Model reduction of discrete time-delay systems based on Charlier polynomials and high-order Krylov subspaces

In this paper, we present an efficient model reduction method for discrete time-delay systems based on the expansions of systems under Charlier polynomials. Making full use of the properties of Charlier polynomials and the structure of discrete time-delay systems, the projection space built by state variables is embedded in a high-order Krylov subspace. Further, a high-order Krylov subspace method is developed to generate discrete time-delay reduced systems. The proposed method is independent of the choice of inputs since the high-order Krylov subspace sequence does not involve the expansion coefficients of inputs. Besides, theoretical analysis shows that the resulting discrete time-delay reduced system characterizes the property of invariable coefficients. Finally, two numerical examples demonstrate the effectiveness of the proposed method.