An enhanced PID control strategy for unstable processes

An enhanced PID control strategy is proposed for unstable processes. Ultimate data sets and the process gain estimated from an improved relay feedback method are used to identify unstable processes as unstable first-order plus time-delay models. We also suggest a simple control structure including an inner feedback loop and the corresponding tuning relations to manipulate unstable processes more efficiently and systematically. The proposed control method not only guarantees the simplicity and the easiness, but also shows much better control performance than previous control methods for unstable processes.