Closed-Loop Evaluation of An Integrated Failure Identification and Fault Tolerant Control System for A Transport Aircraft

Abstract

Formal robustness analysis of aircraft control upset prevention and recovery systems could play an important role in their validation and ultimate certification. Such systems developed for failure detection, identification, and reconfiguration, as well as upset recovery, need to be evaluated over broad regions of the flight envelope or under extreme flight conditions, and should include various sources of uncertainty. To apply formal robustness analysis, formulation of linear fractional transformation (LFT) models of complex parameter-dependent systems is required, which represent system uncertainty due to parameter uncertainty and actuator faults. This paper describes a detailed LFT model formulation procedure from the nonlinear model of a transport aircraft by using a preliminary LFT modeling software tool developed at the NASA Langley Research Center, which utilizes a matrix-based computational approach. The closed-loop system is evaluated over the entire flight envelope based on the generated LFT model which can cover nonlinear dynamics. The robustness analysis results of the closed-loop fault tolerant control system of a transport aircraft are presented. A reliable flight envelope (safe flight regime) is also calculated from the robust performance analysis results, over which the closed-loop system can achieve the desired performance of command tracking and failure detection. * Senior Staff Scientist, Robust and Adaptive Control, AIAA Member, email:shinjy@nianet.org.† Senior Researcher, Dynamic Systems and Control Branch, AIAA Member. ‡ Researcher, Dynamic Systems and Control Branch, AIAA Member.

Robustness Analysis of Integrated LPV-FDI Filters and LTI-FTC System for a Transport Aircraft

“…This analysis framework is applied to the robustness analysis of the LPV-FDI filters integrated with the closed-loop system of a transport aircraft. Robustness analysis of an integrated fault tolerant control (FTC) system with fault detection and isolation (FDI) filters has been of interest to the NASA Aviation Safety Program (NASA AvSP) [23]. Specifically, a fault tolerant control law prevents fault propagation and reduces closed-loop performance degradation due to faults.…”

“…The singular value µ analysis method has been used to analyze robustness of FDI filters on the LTI systems in [11]. In [23], robustness analysis of an integrated system with an FTC law and FDI filters was presented using µ analysis. The nonlinear longitudinal motion of a transport aircraft was converted into a PLPV system using the function substitution method.…”

“…The function substitution method has been modified in [8,22] to minimize variations of decision variables over the scheduling parameter space using linear optimization. The method has been sucessfully applied to develop an LPV model from a nonlinear system including look-up table aerodynamic coefficients [22] or polynominal fitted aerodynamic coefficients [23]. For nonlinear dynamics described in polynominal form, the function substitution method is automatically coded to provide a PLPV model [24] using the symbolic toolbox in MATLAB.…”

Robust Gain-Scheduled Fault Tolerant Control For A Transport Aircraft

“…The nonlinear longitudinal dynamics are documented in Refs. [21], [22]. In this paper, the flight envelope for the longitudinal dynamics is defined as α ∈ [−2 10](deg) and V ∈ [100 250] (m/sec) at an altitude of 7000 m. Aerodynamic coefficients and their derivatives are fit into a polynomial function form such that…”

Validation and Verification of Future Integrated Safety- Critical Systems Operating under Off-Nominal Conditions

“…Applications of LFR-based robustness analysis to aircraft control problems are presented in References [16] and [17] to illustrate the determination of reliable flight regimes for an integrated resilient aircraft control system 16 and a fault tolerant control system…”