A robust PID tuning method for unstable FOPTD process

In this paper, a robust PID controller tuning method based on process model for unstable first order plus time delay (FOPTD) system is proposed. The proposed method is derived under H∞ performance index. The unified PID controller parameters are induced through McLaughlin series expansion and the Pade approximation. The closed-loop transfer function with the proposed PID controller gives an accurate set point filter and the controller setting has a robust performance under uncertainty in the process model parameters. Closed-loop responses tuned by the proposed method are compared with existing methods. The simulation results show that the presented method gives better performances.