Active Magnetic Bearing

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magnetic bearing is a bearing which supports a load using magnetic levitation. Magnetic bearings support
moving machinery without physical contact, for example,they can levitate a rotating shaft and permit relative
motion without friction or wear. In active magnetic bearings (AMB) a stable equilibrium is achieved by
means of one or more control loops. The use of control loop for maintaining the gap between the shaft and
bearing differentiate the active magnetic bearings (AMB) from passive ones. They are in service in such industrial applications as electric power generation, petroleum refining,

The typical AMB system diagram is illustrated in above figure. Besides the controller, the general control system also includes the sensor, A/D and D/A conversion and power amplifier. tected by the position
sensors and converted into signals of standard voltage.

Then compared with the setting value, the error signal enters the controller. After A/D conversion, the controller processes this digital signal according to a given regulating rule (control arithmetic) and generates a signal of current setting. After D/A conversion, this current signal enters the power amplifier, whose function is to maintain the current value in the electric magnet winding at the current level set by the controller. Therefore, if the rotor leaves its center position, the control system will change the electromagnet current in order to change its attraction force and, respectively, draws the rotor back to its balance position.

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