A Note on Observer-Based Frequency Control for a Class of Systems Described by Uncertain Models.

This paper focuses on the robust control problem for a class of linear uncertain systems by using frequency techniques. The controller/observer dynamics are analyzed using Lyapunov techniques, in terms of the state and state estimation error, for an uncertainty constrained over a specified range. A Popov-type criterion, a "circle criterion," defined as the Popov frequency condition and the uncertainty circle, is formulated. It is proved that the closed-loop system is robustly stable if the Popov condition holds at all frequencies. The proposed method is validated against a robust controller for a balancing robot (BR). [ABSTRACT FROM AUTHOR]