Self-sensing magnetic bearings using parameter estimation

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 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 sensor with bandwidth of at least 1 kHz and acceptably low feed-through of the bearing force.