JP2001030072A - Control method for ac arc welding power source and power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent collapse of a switching element by setting a changeover electric current low by arithmetically processing an inductance at the time of polarization changeover with the variation rate of a welding electric current and an arc voltage before the polarization changeover during the time when the output of a first inverter circuit is temporally withheld. SOLUTION: A first inductance value arithmetic and logic unit 37 calculates a first inductance value (L7+L47+L48) between a reactor 7 and welding cables 47 and 48 with inputs of variation rate (di1/dt1) calculated by a first differentiation device 36 and of an output signal from an arc voltage detector 39. An arithmetic and logic unit 38 for polarization changeover electric current calculates a polarization changeover electric current corresponding to the first inductance value (L7+L47+L48) with an input of a result of arithmetic operation from the first inductance value arithmetic and logic unit 37. Or, further, the polarization changeover electric current is calculated by taking the resistances of welding cables 47 and 48 and a voltage drop of a switching element and others into consideration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an AC arc welding power supply device for switching the output polarity using a switching element.

[0002]

2. Description of the Related Art DC power obtained by rectifying a commercial AC power supply is converted into high-frequency AC power by a first inverter circuit, and this high-frequency AC power is converted into power suitable for arc machining, and rectified again. Second element
In an AC arc welding power supply unit that switches between a positive electrode and a negative electrode by an inverter circuit and supplies AC power to an arc load, when the polarity of the output is switched, after the arc once disappears, the voltage of the opposite polarity increases. The arc reignites. In many cases, the AC arc welding power supply device and the place where welding is performed are far from each other, and the two are connected by a welding cable to supply welding power. Therefore, when the polarity of the output is switched using the switching element, an induced electromotive force is generated by the inductance of the welding cable, and the induced electromotive force is used as a re-ignition voltage of the arc. However, if the welding cable is long, the induced electromotive force increases, but if the induced electromotive force is too high, the switching element of the second inverter circuit may be broken.

For this reason, conventionally, the output of a first inverter circuit for converting DC power obtained by rectifying a commercial AC power supply to high-frequency AC power is temporarily stopped, and it is assumed that the length of a welding cable is constant. Then, when the induced electromotive force generated by the inductance of the welding cable becomes higher than the re-ignition voltage of the arc and becomes an appropriate voltage lower than the voltage at which the switching element is destroyed, There is a technique for switching the polarity of the output to facilitate re-ignition of the arc and to prevent the switching element of the second inverter circuit from being destroyed. However, as described later in the section of [Problems to be Solved by the Invention], at the actual welding work site, the inductance of the welding cable changes with the length of the welding cable or the movement of the welding position. Frequently, the requirements of re-ignition of the arc and prevention of destruction of the switching element cannot be satisfied at the same time.

FIG. 1 shows a conventional AC arc welding in which the requirements for the re-ignition of the arc and the prevention of the destruction of the switching element can be simultaneously satisfied only when the length of the welding cable is constant. It is a control block diagram of a power supply device. In FIG. 1, reference numeral 1 denotes an AC power supply, which uses a single-phase commercial AC power supply or a three-phase commercial AC power supply. 2 is a first rectifier circuit that rectifies the output of the AC power supply 1 and converts it to DC power;
3 is a smoothing circuit for smoothing the output of the first rectifier circuit 2, 4 is a first inverter circuit for converting the output of the smoothing circuit 3 to high-frequency AC power, and 5 is an electric power suitable for arc machining of the output of the first inverter circuit 4. 6 is a second rectifier circuit for rectifying the output of the output transformer 5, and 7 is a second rectifier circuit 6.
Reactor connected to one of the terminals. 8a to 8
d is a bridge-connected switching element. 9
a to 9d and 10a to 10d are snubber resistors and snubber capacitors connected in parallel to the switching elements 8a to 8d, and are provided to reduce overvoltage applied to the switching elements 8a to 8d. The second inverter circuit 46 includes the first switching elements 8a and 8d, the second switching elements 8b and 8c, the snubber resistors 9a to 9d, and the snubber capacitors 10a to 10d. The second output is output via the reactor 7.
The output of the rectifier circuit 6 is converted into AC power.

Reference numeral 11 denotes a welding current detector for detecting a welding current; 12 and 13 output terminals; 47, a welding cable connecting the output terminal 12 and the welding torch 14; 48, an output terminal 13 and the workpiece 15; It is a welding cable that connects between Reference numeral 40 denotes a consumable electrode, which is a motor 41 during welding.
The workpiece is fed from the wire reel 43 toward the workpiece 15 by a feed roll 42 driven by the feed roller 42. Reference numeral 44 denotes a motor control circuit for rotatingly driving the motor 41 in accordance with the output signal of the torch switch TS, and feeds the consumable electrode 40 at a relatively low speed at the start of welding, and feeds at a normal speed after starting the arc. It has a known speed control function.

A comparator 17 compares an output signal Ir of a welding current setting circuit 20, which will be described later, with an output signal If of the welding current detector 11, and outputs a difference signal ΔI = Ir−If. 17 is a first inverter control circuit that outputs a pulse signal having a pulse width and a frequency corresponding to the output signal #I to the first inverter circuit 4. Reference numeral 18 denotes a welding current discriminating circuit which compares the output signal of the welding current detector 11 with the output signal of the welding current discriminating value setting unit 45, and when the output signal of the welding current detector 11 is larger, Outputs a high level signal. Reference numeral 21 denotes an arc start current period setting circuit for setting a period during which the arc start current is supplied. When a high level signal of the torch switch TS is input, a high level signal is output, and a high level signal of the welding current determination circuit 18 is output. A signal is input to start a time period, and a high-level signal is output until the time period ends. Reference numeral 22 denotes a positive current period setting circuit for setting a period during which the welding torch 14 is supplied with a positive current having a positive polarity, and reference numeral 23 denotes a negative electrode for setting a period during which the welding torch 14 is supplied with a negative current having a negative polarity. It is a quiescent current period setting circuit.

Reference numeral 20 denotes a welding current setting circuit which sets respective current values of an arc start current period, a positive current period, and a negative current period, and outputs an output signal Ir of each current value for each period. . Reference numeral 34 denotes a polarity switching current value setting device which stops the output of the inverter control circuit 16 during each of the arc start current period, the positive current period, and the negative current period, and the welding current value is reduced during the stop period. A current value at which the polarity is switched due to a decrease is preset. Reference numeral 19 denotes a polarity switching discrimination circuit which compares the output signal of the welding current detector 11 with the output signal of the polarity switching current value setting unit 34, and when the output signal of the welding current detector 11 is larger, Outputs a high level signal. The first switching element 8 is controlled by the polarity switching current value setting device 34 and the polarity switching determination circuit 19.
a and 8d and the second switching elements 8b and 8c are switched, so that the surge voltage generated by the inductance of the welding cable reduces the first switching elements 8a and 8d and the second switching elements 8b and 8c. Protects from destruction.

Reference numeral 26 denotes an RS flip-flop circuit,
A high-level signal is output when the output signal of the negative current period setting circuit 23 is input as a set signal, and a low-level signal is output when a signal obtained by inverting the output signal of the polarity switching determination circuit 19 is input as a reset signal. Is output. An OR circuit 25 receives the output signals of the arc start current period setting circuit 21 and the positive polarity current period setting circuit 22 and outputs a high level signal when any of these signals is at a high level. . Reference numeral 33 denotes a changeover switch, which is connected to the a side when the high level signal of the torch switch TS is input, and connected to the b side when the low level signal of the torch switch TS is input. ing. Reference numeral 27 denotes an RS flip-flop circuit, which inputs a high-level signal of the OR circuit 25 as a set signal, outputs a high-level signal, inputs a signal obtained by inverting the output signal of the switch 33, and outputs a high-level signal. When it is a level signal, it is input as a reset signal and outputs a low level signal.

Reference numeral 29 denotes a first switching element drive circuit, which outputs a drive signal for conducting the first switching elements 8a and 8d when a high level signal of the RS flip-flop circuit 27 is input. Reference numeral 28 denotes a second switching element driving circuit, which outputs a driving signal for conducting the second switching elements 8b and 8c when a high level signal of the RS flip-flop circuit 26 is input. The positive polarity current period setting circuit 22 includes the RS flip-flop circuit 2
The negative current period setting circuit 23 inputs a signal obtained by inverting the output signal of No. 6 and the inverted signal of the output signal of the RS flip-flop circuit 27 via a switch 32 described later. While the RS flip-flop circuit 26 is outputting a high-level signal, the positive polarity current period setting circuit 2
2 does not output a high-level signal, and the negative polarity current period setting circuit 23 does not output a high-level signal while the RS flip-flop circuit 27 is outputting a high-level signal.

The circuit shown in FIG. 1 shows a case where welding is terminated in a positive current period. The switch 32 is turned on when a signal obtained by inverting the high level signal of the torch switch TS is input. When a signal obtained by inverting the low-level signal of the torch switch TS is input, the switch is turned off. The negative polarity current period setting circuit 23 does not output a high-level signal obtained by inverting the low-level signal of the RS flip-flop circuit 27, and does not output a high-level signal. Since the signal has not been input, the high-level signal is not output, and the positive polarity current period setting circuit 22 inputs the high-level signal obtained by inverting the low-level signal of the RS flip-flop circuit 26 and switches the torch switch TS. After being turned off, the operation ends in the positive current period. Reference numeral 30 denotes a NAND circuit which receives a signal obtained by inverting the output signal of the torch switch TS and a signal obtained by inverting the output signal of the positive current period setting circuit 22, and outputs a high level signal when both signals are at a high level. Output. An RS flip-flop circuit 31 outputs a high-level signal when a high-level signal of the torch switch TS is input as a set signal, and outputs a low-level signal when a high-level signal of the NAND circuit 30 is input as a reset signal. Output a signal. The first inverter control circuit 16 receives the high-level signal of the RS flip-flop circuit 31 and outputs a signal for driving the first inverter control circuit 4.

In FIG. 1, when a torch switch TS is pressed, an RS flip-flop circuit 31 inputs a high level signal of the torch switch TS as a set signal, outputs a high level signal, and outputs a high level signal.
Receives a high-level signal from the RS flip-flop circuit 31 and starts up, and outputs a drive signal to the first inverter circuit 4. As a result, the power from the AC power supply 1 becomes the first
After being rectified by the rectifier circuit 2, it is smoothed by the smoothing circuit 3 and converted to high-frequency AC power by the first inverter circuit 4. This output is converted to a voltage suitable for arc machining by the output transformer 5, converted again to DC by the second rectifier circuit 6, supplied to the second inverter circuit 46 via the reactor 7, and converted to high-frequency AC. Is done. This high-frequency AC power is supplied from the output terminals 12 and 13 between the consumable electrode 40 and the workpiece 15.

When the torch switch TS is pressed,
The arc start current period setting circuit 21 receives a high level signal of the torch switch TS and outputs a high level signal to the welding current setting circuit 20. The comparator 17 outputs the output signal If of the welding current detector 11 and the welding current setting circuit 20.
And the inverter control circuit 16 outputs to the first inverter circuit 4 a pulse signal having a pulse width or frequency corresponding to the difference signal ΔI. Drives the first inverter circuit 4 so as to obtain an output having a constant current characteristic. The arc start current period setting circuit 21 outputs a high level signal from the input of the high level signal of the torch switch TS to a high level signal of the welding current discriminating circuit 18 until the end of a preset period for starting a time period. Outputs a level signal.

An arc start current period setting circuit 2
1 outputs a high-level signal to the RS flip-flop circuit 27 via the OR circuit 25 as a set signal,
The S flip-flop circuit 27 receives the set signal and outputs a high-level signal, and the first switching element driving circuit 29 receives the high-level signal and outputs the first signal.
It outputs a drive signal for conducting the switching elements 8a and 8d. When the torch switch TS is pressed, the motor control circuit 44 starts by inputting a high-level signal of the torch switch TS, and the motor 41 starts rotating at a low speed.
The supply of the consumable electrode 40 toward the workpiece 15 is started slowly. When a short circuit occurs between the consumable electrode 40 and the workpiece 15 at this time, an arc is generated between the consumable electrode 40 and the workpiece 15 because a voltage for starting an arc is applied between the consumable electrode 40 and the workpiece 15. The welding current flows.

Thereafter, after the time period of the arc start current period setting circuit 21 ends, the arc start current period setting circuit 2
1 becomes low level, the output signal Ir of the welding current setting circuit 20 becomes zero, and the difference signal ΔI = Ir−If output from the comparator 17 is output to the first inverter control circuit 16. The output of the drive signal output from the first inverter control circuit 16 to the first inverter circuit 4 is stopped, and the first
The inverter circuit 4 stops. Thereafter, the polarity switching determination circuit 19 compares the output signal of the welding current detector 11 with the output signal of the polarity switching current value setting unit 34, and determines that the output signal of the welding current detector 11 is the polarity switching current value setting unit. 34, a low-level signal is output, and a signal obtained by inverting the low-level signal via the switch 33 is output to the RS flip-flop circuit 27 as a reset signal. 27 outputs a low level signal, and the first switching element drive circuit 29 receives this low level signal,
The output of the drive signal for conducting the first switching elements 8a and 8d is stopped, and the first switching elements 8a and 8d are turned off.

The low-level signal output from the RS flip-flop circuit 27 is inverted through the switch 32 and output to the negative current period setting circuit 23. The negative current period setting circuit 23 outputs the low level signal. , A high-level signal is output, and the welding current setting circuit 20 is output.
Receives the high-level signal and outputs a high-level signal, and the comparator 17 receives the high-level signal and
The difference signal ΔI = Ir−If is output, the first inverter control circuit 16 receives the difference signal ΔI, outputs a drive signal to the first inverter circuit 4, and the first inverter circuit 4
The power is output to the negative current period setting circuit 23 for a preset period. The negative current period setting circuit 23 outputs a high level signal to the RS flip-flop circuit 26 as a set signal, and the RS flip-flop circuit 26
Input this set signal, output high level signal,
The second switching element drive circuit 28 receives the high level signal and outputs a drive signal for conducting the second switching elements 8b and 8c. Thereafter, after the time period of the negative current period setting circuit 23 ends, the negative current period setting circuit 2
3 becomes low level, the output signal Ir of the welding current setting circuit 20 becomes zero, the comparator 17 outputs a difference signal ー I = Ir-If, and the first inverter control circuit 16 outputs the difference signal △ By inputting I, the drive signal output to the first inverter circuit 4 is stopped, and the first inverter circuit 4 is stopped.

Thereafter, the polarity switching determination circuit 19 compares the output signal of the welding current detector 11 with the output signal of the polarity switching current value setting unit 34, and determines whether the output signal of the welding current detector 11 is the polarity switching current. When the signal level drops to the output signal of the value setter 34, a low-level signal is output, and a signal obtained by inverting the low-level signal is output to the RS flip-flop circuit 26 as a reset signal. , This set signal is input to output a low level signal, and the second switching element driving circuit 2
8 receives this low-level signal and stops outputting a drive signal for conducting the second switching elements 8b and 8c.
The second switching elements 8b and 8c become non-conductive.

The low-level signal output from the RS flip-flop circuit 26 is inverted and output to the positive-polarity current period setting circuit 22, so that the positive-polarity current period setting circuit 22 outputs a high-level signal. The welding current setting circuit 20 receives the high level signal and outputs a high level signal, and the comparator 17 receives the high level signal and outputs a difference signal ΔI = Ir−If. The first inverter control circuit 16 receives the difference signal ΔI and
A drive signal for driving the inverter circuit 4 is output, and the first inverter circuit 4 receives the drive signal and outputs power to the positive current period setting circuit 22 for a preset period.

The high-level signal output from the positive polarity current period setting circuit 22 is output as a set signal to the RS flip-flop circuit 27 via the OR circuit 25.
The RS flip-flop circuit 27 receives the set signal and outputs a high level signal, and the first switching element drive circuit 29 receives the high level signal and turns on the first switching elements 8a and 8d. Output drive signal. Thereafter, after the time limit of the positive polarity current period setting circuit 22 ends, the output of the positive polarity current period setting circuit 22 becomes low level, the output signal Ir of the welding current setting circuit 20 becomes zero, and the comparator 17 outputs the difference signal △ I = Ir−If is output to the first inverter control circuit 16 and the first inverter control circuit 1
6 stops the output of the drive signal output to the first inverter circuit 4, and the first inverter circuit 4 stops.

Thereafter, the polarity switching discrimination circuit 19 compares the output signal of the welding current detector 11 with the output signal of the polarity switching current value setting unit 34, and determines whether the output signal of the welding current detector 11 is the polarity switching current. When the signal has dropped to the output signal of the value setter 34, a low-level signal is output. A signal obtained by inverting the low-level signal via the switch 33 is output to the RS flip-flop circuit 27 as a reset signal, The flip-flop circuit 27 receives the reset signal and outputs a low level signal, and the first switching element drive circuit 29 receives the low level signal and drives the first switching elements 8a and 8d to conduct. The output of the signal is stopped, and the first switching elements 8a and 8d are turned off.

Thereafter, the welding is completed and the torch switch T
When the S push button is released, a signal obtained by inverting the low-level signal of the torch switch TS is output to the NAND circuit 30. Thereafter, the time limit of the positive current period setting circuit 22 ends, and the positive current period ends. When a signal obtained by inverting the low level signal of the setting circuit 22 is input to the NAND circuit 30,
The NAND circuit 30 outputs a high-level signal so that both input signals become high level, and the RS flip-flop circuit 31 inputs this signal as a reset signal and outputs a low-level signal to the inverter control circuit 16. Outputting, the inverter control circuit 16 stops the signal for driving the first inverter circuit 4, and the first inverter circuit 4 stops.

When the push button of the torch switch TS is released, the switch 33 is connected to the b side, and the high level signal output from the welding current discriminating circuit 18 is switched to the switch 33.
Is output as a reset signal to the RS flip-flop circuit 27, after which the welding current decreases and the arc disappears, and the high level signal of the welding current discriminating circuit 18 becomes a low level signal. , RS flip-flop circuit 27 receives the high-level signal obtained by inverting the low-level signal as a reset signal, outputs a low-level signal, and outputs a first switching element drive circuit 29.
Receives the low-level signal and stops outputting a drive signal for conducting the first switching elements 8a and 8d.
The first switching elements 8a and 8d become non-conductive.

FIG. 2 is a diagram showing waveforms at various parts of the conventional device shown in FIG. In the figure, (A) is the output signal of the torch switch TS, (B) is the output of the first inverter circuit 4, (C) is the output signal of the arc start current period setting circuit 21, and (D) is the negative current period. (E) Output signal of the positive polarity current period setting circuit 22, (F) Output signal of the welding current setting circuit 20, (G)
Is an output signal of the first switching element drive circuit 29,
(H) is the output signal of the second switching element drive circuit 28, (I) is the welding current and the polarity switching current value, (J)
Is an arc voltage generated between the consumable electrode 40 and the workpiece 15, (K) is an output signal of the welding current determination circuit 18,
(L) shows the output signal of the polarity switching determination circuit 19 with the passage of time.

At time t1 shown in FIG. 2, when the torch switch TS is pressed, the torch switch TS becomes (A)
, The RS flip-flop circuit 31 receives the high-level signal as a set signal, outputs a high-level signal, and the inverter control circuit 16 receives the high-level signal. Thus, a signal for driving the first inverter circuit 4 is output, and the first inverter circuit 4 is driven. Thus, the output of the AC power supply 1 is rectified by the first rectifier circuit 2 and then smoothed by the smoothing circuit 3, and the first inverter circuit 4 outputs high-frequency AC power as shown in FIG.

When the torch switch TS is pressed,
The arc start current period setting circuit 21 receives the high level signal of the torch switch TS and outputs a high level signal as shown in FIG. Welding current setting circuit 20
Receives this high-level signal and outputs a high-level signal as shown in FIG. The comparator 17 outputs a difference signal △ I = Ir−If between the output signal If of the welding current detector 11 and the output signal Ir of the welding current setting circuit 20, and the inverter control circuit 16 outputs the difference signal に I By outputting a pulse signal having a corresponding pulse width or frequency to the first inverter circuit 4, the first inverter circuit 4 is driven so that an output having a constant current characteristic is obtained, and the output of the first inverter circuit 4 is output. Is converted to a predetermined voltage by the output transformer 5, converted to a direct current again by the second rectifier circuit 6, and supplied to the second inverter circuit 46 via the reactor 7.

The arc start current period setting circuit 2
1 is output as a set signal to the RS flip-flop circuit 27 via the OR circuit 25, and the RS flip-flop circuit 27 receives the set signal and outputs a high-level signal. The one switching element driving circuit 29 receives this high level signal and outputs a driving signal for conducting the first switching elements 8a and 8d as shown in (G). As a result, the output of the second inverter circuit 46 is supplied from the output terminals 12 and 13 between the consumable electrode 40 and the workpiece 15. When the torch switch TS is pressed, the motor control circuit 44 starts by inputting a high-level signal of the torch switch TS, the motor 41 starts rotating at a low speed, and the consumable electrode 4
0 is slowly fed toward the workpiece 15.

At time t2, when the consumable electrode 40 and the work 15 are short-circuited, an arc start is performed between the consumable electrode 40 and the work 15 as shown in FIG. Arc is generated due to the application of the voltage, and a welding current flows as shown in (I). Then, the welding current discriminating circuit 18 discriminates that the welding current has flowed, and outputs a high-level signal as shown in (K). At the time t3 when the time period ends, the output of the arc start current period setting circuit 21 becomes low level, the output signal Ir of the welding current setting circuit 20 becomes zero, and the comparator 17
Is output to the first inverter control circuit 16 and the first inverter control circuit 1 outputs the difference signal ΔI = Ir−If
The output of the drive signal output from 6 to the first inverter circuit 4 stops, and the first inverter circuit 4 stops.

Thereafter, the welding current decreases as shown in (I), and the polarity switching determination circuit 19 compares the output signal of the welding current detector 11 with the output signal of the polarity switching current value setting unit 34. At time t4 when the welding current falls to the polarity switching current value, a low level signal is output as shown in (L). At this time, since the switch 33 receives the high level signal of the torch switch TS and is connected to the a side, the signal obtained by inverting the low level signal of the polarity switching determination circuit 19 through the switch 33 is transmitted to the RS flip-flop. Is output to the reset circuit 27 as a reset signal. R
The S flip-flop circuit 27 receives the reset signal and outputs a low level signal, and the first switching element drive circuit 29 receives the low level signal and
As shown in (G), the first switching elements 8a and 8d
Is stopped, and the first switching elements 8a and 8d are turned off.

At this time, since the switch 32 receives the high-level signal of the torch switch TS and is conducting, the low-level signal output from the RS flip-flop circuit 27 is inverted via the switch 32 to the negative polarity. Is output to the negative current period setting circuit 23, and the negative current period setting circuit 23 outputs a high level signal as shown in FIG.
The welding current setting circuit 20 receives the high-level signal and outputs a high-level signal as shown in (F). The comparator 17 receives the high-level signal and outputs the difference signal ΔI =
Ir-If is output, the first inverter control circuit 16 receives the difference signal ΔI and outputs a drive signal, and the first inverter circuit 4 receives the drive signal and outputs the drive signal as shown in FIG. Thus, the power is output to the negative current period setting circuit 23 for a preset period. Further, the negative polarity current period setting circuit 23
When a signal obtained by inverting the low-level signal of the above-described RS flip-flop circuit 27 through the switch 32 is input, the high-level signal is output to the RS flip-flop circuit 2.
6 as a set signal, the RS flip-flop circuit 26 receives the set signal and outputs a high level signal, and the second switching element drive circuit 28 receives the high level signal and outputs (H ), A drive signal for turning on the second switching elements 8b and 8c is output, and the second switching elements 8b and 8c are turned on.

Thereafter, at time t5 when the time period of the negative current period setting circuit 23 ends, the output of the negative current period setting circuit 23 becomes low level as shown in FIG. The output signal Ir becomes zero,
The comparator 17 outputs the difference signal ΔI = Ir−If to the first inverter control circuit 16, and the first inverter control circuit 16
The output of the drive signal output to the first inverter circuit 4 is stopped, and the first inverter circuit 4 stops as shown in FIG.

Thereafter, the welding current decreases as shown in (I), and the polarity switching determination circuit 19 compares the output signal of the welding current detector 11 with the output signal of the polarity switching current value setting unit 34. At a time t6 when the welding current falls to the polarity switching current value, a low level signal is output as shown in (L), and the inverted signal of the low level signal is R
The reset signal is output to the S flip-flop circuit 26, the RS flip-flop circuit 26 receives the reset signal and outputs a low level signal, and the second switching element driving circuit 28 receives the low level signal. Then, as shown in (H), the second switching elements 8b and 8
The output of the drive signal for turning on c is stopped, and the second switching elements 8b and 8c are turned off.

A high-level signal obtained by inverting the low-level signal output from the RS flip-flop circuit 26 is output to the positive current period setting circuit 22, and the positive current period setting circuit 22 receives the high level signal as an input. do it,
As shown in (E), a high level signal is output, and the welding current setting circuit 20 receives the high level signal,
A high-level signal is output as shown in FIG.
7 receives this high level signal and generates a difference signal ΔI = Ir
−If, the first inverter control circuit 16 receives the difference signal ΔI and outputs a drive signal to the first inverter circuit 4, and the first inverter circuit 4 outputs the drive signal as shown in FIG. The power is output to the positive polarity current period setting circuit 22 for a predetermined period.

The high-level signal output from the positive polarity current period setting circuit 22 is output to the RS flip-flop circuit 27 via the OR circuit 25 as a set signal.
The RS flip-flop circuit 27 receives the set signal and outputs a high level signal, and the first switching element drive circuit 29 receives the high level signal and
As shown in (G), the first switching elements 8a and 8d
And outputs a driving signal for conducting the first switching element 8.
a and 8d conduct.

Thereafter, at time t7 when the time limit of the positive polarity current period setting circuit 22 ends, the positive polarity current period setting circuit 22
Becomes low as shown in (E), the output signal Ir of the welding current setting circuit 20 becomes zero as shown in (F), and the comparator 17 outputs the difference signal ΔI = Ir−If. Output to the first inverter control circuit 16, the first inverter control circuit 16 stops outputting the drive signal output to the first inverter circuit 4, and the first inverter circuit 4 stops driving as shown in (B). I do.

Thereafter, the welding current decreases as shown in (I), and the polarity switching discrimination circuit 19 outputs the welding current detector 1
The output signal of No. 1 and the output signal of the polarity switching current value setting unit 34 are compared, and a low level signal is output at time t8 when the welding current falls to the polarity switching current value. A signal obtained by inverting the low level signal is output to the RS flip-flop circuit 27 as a reset signal, and the RS flip-flop circuit 27 receives the reset signal,
The first switching element drive circuit 29 outputs a low level signal, and receives the low level signal to stop outputting a drive signal for conducting the first switching elements 8a and 8d as shown in FIG. The first switching elements 8a and 8d are turned off.

Thereafter, the above-described operation from time t4 to time t8 is repeated. At time t9, when the push button of the torch switch TS is released to end welding, the low level signal of the torch switch TS is inverted. Is output to the NAND circuit 30. Thereafter, the positive polarity current period setting circuit 22 outputs a high level signal as shown in (E), and at time t10 when the time period ends, the positive polarity current period When a signal obtained by inverting the low-level signal of the setting circuit 22 is input to the NAND circuit 30, the NAND circuit 30 outputs a high-level signal because both input signals are at a high level. The reset signal is output to the flip-flop circuit 30, and the RS flip-flop circuit 30 receives the reset signal,
A low-level signal is output to the inverter control circuit 16
Receives the low level signal, stops the signal for driving the first inverter circuit 4, and outputs the signal to the first inverter circuit 4.
Stops as shown in FIG. Thereafter, the time t when the welding current decreases as shown in (I) and the arc disappears.
11, the first switching element drive circuit 29 includes (G)
The output of the drive signal for conducting the first switching elements 8a and 8d is stopped as shown in FIG.
a and 8d are made non-conductive.

[0036]

In the above conventional apparatus, the induced electromotive force generated by the inductance of the welding cables 47 and 48 while the output of the first inverter circuit 4 is temporarily stopped is: When the welding current reaches a polarity switching current value that is higher than the arc re-ignition voltage and lower than a voltage that destroys the switching element of the second inverter circuit 46, the AC arc welding power supply device The polarity of the output is switched to prevent the switching element of the second inverter circuit 46 from being broken.

However, since the set value of the polarity switching current value setting unit 34 is previously set to be constant regardless of the length of the welding cables 47 and 48, when the welding cables 47 and 48 are long, that is, Assuming that the inductance values of the welding cables 47 and 48 are large, in order to prevent the induced electromotive force generated by the inductance from destroying the switching element of the second inverter circuit 46, a polarity switching current value setting device is used. It is necessary to set the setting value of 34 small. However, when the setting value of the polarity switching current value setting unit 34 is set to be small as described above, if welding work is performed in a state where the welding cables 47 and 48 are short, an induced electromotive force generated by the inductance of the welding cables 48 and 48 is generated. Since the voltage becomes lower, the voltage becomes lower than the re-ignition voltage of the arc, the arc cannot be re-ignited sufficiently, and the arc disappears, which may hinder the welding operation.

Conversely, when the welding cables 47 and 48 are short, that is, when it is assumed that the inductance values of the welding cables 47 and 48 are small, the induced electromotive force generated by the inductance is small, so that In order to perform re-ignition sufficiently, the set value of the polarity switching current value setting unit 34 is set to a large value. In this case, if the welding operation is performed in a state where the welding cables 47 and 48 are long, the induced electromotive force generated by the inductance of the welding cables 47 and 48 increases, so that the first switching elements 8a and 8d and the second switching element 8b and 8c may be destroyed.

When the welding cables 47 and 48 also move with the movement of the welding operation position, the welding cables 47 and 48 move.
Also, during the welding operation, in order to perform the welding operation at a constant polarity switching current value preset in the polarity switching current value setting device 34, when the polarity switching current value is set small, When the inductance values of the welding cables 47 and 48 increase, the induced electromotive force generated by the inductance of the welding cables 47 and 48 becomes too high, and the switching element of the second inverter circuit 46 may be destroyed. . Conversely, if the value of the inductance of the welding cables 47 and 48 decreases when the polarity switching current value is set to a large value, the induced electromotive force generated by the inductance of the welding cables 47 and 48 becomes too low, and arcing occurs. May not be sufficiently re-ignited, and the arc may be extinguished.

[0040]

According to the first aspect of the present invention, an output obtained by rectifying and smoothing an output of an AC power supply is converted into high-frequency AC power by a first inverter circuit.
The output of the first inverter circuit 4 is converted into electric power suitable for arc machining, rectified and supplied to the reactor 7, and the output of the reactor 7 is converted into AC power by the second inverter circuit 46, and the welding cables 47 and 48 Before switching the polarity of the output of the second inverter circuit 46, the output of the first inverter circuit 4 is temporarily stopped, and when the welding current reaches the polarity switching current value, the second In the AC arc welding power supply control method for switching the polarity of the output of the inverter circuit 46, the first inverter circuit 4
During the period when the output of the second inverter circuit 4 is temporarily stopped.
The change rate (di1 / dt) of the welding current from the output signal of the welding current detector 11 during the period (dt1) before the polarity switching of the output of No. 6
1) calculating the change rate of the welding current at the time of polarity switching, the output signal (Va1) of the arc voltage detector 39 after the lapse of the period (dt1) before the polarity switching, and the change rate (di1) of the welding current. / dt1) and a polarity switching inductance calculation step for calculating the polarity switching inductance between the reactor 7 and the welding cables 47 and 48, and a polarity switching current value calculation for determining the polarity switching current value corresponding to the polarity switching inductance. And a step for controlling the AC arc welding power supply.

According to the invention described in claim 2 at the time of filing, as shown in a first embodiment shown in FIG. 3 described later, the output of the AC power supply 1 is rectified and the smoothed output is converted into high-frequency AC power. The first inverter circuit 4 converts the output of the first inverter circuit 4 into electric power suitable for arc machining, converts the electric power into AC power through the rectified reactor 7, and applies the welding load via welding cables 47 and 48 to the welding load. Before the polarity switching of the output of the second inverter circuit 46, the output of the first inverter circuit 4 is temporarily stopped, and the welding current reaches the polarity switching current value. When the output of the first inverter circuit 4 is temporarily stopped, the output of the second inverter circuit 46 is temporarily stopped in the AC arc welding power supply device that switches the polarity of the output of the second inverter circuit 46. Welding current detector 11 the rate of change of the calculated welding current from the output signal of the sex before switching period (dt1) (di1 / dt1) and said polarity switching previous period (dt
The output signal (Va) of the arc voltage detector 39 after the lapse of 1)
(1) an inductance value calculation circuit for calculating an inductance at the time of polarity switching between the reactor 7 and the welding cables 47 and 48; and a polarity switching current value calculation circuit 38 for determining a polarity switching current value corresponding to the polarity switching inductance. An AC arc welding power supply device provided with a polarity switching current value calculation means comprising:

The invention described in claim 3 at the time of filing applies to claim 2
The polarity-switching current value calculating means described in (1) above receives the output signal of the welding current detector 11 and temporarily stops the output of the first inverter circuit 4 before the polarity of the output of the second inverter circuit 46 is switched. A first differentiator 36 that calculates a change rate (di1 / dt1) of the welding current from a change value (di1) of the welding current during the period (dt1);
Output signal (Va1) of the arc voltage detector 39 after elapse of 1)
And the output signal (di1 / dt1) of the first differentiator 36, and the first inductance value (L7 + L47 + L48) of the reactor 7 and the welding cables 47 and 48 is given by (L7 + L47 + L48) × (di1 / dt1) + Va1 = 0. The first inductance value calculation circuit 3 that calculates from the relational expression of｝
7 and a polarity switching current value calculation circuit 38 which receives the output signal of the first inductance value calculation circuit 37 and calculates a polarity switching current value corresponding to the first inductance value (L7 + L47 + L48). It is an arc welding power supply device.

In the invention according to claim 4 at the time of filing, as shown in a second embodiment shown in FIG. 5 described later, the polarity switching current value calculating means according to claim 2 comprises a welding current detector 1.
1 during which the output of the first inverter circuit 4 is temporarily stopped by inputting the output signal of the first inverter circuit 4 and before the polarity switching of the second inverter circuit 46 (dt1).
The first differentiator 36 for calculating the change rate (di1 / dt1) of the welding current from 1), the output voltage detection signal of the second inverter circuit 46, the output signal of the welding current detector 11, and the output of the arc voltage detector 39 Signals and input the welding cables 47 and 48
And a semiconductor voltage drop value setting device for setting a voltage drop value (Vf) between the second rectifier circuit 6 and the pair of switching elements of the second inverter circuit 46. 53 and an internal resistance value setting device 54 for setting the internal resistance value (Ri) of the AC arc welding power supply device.
And the output signal (Vf) of the semiconductor voltage drop value setting unit 53, the output signal (di1 / dt1) of the first differentiator 36, and the output signal of the arc voltage detector 39 after the lapse of the period (dt1) before the polarity switching. (Va1) and the output signal of the welding current detector 11 (If
1), the output signal (Ro) of the welding cable resistance value calculating means and the output signal (Ri) of the internal resistance value setting device 54 are input, and ｛(L7 + L47 + L48) × (di1 / dt1) + Va1 + (Ro +
From the relational expression of Ri) × If1 + Vf = 0 °, the reactor 7 and the welding cables 47 and 48 are obtained.
A second inductance value calculation circuit 50 for calculating a second inductance value (L7 + L47 + L48) of the following, and a polarity switching current value corresponding to the second inductance value (L7 + L47 + L48) by inputting an output signal of the second inductance value calculation circuit 50 Switching current value calculation circuit 3 for calculating
8 is an AC arc welding power supply device which is a means including

The invention described in claim 5 at the time of filing applies to claim 4
The output terminal voltage detector 5 for detecting the output voltage of the second inverter circuit 46
1, a second differentiator 56 that calculates a change rate (di2 / dt2) of the welding current from a change value (di2) of the welding current during a period (dt2) during operation of the first inverter circuit 4, and a second differentiator. When the output 56 (di2 / dt2) is substantially zero, the output signal (If2) of the welding current detector 11, the output signal (Vo) of the output terminal voltage detector 51, and the output signal (Va2) of the arc voltage detector 39. And a welding cable resistance value calculation circuit 52 for calculating resistance values {Ro = (Vo−Va2) / If2} of the welding cables 47 and 48.

[0045]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] The present invention will be described below with reference to the control block diagram of the first embodiment shown in FIG. The control block diagram of the first embodiment shown in FIG.
Compared to the control block diagram of the conventional device shown in FIG.
The control blocks indicated by bold lines are different, and the different control blocks will be described below. In FIG.
Is a monomultivibrator, which inputs a signal obtained by inverting the output signal of the arc start current period setting circuit 21 and outputs a high level signal for a preset period (dt1) from when the input signal is at a high level. I do. 39 is
An arc voltage detector, a monomultivibrator 35
And the arc voltage Va1 at the end time of this high level signal is detected. Reference numeral 36 denotes a first differentiator which receives the output signal of the welding current detector 11 and the output signal of the monomultivibrator 35, and outputs the welding current during the period dt1 during which the high level signal of the monomultivibrator 35 is input. The change value d of the output signal of the detector 11
The change rate (di1 / dt1) is calculated and output from i1. 37
Is a first inductance value calculation circuit, and the change rate (di / dt) calculated by the first differentiator 36 and the arc voltage detector 3
9, the first inductance value between the reactor 7 and the welding cables 47 and 48 is set to (L
7 + L47 + L48), the first inductance value (L7 + L47 + L4) is obtained from the relational expression of (L7 + L47 + L48) .times. (Di1 / dt1) + Va1 = 0.
8) is calculated.

Numeral 38 denotes a polarity switching current value calculating circuit, which has an inductance value La between the reactor 7 and the welding cable when the length of the welding cable is normal in use.
And the polarity switching current value ia are experimentally obtained,
The inductance value L between the reactor 7 and the welding cable when the length of the welding cable changes is calculated by the first inductance value calculation circuit 37, and the polarity switching current value i when the length of the welding cable changes is calculated as described above. The electromagnetic energy of the inductance value La and the polarity switching current value ia between the reactor 7 and the welding cable obtained experimentally and the reactor 7 when the length of the welding cable changes.
Since the electromagnetic energy between the inductance value L of the welding cable and the polarity switching current value i is equal, (L ×
The calculation is performed with (i × i) / 2 = (La × ia × ia) / 2. The polarity switching current value calculation means according to claim 3 at the time of filing includes a first differentiator 36, a first inductance value calculation circuit 37, and a polarity switching current value calculation circuit 38.

When the torch switch TS is pressed, the arc start current period setting circuit 21 causes the torch switch TS
, And outputs the high-level signal to the welding current setting circuit 20. Further, the arc start current period setting circuit 21 inputs a signal obtained by inverting the output signal to the mono multivibrator 35, and when the output signal of the arc start current period setting circuit 21 changes from high level to low level, The mono multivibrator 35 is
The high level signal is output for a preset period. The arc voltage detector 39 receives the high level signal and detects the arc voltage Va at the end time of the high level signal. The first differentiator 36 receives the output signal of the welding current detector 11 and the output signal of the monomultivibrator 35, and outputs the welding current detector 11 during the period dt1 during which the high-level signal of the monomultivibrator 35 is input. From the output signal change value di1, the change rate (di1 / dt1) is calculated.
The first inductance value calculation circuit 37 includes a first differentiator 36.
(Di1 / dt1) and arc voltage detector 39
Of the first inductance value (L7 + L4) between the reactor 7 and the welding cables 47 and 48.
7 + L48).

The polarity switching current value calculation circuit 38
By inputting the calculation result of the inductance value calculation circuit 37,
A polarity switching current value corresponding to the first inductance value (L7 + L47 + L48) is calculated. Hereinafter, during the arc start current period, the negative current period, and the positive current period, the polarity switching determination circuit 19
Is compared with the output signal of the polarity switching current value calculation circuit 38, and when the output signal of the welding current detector 11 falls to the output signal of the polarity switching current value calculation circuit 38, a low level signal is output. I do.

FIG. 4 is a diagram showing waveforms at various parts in the control block diagram shown in FIG. In FIG. 7, (A) to (L) correspond to (A) to (L) in FIG. (M) is a mono-multi vibrator 35
Are shown over time.

In FIG. 4, only parts different from FIG. 2 will be described. At time t3 when the arc start current period ends,
The output of the arc start current period setting circuit 21 becomes low level, and the mono-multivibrator 35 arcs the high level signal for a preset period from the time of inputting the high level signal obtained by inverting the low level signal. Output to the voltage detector 39. The arc voltage detector 39 receives the high level signal of the mono-multi vibrator 35 and detects the arc voltage Va at the end time of the high level signal. The first differentiator 36 is a welding current detector 1
1 and the output signal of the monomultivibrator 35, and the welding current detector 11 during the period dt1 during which the high level signal of the monomultivibrator 35 is input.
The change rate (di1 / dt1) is calculated from the change value di1 of the output signal and output.

The first inductance value calculation circuit 37 receives the change rate (di1 / dt1) calculated by the first differentiator 36 and the output signal Va of the arc voltage detector 39, and inputs the reactor 7, the welding cable 47, The first inductance value (L7 + L47 + L48) is calculated. The polarity switching current value calculation circuit 38 includes a first inductance value calculation circuit 37.
Of the first inductance value (L7 +
(L47 + L48) is calculated.

In the control block diagram of the first embodiment of the present invention shown in FIG. 3, in calculating the polarity switching current value, the resistance of the welding cables 47 and 48 and the voltage drop value of the switching element are ignored. The following describes a case where the polarity switching current value is calculated in consideration of the above.

[Second Embodiment] FIG. 5 is a control block diagram of a second embodiment of the present invention. The control block diagram of the second embodiment shown in the figure differs from the control block diagram of the first embodiment shown in FIG. 3 in the control block shown by a thick line in FIG. Will be described. In the figure, reference numeral 56 denotes a second differentiator which receives the output signal If of the welding current detector 11 and changes the rate of change (di).
2 / dt2) is calculated. An AND circuit 57 receives the output signal of the arc start current period setting circuit 21 and the output signal of the welding current determination circuit 18 and outputs a high level signal when both signals are at a high level. Reference numeral 55 denotes a current change detector, which receives the output signal of the AND circuit 57 and the output signal of the second differentiator 56 and inputs a high-level signal of the AND circuit 57, that is, the arc start current. When the welding current is flowing during the period, the second differentiator 56
Output signal (di2 / dt2) and the current change determination value setting device 4
9 is compared with the output signal of the second differentiator 56 (d
When (i / dt) is smaller than the output signal of the current change determination value setter 49, the change in the welding current is determined to be substantially zero, and a high level signal is output.

Reference numeral 51 denotes an output terminal voltage detector for detecting the output voltage Vo of the second inverter circuit 46 while the current change detector 55 is outputting a high level signal. 5
Reference numeral 2 denotes a welding cable resistance value calculation circuit for calculating the resistance values of the welding cables 47 and 48, and a current change detector 5
5 outputs a high-level signal, the signal If2 output from the welding current detector 11 and the arc voltage detector 39.
Is input and the output signal Vo of the output terminal voltage detector 51 is input, and the resistance value R47 of the welding cable 47 is input.
Assuming that the sum of the resistance values R48 of the welding cables 48 is Ro, the composite resistance value Ro of the welding cables 47 and 48 can be calculated by the relational expression of Ro = R47 + R48 and Ro = (Vo-Va2) / If2.

Reference numeral 53 denotes a semiconductor voltage drop value setting device.
The output signal If of the welding current detector 11 is input and the voltage drop Vf1 of the second rectifier circuit 6, the voltage drop V8a of the switching element 8a, and the voltage drop V8 of the switching element 8d.
The total voltage drop value of 8d (Vf = Vf1 + V8a + V8d) is set. Here, the voltage drop value Vf1 of the second rectifier circuit 6, the voltage drop value V8a of the switching element 8a, and the voltage drop value V8d of the switching element 8d are determined from the design values as functions of the output signal If of the welding current detector 11. Is done. 54
Is an internal resistance value setting device for setting the internal resistance of the AC arc welding power supply device. The internal resistance value is mainly determined by the resistance of the secondary winding of the output transformer 5 and the resistance of the reactor 7. Yes, determined from design values.

Reference numeral 50 denotes a second inductance value calculation circuit, which is the output signal (di1 / dt1) of the first differentiator 36 and the output signal of the welding current detector 11 at the end time of the high level signal of the monomultivibrator 35. If1 and the output signal Va1 of the arc voltage detector 39, the output signal Ro of the welding cable resistance value calculation circuit 52, and the semiconductor voltage drop value setting device 5
3 and the output signal Ri of the internal resistance value setting unit 54, and the second inductance value between the reactor 7 and the welding cables 47 and 48 is calculated as (L7 + L47 + L
48) as (L7 + L47 + L48) × (di1 / dt1) + Va1 + (Ro + R
i) From the relational expression of × If1 + Vf = 0, the second inductance value (L7 + L47 + L4)
8) is calculated.

The welding cable resistance value calculating means according to the present invention comprises an output terminal voltage detector 51, a second differentiator and a welding cable resistance value calculation circuit 52. Also,
The polarity switching current value calculating means according to claim 5 at the time of filing includes a first differentiator 36, a welding cable resistance value calculating means, a semiconductor voltage drop value setting device 53, an internal resistance value setting device 54, and a second inductance value calculation circuit. 50 and a polarity switching current value calculation circuit 38.

When the torch switch TS is pressed, the arc start current period setting circuit 21 causes the torch switch TS
, And outputs the high-level signal to the welding current setting circuit 20. The arc start current period setting circuit 21 outputs a signal obtained by inverting the output signal,
When input to the monomultivibrator 35 and the output signal of the arc start current period setting circuit 21 changes from high level to low level, the monomultivibrator 3
5 outputs a high-level signal for a preset period. The arc voltage detector 39 receives the high level signal and detects the arc voltage Va1 at the end time of the high level signal. The first differentiator 36 receives the output signal of the welding current detector 11 and the output signal of the monomultivibrator 35, and outputs the welding current detector 11 during the period dt1 during which the high-level signal of the monomultivibrator 35 is input. From the output signal change value di1, the change rate (di1 / dt1) is calculated.

The second differentiator 56 receives the output signal If of the welding current detector 11 and calculates the rate of change (di1 / dt1).
The AND circuit 57 includes an arc start current period setting circuit 2
1 and the output signal of the welding current discriminating circuit 18 are input, and when both signals are at a high level, a high level signal is output. The current change detector 55 includes an AND circuit 57 and a second
When the output signal from the differentiator 56 is input and the high-level signal from the AND circuit 57 is input, (di2 / dt2), which is the output signal from the second differentiator 56, is determined to be substantially zero. At this time, a high level signal is output. Output terminal voltage detector 5
1 detects the output voltage Vo of the second inverter circuit 46 when the output signal of the current change detector 55 is input,
The welding cable resistance value calculation circuit 52 receives the output signal Vo of the output terminal voltage detector 51, the output signal If of the welding current detector 11, and the output signal Va of the arc voltage detector 39, and outputs the welding cables 47 and 48. Is calculated.

The semiconductor voltage drop value setter 53 receives the output signal If of the welding current detector 11 and inputs the output signal If to the second rectifier circuit 6.
, The voltage drop value V8a of the switching element 8a and the voltage drop value V8d of the switching element 8d (Vf = Vf1 + V8a + V8d). The second inductance value calculation circuit 50 outputs the output signal (di1 / dt1) of the first differentiator 36 and the welding current detector 11 at the end time of the high-level signal of the monomultivibrator 35.
And the output signal V of the arc voltage detector 39.
a1 and the output signal Ro of the welding cable resistance value calculation circuit 52
And the output signal Vf of the semiconductor voltage drop value setting device 53 and the output signal Ri of the internal resistance value setting device 54, and calculate the second inductance value (L7 + L47 + L48) of the reactor 7 and the welding cables 47 and 48. I do.

The polarity switching current value calculation circuit 38
By inputting the calculation result of the inductance value calculation circuit 50,
A polarity switching current value corresponding to the second inductance value (L7 + L47 + L48) is calculated. Hereinafter, during the arc start current period, the negative current period, and the positive current period, the polarity switching determination circuit 19
Is compared with the output signal of the polarity switching current value calculation circuit 38, and when the output signal of the welding current detector 11 falls to the output signal of the polarity switching current value calculation circuit 38, a low level signal is output. I do.

FIG. 6 is a diagram showing waveforms at various points in the control block diagram shown in FIG. In the figure, (A) to (M) correspond to (A) to (M) shown in FIG. (N) shows the output signal of the current change detector 55 over time.

In FIG. 6, only parts different from FIG. 4 will be described. At time t2, the consumable electrode 40 and the workpiece 15
Is short-circuited at this time, an arc is generated between the consumable electrode 40 and the workpiece 15 because a voltage for starting the arc is applied, and an arc is generated, as shown in FIG. The welding current flows through. Then, the welding current determination circuit 1
8 determines that the welding current has flowed, and outputs a high-level signal as shown in (K). At this time, the AND circuit 5
7 outputs a high level signal because both the output signal of the arc start current period setting circuit 21 and the output signal of the welding current discriminating circuit 18 which are input signals are at a high level, and the current change detector 55 , The high-level signal of the AND circuit 57 and the output signal (di2 / dt2) of the second differentiator 56 are input, and from the time t21 when the output signal (di2 / dt2) of the second differentiator 56 is determined to be substantially zero, Output signal of the 2 differentiator 56 (di2 / dt2)
Is high, a high-level signal is output as shown in (N). The output terminal voltage detector 51 detects the output voltage Vo of the second inverter circuit 46 when the output signal of the current change detector 55 is being input.

The arc start current period setting circuit 21
The time period starts after the welding current determination circuit 18 determines that the welding current has flowed. At time t3 when the time period ends, the output of the arc start current period setting circuit 21 becomes low level, and the welding current setting circuit 20 Becomes zero, and the difference signal ΔI = Ir−If output from the comparator 17
Is output to the first inverter control circuit 16, the output of the drive signal output from the first inverter control circuit 16 to the first inverter circuit 4 is stopped, and the first inverter circuit 4 is stopped.

At time t3 when the arc start current period ends, the welding current starts to change as shown in (I), and the output (di / dt) of the second differentiator 56 changes to the current change determination value setting device. When the value exceeds the set value of 49, the high-level signal of the current change detector 55 stops as shown in (N).

At time t3 when the arc start current period ends, the output of the arc start current period setting circuit 21 goes low, and the monomultivibrator 35
Outputs a high-level signal to the arc voltage detector 39 for a preset period from when the high-level signal obtained by inverting the low-level signal is input. The arc voltage detector 39 receives the high level signal of the mono-multi vibrator 35 and detects the arc voltage Va at the end time of the high level signal.

The first differentiator 36 receives the output signal of the welding current detector 11 and the output signal of the monomultivibrator 35, and outputs the welding current during the period dt1 when the high level signal of the monomultivibrator 35 is input. From the change value di1 of the output signal of the detector 11, a change rate (di1 / dt1) is calculated and output. The second inductance value calculation circuit 50 is configured to
The output signal (di1 / dt1) of the differentiator 36 and the welding current detector 1
1, the output signal Va of the arc voltage detector 39, and the output signal R of the welding cable resistance value calculation circuit 52.
o, the output signal Vf of the semiconductor voltage drop value setter 53,
The output signal Ri of the internal resistance value setting unit 54 is input, and the inductance value (L7 + L47 + L48) between the reactor 7 and the welding cables 47 and 48 is calculated. The polarity switching current value calculation circuit 38 receives the calculation result of the second inductance value calculation circuit 50 and outputs the inductance value (L7 + L47 + L4) between the reactor 7 and the welding cables 47 and 48.
Calculate the polarity switching current value corresponding to 8).

In the first and second embodiments, after the end of the arc start current period, the change value di1 of the output signal of the welding current detector 11 is detected.
The change rate (di1 / dt1) is calculated, the arc voltage Va1 is detected, and the polarity switching current value is calculated. However, after the positive current period or the negative current period ends, the welding current detector 1
1 is detected and the change rate (di1 / dt) is detected.
1), the arc voltage Va1 may be detected, and the polarity switching current value may be calculated.

In the first and second embodiments, each time the torch switch TS is pressed after the power of the welding power supply is turned on, the change value di1 of the output signal of the welding current detector 11 is detected. Then, the change rate (di1 / dt1) is calculated, the arc voltage Va1 is detected, and the polarity switching current value is calculated. However, after turning on the power of the welding power supply, the torch switch TS is first pressed. Only at this time, the polarity switching current value may be calculated, and thereafter, the same polarity switching current value may be used until the power source of the welding power supply device is turned off.

In the first and second embodiments, the change value (di1 / dt1) of the output signal of the welding current detector 11 is detected to calculate the change rate (di1 / dt1), and the arc voltage Va is calculated.
1 is detected and the polarity switching current value is calculated.
When the start condition is stable and the change in the arc length is small, the arc voltage is fixed, and simply the change value di1 of the output signal of the welding current detector 11 is detected without simply detecting the arc voltage Va1. Then, the change rate (di1 / dt1) may be calculated to calculate the polarity switching current value.

In the first embodiment and the second embodiment, the polarity switching current value between the positive current period and the negative current period is the same, but the positive current period and the negative current period are the same. Because there is a difference in the re-ignition property of the arc,
In the positive current period and the negative current period, the change value di1 of the output signal of each welding current detector 11 is detected, the change rate (di1 / dt1) is calculated, and the arc voltage Va1 is detected. The polarity switching current value may be calculated.

In the above, the embodiment in which the present invention is applied to an AC arc welding power supply device using a consumable electrode has been described. However, the present invention relates to an AC TIG using a non-consumable electrode.
The present invention can be similarly applied to an arc welding power supply device.

[0073]

As described above, in the first embodiment shown in FIG. 3, the output of the first inverter circuit is temporarily stopped before each polarity switching of the second inverter circuit, and the welding current is changed to the polarity switching current. In the AC arc welding power supply unit that switches the polarity of the second inverter circuit when the value reaches a value, an arc voltage and a welding current are detected, a change rate of the welding current is calculated from the welding current value, and the reactor and the welding are determined from these values. By calculating the inductance value with the cable and calculating the polarity switching current value from this inductance value, the polarity switching current value when switching the switching element of the second inverter circuit is set in advance as in the prior art. When the welding cable is short or long instead of a fixed value, the polarity is switched according to the length of each welding cable. By calculating the current value, it is possible to set the polarity switching current value when switching the switching elements of the second inverter circuit. Therefore, when the length of the welding cable is long, the polarity switching current value can be set low so that the induced electromotive force generated by the inductance of the welding cable does not increase to a voltage that destroys the switching element. There is no destruction of the switching element. Conversely, when the length of the welding cable is short, the polarity switching current value can be set high so that the induced electromotive force generated by the inductance of the welding cable becomes sufficiently higher than the restriking voltage of the arc. , The arc can be reignited sufficiently.

Furthermore, even if the welding cable moves during the welding operation and the inductance of the welding cable changes, the polarity switching current value can be changed to a value corresponding to the inductance of the welding cable. If the inductance of the cable increases, the induced electromotive force generated by the inductance of the welding cable does not increase to a voltage at which the switching element is destroyed. There is no destruction. Conversely, when the inductance of the welding cable becomes small, the induced electromotive force generated by the inductance of the welding cable becomes higher than the voltage at which the arc is re-ignited in order to set the polarity switching current value large. This has the effect that the arc can be reignited sufficiently and does not hinder the welding operation.

In the second embodiment shown in FIG. 5, in calculating the polarity switching current value, the resistance value of the welding cable, the voltage drop value of the switching element and the internal resistance value of the AC arc welding power supply are calculated. Since the calculation is performed in consideration of the above, a more accurate polarity switching current value can be calculated as compared with the first embodiment shown in FIG.
The risk of destroying the switching element of the first embodiment is further reduced, and the effect is larger than the effect of sufficiently re-igniting the arc.

[Brief description of the drawings]

FIG. 1 is a control block diagram of a conventional AC arc welding power supply device.

FIG. 2 is a diagram showing waveforms at various points in the control block diagram shown in FIG. 1;

FIG. 3 is a control block diagram of the first embodiment of the present invention.

FIG. 4 is a diagram showing waveforms at various points in the control block diagram shown in FIG. 3;

FIG. 5 is a control block diagram of a second embodiment of the present invention.

FIG. 6 is a diagram showing waveforms at various points in the control block diagram shown in FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply 2 1st rectifier circuit 3 Smoothing circuit 4 1st inverter circuit 5 Output transformer 6 2nd rectifier circuit 7 Reactor 8a, 8d 1st switching element 8b, 8c 2nd switching element 9a-9d Snubber resistor 10a-10d Snubber capacitor 11 Welding current detector 12, 13 Output terminal 14 Welding torch 15 Workpiece 16 Inverter control circuit 17 Comparator 18 Welding current discriminating circuit 19 Polarity switching discriminating circuit 20 Welding current setting circuit 21 Arc start current period setting circuit 22 Positive electrode Negative current period setting circuit 23 Negative current period setting circuit 25 OR circuit 26, 27 RS flip-flop circuit 28 Second switching element drive circuit 29 First switching element drive circuit 30 NAND circuit 31 RS flip-flop circuit 32, 33 Switch 34 Polarity Switching current value setting device 35 Mono multivibrator 36 First differentiator 37 First inductance value calculation circuit 38 Polarity switching current value calculation circuit 39 Arc voltage detector 40 Consumable electrode 41 Electric motor 42 Feeding roll 43 Wire reel 44 Motor control circuit 45 Welding current discriminating value setting device 46 second inverter circuit 47, 48 welding cable 49 current change discriminating value setting device 50 second inductance value calculating circuit 51 output terminal voltage detector 52 welding cable resistance value calculating circuit 53 semiconductor voltage drop value setting device 54 internal resistance value setting device 55 current change detector 56 second differentiator 57 AND circuit TS torch switch

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroyasu Mizutori 2-1-1-11 Tagawa, Yodogawa-ku, Osaka-shi Inside Daihen Co., Ltd. (72) Kosaku Yamaguchi 2-1-1-11 Tagawa, Yodogawa-ku, Osaka-shi Shares F-term in the company Daihen (reference) 4E082 BA02 CA02 DA02 EB14 EC03 EC13 EC14 ED01 EE01 EE03 EE05 EE07 EF07 GA03

Claims (5)

[Claims] After rectifying and smoothing the output of an AC power supply, a first inverter circuit converts the output into high-frequency AC power, and converts the output of the first inverter circuit into power suitable for arc machining and rectifies the converted power. Supply to a reactor, the output of the reactor is converted into AC power by a second inverter circuit, and supplied to a welding load via a welding cable;
The output of the first inverter circuit is temporarily stopped before switching the polarity of the output of the second inverter circuit, and the polarity of the output of the second inverter circuit is switched when the welding current reaches the polarity switching current value. In the AC arc welding power supply control method, the rate of change of the welding current from the output signal of the welding current detector during a period before the polarity of the output of the second inverter circuit is changed during a period when the output of the first inverter circuit is temporarily stopped. And a polarity switching between the reactor and the welding cable from the output signal of the arc voltage detector after the elapse of the period before the polarity switching and the rate of change of the welding current. The polarity switching inductance calculating step of calculating the time inductance; and AC arc welding power-supply control method comprising a polarity switching current value calculation step of determining a polarity switching current value is compliant. 2. A first inverter circuit for rectifying the output of an AC power supply and converting the smoothed output to high-frequency AC power, and a reactor for converting the output of the first inverter circuit to electric power suitable for arc machining and rectifying the output. And a second inverter circuit for supplying power converted to AC power to the welding load via a welding cable via a welding cable, wherein the output of the first inverter circuit is switched before each polarity of the output of the second inverter circuit is switched. , The output of the first inverter circuit was temporarily stopped in an AC arc welding power supply device for switching the polarity of the output of the second inverter circuit when the welding current reached the polarity switching current value. The change rate of the welding current calculated from the output signal of the welding current detector during the period before the polarity switching of the output of the second inverter circuit during the period and the polarity switching. An inductance value calculation circuit for calculating an inductance when the polarity is switched between the reactor and the welding cable from an output signal of the arc voltage detector after a lapse of a period before the replacement, and a polarity switch corresponding to the polarity switching inductance An AC arc welding power supply device comprising a polarity switching current value calculation means including a polarity switching current value calculation circuit for determining a current value. 3. The output of the second inverter circuit during a period in which the polarity switching current value calculation means receives the output signal of the welding current detector and temporarily stops the output of the first inverter circuit. Period before polarity switching (dt1)
A first differentiator for calculating a change rate (di1 / dt1) of the welding current from a welding current change value (di1), and an output signal of the arc voltage detector after a lapse of a period (dt1) before the polarity switching. (Va1) and the output signal of the first differentiator (di1 / d
t1) to calculate a first inductance value (L7 + L47 + L48) of the reactor and the welding cable from a relational expression of {(L7 + L47 + L48) × (di1 / dt1) + Va1 = 0}. 3. The means according to claim 2, further comprising: a polarity switching current value calculation circuit that receives an output signal of the first inductance value calculation circuit and calculates a polarity switching current value corresponding to the first inductance value. AC arc welding power supply. 4. The polarity switching of the second inverter circuit during a period in which the polarity switching current value calculating means receives an output signal of the welding current detector and temporarily stops the output of the first inverter circuit. From the change value (di1) of the welding current in the previous period (dt1), the rate of change (di1 /
dt1), an output voltage detection signal of the second inverter circuit, an output signal of the welding current detector, and an output signal of the arc voltage detector to input a resistance value of the welding cable. (Ro), and a voltage drop value (V) between the welding cable resistance value calculating means and a pair of switching elements of the second rectifier circuit and the second inverter circuit.
f) a semiconductor voltage drop value setting device, an internal resistance value setting device for setting an internal resistance value (Ri) of the AC arc welding power supply device, and an output signal (Vf) of the semiconductor voltage drop value setting device. An output signal (Di1 / dt1) of the first differentiator, an output signal (Va1) of the arc voltage detector after a lapse of a period (dt1) before the polarity switching, and an output signal (If1) of the welding current detector. And the output signal (Ro) of the welding cable resistance value calculating means and the output signal (Ri) of the internal resistance value setting device are input as follows: ｛(L7 + L47 + L48) × (di1 / dt1) + Va1 + (Ro +
Ri) × If1 + Vf = 0 °, a second inductance value calculation circuit for calculating a second inductance value (L7 + L47 + L48) between the reactor and the welding cable, and an output signal of the second inductance value calculation circuit, 3. The AC arc welding power supply device according to claim 2, further comprising a polarity switching current value calculation circuit that calculates a polarity switching current value corresponding to the second inductance value. 5. An output terminal voltage detector for detecting an output voltage of the second inverter circuit, wherein the welding cable resistance value calculating means detects a change in welding current during a period (dt2) during operation of the first inverter circuit. A second differentiator for calculating a change rate (di2 / dt2) of the welding current from the value (di2), and an output signal of the welding current detector when the output (di2 / dt2) of the second differentiator is substantially zero (If2) and the output signal (Vo) of the output terminal voltage detector and the output signal (Va2) of the arc voltage detector, and the resistance value of the welding cable ｛R
5. The AC arc welding power supply device according to claim 4, further comprising a welding cable resistance value calculating circuit for calculating o = (Vo−Va2) / If2}.