Active vibration control of rotor imbalance in active magnetic bearing systems

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.