Fault detection and fault-tolerant control of a civil aircraft using a sliding-mode-based scheme

Journal ArticleThis paper presents a sliding-mode approach for fault-tolerant control of a civil aircraft, where both actuator and sensor faults are considered. For actuator faults, a controller is designed around a state-feedback sliding-mode scheme where the gain of the nonlinear unit vector term is allowed to adaptively increase at the onset of a fault. Unexpected deviation of the switching variables from their nominal condition triggers the adaptation mechanism. The controller proposed here is relatively simple and yet is shown to work across the entire "up and away"flight envelope. For sensor faults, the application of a robust method for fault reconstruction using a sliding-mode observer is considered. The novelty lies in the application of the sensor fault reconstruction scheme to correct the corrupted measured signals before they are used by the controller, and therefore the controller does not need to be reconfigured. © 2008 IEEE.Engineering and Physical Sciences Research Council (EPSRC

Fault tolerant control of multi-rotor unmanned aerial vehicles using sliding mode based schemes

This thesis investigates fault-tolerant control (FTC) for the specific application of small multirotor unmanned aerial vehicles (Unmanned Aerial Vehicle (UAV)s). The fault-tolerant controllers in this thesis are based on the combination of sliding mode control with control allocation where the control signals are distributed based on motors' health level. This alleviates the need to reconfigure the overall structure of the controllers. The thesis considered both the over actuated (sufficient redundancy) and under-actuated UAVs. Three multirotor UAVs have been considered in this thesis which includes a quadrotor (4 rotors), an Octocopter (8 rotors) and a spherical UAV. The non-linear mathematical models for each of the UAVs are presented. One of the main contributions of this thesis is the hardware implementation of the sliding mode Fault Tolerant Control (FTC) scheme on an open-source autopilot microcontroller called Pixhawk for a quadrotor UAV. The controller was developed in Simulink and implemented on the microcontroller using the Matlab/Simulink support packages. A gimbal- based test rig was developed and built to offer a safe test bed for testing control designs. Actual flight tests were done which showed sound responses during fault-free and faulty scenarios. This work represents one of successful implementation work of sliding mode FTC in the literature. Another key contribution of this thesis is the development of the mathematical model of a unique spherical UAV with highly redundant control inputs. The use of novel 8 flaps and 2 rotors configuration of the spherical UAV considered in this thesis provides a unique fault tolerant capability, especially when combined with the sliding mode-based FTC scheme. A key development in the later chapters of the thesis considers fault-tolerant control strategy when no redundancy is available. Unlike many works which consider FTC on quadrotors in the literature (which can only handle faults), the proposed schemes in the later chapters also include cases when failures also occur converting the system to an under actuated system. In one chapter, a bespoke Linear Parameter Varying (LPV) based controller is developed for a reduced attitude dynamics system by exploiting non-standard equation of motions which relates to position acceleration and load factor dynamics. This is unique as compared to the typical Euler angle control (roll, pitch and yaw angle control). In the last chapter, a fault-tolerant control scheme which can handle both the over and under actuated system is presented. The scheme considers an octocopter and can be used in fault-free, faulty and failure conditions up to two remaining motors. The scheme exploits the differential flatness property, another unique property of multirotor UAVs. This allows both inner loop and outer loop controller to be designed using sliding mode (as opposed to many sliding mode FTC in the literature, which only considers sliding mode for the inner loop control)

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

This is the final version. Available on open access from Elsevier via the DOI in this recordThis 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.European Commissio

Fault reconstruction using a LPV sliding mode observer for a class of LPV systems

Journal ArticleCopyright © 2012 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Journal of The Franklin Institute. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of The Franklin Institute (2012), DOI: 10.1016/j.jfranklin.2011.06.026This paper proposes a new sliding mode observer for fault reconstruction, applicable for a class of linear parameter varying (LPV) systems. Observer schemes for actuator and sensor fault reconstruction are presented. For the actuator fault reconstruction scheme, a virtual system comprising the system matrix and a fixed input distribution matrix is used for the design of the observer. The fixed input distribution matrix is instrumental in simplifying the synthesis procedure to create the observer gains to ensure a stable closed-loop reduced order sliding motion. The 'output error injection signals' from the observer are used as the basis for reconstructing the fault signals. For the sensor fault observer design, augmenting the LPV system with a filtered version of the faulty measurements allows the sensor fault reconstruction problem to be posed as an actuator fault reconstruction scenario. Simulation tests based on a high-fidelity nonlinear model of a transport aircraft have been used to demonstrate the proposed actuator and sensor FDI schemes. The simulation results show their efficacy. © 2011 The Franklin Institute. Published by Elsevier Ltd. All rights reserved

A fault tolerant direct control allocation scheme with integral sliding modes

PublishedJournal Article© by Mirza Tariq Hamayun 2015. In this paper, integral sliding mode control ideas are combined with direct control allocation in order to create a fault tolerant control scheme. Traditional integral sliding mode control can directly handle actuator faults; however, it cannot do so with actuator failures. Therefore, a mechanism needs to be adopted to distribute the control effort amongst the remaining functioning actuators in cases of faults or failures, so that an acceptable level of closed-loop performance can be retained. This paper considers the possibility of introducing fault tolerance even if fault or failure information is not provided to the control strategy. To demonstrate the efficacy of the proposed scheme, a high fidelity nonlinear model of a large civil aircraft is considered in the simulations in the presence of wind, gusts and sensor noise.This paper was partially funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah, under the grant no. Gr/33/5. The first and the last author, therefore, acknowledge with thanks the DSR financial support

Development and Evaluation of an Integral Sliding Mode Fault Tolerant Control Scheme on the RECONFIGURE Benchmark

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.This paper describes the development, application and evaluation of a linear parameter-varying integral sliding mode control allocation scheme to the RECONFIGURE benchmark model to deal with an actuator failure/fault scenario. The proposed scheme has the capability to maintain close to nominal (fault free) load factor control performance in the face of elevator failures/faults, by including a retro-fitted integral sliding mode term and then re-routing (via control allocation) the augmented control signal to healthy elevators without reconfiguring the baseline controller. In order to mitigate any chattering appearing in the elevator demands, the retro-fitted signal is based on a super-twisting sliding mode structure. This produces a control signal which is continuous and does not have the discontinuous switching nature of traditional sliding mode schemes. The scheme is evaluated using an industrial Functional Engineering Simulator developed as part of the RECONFIGURE project. Monte-Carlo campaign results are shown to demonstrate the performance of the proposed scheme.The work in this paper is supported by EU-FP7 Grant (FP7-AAT-2012-314544): RECONFIGUR

Sensor Fault Estimation Using LPV Sliding Mode Observers with Erroneous Scheduling Parameters

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.This paper proposes a linear parameter-varying sliding mode observer for the purpose of simultaneously estimating the system states and reconstructing sensor faults. Furthermore, some of the measured scheduling parameters are also assumed to be unreliable, and the corresponding values used in the observer are adapted to maintain the performance level of the observer. The adaptive algorithm is driven by the ‘equivalent output error injection’ signal associated with the reduced-order sliding motion. Sufficient conditions are given to ensure asymptotic stability of the state estimation error system, ensuring both the state estimation errors and the estimation errors associated with the scheduling parameters converge to zero. The efficacy of the scheme has been evaluated based upon an industrial high-fidelity aircraft benchmark scenario involving a simultaneous total loss of airspeed and angle of attack measurements

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

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.This paper develops novel fault tolerant integral sliding mode control allocation schemes for a class of over-actuated 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 the healthy actuators using knowledge of the 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

Flight evaluations of sliding mode fault tolerant controllers

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordThis paper considers the development of fault tolerant controllers (FTC) and their application to aerospace system. In particular, given the extensive and growing literature in this area, this paper focusses on methods where the schemes have been implemented and flight tested. One thread of the fault tolerant control literature has involved sliding mode controllers. This paper considers a specific class of sliding mode FTC which incorporates control allocation to exploit over-actuation (which is typically present in aerospace systems). The paper describes implementations of these ideas on a small quadrotor UAV and also piloted flight tests on a full-scale twin-engined aircraft

A fault tolerant control allocation scheme with output integral sliding modes

Copyright © 2013 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Automatica. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Automatica Vol. 49 (2013), DOI: 10.1016/j.automatica.2013.02.043In this paper a new fault tolerant control scheme is proposed, where only measured system outputs are assumed to be available. The scheme ensures closed-loop stability throughout the entire closed-loop response of the system even in the presence of certain actuator faults/failures. This is accomplished by incorporating ideas of integral sliding modes, unknown input observers and a fixed control allocation scheme. A rigorous closed-loop stability analysis is undertaken, and in fact a convex representation of the problem is created in order to synthesize the controller and observer gains. The efficacy of the proposed scheme is tested by applying it to a benchmark civil aircraft model