JPH0124644Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention is a DC arc machining process in which the output current of a phase-controlled rectifier circuit and the output current of a non-phase-controlled rectifier circuit are superimposed and supplied to an arc load. It is related to power supply.

[Prior art] A phase control method using a thyristor is widely used as a method for adjusting the output current or output voltage of a DC arc machining power supply, but this method causes large ripples in the output waveform due to phase control, causing problems with the firing phase and Depending on the state of the load, a cutoff period due to phase control occurs in the output current of the phase control rectifier circuit. Therefore, in order to improve the output waveform of a phase-controlled rectifier circuit, a multi-phase rectification system with six or more phases, such as a six-phase half-wave rectification system with an interphase reactor, is adopted, or the output current is improved by phase control. In order to eliminate the cut-off period, a method is adopted in which the output current of a rectifier circuit that does not perform phase control is superimposed on the output current of a phase control rectifier circuit.

[Problems to be solved by the invention] In the former multi-phase rectification method with six or more phases, the output waveform becomes close to direct current and is therefore suitable for arc loads, but the circuit is complex and requires interphase reactors. Not only is it large and expensive, but the smoothing reactor also serves to smooth the output current both during arc continuation and during short circuit, so it is important to select the optimal inductance value for each. I can't. Further, although the latter superimposition method has a simpler circuit, is smaller in size, and is less expensive than the former, it is difficult to obtain a wide range of output suitable for various arc loads. The reason for this is that in the latter case, the output of the phase control rectifier circuit becomes pulsed, which is undesirable, so a smoothing reactor is connected between the rectifier circuit and the load to smooth it and maintain arc stability. However, it is nearly impossible to select the inductance value of this reactor so as to obtain an output suitable for various arc loads. Therefore, the inductance value of the reactor must be changed in accordance with the output suitable for the predetermined conditions of the arc load. Further, even if the arc load is the same, the appropriate inductance value of the reactor differs depending on the arc load state, for example, when an arc is generated between the electrode and the workpiece, and when a short circuit occurs between them. When the arc load is a carbon dioxide arc welding load or MIG welding load, the inductance value of the reactor has a subtle effect on the arc load because the output voltage and current characteristics of the DC arc processing power source are usually constant voltage characteristics. . In other words, the conditions required for a reactor to obtain a stable arc are: (1) the inductance value of the reactor must be small to ensure a good arc start, and (2) the inductance value of the reactor must be small during the period when the arc is occurring. , The smaller the output current ripple, the more stable the arc, so the inductance value of the reactor should be as large as possible. (3) The rise speed is Since a large and appropriate amount of current is required, it is desirable that the inductance value of the reactor is small.

Therefore, in the latter superposition type machining power supply,
It cannot be applied to various arc loads without changing the inductance value of the reactor.
Furthermore, there is a drawback that it is not possible to obtain appropriate effects depending on the state of the arc load even for the same arc load.

Here, in order to clarify the effects of the conventional superimposed type machining power source and the arc machining power source of the present invention, which will be described later, we will first explain the conventional superimposed type machining power source with reference to FIGS. I will explain about it.

FIG. 1 is a configuration diagram of a conventional superimposed type arc machining power supply, in which 1 and 2 are transformer output windings, 3 is a phase control rectifier circuit including a thyristor,
4 is a diode rectifier circuit without phase control, and 5 is a smoothing reactor connected between the parallel connection point and the arc load L after both rectifier circuits 3 and 4 are connected in parallel.

FIG. 2 is a connection diagram showing a specific example of the configuration diagram in FIG.
It is a primary winding that is also used as phase output windings 1 and 2,
1a to 1c and 2a to 2c are the first
and the secondary winding of the second transformer. 3a to 3c are thyristors whose conduction/cutoff and ignition phase are controlled by a phase control circuit (not shown) and constitute the phase control rectifier circuit 3, and 4a to 4c are rectifiers made of diodes which constitute the rectifier circuit 4. Configure. 5 is a smoothing reactor having taps 5a to 5c, S1 is a contact that opens and closes the rectifier circuit 4 by a signal circuit (not shown), and S2 is a smoothing reactor having taps 5a to 5c.
is a switch for switching the taps 5a to 5c of the reactor 5.

FIG. 3 shows the output waveforms of each part in FIG. 2 when the thyristors 3a to 3c shown in FIG. 2 are phase-controlled by a phase control circuit and a signal circuit (not shown) and the contact S1 is closed. Figure 3a is
In the output voltage waveform diagram at point A shown in FIG. A solid sine waveform on the line is an output voltage waveform diagram of the other secondary windings 2a to 2c of the transformer. Further, based on the waveforms shown by the solid lines on the dashed-dotted line, that is, _the respective times t ₁ , t ₄ , t _{7 .} ,...from t ₅ ,
The waveform up to _t8 ... is the output voltage waveform of the thyristors 3a to 3c that constitute the rectifier circuit 3 whose phase is controlled by a phase control signal (not shown), that is, the second waveform.
This is the waveform at point A in the figure. Further, the waveform shown by the solid line on the dotted line, that is, the waveform during the period of the control angle α, is the output voltage waveform of the rectifiers 4a to 4c forming the rectifier circuit 4 whose phase is not controlled while the output of the rectifier circuit 3 is cut off. That is, this is the waveform at point A in FIG. In other words, when the thyristor of either phase becomes conductive after the control angle α has elapsed, a voltage in the opposite direction is applied to each rectifier and each rectifier is cut off, and the output voltage of the rectifier circuit 3 is shown at point A in FIG. occurs. When the conductive thyristor reaches time t ₂ , t ₅ , t ₈ . . . when the voltage applied to the thyristor becomes lower than the voltage applied to the diode of the rectifier circuit 4, a voltage is applied in the opposite direction and the thyristor is cut off. Become. Thereafter, the same process is repeated, and a voltage having the waveform shown in FIG. 3a is generated at point A in FIG. 2. Therefore, if the control angle α is made smaller, the duration of the voltage output from the rectifier circuit 3 becomes longer, and the average output voltage becomes larger. Conversely, if the control angle α is made larger, the output from the rectifier circuit 4 becomes longer. The duration of the voltage applied increases,
The average output voltage becomes small and the output voltage waveform becomes pulse-like. FIG. 3b shows the voltage waveform of the arc load L when short-circuit transfer arc welding of MIG welding or carbon dioxide arc welding is performed using an arc machining power supply having such an output voltage waveform. In the figure, the arc load L is short-circuited between times _t11 and _t12 , _t13 and _t14 , _t15 and _t16 , and so on, and an arc is generated during other periods. FIG. 3c shows the current flowing through the arc load when the arc load repeats such a short-circuit state and an arc state. Between the short circuit period t ₁₁ and t ₁₂ in Figure b,
As shown in figure a, the thyristor is conducting, so that a current _i1 larger than the current indicated by Y, which will be described later, flows from the thyristor, as indicated by X in figure c.

On the other hand, between the short-circuit period _t13 and _t14 in Figure 3b, the rectifier is conducting as shown in Figure 3a, so as shown in Y in Figure 3c, the aforementioned A current i ₂ smaller than the current shown at X flows from the rectifier. Also, the arc duration t ₁₂ in Figure b
t ₁₃ as well, when the rectifier in a of the same figure is conducting, N as shown by M in c of the same figure will be described later.
A current i ₂ smaller than the current shown by flows, but
Even if the arc duration is the same, when the thyristor shown in figure a is conducting, the current i ₁ is larger than the current shown by M mentioned above, as shown by N in figure c.
flows.

In the superimposed type DC arc machining power supply shown in Fig. 2, since the reactor 5 of both rectifier circuits is common, the lower limit value of the output current is the output of the rectifier circuit 4 without phase control, and the upper limit value is the output of the rectifier circuit 4 without phase control. This is the output of the rectifier circuit 3 that performs the following.

In this way, in the conventional superimposed type DC arc machining power supply, even during the same short-circuit or arc continuation period, it depends on whether the thyristor is conducting or the diode is conducting. However, since the output current fluctuates, there is a drawback that it is not possible to supply a current with an appropriate constant waveform while the arc is continuing and immediately after a short circuit.

Note that if you increase the inductance of the reactor in an attempt to eliminate these drawbacks, the fluctuations in the output current under the same conditions will be reduced, but as mentioned above, the rise speed of the output current immediately after a short circuit will decrease, and it will also be necessary to Another disadvantage arises in that it is no longer possible to obtain short-circuit currents of this magnitude.

[Means for Solving the Problems] The present invention is a DC arc machining power supply that generates an arc between a consumable electrode and a workpiece and is used for arc machining. The second is to supply a short-circuit current that has a high rising speed when the short-circuit state changes from a state to a short-circuit state.Secondly, it is possible to maintain a stable arc with small ripples during arc generation, and furthermore, to supply an output current that allows the current value to be adjusted. The purpose of the present invention is to provide a power source for arc machining that can perform arc machining, and as shown in FIG. 4, it has the following configuration.

After generating an arc, the first transformer output winding 1 outputs a no-load voltage higher than the arc voltage that can maintain the arc, and the output current needs to be adjusted depending on the arc processing conditions. and a phase control rectifier circuit 3 for controlling the phase of the output voltage of the transformer output winding 1 using a thyristor; The first one has a sufficiently large inductance value to smooth the output voltage of the controlled rectifier circuit 3.
With the reactor 5, there is no need to maintain the arc and a no-load voltage lower than the arc voltage is applied in order to flow the short circuit current and immediately generate or re-ignite the arc at the time of arc start or short circuit during arc generation. Since there is no need to adjust the output current over a wide range by simply passing a short-circuit current between the second transformer output winding 2 and the output voltage of the transformer output winding 2, there is no need to adjust the output voltage and phase of the transformer output winding 2 using diodes. In order to ensure that the arc is generated or re-ignited by passing a short-circuit current with a fast rising speed at the time of arc start or short circuit during arc generation,
A second reactor 6 has an inductance value smaller than an inductance value of the first reactor 5, and the output voltage of the rectifier circuit 4 is adjusted to the output voltage of the first reactor 5 and the second reactor 6. This is a DC arc machining power supply that connects the output voltages of the two in parallel so that they have the same polarity and supplies them to an arc load L consisting of a consumable electrode and a workpiece.

[Example] Hereinafter, an example that embodies the configuration of the present invention shown in FIG. 4 will be described.

FIG. 5 is a connection diagram showing a specific example of the configuration diagram in FIG. 4, and in FIG.
c and S1 are the same as the configuration in FIG. 2, and
A primary winding that also serves as a transformer core, a secondary winding that constitutes the first output winding 1, a secondary winding that constitutes the second output winding 2, and a phase control rectifier circuit 3. These are a thyristor, a diode that constitutes the rectifier circuit 4 without phase control, and a contact that opens and closes the rectifier circuit 4. 5 and 6 are the reactor with a large inductance value and the first and second reactors with a small inductance value as explained in FIG.

In the processing power source according to the embodiment of the present invention, in a normal arc state, current is supplied to the arc load L through the phase control rectifier circuit 3 and the reactor 5 connected to it with a sufficiently large inductance value, and the short circuit Since this is a power source that supplies current to the arc load through the rectifier circuit 4 that does not perform phase control only in the state of
Since it is not necessary to supply an output current with a large rise speed during a short circuit of the arc load, the inductance value of the reactor 5 is adjusted so that the current with a cutoff period by phase control becomes a continuous current with few ripples. It can be made large enough.

That is, in the conventional superimposed processing power source shown in FIGS. 1 and 2, the inductance value of the reactor suitable for normal short-circuit transition type arc welding had to be 500 μH or less.

However, with the processing power source of the present invention, it is sufficient to smooth the phase-controlled current regardless of the inductance value required for short-circuit transitional arc welding, so the inductance value required for normal short-circuit transitional arc welding is The inductance value can be made sufficiently larger than the maximum value of , for example, 1000 μH or more. Furthermore, the current supplied to the reactor 6 is not phase-controlled, and a continuous output current with little ripple can be obtained even with a sufficiently small inductance value. Therefore, immediately after the arc load is short-circuited,
It is possible to obtain an output current with a large rise speed,
In addition, since the inductance value can be selected to a value suitable for short-circuiting of the arc load and the short-circuit current value can be set to an appropriate value, short-circuit transfer type arc welding can be performed smoothly and good welding results can be obtained. Furthermore, since the inductance value of the reactor 6 is smaller than the inductance value of the smoothing reactor of conventional processing equipment, the rising speed is high even at arc start, and an output current with an appropriate current value can be obtained. It is possible to eliminate arc start failures that often occur in short-circuit transitional arc welding.

FIG. 6 is a waveform chart for explaining the operation of the embodiment shown in FIG. 5. Similarly to FIG. 3b, FIG. It shows _{the voltage} waveform _of arc _load L _when
The arc load L is short-circuited between t ₁₆ , . . . , and an arc is generated during the other periods.

When the arc load repeats such a short circuit state and an arc state, the output current of the reactor 5
i ₁₀ , the output current i ₂₀ of the reactor 6, and the current i ₁₀ +i ₂₀ flowing through the arc load L are shown in FIGS. 6b to 6d, respectively. Since the reactor 5 has a sufficiently large inductance value as described above,
The output current i ₁₀ of the reactor has a small ripple and has a substantially constant value, as shown in FIG. The input voltage of the rectifier circuit 4 is set lower than the input voltage of the phase control rectifier circuit 3 and below the arc voltage, and both rectifier circuits are connected through separate reactors.
Therefore, when the arc load is in an arc state, a reverse voltage is supplied to the diodes 4a to 4c, so the output current _i20 of the rectifier circuit 4 does not flow.
The current flows only when the arc load is short-circuited, as shown in c of the same figure. This current i ₂₀ has a substantially constant waveform determined by the load voltage, regardless of whether any of the thyristors in the phase control rectifier circuit 3 is conducting. In addition, the first reactor 5
is, after electromagnetic energy is accumulated from time t ₁₁ at the start of the short circuit of the arc load to time t ₁₂ at the end of the short circuit,
The electromagnetic energy accumulated between time _t12 and time _t13 is released, and the output current _i20 of the second reactor 6 becomes zero at time _t23 . Figure 6d
The current i ₁₀ + i ₂₀ supplied to the arc load L shown in
Regardless of whether any thyristor in the phase control rectifier circuit 3 is conducting or not, when the arc load is in an arc state, the output current has a constant waveform determined by the characteristics of the phase control rectifier circuit 3 and the reactor 5. i ₁₀ and when the arc load is in a short-circuited state, the output current has a constant waveform that is the sum of the output current i ₁₀ of the reactor 5 and the output current i ₂₀ of the reactor 6. Note that the output current of the rectifier circuit 4 flows through the reactor 6 only when the arc load is short-circuited, and short-circuit transition short-circuit transition type arc welding is normally in a small current range.
It requires a much smaller capacity.

Fig. 7 is a connection diagram of another embodiment of the processing power supply of the present invention, in which 1a to 1c are secondary windings of a three-phase transformer, and the voltage between the terminals of these secondary windings √3E is the phase control Furthermore, each phase voltage E of these secondary windings becomes an input voltage of a rectifier circuit whose phase is not controlled. 3a to 3c
is a thyristor, and 3e to 3g are diodes, which constitute a three-phase mixed bridge type phase control rectifier circuit 3. Reference numeral 4d denotes a rectifier, and this and the rectifiers 3e to 3g constitute a rectifier circuit 4 with a three-phase half-waveform whose phase is not controlled. The output current of each of these rectifier circuits is supplied to the arc load L via reactors 5 and 6, respectively, which have the same inductance as described in FIGS. 4 and 5.

However, the output current adjustment range of the processing power source of the embodiment shown in FIG. 7 is larger than the output voltage 1.17E of the half-wave rectifier circuit as the rectifier circuit 4 without phase control.
And it is smaller than the output voltage 1.35×√3ECOSα of the mixed bridge rectifier circuit as the phase control rectifier circuit 3, and the maximum value of the ratio is 1.17E/(1.35×√3
E) = 0.5, that is, the output current adjustment range is 50
It becomes narrower at ~100%. The waveforms of the output currents of the reactors 5 and 6 when short-circuit transitional arc welding is performed using the processing power source shown in the figure are the same as in the case of FIG. 6 described above.

In the above embodiments, a three-phase half-wave rectifier circuit or a three-phase bridge rectifier circuit has been described as each rectifier circuit, but various single-phase rectifier circuits, multi-phase rectifier circuits, and combinations thereof may be used. Further, as a rectifier circuit that does not perform phase control, a thyristor may be used instead of the rectifier and the contact of the switch to perform only switching control without phase control. Furthermore, reactors 5 and 6 are not limited to linear characteristics; reactor 5 satisfies the condition of converting a phase-controlled intermittent waveform current into a continuous waveform current, and reactor 6 controls the current rise speed. A reactor with nonlinear characteristics in which the inductance value changes with the applied current may be used as long as the conditions for making the necessary large value are satisfied. These reactors 5 and 6 may have different inductance values by selecting different numbers of turns using a common iron core. Furthermore, we have described the case where the DC arc processing power supply of the present invention is applied to short-circuit transition type arc welding, but in addition to normal arc welding, arc load fluctuations are particularly severe in arc cutting, arc heating, arc brazing, etc. Similar effects can be obtained when used for other purposes.

FIG. 8 shows another application example of the present invention in which a freewheel diode 7 is connected in parallel to the output of the phase control rectifier circuit 3 of the processing power source of the present invention. A reactor 5 with a large inductance value that allows the current to flow continuously is connected to the phase control rectifier circuit 3. The reactor 5 absorbs a part of the transformer secondary winding voltage as electromagnetic energy, and the winding voltage increases. When it drops or becomes negative, it releases the absorbed energy to prevent the current flowing through the reactor from dropping. By repeating this, the current exiting the reactor 5 is smoothed. In this case, reactor 5
The electromagnetic energy absorbed by the reactor is released through the arc load L, the secondary winding of the transformer, and the thyristor, but when the voltage of the secondary winding of the transformer becomes negative, part of the energy stored in the reactor is converted into reactive power. It is returned to the power supply side. Freewheel diode 7 connected in parallel to the output of phase control rectifier circuit 3
prevents a part of the stored energy from being returned to the power supply side as reactive power, and the stored energy of the reactor is consumed by the arc load L as active power. Therefore, by connecting the freewheel diode 7, the output current waveform of the phase control rectifier circuit 3, shown in FIG. Increase.

[Effect of the invention] As described above, according to the DC arc machining power supply of the invention, the output current of the phase control rectifier circuit 3 is sufficiently large to the extent that the output current supplied to the arc load is continuous. is supplied to the arc load L through a reactor 5 having an inductance value,
The output current of the non-phase controlled rectifier circuit 4 with a lower no-load voltage than the phase controlled rectifier circuit 3 is a comparison in which the rise speed of the output current is large and an appropriate current value is obtained at the start of the arc load L or immediately after a short circuit. Since the arc load is supplied through reactors with a relatively small inductance value, the required inductance value can be selected individually for each reactor. Therefore, (1) It is possible to adapt to various arc loads without switching by providing a tap on the smoothing reactor, and a reactor with a fixed tap can be used even if the load type, load current value, etc. are different. It has a wide range of application, and can be used for different arc loads, such as a load with few short circuits and a load with many short circuits.

(2) Even if the type of load and the set load rectification value are constant, if the arc load suddenly changes such as a short circuit, set an appropriate inductance value for each changed load. Since the material can be selected, good arc machining can be performed.

(3) Regardless of the presence or absence of the output current of the phase control rectifier circuit, the set output current flows only depending on the arc load state, for example, whether an arc is occurring or a short circuit is occurring, so the arc load state changes regularly. Since the process is repeated, it is possible to perform arc processing with constant quality.

(4) Only when the arc load is short-circuited, the amount added to the arc current can be supplied from the non-phase controlled rectifier circuit, so the capacity of the non-phase controlled rectifier circuit can be reduced.

(5) It has great practical value as it allows for good arc starting.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional DC arc machining power supply using the output current superimposition method, Figure 2 is a connection diagram of a specific embodiment of the configuration diagram in Figure 1, and Figure 3a is shown in Figure 2. Output voltage waveform diagram of rectifier circuit of arc processing power supply,
Figures b and c show the terminal voltage Ea of the arc load L when the arc load connected to the arc machining power supply shown in Figure 2 is a short-circuit transfer type arc.
and the waveform diagram of the output current i ₀ supplied to the arc load. Figure 4 is a configuration diagram of the DC arc machining power supply using the output current superimposition method of the present invention. Figures 5 and 7
8 and 8 are respectively connection diagrams of specific embodiments of the configuration diagram in FIG. 4, and FIGS. 6 a to 6 d are respectively connection diagrams in which the arc load connected to the arc machining power source shown in FIG. 5 is short-circuit transition type. Waveform diagram of terminal voltage Ea of arc load L, waveform diagram of output current i ₁₀ from reactor 5, and reactor 6 in the case of arcing, respectively.
2 is a waveform diagram of the output current from the arc load and a waveform diagram of the output current i ₀ supplied to the arc load. DESCRIPTION OF SYMBOLS 1...First transformer output winding, 2...Second transformer output winding, 3...Phase control rectifier circuit, 4...
Rectifier circuit (not phase controlled), 5...first reactor, 6...second reactor, L...arc load.

Claims (1)

[Scope of utility model registration request] In the DC arc machining power supply used for consumable electrode arc machining, which generates an arc between the consumable electrode and the workpiece and causes a short circuit between the consumable electrode and the workpiece,
a first transformer output winding 1 that outputs a no-load voltage that maintains the arc; a phase control rectifier circuit 3 that controls the phase of the output voltage of the first output winding 1 using a thyristor; and the phase control A first reactor 5 having a sufficiently large inductance value to smooth the output voltage of the rectifier circuit 3, and a second transformer output winding that outputs a no-load voltage lower than the no-load voltage of the first output winding. wire 2 and said second output winding 2
a rectifier circuit 4 that rectifies the output voltage of the rectifier circuit 4 with a diode, and a second reactor 6 that smoothes the output voltage of the rectifier circuit 4 and has an inductance value smaller than that of the first reactor; The output voltage of a reactor 5 and the output voltage of a second reactor 6 are connected in parallel with the same polarity, and are supplied between the consumable electrode and the workpiece.