Enhancing disturbance rejection performance for the magnitude-optimum-tuned PI controller

The Magnitude Optimum (MO) tuning method for PI and PID controllers, applied on stable and non-oscillating plants, usually gives fast tracking responses and offers very good process output disturbance-rejection performance, even if the process contains significant dead time. On the other hand, in the cases of plant-input disturbances slow responses may be obtained. The paper deals with this problem for the PI controller case. Enhancing the disturbance-rejection performance is achieved by means of additional filter designed so that the stability margin properties of the MO tuning are preserved.