Improved Performance with PID Filter Controllers for Unstable Processes Involving Time Delays

Using the direct synthesis method, a proportional-integral-derivative (PID) controller in series with a lead- lag filter is designed for control of the open-loop unstable processes with time delay. Pade´s 2^nd order approximation for the time delay term is considered for obtaining the controller structures of PID. Study of the performance of the designed controllers has been carried out on various unstable processes. Set-point weighting is considered to reduce the overshoot. The proposed scheme consists of only one tuning parameter, and systematic guidelines are provided for selection of the tuning parameter based on the peak value of the sensitivity function. Robustness analysis has been carried out based on small gain theorem. Nominal and robust control performances are achieved with the proposed method and improved closed loop performances are obtained when compared to the recently reported methods in the literature.