Vibration Measurement And Analysis Of Flywheel Energy Storage System

Flywheel energy storage is an advanced energy storage technology that has bright prospect for application and has been used practically. Only if the flywheel could arrive at a high speed smoothly, can the flywheel energy storage system (FESS) charge and discharge. The subject studied in this paper is a 20kW/1kWh FESS. In-depth theoretical study and a great deal of experiments have been done to make the flywheel arrive at a high speed.The flywheel is made of high strength alloy steel. In the system, there is a permanent magnetic bearing to support most of the flywheel's weight and two radial ball-bearing. Outside of the bearing seat, there are elastomeric O-rings, acting as dampers. This system's shafting structure is much different from the rest FESS in our lab. It's very necessary to study the dynamics characteristic of this FESS.The stiffness and damping coefficient of the elastomeric O-ring is the key parameter that influences the dynamics characteristic of the FESS. A scheme was designed and the experiment rig was built to measure the stiffness and damp coefficient of the elastomeric O-ring. According to the relation between forces and displacements, the O-ring's stiffness was obtained; and the damping coefficient of O-ring was measured by the free attenuation method.The simplified dynamics model of the rotor-bearing system was built, and the vibration equations were established based on the Lagrange equation. By solving the vibration equations, the modal frequencies, modal shapes and the relations between modal damping ratios and rotational speeds were obtained. The relations between stiffness, damping coefficient of dampers and the dynamics characteristic were analyzed, which provided a necessary theoretical basis for the dynamics optimization.A series of spin tests were done. The flywheel's speed exceeded 260r/s for several times. The highest speed reached 280r/s, while the rim line speed was 277.8m/s, the energy stored was 0.52kWh and the energy density was 5.2Wh/kg. Several eddy-current sensors were made to measure the system's vibration. The resonance frequencies obtained by theoretical calculation were basically in concordance with the experimental results. The system's powers during the tests were analyzed, and the conclusion was drawn that the motor efficiency which was less than 50% was one of the key factors that restricted the I/O power and highest speed of our FESS.