Stability Considerations for a Vertical Mount Energy Storage Flywheel

The optimum design of a flywheel mechanical battery system would have a minimum friction resistance from the bearings and the aerodynamic drag forces acting on the rotor system. To investigate the complexities involved in the design of a flywheel mechanical battery system, a test rig has been constructed at the Virginia Tech Rotor Dynamics Laboratory. This test rig consists of a fifty-pound steel flywheel that is mounted on a vertical shaft system and driven by a brushless permanent magnet motor. Initially, it was thought that the rotor could be supported with a single bearing, positioned at the upper mount point of the rotor. This pendulum-type configuration was found to have a major instability at low frequency. This paper will discuss these initial results and the further analysis and testing of a two bearing vertical shaft design. In addition, analyses of both systems have been performed using DyRoBeS, a finite element based rotor dynamics analysis code. The conclusions and recommendations presented here will be of interest to designers of future vertical rotors for such flywheel systems.