Environmental Engineering Reference
In-Depth Information
TRASMISSION
DC-DC
Fuel Cell
System
DC-AC
CONVERTER
ELECTRIC
MOTOR
Electric Drive
H2 TANK
Rechargeable
BATTERY
Fig. 5.23
Configuration of fuel cell vehicle equipped with rechargeable batteries
while a small battery would permit the vehicle start up. This option would permit
the elimination of a heavy and large battery pack, but requires the FCS follows all
the load variations imposed by the road mission. As seen in
Chap. 4
, such a
solution implies the acquisition of a stack of power at least equal to that of the
electric drive, with consequent significant impact on costs, and the difficulty of
the FCS to follow in a reliable way all fast dynamic demands typical of automotive
applications. For this reason, the hybrid configuration is generally preferred in a
fuel cell propulsion system, where the electric energy storage system is generally
connected in electric parallel with the fuel cell system, and a DC-DC converter is
used to match the FCS variable voltage to the voltage required by the electric drive
(Fig.
5.23
).
The simultaneous utilization of FCS and battery within a fuel cell pro-
pulsion system can be accomplished by two basic ways: (i) the battery pack
can be minimized (but not eliminated as in full power) assigning the role of
generating most energy required by the load to the FCS (soft hybrid config-
uration), (ii) the FCS can be sized to provide the base load, i.e. a power value
close to the average power of the expectable road mission (hard hybrid
configuration), while larger battery pack are necessary to satisfy the dynamic
requirements.
The main benefit of the soft hybrid option is the reduced use of batteries, which
could have the minimum capacity necessary to feed the vehicle auxiliaries, giving
a limited contribution to peak powers and save energy during the regenerative
braking phases. On the other hand, the hard hybrid option offers the possibility to
limit the cost of the FCS, which would work mainly in steady-state conditions,
then in more reliable way.
The soft hybrid configuration represents the most flexible solution for the
energy management in all the possible driving conditions of an automotive
