Bearingless motor’s radial suspension force control based on flux equivalent with virtual winding current analysis method

A bearingless motor has two sets of intercoupling stator windings, namely torque windings and sus-pension force windings. The decoupling control of the two sets is difficult and a key technology to stable operation for a bearingless motor. In this paper, a simple, reliable and accurate analysis method is put forward using the concept of flux equivalent with virtual winding currents. By this method, the suspension operation condition PB=PM±1 for bearingless motors is testified, and under the rotation condition of the motor, it is also proved that currents in suspension force windings must have the same phase sequence and frequency as torque windings to generate a stable single direction radial force in the rotor’s whole circumference. On this basis, the control strategy of realizing the suspension opera-tion of the bearingless motor is presented, and a prototype of the bearingless surface-mounted per-manent magnet synchronous motor is tested. The research results have indicated that the experimental results correspond with theoretical analysis adopting this method, a stable and reliable radial suspen-sion force can be generated, and the validity and feasibility of this control strategy are confirmed.