LPV model-based robust diagnosis of flight actuator faults

A linear parameter-varying (LPV) model-based synthesis, tuning and assessment methodology is developed and applied for the design of a robust fault detection and diagnosis (FDD) system for several types of flight actuator faults such as jamming, runaway, oscillatory failure, or loss of efficiency. The robust fault detection is achieved by using a synthesis approach based on an accurate approximation of the nonlinear actuator-control surface dynamics via an LPV model and an optimal tuning of the free parameters of the FDD system using multi-objective optimization techniques. Real-time signal processing is employed for identification of different fault types. The assessment of the FDD system robustness has been performed using both standard Monte Carlo methods as well as advanced worst-case search based optimization-driven robustness analysis. A supplementary industrial validation performed on the AIRBUS actuator test bench for the monitoring of jamming, confirmed the satisfactory performance of the FDD system in a true industrial setting

Synthèse et validation d'une lois de contrôle de charge a deux degrés de liberté

International audienceThe design and assessment of a two degree of freedom gust load allevi-ation control system for a business jet aircraft is presented in this paper. The two degrees of freedom are a disturbance estimator to compute the incoming gusts as well as a feedback control law to mitigate the estimated disturbance to reduce the aircraft loads. To facilitate the estimator design, high order, infinite models of the structural and aerodynamic aircraft dynamics are approximated by low order models using advanced model reduction techniques. For the robust disturbance estimator design an innovative approach relying on nullspace based techniques together with non-linear optimizations is proposed. Time delays, originating from the aerodynamics modeling, the discrete control loop, and the sensor and actuator dynamics, play a key role in the stability and performance assessment of a gust load alleviation controller. Thus, a novel analytical analysis method is presented to explicitly evaluate the influence of these time delays on the closed loop. Finally, the developed tool-chain is applied to a fly-by-wire business jet aircraft. The resulting two degree of freedom gust load alleviation system is verified in a simulation campaign using a closed loop, non-linear simulator of the aircraft

A Versatile Simulation Environment of FTC Architectures for Large Transport Aircraft

We present a simulation environment with 3-D stereo visualization facilities destined for an easy setup and versatile assessment of fault detection and diagnosis based fault tolerant control systems. This environment has been primarily developed as a technology demonstrator of advanced reconfigurable flight control systems and is based on a realistic six degree of freedom flexible aircraft model. The aircraft control system architecture includes a flexible fault detection and diagnosis system and a reconfigurable nonlinear dynamic inversion based controller, able to handle different fault situations

Combining sensor monitoring and fault tolerant control to maintain flight control system functionalities

To maintain nominal flight control system functionalities during fault scenarios, enhancements of the state-of-practise angle of attack and airspeed sensor fault accommodation strategies are presented. The strategy combines a fault detection and diagnosis (FDD) system with a robust fault tolerant control law. The FDD system allows to maintain the nominal flight control law as long as at least one angle of attack and airspeed sensor are available. The FDD system is designed using advanced nullspace computation, optimization, and signal processing techniques. For the scenario of a total airspeed measurement loss, an airspeed independent longitudinal backup control law is designed using global optimization techniques. Using this law avoids the state-of-practise switch to a direct law in which the pilot must control the Elevator positions directly. The results from an extensive industrial validation and veri�cation campaign are reported

Fault-Tolerant Control for a High Altitude Long Endurance Aircraft

High Altitude Long Endurance (HALE) aircraft consist of extremely light-weight structures in combination with a high wingspan and high aspect ratio. The combination of these properties results in an unique dynamic behavior of the aircraft system featuring a strong interaction of structural and rigid body eigenmodes. These characteristics lead to specific demands on the robustness and fault tolerance of flight control algorithms of such aircraft. The control system must be able to navigate the aircraft safely along defined tracks even in case of fault scenarios. Due to the size of these aircraft they are usually over-actuated featuring multiple redundant control surfaces. This redundancy is used in this paper to design a fault tolerant control system ensuring optimal control performance during fault scenarios. The strategy is based on a fault detection and isolation (FDI) algorithm to detect malfunctioning control surfaces. This fault information is used to switch to alternate control laws in a multi-model control approach. The FDI filters are designed using the nullspace-based design paradigm, while the alternate controllers are synthesized applying structured H1 control design techniques

Blending of Inputs and Outputs for Modal Velocity Feedback

Dynamical systems like mechanical structures can be effectively damped by applying forces which oppose the velocity measured at the very same location. To apply this principle also to systems with multiple actuators and sensors of different type and at different locations, a novel control approach is presented in this paper. The control approach aims to damp individual modes by a minimum-gain feedback of blended measurement outputs to blended control inputs. To that end, a numerically efficient algorithm is proposed for computing input and output blending vectors which yield the desired isolation of the target mode(s). The effectiveness of the proposed approach is demonstrated by increasing the modal damping of an aeroelastic syste

Baseline Flight Control System for High Altitude Long Endurance Aircraft

High Altitude Long Endurance (HALE) aircraft consist of extremely light-weight structures in combination with a high wingspan and high aspect ratio. The coupling of these properties results in a dynamic behavior of the aircraft system which is different to classical transport or unmanned aircraft configurations. The key finding in the analysis of the dynamic behavior ofthe aeroelastic HALE aircraft is a strong interaction of structural and rigid body eigenmodes.This leads to challenges in the design of a robust flight control algorithm for the full flight envelope with state-of-the-art techniques. This work addresses these difficulties and proposes a generic design process which can be used to develop flight control algorithms for HALE aircraft. The design process starts with the definition of specific performance and robustness criteriafor HALE flight control laws which emerge from the combination of general aircraft design standards with the limitations and capabilities of theHALEconfiguration. Subsequently, again-scheduled, fixed structure control design architecture is proposed. The inner loop controldesign is enriched with envelope protection functionalities. The design process concludes withan extensive validation and verification process to clear the baseline flight control system forflight testing. The proposed design process is applied to the German Aerospace Center’s newlydeveloped HALE platform

Robust Path-following Control with Anti-Windup for HALE Aircraft

In this paper, a robust path-tracking controller for a High Altitude Long Endurance (HALE) aircraft is presented. The main control paradigm for operating a HALE aircraft consists of a basic path following control, i.e. tracking a reference flight path and airspeed while dealing with very limited thrust. The priority lies in keeping airspeed inside the small flight envelope of HALE aircraft even during saturated thrust. For the basic path following objective, a mixed sensitivity approach is proposed which can easily deal with decoupled tracking and robustness requirements. To deal with saturated control inputs, an anti-windup scheme is incorporated in the control design. A novel observer-based mixed sensitivity design is used which allows directly using classical anti-windup methods based on back-calculation. The control design is verified in nonlinear simulation and compared to a classical total energy control based controller