A control frequency selection procedure for frequency domain autotuning methods on PID controllers

Classical PID controller tuning methods in the frequency domain have as their fundamental target the achievement of a certain phase margin or gain margin at a control frequency (w_c). In both cases the task of w_c selection is key due to the fact that the control system stability and bandwidth are fully dependent on it.. The classical methodology can produce unstable systems if w_c is not adequately selected. When a precise process model is available, it is possible to select w_c to provide a controller that better satisfies the design specifications, but this task is not easy to implement when the process dynamics are unknown. A recursive procedure for the selection of w_c that guarantees system stability and the design specifications without the availability of a process model is presented in this work.