Combined Fractional Feedback-Feedforward Controller Design for Electrical Drives

This paper focuses on a design method for feedback and feedforward fractional order control of electromechanical systems. The architecture combines a fractional order proportional-integral controller and a set-point filter. First, the open-loop frequency response is shaped to obtain robustness specifications and to approximate an optimal feedback system in the input-output tracking, at least in a specified bandwidth. Secondly, the set-point filter is designed by dynamic inversion to minimize the difference between the ideal synthesized command signal, that provides a smooth monotonic response, and the filter step response. Tests on the position/speed control of DC and permanent magnet synchronous motors show the effectiveness of the methodology in comparison with PI controller tuned by symmetrical optimum and coupled with a smoothing filter.