Output feedback stabilisation of uncertain nonminimum-phase systems

In this paper the I&I methodology is applied to the problem of asymptotic stabilisation by means of output feedback. The approach consists in writing the closed-loop system as a cascaded interconnection of two stable systems possessing specific input-output and asymptotic properties. The methodology is further extended to tackle systems with unstructured uncertainties, i.e., with unknown functions appearing in the system equations, thus yielding a robust stabilisation result. This is mainly achieved by expressing the system as a feedback interconnection of input-to-state stable (ISS) systems and applying a small-gain argument. The approach is illustrated with two practical examples. The first is the problem of output voltage regulation for a DC-DC boost converter. The second is the design of a globally asymptotically stabilising controller for the benchmark translational oscillator/rotational actuator (TORA) system, where only the rotation angle is measurable.