Reduction of force interference and performance improvement of a consequent-pole bearingless motor

A bearingless motor combines the functions of both magnetic suspension and torque generation together in a single motor. A consequent-pole type of bearingless motor has already been proposed. In contrast to conventional bearingless motors, it is free from the trade-off between suspension force and torque. In addition, stable suspension can be achieved without detecting the rotational angle. However, a part of the X-axis current generates undesirable force in the Y-axis. This force interference influences the performances of bearingless motors; thus, the interference should be eliminated. In this paper, the authors propose an optimal winding design of the consequent-pole bearingless motor to minimize the suspension force interference. Here, the suspension forces in the radial direction are numerically calculated using the magneto-motive force distribution of the bearingless motor, and are compared with the analytical results of finite element method. To verify the theory, static and dynamic performance tests were carried out. It was found that the improved winding configuration significantly reduced the suspension force interference by 90% compared with the previous winding configuration. It was also found that the radial shaft vibration and the power consumption were considerably decreased, by approximately 16% and 44%, respectively.

► A novel configuration of the suspension winding in a consequent-pole bearingless motor was proposed.
► Additional sub-coils were employed to reduce the MMF harmonics induced from the suspension windings.
► Significant reduction of error angle and suspension force variation was achieved when the ratio of the number of turns of the sub-coil with respect to that of the main-coil was 0.366.
► Compared with the conventional winding configuration, the proposed configuration reduced the rotor vibration by 16% and the power consumption by 44%.