Page 247 - Power Electronic Control in Electrical Systems

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Power electronic control in electrical systems 235

Field replaceable Ball bearings
bearing cartridge
Bronze
backup bearing

Magnetic bearing
integrated into
field circuit Field coils

Flywheel, motor
rotor
Air-gap
armature
No permanent magnets
enables high tip-speed
and high output power
Smooth back-iron,
no slots and low loss
Fig. 6.59 Exploded view of a modern flywheel motor/generator structure. (Courtesy of Active Power Inc., USA.)

Fig. 6.60 Modern flywheel energy storage system based on VSC.

generator as shown in Figure 6.62. Such a system is called continuous power supply
(CPS). It differs from the conventional UPS system as the critical load is connected to
the AC mains used as a primary source of power. The static UPS systems use backup
battery power and the CPS uses a dynamic energy storage system, a flywheel for
example. Finally CPS systems condition the power coming from the utility or in case
of emergency from a diesel generator providing also power factor correction and
reduction in current harmonics.
A flywheel may be part of a power quality system or else power conditioning
system used to eliminate network problems associated with voltage sags, short
notches and swells, harmonic distortion and power factor. Figure 6.63 shows a block
diagram of a typical configuration based on a flywheel.
Finally in case of a UPS system requiring a battery bank, in order to extend
the life of the battery arrangement, a flywheel system maybe used as shown in Figure
6.64. Uninterruptible power supplies systems are designed and used to provide the