21
-
A complex regulation strategy is called for
(3) The output voltage tends towards operating point (4) as a result of the load resistance becoming smaller
-
At operating point (3), a decrease in the frequency corresponds to an increase in the output voltage
-
Also at operating point (4), a decrease in the frequency corresponds to an increase in the output voltage
-
By decreasing the frequency, then, the output voltage can be clearly brought back towards the value for operating
point (3)
Applying the
resonance
converter
principle
U
DC
T1
C
S
L
S
P
D
C
P
Inductor
S
ocket
S
ocket
Fig.9
Block diagram of theTP 1500 power-pack
T2
S
T3
T3
The power transistors T1 and T4 apply the
voltage for the positive half-wave to the
primary winding of the transformer. The
capacitor C
S
, the primary winding P and
the coil L
S
together constitute the series
resonance circuit here. The negative half-
wave is switched to the series resonance
circuit by the power transistors T3 and T2.
The secondary winding S of the
transformer transmits the positive and
negative half-waves - as the welding
current - to the secondary diode D, which
actually consists of two separate diodes.
The parameters “welding current” and “welding voltage” are constantly measured. A
microcontroller continually compares the welding current that was pre-set on the setting
dial with the actual welding current that is measured by the shunt. The transistors of the
power-pack are addressed so as to raise or lower the welding voltage to the value that
is needed for keeping the pre-set welding current constant.
Taking the rod-electrode welding process as an example, Fig. 10 shows the working
ranges of the power source as a function of the actual condition of the arc.
Measuring and
regulating the
parameters
“welding current”
and “welding
voltage”
A special feature here is the centre-tap of the secondary winding, which determines the
frame potential of the welding voltage.
Positive half-waves are fed to the socket via one of the two end-taps of the secondary
winding and one of the two secondary diodes. Negative half-waves are routed to the
socket via the other of the two end-taps and the other secondary diode.
In this way, full-wave rectification is achieved, yet with no need for a space-intensive 4-
diode bridge rectifier, which would also generate increased heat-loss. In keeping with
the series-parallel resonance converter, the capacitor C
P
is located parallel to the load
resistor (=welding process).
The increase in the output voltage brought about by capacitor C
P
in response to an
increase in the load resistance (arc threatens to break) plays a major role in optimising
the welding properties. Furthermore, in order to achieve a perfect welding result and
outstanding welding properties, the welding current and welding voltage need to be
constantly realigned.
Complex
regulation
(continued)
Содержание TP 1500
Страница 1: ...1 Service Manual...
Страница 53: ...53 Overall circuit diagram...
Страница 54: ...54...
Страница 114: ...114...