Fragility-Rings - A Graphic Tool for PI/PID Controllers Robustness-Fragility Analysis

The aim of the paper is to present the Delta 20 Fragility-Rings plot and its use for robustness-fragility analysis of proportional integral (PI) and proportional integral derivative (PID) controllers. Using the Delta 20 Fragility Index and the Nyquist plot it shows the areas on the L(jω) plane corresponding to robustness-fragile, robustness-non-fragile and robustness-resilient controllers providing a visual aid for evaluation of the controller robustness-fragility when its parameters are perturbed.