Adaptive Control for Stabilizing Nonnecessarily Inversely Stable Plants by Using Multiple Estimation Models with Multirate Input and Fractional-Order Holds

This paper presents a multi-estimation adaptive control strategy for stabilizing a potentially noninversely stable, linear and time-invariant plant. Such a strategy works with several discretization models of the plant. Each one of them is obtained by means of a fractional-order hold (FROH) and a multirate input in order to place its zeros into the stability region. A supervisor activates one of such models and maintains it in operation during at least a minimum residence time for stability purposes. That estimation model parameterizes a discrete-time adaptive controller for asymptotically matching a stable reference model at sampling instants