Model order reduction for bilinear systems with non-zero initial states – different approaches with error bounds

Abstract

In this paper, we consider model order reduction for bilinear systems with non-zero initial conditions. We discuss the choices of Gramians for both the homogeneous and the inhomogeneous parts of the system individually and prove how these Gramians characterise the respective dominant subspaces of each of the two subsystems. Proposing different, not necessarily structure preserving, reduced-order methods for each subsystem, we establish several strategies to reduce the dimension of the full system. For all these approaches, error bounds are shown depending on the truncated Hankel singular values of the subsystems. Besides the error analysis, stability is discussed. In particular, a focus is on a new criterion for the homogeneous subsystem guaranteeing the existence of the associated Gramians and an asymptotically stable realisation of the system.