B. FESS Hardware
Fig. 2 depicts the scheme of a FESS. The main component is the high speed spinning flywheel rotor which stores kinetic energy. To reduce the friction losses, the rotor is usually suspended with magnetic bearings (MB) and placed in a vacuum container. A motor/generator (M/G) is used for electro-mechanical energy conversion. It operates as a motor to accelerate the rotor when the FESS is charged and as a generator when being discharged. The other auxiliary components are: an inverter for the M/G, a control system for the MB, a cooling system and a vacuum pump. All these
components are connected to the power network.