IQC-Based LPV Controller Synthesis for the NASA HL20 Atmospheric Re-entry Vehicle

Abstract

The synthesis of linear parameter-varying (LPV) controllers for complicated nonlinear systems is mostly considered as very challenging. Moreover, the available methods and tools suggested in the literature are scarce and not well tested on complex applications. In this paper, the design of an LPV controller for the NASA HL20 vehicle during re-entry is addressed. The strongly nonlinear longitudinal motion of the dynamical system has to be stabilized and must exhibit high performance over a large operation range. A general design philosophy is provided which serves as a road-map to ensure a successful synthesis, starting from a linear fractional representation (LFR) of the LPV plant, which is obtained by trimming and linearization of the nonlinear dynamical equations. The design is performed based on LPV synthesis theory which involves Linear Matrix Inequalities (LMIs). The design is validated based on standard Bode-magnitude plots, time-domain simulations within a non-linear simulation environment and analysis results based on the Integral Quadratic Constraint (IQC) framework.