Design of a High-Speed Flywheel Energy Storage Demonstrator

Flywheels are kinetic energy storage devices, which are characterised by high conversion power and high discharge rate. They can be used as a buffer to smooth the highly fluctuating power in a power supply system, such as in transportation systems, where highly frequent power peaks can be seen during the acceleration and deceleration phases. This paper presents the design of the main components of a flywheel system, built as a demonstration for the implementation in a tramway system. The demonstrator has a capacity of 0.5 kWh and a rated power of 28 kW. The mechanical design of the flywheel rotor, based on the energy requirement, and the material strength is presented. The levitation system, including a radial homo-polar magnetic bearing and a combined radial-axial homo-polar magnetic bearing, is introduced. The system uses a permanent magnet synchronous machine for energy conversion. Based on the loss calculation of each component, the thermal performance of the system is analysed as a validation of the design.