Automatic tuning algorithm of the PID controller using two Nyquist points identification

This paper deals with an advanced automatic tuning algorithm of the PID controller using two Nyquist points identification. The critical point on the Nyquist plot and its neighboring point are identified from the modified relay feedback experiment and used to make the formulas to determine the parameters of the PID controller. The formulas are derived from the dominant poles approximation and placement method. We can consider the time domain response of the process with damping ratio (ζ) as a design specification