Date of Award

Summer 2002

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical & Computer Engineering

Program/Concentration

Electrical Engineering

Committee Director

Oscar R. Gonzalez

Committee Member

W. Steven Gray

Committee Member

Linda L. Vahala

Call Number for Print

Special Collections LD4331.E55 R85 2002

Abstract

Life-critical, real-time applications like flight-by-wire aircraft, rely on closed-loop digital control systems and fault-tolerant computer systems to reliably achieve the desired operation. The computer systems, however, may be affected by random hardware/software faults induced mainly by environmental conditions such as high intensity radiated fields (HIRF) and lightning. These harsh electromagnetic environments are known to induce common­ mode faults (CMF) in aircraft electronic systems, which disrupt fault-tolerant provisions and possibly affect the operation of the digital control system. Current flight-by-wire aircraft have computer systems that can neither detect CMF nor recover from them. New systems are under investigation that can recover from CMF using error recovery techniques. Never- the less, little is known about the effect of these recovery algorithms on the stability of the closed-loop flight control system.

The main objectives of this research are to analyze the stability of closed-loop discrete­ time digital flight control systems with error recovery capabilities that are triggered by a harsh electromagnetic environment and to compare the strengths and weaknesses of typical fault recovery methods. This research is an extension of previous work in which the environment is assumed to induce abrupt changes on the structure of the closed-loop representation, but the effect of error recovery systems was not considered. Three error recovery algorithms were considered: rollback, reset and cold-restart. For each case new closed-loop models that include their effect were developed. These models were then used with existing stochastic stability theory to determine the effect on stability. The theoretical analysis was then validated with Monte Carlo simulations, including two aircraft examples. An important consequence of this research is the availability of a new design tool that allow designers of error recovery systems to compare the benefits of the recovery algorithms and the impact of their parameters on the stability of the closed-loop flight control systems.

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DOI

10.25777/5qkd-mj55

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