Generalized robust stability regions for fractional PID controllers

Fractional-order PID controller (FOPID) design and implementation is one of emerging research areas. This paper presents a method for computing generalized robust stability regions in controller parameter plane. The method can cope with arbitrary linear process model of integer or fractional order. It allows to fulfill essential frequency domain design specifications, namely gain and phase margins, closed loop bandwidth, etc. Further, it can operate simultaneously with number of processes hence can work with uncertainty given e.g. by model set or by parameter intervals. Moreover, the regions can be computed even for selected filter in derivative part of the FOPID controller. The method described is partly available in the interactive Java applet freely accessible at www.pidlab.com. The illustrative example demonstrates that FOPID controller can fulfill stricter design specifications compared to traditional PID.