Networked unknown input observer analysis and design for time-delay systems

The insertion of communication networks in the feedback loops of control systems is a defining feature of modern control systems. These systems are often subject to unknown inputs in a form of disturbances, perturbations, or attacks. The objective of this paper is to analyze and design an observer for networked systems with unknown disturbances and inputs. The network effect can be viewed as either a perturbation or time-delay to the exchanged signals. In this paper, we focus on the time-delay representation of the network. First, we review an Unknown Input Observer (UIO) design for non-networked system from the UIO literature. Second, we derive the dynamics of the UlO-based NCS, also referred to as Networked Unknown Input Observer (N_etUIO). Third, we design the N_etUIO such that the effect of higher delay order terms are nullified, assuring that the effect of the unknown inputs on the plant state estimation is minimized. Fourth, we derive a bound on the maximum allowable time-delay for the N_etUIO. Finally, a numerical example is shown to illustrate the usefulness of the proposed model.