PID tuning for unstable processes with sensitivity specification

PID control is widely used to control stable processes, however its application to unstable processes is less common. In the paper, the formulas are derived to tune PID controller for unstable processes with time delay to meet sensitivity specification. It adopts two feedback loop design technique, and obtains a tuning method for PID controller with setpoint weighting which can overcome structural limitation of the typical PID controller for unstable processes. With the proposed PID tuning method, a loop transfer function with desired sensitivity specification is obtained, which guarantees both robustness and performance. Simulation examples are given to show good performance of the proposed tuning method.