Active Balancing of a High Speed Rotor in Magnetic Bearings

This paper describes the application of an open loop control technique for the attenuation of unbalance response in a high speed rotor. The test rig is a mock up of a dual wheel compressor with an operating speed range of 30,000 to 70,000 rpm. The rotor has a third critical speed (first bending mode) at 24,050 rpm which is lightly damped. Excessive rotor synchronous response occurs during run-up at this speed and intermittently causes loss of support. An open loop control is used to introduce a rotating magnetic force to balance the rotor and reduce rotor synchronous response at this speed. With this control, the third critical speed is essentially canceled. Also demonstrated is the use of the open loop control to attenuate housing structure vibrations when the rotor is operating at one of the housing’s natural frequencies, 42,300 rpm.