Uniform practical asymptotic stability of time-varying parameterized discrete-time cascades

We present two theorems on semiglobal practical asymptotic stability of parameterized time-varying discrete-time cascaded systems. This class of models arises naturally when one uses an approximate discrete-time model to design a stabilizing or tracking controller for a sampled-data plant. Even though our results parallel their continuous-time counterparts, the stability properties that are considered, the conditions that are imposed and the the proof techniques that are used are tailored for approximate discrete-time systems and are technically different from those in the continuous-time context.