Self-sensing Magnetic Bearing using the Principle of Differential Transformer

A new method of self-sensing magnetic bearing is introduced. It is intended for push-pull type magnetic bearings to have both functions of forcing actuator· and gap sensor. Each magnet has two coils; one is a bia8 coil which gives con8tant bias flux to the air gap. Another one i8 a control coil which increases one side of gap flux and degrea8es another side of gap flux. The magnetic for·ce i8 linearized 1~sing this technique. The actuating coils are also u8ed as a differential transformer type displacement sensor. The current of the bias coil is adjusted by changing the duty ratio of Pulse Width Modulated signal. The induced carrier frequency component in the control coil is detected and put into the demodulating circuit to get the rotor displacement. Two set of driving and demodulating circuits are made to detect the horizontal and vertical dispracements of the rotor. The position of the rotor is successfully controlled by the proposed method.