8 August 2008 Minimum variance control in presence of actuator saturation in adaptive optics
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Abstract
Voltage saturation mechanisms are always present on deformable mirrors (DMs) used in adaptive optics (AO) systems, so as to prevent possibly irreversible degradation of the DM. This may happen most often in a strong turbulence context, where too high voltage values are computed by control algorithms trying to compensate for high phase shifts. In minimum variance control, it is well known that input saturation in linear systems destroys separation, leading to untractable optimal control problems. We show that, in the absence of DM's dynamics, separation and certainty equivalence hold in AO even when saturations are present on the system. The optimal control can then be computed by solving a constrained projection problem. As this is computationally intensive, we also propose a sub-optimal control with lower computational burden, which guarantees optimal estimation of the turbulent phase. Optimal and suboptimal controls show a dramatic improvement in performance (measured by the Strehl ratio) compared with those obtained with integral controllers equipped with adequate clipping and anti-wind-up mechanisms. All simulation results are obtained in bad seeing conditions using a VLT Paranal type configuration.
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Caroline Kulcsár, Caroline Kulcsár, Henri-François Raynaud, Henri-François Raynaud, Cyril Petit, Cyril Petit, Jean-Marc Conan, Jean-Marc Conan, } "Minimum variance control in presence of actuator saturation in adaptive optics", Proc. SPIE 7015, Adaptive Optics Systems, 70151G (8 August 2008); doi: 10.1117/12.789215; https://doi.org/10.1117/12.789215
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