Environmental Engineering Reference
In-Depth Information
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DC-AC
CONVERTER
T
RASMISSIO
N
MACHINE
MOTOR
Gear Box
Clutch
Fig. 5.15
Principle of operation of a vehicle using a flywheel as auxiliary energy storage
5.4 Alternative Energy Storage Systems
In this section, the main characteristics of alternative electrical energy storage
systems, such flywheels and super capacitors, are described, as these devices
might play an important role in the development of vehicles powered by electric
propulsion systems.
5.4.1 Flywheels
An energy storage system using flywheels is essentially composed by a plane disk
rotating around its axis of symmetry. The kinetic energy of the spinning disk is
released when the rotating velocity slows down. This can be obtained connecting
an electric machine working as a generator to the disk by means of a gearbox, as
shown in Fig.
5.15
. Power electronics is required to match the electric generator
output to the electric drive to power the vehicle. The flywheel is reaccelerated
mainly during the regenerative braking, when the kinetic energy of the vehicle can
be transformed in kinetic energy of the spinning disk. In particular, the electric
energy coming from the main power drive of the vehicle during breaking supplies
the electric machine, which works as a motor in this case. Alternatively, the
flywheel is connected to the wheels of the vehicle by means of a clutch. The
intervention of the clutch depends on both the speed of the vehicle and the power
chosen by the designer for the electric machine and the control technique of the
DC-AC converter [
3
,
4
].
The energy E stored by a flywheel is given by:
E
¼
1
2
I
m
x
2
ð
5
:
30
Þ
