Uncertainty Modeling for Robust Multivariable Control Synthesis of Hypersonic Flight Vehicles

Abstract

The non-standard dynamic characteristics of air-breathing hypersonic flight vehicles (AHFVs) and model uncertainties make the flight control of these vehicles highly challenging. In addition to the significant interactions between engine and structural dynamics, the operating conditions and mass distribution vary significantly over the flight envelope. Even considering only a single operating condition, one needs to describe the subsystem interactions and uncertainties and incorporate them into the flight control design. Focusing on robust control approaches, the description of the subsystems involves developing effective uncertainty models for AHFVs. The uncertainty modeling studies reported in the literature so far are based on linearized dynamics and incorporate the uncertainty of each individual parameter in fictitious ways, ignoring the physical nature of the sources of the uncertainties. The focus of this paper is to derive uncertainty models for the longitudinal motion dynamics of AHFVs based on a nonlinear nominal model incorporating norm bounded parametric uncertainties, and to analyze how the uncertainty in each parameter enters into the system dynamics and how it affects the performance of the system. The technique used in developing uncertainty model for AHFVs is demonstrated to be systematic and is presented in a form suitable for the application of robust control design procedures for the stabilization of longitudinal dynamics of AHFVs.