Dynamic Modeling and Experimental Validations of Passing Through Critical Speeds by High Acceleration in One-Axis Actively Positioned Bearingless Motors

Abstract

One-axis actively positioned bearingless motors have been studied for industry applications such as pumps and cooling fans. In particular, single-drive bearingless motors have a great advantage of simple regulation system. Only one three-phase inverter is required for generating torque and active axial force by q- and d-axis currents. On the other hand, radial and tilting motions of the rotor shaft are passively stabilized by passive magnetic bearings. These passive force and torque are just spring force. Inherently, damping force and torque are not generated. As a result, the rotor vibrations in the radial and tilting directions are considerable high at resonant frequencies. In this paper, a valuable strategy is proposed to pass through the critical speed by high angular acceleration with a fan blade. The dynamic modeling of the radial and tilting motions is proposed and simulated to find out the possibility to pass through the critical speed. In the experiment, it is demonstrated that a prototype machine of the one-axis actively positioned bearingless motor can successfully pass through the critical speed without touch-down.