Environmental Engineering Reference
In-Depth Information
k
t
¼
0.0085 Nm/A. The isolation relay shown at the bottom of Figure 10.26 is left
open during the following simulation.
10.2.3 Ultra-capacitors combined with batteries
Capacitors must be combined with electrochemical storage systems in most vehicle
applications to realize maximum benefit. For instance, an ultra-capacitor may be
used independently as an energy recovery and delivery device for capturing vehicle
kinetic energy in an idle-stop situation. Some of the energy may be used during
vehicle launch and acceleration, but in general such applications require suboptimal
capacitor mass since the traction inverter is rated over a relatively narrow voltage
window of 2:1 or less. Capacitors, in combination with batteries, are the most
common architectures and there are two possible connections: (1) parallel battery
and capacitor (read this as ultra-capacitor or super-capacitor/electrochemical
capacitor, a tandem connection) or (2) capacitor with independent power processor,
active parallel. These two cases are illustrated in Figure 10.27.
V
d
+0.16%, -22%
V
d
+0.16%, -22%
U
c
U
b
U
b
m
b
g
E
b
g
P
b
m
b
g
E
b
g
P
b
m
c
g
E
c
g
P
c
U
c
m
c
g
E
c
g
P
c
(a)
(b)
Figure 10.27 Battery-capacitor combinations: (a) direct parallel, (b) independent
power converter architectures of active parallel type
For the analysis of what is the optimal sizing of battery and capacitor combi-
nations, the following assumptions apply:
M
stor
¼
m
b
þ
m
c
0
:
78 pu
V
dnom
1
:
16 pu
P
pk
¼
40 kW
g
FC
¼
0
:
30 kWh
=
mi
ð
10
:
32
Þ
Furthermore, it will be assumed that the mid-sized sedan under consideration
will have its energy storage mass restricted to 75 kg for the specific fuel con-
sumption noted in (10.32). The nominal system voltage will be taken as
U
dnom
¼
550 V, the open circuit voltage of a 440 cell NiMH battery pack. The vehicle has
attributes listed in Table 10.5, including performance targets.
