A Levitation Control Strategy Based on Online Corrected Levitation-Force Sharing Function for 12/4 BSRM

The torque and levitation force in a single-winding bearingless switched reluctance motor (BSRM) are generally generated by the windings of each phase simultaneously. However, the commutation of the BSRM results in significant decrease and ripple of the levitation force due to the lower current rising rate at high speeds, requiring advancements in the existing levitation control to ensure stable levitation. To compensate for this deficiency, this article reallocates the conduction intervals of the levitation force while ensuring torque performance. By extending the conduction period, the levitation force for each phase is allocated based on the proposed levitation-force sharing function (LFSF). In addition, an online correction algorithm is proposed to adjust the reference levitation force of the previous phase, which can smooth the levitation force at the beginning of next-phase conduction. The improved LFSF exhibits better adaptability to speed variation. Finally, the feasibility of the proposed strategy is verified on a test rig of 12/4 BSRM.