H∞ robust control synthesis for a large space structure

In a design study involving the use of H^∞ optimal control theory, an 11-state control law is generated for a 116-state model of a large flexible space structure. A combination of co-located rate feedback, modal truncation, and optimal Hankel-norm model techniques is found to lead to a vastly simplified four-state model for the structure which, by singular-value theory, is proved to be satisfactory for design of a controller whose bandwidth exceeds the natural frequencies of all of the modes of the original 116-state model. Specifications regarding disturbance attenuation, bandwidth, and stability robustness are quantitatively expressed as weighting functions in a mixed-sensitivity H^∞ optimal control synthesis problem, the solution to which is computed by the authors´ program LINF.