Uncertainty modeling and robust minimax LQR control of hypersonic flight vehicles

Abstract

Longitudinal flexible body models of canard configured air-breathing hypersonic flight vehicles (AHFV) with intricate couplings and interactions are difficult to feedback linearize. The presence of input terms in the low order derivatives of the outputs and uncertainty in the system makes the feedback linearization a highly challenging task. In this paper, we approach this problem in a robust way such that all the uncertainties are lumped together and can be written in a way that is useful for controller synthesis. Using this approach, we derive a control-oriented linearized uncertainty model (CLUM) for an AHFV. In this study, twenty four inertial and aerodynamic parameters are considered to be uncertain. Furthermore, using the derived CLUM, a robust minimax LQR controller is synthesized to track velocity and altitude step input commands. Simulation results using a curve fitted model (CFM) and varying uncertain parameters are presented to demonstrate the effectiveness of the CLUM and minimax control design method.