Simple PI/PID Controller Tuning Rules for FOPDT Plants with Guaranteed Closed-Loop Stability Margin

In the paper we present tuning rules for PI and PID controllers and the first order plus dead time (FOPDT) process model. The settings respect both performance and stability indices and provide a high degree of robustness for any value of the dead time parameter. As the performance index we are using the well known modulus optimum criterion, which requires that the amplitude of the closed-loop frequency response is close to one for low frequencies. This criterion produces simple tuning formulas with very favourable properties in time domain. Although optimal values of the parameters are valid for the reference tracking problem, a compensation of the disturbance lag that preserves the stability margin is proposed in the case of the disturbance rejection task.