Dynamics of a Flexible Mobile Flywheel Energy Storage System – Theoretical Modeling and Analysis

Flywheel energy storage systems (FESSs) based on active and passive magnetic bearings (MBs) have a huge energy storing potential in mobile applications. Under such operating conditions the FESS is exposed to gyroscopic forces, which can be handled by mounting the FESS in a passive gimbal. The purpose of this article is to investigate the coupled dynamics among the flexible bodies: gimbal, housing, and rotor in a FESS.

This is carried out by theoretical modal analysis of each body and the FESS by utilizing the finite element (FE) method. Modeling of the bodies are carried out in ANSYS MAPDL using SOLID186 elements. The model of the FESS has been built by assembling the FE models of the bodies, representing the MB forces by linear springs using the MATRIX27 element.

The first six natural frequencies and mode shapes have been identified for the gimbal, housing, and rotor occurring in the range of 195-801 Hz, 2882-4580 Hz, and 1346-6504 Hz respectively. The model of the FESS indicates 23 natural frequencies in the range 0-2000 Hz. Decoupled vibrations are noticed, such as isolated vibrations corresponding to the fifth mode shape for the gimbal and the first bending mode for the rotor.

Coupled vibrations are also observed between the gimbal, housing, and rotor for which the active MB controllers must be designed taking such dynamics into account.