Environmental Engineering Reference
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Fig. 7.56 Power distribution
between FCS, electric engine,
and batteries as function of
cycle length for R40 cycle at
5As -1 as stack current var-
iation rate
30
FCS Power (DC-DC OUT)
Battery Power
Elec. Drive Power
25
20
15
10
5
0
-5
-10
-15
0
50
100
150
200
Time [s]
Table 7.3 Efficiency
calculation for the 30 kW
fuel cell power train on R40
driving cycle
Efficiencies
(%)
Experiment
of Fig. 7.56
Experiment
of Fig. 7.57
Experiment
of Fig. 7.58
g FCS
46
45
48
g DC
78
77
84
g ED
74
74
75
g PT
27
26
30
and recharges the batteries (Fig. 7.56 ). The results of the previous paragraph
guarantee that no dynamic limitation can be expected during this experiment. The
batteries are recharged during both deceleration phases (regenerative braking) and
stationary phase when the FCS power overcomes the engine demands. The
behavior of battery power affects its state of charge (SOC) during the cycle, in fact
a slight decrease of battery SOC is observed (about 0.2%) at the end of a single
R40 cycle managed according to Fig. 7.56 . In Table 7.3 , the values of efficiencies
calculated for the power train and its main components on the R40 cycle are
reported. The total efficiency of the FCS (g FCS ) is calculated as ratio between the
power at DC-DC converter input and the theoretical power associated with the
fuel entering the stack. The DC-DC converter (g DC ) and electrical drive (g ED )
efficiencies are calculated as ratio between outlet and inlet power of the devices.
Then the total efficiency of the power train (g PT ) on the driving cycle is determined
using the following equation, assuming a battery efficiency of 100% and taking
back the final SOC to the initial level [ 8 ]:
g PT ¼ g FCS
g DC
g ED :
ð 7 : 4 Þ
For the test reported in Fig. 7.56 , an efficiency of 46% is obtained for the FCS,
which operates on the cycle mainly in conditions of partial loads, characterized by
high efficiency [ 3 ]. For DC-DC converter and electric drive efficiencies of 78 and
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