Observers for sensorless control of industrial magnetic bearings

A nonlinear state estimator for industrial magnetic bearings is presented. The estimator uses voltage measurements, current measurements, and a magnetic flux model to estimate the bearing air gap dimension. The accuracy of the proposed state estimator is model dependent, but appears to be much less sensitive than linear observers that have been used in this application. Also presented in the paper is a description of the test hardware system, and a brief summary of other nonlinear state estimation methods that have been examined. The work is motivated by the desire to eliminate the proximity probes that are a significant factor of the overall system cost and reliability. In systems where probes must be used, the state estimator can still be used to offer a measure of feedback redundancy that improves overall system reliability.