Development of one-axis active controlled bearingless motor working at extremely low temperature

Abstract

This paper discusses the manufactured one-axis controlled bearingless motor and its experimental results in liquid nitrogen. The bearingless motor is an axial type bearingless motor. It generates a force in the axial direction to control the axial displacement of the rotor and a rotation torque for the motor. The axial displacement is actively controlled using a PID controller, and the rotation speed of the rotor is also actively controlled using a PI controller. The other degrees of freedom are passively supported by the repulsive force of the permanent magnet bearings. The axial type bearingless motor consists of a stator, a rotor, three displacement sensors, and three Hall sensors. Displacement sensors and Hall sensors are used to measure the axial displacement and rotation angle of the rotor. The stator has six salient poles, and the rotor has four poles with four permanent magnets. The air gap between the stator and rotor is 1.5 mm at the center position. The axial type bearingless motor and permanent magnet bearings are set in liquid nitrogen in the experiment. The experimental results show an impulse response at 0 rpm, the relationship between the displacement of the rotor and rotation speed, the relationship between the driving current and the rotation speeds, and a step response from 500 rpm to 1,000 rpm in the rotation speed. From experimental results, it is confirmed the stable levitation and rotation of the bearingless motor at liquid nitrogen temperature.