Adaptive Output-Feedback Stabilization and Disturbance Attenuation for Feedforward Systems with ISS Appended Dynamics

We propose an adaptive output-feedback control design technique for feedforward systems with Input-to-State Stable (ISS) appended dynamics and disturbance inputs. The design is based on our recent results on the application of dynamic high-gain scaling to state-feedback and output-feedback control of feedforward systems. Unlike previous approaches to the control of feedforward systems, the dynamic high-gain scaling technique provides robustness to additive disturbances and enabled the first output-feedback controller design for feedforward systems. In this paper, we further investigate the robustness properties of the dynamic high-gain scaling approach by introducing exogenous disturbance inputs and ISS appended dynamics coupled with all the system states and the input. The designed adaptive output-feedback controller achieves BIBS stability with respect to disturbance inputs and also provides a disturbance attenuation result. This provides the first results for feedforward systems with ISS appended dynamics and disturbance inputs.