Mechanism and Mitigation of Actuator Saturation-Induced Vibration in Active Magnetic Bearing-Based Motors

Abstract

This study investigates the occurrence of nonsynchronous, low-frequency vibrations in high-speed motor systems equipped with active magnetic bearings (AMBs). The underlying mechanism is analyzed by considering three factors: actuator saturation, eddy current effects, and external noise. The findings reveal that actuator saturation, characterized by a decrease in gain, is the primary cause of low-frequency vibrations. The nonlinearities of the electromagnetic force and switching power amplifier exacerbate this effect. Although eddy current effects and external noise do not directly initiate low-frequency vibrations, they increase the susceptibility of the actuator to saturation, indirectly impacting the system. To address this issue, the stability of the AMB system affected by saturation nonlinearity is analyzed using the extended Nyquist stability criterion. A compensatory strategy based on the synchronous rotating frame is proposed. A prototype of a 100 kW AMB-based permanent magnet synchronous motor system is developed to validate the approach. Vibration response experiments conducted on the prototype demonstrate the effectiveness of the proposed strategy, effectively filtering out the synchronous component of the control current and mitigating actuator saturation. Furthermore, at the rated speed of 30000 r/min, the implementation of the compensator reduces the maximum rotor vibration amplitude by approximately 21% compared to using a standalone proportional–integral–derivative controller.

Keywords

• Active magnetic bearing
• low-frequency vibration
• describing function method
• vibration compensation