This paper addresses the design of a sliding mode tracking controller for single-input-single-output (SISO) uncertain plants with relative degree one and unknown sign of the high frequency gain (HFG), i.e., with unknown control direction. We demonstrate that it is possible to achieve global exact tracking using only output-feedback by means of a periodic switching function and input-output filters based framework. One significant advantage of the new scheme is its robustness to time-varying control direction which has been theoretically justified for jump variations and successfully tested by simulation. Such property makes it adequate for solving extremum-seeking problems. A nonderivative optimizer application illustrates the practical viability of the proposed control scheme.
sliding mode control; output-feedback; uncertain systems; unknown control direction; global tracking; extremum-seeking control
