Environmental Engineering Reference
In-Depth Information
relation used to obtain the value in (10.51) for the magnitude of capacitor pulse
power, assuming a power invariant or housekeeping logic mass,
m
I
0
, of 5 kg is
P
cap
g
PI
þ
m
I
0
m
I
¼
ð
kg
Þ
ð
10
:
52
Þ
The total system mass then becomes the combination of (10.47), (10.48) and
(10.52), which, after some rearranging, becomes
m
c
þ
m
b
þ
m
I
0
g
P
c
g
PI
1
þ h
c
ð
1
s
2
M
stor
¼
Þ
ð
kg
Þ
ð
10
:
53
Þ
Equation (10.53) for total storage system mass is intriguing because it illus-
trates the significant role that the added power processor plays. In (10.53) the
second term multiplying capacitor mass is actually derived from (10.52) for power
processor mass and shows that as voltage swing increases the converter mass
increases in proportion, which adds more mass to the total storage system. Coun-
tering this trend with increasing voltage swing, hence higher energy extraction, is
the power processor specific power density. As technology improves, the converter
power density will improve and further reduce the additional mass to this config-
uration. In any event, the resulting mass contributions are as given in (10.51).
Summarizing the component masses for a direct parallel and independent
power converter configuration yields the results noted in Table 10.6.
Table 10.6 Comparison of component mass
Component
(all masses in kg)
Direct parallel
combination
Independent power
processor combination
Advanced battery, NiMH
1.472
1.472
Ultra-capacitor (kg/%total)
109.7/(98.6)
49.05/(77)
Power processor
0
12.868
Totals/(% mass saved)
111.2
63.39/(43)
Mass saved
0
47.81
Table 10.6 shows that with an independent power processor not only is the
ultra-capacitor mass minimized, but the total system mass is reduced by 43%. If
the additional cost of the power processor does not offset the savings obtained
from the energy components, in that case the independent power processor archi-
tecture would be the correct approach.
10.2.4 Hybridized battery example
This section examines the case of the active parallel configuration for a BEV [24] - in
particular, the physical level combination of the symmetric carbon ultra-capacitor and
an iron phosphate based lithium ion battery having an advanced and safe chemistry.
