Andrew Kenny

Single Plane Radial, Magnetic Bearings Biased With Poles Containing Permanent Magnets

Magnetic bearings biased with permanent magnets have lower coil resistance power losses, and the magnets can also be used to help support a constant side load. In this paper, the performance of a single plane radial magnetic bearing biased with permanent magnets in several poles is presented. Although it has less load capacity and stiffness than a similarly sized electrically biased single plane heteropolar bearing, it does not require bias current, and its ratio of load capacity to coil resistance power loss is significantly better. This type of permanent magnet bearing has only a single plane of poles. It can be distinguished from the homopolar bearing type which has two planes and which can also be biased with permanent magnets. Magnetic circuit models for the novel single plane bearing are presented along with verification by finite element models. Equations for the key performance parameters of load capacity, stiffness, coil inductance and resistive power loss are also presented.

Comparison of the dynamic response of radial and tangential magnetic flux thrust bearings

Theoretical predictions were made for the dynamic performance of a tangential flux magnetic thrust bearing. A prototype bearing was built with the stators and rotors made from tape wound strip. The performance of this bearing was measured and compared to the theoretical predictions and also to the performance of a radial flux thrust bearing. Tangential flux bearings are intrinsically amenable to construction from tape wound cores. Tape wound cores come in high saturation alloys like supermenduer which can give the bearing a high force to size ratio. The thin tape laminates give the bearing a broad frequency bandwidth. By comparison the paper shows that it is difficult to make a laminated rotor magnetically efficient for radial flux bearings. A test rig is described that was built to measure the performance of the tangential flux bearing. A power amplifier with current feedback provides DC and harmonic currents to the coils. A load cell was built into the test rig to measure the axial thrust, an inductive/Hall sensor was included to measure the coil current, and a Hall probe was used to measure the gap flux.

Redesign of Glenn research center D1 flywheel module

Glenn Research Center has completed the redesign of the D1 flywheel module. The redesign includes a new rotor with a composite rim, motor/generator, touchdown bearings, sensors, and a magnetic actuator. The purpose of the relatively low cost module upgrade is to enable it to continuously operate throughout its speed range of 0-60,000 RPM. The module will be used as part of a combined attitude control and bus regulation experiment.

Fail Safe, High Temperature Magnetic Bearings

This paper contributes to the magnetic bearing literature in two distinct areas: high temperature and redundant actuation. Design considerations and test results are given for the first published combined 538°C (1000°F)-high speed rotating test performance of a magnetic bearing. Secondly, a significant extension of the flux isolation based, redundant actuator control algorithm is proposed to eliminate the prior deficiency of changing position stiffness after failure. The benefit of the novel extension was not experimentally demonstrated due to a high active stiffness requirement. In addition, test results are given for actuator failure tests at 399°C (750°F), 12,500rpm. Finally, simulation results are presented confirming the experimental data and validating the redundant control algorithm.Copyright

MAGNETIC BEARING DEVELOPMENT FOR SUPPORT OF SATELLITE FLYWHEELS

The use of magnetic bearings (MB) for support of space based flywheels can provide significant improvement in efficiency due to reduction in drag torque. A NASA supported program directed through the Texas A&M Center for Space Power has been formed to advance the technology of MB’s for satellite flywheel applications. The five areas of the program are: (a) Magnetic Field Simulation, (b) MB controller Development, (c) Electromechanical Rotordynamics Modeling, (d) Testing and (e) Technology Exchange. Planned innovations in these tasks include eddy current drag torque and power loss determination including moving conductor effects, digital (DSP) based control for high speed operation, MATLAB-based coupled flexible rotor/controller/actuator electromechanical model with fuzzy logic nonlinear control, and ultra high speed>100 krpm measurement of drag torque. The paper examines these areas and provides an overview of the project.

Flywheel magnetic suspension developments

The authors provide an overview of many areas of the flywheel magnetic suspension (MS) R&D being performed at the Texas A&M Vibration Control and Electromechanics Lab (TAMU-VCEL). This includes system response prediction, actuator optimization and redundancy, controller realizations and stages, sensor enhancements and backup bearing reliability.

Fail Safe, High Temperature Magnetic Bearing for High Efficiency Gas Turbine Engine Applications

This paper contributes to the magnetic bearing literature in two distinct areas: high temperature and redundant actuation. Design considerations test results are given for the first published combined 538°C (1000°F)-high speed rotating test performance of a magnetic bearing. Secondly, a significant extension of the flux isolation based, redundant actuator control algorithm is proposed to eliminate the prior deficiency of changing position stiffness after failure.Copyright

High Temperature, Permanent Magnet Biased, Fault Tolerant, Homopolar Magnetic Bearing Development

This paper summarizes the development of a magnetic bearing designed to operate at 1,000F. A novel feature of this high temperature magnetic bearing is its homopolar construction which incorporates state of the art high temperature, 1,000F, permanent magnets. A second feature is its fault tolerance capability which provides the desired control forces with over one-half of the coils failed. The construction and design methodology of the bearing is outlined and test results are shown. The agreement between a 3D finite element, magnetic field based prediction for force is shown to be in good agreement with predictions at room and high temperature. A 5 axis test rig will be complete soon to provide a means to test the magnetic bearings at high temperature and speed.

Theory and Test Correlation for Laminate Stacking Factor Effect on Homopolar Bearing Stiffness

The effect of the laminate stacking factor on homopolar magnetic bearing performance is examined. Stacked laminates are used on the bearing rotor and in the stator. These laminate stacks have anisotropic permeability. Equations for the effect of the stacking factor on homopolar bearing position stiffness are derived. Numerical results are calculated and compared to measurements. These results provide an answer for the common discrepancy between test and theory for homopolar magnetic bearing position stiffnesses.

An integrated magnetic circuit model and finite element model approach to magnetic bearing design

A code for designing magnetic bearings is described. The code generates curves from magnetic circuit equations relating important bearing performance parameters. Bearing parameters selected from the curves by a designer to meet the requirements of a particular application are input directly by the code into a three dimensional finite element analysis preprocessor. This means that a three dimensional computer model of the bearing being developed is immediately available for viewing. The finite element model solution can be used to show areas of magnetic saturation and make more accurate predictions of the bearing load capacity, current stiffness, position stiffness, and inductance than the magnetic circuit equations did at the start of the design process. In summary the code combines one dimensional and three dimensional modeling methods for designing magnetic bearings.