FUNCTION BLOCK IMPLEMENTATION OF PROPORTIONAL-INTEGRAL-DERIVATIVE GAIN SCHEDULING ON DISTRIBUTED CONTROL SYSTEM MODELED CENTUM VP

This article presents an engineering technique to practically implement a gain scheduling for a proportional-integral-derivative (PID) control loop, which consists of software function blocks executing in an industrial distributed control system (DCS) modeled CENTUM VP. The main feature of the proposed technique is to use a standard graphical language of function block diagram, which supports simplicity and reality for industrial applications. The implementation of the PID loop with gain scheduling by using regulatory control blocks and calculation blocks is described. The proportional band, integral time, and derivative time of the PID control block are continuously adjusted with a scheduling variable, which is selectively set to be the manipulated output value, setpoint value, process variable, control deviation value, or other measured variables. Based on a virtual test function of the DCS, simulation results of the PID loops with/without gain scheduling to control a simulated first-order plus time-delay process are included to demonstrate the performance of the implemented gain scheduler. Compared with the PID block with constant tuning parameters, the PID block with varying tuning parameters can provide better stability and performance of setpoint tracking.