Output-feedback control of Lur’e-type systems with set-valued nonlinearities: A Popov-criterion approach

This paper presents an output-feedback controller design for Lur´e-type systems with set-valued nonlinearities in the feedback loop based on a generalization of a Popov-like criterion. Hereto, we introduce the concept of absolute input-to-state stability (ISS) that generalizes the well-known absolute stability property. The latter concept is used to design a state-feedback controller that renders the closed-loop system absolutely ISS and, therewith, robust to uncertainties in the nonlinearities and disturbances, such as measurement noise. Furthermore, an output-feedback controller design is constructed by exploiting the ISS property, where a model- based observer is used to estimate the system state. The control strategy is applied to a mechanical motion system with non-collocation of actuation and dry friction for which well-known strategies such as direct friction compensation fail. The effectiveness of the proposed output-feedback control strategy is shown in simulations.