Robust tuning of 2DoF five-parameter PID controllers for inverse response controlled processes

The aim of this paper is to present a robust tuning method for two-degree-of-freedom (2DoF) proportional integral derivative controllers with filter (PID2F) for inverse response controlled processes modeled by a second-order plus a right-half plane zero (SOPRHPZ) transfer function. This is based on the use of a model-reference optimization procedure with servo and regulatory closed-loop transfer functions targets. The robustness of the control system is also taken into account. Model right-half plane zero relative positions in the range from 0.10 to 3.0 are analyzed, and it is found that the zero position constrains the achievable control system robustness level. The designer is allowed to deal with the performance/robustness trade-off of the closed-loop control system by specifying the desired robustness by means of selecting between two levels for the control system maximum sensitivity (M-S(t) is an element of {2.0, 1.6}). In addition, a smooth servo/regulatory performance combination is obtained. A comparative analysis shows that, for inverse response processes, PID controllers allow to improve control system performance while achieving the same robustness of PI controllers. Small controlled variable undershoots and smooth controller output signal are distinctive characteristics of the proposed model reference robust tuning method. (c) 2013 Elsevier Ltd. All rights reserved.