On the existence of strong functional observer

TL;DR

This paper investigates the conditions under which a strong functional observer exists for linear time-invariant systems, ensuring reliable estimation of a function of the state and input regardless of initial conditions or inputs.

Contribution

It provides necessary and sufficient conditions for the existence of strong functional observers, generalizing previous results and encompassing cases with known or unknown inputs.

Findings

Derived conditions based on functional detectability.

Unified framework for observer existence for arbitrary inputs.

Retrieval of known results as special cases.

Abstract

For arbitrary linear time-invariant systems, the existence of a strong functional observer is investigated. Such observer determines, from the available measurement on the plant, an estimate of a function of the state and the input. This estimate converges irrespective to initial state and input. This formulation encompass the cases of observer existence for known or unknown inputs and generalizes state-of-art. Necessary and sufficient conditions for such an existence are proposed, in the framework of state-space representation. These conditions are based on functional detectability property and its generalizations for arbitrary input, which include considerations on convergence of the estimation, irrespective to the initial state and the input. Known results on state detectability, input reconstruction or functional detectability are retrieved by particularizing the proposed conditions.