Sensorless control of three-pole active magnetic bearings using saliency-tracking based methods

This paper proposes the use of saliency-tracking based techniques for sensorless control of three-pole active magnetic bearings. Changes in the air gap resulting from misalignment between stator and rotor axis result in an unbalance in the stator electromagnetic circuit. Injection of a high frequency signal voltage, which is superimposed to the fundamental excitation providing active control, allows measurement of the unbalance, from which an estimation of the rotor position can be obtained. Two different signals are studied for this purpose: 1) negative sequence high frequency current and 2) zero sequence high frequency voltage. The paper develops analytical models of three-pole magnetic bearings, both for control and for position estimation which are evaluated through experimental analysis.