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Control of uncertain nonlinear systems with arbitrary relative degree and unknown control direction using sliding modes

The control of uncertain nonlinear systems by output feedback is addressed. A model‐reference tracking sliding mode controller is designed for uncertain plants with arbitrary relative degree. Nonlinearities of a given class are incorporated as state dependent and possibly unmatched disturbances of a linear plant. Such class encompasses nonlinear systems which are triangular in the unmeasured states. In contrast with previous works, exact tracking is achieved by means of a switching strategy based on a locally exact differentiator, and a monitoring function is used to cope with the lack of knowledge of the control direction. Global or semi‐global stability properties of the closed‐loop system are proved. Copyright © 2007 John Wiley & Sons, Ltd.