A Compact HTS 5 kWh/250 kW Flywheel Energy Storage System

Flywheel energy storage systems (FESS) are expected to contribute to uninterruptible power supplies (UPS) and power quality tasks significantly. We present design and the component results of a compact 5 kWh/250 kW HTS flywheel whereby the rotor will be totally magnetically stabilized. The design is optimized for highly integrated functionality of rotor body, generator/motor and bearings. The heart of the FESS is an ironless high power PM generator/motor delivering 250 kW. An advanced flywheel body manufactured from graphite fiber is stabilized by two magnetic bearings. A prototype 200 mm HTS bearing has been constructed and tested up to a load of 1 ton axially and 0.47 ton radially capable to carry the rotor weight of about 0.5 t. With a coefficient of friction (COF) of about 10^-6 the rotational drag was low. A passive PM bearing giving 80 N/mm radial stiffness/per pole was studied. HTS-PM damping response dependent on the temperature shows Lehr factors of 5-10% damping between 50 and 80 K. Eddy current dampers could support rotor dynamic stability.