JPS60187470A - Arc welding power source - Google Patents

Abstract

PURPOSE:To eliminate the ripple of a power source output voltage by providing a feed forward control means which changes the output pulse width or output frequency of an inverter with the pulsation voltage obtd. by rectifying a commercial frequency power source as a control signal. CONSTITUTION:A three-phase full-wave rectifier circuit 11 of the same system as the system of a primary rectifier 2 of a main transformer 5 is provided to a DC arc welding power source using an inverter 4 and a pulsation voltage C for a control signal is obtd. from the commercial frequency voltage by a three- phase transformer 10 and the circuit 11. An adder circuit 13 outputs the output voltage A obtd. by subtracting the voltage C from the output voltage B of a circuit 14 for setting the welding voltage as a control bias for an inverter driving circuit 12. The circuit 12 operates the inverter 4 by the output pulse width or output frequency corresponding to the control bias and performs feed forward control so as not to produce the ripple in the stage of loading in the output voltage Vo. The titled power source which is small in size and light in weight and is free from the ripple of the output voltage is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION 5 [Field of Application of the Invention] The present invention relates to a DC arc welding power source with constant voltage characteristics in which multiple output voltages are controlled by an inverter.

[Background of the invention]

As a type of arc welding power source, the commercial frequency voltage is transferred to the rectifier circuit and inverter, and then the commercial frequency voltage is transferred to the rectifier circuit and inverter.

Convert it to a higher frequency alternating current and add it to the 9th side of the main transformer, rectify the secondary output of the main transformer and weld it.

Some devices are designed to obtain direct current output.

This method makes the main transformer smaller and lighter.

The output voltage is controlled by the inverter's output pulse.

It can be done by changing the width or output frequency.

Ru.

In conventional auxiliary welding power sources, high frequency rip of several Klh to several tens of Klh is generated from the inverter.

The current level is smoothed by a DC reactor installed on the secondary side of the main transformer.

- Ripples at a relatively low frequency (150Hg in a three-phase full-wave rectifier circuit) included in the output of the next-side rectifier circuit were not smoothed and remained as ripples in the welding power source output voltage. 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 main transformer, the next side rectifier circuit and the inverter, as you would normally think, you would end up with a very large smoothing reactor. Or smooth.

It requires a special capacitor, which is expensive.

Compact and lightweight due to the use of an inverter.

This is because the benefits of conversion are diminished. .

But generally welding power supply output voltage ripple.

is unfavorable for arc stabilization, especially for arc stabilization.

This prevents stable arc generation in the small current range.

become an element.

[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 1 degree less ripple in its output voltage.

[Summary of the Invention] The present invention provides a DC arc welding power source using an inverter as described above, in which a pulse voltage obtained by rectifying a commercial frequency voltage using the same rectification method as that of the main transformer downstream side 5 is provided. The inverter is characterized by comprising feedforward control means for changing the output pulse width or output frequency of the inverter using current voltage as a control signal so as to cancel the output ripple of the main transformer-next side rectifier circuit. be. .

[Embodiments of the invention]

An embodiment of the present invention is shown in Fig. 1.

To explain the configuration, it is connected to a three-phase AC power supply.

A circuit from an input terminal 1 to a three-phase full-wave rectifier circuit 2, a smoothing capacitor 3, and an inverter 4 to the negative side of the main transformer 5, and a secondary side of the main transformer 5.

The arc load passes through the rectifier 6 and the DC reactor 7.

8. The welding power supply has a bug-eye view with the entire circuit to the bath welding base material 9.

The circuit is constructed using a conventional inverter.1. .

There is basically no difference from the DC arc welding illumination.

Feedforward 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, a three-phase full-wave rectifier circuit 11, and an adder circuit 13. After converting the commercial frequency voltage from the three-phase AC power source to a voltage level suitable for control in the three-phase transformer 10, the main transformer converts the commercial frequency voltage from the three-phase AC power supply into a three-phase transformer with the same rectification method as the next side. The pulse obtained through the full-wave rectifier circuit 11, 3
.

The current voltage C is input to the adding circuit 13 as a control signal, and the voltage C is obtained from the output voltage B of the welding voltage setting circuit 14.

The subtracted output voltage A of the adder circuit 13 is inverted.

This is used as a control bias for the drive circuit 12. .

The inverter drive circuit 12 corresponds to control bias.

inverter with output pulse width or output frequency.

Switch on the transistor in the circuit that activates 4.

In the case of pulse width control using a switching element, 1. When the control bias becomes high, switching is turned on.

The duty is increased to increase the output pulse width, and when the In control bias becomes low, the switching on duty is shortened and the output pulse width is decreased.

Next, the action will be explained.

Voltage V of smoothing capacitor 3 in FIG. 1. When there is no load, the peak rectified voltage is a smooth waveform as shown in Figure 2 (a), but when it is loaded, there is no smoothing reactor next to the main transformer, so the waveform is as shown in Figure 2 (b). The waveform has the same ripple as the three-phase full-wave rectified waveform shown in (actually, the inverters 4 and 4).

Small ripple at the same frequency as the output frequency.

further added).

Therefore, welding voltage setting circuit as usual.

A constant on-duty determined only by the output voltage B of No. 14.

Negative if inverter 4 is activated on the tee.

Welding power supply output voltage V when loaded. is the same as Figure 2(b).

This results in a waveform with tuples. I love this.

In this example, all three phases are connected to the main transformer and the next side.

It has a ripple that is in phase with the ripple of the rectified waveform.

1 due to the output voltage C of the control three-phase full-wave rectifier circuit 11, and the capacitor voltage V shown in FIG. 2(b). When V increases, the on-duty of inverter 4 is shortened and the capacitor voltage V
. When V decreases, the control bias A changes to lengthen the on-duty of the inverter 40, and the capacitor voltage V
Since feedforward control is performed to cancel the ripple of C by 1°, the output voltage V of the welding power source under load can be reduced without installing a large smoothing reactor or smoothing capacitor next to the main transformer. can be made into a smooth waveform without ripples as shown in FIG. 2(d).

The switching frequency of inverter 4 is the commercial layer.

This is because the frequency is more than two orders of magnitude higher than that of waves.

The low frequency ripple 9 with the commercial frequency as the fundamental wave is sufficiently eliminated by the feedforward control described above.

I can leave.

Note that this feedforward control is performed.

When there is no load, the main transformer is connected to the next side.

Even though the sensor voltage Vc has a smooth waveform, the output voltage.

Vo is a wave with ripples as shown in Figure 2 (C).

However, as a welding power source, the output horse under load.

There is no problem as long as there is no ripple in the output voltage, and there is no problem even if there is ripple in the output voltage at no load.

〔Effect of the invention〕

According to the present invention, it is possible to obtain an output voltage with almost no ripple during load without providing a large smoothing reactor or smoothing capacitor on the downstream side of the main transformer.
The circuit components required for this (control three-phase transformer 10, three-phase full-wave rectifier circuit 11, etc.) need only be small enough to generate control signals, so they are small, lightweight, inexpensive, and compact. It is possible to provide a DC arc welding power source with good arc stability even in the current range.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, and FIG. 2 shows VC and V in FIG. 1. (a) is a diagram showing the voltage waveform of
, ((ri is the waveform at no load, (b), (d) is the waveform at load. 2... Main transformer - next side rectifier circuit, 4... In 8 -
5...Main transformer, 6...Main transformer secondary side. rectifier, 10, 11.13... Feedforward 1.1 control means (10... three-phase transformer for control, 11...
...For control. three-phase full-wave rectifier circuit, 13...addition circuit), 12.
.... Inverter drive circuit, 14... welding voltage setting circuit. □□□－－－－”

Claims (1)

[Claims] Commercial frequency voltage is converted to a rectifier circuit and an inverter. It is converted into alternating current with a frequency higher than the commercial frequency. In addition to the secondary side of the voltage transformer, it also rectifies the secondary output of the main transformer. In an arc welding power source that obtains DC output for welding. The main transformer has the same rectification method as the next side. The ripple current voltage obtained by rectifying the commercial frequency voltage. A welding power source characterized by comprising feedforward control means for changing the output pulse width or output frequency of the inverter as a control signal so as to cancel out ripples in the output power of the main transformer-next side rectifier circuit. .