Sliding Mode Control of Uncertain Systems with Arbitrary Relative Degree and Unknown Control Direction: Theory and Experiments

This paper addresses the design of output feedback sliding mode tracking control for single-input-single-output (SISO) uncertain linear plants with arbitrary relative degree. A monitoring function is used to cope with the lack of knowledge of the control direction, i.e., the high frequency gain sign. The proposed scheme guarantees global asymptotic stability with respect to a compact set. Moreover, asymptotically exact output tracking is obtained. To this end, a key element is a hybrid nonlinear filter which performs exact signal differentiation based on higher order sliding modes. The proposed controller is evaluated with a DC motor control experiment