Hyung Bo Shim

In this paper, we analyze the classical linear disturbance observer (DOB) approach in the state space. Our tool for the analysis is the singular perturbation theory. With the tool, an almost necessary and sufficient condition is proposed for robust stability of the closed-loop system with the DOB when the Q-filter has sufficiently large bandwidth. The proposed analysis enlightens the power and the limitations of the classical DOB approach, which have not been well discussed in the literature.

Abstract: It is known that HIV (Human Immunodeficiency Virus) infection, which causes AIDS after some latent period, is a dynamic process that can be modeled mathematically. Effects of available anti-viral drugs, which prevent HIV from infecting healthy cells, can also be included in the model. In this paper we illustrate control theory can be applied to a model of HIV infec-tion. In particular, the drug dose is regarded as control input and the goal is to excite an immune response so that the s

This paper formulates and studies the concept of quasi-Disturbance-to-Error Stability (qDES) which characterizes robustness of a nonlinear observer to an output measurement disturbance. In essence, an observer is qDES if its error dynamics are input-to-state stable (ISS) with respect to the disturbance as long as the plant's input and state remain bounded. We develop Lyapunov-based sufficient conditions for checking the qDES property for both full-order and reduced-order observers. We use these

The behavior of heterogeneous multi-agent systems is studied when the coupling matrices are possibly all different and/or singular, that is, its rank is less than the system dimension. Rank-deficient coupling allows exchange of limited state information, which is suitable for the study of multi-agent systems under output coupling. We present a coordinate change that transforms the heterogeneous multi-agent system into a singularly perturbed form. The slow dynamics is still a reduced-order multi-

Motivated by the fact that the application of the disturbance observer (DOB) approach has been limited to minimum phase systems, we propose a new DOB configuration for non-minimum phase systems. The proposed configuration introduces a new filter, which corresponds to the Q-filter of the classical linear DOB, in a different place of the inner-loop. This new configuration enables an application of DOB idea to the non-minimum phase systems. After analyzing robust internal stability of the proposed