Sliding mode control of a coupled tank system with a state varying sliding surface parameter

In general, sliding mode controllers with moving sliding surfaces are achieved by using time-dependent expressions. In this situation, the parameters of the sliding surface have to be rearranged if the initial conditions of the error phase plane are changed. This paper presents a special purpose approach with a state dependent moving algorithm for the control of the coupled tank system where the state variables are defined as the liquid levels of the tanks. Instead of using a time-dependent parameter, sliding surface parameter is adjusted by directly using the state variables of the tank system. The comparisons with a conventional sliding mode controller for different desired liquid levels are presented via simulations. The simulation results show that sliding mode controller with a state varying sliding surface parameter has a better performance with respect to conventional sliding mode controller even when the system initial conditions of the error phase plane are varied.