Optimal fuzzy sliding mode control with a time-varying sliding surface

It is well known that sliding mode control can achieve good transient performance and system robustness. However, the sensitivity of the sliding mode control before reaching the sliding surface and the presence of chattering may introduce problems to the tracking control of the system. In this paper, a new sliding surface design approach is proposed that varies the sliding surface in a nonlinear and time-varying fashion. Slope constant of the sliding surface is varied by fuzzy controller based on the ratio between the derivate of error and error itself. Optimal parameters of the fuzzy controller are determined using genetic algorithms. Proposed optimal fuzzy sliding mode control has been applied to an electrical servo drive system and the performed experiments have verified efficiency and improvements of a new control method.