Switched/time-based adaptation for second-order sliding mode control

Controlling highly uncertain nonlinear systems is in general a quite difficult task, for which Sliding Mode (SM) control has proved to be an effective option. This brief proposes a SM control strategy which combines a switched policy with a time-based adaptation of the control gain, thereby allowing to effectively deal with a very conservative prior knowledge of the upper bounds on the uncertainties, that usually leads to a large control authority, and related performance degradation. With the proposed approach, the control effort is adjusted online according to the actual magnitude of the uncertain terms, eliminating the conservatism in the selection of the control gain.