Radial Force Control of Bearingless Motor with Flux Equivalent Air-Gap Virtual Winding Current

A bearingless motor has two kinds of coupling windings, driving windings and bearing windings. The decoupling control for two sets of winding currents is difficult problem and key technology to stable operation of bearingless motors. A simple, reliable and accurate analyzing method for bearingless motors is put forward using the concept of flux equivalent air-gap virtual winding currents. Adopting this method, the operation condition PB=PM±1 for bearingless motor is quoted, and the necessary satisfied condition of generating a stable radial force in single direction on whole rotor’s circumference is derived. On this basis, the control strategy of realizing bearingless motor’s suspension operation is brought forward, and a prototype of bearingless surface-mounted permanent magnet synchronous motor is built and tested. The experiment results have shown that theory analysis of this strategy is accurate, a stable and reliable radial suspension force is obtained, and the validity and feasibility of this strategy is confirmed.