A simple auto-tuner in frequency domain

A new frequency domain controller design method is proposed based on process frequency response data identified through relay feedback test. Multiple points on Nyquist curve are used. A desired closed-loop model is specified and controller parameters are computed using least squares method. The controller is equal to PI or PID controller when it is of low order. The procedures are tested against linear systems with and without noise. Compared with most methods, which use only one point on Nyquist curve, this method has obvious superiority.