Modified PI Controller for Stiction Compensation

Stiction is a well known problem of the process performance. Compensate its effect is essential, because most of sticky valves cannot be replaced and they remain working for months or years. The scope of this work is to propose a novel methodology to compensate stiction effects, through the modification of the controller (PI) block in the control loop. The proposed approach is based on the two moves method, however it allows to specify closed loop performances faster than open loop and reject load disturbances efficiently. We assume here that a small offset between process variable and setpoint is accepted, what decreases significantly the valve traveling, comparing with available approaches. The method is described for both setpoint tracking and disturbance rejection. The efficacy is corroborated by a case study, considering setpoint changes and disturbance rejection.