A new view to Ziegler-Nichols step response tuning method: Analytic non-fragility justification

Recently, exploiting the centroids of stability regions (admissible regions) to be used in tuning two-parameter controllers has been considered as an approach to obtain non-fragile two-parameter controllers. Such an approach can be extended for three-dimensional stability spaces (admissible spaces) by considering the center of mass of these spaces in tuning three-parameter controllers. In this paper, the mentioned approach is used to tune PID controllers for controlling integrator plus dead-time (IPDT) and first order plus dead-time (FOPDT) processes. It is shown that the tuning method resulted from this approach is very similar to the Ziegler-Nichols step response tuning method. Consequently, this paper presents an analytic non-fragility justification for the mentioned tuning method. (C) 2012 Elsevier Ltd. All rights reserved,