Two degrees of freedom PID auto-tuning controller with supervisor function

A proportional-integral-derivative (PID) autotuning controller based on the two-degree-of-freedom PID autotuning method is developed. The method requires no prior knowledge of the process-order or deadtime and is effective even if the process is a nonminimum-phase system. A practical autotuning system with supervisory function (PASS) is developed which has following three basic parts: (1) a frequency-domain-based autotuning function; (2) a setup function based on the step response method that provides initial PID parameters, a sample period, and an amplitude of test signal for the tuning function; and (3) a supervisor function which observes and judges the state of the control system and instructs the tuning function to start or decrease control system gain when an unsafe system state is detected. The PASS system is applied as a package in the TOSDIC 215D one-loop controller.