Healthy Actuators Research Articles

An Average Dwell-Time Method for Fault-Tolerant Control of Switched Time-Delay Systems and Its Application

This paper presents an average dwell-time method for fault-tolerant control of a class of uncertain switched linear time-delay systems and also designs an algorithm to determine the parameters pertaining to the dwell-time condition. Compared to the literature results, this paper features the following: 1) the proposed method is independent of switching polices if switchings are slow enough in the average sense; 2) the proposed control design guarantees exponential stabilization of this class of time-delay linear systems with actuator faults; and 3) this method treats all actuators in a unified manner without a need to identify which are faulty or healthy actuators. The proposed method is applied to the water pollution control problem, for the first time, to deal with different ratios of stream flow rates to effluent flow rates.

A model‐based flight qualities evaluation approach for civil aircraft

SummaryEvaluation of flight qualities plays an important role in the design of a civil aircraft. An appropriate level of flight qualities will be the key to achieve the airworthiness certification. With the objective to provide an overall view of flight qualities evaluation for a civil aircraft, a model‐based approach is proposed. Some terms related to flight qualities are defined formally, and the model‐based flight qualities evaluation approach under different situations is formed and proposed. Two working conditions of actuators are considered in the evaluation of flight qualities. When no actuator fails, linearization is adopted to build a linear flight dynamics model for analyzing the main parameter of flight qualities. When some actuators fail, a new off‐line approach for handling qualities evaluation, which employs a controller that generates appropriate commands for healthy actuators, is proposed. The design of the controller is following the idea of classical predictive control technique, and a recurrent linear quadratic programming problem is formulated to find the maximum remaining maneuverability while not avoiding any constraints. Taking the rotational maneuver as a study example, a test‐bed for handling qualities evaluation is built. The numerical simulation results show the feasibility of proposed evaluation approach.

Active fault-tolerant control for vertical tail damaged aircraft with dissimilar redundant actuation system using integral sliding mode control

The research about the dissimilar redundant actuation system has indicated the potential fault-tolerant capability in modern aircraft. This paper proposed a new design methodology to achieve fault-tolerant control of an aircraft equipped with dissimilar actuators and is suffered from vertical tail damage. The proposed design is based on the concept of online control allocation to redistribute the control signals among healthy actuators and integral sliding mode controller is designed to achieve the closed-loop stability in the presence of both component and actuator faults. To cope with severe damage condition, the aircraft is equipped with dissimilar actuators (hydraulic and electrohydraulic actuators). In this paper, the performance degradation due to slower dynamics of electrohydraulic actuator is taken in account. Therefore, the feed-forward compensator is designed for electrohydraulic actuator based on fractional-order control strategy. In case of failure of hydraulic actuator subject to severe damage of vertical tail, an active switching mechanism is developed based on the information of fault estimation unit. Additionally, a severe type of actuator failure so-called actuator saturation or actuator lock in place is also taken into account in this work. The proposed strategy is compared with the existing control strategies in the literature. Simulation results indicate the dominant performance of the proposed scheme. Moreover, the proposed controller is found robust with a certain level of mismatch between the actuator effectiveness level and its estimate.

Integral sliding mode fault‐tolerant control allocation for a class of affine nonlinear system

SummaryThis paper develops novel fault‐tolerant integral sliding mode control allocation schemes for a class of an overactuated affine nonlinear system. The proposed schemes rely on an existing baseline controller, and the objective is to retain the nominal (fault‐free) closed‐loop performance in the face of actuator faults/failures by effectively utilizing actuator redundancy. The online control allocation reroutes the control effort to healthy actuators using the knowledge of actuator effectiveness level estimates. One of the proposed schemes is tested in simulation using a well‐known high‐fidelity model of a large civil transport aircraft (B747) from the literature. Good simulation results show the efficacy of the scheme.

Aircraft Fault Accommodation With Consideration of Actuator Control Authority and Gyro Availability

When faults of some flight actuators have occurred, an unexpected need to use larger magnitudes and higher actuation rates of fault-free actuators is often caused if fault-tolerance design is not considered. This paper presents a fault-tolerant flight control (FTFC) capable of accommodating aircraft actuator failures while respecting to the physical control authority of healthy actuators, on the basis of sliding mode (SM) and adaptive techniques. Furthermore, this paper accounts for the availability of the measured angular rate. In the presence of reliable gyro onboard, the sensed pitch rate can be applied to the developed FTFC loop. In the absence of pitch rate measurement, a SM observer (SMO) is exploited to recover the pitch rate information, while the integrated design of the SMO and FTFC is investigated. Simulation studies of a nonlinear Boeing 747 longitudinal model are conducted to manifest the effectiveness of the proposed schemes.

Dynamic Control Allocation for Damping of Inter-Area Oscillations

Use of actuator redundancy to achieve higher reliability is a widely accepted engineering design technique and is used in this study to build resiliency and ensure power system stability in the presence of high levels of renewables. This paper presents a new design method for fault-tolerant wide-area damping controllers (WADCs) using modal-based control allocation (MB-CA), which coordinates a set of actuators to contribute to damping of inter-area oscillations. In our proposed method, when an actuator fails or is unavailable (e.g., due to communication failure), the supervisory MB-CA distributes the control signals to the remaining healthy actuators based on effects on the modal system, desired control actions, and actuator constraints. Our proposed block offers the benefits of modular design where it is independent of the nominal WADC. The proposed method consists of mainly two design steps. The first step is to design a WADC based on a fault-free model using robust control methods. The second step is to design an MB-CA to manage actuator availability and constraints. To validate the feasibility and demonstrate the design principles, a set of comprehensive case studies are conducted on a modified 192-bus Western Electricity Coordinating Council system. Numerical results verify the effectiveness of the proposed approach in ensuring resiliency to different actuator failures and actuator availability.

Fault Diagnosis and Fault-Tolerant Control of an Octorotor UAV using motors speeds measurements

This paper presents an active fault-tolerant control strategy (AFTCS) for an octorotor unmanned aerial vehicle (UAV) regarding several motors failures or rotors damages. A complete AFTC architecture including error detection, fault isolation and system recovery is presented. The diagnosis system is based on the motors speeds and currents measurements. Once the motor failure or the rotor loss is diagnosed, a recovery algorithm is applied. It uses the pseudo-inverse control allocation approach to redistribute the control efforts among the healthy actuators. This architecture is validated in real flights.

Adaptive fault-tolerant control for actuator failures: A switching strategy

In this paper, a new adaptive fault-tolerant control (FTC) scheme based on a switching strategy is proposed for a class of nonlinear systems with uncertain parameters and actuator failures, for which some healthy actuators are available as backups. By designing a set of monitoring functions (MFs) to supervise the behavior of some variables, it is shown that the failure detection and the switching from a faulty actuator to a healthy one can be performed simultaneously without any knowledge of failure patterns, and the prescribed transient and steady-state performance for the tracking error can be achieved regardless of the switching.

Emergency Control of AR Drone Quadrotor UAV Suffering a Total Loss of One Rotor

In this paper, an emergency fault-tolerant controller is developed for quadrotor unmanned aerial vehicles (UAVs) suffering a total loss of one actuator (rotor/motor). The proposed controller is based on control allocation where the infected actuator is exempted from the control effect, and control efforts are redistributed among healthy actuators. As a result, the emergency controller transforms the infected quadrotor into a trirotor and uses the remaining actuators to ensure that the UAV continues following its path. The main advantage of the new controller is that it uses the same simple proportional-integral-derivative (PID) controller applied in fault-free cases by redistributing its controls, rather than designing complex and memory consumable controllers. Experimental results using the augmented reality (AR) Drone 2 platform show that by implementing the quadrotor to trirotor conversion maneuver, the nominal PID controller gains powerful fault-tolerant capabilities and the infected UAV is successful in maintaining its desired path. Performance degradation seen as oscillations did not cause the drone to crash despite the total loss of yaw control, the presence of activation delay, the nonsymmetric structure of the trirotor, and its odd number of rotors that produces imbalance of the rotor moments.

Performance Comparison of Controllers with Fault-Dependent Control Allocation for UAVs

This paper combines fault-dependent control allocation with three different control schemes to obtain fault tolerance in the longitudinal control of unmanned aerial vehicles. The paper shows that fault-dependent control allocation is able to accommodate actuator faults that would otherwise be critical and it makes a performance assessment for the different control algorithms: an ź1$\mathcal {L}_{1}$ adaptive backstepping controller; a robust sliding mode controller; and a standard PID controller. The actuator faults considered are the partial to total loss of the elevator, which is a critical component for the safe operation of unmanned aerial vehicles. During nominal operation, only the main actuator, namely the elevator, is active for pitch control. In the event of a partial or total loss of the elevator, fault-dependent control allocation is used to redistribute control to available healthy actuators. Using simulations of a Cessna 182 aircraft model, controller performance and robustness are evaluated by metrics that assess control accuracy and energy use. System uncertainties are investigated over an envelope of pertinent variation, showing that sliding mode and ź1$\mathcal {L}_{1}$ adaptive backstepping provide robustness, where PID control falls short. Additionally, a key finding is that the fault-dependent control allocation is instrumental when handling actuator faults.

Actuator fault monitoring and fault tolerant control in distillation columns

This paper presents, from a practical viewpoint, an investigation of real-time actuator fault detection, propagation and accommodation in distillation columns. Addressing faults in industrial processes, coupled with the growing demand for higher performance, improved safety and reliability necessitates implementation of less complex alternative control strategies in the events of malfunctions in actuators, sensors and or other system components. This work demonstrates frugality in the design and implementation of fault tolerant control system by integrating fault detection and diagnosis techniques with simple active restructurable feedback controllers and with backup feedback signals and switchable reference points to accommodate actuator fault in distillation columns based on a priori assessed control structures. A multivariate statistical process monitoring based fault detection and diagnosis technique through dynamic principal components analysis is integrated with one-point control or alternative control structure for prompt and effective fault detection, isolation and accommodation. The work also investigates effects of disturbances on fault propagation and detection. Specifically, the reflux and vapor boil-up control strategy used for a binary distillation column during normal operation is switched to one point control of the more valued product by utilizing the remaining healthy actuator. The proposed approach was implemented on two distillation processes: a simulated methanol-water separation column and the benchmark Shell standard heavy oil fractionation process to assess its effectiveness.

Terminal Sliding Mode Control Allocation for Nonlinear Systems

In this paper, the problem of tracking control is studied for a class of nonlinear systems with actuator faults/failures. The control strategy has two steps. In the first step, a virtual control input is found using terminal sliding mode control which can easily tackle the output tracking control problem in a finite time. In the second step, control allocation (CA) transforms the virtual control signals to the real-control inputs. The CA problem is solved using a neural network which satisfies control constraints and during faults or failures redistributes the control signals to the healthy actuators. The effectiveness of the proposed control approach is demonstrated by the simulation results of the near space vehicle system.

Fault-Tolerant Formation Control of Unmanned Aerial Vehicles in the Presence of Actuator Faults and Obstacles

This paper presents a leader-follower type of fault-tolerant formation control (FTFC) methodology with application to multiple unmanned aerial vehicles (UAVs) in the presence of actuator failures and potential collisions. The proposed FTFC scheme consists of both outer-loop and inner-loop controllers. First, a leader-follower control scheme with integration of a collision avoidance mechanism is designed as the outer-loop controller for guaranteeing UAVs to keep the desired formation while avoiding the approaching obstacles. Then, an active fault-tolerant control (FTC) strategy for counteracting the actuator failures and also for preventing the healthy actuators from saturation is synthesized as the inner-loop controller. Finally, a group of numerical simulations are carried out to verify the effectiveness of the proposed approach.

Active vibration control of smart composite laminates with partial debonding of actuator

The effect of actuator debonding on the performance of active vibration control is analytically investigated through an optimal control strategy. An improved layerwise theory with Heaviside step functions, which addresses discontinuous displacement fields, is used for modeling the actuator debonding. General finite element procedures are developed to derive the governing equation taking into consideration the electro-mechanical coupling effect. A reduced-order model based on the state-space model is adopted for the design of the active controller. Generally, debonding in actuators reduces their load carrying capability, dynamic properties and vibration control characteristics. The effect of debonding on the vibration control is investigated by the proposed analytical modeling. Numerical results using a 16-layer cross-ply laminate with healthy actuator and partially debonded actuator are given for the investigation of the vibration suppression efficiency and control effort. It is observed that the control authority of the composite laminates with partially debonded piezoelectric actuator is dramatically reduced by increasing the size of the actuator debonding. Since debonding failure may occur during the service life of smart composite laminates, the results showed that actuator debonding must be considered as an uncertainty parameter in the design of active controllers.

Investigation of actuator debonding effects on active control in smart composite laminates

This article presents a numerical study of active vibration control of smart composite laminates in the presence of actuator debonding failures. A comparison between the smart composite laminates with healthy actuator and various partially debonded actuator cases is performed to investigate the debonding effects on the vibration suppression. The improved layerwise theory with Heaviside’s unit step function is adopted to model the displacement field with actuator debonding failure. The higher order electric potential field is adopted to describe the potential variation through the thickness. The finite element method–based formulations are derived using the plate element, taking into consideration the electro-mechanical coupling effect. The reduced-order model is represented by the state-space form and further for the vibration suppression using a simple constant gain velocity feedback control strategy. For the purpose of demonstration, a 16-layer cross-ply substrate laminate ([0/90]4s) is employed for the numerical study. The results show that the actuator debonding affects the closed-loop frequencies, active damping ratios, and efficiency of vibration suppression.

Optimized Reconfigurable Control Design for Aircraft using Genetic Algorithm

In this study, we propose a Genetic Algorithm (GA) based modular reconfigurable control scheme for an over-actuated non-linear aircraft model. The reconfiguration of the flight controller is achieved for the case of control surface faults/failures using a separate control distribution algorithm without modifying the base-line control law. The baseline Multi-Input Multi-Output (MIMO) Linear Quadratic Regulator (LQR) is optimized using GA to produce desired moment commands. Then, a GA based weighted pseudo-inverse method is used for effective distribution of commands between redundant control surfaces. Control surface effectiveness levels are used to redistribute the control commands to healthy actuators when a fault or failure occurs. Simulation results using ADMIRE aircraft model show the satisfactory performance in accommodating different faults, which confirm the efficiency of optimized reconfigurable design strategy.

Observer-Based Fault Diagnosis Incorporating Online Control Allocation for Spacecraft Attitude Stabilization under Actuator Failures

This paper proposes a novel observer-based fault diagnosis method, incorporating an online control allocation scheme, for an orbiting spacecraft in the presence of actuator failures/faults, unexpected disturbances and input saturation. The proposed scheme solves a difficult problem in spacecraft fault tolerant control design by compensating for the loss in effectiveness and time-varying faults using redundant actuators, so that the overall system is stable, despite external disturbances and input saturation. This is accomplished by developing an observer-based fault diagnosis mechanism to reconstruct or estimate the actuator faults/failures. An online control allocation scheme is then used to redistribute the control signals to the healthy actuators in the case of faults/failures, without reconfiguring the controller, so that the control signal distribution is based on the reconstructed actuator effectiveness level. Simulation results using a rigid spacecraft model show good performance in the presence of faults, including total actuator failure scenarios, external disturbances and actuator input saturation, which validates the effectiveness and feasibility of the proposed scheme.

Adaptive Fault-Tolerant Control for Flight Systems with Input Saturation and Model Mismatch

A novel scheme for fault-tolerant control is proposed in this paper, in which model reference adaptive control method is incorporated with control allocation to cope with simultaneous actuator failures, input saturation, and model mismatch in the flight system. In order to reduce performance degradation caused by actuator failures, the proposed scheme redistributes the control signal to healthy actuators and updates the weighting matrix based on actuator effectiveness. Because of saturation errors resulting from actuator constraints and model mismatch caused by abnormal changes in the system, the original reference model may not be appropriate. Under this circumstance, an adaptive reference model which can also provide satisfactory performance is designed. Simulations of a flight control example are given to illustrate the effectiveness of the proposed scheme.

Fault-tolerant control of a class of switched systems with strong structural uncertainties with application to haptic display systems

This paper presents a robust fault-tolerant control method for a class of uncertain switched systems with strong structural uncertainties and applied it to haptic display systems. The proposed controller can stabilize the switched systems containing strong uncertainties with actuator faults and its nominal systems (i.e., without actuator faults) without necessarily changing any structures and/or parameters of the proposed controllers, and treats faulty and healthy actuators in a unified way. The proposed method is independent of arbitrary switching laws. A practical haptic display system with switched virtual environments shows the effectiveness of the proposed method.

Design and Analysis of an Integral Sliding Mode Fault-Tolerant Control Scheme

A novel scheme for fault-tolerant control is proposed in this paper, in which integral sliding mode ideas are incorporated with control allocation to cope with the total failure of certain actuators, under the assumption that redundancy is available in the system. The proposed scheme uses the effectiveness level of the actuators to redistribute the control signals to healthy actuators without reconfiguring the controller. The effectiveness of the proposed scheme against faults or failures is tested in simulation based on a large transport aircraft model.