Increasing The Output Voltage By Means Of Series-Parallel Resonance; Limiting The Increased Output Voltage In Open Circuit; Complex Regulation - Fronius Transpocket 1500 Erdstrom Serviceanleitung, Ersatzteilliste

Series-parallel The voltage increase occurring in the "resonant frequency" region, in the capacitor
resonance component, is thus available partly on capacitor C
converter resistor R
(continued) encouraged by a high load resistance, which shunts out the capacitor C
minimum possible extent.
Increasing the The "series-parallel resonance converter" principle utilised for the resonance inverter of
output voltage by the TP 1500 power source makes possible an output voltage that climbs exponentially
means of series- the higher the load resistance is increased (see Fig.3, "ideal characteristic") and that
parallel must be limited in open circuit.
resonance
An increased load resistance means a longer arc or an arc that threatens to break at
any moment. On the other hand, the climbing voltage counteracts any tendency to
break on the part of the arc.
Limiting the
increased output
Max.
voltage in open
circuit
Mean
Min.
Fig.7
In the same way as with the series resonance converter, the output voltage is
dependent upon the addressing frequency of the switching transistors relative to the
resonance frequency. In the case of series-parallel resonance, the maximum voltage
increase is also reached in the resonant-frequency region.
Complex
Relationship of output voltage
regulation
to input voltage
2.5
1.5
Fig.8
Legend:
(1) The output voltage tends towards operating point (2) as a result of the load resistance becoming larger
-
-
-
, a voltage arises which may be higher than the input voltage. This effect is
L
U
out
F = 3.6 Hz
Output voltage in open circuit
(2)
Hard-to-
2
compensate
load
fluctuation
(1)
1
Small load
resistance
0
0 50 100 150
Switching frequency of the transistors (kHz)
Complex regulation of the output voltage
At operating point (1), an increase in the frequency corresponds to a decrease in the output voltage
At operating point (2), an increase in the frequency would cause a further increase in the output voltage
thereby acting contrary to the goal of returning the output voltage to the value for operating point (1)
P
Because virtually unlimited output voltage
is possible in the open circuit, the open-
circuit voltage applied to the welding
sockets is clocked at a frequency of
approx. 3.6 Hz.
The result is a "saw-tooth" output voltage
t
whose minimum and mean values are
considerably below those of the unclocked
output voltage. The unclocked output
voltage would constantly correspond to
the maximum.
The great difficulty with series-parallel
resonance is to do with the fact that the
resonant frequency tends to change along
with the load (i.e. with the arc
characteristic). This means that as well as
(3)
the load resistance, the (related) resonant
Easy-to-
frequency is also a crucial influencing
compensate
load fluctuation
parameter when it comes to regulating a
series-parallel resonance converter.
Large load
Because the necessary addressing
resistance
frequency for the switching transistors is
dependent upon two separate
(4)
parameters, complex regulation of the
output voltage is required.
200 250
20
and partly on load resistor R
to the
P
. On
L