Robustness versus unmatched uncertainties of a hybrid variable structure control strategy

The robustness features versus unmatched uncertainties of a hybrid variable structure control strategy for a class of second order systems are analyzed in this paper. The hybrid control relies on a subdivision of the system state space into nested regions, and on an event-driven switching among the control laws associated with each region. By componing globally stabilizing variable structure laws, and avoiding the generation of limit cycles, the proposed strategy proves to globally stabilize the origin of the system state space. Moreover, the equivalent system state is proved to be ultimately bounded with respect to an arbitrarily small set.