  This paper proposes a balancing-based model reduction approach for an
interconnection of passive dynamic subsystems. This approach preserves the
passivity and stability of both the subsystems and the interconnected system.
Hereto, one Linear Matrix Inequality (LMI) per subsystem and a single Lyapunov
equation for the entire interconnected system needs to be solved, the latter of
which warrants the relevance of the reduction of the subsystems for the
accurate reduction of the interconnected system, while preserving the
modularity of the reduction approach. In a numerical example from structural
dynamics, the presented approach displays superior accuracy with respect to an
approach in which the individual subsystems are reduced independently.
