Adaptive optics are an increasingly important feature of large ground-based telescopes. Large homogeneous deformable secondary mirrors controlled by voice-coil motors, co-located to capacitive position sensors, are a proven working design. Their shape control is mainly based on a completely decentralized high-frequency feedback, combined with a low-frequency centralized feedforward. This paper investigates the possible improvements achievable through the adoption of partially centralized feedback solutions, comparing their performances with those of fully centralized optimal solutions. The controllers design is based on well-known techniques, such as full state linear quadratic regulator, mini-max feedback and independent modal space control.
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