In this contribution, fractional-order controllers of the type PD and PI are applied to a class of irrational transfer function models that appear in large-scale systems, such as networks of mechanical/electrical elements and distributed parameter systems. More precisely, by considering the fractional-order controller k p + k s in the Laplace domain with −1 ≤ ≤ 1, a stability analysis in the parameter-space (k p , k ,) is presented. Furthermore, as a way to measure the controller robustness, the controller's fragility analysis using the parameter-space (k p , k ,) is derived. Finally, several applications that demonstrate the utility of our results are included.