An Integrated Modified Smith Predictor with PID Controller for Integrator Plus Deadtime Processes

"Smith predictor", as proposed by Smith in the 1950s, is used as a dead-time compensating tool in chemical process industries. But its applicability was limited because of its poor performance in load-change cases. In the present work, a novel control scheme is proposed by integrating Smith predictor (SP) and a proportional-integral-derivative (PID) controller and is named as SPPID. By introducing a tuning parameter (Ksp) in the control law, to switch between SP and PID mode, a modified SPPID is synthesized (namely MSP-PID) to counteract the offset. Set-point changes and load disturbances are studied for integrator and dead-time processes under this control strategy. The validity of the control scheme in the presence of model mismatch is also studied.