Design of a fractional - Order controller for the setpoint ramp tracking problem

It is well known that a classical PI controller cannot accurately follow a ramp setpoint. A real world situation which shows this behavior could be a system composed of a direct current motor whose input setpoint is an acceleration/deceleration ramp. In this paper, we propose the design of a fractional PI^λ controller, with a fractional-order parameter λ > 1, as a well suited approach to solve this problem. The design methodology is frequency-based, which allows finding the corresponding fractional controller parameters in order to guarantee stability, robustness and zero steady-state error.