Active Magnetic Bearing

ACTI VE M AGNETI C BEARI NGS (AM B)
A 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, machine tool operation and natural gas pipelines BASI C OPERATI ON

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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I M PROVED M ACHI NE PERFORM ANCE
CONTROL TECHNOLOGY

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Active Magnetic Bearings (AMBs) with their control system inherently offer the possibility of continuously recording bearing forces and rotor displacements. This allows on-line monitoring of critical process parameters and early detection of incipient