Environmental Engineering Reference
In-Depth Information
from rural to urban settings on its circuit. Many other choices of assigning occu-
pancy numbers can, of course, be made.
55
45
35
25
15
5
0
N
exp
0
t1
t2
t3
t4
t5
t6
t7
t8
t9
t10
Event interval
Figure 4.30 Commuter bus occupancy assumptions for energy storage sizing
study example
In the process of calculating the road load, the simulator will adjust the gross
mass of the bus during each interval to correspond to the total number of passen-
gers, each at an assumed standard mass of
m
p
, noted in Table 4.13. This will impose
a burden on the tractive effort necessary for acceleration, which in turn will be
reflected back up the driveline to the power supply.
The final step is to assign a control strategy to the simulation of bus road load
and its attendant power supply needed to meet our sizing requirements. To do this
we select an ESS technology and subject it to the customer usage profile. For the
present hybrid city bus example, we will assume a nickel-cadmium battery pack in
combination with an ultra-capacitor bank. Next, we state the limitations of the
selected technologies in terms of discharge rate and charge acceptance rate during
generator recharging or during recuperation of vehicle kinetic energy. For our NiCd
cell having capacity,
C
b
Ah, these relations are
I
b
mx
chg
0
:
2
C
b
ð
4
:
16
Þ
I
b
mx
dchg
2
:
5
C
b
ð
4
:
17
Þ
U
c
min
1
:
1V
ð
4
:
18
Þ
U
c
mx
1
:
45 V
ð
4
:
19
Þ
U
c
min
U
c
mx
0
:
71
s
u
¼
ð
4
:
20
Þ
