Unknown input observer design and analysis for networked control systems

Abstract

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 design and analyse an observer for networked dynamical systems with unknown inputs. The network effect can be viewed as either a perturbation or time-delay to the exchanged signals. In this paper, we (1) review an unknown input observer (UIO) design for a non-networked system, (2) derive the networked unknown input observer (N_etUIO) dynamics, (3) design a N_etUIO such that the effect of higher delay order terms are nullified and (4) establish stability-guaranteeing bounds on the networked-induced time-delay and perturbation. The formulation and results derived in this paper can be generalised to scenarios and applications where the signals are perturbed due to a different source of perturbation or delay.

Keywords:

• networked control systems
• unknown input observers
• N_etUIO
• time-delay systems

Acknowledgements

The authors gratefully acknowledge the constructive comments by the reviewers.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. Note that $\widehat{\mathbf{y}}$ and ${\widehat{\mathbf{u}}}_1$ are both piece-wise constant functions, thus $\dot{\widehat{\mathbf{y}}}={\dot{\widehat{\mathbf{u}}}}_1=\mathbf{0}$ (Tabbara et al., 2008).

Additional information

Funding

This study was financially supported by the National Science Foundation through NSF CMMI [grant number 1201114], [grant number 1265622].