Journal of Process Control, Vol.22, No.6, 1063-1078, 2012
Revisiting the Magnitude Optimum criterion for robust tuning of PID type-I control loops
The revision of the conventional Magnitude Optimum design criterion for tuning the PID type controller's parameters reveals three fundamental drawbacks. These drawbacks restrict the PID controller's optimal tuning in terms of robustness and disturbance rejection at the output of the controlled process. Specifically (1) the conventional PID tuning via the Magnitude Optimum criterion restricts the controller's zeros to be tuned only with real values, (2) for determining the PID controller's zeros, exact pole-zero cancellation has to be achieved between the process's poles and the controller's zeros and (3) the conventional design procedure via the Magnitude Optimum criterion has been tested only to a limited class of simple process models. To overcome the aforementioned drawbacks a revised PID type control law is proposed in this work. For the development of the control law a general transfer function of the process model is employed in the frequency domain. The final control law consists of analytical expressions that involve all modelled process parameters. The resulting control law can be applied directly to any linear Single Input Single Output stable process regardless of its complexity. For evaluating the proposed theory, an extensive simulation test batch between the conventional and the revised PID tuning is performed for various benchmark processes. Throughout this evaluation, the validity of several literature comments related to the Magnitude Optimum criterion is discussed. Finally, it is shown that the performance of the proposed control law compared to the conventional PID design procedure achieves satisfactory results both in the time and the frequency domain, in terms of robustness and disturbance rejection. (C) 2012 Elsevier Ltd. All rights reserved.
Keywords:PID control;Design;Tuning;Optimization;Process control;Control engineering;Industrial control