A magnetic suspension control strategy by 3-phase inverters in bearingless brushless DC motors

This paper presents a new magnetic suspension control strategy for the bearingless brushless DC motor. In the proposed control strategy, general-purpose 3-phase inverters are used to control the rotor radial position; in conventional control schemes, 2-phase inverters are usually used. By using 3-phase inverters, the number of inverters and controllers can be decreased. In addition, the suspension force is increased when compared using a motor with the same dimensions and current rating because three suspension windings are excited during the same period of operation. This causes an unbalance in air-gap flux density which, in turn, produces the suspension force. In this paper, a new suspension winding arrangement on the stator core is described and the principle of suspension force generation for the bearingless brushless DC motor is explained. The new suspension control method, using general-purpose 3-phase inverters, is then introduced. The suspension force is computed using the Finite Element Method (FEM) and a suitable machine model. The increase in the suspension force is verified by the computed results. The proposed magnetic suspension control method is quite reasonable for the bearingless brushless DC motor.