant control against actuator faults

This paper investigates the problem of adaptive fault tolerant control for a class of dynamic systems with unknown un‐modeled actuator faults. The fault model is assumed to be an unknown nonlinear function of control input, not in the traditional form in which the faults can be described as gain and/or bias faults. Using the property of the basic function of neural networks and the implicit function theorem, a novel neural networks‐based fault tolerant controller is designed. Finally, the lateral dynamics of a front‐wheeled steered vehicle is used to demonstrate the efficiency of the proposed design techniques. Copyright © 2016 John Wiley & Sons, Ltd.     

Adaptive reconfigurable control of systems with time‐varying delay against unknown actuator faults

This work is concerned with the problem of delay‐dependent adaptive fault‐tolerant controller design against unknown actuator faults for linear continuous systems with time‐varying delay. Based on the online estimation of possible faults by discontinuous adaptation law, identification parameters of the adaptive state feedback controller are updated autonomously to compensate the fault effects on the delayed system. For the first time, a convex combination idea and a projection‐type adaptive approach are combined organically to derive the main results. A set of new delay‐dependent reconfigurable stabilization criteria, which guarantee the stability of closed‐loop systems in both fault‐free and faulty cases, is established in terms of linear matrix inequalities. Two numerical instances for linear delayed systems and the linearized model for the lateral motion of Boeing 747 are respectively simulated to illustrate the superiority and the effectiveness of the presented adaptive delay‐dependent results. Copyright © 2013 John Wiley & Sons, Ltd.     

基于键合图的鲁棒故障诊断及容错控制

研究了一种基于键合图(BG)建模的混杂系统鲁棒诊断和容错控制算法。在BG理论的基础上,针对混杂系统存在参数不确定性问题。首先,设计了系统鲁棒诊断观测器,将线性分式变化的键合图(BG-LFT)和比例积分(PI)观测器结合实现鲁棒故障诊断和故障估计。该观测器能实时跟踪系统变量的动态行为,有效降低误报率和漏报率,改善检测效果。然后,提出基于状态及故障估计的主动容错控制算法(AFTC),保证系统发生故障时仍能稳定运行。最后,通过仿真验证了该方法的有效性和可行性。     

Active fault tolerant control systems by the semi‐Markov model approach

This paper investigates the active fault tolerant control problem via the H _∞ state feedback controller. Because of the limitations of Markov processes, we apply semi‐Markov process in the system modeling. Two random processes are involved in the system: the failure process and the fault detection process. Therefore, two corresponding semi‐Markov processes are integrated in the closed‐loop system model. This framework can generally accommodate different types of system faults, including the randomly happening sensor faults and actuator faults. A controller is designed to guarantee the closed‐loop system stability with a prescribed noise/disturbance attenuation level. The controller can be readily solved by using convex optimization techniques. A vertical take‐off and landing vehicle example with actuation faults is used to demonstrate the effectiveness of the proposed technique. Copyright © 2013 John Wiley & Sons, Ltd.     

Actuator fault‐tolerant control based on set separation

In this paper, an actuator fault‐tolerant control (FTC) strategy based on set separation is presented. The proposed scheme employs a standard configuration consisting of a bank of observers which match the different fault situations that can occur in the plant. Each of these observers has an associated estimation error with a distinctive behaviour when a estimator matches the current fault situation of the plant. With this information from each observer, a fault diagnosis and isolation (FDI) module is able to reconfigure the control loop by selecting the appropriate stabilising controller from a bank of precomputed control laws, each of them related to one of the considered fault models. The control law consists of a reference feedforward term and a feedback gain multiplying the state estimate provided by the matching observer. A novel feature of the proposed scheme resides in the decision criteria of the FDI, which is based on the computation of sets towards which the output estimation errors related to each fault scenario and for each control configuration converge. Conditions for the design of the FDI module and for fault tolerant closed‐loop stability are given, and the effectiveness of the approach is illustrated by means of a numerical example. Copyright © 2010 John Wiley & Sons, Ltd.     

Active fault‐tolerant control system design with trajectory re‐planning against actuator faults and saturation: Application to a quadrotor unmanned aerial vehicle

During the past 30 years, various fault‐tolerant control (FTC) methods have been developed to address actuator or component faults for various systems with or without tracking control objectives. However, very few FTC strategies establish a relation between the post‐fault reference trajectory to track and the remaining resources in the system after fault occurrence. This is an open problem that is not well considered in the literature. The main contribution of this paper is in the design of a reconfigurable FTC and trajectory planning scheme with emphasis on online decision making using differential flatness. In the fault‐free case and on the basis of the available actuator resources, the reference trajectories are synthesized so as to drive the system as fast as possible to its desired setpoint without violating system constraints. In the fault case, the proposed active FTC system (AFTCS) consists in synthesizing a reconfigurable feedback control along with a modified reference trajectories once an actuator fault has been diagnosed by a fault detection and diagnosis scheme, which uses a parameter‐estimation‐based unscented Kalman filter. Benefited with the integration of trajectory re‐planning using the flatness concept and the compensation‐based reconfigurable controller, both faults and saturation in actuators can be handled effectively with the proposed AFTCS design. Advantages and limitations of the proposed AFTCS are illustrated using an experimental quadrotor unmanned aerial vehicle testbed.Copyright © 2013 John Wiley & Sons, Ltd.     

Two‐stage Kalman filter‐based actuator/surface fault identification and reconfigurable control applied to F‐16 fighter dynamics

In this study, an active fault‐tolerant control technique with reconfiguration against actuator/surface failures is presented. A two‐stage Kalman filter is designed in order to identify the control distribution matrix elements that correspond to the faulty actuator/surface; thus, the control reconfiguration is carried out using this identified control distribution matrix. The actuator/surface fault identification problem is solved through two jointly operating Kalman filters: the first one is for the estimation of the control distribution matrix elements that correspond to the faulty actuator/surface, and the second one is for the estimation of the state variables of the aircraft model. A structure for the active fault‐tolerant aircraft flight control system with reconfiguration against actuator/surface failures is presented. A control reconfiguration action is taken in order to keep the performance of the impaired aircraft the same as that of the unimpaired aircraft. In simulations, the nonlinear flight dynamics of an AFTI/F‐16 fighter model is considered, and the performance of the proposed actuator/surface failure identification and reconfigurable control schemes are examined for this model. Copyright © 2012 John Wiley & Sons, Ltd.     

Model‐free fault‐tolerant control approach for uncertain state‐constrained linear systems with actuator faults

This paper investigates the robust adaptive fault‐tolerant control problem for state‐constrained continuous‐time linear systems with parameter uncertainties, external disturbances, and actuator faults including stuck, outage, and loss of effectiveness. It is assumed that the knowledge of the system matrices, as well as the upper bounds of the disturbances and faults, is unknown. By incorporating a barrier‐function like term into the Lyapunov function design, a novel model‐free fault‐tolerant control scheme is proposed in a parameter‐dependent form, and the state constraint requirements are guaranteed. The time‐varying parameters are adjusted online based on an adaptive method to prevent the states from violating the constraints and compensate automatically the uncertainties, disturbances, and actuator faults. The time‐invariant parameters solved by using data‐based policy iteration algorithm are introduced for helping to stabilize the system. Furthermore, it is shown that the states converge asymptotically to zero without transgression of the constraints and all signals in the resulting closed‐loop system are uniformly bounded. Finally, two simulation examples are provided to show the effectiveness of the proposed approach. Copyright © 2016 John Wiley & Sons, Ltd.     

Supervisory fault‐tolerant control with mutual performance optimization

The problem of active fault‐tolerant control with reconfiguration mechanism for uncertain linear systems with external disturbances is addressed applying the supervisory control approach. A key feature of the proposed approach is establishment of a set of conditions providing mutual performance in the sense of taking into account the interaction of the fault detection, isolation, and accommodation subsystems in order to achieve global fault‐tolerance performance with guaranteed global stability. The efficiency of the approach is demonstrated in an example of computer simulation for a flight system benchmark. Copyright © 2012 John Wiley & Sons, Ltd.