Fault-Tolerant Flight Control for Elevator Faults Using S/CAS and Feedforward via Structured H∞ Control

Abstract

This paper addresses the design problem of Fault-Tolerant Control (FTC) for airplane longitudinal motions against possible elevator efficiency reduction. The supposed FTC is composed of a feedforward gain and the conventional airplane control system, i.e. Stability/Control Augmentation System (S/CAS). The FTC is required to maintain good tracking performance with respect to pitch angle control under time-invariant plant modeling errors as well as time-varying possible elevator faults. The design problem is then formulated as structured robust H∞ controller design for parameter-dependent systems, i.e. single structured H∞ controller design for parameter-varying plant models. It is hard to obtain the globally optimal controllers for the problem due to the structural constraint for the controllers and the parameter-varying plant models. We thus adopt two-step design, viz., we first design a single common structured H∞ controller for finitely many plant models using non-smooth optimization technique, which has been implemented to Matlab® as hinfstruct, under the supposition that the elevator faults are time-invariant, and we then check the control performance of the designed FTC for the parameter-varying closed-loop system via Linear Matrix Inequality (LMI) condition. The control performance is examined via linear simulations as well as hardware-in-the-loop simulations.