Other Robust Control Techniques

In Chapter 4 we introduced the idea of robust control and basic controllers to fulfil this characteristic. In the frequency domain, we can say that Bode’s ideal loop transfer function in Section 2.3.4 is the reference model to achieve a robust performance. The purpose is to obtain an open-loop characteristic similar to that of this reference model, ensuring in this way a constant phase margin around a frequency of interest and, therefore, a constant overshoot of the time responses to plant gain variations.

This idea was developed extensively by Oustaloup [50], who studied the fractional-order algorithms for the control of dynamic systems and demonstrated the superior performance of the CRONE (Commande Robuste d’Ordre Non Entier, meaning Non-integer-order Robust Control) method over the PID controller. There are three generations of CRONE controllers [51], and we will briefly review all of them in this chapter.