Simulation Analysis of Influence of Third Harmonic Noise on Movement of Magnetically Suspended Rotor

The flywheel rotor supported by magnetic bearing with permanent magnet bias is to be used in single gimbal control momentum gyro (SGCMG), since magnetic bearing with permanent magnet bias has unique advantages of non-contact, elimination of lubrication, low power loss, automatic balancing capability, and controllability of bearing dynamics characteristics comparing with conventional ball bearings for attitude control. The flywheel rotor orbit supported by magnetic bearing in the SGCMG was analyzed and tested, and a mathematic model of third harmonic was proposed. Because of eccentricities and disturbances, a approximately circular shaped orbit was expected, but the third harmonic noise distorted rotor orbit, the approximately rectangular and diamond shaped orbit from different radial magnetic were observed, which demanded unnecessary voltage and current outputs from the control system. The reasons to cause harmonic noise were given.