Reconfigurable Control Law Research Articles

Fixed-time active fault-tolerant control for a class of nonlinear systems with intermittent faults and input saturation

In this paper, the problem of fixed-time active fault-tolerant control is studied for systems with sector-bounded nonlinearities, intermittent faults, and input saturation. Since intermittent faults appear and disappear randomly, a fixed-time scheme is considered in the active fault-tolerant control algorithm, composed of detection, isolation, estimation, and the control unit. Utilizing homogeneity-based observers, the fixed-time state estimation is available in the presence of unknown but bounded disturbances, and a fault diagnosis unit is proposed. An input saturation compensator is introduced to analyze the effect of input saturation, and its auxiliary variables are used in the reconfigurable control law. The fault-tolerant controller, which is constructed via the information provided by the fault diagnosis unit and saturation compensator, has two switching modes. As a consequence, intermittent faults are compensated via the designed active fault-tolerant control method and the system reaches practical stability with the entire convergence time bounded in a fixed time. Finally, the example of a heat control system is exploited to demonstrate the effectiveness of the developed active fault-tolerant control scheme.

Reconfiguration Strategy for Fault-Tolerant Control of High-Rise Adaptive Structures

Adaptive structures comprise sensors, a control unit as well as actuators and are able to actively counteract to external disturbances. However, an actuator failure can lead to a significant performance degradation, which can be reduced by designing a reconfigurable control law. In this letter, a fault-tolerant controller for an adaptive high-rise structure is designed, which is able to adapt to multiple actuator failures and thus is an important step for the automation of adaptive structures. The proposed control law consists of two parts - a static offset compensation, which counteracts the constant force applied by the faulty actuators on the mechanical structure, and a reconfigurable linear quadratic regulator, which optimally minimizes the vibrations of the structure using the remaining functioning actuators. The introduced approach is evaluated in a simulation study considering a wind disturbance. As a result the fault tolerant control scheme ensures a more efficient energy operation and yields a performance improvement of up to 33% compared to a nominal controller. Consequently, the reliability of adaptive structures is increased.

Integrated fault estimation and fault-tolerant control for a flexible regional aircraft

The article focuses on the design and application of an active reconfigurable controller that mitigates the effects of gust load and actuator faults on a flexible aircraft. A novel integrated adaptive output feedback scheme is investigated to address the actuator faults. The real-time fault values provided by the fault estimation module are considered in the reconfigurable control law to improve the fault-tolerant capability. The estimate values of faults and control gains are calculated by analyzing the stability of the overall system. The proposed controller is simulated using a flexible aircraft model with a discrete ‘1-cosine’ gust, and the results show that it can effectively mitigate the wing root moments and recover the flight maneuver stability after the aircraft suffered from gusts.

A novel approach to the attitude stabilization structure for ducted-fan operative aerial robots: Finding improvements for modeling error and strong external transient disturbance

This research concerns a novel attitude stabilization structure for a ducted-fan aerial robot to work against modeling error and strong external transient disturbance, and it focuses on two main control targets: modeling error compensation, and the improvement of disturbance resistance along the rolling channel. For the first research objective, we proposed an adaptive nominal controller with the reconfigurable control law design based on the estimation of the modeling error found in the closed-loop. Results of simulations and corresponding flight tests verified that the proposed adaptive control structure is robust against both constant and time-varying modeling error. For the other research objective, a SAC (Stability Augmentation Control) structure was devised based on the CMG (Control Moment Gyroscope) theory in order to provide extra moment which effectively withstands the transient disturbance beyond the CDG (Critical Disturbance Gain). Furthermore, we studied the corresponding controller for the SAC via the SMC (sliding mode control) theory, while the working mechanism and performance of the SAC were verified through a specially devised prototype.

Postcapture Attitude Takeover Control of a Partially Failed Spacecraft With Parametric Uncertainties

The postcapture of a partially failed spacecraft by space manipulators will bring a mutation in the dynamics of the combination. Both the inertia properties and the thruster configuration matrix will change significantly. The unknown dynamics of the partially failed spacecraft also cause a tremendous technical challenge for attitude takeover control. Accordingly, this paper describes a novel reconfigurable control system for postcapture attitude takeover of a partially failed spacecraft with parametric uncertainties, whose fuel has been exhausted or whose actuators have partial malfunctions. First, the reconfigurable control law is designed by command filtering adaptive back-stepping control to guarantee the system performance and global asymptotic stability considering inertia parametric uncertainties. Second, the thrusters are reconstituted, without changing the thruster physical configuration. Finally, the thrusters' forces can be redistributed by the dynamic control reallocation method based on constrained quadratic programing. Numerical simulations validate the feasibility of the proposed approach for postcapture attitude takeover control of a partially failed spacecraft with parametric uncertainties. Note to Practitioners-This paper presents a methodology for a partially failed spacecraft with parametric uncertainties. It focuses on solving the attitude takeover control of the partially failed spacecraft perfectly, while considering the position and speed constraints of the actuator and avoiding the plume impact to the spacecraft. The proposed command filtering adaptive back-stepping control can be used for spacecraft's thruster reconfiguration considering the parametric uncertainties. Furthermore, the dynamic control reallocation method is particularly useful for future applications that include spacecraft with redundant actuators.

Fault detection and recovery of spacecraft formation flying using nonlinear observer and reconfigurable controller

This paper addresses fault tolerant spacecraft leader–follower formation control through the development of a fault observer and a re-configurable control law. Using carrier-phase differential GPS measurements for relative position and velocity, an estimate of the true thrust output on all three axes of the follower spacecraft is accomplished using a pair of super twisting sliding mode observers. Modifications on the ‘broken’ super twisting observer are applied in order to accommodate additional sensor feedback inputs for relative position and velocity between the leader and the follower spacecraft. A fault observer estimating the true thrust output of the follower spacecraft is developed which functions in parallel with a re-configurable control law capable of formation maintenance in the event thrust in the along-track and radial axes are no longer available. Simulation results show fault reconstruction and recovery with formation stabilization even in the presence of external disturbances which are unknown to both the controller and the observer.

Spacecraft Attitude Fault Detection and Recovery Using Non-Linear Observer and Reconfigurable Controller

This paper addresses fault tolerant attitude control through the development of a fault observer and re-configurable control law. Using attitude sensor measurements for angular position and velocity, an estimate of the true torque on all three axes is accomplished using a pair of super twisting sliding mode observers. Modifications on the `broken' super twisting observer is applied in order to accommodate additional sensor feedback inputs. Using this method, reconstruction of torque faults can be accomplished and fault information is then sent to a re-configurable controller which switches to an appropriate control law to recover and mitigate the effects of the actuator fault. Simulation results are presented to show fault reconstruction and recovery with attitude stabilization in the presence of orbital disturbances - some which are partially unknown to both controller and observer.

A Model Reference Adaptive Variable Structure Controller for Reconfigurable Flight Control Systems

This paper presents a new design of reconfigurable flight controller, applying both variable structure control and model reference adaptive control. In case of control effectors failures, aircraft model will vary, and unknown disturbances will affect the characteristics of controller. To study this problem, a model reference adaptive variable structure control law is designed, which composes a model-following adaptive control part and a variable structure control part. According to the model matching condition, an update scheme is used in the adaptive control part to eliminate system errors caused by model mismatch. With an adaptive sliding-mode gain the variable structure control part can deal with uncertain bounded disturbances of flight system. An aircraft example with stabilsator failure is presented to demonstrate the feasibility of the proposed reconfigurable control law. Simulation results show the control law is effective for reconfigurable flight control systems.

An approximation for reconfigurable Fuzzy Takagi-Sugeno networked control

The paper propose a control strategy from the definition of a Takagi-Sugeno approach, considering computer network reconfiguration. The focus is on computer networks and how control techniques are modified using Fuzzy Takagi-Sugeno control. Control reconfiguration is presented as an available approach for fault coverage in order to keep system performance. Reconfiguration is pursued as a response of time delay modification rather than fault appearance, although this is the basis for control reconfiguration. The focus is on reconfigurable control law due to the presence of local faults and its resulting time delays.

Reconfigurable NDI controller using inertial sensor failure detection & isolation

A modified derivation of nonlinear dynamic inversion provides the theoretical underpinnings for a reconfigurable control law for aircraft that have suffered combinations of actuator failures, missing effector surfaces, and aerodynamic changes. The approach makes use of acceleration feedback to extract information pertaining to any aerodynamic change and thus does not require a complete aerodynamic model of the aircraft. The control law does require feedback of effector positions to accommodate actuator dynamics. Both accelerometer and rate gyro failure detection and isolation (FDI) systems are implemented, allowing up to three independent failures for each FDI system as long as they are in different axes. Nonlinear simulation results show that the FDI systems improve the robustness to accelerometer/rate gyro uncertainties. An advanced tailless aircraft model is used to demonstrate the concepts. The simulation includes accelerometer and rate gyro noise and bias, failures due to accelerometers, rate gyros, and actuators, and modeled missing surfaces that cause airplane aerodynamic changes.