Integrated Fault Tolerant Control Research Articles

Robust fuzzy observer‐based fault‐tolerant control: A homogeneous polynomial Lyapunov function approach

In this paper, a homogeneous polynomial Lyapunov function (HPLF) is employed in robust observer-based Integrated Fault-Tolerant Control (IFTC) of nonlinear systems modelled by the polynomial fuzzy model (PFM). This makes the design problem benefit from the conservative reduction property of polynomial Lyapunov functions (PLFs) and simultaneously avoid the emergence of non-convex terms due to differentiation of the polynomial Lyapunov matrix. As a result, the less conservative sum of square (SOS) conditions are obtained in the form of polynomial matrix inequalities (PMI), which are solved via SOSTOOLS. For the first time, a non-quadratic Lyapunov function is used to design a polynomial fuzzy unknown-input observer that estimates the system's states and actuator faults in the presence of model uncertainties and external disturbances. The effectiveness of the proposed approach in providing more relaxed and less conservative results along with the better fault tolerance is illustrated through three simulating examples and compared with the quadratic Lyapunov function (QLF) approach.

Aggressive maneuver oriented integrated fault-tolerant control of a 3-DOF helicopter with experimental validation

In this paper, an integrated fault-tolerant control (FTC) strategy is proposed for unmanned helicopter system under aggressive maneuvers. In order to handle the effect of strong nonlinearities caused by large pitch angle, linear parameter varying (LPV) technique is adopted in the helicopter system modeling. Then, LPV model-based unknown input observer (UIO) design is conducted to simultaneously realize actuator faults and system state estimation, based on which an active fault-tolerant controlleris also constructed. Considering bi-directional robustness interactions between fault as well as state observer and active fault-tolerant controller, an integrated fault-tolerant controller design is further developed. Besides, actuator saturation is also considered in LPV modeling as well as integrated fault-tolerant controller design of the helicopter system. In order to guarantee the robust performance of proposed integrated fault tolerant controller design of helicopter system, energy-to-energy strategy is adopted. And the linear matrix inequality (LMI) toolbox is utilized for gain calculation. Finally, comparative experimental tests are carried out to show the effectiveness and advantages of the proposed FTC strategy.

Integrated fault‐tolerant control system design based on continuous model predictive control for longitudinal manoeuvre of hypersonic vehicle with actuator faults

In this study, an integrated fault-tolerant control (IFTC) approach with a two-layer structure is proposed for longitudinal manoeuvre of the hypersonic vehicle with elevator deflection faults. On the top, longitudinal manoeuvre trajectory optimisation problem being subjected to state and input constraints is formulated. The minimum oscillation is taken as the objective function, and the direct collocation method is introduced to calculate the optimal manoeuvre reference trajectory online. On the bottom, diverse elevator deflection faults of the hypersonic vehicle are considered. The faulty longitudinal model is reformulated by input–output feedback linearisation, and the faults are equivalently lumped into additional uncertainties. For the lumped uncertainties and high-order derivatives of velocity and altitude of manoeuvre feasible trajectory, an extended state observer is used for online estimation. The fault-tolerant control based on continuous model predictive control is designed, where predictive models are derived by Taylor expansion approximation. To guarantee that the control inputs do not violate constraints, the analytical control law is improved by the optimal-aim distance criterion. The stability of the closed-loop control system and boundedness of observation errors are proved. The simulations verify the effectiveness of the proposed IFTC approach.

Integrated fault tolerant attitude control approach for satellite attitude system with sensor faults

SummaryIn this study, a novel integrated fault tolerant control (FTC) strategy is proposed for a rigid satellite attitude systems under the case of external disturbance, Lipschitz nonlinearity, and sensor faults. Different from the traditional adaptive fault estimation method, an augmented fault estimation observer is designed for the considered faulty satellite attitude system, which could be used for estimating both system state and sensor fault. A virtual observer is firstly introduced, and then, a real observer is derived as a result of the unmeasurable information to be used for the design of the virtual observer. On this basis, an integrated FTC approach is developed for the considered faulty satellite attitude system by combining backstepping control and fractional order nonsingular terminal sliding mode control techniques, such that the closed‐loop system not only has good robustness to external disturbance but also has better fault tolerance capability to unknown sensor fault. Finally, a simulation example is provided to demonstrate the feasibility and advantage of the proposed FTC scheme.

On the synthesis of an integrated active LPV FTC scheme using sliding modes

This paper proposes an integrated fault tolerant control scheme for a class of systems, modelled in a linear parameter-varying (LPV) framework and subject to sensor faults. The gain in the LPV sliding mode observer (SMO) and the gain in the LPV static feedback controller are synthesized simultaneously to optimize the performance of the closed-loop system in an L2 sense. In the proposed scheme, the sensor faults are reconstructed by the SMO and these estimates are subsequently used to compensate the corrupted sensor measurements before they are used by the feedback controller. To address the synthesis problem, an iterative algorithm is proposed based on a diagonalization of the closed-loop Lyapunov matrix at each iteration. As a result the NP-hard, non-convex linear parameter-varying bilinear matrix inequality (LPV/BMI) associated with the Bounded Real Lemma formulation, is simplified into a tractable convex LPV/LMI problem. A benchmark scenario, involving the loss of the angle of attack sensor in a civil aircraft, is used as a case study to demonstrate the effectiveness of the scheme.

Integrated Fault Tolerant Control for Saturated Systems with Additive Faults: A Comparative Study of Saturation Models

In this paper, the integrated design problem of Fault Estimation (FE) and Fault Tolerant Control (FTC) for saturated systems is considered. The system suffers from input saturation and L2-bounded disturbances. To design an adaptive observer-based FE, the actuator output measurements are not used, when the actuator is saturated, there exist new interactions between FE and FTC. In such a case the separation principle for FE and FTC design does not hold anymore. In this paper, a method is introduced for integrated design of FE and FTC, which guarantees boundedness stability of such a system. To extract sufficient conditions for stability and minimum L2-gain performance for disturbance rejection, the Modified Sector Condition (MSC) is employed for saturation modeling. Also, Quadratic Polytopic Differential Inclusion (QPDI) approach is developed for the comparative study. All conditions are cast as Linear Matrix Inequality(LMIs) that can be evaluated in a single step. In a numerical example, the feasibility of the introduced method for stability guarantee is demonstrated and performance characteristics of FE and FTC in disturbance rejection are compared for both modeling approaches.

Robust Fault Tolerant Control for Discrete-Time Dynamic Systems With Applications to Aero Engineering Systems

Unexpected faults in actuators and sensors may degrade the reliability and safety of aero engineering systems. Therefore, there is motivation to develop integrated fault tolerant control techniques with applications to aero engineering systems. In this paper, discrete-time dynamic systems, in the presence of simultaneous actuator/sensor faults, partially decoupled unknown input disturbances, and sensor noises, are investigated. A jointly state/fault estimator is formulated by integrating an unknown input observer, augmented system approach, and optimization algorithm. Unknown input disturbances can be either decoupled by an unknown input observer, or attenuated by a linear matrix inequality optimization, enabling the estimation error to be input-to-state stable. Estimator-based signal compensation is then implemented to mitigate adverse effects from the unanticipated actuator and sensor faults. A pre-designed controller, which maintains normal system behaviors under a fault-free scenario, is allowed to work along with the presented fault tolerant mechanism of the signal compensations. The fault-tolerant closed-loop system can be ensured to mitigate the effects from the faults, guarantee the input-to-state stability, and satisfy the required robustness performance. The proposed fault estimation and fault tolerant control methods are developed for both discrete-time linear and discrete-time Lipschitz nonlinear systems. Finally, the proposed techniques are applied to a jet engine system and a flight control system for simulation validation.

Robust adaptive fault tolerant control for a class of linearly parameterized uncertain nonlinear systems: An integrated method

In the fault tolerant control systems, there often exist coupled uncertainties between the fault estimate subsystems and the state control subsystems. The coupled uncertainties are often ignored in the conventional separated design approaches, and the control performance degradation or even in-stability may be induced. To address this problem, an integrated fault tolerant control method is developed in this paper. The key point of this paper is to design the fault estimator and the fault tolerant controller from the perspective of the composite system comprised of the two subsystems. A combined weight update law, associating with both the state control dynamic equation and the observation error subsystem, is obtained. A new sufficient condition for the closed-loop stability is derived in terms of linear matrix inequalities. Based on a combined Lyapunov function, the composite closed-loop system is proven to be globally stable. Meanwhile, with the parameterized nonlinear functions and the unknown actuator/sensor faults, the coupled uncertainties are analyzed. Several illustrative examples are employed and the simulation results demonstrate the effectiveness of the proposed method.

INTEGRATED FAULT TOLERANT FLIGHT CONTROL DESIGN WITH APPLICATION TO AN F-16 AIRCRAFT

An integrated fault tolerant control (FTC) scheme, which combines the insensitivity and robustness properties of sliding mode control to certain types of disturbances and uncertainties with the accommodation properties of adaptive control to parametric and structural uncertainties is proposed in this paper for high performance flight control systems.

DESIGN OF AUGMENTED FAULT DETECTION FILTER FOR FAULT TOLERANT CONTROL

In this paper, a new Fault-Tolerant Control System strategy is presented for linear dynamic systems. The detection and isolation of each jump is achieved by the Kalman filter designed under a dead beat constraint allowing the maximum adaptability of the fault magnitude estimation in the case of abrupt change. By using the state estimation corrected by the estimation of jumps we will describe a integrated Fault Tolerant Control via a particular LQG approach.