Optimal design of a multi-phase double-stator bearingless brushless direct current motor

Abstract

To overcome the serious coupling between torque and levitation forces, increase the output torque, and improve fault tolerance performance for the bearingless brushless direct current motor, a multi-phase double-stator bearingless brushless direct current motor is designed in this article. First, basic structure and operation principle of the bearingless brushless direct current motor are analyzed in detail. The proposed motor is composed of inner and outer stator, the levitation force windings on the inner stator realize suspending function, while the torque windings on the outer stator realize the rotating function of the rotor. Second, the mathematical model of the levitation forces is deduced, which indicates that the levitation forces are independent of the torque. Finally, based on the finite element analysis method, a 20-slot/18-pole five-phase double-stator bearingless brushless direct current motor model is established. The optimizations are carried for its main parameters to minimize the cogging torque and improve the motor performance. The simulation results confirm that the proposed bearingless brushless direct current motor has the superior decoupling characteristics compared with the double-winding bearingless brushless direct current motor. Meanwhile, the motor has the higher output torque and the better fault tolerance performance. According to the simulation model, a prototype is made and measured to validate the analyses. Since there is little relationship between the torque and levitation forces, they can be designed independently and controlled with high precision easily.