JPS63286275A - Power unit for ac arc welding machine - Google Patents

Abstract

PURPOSE:To prevent switching transistors from breaking down by providing a voltage feedback circuit to rectify the secondary side output voltage of a transformer for the voltage feedback and feed it back to a smoothing capacitor of a rectifier circuit. CONSTITUTION:A part of a current based on the induced voltage of a reactor 25 is allowed to flow to a primary side of the transformer 26b for the voltage feedback after passing through a capacitor 26a for eliminating a DC part. As a result, the primary side is excited and the voltage is generated on the secondary side. The voltage is rectified by a rectifier 26d and fed back to the smoothing capacitor 3 of the first rectifier circuit. By this method, the size of the feedback current flowing to a smoothing capacitor 11 is extremely reduced and the charging voltage of said capacitor is prevented from rising up to such an extent to break down the switching transistors.

Description

DETAILED DESCRIPTION OF THE INVENTION (aJ Field of Industrial Application) The present invention relates to a power supply device for an AC arc welding machine that performs AC arc welding on aluminum or the like using a switching I transistor or the like.

fb) Prior Art As a conventional power supply device for an AC arc welding machine, a power supply device for an AC arc welding machine has been put into practical use, which once converts a commercial power source into a high frequency wave, and then transforms the voltage and shapes the wave into a rectangular wave. A circuit diagram of this power supply device for an AC arc welding machine is shown in FIG.

In this power supply device, as shown in the figure, after rectifying and smoothing a three-phase AC power supply 1 with a rectifier circuit 2 and a smoothing capacitor 3,
Switching transistor 4.5 and output control circuit 6
High frequency switching is performed at high frequency (usually 2 to 20K).
Hz). Furthermore, the high frequency output is transformed into several tens to several digit volts by a transformer 7, and then converted back to direct current by a rectifier 8.9, a smoothing reactor 10, and a smoothing capacitor 11. After that, the switching transistors 12 to 15 and the low frequency control circuit 16 perform an inversion switching operation to generate a highly accurate rectangular wave (usually 50' to 100'Hz).
I am trying to obtain a welding current of . In the figure, 17 is a high frequency oscillator to facilitate arc ignition at the start of operation when performing IG welding, etc., and 20 is a current detector, whose detected value is fed back to the output control circuit 6. constant current control of the output. Further, the switching transistors 12 to 15 are usually provided with protection diodes 21 to 15 to protect them.
24 are connected in parallel.

In the above-mentioned power supply device for an AC arc welding machine, since voltage transformation and rectification can be performed at high frequency, the transformer and accelerator can be configured for high frequency use, making it possible to achieve miniaturization and cost reduction, and the detection value of the current detector 20 Based on this, the current control of the output control circuit 6 can be performed accurately with a fast response speed. Further, the low frequency control circuit 16 performs switching operation of the switching transistor to perform AC arc welding, while the switching l-run raster 12, 15 or 13
．． There is also the advantage that direct current arc welding can be performed by keeping either one of 14 in the on state.

(C) Problems to be solved by the invention However, in the above power supply device for an AC arc welding machine,
If the distance between the power supply device and the thick cable 119 is long, it is necessary to lengthen the cable attached to the power supply device. If this long cable is attached, the cable may become coiled if the base material is placed close to the power supply unit. In such a case, the reactor 25 is formed by the cable itself as shown in the figure.

Now considering that the switching transistors 14 and 13 are on, the load current flows through the switching transistor 14, the reactor 25, the base metal 19, the welding electrode 18, the high frequency oscillator 17, and the switching transistor 13. Is voltage generated in the direction shown by the solid line in the figure?
4. At the moment when 13 turned off, reactor 2
5, a voltage indicated by a dotted line in the figure is induced. Based on this voltage, a circulating current i flows through the path of base material 19, welding electrode 18, high frequency oscillator 17, protection diode 21, smoothing capacitor 11, and protection diode 24, and smoothing capacitor 11 is charged. Circulating current i flows in the same direction when switching transistors 12, 15 turn from on to off, and capacitor 11 is charged by this circulating current. Therefore, depending on the size of the reactor 25 generated in the cable, a considerably high voltage may be charged to the smoothing capacitor 11, and this voltage may destroy the switching transistors 12 to 15. For example 20
When a cable of m length is wound with a diameter of 400 mm, the interfedance is approximately 85 μI-I. 300A to this cable
When a current of (when the capacitor is 1000 μF) flows, the voltage generated in the reactor 25 is approximately 123V.

In the conventional power supply device, since a high voltage may be generated in the reactor 25 as described above, the charging voltage of the smoothing capacitor 11 gradually decreases during use.

Eventually, there was a possibility that the switching transistors 12 to 15 would be destroyed by this voltage.

The purpose of this invention is that the voltage generated when the cable is wound and a reactor is generated is an alternating voltage that is different from the square wave voltage applied to the load, so it is possible to extract only this alternating voltage. It is an object of the present invention to provide a power supply device for an AC arc welding machine in which the charging voltage of the smoothing capacitor is prevented from exceeding a certain level by feeding the voltage back to the smoothing capacitor of the first rectifying circuit.

(('') Means for Solving the Problems This invention comprises a first rectifier circuit that rectifies and smoothes an AC power source, a high frequency conversion circuit that converts a DC voltage into a high frequency voltage, and a high frequency conversion circuit that converts a high frequency voltage into a high frequency voltage. a smoothing circuit including a smoothing reactor and a smoothing capacitor for smoothing the rectified output; a smoothing circuit including a smoothing reactor and a smoothing capacitor for smoothing the rectified output; and a smoothing output of the smoothing circuit. In a power supply device for an AC arc welding machine, the power supply device has an opening/closing circuit that applies a positive or negative polarity to a welding electrode and a base material, and the opening/closing circuit includes a switching element that turns on and off alternately and a protection diode for the switching element, A series circuit consisting of a DC component removal capacitor and the primary winding of the voltage feedback transformer is connected between the output terminals of the switching circuit, and the secondary output voltage of the voltage feedback transformer is rectified. The present invention is characterized by providing a voltage feedback circuit that feeds back to the smoothing capacitor of the first rectifier circuit.

te1 Effect In the type # device for an AC arc welding machine according to the present invention, AC power is once rectified into DC in the first rectifier circuit, and then converted into high frequency in the high frequency conversion circuit. Further, the high frequency voltage is transformed by a transformer, rectified and smoothed by a second rectifier circuit, and outputted to the switching circuit. In the open/close circuit, switching elements alternately turn on and off to convert the current into a low-frequency rectangular wave.
Output to the welding electrode and base metal. When performing AC arc welding, if a reactor is formed in the cable connecting the base metal and the power supply, during switching,
That is, a voltage is induced in the reactor at the timing when the polarity changes from positive polarity (or negative polarity) to negative polarity (or positive polarity). The direction of the voltage induced at this time is the direction of the current that was flowing immediately before. Therefore, the polarity of the protection diode connected to the C switching element is in the forward direction with respect to the polarity of this induced voltage, and a circulating current flows through the welding electrode, the base material, and the protection diode based on the induced voltage. This circulating current charges the smoothing capacitor of the smoothing circuit. However, since this circulating current flows based on the kick voltage of the accelerator, unlike the load current waveform (rectangular wave), ldi/dtl is always positive. In other words, it changes in an alternating current manner. Therefore, a part of the current based on the induced voltage of the reactor passes through the DC component removal capacitor connected between the output terminals of the switching circuit and is applied to the primary winding of the voltage feedback transformer. The secondary winding output voltage of the voltage feedback transformer is rectified by the feedback circuit and fed back to the smoothing capacitor of the first rectifier circuit.

Therefore, a part of the voltage formed in the cable or generated in the axle is returned to the smoothing capacitor of the first rectifier circuit by the feedback circuit, so that the circulating current flows and the smoothing capacitor of the smoothing circuit is unlimitedly charged. never done. Therefore, the increase in the charging voltage of the smoothing capacitor can be limited to below the breakdown voltage of the switching element of the opening/closing circuit. When a reactor is formed and a kick voltage is generated across the reactor, the voltage is fed back to the first rectifier circuit, so no energy loss occurs.

(f) (b) Embodiment FIG. 1 is a circuit diagram of a power supply device for an AC arc welding machine which is an embodiment of the present invention.

The difference between this embodiment and the power supply device shown in FIG. 4 above is that a series circuit of a DC component removal capacitor 26a and a primary winding of a voltage feedback transformer 26b is connected between the output terminals a and b of the switching circuit. Connect and also connect a capacitor for high frequency removal in parallel to the series circuit! A rectifier 2Gd forming a feedback circuit is connected between the secondary winding output terminals of the voltage feedback transformer 26b, and the rectified output terminal is connected to the smoothing capacitor of the first rectifier circuit. This is the point connected to 3.

Next, the operation will be explained.

When the power is turned on, the AC voltage first passes through the first rectifier circuit 2.
After being rectified and smoothed by a smoothing capacitor 3, it is switched at a predetermined duty by switching transistors 4 and 5 of a high frequency conversion circuit. The switching voltage is transformed by a transformer 7, rectified by diodes 8 and 9, and sent to a smoothing circuit. The output smoothed by the smoothing reactor 10 and the smoothing capacitor 11 is output to a switching circuit having four switching transistors and stars 12 to 15, where it is alternately switched to positive polarity or negative polarity and supplied to a load. In the case of positive polarity, transistor 13.
14 is turned on. In this positive polarity, the smoothed output is the transistor 14, the reactor 25 formed in the cable.
, the base metal 19, the welding mold 18, the high frequency oscillator 17.1, and the transistor 13. Also, when the polarity is negative, transistors 12 and 15 are turned on, and the smoothed output is provided by transistors 2 and 2.
The current flows through the high frequency oscillator 17, the welding electrode 18, the base material 19, the reactor 25, and the transistor 15. At the time of arc start, the high frequency oscillator 17 is activated to facilitate transition to the arc state. When an arc occurs, the high frequency oscillator 17 is turned off, and the load current flows alternately with positive polarity and negative polarity. The load current is detected by the current detector 20, and the detected value is output to the output control circuit 6. The output control circuit 6 compares the detected value from the current detector 20 with a reference value set by the variable resistor 6a, and determines the duty of the switching pulse output to the switching transistors 4 and 5 based on the magnitude of the error. Control. That is, the duty of the switching pulse is controlled so that the detected value and the reference value are equal. By performing this operation, constant current control of the load current (output current) is performed. Further, the low frequency control circuit 16 outputs switching pulses that alternately turn on and off the switching transistors 12 to I5, and the switching frequency can be changed by a variable resistor I6a. Such a circuit can be easily constructed using a multi-by-break circuit. The frequency of the switching pulse generated by the output control circuit 6 is normally controlled in the range of 2 to 20KH2,
The frequency of the switching pulses generated at 6 is typically 50
It is controlled in the range of ~100Hz.

During arc operation, the voltage induced in the reactor 25 at the time of switching (the moment of switching from positive polarity to negative polarity or the moment of switching from negative polarity to positive polarity),
The protection diode connected to the transistor that is being switched from on to off is in the forward direction. Therefore, based on the induced voltage, the base material 19. Welding electrode 18. A circulating current flowing through the high frequency oscillator 17 flows into the smoothing circuit, and the smoothing capacitor 11 is charged by the current.

Since this circulating current flows every time the polarity changes, the charging voltage of the smoothing capacitor 11 tends to gradually increase. However, a part of the current based on the induced voltage of the reactor 25 passes through the DC component removal capacitor 26a and flows to the primary side of the voltage feedback transformer 26b. Therefore, its negative side is excited and a voltage is generated on the secondary side. This voltage is rectifier 2
6d and fed back to the smoothing capacitor 3 of the first rectifier circuit. Note that the turns ratio between the primary side and the secondary side of the voltage feedback transformer 26d is set to such an extent that the output voltage on the secondary side is approximately equal to the rectified output voltage of the first rectifier circuit.

Due to the above-mentioned effect, the magnitude of the feedback current flowing through the smoothing capacitor 11 becomes extremely small, and it is possible to prevent the charging voltage of the capacitor from increasing to the extent that it will destroy the switching transistor. Note that the high frequency removal capacitor 26C is for removing high frequency components generated during switching.

The fact that a certain amount of voltage is generated on the primary side of the voltage feedback transformer 26b means that a reactor is formed in the cable connected to the base material 19. This reactor causes the charging voltage of the smoothing capacitor to increase as described above, and also slows down the load current. Ideally, the load current is a rectangular wave, but if it is no longer a rectangular wave due to the reactor, the welding current may become insufficient and a smelting defect may occur. Furthermore, when performing 1% aluminum welding, there are cases where the leaning action cannot be performed sufficiently when the polarity is negative, making welding impossible. In order to avoid such a situation, in the example shown in FIG. 2, the voltage on the primary side of the voltage feedback transformer 26d is rectified and compared with the reference voltage E0 by the comparator 31. -The voltage on the next side is the reference voltage E. When the temperature exceeds that level, the alarm circuit 29 is activated.
An alarm sound is emitted from the speaker 30 to the outside. When the alarm sounds in this way, workers nearby can see that the cable is coiled and a reactor is formed, so when the alarm sounds, the It is possible to straighten the rolled part.

FIG. 3 shows another embodiment of the invention.

In this embodiment, the switching transistors 4.5 are connected in a half-bridge manner on the primary side of the transformer 7. Further, the secondary output of the transformer 7 is rectified into positive and negative by the diodes 31 to 34, the positive rectified output passes through the first smoothing reactor 50, and the negative rectified output passes through the second smoothing reactor 51. . The positive output flowing through the first smoothing reactor 50 is connected to the smoothing capacitor 11 via the diode 27.
The charging voltage is applied between the welding electrode 18 and the base material 19 via the first switching transistor 36. Further, the negative current flowing through the second smoothing reactor 51 charges the smoothing capacitor 11, and the charging voltage is applied between the welding electrode 18 and the base material 19 via the second switching transistor 37. In this embodiment, two switching transistors 36 and 37 are used as switching elements of the opening/closing circuit as described above, and each transistor alternately supplies a positive output and a negative output to the load. The low frequency control circuit 16 includes a variable resistor 1
A switching pulse having a frequency set by 6a is supplied to the transistors 36 and 37, and each transistor 3G and 37 is turned on and off alternately by this pulse. 44 and 45 are protection diodes connected in parallel to these switching transistors 36 and 37.

Further, in this embodiment, the iron cores of the first smoothing reactor 50 and the second smoothing reactor 51 are made the same, and their respective windings are coupled. The direction of the bond is in the opposite direction. Therefore, as shown in the figure, a voltage V2 is induced in the second smoothing reactor 51 in the M direction by the induced voltage (1) generated in the L direction in the first smoothing reactor 50. With this configuration, when a voltage of positive polarity is applied to the load, that is, from a state where the switching transistor 36 is on, the voltage is switched to negative polarity.
At the timing of the switching, a voltage ■1 is generated in the first smoothing reactor 50 in the direction shown in the figure, and induced by this voltage, a voltage ■1 is generated in the second smoothing reactor 51 in the M direction.
2 will occur.

This voltage V2 is added to the negative voltage rectified by the diodes 33 and 34 when the polarity changes from positive to negative, so the moment the polarity changes to negative,
A large voltage is applied between the welding electrode 18 and the base material 19.

Therefore, it is possible to prevent the arc from misfiring at this electrode time, and there is an advantage that a stable arc state can be maintained.

At the output of the switching circuit of the AC arc welding power supply device having the above configuration, there is a series circuit of the DC removal capacitor 26a and the voltage feedback transformer-next winding, and a high frequency removal circuit is connected in parallel to the series circuit. Condenser 26b is connected. Further, the secondary winding output of the voltage feedback transformer 26b is connected to a rectifier 26d, and the rectified output terminal is connected to the smoothing capacitor 3a to the input side of the high frequency conversion circuit.

It is connected to the terminal 3b. When the voltage across the primary winding of the voltage feedback transformer 26b exceeds a certain level, the output from the secondary winding is rectified and returned to the smoothing capacitors 3a, 3b on the power supply rectification side.

(g) Effects of the Invention According to this invention, even if the cable is in a wound state and a reactor component is formed in that part, the charging voltage of the smoothing capacitor is prevented from rising above a certain voltage. Therefore, it is possible to prevent the switching transistor in the switching circuit from being destroyed. Further, since the voltage feedback circuit operates to return excess energy stored in the smoothing capacitor to the primary side (smoothing capacitor of the first rectifier circuit), there is an advantage that there is no energy loss.

[Brief explanation of drawings]

FIG. 1 shows a circuit diagram of an embodiment of the invention. FIG. 2 shows a partial circuit diagram of another embodiment, and FIG. 3 shows a circuit diagram of still another embodiment. Further, FIG. 4 shows a circuit diagram of a conventional power supply device. 12-15.36, 37, - Switching element (switching transistor) of opening/closing circuit, 21-24.44.
45-protection diode, 26a-capacitor for direct current removal, 26b--voltage feedback transformer, 26d-rectifier (voltage feedback circuit).

Claims (1)

[Claims] (1) A first rectifier circuit that rectifies and smoothes an AC power source;
a high-frequency conversion circuit that converts DC voltage into high frequency; a transformer that transforms the high-frequency voltage; a second rectifier circuit that rectifies the output of the transformer into positive and negative; and a smoothing circuit that smooths the rectified output. It has a smoothing circuit including a reactor and a smoothing capacitor, and an opening/closing circuit that switches the smoothed output of the smoothing circuit and applies it to a welding electrode and a base material with positive polarity or negative polarity, and the opening/closing circuit is a switching element that is turned on and off alternately. In the power supply device for an AC arc welding machine comprising a protection diode, a series circuit of a DC component removal capacitor and a primary winding of a voltage feedback transformer is connected between the output terminals of the switching circuit, and A power supply device for an AC arc welding machine, comprising a voltage feedback circuit that rectifies the secondary output voltage of the feedback transformer and returns it to the smoothing capacitor of the first rectifier circuit.