Intelligent Ratio Control in Presence of Pneumatic Control Valve Stiction

Abstract

The presence of hard nonlinearities, such as control valve stiction, may severely degrade the plant profitability by introducing limit cycles in the process variable. This paper presents an innovative use of a recently developed intelligent controller for effective ratio control in the presence of a sticky control valve. The intelligent controller, stiction combating intelligent controller (SCIC), is inherently a fuzzy controller which makes use of Takagi–Sugeno model and changes its gain in run time to deal with stiction nonlinearity. Some of the various advantages which SCIC controller offers are, its simple structure, non-requirement of process parameters’ estimation and its capability to provide standalone solution to stiction nonlinearity. These qualities of SCIC controller make it a front runner among other solutions, for the effective ratio control in the presence of a sticky pneumatic control valve. The efficacy of the SCIC controller in ratio control is experimentally verified on a laboratory scale plant with uncertain parameters. A performance comparison between SCIC and linear proportional integral (PI) controller is also made for their setpoint tracking, disturbance rejection and trajectory tracking capabilities at various operating points. Based on extensive experimental studies, it can be concluded that SCIC controller, undoubtedly, outperformed the linear PI controller for all investigated cases and also efficiently handled uncertainties in the plant parameters.