Control of lightly damped, flexible modes in the controller crossover region

Many proposed future space structures have closely spaced, lightly damped flexible modes that must actively be controlled to achieve desired performance objectives. These densely packed structural modes require a controller to roll off in a region of modes that have some amount of modeling error or uncertainty in their damping levels, natural frequencies, and/or mode shapes. Therefore, a delicate balance must be found between the level of closed-loop performance of the control system and its robustness to various types of uncertainty. This paper focuses on using the structured singular value (u) control design technique to achieve performance and robustness objectives in the presences of uncertainty flexible modes in the controller crossover region. Controllers are synthesized for a lightly damped, flexible structure experiment with noncollocated sensors and actuators to show the role played by uncertainty modeling in achieving desired performance objectives.

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