A comparative study for flow control using SCIC and NPIC controllers

Flow control is essentially a very important part of the process control industries. The flow control loops often employ pneumatic control valves as the final control element. These control valves suffer from various nonlinearities and stiction is most common of these. Due to stiction effect in the pneumatic control valves, the commonly used proportional-integral-derivative (PID) controller introduces limit cycles in the flow control loops, which essentially deteriorates the productivity of the industrial environment. To curb such non sinusoidal oscillations in these control loops, recently two novel controllers have been proposed namely, Stiction Combating Intelligent Controller (SCIC) and Nonlinear Proportional Integral Controller (NPIC). These two controllers have been earlier thoroughly evaluated for flow control studies and are claimed to be very efficient for curbing the limit cycle behavior in the control loops. However, a comparative study between them is missing for the same, which would fill the void existing at present. This paper addresses the same issue and a comparative study between the two controllers is performed and presented in this paper for the setpoint tracking, disturbance rejection and parametric uncertainty problems.