  This work presents a hierarchical architecture for the optimal management of
an ensemble of steam generators, which needs to jointly sustain a common load.
The coordination of independent subsystems is provided by a multi-layer control
scheme. A high-level optimizer computes the optimal shares of production to be
allocated to single generators. At medium level, a robust tube-based model
predictive control (MPC) is proposed to track the time-varying demand of the
ensemble using a centralized, but aggregated model, whose order does not scale
with the number of subsystems. At low level, decentralized controllers are in
place to stabilize the internal boiler pressure. The control architecture
enables the dynamic modification of the ensemble configuration and plug and
play operations. Simulation results are reported to demonstrate the
potentialities of the proposed approach.
