# IGBT Modules - Technologies, Driver and Application (Second Edition) - page 397

385
1
out
in
1
out
in
on
off ,L
L
) U U(T)D1(
L
) U U( t
I
− ⋅ ⋅
=
− ⋅
= ∆
Eq. 11.14
Assuming that the stored energy in the inductor at the beginning and end of each period
will be at the same value (neglecting all losses), the sum of the currents
I
L,on
and
I
L,off
over oneperiod has to be0A. This then results in:
D1
U U
0
L
) U U(T)D1(
L
UTD
0 I
I
in
out
1
out
in
1
in
off ,L
on,L
= ⇔
=
− ⋅ ⋅
+
⋅ ⋅
= ∆+ ∆
Eq. 11.15
Similar to the buck converter, three different operating modes are distinguished for the
boost converter, which are defined respectively by the current through the inductor L
1
.
pplies for the CCM mode and
for the DCM operating mode
(without going intoderivationhere).
in
1
in
2
out
U
I L2
UTD1 U
⋅ ⋅
⋅ ⋅
+ =
Eq. 11.16
11.3.3Buck-boost converter
If the principles of a buck converter and a boost converter are combined, it becomes the
so-called buck-boost converter. A frequently used variant, for example in hybrid vehicles
is depicted in
In boost mode T
2
(T
1
is permanently switched off) andD
1
work
together in order to increase (boost) the voltage of U
1
toU
2
. In buckmode, however, T
1
(T
2
is permanently switchedoff) andD
2
work together to reduce the voltageU
2
toU
1
.
Fig. 11.18
Buck-boost converter
In another variant of the buck-boost converter, the input voltage is transformed to an
output voltage of opposite polarity and, depending on the operating mode, a lower or
higher value.
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