Environmental Engineering Reference
In-Depth Information
Bidirectional
buck/boost converter
+
50 V <
U
in
< 300 V;
lin < 600 A
High
side
filter
100 V <
U
o
< 450 V;
lo < 150 A
+
Low
side
filter
-
-
Enable
Controller
CAN
Figure 4.11 Bidirectional power converter for active parallel combination of
ultra-capacitor and lithium ion
In this converter the lower switch and upper diode along with the input inductor are
used to boost low side voltage to high side voltage. For regenerative power flow the
high side voltage is down converted through the action of the top switch and bottom
diode along with the inductor. This configuration is implemented in simulation by
state space averaging the switching action to make a very fast simulation that
approaches the behaviour of a dc transformer (Figure 4.12).
To understand the operation of the converter in Figure 4.11, consider the low
side port as the ultra-capacitor input port with intensive variable
U
c
and extensive
variable
I
c
for ultra-capacitor voltage and current, respectively. The battery is
connected at the high side port with intensive variable
U
d
and extensive variable
I
d
for converter dc voltage and current, respectively:
I
c
U
c
¼
I
d
U
d
I
d
¼
I
L
I
b
1
U
c
1
d
2
I
d
U
d
I
d
¼
I
c
¼
ð
4
:
6
Þ
d
1
¼
ð
U
d
U
c
Þ
U
d
¼ð
1
d
2
Þ
Referring to (4.6) some very important observations can be made regarding the
operation of this converter:
Simplified modelling results in 100% efficient operation, a useful first approach.
●
According to the top line in (4.6) the conversion process is power invariant.
●
