Current injection solutions for active suspension in bearingless motors

Traditionally, active magnetic levitation systems in rotor applications comprise separate motor for torque production, two or more radial active magnetic bearings (AMBs) and one axial AMB. Such an arrangement produces long rotors. Resulting AMB-rotor systems are often supercritical making the levitation control challenging. The centralization of the torque and force producing actuators shortens the rotor and allows for better control of unbalance magnetic pull from the rotor eccentricity. However, traditional bearingless motors employ separate windings for torque and for force production using a single actuator. This in turn lengthens the motor flux paths, increases the stator diameters, and reduces efficiency. This work studies performance and limitations of three current injection methods applied for active levitation control where the same winding is used for torque and for levitation force production. The FEM time stepping simulation results are presented and quantitative comparison is given. The case study bearingless motor system is of considerable power and high speed ratings. The use of the single winding system with the current injection control is suitable for the high-power and high-speed bearingless motor applications.