Abstract

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.

Highlights

  • High pointing stability is required in high-resolution Earth observation satellites, which are equipped with many sensitive payloads [1]

  • To further reduce the harmonic currents induced by the sensor runout, a repetitive control method is proposed

  • This means the field balancing and harmonic vibration suppression are well achieved, and the frequencies other than the harmonics of the vibrations are not affected by the proposed methods

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Summary

Introduction

High pointing stability is required in high-resolution Earth observation satellites, which are equipped with many sensitive payloads [1]. The pointing stability is severely affected by undesirable harmonic vibrations of rapidly spinning rigid rotors in momentum exchange devices, such as flywheels and control moment gyros [2,3] These harmonic vibrations are mainly caused by the rotor mass imbalance and imperfect bearing properties [4]. For the control moment gyro in high-resolution Earth observation satellites, the undesirable harmonic vibrations induced by the rotor imbalances and the sensor runout have to be effectively suppressed. The synchronous vibrations caused by the rotor imbalance and the displacement stiffness still remain, if only the repetitive control method is employed without balancing the rotor. The effectiveness of the field balancing and harmonic vibration suppression strategies are demonstrated by simulations and experiments performed on a control moment gyro test rig with a high-speed rigid AMB-rotor system

Modeling of the AMB-Rotor System
Design of the Synchronous Current Reduction Controller
I s G s
G G j G
G R J r J z Ω 2 2 k x lm 2
Suppression of the Harmonic Vibrations Induce by the Sensor Runout
FL s e
Simulations and Experiments
Conclusion
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