Choice of controller zeros

Abstract

The optimal choice of controller zeros is found to be vastly different for set-point and load-rejection responses. The positioning of the controller zeros near the slow process poles, though producing dramatic improvement in the speed of response for a set-point change, can be detrimental to load rejection. This result is used to explain the heuristics used in the Ziegler-Nichols tuning formula for proportional-integral-derivative controllers and in the positioning of controller zeros in pole-placement controllers and phase-lag compensators.