Robust continuous-time asymptotic tracking and regulation for sampled-data systems with structured parametric uncertainties

In this paper, the problem of the robust continuous-time (i.e., ripple-free) asymptotic tracking and disturbance rejection for a multivariable sampled-data system is studied, for the case when the available description of the continuous-time plant has a known dependence on some "physical" parameters and possibly only some of the scalar outputs must track corresponding reference signals. The necessary and sufficient conditions for the existence of a hybrid control system for which exponential stability and a continuous-time convergence to zero of the tracking error is guaranteed at least in a neighbourhood of the nominal parameters, are derived here, together with the necessity of a wholly continuous-time internal model of the exogenous signals.