JPH0369624B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a DC arc welding power source with constant voltage characteristics whose output voltage is controlled by an inverter.

[Background of the invention]

As a type of arc welding power source, a rectifier circuit and an inverter convert the commercial frequency voltage into alternating current with a frequency higher than the commercial frequency and apply it to the primary side of the main transformer.The secondary output of the main transformer is then rectified to produce direct current for welding. There is one that allows you to get output.

According to this method, the main transformer can be made smaller and lighter, and the output voltage can be controlled by changing the output pulse width or output frequency of the inverter.

In conventional welding power sources of this type, high frequency ripples of several KHz to several + KHz generated from the inverter are smoothed by a DC reactor installed on the secondary side of the main transformer, but Ripples at a relatively low frequency (150 Hz for a three-phase full-wave rectifier circuit) included in the output of the side rectifier circuit were not smoothed and remained as ripples in the output voltage of the welding power source. This is because if you try to smooth out the above-mentioned low frequency ripple by installing a smoothing reactor or a smoothing capacitor between the rectifier circuit on the primary side of the main transformer and the inverter, as you would normally think, you would end up with a very large smoothing reactor or a smoothing capacitor. Requires smoothing capacitor,
This is because not only is it expensive, but the advantage of being smaller and lighter by using an inverter is diminished.

However, ripples in the output voltage of a welding power source are generally unfavorable for stabilizing the arc, and are a factor that prevents stable arc generation, particularly in a small current range.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a DC arc welding power source that is small, lightweight, inexpensive, and has little output voltage ripple.

[Summary of the invention]

The present invention provides a DC arc welding power source using an inverter as described above, in which a pulsating voltage obtained by rectifying a commercial frequency voltage using the same rectification method as the primary side rectification method of the main transformer is used as a control signal to control the main transformer. The present invention is characterized in that a feedforward control means is provided for changing the output pulse width or output frequency of the inverter so as to cancel the ripple in the output of the primary side rectifier circuit.

[Embodiments of the invention]

An embodiment of the present invention is shown in FIG.

To explain the configuration, there is a circuit from the input terminal 1 connected to the three-phase AC power supply, through the three-phase full-wave rectifier circuit 2, the smoothing capacitor 3, and the inverter 4 to the primary side of the main transformer 5. The main circuit of the welding power source consists of a circuit from the secondary side through the rectifier 6 and DC reactor 7 to the arc load 8 and the welding base material 9, which is basically the same as a conventional DC arc welding power source using an inverter. There is no difference.

Feed forward control means for preventing ripples in the output of the three-phase full-wave rectifier circuit 2 from appearing in the output of the welding power source includes a three-phase control transformer 10, the three-phase full-wave rectifier circuit 11, and an adder. The circuit consists of a circuit 13, which converts the commercial frequency voltage from the three-phase AC power supply into a voltage level suitable for control using the three-phase transformer 10, and then transforms the commercial frequency voltage from the three-phase AC power supply into a three-phase transformer with the same rectification method as the primary side of the main transformer. The pulsating voltage C obtained through the full-wave rectifier circuit 11 is input as a control signal to the adding circuit 13, and the output voltage A of the adding circuit 13, which is obtained by subtracting the voltage C from the output voltage B of the welding voltage establishing circuit 14, is input to the inverter. This is used as a control bias for the drive circuit 12. The inverter drive circuit 12 is a circuit that operates the inverter 4 with an output pulse width or an internal force frequency that corresponds to the control bias.In the case of pulse width control using transistors as switching elements, the higher the control bias, the longer the switching on-duty. When the control bias becomes low, the switching on-duty is shortened and the output pulse width is made small.

Next, the action will be explained.

The voltage V _c of the smoothing capacitor 3 in Fig. 1 is
When there is no load, the peak rectified voltage has a smooth waveform as shown in Figure 2a, but when there is a load, there is no smoothing reactor on the primary side of the main transformer, so three-phase full-wave rectification as shown in Figure 2b occurs. The resulting waveform has the same ripples as the waveform (actually, a small ripple with the same frequency as the output frequency of the inverter 4 is further added).

Therefore, as usual, welding voltage setting circuit 1
When the inverter 4 is operated at a constant on-duty determined only by the output voltage B of the welding power source 4, the welding power source output voltage _Vp under load will have a waveform with the same ripples as shown in FIG. 2b. In contrast, in this embodiment, the output voltage C of the control three-phase full-wave rectifier circuit 11 having ripples in the same phase as the ripples of the three-phase full-wave rectifier waveform on the primary side of the main transformer is used as shown in FIG.
When the capacitor voltage V _c increases as shown in , the on-duty of inverter 4 is shortened and the capacitor voltage
When V _c decreases, control bias A changes to lengthen the on-duty of inverter 4, and feedforward control is performed to cancel ripples in capacitor voltage V _c , so a large smoothing effect is applied to the primary side of the main transformer. Even without providing a reactor or a smoothing capacitor, the output voltage V _p of the welding power source under load can be made into a ripple-free smooth waveform as shown in FIG. 2d.

Since the switching frequency of the inverter 4 is two or more orders of magnitude higher than the commercial frequency, ripples at low frequencies with the commercial frequency as the fundamental wave can be sufficiently eliminated by the feed forward control described above.

Note that when this feed-forward control is performed, the capacitor voltage V _c on the primary side of the main transformer has a smooth waveform when there is no load, but the output voltage V _p has ripples as shown in Figure 2 c. However, as a welding power source, it is sufficient as long as there is no ripple in the output voltage under load, and there is no problem even if there is ripple in the output voltage under no load.

〔Effect of the invention〕

According to the present invention, it is possible to obtain an output voltage with almost no ripples during load without installing a large smoothing reactor or smoothing capacitor on the primary side of the main transformer, and the circuit components necessary for this (control three-phase transformer 1
0, three-phase full-wave rectifier circuit 11, etc.) need only have a small capacity to generate control signals, providing a DC arc welding power source that is small, lightweight, and inexpensive, and has good arc stability even in a small current range. can do.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure shows the voltage waveforms of V _c and V _p in Figure 1.
a and c are waveforms under no load, and b and d are waveforms under load. 2... Main transformer primary side rectifier circuit, 4... Inverter, 5... Main transformer, 6... Main transformer secondary side rectifier, 10, 11, 13... Feed forward control means (10 ...Control three-phase transformer, 11...
...3-phase full-wave rectifier circuit for control, 13...addition circuit),
12... Inverter drive circuit, 14... Welding voltage setting circuit.

Claims (1)

[Claims] 1 A rectifier circuit whose input side is connected to an AC power supply,
It consists of an inverter connected to the output side of the rectifier circuit on the input side, a welding voltage setting circuit, and a drive circuit that drives the inverter using signals from the welding voltage setting circuit. A welding power supply device that supplies output from an inverter to a welding part, comprising a transformer, a second rectifier circuit,
an adder circuit, the input side of the transformer is connected in parallel with the input side of the rectifier circuit, the output side is connected to the input side of the second rectifier circuit, and the output side of the second rectifier circuit A welding power supply device characterized in that a signal from the welding voltage setting circuit is connected to an adder circuit, and the drive circuit is driven so as to cancel ripples in the output of the rectifier circuit.