Lejun Chen

Reconstruction of simultaneous actuator and sensor faults for the RECONFIGURE benchmark using a sliding mode observer

Abstract This paper considers the problem of reconstructing, simultaneously occurring actuator and sensor faults in a nonlinear system. The theory which will be developed in this paper is based on a sliding mode observer formulation, designed around an LPV model approximation of the nonlinear system. It extends previous work which has independently considered actuator and sensor faults reconstruction. Here a single observer structure will be synthesized which can cope with simultaneous actuator and sensor faults. The paper will describe the development of the LPV model, the theory and synthesis of the sliding mode observer, and the results of applying this technique to the RECONFIGURE benchmark problem.

A Mixed H/H∞ LPV Approach to Adaptive Fault Compensation for a Nonlinear UAV

Abstract The current study is motivated by the need to implement a linear model-based fault detection and isolation/ diagnosis (FDD) methodology and a corresponding active fault tolerant control (FTC) scheme onto a nonlinear aircraft system directly without control law reconfiguration The nonlinear model is expressed in linear parameter varying (LPV) form. The mixed quadratic H/H∞ LPV observer is then developed to maximize the robustness of the residual to uncertainty or disturbances as well as achieving the specific minimum sensitivity of the residual to faults, whilst the fault estimation can also be achieved for active on-line FTC via adaptive control. Instead of constant observer gains, parameter-varying gains are used in the LPV observer and the free design parameters are parameterized via a generalized inverse to improve the conservatism of the robust solution. The FDD approach together with FTC scheme developed is then applied in non-linear simulation to the example of faults in the yaw rate sensor of a UAV aircraft (Machan).

Polytope LPV estimation for non-linear flight control

Abstract The current study is motivated by the need to implement the linear based model-based fault detection and isolation (FDI) methodology onto the nonlinear aircraft system directly. The nonlinear model is expressed in the linear parameter varying (LPV) manner and the corresponding LPV FDI estimator can be developed through the combination of the polytopic FDI estimators developed on each system vertex. The proposed design strategy is applied to the nonlinear longitudinal motion of a UAV aircraft (Machan) with different faults acting on the elevator actuator and wind turbulence affecting the vertical force.

Increasing eigenstructure assignment design degree of freedom using lifting

ABSTRACT This paper presents the exposition of an output-lifting eigenstructure assignment (EA) design framework, wherein the available EA design degrees of freedom (DoF) is significantly increased, and the desired eigenstructure of a single-rate full state feedback solution can be achieved within an output feedback system. A structural mapping is introduced to release the output-lifting causality constraint. Additionally, the available design DoF can be further enlarged via involving the input-lifting into the output-lifting EA framework. The newly induced design DoF can be utilised to calculate a structurally constrained, causal gain matrix which will maintain the same assignment capability. In this paper, the robustification of the output-lifting EA is also proposed, which allows a trade-off between performance and robustness in the presence of structured model uncertainties to be established. A lateral flight control benchmark in the EA literature and a numerical example are used to demonstrate the effectiveness of the design framework.

LPV approach to friction estimation as a fault diagnosis problem

The control of systems that involve friction presents interesting challenges. Recent research has focused on detailed modelling of friction phenomena as a very complex and difficult modelling challenge. However, the friction effects acting in a dynamic system can be viewed as actuator faults with time-varying characteristics to be estimated and compensated within a Fault Detection and Diagnosis (FDD) scheme, so that the limitations arising from the use of a friction model are obviated. This work is motivated by the utilisation of robust Linear Parameter Varying (LPV) estimation approach providing effective and robust fault estimation. The approach is illustrated using a two-link manipulator system with Stribeck friction. Results show that the time-varying friction forces on each joint can be simultaneously and robustly estimated through the online measurement of the varying parameters.

Robust Fault Estimation and Performance Evaluation based upon the ADDSAFE Benchmark Model

Abstract This work is motivated through a European Union FP7 funded project entitled Advanced Fault Diagnosis for Sustainable Flight Guidance and Control (ADDSAFE), following an interest in implementing a mixed quadratic linear parameter-varying (LPV) H/H ∞ model-based fault detection and isolation/diagnosis (FDI/FDD) observer. The approach uses free parameterised observer gains, on a high fidelity nonlinear aircraft model from AIRBUS, in order to estimate the various fault scenarios occurring for different flight conditions. The main design goal is to maximize the robustness of the reference-actual residual error signal to nonlinear uncertainty, disturbances, faults and system inputs, whilst also achieving the specific minimum sensitivity of the actual residual signal to faults. Considering sources from various fault occurrences, the local actuator model and the global aircraft model are used in observer estimation schemes to estimate simultaneously the ADIRS yaw rate sensor faults and the abnormal aircraft configurations. The detection results are evaluated on the ADDSAFE Functional Engineering Simulator (FES).

Actuator faults and blow-down limit detection, and fault tolerant control for the RECONFIGURE benchmark problem

Despite their low probability, faults and failures can occur in aircraft for various internal or external mechanisms. The control surfaces of an aircraft can become faulty due to various reasons; they can either become permanently jammed (due to hydraulic or mechanical problems) or temporarily stuck (due to blow-down limits). A blow-down limit is a phenomenon where the actuator surface become stuck temporarily due to aerodynamic constraints during a particular manoeuvre. Once the aerodynamic forces are restored to their normal values, the blow-down limit phase ends and the actuator surfaces move normally. In this paper a sliding mode fault tolerant controller and a control allocation scheme is proposed to deal with actuator jams and blow-down limit problems. The proposed scheme has an ability to distinguish between an actuator jam and a blow-down limit, and reallocates the control signal accordingly to recover the nominal performance. The proposed scheme has been implemented on the RECONFIGURE benchmark problem, which represents a high fidelity model of a generic civil aircraft. Good results have been obtained.

Application and evaluation of an LPV integral sliding mode fault tolerant control scheme on the RECONFIGURE benchmark

This paper describes the application of a linear parameter-varying integral sliding mode control allocation scheme to the RECONFIGURE benchmark model to deal with an elevator failure/fault scenario. The proposed scheme has the capability to maintain the closed-loop nominal load factor control performance in the face of elevator failures/faults, by effectively redistributing a retro-fitted signal to the healthy elevators without reconfiguring the baseline controller. In order to reduce any chattering appearing in the elevator demands, the retro-fitted signal is based on a super-twisting sliding mode structure. The efficiency of the scheme is evaluated using an industrial functional engineering simulator (FES) as part of the RECONFIGURE project.

Multistage Output-lifting Eigenstructure Assignment: A Multirate Ball and Plate Example

ABSTRACT By exploiting both the left and the right allowable subspaces in consecutive stages, this paper extends a recently developed output-lifting eigenstructure assignment approach into a multistage eigenstructure assignment scheme. In this scheme, design degrees of freedom, enlarged via output-lifting, are further exploited to improve eigenvector assignment. To mitigate the inherent conflicts between the theoretical development of eigenstructure assignment and inherent physical system characteristics, the paper also clearly demonstrates how to derive an ideal eigenstructure, particularly the desired eigenvectors, to distribute and decouple the natural modes among appropriate states or outputs, based upon an example: a novel multirate ball and plate system. The design and simulation results show the efficacy of the scheme.

Hardware-in-the-loop evaluation of an LPV sliding mode fixed control allocation scheme on the MuPAL-α research aircraft

This paper develops a sliding mode fault tolerant control scheme based on an LPV system representation of the plant. The scheme involves a control allocation component, which is capable of fully utilizing the available actuators in the face of actuator faults. In this paper, information about the actuator faults is assumed not to be available and therefore a fixed control allocation structure is utilised in the event of faults. The proposed scheme is validated using the Japanese Aerospace Exploration Agencys Multi-Purpose Aviation Laboratory (MuPAL-α) research aircraft. This paper describes initial hardware-in-the-loop (HIL) tests which serve as a precursor to upcoming real flight tests. The validation results show good lateral-directional state tracking performance in the fault free case with no visible performance degradation in the presence of (aileron) faults. Successful HIL tests demonstrate the potential of the proposed scheme which will be flight tested later this year.