Position Regulator with Variable Cut-Off Frequency Mechanism for Hybrid-Type Stepper Motors

This study addresses the position-tracking problem for hybrid-type stepper motors in the rotational $d-q$ coordinate system. The proposed controller aims to govern position behavior with the desired low-pass filter from the reference (input) to the position (output). A perturbed form of machine dynamics is adopted to handle both parameter variations and load uncertainties and the control law has two main advantages. First, the real-time auto-tuner increases the closed-loop cut-off frequency during transient periods and restores it to its nominal value as it approaches the steady state. Second, disturbance observers improve the closed-loop robustness against high-frequency disturbances and ensure the offset-free property without additional integral actions. The experimental results validate the practical advantages from the proposed controller with a 10-W prototype stepper motor control system.