Self-Sensing Magnetic Bearing (Part I)

A signal processing technique is presented by which the position of a rotor supported in magnetic bearings may be deduced from the bearing current waveform. The bearing currents are presumed to be developed with a two state switching amplifier which produces a substantial high frequency switching ripple. This ripple is demodulated using a model reference parameter estimation technique which extracts the length of the bearing air gap while rejecting the influence of amplifier voltage and duty cycle variation. The performance of the estimator is evaluated both by simulation and experiment. The method is demonstrated to produce a fairly wide bandwidth sensor with acceptably low feed-through of the bearing force.