JPH03124374A - Ac arc welding power source - Google Patents

Abstract

PURPOSE:To lessen the generation of deviated magnetism by a difference in the primary current of a transformer and to prevent the burn of the transformer by providing inverter circuits to the primary side and secondary side of the transformer and controlling the output. CONSTITUTION:The AC voltage of the high frequency outputted from the primary inverter circuit 4 is dropped to the voltage suitable for welding and is outputted from the secondary side by an inverter transformer 5 for welding. The dropped AC voltage of a high frequency is rectified to a DC by a diode bridge 23 consisting of rectifying diodes 6, 7, 8, 9 and is smoothed by reactors 10, 11 for smoothing. The smoothed DC voltage is converted again to the AC by the secondary inverter circuit constituted of secondary transistors 14, 15. This AC is outputted to an output terminal 18.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an AC arc welding power source for an AC arc welding machine.

Conventional AC arc welding has different welding characteristics depending on its polarity. Positive polarity, where the electrode is the cathode and the base metal is the anode, provides deep penetration, while reverse welding, where the electrode is the anode and the base metal is the cathode, results in deep penetration. With polarity, penetration is shallow, but it has the effect of removing the oxide film on the base metal, that is, the cleaning effect. Conventionally, when welding aluminum, this cleaning action is used to
An AC arc welding power source is used to remove the oxide film (aluminum oxide A120B) formed on the aluminum surface.

An AC arc welding power source for obtaining this type of AC arc is described, for example, in Japanese Patent Publication No. 15537/1983. As shown in FIG.
3. Connect the capacitor 34 and resistor 35 in series,
A sine wave or rectangular wave AC output was obtained for the AC input to the primary side of the transformer 31. However, in the case of an AC arc, due to the difference in electron emission ability between the electrode 32 and the base material 36, the load impedance is lower during positive polarity than when reverse polarity, and there is a difference in load current between positive polarity and reverse polarity. This caused biased magnetism to occur in the transformer.

Problems to be Solved by the Invention As mentioned above, in order to maximize the effect of the welding characteristics due to the polarity of the AC arc, it is necessary to reduce the biased magnetization of the transformer and prevent burnout of the transformer. I had to. For this reason, conventionally there has been a problem that the volume and weight of the transformer are large compared to the maximum load current, and the price is also high.

In addition, when switching between positive and reverse polarity, a back electromotive force is generated due to the inductance of the inductive element connected to the load, such as the inductance of cables connected to the base material or electrode, and a diode or other voltage is generated on the secondary side of the transformer. When a semiconductor element such as a transistor is used, there is a risk that the semiconductor element may be damaged by this back electromotive force. For this reason, it has conventionally been necessary to increase the breakdown voltage of semiconductor elements more than necessary.

Further, the conventional AC arc welding power source has a problem in that it is not possible to obtain the optimum current conduction ratio for the base material by changing the current conduction ratio of positive polarity and reverse polarity depending on the material of the base material.

The present invention solves these conventional problems, and eliminates biased magnetism in the transformer to prevent burnout of the transformer, as well as prevent damage to semiconductor elements used on the secondary side of the transformer. It is an object of the present invention to provide an excellent AC arc welding power source that can prevent such problems and obtain an optimum energization ratio for the base material.

Means for Solving the Problems In order to solve the above problems, the present invention provides a rectifier circuit 110 connected to an input terminal 100 to rectify alternating current into direct current, as shown in FIG. a primary inverter circuit 120 connected to the primary inverter circuit 120 for converting rectified DC output into high-frequency AC;
A welding inverter transformer 130 is connected to the welding inverter transformer 130 for stepping down the converted high-frequency AC voltage to a voltage suitable for welding, and is connected between both ends of the secondary winding of the welding inverter transformer 130 and an intermediate tap. a positive and negative power supply circuit 140 having a diode bridge, a smoothing reactor, and a secondary smoothing capacitor for rectifying the high-frequency AC voltage stepped down into DC;
A secondary inverter circuit 150 that combines a secondary transistor with a power supply circuit 140 and outputs low-frequency alternating current to an output terminal 160; and a secondary inverter circuit 150 that is connected to the primary inverter circuit 110 and controls the conduction time of the primary inverter circuit 110 using PWM. a primary inverter control circuit 170 for controlling the output current; a waveform control circuit 180 connected to the primary inverter control circuit 170 for waveform control of the output current;
2 for driving the secondary transistor.
and a transistor drive circuit 190.

Effects The present invention has the above-mentioned configuration to reduce fluctuations in the load current in the welding inverter transformer.
By reducing the occurrence of biased magnetism, it is possible to prevent burnout of the transformer. Further, since the back electromotive force generated when switching between positive and reverse polarity can be absorbed by the secondary smoothing capacitor, damage to the semiconductor element can be prevented.

Furthermore, since the energization ratio of positive polarity and reverse polarity can be controlled,
It has the effect of being able to obtain the optimum energization ratio for the base material.

Example FIG. 2 shows the configuration of an embodiment of the present invention.

In Figure 2, 1 is the input terminal of the welding power source, 2 is a bridge diode connected to input terminal 1 to rectify the AC input to DC, and 3 is connected to the bridge diode 2 to smooth the rectified DC output. A smoothing capacitor 4 is connected to the smoothing capacitor 3 to convert the smoothed DC output into high frequency AC, and 5 is a primary inverter circuit connected to the primary inverter circuit 4 to convert the smoothed DC output into high frequency AC. A welding inverter transformer 6.7.8.9 is connected to the secondary side of the welding inverter transformer 5 to convert the stepped-down high frequency AC voltage into DC voltage. rectifier diode to rectify the
10.11 is a smoothing reactor for smoothing the rectified DC output, and 12.13 is for absorbing the back electromotive force of the cable inductance connected between the output terminals of the welding power source via the flywheel diode 16.17. The secondary smoothing capacitor 14.15 constitutes the secondary inverter circuit for converting DC output to low frequency AC.
16 and 17 are flywheel diodes connected in parallel to the secondary transistors 14 and 15, 18 is a welding power source output terminal, and 19 is for detecting the current flowing through the center tap 5b of the welding inverter transformer 5. A current transformer 20 sets the conduction time of the primary inverter circuit 4 by P W M (P pulse widthMod
The primary inverter control circuit 21 outputs a primary inverter control signal to the primary inverter control circuit 20 and outputs a secondary inverter control signal to the secondary transistor drive circuit 22 to control the output current. A waveform control circuit 22 is a secondary transistor drive circuit for driving the secondary transistors 14 and 15.

One end 5a of the secondary winding of the welding inverter transformer 5 is
It is connected to a common connection point between the anode and cathode of a pair of anode-cathode series diodes 6.8 of a diode bridge 23, which has four rectifier diodes 6.7.8.9 in a bridge configuration, and The end 5c is connected to the common connection point of the anode and cathode of another set of anode-cathode series diodes 7.9. Further, one end of one smoothing reactor 10 is connected to the cathode common connection point of this diode bridge 23, and one end of one secondary smoothing capacitor 12 is connected to the other end of this smoothing reactor 10. . In addition, the secondary smoothing capacitor 12
The other end is connected to the center tap 5b of the secondary winding of the welding inverter transformer 5 via the current transformer 19, and is also connected to one end of another secondary smoothing capacitor 13. The other end of the other secondary smoothing capacitor 13 is connected to one end of another smoothing reactor 11, and the other end of the other smoothing reactor 11 is connected to the anode common connection point of the diode bridge 23. Further, both ends of the current transformer 19 are connected to inputs A and B of the waveform control circuit 21, respectively, so that a secondary current signal can be obtained. With such a connection, the secondary smoothing capacitor 12.13
The common connection point 24 of the smoothing reactor 10 is set to O potential, and the smoothing reactor 10
A two-power circuit is constructed in which a connection point 25 between the smoothing reactor 11 and the secondary smoothing capacitor 12 is a positive power terminal, and a connection point 26 between the smoothing reactor 11 and the secondary smoothing capacitor 13 is a negative power terminal.

The collector of one secondary transistor 14 is connected to the positive power terminal 25 of this dual power supply circuit, and the emitter of the secondary transistor 14 is connected to the collector of the other secondary transistor 15. The other secondary transistor 15
The emitter is connected to the other smoothing reactor 11 and the other 2
It is connected to a negative power supply terminal 26 which is a connection point with the next smoothing capacitor 13. The connection point between the emitter of the secondary transistor 14 and the collector of the other secondary transistor 15 is connected to one end of the output terminal 18, and the other end of the output terminal 18 is connected to the common connection point of the secondary smoothing capacitors 12 and 13. It is connected. Further, outputs 0a and b of the secondary transistor drive circuit 22 are connected to the base and emitter of one secondary transistor 14, respectively, and outputs c and d are connected to the base and emitter of the other secondary transistor 15. . Such a connection constitutes a secondary inverter circuit.

Next, the operation of the above embodiment will be explained. In FIG. 1, an AC input input to a welding power supply input terminal 1 is converted into DC by a rectifying bridge diode 2, and this converted DC output is smoothed by a smoothing capacitor 3, and then is connected to a primary inverter circuit. 4 is input. Next, the DC voltage input to the primary inverter circuit 4 is converted to high-frequency AC, and the DC voltage is converted to high-frequency AC.
Input to the next side. The high frequency AC voltage output from the primary inverter circuit 4 is transferred to a welding inverter transformer 5.
The voltage is stepped down from the secondary side to a voltage suitable for welding and output. This stepped down high frequency AC voltage is passed through a diode bridge 2 consisting of rectifier diodes 6,7,8,9.
3, the current is rectified into DC, and then the smoothing reactor 10
, 11. The smoothed DC voltage is converted back into AC by a secondary inverter circuit composed of secondary transistors 14 and 15, and rectangular wave currents 11 and I2 as shown in FIG. 3 are output to the output terminal 18. .

The current 11 shown by the solid line in FIG. inverter transformer 5
intermediate tap 5b.

It flows through the path of the rectifier diode 6.7 and the smoothing rear phthalate 1o. When this current (1) is turned off and a current I2 of the opposite polarity flows, the induced voltage generated by the inductance of the output cable connected to the output terminal 18 is absorbed by the secondary smoothing capacitor 13. The voltage absorption function of the smoothing capacitor 13 suppresses the application of excessive voltage to the secondary transistor 14.

In addition, a current I2 of opposite polarity shown by a broken line is generated by connecting the other smoothing reactor 11 and the secondary smoothing capacitor 1 2 to the negative power terminal 26 to the smoothing reactor 11 . Rectifier diode 8.9, intermediate tap 5b of welding inverter transformer 5.

The current flows through the current transformer 19, the output terminal 18, and the secondary transistor 15. When this current I2 is turned off and the current 11 of the opposite positive polarity flows again, the induced voltage generated by the inductance of the output cable connected to the output terminal 18 is absorbed by the secondary smoothing capacitor 12. This 2
Due to the voltage absorption function of the secondary smoothing capacitor 12, application of the maximum voltage to the secondary transistor 15 is suppressed.

These main circuit currents 1 and I2 have AC waveforms as shown in Fig. 3, but the peak value Ia of each current is
, the ratio of the currents 1 and 12 and the alternating current frequency f due to changes in the pulse width Td are controlled by the waveform control circuit 21. Further, the current peak value ■a is controlled by PWM control of the primary inverter circuit 4. The Td change and AC switching for ratio control are controlled by a waveform control circuit 21 and a secondary transistor drive circuit 22.

As described above, according to the above embodiment, it is possible to output a low frequency alternating current rectangular wave current as shown in FIG.

Effects of the Invention As is clear from the above embodiments, the present invention provides inverter circuits on the primary and secondary sides of the transformer to control the output. The occurrence of biased magnetism can be reduced, and burnout of the transformer can be prevented. In addition, in order to absorb the back electromotive force generated in the output cable when switching polarity with a secondary smoothing capacitor before the next polarity starts, semiconductor elements such as transistors and diodes used on the secondary side of the transformer are used. Therefore, it is possible to obtain a safe, reliable, and inexpensive AC arc welding power source. moreover,
Since the energization ratio of positive polarity and reverse polarity can be set arbitrarily, it is possible to obtain the optimum energization ratio for the base material, and to maximize the effect of the welding characteristics of each polarity in AC arc welding. It has the effect of

3 4

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the overall configuration of the present invention, Fig. 2 is a schematic circuit diagram of an AC arc welding power source showing an embodiment of the present invention, and Fig. 3 is a current waveform diagram showing the current waveform in the same embodiment. , FIG. 4 is a circuit diagram showing an example of a conventional AC arc welding power source. 1... Welding power supply input terminal, 2... Bridge diode, 3... Smoothing capacitor, 4... Primary inverter circuit, 5... Welding inverter transformer, 6.7.
8.9... Rectifier diode, 10.11... Smoothing reactor, 12.13... Secondary smoothing capacitor,
14.15... Secondary transistor, 16.17...
Flywheel diode, 18... Welding power supply output terminal, 19... Current transformer, 20... Primary inverter control circuit, 21... Waveform control circuit, 22... Secondary transistor drive circuit, 23 ...Diode bridge, 2
4...2 power circuit positive power terminal, 25...2 power circuit negative power terminal. 100... Input terminal, 110... Rectifier circuit, 120
...Primary inverter circuit, 130...Inverter transformer for welding, 140...2 power supply circuit, 150...
Secondary inverter circuit, 160...output terminal, 170...
...Primary inverter control circuit, 180... Waveform control circuit, 190... Secondary transistor drive circuit.

Claims (1)

[Claims] A rectifier circuit connected to an input terminal for rectifying alternating current into direct current; and a rectifier circuit connected to the rectifier circuit for converting the DC voltage rectified by the rectifier circuit into high-frequency alternating current. a primary inverter circuit; a welding inverter transformer connected to the primary inverter circuit to step down the high frequency AC voltage converted by the primary inverter circuit to a voltage suitable for welding; and the welding inverter. A diode bridge, a smoothing reactor, and a secondary smoothing capacitor connected between both ends of the secondary winding of the transformer and the intermediate tap for rectifying the high frequency AC voltage stepped down by the welding inverter transformer into DC. a secondary inverter circuit that combines a secondary transistor with the two power supply circuits and outputs low-frequency alternating current to an output terminal; and a secondary inverter circuit that is connected to the primary inverter circuit and that a primary inverter control circuit for PWM control of the conduction time of the inverter circuit; a waveform control circuit connected to the primary inverter control circuit for waveform control of the output current; An AC arc welding power source comprising a secondary transistor drive circuit for driving a secondary transistor.