Compensation control of suspension force for LS-BLPMSM

To overcome the difficulty in start-up of bearingless permanent magnet synchronous motor (BLPMSM), a novel structure of line-starting BLPMSM (LS-BLPMSM) is presented in this study, which has the ability of self-starting. First, the operation principle of the LS-BLPMSM is expounded and the suspension operation condition is deduced. Since two sets of windings are arranged in the stator of bearingless motor, different pole-pair cooperation between two sets of windings cause breaking or driving torque, and the theory of pole-pair cooperation is analysed. Second, the interference of squirrel-cage on suspension force magnetic field is studied based on the T-type equivalent circuit model of the equivalent induction motor formed by the suspension force windings and squirrel-cage bars, and a suspension force compensation strategy is presented. Finally, an experimental prototype with 2-pole-pair torque windings and 1-pole-pair suspension force windings is tested under different working conditions with the proposed control strategy. The rotation speed and the displacements in x and y axes are provided. The simulation and experimental results have shown that the motor has good rotation and suspension performance, and the validity and feasibility of this control strategy are confirmed.