JPS6311100B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AC arc welding power supply device that can improve the welding current waveform to one suitable for arc welding.

Recently, an AC arc welding power supply device has been developed in which an AC phase control circuit using electronic switching means such as a thyristor is used as an output current adjustment means.
This device is impractical because if the output of the AC phase control circuit is directly output, there will be a period in which the current value is zero when the polarity of the welding current is reversed, that is, a zero current period, and the arc will be extinguished during this period. ,
Normally, the output is made through a reactor as shown in Figure 1.

In FIG. 1, 1 is an AC power source, 2 is an AC phase control circuit, and 3 is an arc welding load. The AC phase control circuit 2 has thyristors 4 and 5 connected in parallel in opposite directions, and a reactor 6 is commonly connected in series to each thyristor 4 and 5, respectively.
The arc welding load 3 has a workpiece 8 and an electrode 9 disposed facing each other, and an arc 10 is generated between the two. The welding current waveform in this type of device is a continuous waveform with no current zero period, but as shown in FIG. 2, it is a distorted waveform with a low rise when the polarity is reversed. Therefore, since the current value at the beginning of a half cycle is small, the arc cannot be re-ignited smoothly, resulting in a lack of stability. Also, for example, for a practical device with a rating of 300A, the current adjustment range is
It needs to be in the range of around 15A to 320-330A, but in order to satisfy that current adjustment range, the capacity of the reactor must be reduced to some extent, and in that case, the above-mentioned current in the small current range A zero period begins to occur, and in practice there is a problem in that the current adjustment range must be made sufficiently smaller than the above-mentioned width.

An object of the present invention is to make welding current a continuous waveform with no current zero period in a wide current adjustment range, and to make the rise characteristic at the beginning of each half cycle steep.
The stability of arc restriking can be increased,
An object of the present invention is to provide an AC arc welding power supply device equipped with an AC phase control circuit capable of performing good and stable arc welding.

Embodiments of the present invention will be described below with reference to the drawings.

First, an example of the circuit configuration shown in FIG. 3 will be explained. In FIG. 3, 11 is an AC power source, 12 is a welding transformer connected to the AC power source 11 via a power switch 13, and 14 is an AC phase control circuit, 15
is an arc welding load connected to the welding transformer 12 via the AC phase control circuit 14. The AC phase control circuit 14 has a pair of thyristors 16 and 17 connected in antiparallel, and the thyristor 1
Reactors 18 and 19 are connected in series to 6 and 17, respectively. Thyristors 20 and 21 are connected in parallel to each reactor 18 and 19 as a self-excitation circuit, respectively.

The thyristors 16 and 21 are supplied with gate signal A during the positive half cycle of the input voltage (output voltage of the welding transformer 12) vi, and the thyristors 17 and 20 are supplied with gate signal B during the negative half cycle of the input voltage _vi . I am trying to power it. Gate signal A,
B is generated from a gate signal generation circuit (not shown) so that the phase can be adjusted with respect to the input voltage v _i .

The arc welding load 15 has a workpiece 22 and an electrode 23 disposed facing each other, and an arc 24 is generated between them.

Next, the operation will be explained with reference to FIGS. 4, 5, 11, and 12. Input voltage Vi
In the positive half cycle of , the thyristors 16 and 21 are turned on at a certain phase by the gate signal A,
In the negative half cycle, the thyristors 17 and 20 are turned on in a certain phase by the gate signal B, so the arc welding load 15 includes the thyristor 16-reactor 18 circuit and the thyristor 17-reactor 19 circuit. Welding current iw flows through alternately.

Here, regarding the operation of a reactor in a circuit that flows current to a load via a reactor, the 11th
This will be explained in detail with reference to the drawings and FIG.

Thyristor 1 with phase control angle T ₁ shown in Fig. 11
When the ignition signal A is applied to the welding transformer 12, the thyristor 16 becomes conductive, the welding current iw is applied to the terminal S ₁ of the welding transformer 12, the thyristor 16,
It flows to the reactor 18, the arc load Ra and the terminal S ₂ of the welding transformer 12. Welding transformer 1 at this time
2. The polarity of the reactor 18 and the arc load Ra are as shown in Figure 12a, and Vi>iw・Ra, so the reactor 18 has a starting force of Vi−iw・Ra (=Ldi/dt) as shown in the figure. occurs in polarity, and in Figure 11
Energy corresponding to the shaded portion A between T ₁ and T ₂ is stored.

Next, in the period T ₂ − T ₃ , Vi<
However, as shown in Figure 12b, the reactor 18 generates a starting force of -Ldi/dt and releases the previously stored energy, so the welding current
iw continues to flow in the same direction as during the _T1 - _T2 period.

As time passes further and the phase control angle reaches T ₃ ,
Although the polarity of the input voltage Vi is reversed as shown _{in FIG .}
The welding current iw continues to flow in the same direction as during the −T ₃ period.

Next, when the phase control angle T ₄ is reached, thyristor 1
When the ignition signal B is applied to the thyristor 7 and the thyristor 17 becomes conductive, the welding current iw increases as shown in FIG. 12d.
are terminal S ₂ of welding transformer 12, arc load Ra, reactor 19, thyristor 17, welding transformer 12
flows to terminal S ₁ of.

Furthermore, since the ignition signal B is also given to the thyristor 20, when this thyristor 20 becomes conductive, the reactor 18 releases the energy that has not yet been released in a closed circuit passing through the thyristor 20, but in the forward direction of the thyristor. Since the resistance (Rth) of the reactor and the internal resistance (R _L ) of the reactor are small, energy consumption in this closed circuit W = (i ₁₈ ) ²
(Rth+R _L ) is extremely small and is hardly consumed during the half-cycle period of the load when the welding current iw is reversed, that is, during the period T ₄ −T ₇ .

Further, at this point, the arc load Ra and the polarity of the reactor 19 are as shown in _FIG . Since is already negative, the thyristor 16 is turned off.

Thereafter, the same operation as described above is repeated over time from phase control angle T ₄ to T ₅ , T ₆ , . . . .

By the way, in a circuit such as this in which current flows through a load through a reactor, the value of the current is derived from the magnetomotive force corresponding to the magnetic flux of the reactor, so the value follows the magnetization characteristic curve shown in FIG. 4.

In addition, in such a circuit, the relational expression of instantaneous value of input voltage = instantaneous value of voltage between reactor terminals + instantaneous value of load voltage must be satisfied, so the reactor magnetic flux is calculated by the instantaneous value of input voltage Vi and the load voltage. It increases until the phase where the instantaneous value of

Therefore, the welding current iw also changes in response to such changes in magnetic flux.

By appropriately selecting the capacities of the reactors 18 and 19, for example, the input voltage Vi
During the positive half cycle, the positive current flowing through the thyristor 16 and the reactor 18 can be extended to the next negative half cycle.

That is, even if the gate signal A or B disappears within the corresponding positive or negative half cycle as shown in FIGS. 5b and 5c, the gate signals shown in FIGS.
The thyristor 16 or 17 can remain on until the next half-cycle phase, as shown in FIG.

Thyristors 16 and 17 are connected to thyristors 2 and 2 connected in parallel to each reactor 18 and 19.
0 and 21 are turned on, and each reactor 18,
The currents i ₁₈ and i ₁₉ flowing through the arc welding load 19 by self-induction are restrained within a closed circuit constituted by the reactors 18 and 19 and the thyristors 20 and 21, and are prohibited from flowing to the arc welding load 15 side. Turn off at the right timing.

On the other hand, thyristors 20 and 21 are
6 and 17 are turned on when triggered by the gate signals A and B, and turned off at the timing when the input voltage Vi in the opposite direction is applied.

Therefore, the thyristors 16 and 21 and the thyristors 17 and 20 are turned on and off in synchronization with the rising timing of the gate signals A and B, as shown in FIG. 5d and f.

By the way, the current i ₁₈ confined in the closed circuit,
i ₁₉ circulates in the closed circuit to reactor 18,
19 is excited to a constant magnetization state, that is, self-excited.

Since the terminal voltages of the reactors 18 and 19 are approximately zero and hardly attenuate, the thyristors 20 and 21
will hold a constant value until the next half cycle, when it turns off and releases its constraint.

Now, as mentioned above, the reactors 18 and 19 are fixed in a constant magnetized state during the non-voltage application period when the thyristors 16 and 17 connected in series are off, so when the thyristors 16 and 17 are turned on and the parallel During the voltage application period in which the thyristors 20 and 21 are turned off, their magnetization state starts from the above-mentioned fixed magnetization state and changes to the input voltage as described above.
It will change as Vi changes.

That is, in FIG. 4, if point Q ₁ is the fixed magnetization position and point Q ₂ is the maximum magnetization position, the magnetization states of the reactors 18 and 19 will be the magnetization characteristic curve between points Q ₁ and Q ₂ . It reciprocates according to the fourth
As shown in the figure, the magnetic flux changes between φ ₁ and φ ₂ , so that the currents i ₁₈ and i ₁₉ change in the same way between A ₁ and A ₂ .

The welding current flowing through the arc welding load 15
iw is the reactor 18,
Since it is a composite of the currents i ₁₈ and i ₁₉ flowing through the terminals 19, it has a waveform as shown in FIG. 5h.

Also, during the voltage application period, the reactor 1
Since the initial values of the currents i ₁₈ and i ₁₉ flowing through the thyristors 20 and 21 are equal to the current values when the circuits are constrained to the closed circuit, by appropriately setting the constraint current values, reactor 18,1
9 and the phase at which the thyristors 20 and 21 are turned on, that is, the generation phase of the gate signals A and B. By adjusting the phase shift of the generation phase of the gate signals A and B, arc re-ignition can be achieved. This makes it suitable for Therefore, the welding current iw can be made into a waveform that instantly rises to a current value suitable for arc restriking when the polarity is reversed, such as a superimposed square wave and a sine wave. High stability and stable arc welding. Furthermore, since no current zero period occurs when the polarity is reversed, the stability of arc restriking can be maintained even if the current is adjusted over a wide range. Incidentally, when the apparatus shown in FIG. 3 is used for AC TIG arc welding of aluminum, the generation phases of gate signals A and B may be controlled independently of each other.

In other words, when welding aluminum by AC TIG arc welding, it is known that if an AC voltage with positive and negative symmetry is supplied to the arc welding load, the welding current waveform will become a positive and negative asymmetric waveform including a DC component. ing. This phenomenon occurs due to a decrease in the positive half-wave current value when the welding object is a cathode, which provides the effect of removing the oxide film on the surface of the object, the so-called cleaning effect. This reduces the cleaning effect and adversely affects welding, and the presence of the DC component causes the primary and secondary sides of the welding transformer to be overloaded, increasing the risk of burning out the windings. However, if the generation phases of gate signals A and B can be controlled independently as described above, for example, the conduction periods of thyristors 17 and 20 can be held constant, and the conduction periods of thyristors 16 and 21 can be increased. For example, it is possible to increase the current value in the positive half-wave of the welding current, making the current values in the positive and negative half-waves equal, and solving the above-mentioned problems specific to AC TIG arc welding of aluminum. be. Moreover, since the thyristors 20 and 21 are connected in parallel to the reactors 18 and 19 as a self-excitation circuit, the welding current waveform can be set such that the welding current suddenly rises to a certain value when the polarity is changed, as described above. , Aluminum AC in stable condition
TIG arc welding can be performed. FIG. 6 is a waveform diagram when performing the above-mentioned AC TIG arc welding of aluminum.

Next, an embodiment whose circuit configuration is shown in FIG. 7 will be described.

In this embodiment, variable resistors 25 and 26 are inserted in series as variable impedance elements in the self-excitation circuit in the embodiment shown in FIG. Resistors 25 and 26 are connected in series, and the other circuit configurations are the same.

With such a configuration, when the thyristors 20 and 21 are turned on, the currents i18 and i19 flowing through the reactors 18 and 19 are restrained in a closed circuit between the self-excitation circuit and each reactor 18 and 19, as in the above embodiment. However, in this case, not only the thyristors 20 and 21 but also the variable resistor 2 are included in the self-excitation circuit.
5 and 26, the current attenuates over time. In addition, variable resistors 25, 2
6 and the resistance value of the arc welding load 15, the current is also shunted to the arc welding load 15 side. Of course, the resistance values of the variable resistors 25 and 26 are selected to be very small compared to the resistance value of the arc welding load 15, so the attenuation of the current in the self-excitation circuit is minute, and the current is not applied to the arc welding load 15 side. The branch flow is also minute.

However, the current i flowing through the reactors 18 and 19
18 and i19 are slightly different from the case of the above embodiment due to the above-mentioned attenuation and shunting, and as shown in FIGS. Moreover, the rising level of the current is slightly lower than the level when the thyristors 20 and 21 are turned on. Therefore, the welding current is a composite of the currents i18 and i19 during the period when the thyristors 20 and 21 are off.
As shown in FIG. 8c, iw also changes to a slightly slower rise and fall of the current when the polarity is reversed. The current rise and fall characteristics of each half cycle of this welding current iw can be controlled by the resistance values of the variable resistors 25 and 26. For example, as shown enlarged in FIG. 9, the resistance value R of the variable resistors 25 and 26 ₁ , R ₂ , and R ₃ . In addition, in FIG. 9, R ₁
<R ₂ <R ₃ . In this way, by controlling the current rise and fall characteristics at the time of polarity change of the welding current iw, the waveform can be optimized to ensure stable arc re-ignition and suppress spatter. It is something that can be adjusted. Next, an embodiment whose circuit configuration is shown in FIG. 10 will be described.

This embodiment is made by adding changeover switches 27, 28, 29, 30 and a diode 31 to the embodiment shown in FIG. Of course, it can also be used for DC arc welding. In FIG. 10, if the switching contacts of the switching switches 27, 28, 29, and 30 are switched to the a side, they can be used for AC arc welding, and if they are switched to the b side, they can be used for DC arc welding. In addition, the changeover switch 28 can be used as an output adjustment switch when used for DC arc welding, and the diode 31 is configured to adjust the instantaneous value at both ends of the reactors 18 and 19 from the instantaneous value of the output voltage of the welding transformer 12. When the current value increases, the electromagnetic energy of the reactor is consumed by the arc welding load, preventing the current value from attenuating and acting as a so-called freewheeling diode to obtain a smooth DC current with little ripple.

Although each of the above embodiments is equipped with an AC phase control circuit in which thyristors are connected in antiparallel, it is also possible to use an AC phase control circuit with other circuit configurations or other electronic switching means. The present invention is applicable.

As is clear from the above explanation, the present invention allows currents of different polarities that are phase-controlled by an AC phase control circuit to flow through different reactors, and each reactor is provided with an excitation circuit. During the voltage application period, the reactor is excited to a predetermined magnetization state by the excitation circuit, and during the voltage application period, a current corresponding to the magnetization state immediately flows, so that a zero current period does not occur when the polarity is reversed. Therefore, it is possible to provide an AC arc welding power supply device that can adjust the current over a wide range and maintain the stability of arc restriking.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of a conventional AC arc welding power supply device, Fig. 2 is a welding current waveform diagram of the same device, Fig. 3 is a circuit diagram showing an embodiment of the present invention, and Fig. 4 is a circuit diagram showing an example of a conventional AC arc welding power supply device. Figure 5 is a diagram of the magnetization characteristic curve of the reactor, Figure 5 is a current and voltage waveform diagram of the main parts of the same example, Figure 6 is a current and voltage waveform diagram of the main parts of the same example during AC TIG arc welding, and Figure 7 is a diagram of the current and voltage waveforms of the main parts of the same example. A circuit diagram showing another embodiment of the present invention, FIG. 8 is a current waveform diagram of the main part of the same embodiment, and FIG.
The figure is an enlarged waveform diagram of the welding current of the same embodiment, and FIG. 10 is a circuit diagram showing still another embodiment of the present invention. FIG. 11 is a waveform diagram illustrating the action of the reactor of the same embodiment, and FIGS. 12 a to 12 d are circuit diagrams illustrating the action of the reactor of the same embodiment. 14... AC phase control circuit, 16, 17, 2
0,21...Thyristor, 18,19...Reactor.

Claims (1)

[Scope of Claims] 1. A welding transformer, an AC phase control circuit in which semiconductor switching elements are connected in antiparallel to each other, which is inserted between the secondary side of this welding transformer and a welding load, and this AC phase control circuit. A reactor connected in series to each semiconductor switching element of the circuit, and a semiconductor switching element connected in parallel to each of the reactors and connected in series to the reactor, maintain the reactor in a magnetized state while the semiconductor switching element is in a non-conducting state. The present invention is characterized by comprising: an excitation circuit equipped with a semiconductor switching element that is connected to the semiconductor switching element; and a gate signal generation circuit that outputs a gate signal to each of the semiconductor switching elements to control the conduction phase of each semiconductor switching element. A power supply device for AC arc welding. 2. The alternating current arc according to claim 1, wherein the excitation circuit short-circuits both ends of the reactors only by semiconductor switching elements connected in parallel to each reactor. Power supply device for welding. 3. The AC arc welding power supply device according to claim 1, wherein the excitation circuit is a series circuit of a semiconductor switching element and an impedance element connected between both ends of each reactor. 4. The AC arc welding power supply device according to claim 3, wherein the impedance element is a variable impedance element.