Cascade Observer-Based Disturbance Estimation and Suppression for the Suspended Rotor in Maglev Hydrogen Recirculation Pump

Magnetic bearing hydrogen recirculation pumps enable high-speed, wear-free operation but are sensitive to flow-induced disturbances. This study proposes a cascade-structured disturbance observer (CDOB) that fuses rotor displacement and bearing current signals to achieve robust disturbance estimation under model uncertainties, with low-pass filtering to ensure stability. The proposed method is validated through simulations and repeated experiments at multiple axial positions. Based on raw displacement signals, the CDOB reduces the average peak-to-peak axial displacement by approximately 35% compared with a traditional disturbance observer. Under axial offset conditions of −100 μm and +100 μm, the CDOB consistently achieves average displacement reductions of approximately 23% and 24%, respectively, demonstrating consistent disturbance suppression and robustness across repeated tests. These results indicate that the CDOB provides an effective and practical solution for disturbance suppression in magnetic bearing systems.