Self-sensing magnetic bearing using the differential transformer principle

Abstract

A new method of self-sensing magnetic bearings is introduced. Magnetic bearings are intended to function both as a forcing actuator and a gap sensor. The magnet has two coils. One is a bias coil which provides constant bias flux to the air gaps. The other is a control coil which increases one gap flux and degreases the other gap flux. The magnetic force is linearized to the control coil current using this technique. The coils are also used as a differential transformer-type displacement sensor. The current of the bias coil is adjusted by changing the dusy ratio of the pulse-width-modulated signal. The induced carrier frequency component in the control coil is detected and put into the demodulating circuit to obtain the rotor displacement. Two sets of driving and demodulating circuits are used to detect the horizontal and vertical displacements of the rotor. The position of the rotor is controlled using the proposed method. The rotor can run up to 12 000 rpm using the self-sensing magnetic bearings.