Liquid level control in tanks is essential in petrochemical, paper, pharmaceutics and other industries; therefore, several papers on twin-tank systems consisting of two tanks coupled by a pipe have been published in the last years. In this paper, a three tanks system is investigated. At first, the authors develop a new non-linear multiple input, single output (MISO) state model of such a plant and determine its transfer function; a sliding mode controller (SMC) for liquid level control is designed and an interesting simulation in MATLAB\SIMULINK for testing the non-linear three coupled tank system controlled in two different ways is created. The performance of the system with a sliding mode controller is compared with the performance of the system using a PID controller.

Keywords: Sliding mode control (SMC), Proportional integral differential (PID), Sliding surface, Coupled tank system, Level control