Invariant Subspaces of Riesz Spectral Systems with Application to Fault Detection and Isolation

TL;DR

This paper investigates invariant subspaces of Riesz spectral systems, establishing their properties and developing a geometric fault detection and isolation methodology applicable to infinite-dimensional PDE systems.

Contribution

It introduces the equivalence of invariant subspace concepts for RS systems, defines unobservability subspaces, and develops finite-step algorithms for invariant subspace computation, advancing FDI techniques.

Findings

Established conditions for invariant subspace equivalence

Developed finite-step algorithms for invariant subspace computation

Proposed a geometric FDI methodology for RS systems

Abstract

A large class of hyperbolic and parabolic partial differential equation (PDE) systems, such as reaction-diffusion processes, when expressed in the infinite-dimensional (Inf-D) framework can be represented as Riesz spectral (RS) systems. Compared to the finite dimensional (Fin-D) systems, the geometric theory of Inf-D systems for addressing certain fundamental control problems, such as disturbance decoupling and fault detection and isolation (FDI), is rather quite limited due to complexity and existence of various types of invariant subspaces notions. Interestingly enough, these invariant concepts are equivalent for Fin-D systems, although they are different in Inf-D representation. In this work, first equivalence of various types of invariant subspaces that are defined for RS systems are investigated. This enables one to define and specify the unobservability subspace for RS systems. Specifically, necessary and sufficient conditions are derived for equivalence of various types of conditioned invariant subspaces. Moreover, by using duality properties, various controlled invariant subspaces are developed. It is then shown that finite-rankness of the output operator enables one to derive algorithms for computing invariant subspaces that under certain conditions, and unlike methods in the literature, converge in a finite number of steps. A geometric FDI methodology for RS systems is then developed by invoking the introduced invariant subspaces. Finally, necessary and sufficient conditions for solvability of the FDI problem are provided and analyzed