Design of magnetic bearings for turbo refrigerant compressors

Abstract

Magnetic bearings are oil-free bearings that are widely employed in turbo machineries such as turbo refrigerant compressors in order to eliminate lubrication systems, avoid contamination, and increase efficiency. We have developed a 145 refrigerant ton (RT)-class turbo refrigerant compressor using homopolar-type radial hybrid magnetic bearings (HMBs) and thrust magnetic bearings. The thrust magnetic bearing comprises a thrust HMB and a permanent magnet that generate downward forces to overcome high upward thrust forces of 2000 N at 21 000 rpm. A test rig and controller for the compressor with magnetic bearings were fabricated, and rotordynamics such as the unbalance response and axial displacement were investigated. Rotordynamics analyses using the finite element method predicted that the 1st bending mode is located at a high frequency with sufficient margin from the operating speeds. Further, the zero-to-peak displacement caused by the unbalanced response was sufficiently small. The rotor was stably supported with few vibrations across the entire range of the operational speeds. Our results demonstrate that the advantages of oil-free bearings can be easily exploited in turbo machineries such as turbo refrigerant compressors by adopting HMBs.

Electromagnetic Performance Analysis on the Bearingless Permanent Magnet Synchronous Motor With Halbach Magnetized Rotor

“…High-order harmonics in the air-gap magnetic field can lead to motor performance degradation, such as large torque ripple, levitation force ripple, loss and serious motor heating [24]- [28]. Furthermore, there is a tradeoff between the permanent magnet thickness (and, hence, torque density) and radial suspension force generation [29]- [31]. Thus, optimizing the magnetization of permanent magnets and reducing the harmonics in the air-gap magnetic field are of great significances to improve the performance of the BPMSM [7], [32]- [35].…”

High-Precision Roller Supported by Active Magnetic Bearings

“…Since these forces are not large, the required force of the thrust magnetic bearing was set to 100 N. The roller, rotor of the motor, roller printing section, and shaft core were designed to be integrated as one part for ease of control and complete levitation. The design parameters of the radial and axial magnetic bearings were selected based on the magnetic circuit and the magnetic force equation, and they were examined using Maxwell, a finite element electromagnetic field analysis software program [20,21]. The dimensions of the magnetic bearings were selected based on the roller used for the test, but these dimensions may need to be increased depending on the specific application and roller used because larger bearings will be required to support heavier industrial rollers.…”

Optimization and dynamic characteristics of a new type of permanent magnet bias bearing

“…1 But it is unsuitable for vibration control owing to their low stiffness and damping, especially in flexible rotor systems. 12…”

“…This bearing can reduce the number of control winding turns, the volume, weight, and power loss, and also improve the space utilization and magnetoelectric efficiency. 13 Furthermore, since it can generate a greater magnetic force than an active magnetic bearing with the same amount of current, 12 it has higher work efficiency and a broad application prospect in the fields of energy storage flywheel, 14 high-speed precision machine tool, 3 compressor, 12 gyroscope, 15 and medical treatment. 16 Tatsuya et al.…”