Robustness Study of the Dynamic Inversion Based Indirect Adaptive Control of Flight Vehicles with Uncertain Model Data

摘要

The objective of this paper is to analyze the stability robustness of dynamic inversion based control laws being used for flight control with uncertainties in model data such as the aerodynamic stability and control derivatives. In particular, the paper is aimed at determining the robustness of an indirect adaptive control system developed by the researchers at the AFRL, which is built around a baseline dynamic inversion inner loop.. The controller, which is used to track the desired angular velocity commands, under perfect dynamic inversion, would result in a bank of integrators in the three angular velocity channels. While this control law is quite successful in tracking the desired angular velocity commands, no explicit parametric stability robustness margins are provided. A static approach to online system identification is used to estimate the vehicle's changing control derivatives. Due to the existence of dynamic inversion errors resulting from uncertainties in these control derivatives, robustness of the designed control system needs to be guaranteed. In order to study the robustness of the controller, stability of the nominal system is guaranteed by the Input to State Stability criterion. The control derivatives are studied to determine the margins of perturbations under which the nonlinear stability margin between the input and the state of the rotational dynamics of the system are decreasing.