Magnetic bearing, rotating machine mounting the same, and method for driving rotating machine

A rotating machine including a rotor and a DC brushless motor for rotary-driving said rotor, and mounting a pair of radial magnetic bearings for rotatably supporting said rotor, comprising:

• a motor control circuit for controlling said DC brushless motor;
• means, provided in said motor control circuit, for detecting a rotation position of said motor and providing a rotation position signal;
• and
• a magnetic bearing control circuit for controlling the rotor driven beyond a third order critical speed at which unbalance forces may be produced, the control circuit applying a control voltage to said magnetic bearing in relation to said rotation position signal to control any unbalance forces;
• said motor control circuit calculating a phase difference between a terminal voltage and an induced voltage based upon the terminal voltages of three-phase windings of said DC brushless motor and motor phase currents of said windings, and outputting the rotation position signal based upon said phase difference.

A rotating machine, comprising:

• a DC brushless motor having a permanent magnet rotor and three-phase windings;
• centrifugal impellers mounted on both shaft end portions of said rotor;
• a pair of radial magnetic bearings and a thrust magnetic bearing, which rotatably support said rotor and are mounted on said rotating machine;
• magnetic bearing control means for controlling said radial magnetic bearings at a third order critical speed of the rotating machine at which unbalance forces of the rotor may occur, and for controlling said thrust magnetic bearing;
• rotation position detecting means for calculating an induced voltage induced from said three-phase windings for rotating said rotor based upon a winding current of said winding and a terminal voltage of said winding;
• and for producing a 1 pulse signal per 1 rotation of said rotor based on an induced voltage of said three-phase windings as a rotational signal, wherein the induced voltage is calculated from a winding current of said windings and at a terminal voltage of said windings;
• means for inputting the rotation signal produced from said rotation position detecting means into said magnetic bearing control means.