Performance Investigation of Asymmetric Consequents in a Fuzzy Logic Controller for a Nonlinear Flow Loop

This study explores enhancing control performance for a nonlinear flow process control loop through the integration of asymmetrically put consequents in fuzzy logic controllers. The flow control loop poses a critical control problem once it encompasses a pneumatic control valve serving as final control elements. These valves are manly characterized by typical hard nonlinearities such as stiction along with their own nonlinear valve flow-stem displacement relationships. While proportional-integral (PI) controllers are commonly employed in majority of flow control loops, their effectiveness is hampered by challenges in managing the inherent nonlinearities and uncertainties of such processes. By incorporating a fuzzy logic controller (FLC) in place of the PI controller, the system gains adaptability to adjust control actions in real-time according to variations in process dynamics. The FLC utilized in this research is of single-input-single-output nature which makes it highly resource efficient. The proposed controller takes into account the sum of scaled error and scaled integration of error as input, with outputs asymmetrically positioned within its universe of discourse. Integrating FLC with pneumatic control valves shows promise for enhancing control performance, particularly in systems marked by nonlinearities and uncertainties. Experimental testing for setpoint tracking and disturbance rejection was conducted at four distinct operating points, alongside extensive studies for parametric uncertainty handling. The comparative investigations among PI controller, symmetric FLC and asymmetric FLC, clearly underscore the superior performance obtained by asymmetrically put consequent in comparison of all the considered controllers.