Robust control of large flexible space structures using a coprime factor plant description

Dynamics of large flexible space structures (LFSS) characterized by their high order and their significant number of closely-spaced, lightly-damped, clustered low-frequency modes. Finite-element (FE) models of LFSS are known to be accurate only for the first few modes of the structure. Moreover, these models do not provide the modal damping ratios. Model identification of LFSS is often impractical because such structures are assembled in space. Thus it would be desirable to have a design procedure that would directly use an uncertain FE model to produce a controller that could be implemented on real LFSS with good confidence. This paper presents a simple description of uncertainties in LFSS as stable perturbations in the factors of a nominal left-coprime factorization (LCF) of LFSS dynamics. This leads to a better, less conservative description of the uncertainty set and hence improves achievable closed-loop performance.