Magnetic-Flux Balance Control to Eliminate Voltage Deviation on Split Phase Capacitor for 4-DOF Bearingless SRM

The four degrees of freedom (4-DOF) 12/4 bearingless switched reluctance motor (BSRM) generally requires 48 power devices, 24 current sensors, and 2 microchips to simultaneously achieve rotation and levitation. To reduce the number of power devices and sensors used in the system, a split-phase converter and a multiplexed-sensor method are employed. However, significant voltage deviation occurs on the two split-phase capacitors due to the inconsistent levitation currents, which deteriorates the levitation performance. Therefore, this paper proposes a magnetic-flux balance control (MFBC) method to solve this problem. The method constrains the total current of all windings in each phase to form a balanced bias magnetic flux. By balancing the discharge depth of the two split-phase capacitors, voltage deviation is eliminated and stable levitation operation is ensured. Moreover, an improved multiplexed-sensor method is developed to enhance levitation stability at high speeds. Finally, the demonstrated performance of the proposed scheme is verified on a test rig of a 4-DOF 12/4 BSRM-type magnetic levitation system.