Environmental Engineering Reference
In-Depth Information
been experimentally verified that very low energy losses can be detected if charge
and discharge operations are very fast, in particular in short cycles of charge and
discharge (about 30 min) an energy efficiency higher than 92% has been obtained.
Since for the experiments presented in this case study and the following in the next
chapter the single periods of charge and discharge of the battery pack last not more
than 2 min, and the current involved is higher than 10 A only during the fast
acceleration phase of the R47 cycle (see next paragraphs), a value of 100% for the
battery energy efficiency is assumed valid in all tests. On this hypothesis, it is
possible to define the battery state of charge as:
SOC
ðÞ¼
SOC
0
þ
Z
t
I
batt
ðÞ
dt
ð
6
:
4
Þ
t
0
where SOC
0
is the known battery state of charge at the time t
0
. This definition is
utilized in this paper to instantaneously calculate the battery SOC during the
driving cycles, starting from the experimental measurements of battery current and
voltage.
Finally, the total efficiency of the power train (g
PT
) on the driving cycle is
defined by the following equation:
E
load
E
H
2
þ
E
batt
g
PT
¼
ð
6
:
5
Þ
where:
E
batt
¼
Z
t
2
V
batt
I
batt
dt
ð
6
:
6
Þ
t
1
E
load
¼
Z
t
2
T
m
x
m
dt
ð
6
:
7
Þ
t
1
Z
t
2
1
g
util
n
cells
I
D
H
f
E
H
2
¼
M
H
2
2F
dt
ð
6
:
8
Þ
t
1
where V
batt
is the battery voltage, I
batt
the battery current, T
m
the brake torque, k
m
the engine speed, M
H
2
the hydrogen molecular weight, n
cells
the cell number, I the
stack current, E
load
the energy provided by the engine during the overall test
procedure, while E
H
2
is the energy coming from hydrogen and E
batt
is the net
energy exchanged by the battery pack during the cycle.
