  We introduce a novel model order reduction method for large-scale linear
switched systems (LSS) where the coefficient matrices are affected by a
low-rank switching. The key idea is to replace the LSS by a non-switched system
with extended input and output vectors - called the envelope system - which is
able to reproduce the dynamical behavior of the original LSS by applying a
certain feedback law. The envelope system can be reduced using standard model
order reduction schemes and then transformed back to an LSS. Furthermore, we
present an upper bound for the output error of the reduced-order LSS and show
how to preserve quadratic Lyapunov stability. The approach is tested by means
of various numerical examples demonstrating the efficacy of the presented
method.
