Reconciling Full-Order LPV Design and Augmented Structured ℋ∞ via Internal Model Principle: a Launch Vehicle Application *

Abstract

This article presents an indirect method to characterize a wind disturbance internal model that can be used to augment the capabilities of a classical controller structure for the atmospheric-phase thrust vector control (TVC) system of the VEGA launcher. This characterization is based on a comparison between a structured ℋ∞ and a full-order LPV controller with better performance levels. The identified wind model is then explicitly employed to re-design the structured ℋ∞ controller in order to achieve similar levels as the full-order LPV controller. This design reconciles the current VEGA control system architecture with the internal model principle, which states that a controller must have structural features to contain the internal model of the signal to be controlled. The effect of this new controller structure is analysed in terms of robust stability and performance using the singular structured value µ technique. The results show that embedding the internal model structure in the control system provides an extra degree of freedom to improve the launcher performance against wind gusts.