Model reference adaptive control of dynamic output feedback linearisable systems with unknown high frequency gain

The paper deals with model reference adaptive control of single-input/single-output nonlinear systems which are linearisable by dynamic output feedback. A class of systems discussed is specified by a set of coordinate-free geometric conditions. The systems are linear with respect to the input and unknown constant parameters. The nonlinear terms, in suitable coordinates, depend on the output only. When the parameters are known, the systems can be exactly linearised by dynamic output feedback. A key feature of the class of nonlinear systems considered in this paper is that no a priori information is assumed on the high frequency gain. A global adaptive control algorithm with a Nussbaum gain is proposed for the systems considered and is demonstrated by a physical example.