Analysis of Rotor Vibration Characteristics in an Active Magnetic Suspension Flywheel Energy Storage System Considering the Unbalanced Magnetic Pull Force of the Motor

A flywheel energy storage system (FESS) is a device that employs a high-speed rotating flywheel for energy storage, where the motor is a core component enabling the energy conversion. Since the motor rotor is integrated onto the flywheel rotor (FR), when the FESS operates, the vortex motion of the FR causes misalignment between the motor rotor and stator, and the resulting unbalanced magnetic pull (UMP) will induce changes in the vibration characteristics of the FR. This paper presents a permanent magnet synchronous motor (PMSM) designed for a FESS and analyzes the variation pattern of the UMP induced by rotor eccentricity in this motor utilizing the finite element method. Furthermore, the UMP is equivalently modeled using the motor stiffness, and a dynamic model of an active magnetically suspended rigid flywheel rotor that considers the UMP in the motor is established. In this study, the motor position offset ratio β is defined to quantify the axial distance between the motor position and the FR mass center. This paper analyzes the variation law of the vibration characteristics of the FR with the magnitudes of the UMP and the motor position offset ratio β using numerical calculations. Finally, the correctness of the calculated results is verified using experimental testing. This investigation demonstrates that the value of UMP fluctuates as the rotor’s rotation angle increases, while its average value exhibits a linear increasing trend with the growth in rotor eccentricity. As UMP and β increase, the first- and second-order critical speeds of FR exhibit a clear decreasing trend. Meanwhile, variations in these two factors also exert different influences on the vibration amplitude induced by the mass imbalance response of the FR. Therefore, when designing an active magnetically levitated flywheel energy storage system, the influence of motor parameters on the vibration characteristics of FR should be taken into consideration.