Effect of Control Algorithms on Magnetic Journal Bearing Properties

[+] Author and Article Information
R. R. Humphris, R. D. Kelm, D. W. Lewis, P. E. Allaire

Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, VA 22901

J. Eng. Gas Turbines Power 108(4), 624-632 (Oct 01, 1986) (9 pages) doi:10.1115/1.3239957 History: Received January 10, 1986; Online October 15, 2009


Magnetic journal bearings are coming into increasing use in industry today. They are primarily used to replace either rolling element or fluid film bearings in rotating machinery. The major advantages are elimination of oil systems and associated seals, expected very long life, very low power losses, and great potential for vibration reduction. Disadvantages include lack of field experience, unknown reliability over a long time, high cost (so far primarily due to the small quantity being made for a given application), and advanced automatic control design required. This paper discusses the design of a magnetic journal bearing with four electromagnets arranged radially around a shaft to fully support a rotor. Each electromagnetic is connected to a controlling electronics circuit which regulates the current to the magnet. For the measurements presented here, only the top magnet was tested and the shaft was not rotating. Thus a single control algorithm was isolated from other effects. This paper compares two control algorithms with differing circuit band widths of 1.2 kHz and 50 kHz. The wider bandwidth algorithm produced approximately a sixfold increase in magnetic bearing stiffness and a much greater stable operating region compared to the lower bandwidth algorithm. Overall, the calculated effective stiffness and damping coefficients were within 20 to 30 percent of the measured values.

Copyright © 1986 by ASME
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