A novel middle-point current-injection type bearingless motor for vibration suppression

With the developments of power electronics technology and increments of high rotational speed of motors, a critical speed is one of the problems in high speed motors. Flexible shaft bending is reported to be suppressed by proper generation of magnetic force of bearingless motors. In general bearingless motors, motor windings and suppression windings are separately enclosed in the stator slot. For only vibration suppression, however, suppression windings are not used expect the critical speed. In this paper, a novel middle-point current-injection type bearingless motor is proposed. This motor has only motor windings. Only middle point terminals are needed to inject currents to generate suppression magnetic forces. Principles, basic structure and effectiveness of the proposed bearingless motor are presented with a comparison of conventional vibration bearingless motors. Test results of a prototype machine are also presented.