Series Resonance Converter; Series-Parallel Resonance Converter - Fronius TransPocket 1500 Service Manual

Resonance
converter
80V
(continued)
Fig.4
-
-
-
Series resonance
converter
U
DC
Fig.5
If transistor T1 becomes conductive, the series resonance circuit (i.e. coil and capacitor)
generates a positive, sinusoidal half-wave that is discharged via the resistor R
The negative half-wave resulting from the oscillatory behaviour of the series resonance
circuit flows via: R
transistor T2 becomes conductive).
If the addressing frequency is identical with the resonance frequency of the series
resonance circuit, the output voltage at the load resistor R
voltage U
output voltage will decrease. This is the means by which the resonance converter can
be controlled.
Series-parallel
resonance
converter
U
DC
Fig.6
Pmax! With PWM,
U
out
max. power is needed
Characterisitic
(for pulse-width
modulation)
Ideal
characteristic
Standard characteristic WIG
Characteristic on resonance converter, WIG
The fact that the characteristic is relatively flat in the vicinity of the operating point
prevents unnecessarily high output powers
This not only has a positive effect on the power consumption, but also helps to avoid
overdimensioned components
Although it dispenses with all the weight and space-intensive auxiliary components
that used to be added in order to improve the welding properties, it nevertheless still
achieves superlative results
T1
C
S
L
S
T2

Series resonance converter

, the capacitor C, the coil L
L
. At higher or lower frequencies (relative to the resonance frequence) the
DC
T1
C
L
S
T2

Series-parallel resonance converter

In spite of the complicated controlling
system needed for use in welding, the
resonance-converter principle offers a
number of useful advantages:
- The resonance structure makes it
possible to achieve a nearly "ideal
output characteristic"
- Reduced switching losses permit
higher switching frequencies yet with
optimum efficiency
150 A
I
out
A series resonance converter consists of
the following components:
- series resonance circuit (coil and
capacitor)
- load resistor
- transistors for addressing the resonant
R
L
circuit
Transistors T1 and T2 are addressed
alternately
and the transistor T2 (as soon as
S
The outcome of further development work
on the series resonance converter is the
"series-parallel resonance converter":
S
The series-parallel resonance converter
has an additional capacitor C
connected in parallel to the resistor R
C
R
P
L
Together with R
C constitute a loaded capacitive voltage
P
divider. For this reason, the resonance
circuit (coil and capacitor) has a capacitor
component that is divided up into C
C .
P
19
.
L
will correspond to the input
L
, which is
P
L
, the capacitors C and
L S
and
S
.