Robust and H∞ stabilisation of interconnected systems with delays

The problems of decentralised robust stabilisation and robust H∞ performance for a class of interconnected systems with unknown delays and norm-bounded parametric uncertainties are addressed in the paper. The delays are time-varying in the state of each subsystem as well as in the interconnections among the subsystems. A class of decentralised observer-based feedback controllers is developed to render the closed-loop interconnected system asymptotically stable. All the design effort is undertaken at the subsystem level. It is shown that the robust control design problems can be solved with the aid of two algebraic Riccati inequalities. The developed theory is illustrated by simulation of a multireach pollution model of a representative segment of the River Nile.