Environmental Engineering Reference
In-Depth Information
Equation (4.29) describes the total energy available from the capacitor based
on slow discharge. Capacitance is then verified by conditions of the test. Specific
energy is then the ratio of available energy calculated in (4.29) divided by the ultra-
capacitor mass. Available pulse power from the ultra-capacitor is calculated at 95%
efficiency defined power out into a resistive load divided by discharge power
available:
2
¼
ð
V
c
R
L
Þ=ð
R
L
þ
R
i
Þ
h
V
c
=ð
R
L
þ
R
i
Þ
ð
4
:
30
Þ
h
ð
1
R
L
¼
R
i
h
Þ
The ultra-capacitor internal resistance is computed as defined in (4.29). Given
a pulse power, discharge at 95% efficiency results in a resistive load having the
value defined in (4.30). Specific power is then the computed power available at
95% discharge efficiency divided by the ultra-capacitor mass.
A study was performed to determine the benefit of ultra-capacitor and battery
parallel combinations, but using a switch interface to connect or disconnect either
the ultra-capacitor or the battery from the 42 V ISA component [37]. The vehicle
electrical loads remain connected to the 42 V battery regardless of whether it is
connected to the ISA or not. The switching combination choices are shown in
Figure 4.42.
S1
S2
UC
42 V
Batt.
ISA
M/G
Loads
Engine
Figure 4.42 Switched battery ultra-capacitor ISA architecture
The switch functions in this ISA architecture are listed in Table 4.21. The
battery is a 28 Ah lead-acid module, and the capacitor is a Maxwell-Montena
60 V, 113 F module built from the series connection of 24, each 2,700 F power
cache ultra-capacitors capable of 10 kW for 12 s discharge.
Compared to a single lead-acid battery alone, the switched ultra-capacitor
architecture increased boosting power from 4 to 10 kW and increased regeneration
power levels from 1 to 10 kW in a compact car.
