High-Power Low-Energy Flywheels for Power System Support: A Review

With modern power systems and uninterruptable power supplies, there is a need for alternative energy storage solutions with higher levels of power delivery and energy storage. Energy can be stored in kinetic form using flywheels. Traditional flywheels are high-inertia slow-speed units whereas modern flywheels are high strength composites with low inertia and high speed rotation. The suspension and control of the wheel is difficult and energy losses due to friction and windage needs to be minimized. Vacuums can be used to reduce air friction and magnetic bearings can be used to reduce bearing friction. Superconductors can be applied for levitation. The electro-mechanical energy conversion unit has to have high efficiency; the use of permanent magnet machines is often advocated. Superconducting machines can also give high efficiency conversion.This paper reviews some current flywheel technologies in terms of high power for short term bursts in applications such as power system support for transient outages and subway operation where trains rapidly stop and start. The work will address issues such as design, operation, magnetic levitation, energy conversion and superconducting applications. Examples will be addressed.