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Rotor imbalance causes undesirable synchronous vibrations of displacement, force and torque. An active vibration control (AVC) method achieving the minimum vibration force and torque within a desired vibration displacement is presented in an active magnetic bearing (AMB) system. First, the dynamics of the AMB system with static imbalance and dynamic imbalance are introduced, and the dimensional displacement relationships of the rotation, geometric and inertial axes of the rotor are described. Demands of the AVC are analyzed, and the results indicate that the rotation axis has to be controlled to move along the center line and the inclination direction of the geometric axis and the inertial axis, respectively. Then the synchronous vibration displacement is identified with a general notch filter, and a feedforward controller is designed to control the rotation axis by providing a synchronous control current. A gain phase modifier (GPM) is proposed to achieve a precise synchronous control current and to compensate the gain and phase errors caused by the power amplifier. The GPM is incorporated into the feedforward controller to formulate two closed loops, which can adaptively tune the gain and phase of the synchronous control current, respectively. Finally, simulations and experiments have been carried out to indicate the effectiveness of the proposed approach, which can be widely used since vibrations of displacement, force and torque can be controlled simultaneously to satisfy various requirements.

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Harmonic vibrations of high-speed rotors in momentum exchange devices are primary disturbances for attitude control of spacecraft. Active magnetic bearings (AMBs), offering the ability to control the AMB-rotor dynamic behaviors, are preferred in high-precision and micro-vibration applications, such as high-solution Earth observation satellites. However, undesirable harmonic displacements, currents, and vibrations also occur in the AMB-rotor system owing to the mixed rotor imbalances and sensor runout. To compensate the rotor imbalances and to suppress the harmonic vibrations, two control methods are presented. Firstly, a four degrees-of-freedom AMB-rotor model with the static imbalance, dynamic imbalance, and the sensor runout are described. Next, a synchronous current reduction approach with a variable-phase notch feedback is proposed, so that the rotor imbalances can be identified on-line through the analysis of the synchronous displacement relationships of the geometric, inertial, and rotational axes of the rotor. Then, the identified rotor imbalances, which can be represented at two prescribed balancing planes of the rotor, are compensated by discrete add-on weights whose masses are calculated in the vector form. Finally, a repetitive control algorithm is utilized to suppress the residual harmonic vibrations. The proposed field balancing and harmonic vibration suppression strategies are verified by simulations and experiments performed on a control moment gyro test rig with a rigid AMB-rotor system. Compared with existing methods, the proposed strategies do not require trial weights or an accurate model of the AMB-rotor system. Moreover, the harmonic displacements, currents, and vibrations can be well-attenuated simultaneously.