Variable Structure Control with Adaptive Fuzzy Sliding Surface

An adaptive fuzzy sliding mode control scheme is presented in this article. Despite the advantages of sliding mode control design for uncertain dynamic systems, classical sliding mode control has a major problem in the form of chattering, produced by the rapid switching used to conduct the state trajectories toward the sliding surfaces. A variety of methods are used to achieve chattering-free motion by smoothing out the switching functions; a fuzzy method is introduced in this article. In the proposed approach, the switching functions are replaced by adaptive fuzzy control signals such that the Lyapunov stability conditions are satisfied. This adaptive fuzzy controller can improve the performance and also eliminate the high frequency chattering in the control signals by preventing the application of large control gains where these are unnecessary, especially when the state trajectories are close to the sliding surfaces. The proposed approach and the classical sliding mode control are both applied to a flexible transmission system and comparisons between these control schemes are shown using simulations. The results confirm that the proposed adaptive fuzzy sliding mode control scheme is a powerful tool for the elimination of chattering and for obtaining smooth control signals for applying to the system.