Synthesis of fractional-order PI controllers and fractional-order filters for industrial electrical drives

This paper introduces an electrical drives control architecture combining a fractional-order controller and a set-point pre-filter. The former is based on a fractional-order proportional-integral (PI) unit, with a non-integer order integral action, while the latter can be of integer or non-integer type. To satisfy robustness and dynamic performance specifications, the feedback controller is designed by a loop-shaping technique in the frequency domain. In particular, optimality of the feedback system is pursued to achieve input-output tracking. The set-point pre-filter is designed by a dynamic inversion technique minimizing the difference between the ideal synthesized command signal (i.e. a smooth monotonic response) and the pre-filter step response. Experimental tests validate the methodology and compare the performance of the proposed architecture with well-established control schemes that employ the classical PI-based symmetrical optimum method with a smoothing pre-filter.