Adaptable iISS Small-Gain Formulation and Its Application to Observer-Based Output Feedback Design

Abstract

For a popular class of nonlinear systems, an observer can be constructed by rendering estimation error dynamics linear in unmeasured state variables. However, measurement disturbance violates the structure of the error dynamics and brings in undesirable terms in which the estimation error and the plant state are often coupled and multiplied by the measurement disturbance. This is why local analysis and semi-global design have been performed in many cases. This paper introduces new flexibility into the iISS small-gain framework to accommodate such terms. It is demonstrated how the flexible framework enables global analysis of observer-based output feedback control systems to achieve convergence and boundedness in the presence of measurement disturbance.