A Fuzzy Sliding Mode Controller Using Nonlinear Sliding Surface Applied to the Coupled Tanks System

Several methods of chattering reduction have been reported. One approach [5] places a boundary layer around the switching surface such that the relay control is replaced by a saturation function. Another method [6] replaces a max-min-type control by a unit vector function. These approaches involve a trade-off between chattering and robustness. The aim of this paper is to develop a Fuzzy sliding mode controller (FSMC) with a nonlinear sliding surface for a coupled Tanks system. In the present work, a first-order nonlinear sliding surface is presented, on which the developed control law is based. Mathematical proof for the stability and convergence of the system is presented. In order to reduce the chattering in sliding mode controller (SMC), a fixed boundary layer around the switch surface is used. Within the boundary layer, since the fuzzy logic control is applied, the chattering phenomenon, which is inherent in a sliding mode control, is avoided by smoothing the switch signal. Outside the boundary, the sliding mode control is applied to driving the system states into the boundary layer. Experimental studies carried out on a coupled Tanks system indicate that the proposed approach is a good candidate for control applications.