Fuzzy Sliding-Mode State-Feedback Control of Non-Minimum Phase Quadruple Tank System

This paper considers control of a laboratory Quadruple Tank System (QTS) in its non-minimum phase mode. This system is a well-known laboratory process suitable to illustrate the concepts of multivariable control methods. The objective of this paper was to design a controller based on combination of the sliding-mode and the state-feedback control methods using fuzzy logic. The proposed method takes advantage of the fast transient response of the sliding-mode controller and the zero steady-state error of the state-feedback controller. In other words, the fuzzy system uses the SMC when the QTS is in the transient mode and utilizes the SFC when it is near the steady-state mode. Hence, the advantages of both controllers have been used simultaneously. The switching between these two controllers is continuous and smooth based on a few simple fuzzy rules. Stability analysis of the proposed method is presented based on the Lyapunov stability direct method. Experimental results confirmed effectiveness of the proposed method as compared with the stand-alone controllers, especially when there are uncertainties in the system parameters.