Design of fractional-order PD Controller for Unstable and Integrating Systems

This paper presents a new strategy for designing of Fractional-order proportional derivative (FOPD) controller for unstable and integrating systems. The open loop transfer function is compared with the bode's ideal transfer function whose closed loop response is always stable and comparison is done in frequency domain i.e. to match magnitude and phase response of the system with the standard Fractional-order (FO) transfer function. The slope of the Nyquist plot of the standard FO transfer function is also compared with the given open loop system with FOPD controller. The properly tuned FOPD controller's results are better than its integer order PD and PID counter-part.