JP2537516B2 - Control method and apparatus for arc welding power source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a power source for arc welding, particularly an AC power source for AC TIG welding of an inverter control type, which can reverse the polarity of the output current without generating an excessive transient voltage. The present invention relates to a stable and reliable control method and device.

[Conventional technology]

In recent years, an AC dual-purpose arc welding power source has been put into practical use, which has been made smaller and lighter by adopting inverter control. FIG. 6 shows the circuit configuration, and FIG. 7 shows the operation waveform.

In FIG. 6, an AC voltage of 200V applied from the commercial power source to the input terminal 1 is converted into a DC of about 280V by the input side rectification unit 2, and this is converted into a high frequency AC (for example, 20KHz) by the input side inverter unit 3. Apply to main transformer 4. Then, it is stepped down to a voltage suitable for welding by the main transformer 70
An AC voltage of about V is made into a smooth DC by the output side rectification unit 6, the reactor 7, and the capacitor 8 via the current detector 5,
This is converted into alternating current again in the output side inverter unit 9 and supplied from the output terminal 10 to an arc load (not shown).

Here, the set value of the output current setter 14 is the current control circuit 13
After that, the error amplifier 12 compares the detected value with the detection value of the current detector 5, and the pulse width control circuit 11 controls the output pulse width of the input side inverter unit 3 so that they are equal.

That is, for example, when the arc length increases due to the shaking of the hand of the operator, the arc voltage increases, and as a result, the welding current, that is, the detection value of the current detector 5 decreases. Then, the pulse width control circuit 11 widens the output pulse width of the input side inverter unit 3 so that the welding current becomes equal to the set value of the output current setter 14. As a result, the welding current is controlled to be substantially constant even if the arc voltage fluctuates.

On the other hand, the rectangular wave generator 16 generates a reference rectangular wave signal having a repetition frequency and a duty ratio corresponding to the set values of the inversion frequency setting device 17 and the positive polarity reverse polarity ratio setting device 18, and the reference rectangular wave signal The output side inverter unit 9 reverses the polarity of the output current via the drive circuit 24 at the time of rising and falling. This relationship is shown in FIG. As shown in FIG. 2, the output side inverter unit 9 is configured by bridge-connecting inversion transistors T _{1 to} T ₄ and diodes D _{1 to} D ₄ , and as described above, the rising edge of the reference rectangular wave signal If the two transistors T ₁ , T ₂ and T ₃ , T ₄ are turned on and off alternately in synchronization with the falling edge, the output becomes AC and the rectangular wave generator 16
If the output of is maintained at "0" or "1" and any one set of transistors is kept on, the output becomes DC. Then, the positive polarity reverse polarity ratio is set according to the material of the object to be welded and the purpose of welding.

[Problems to be solved by the invention]

In FIG. 6, when the polarity of the output current is reversed, the main transformer 4
When it is not possible to re-ignite the arc with only the voltage supplied from, a transient voltage is generated in the reactor 7 of the output circuit due to the rapid decrease in the load current, and the magnitude of the transient voltage depends on the inductance value of the reactor 7. It depends on the value of the current flowing when the polarity is reversed. In the circuit of FIG. 6, the current value at the time of polarity reversal is equal to the welding current and changes over a wide range from 300 A to 100 A or less, and in response to this, the transient voltage generated in the reactor 7 also changes over a wide range. . Therefore, when the transient voltage is excessive, the capacitor 8 having a large capacity for absorbing the transient voltage to prevent the transistor of the output side inverter unit 9 from being destroyed, and the transient voltage being too small and the voltage of the capacitor 8 being re-ignited. If the voltage is not reached,
A large-capacity re-ignition auxiliary circuit 25 that supplies a voltage (200 V or more) necessary for re-ignition of the arc is required, which makes the device expensive. In addition, the inductance value of the reactor 7 is limited in order to avoid the generation of an excessive transient voltage, and the current ripple cannot be sufficiently smoothed, or the responsiveness of the output control is impaired by increasing the capacity of the capacitor 8. Sometimes it is.

Further, in Japanese Patent Laid-Open No. 58-112657, when the polarity is reversed, the power supply is first stopped while the circuit on the load side is still connected to release the energy stored in the circuit, which is set in advance. A technique is disclosed in which a circuit on the load side is connected after the suspension period and power supply is started. In this case, it is possible to prevent the control element from being destroyed by the transient voltage generated when the polarity is reversed. However, the transient voltage must always have a magnitude that occurs when the current flowing to the load side is maximum, that is, at the rated current. Therefore, the inductance of the reactor must be increased and two reactors are required.

Also, when the current flowing to the load side is small, the temperature of the space between the electrode and the base material decreases during the rest period, and the number of ions decreases.As a result, re-ignition is difficult even when the current rises sharply. , Needed a re-ignition assistance circuit.

An object of the present invention is to provide an inverter-controlled power source for arc welding, which is capable of performing stable and reliable polarity reversal operation without generating an excessive transient voltage and is economical.

[Means for solving problems]

The first invention of the present application, the high-frequency AC output of the input side inverter unit is stepped down, rectified, smoothed by the reactor and the capacitor, the polarity is inverted in the output side inverter unit, is converted again to AC, and is supplied to the arc load, In an arc welding power source that controls the output current with a constant current in the input side inverter unit, the current setting value of the current control system is switched from the steady output current value to the output current value at the time of polarity reversal immediately before the polarity reversal of the output current The method for controlling an arc welding power source is characterized in that

A second invention relates to an apparatus for carrying out the above method, which comprises means for generating two control rectangular wave signals having a predetermined phase difference, and a first current setting for setting a steady output current value. And the second to set the output current value when the polarity is reversed
Of the current setting device and the output current setting value of the current control system from the setting values of the first current setting device in synchronization with the rising / falling of the rectangular wave signal of the leading phase of the both rectangular wave signals. A current control circuit for shifting to the setting value of the current setting device of No. 2,
A drive circuit for inverting the output-side inverter unit in synchronism with the rising and falling edges of a rectangular wave signal having a delay phase of the two rectangular wave signals is provided, and the output current value is equal to the setting value of the second current setting device. This is a control device for an arc welding power source, which is characterized in that the polarity of the output current is reversed when they become substantially equal.

[Action]

The power source for arc welding of the present invention has a reactor for smoothing current ripples inserted in the output circuit, and when the polarity of the output current is reversed, a transient voltage corresponding to the current value flowing at that time is generated. Although generated in the reactor, the output current value is changed immediately before the polarity reversal of the output current, and the polarity reversal is performed at a preset current value. As a result, the transient voltage generated during polarity reversal is leveled, and the arc can be stably maintained even during small current welding without generating excessive transient voltage during large current welding.

In the second invention, two rectangular wave signals having a predetermined phase difference are used, and the output current set value is switched at the time of rising and falling of the rectangular wave signal of the leading phase, and the rectangular wave signal of the lagging phase is changed. The polarity of the output current is inverted at the rising and falling edges, and the delay time corresponding to the phase difference between both rectangular wave signals gives sufficient time for the change in the output current value immediately before the inversion.
As a result, the function of the first invention can be easily realized, and the output current value smoothly shifts from the steady output current setting value to the current setting value at the time of polarity reversal according to a predetermined time constant within the delay time. Can be made.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a block diagram showing a circuit configuration of an embodiment embodying the second invention. In FIG. 1, the AC voltage applied from the commercial power source to the input terminal 1 is converted to DC by the input side rectification unit 2, and this is converted into high frequency AC (for example, 20 KHz) by the input side inverter unit 3 and converted into the main transformer 4. The AC voltage applied and reduced to a voltage suitable for welding by the main transformer 4 is made into a smooth DC by the output side rectification section 6, the reactor 7 and the capacitor 8 via the current detector 5, and this is output side inverter section. It is converted into alternating current again at 9 and supplied from an output terminal 10 to an arc load (not shown). The above is the same as the conventional example shown in FIG.

Here, the first current setting device 14 is for setting a steady output current value.
Any current value up to 100A can be selected. On the other hand, the second current setting device 15 is for setting a current value at the time of polarity reversal (hereinafter referred to as reversal current value), and the set value is a predetermined current value determined by the specifications of the welding machine. (Eg, 100A), and does not need to be variable. The set values of the respective current setters 14 and 15 are transmitted to the current control circuit 13 as voltage signals, and the set value selected by the current control circuit 13 is compared with the detected value of the current detector 5 by the error amplifier 12, and both are set. The output pulse width of the input side inverter unit 3 is controlled by the pulse width control circuit 11 so that they become equal.

On the other hand, from the square wave generator 16, the inversion frequency setting device 17
A rectangular wave signal (hereinafter referred to as a reference rectangular wave signal) having a lead phase having a repetition frequency and a duty ratio corresponding to the set value of the positive polarity reverse polarity ratio setting unit 18 is generated. This rectangular wave generator 16 is known as a function generator. The current control circuit 13 sets the output current setting value, which is compared with the detection value of the current detector 5 described above at the rising and falling edges of the reference rectangular wave signal, from the setting value of the first current setting unit 14 to the second current setting value. Switch to the set value of the device 15 with a predetermined time constant. Further, there is a delay circuit 21 that gives a delay time t _D sufficient for the change of the output current value from the rising and falling edges of the reference rectangular wave signal, and the signal indicating that the delay time t _D has elapsed is output from this delay circuit 21. When it is output, it receives it and the rectangular wave generator 23
Then, a rectangular wave signal having a delayed phase (hereinafter referred to as a delayed rectangular wave signal) is generated. The rectangular wave generator 23 is composed of a flip-flop or the like that is set / reset by a signal from the delay circuit 21. At the rising and falling edges of this slow-phase rectangular wave signal, two sets of transistors T ₁ , T ₂ and T ₃ , T ₄ of the output side inverter unit 9 shown in FIG. , Reverses the polarity of the output current. The current control circuit 13 receives the operation signal from the drive circuit 24 and receives the current detector 5
The output current set value compared with the detected value of 1 is returned to the set value of the first current setter 14.

The operation will be further described below with reference to FIGS. 3 and 5. The circuit shown in FIG. 3 is a flip-flop 30 which is set when the reference rectangular wave signal rises and falls and is reset when the drive circuit 24 operates (when the slow phase rectangular wave signal rises and falls). An analog switch 31, which is turned on / off by the Q output of the flip-flop 30, a flip-flop 30
Analog switches 32 and 3 that are turned on and off by the Q output of
3, the resistors 34 and 35, and the capacitor 36.
FIG. 5 is a diagram showing the relationship between the reference rectangular wave signal, the delayed rectangular wave signal, and the output current.

Immediately after the slow rectangular wave signal in FIG. 5 rises (hereinafter, referred to as time t), the analog switches 32 and 33 are
Is on, the analog switch 31 is off, T ₁ and T ₂ of the output side inverter unit 9 shown in FIG. ₂ are on, and T ₃ and T ₄ are off.

From time t until the reference rectangular wave signal falls: The set value of the current setter 14 is output as a voltage signal, the output current set by the current setter 14 flows, and the capacitor 36 is charged by this voltage.

Fall of the reference rectangular wave signal: The analog switch 31 is turned on and the analog switches 32 and 33 are turned off by the fall of the reference rectangular wave signal.

From the falling of the reference rectangular wave signal to the falling of the slow rectangular wave signal: The electric charge charged in the capacitor 36 via the resistor 35 is output as a voltage that changes according to a predetermined time constant determined by the resistor 34 and the capacitor 36, As a result of outputting this signal voltage as a signal corresponding to the set value of the output current, the output current gradually switches to the set value of the second current setter 15.

The delayed rectangular wave signal falls: T ₁ and T ₂ of the output side inverter unit 9 shown in FIG. ₂ are turned off,
T _3, T ₄ is turned off, the direction of the current flowing through the weld is inverted.

From the falling edge of the slow-phase rectangular wave signal to the rising edge of the reference rectangular wave signal: As in the case of, the set value of the current setter 14 is output as a voltage signal, and the output current set by the current setter 14 flows The voltage charges the capacitor 36. Anaguro switch 32, 33 is on, analog switch
31 is off and capacitor 36 is charged.

The reference rectangular wave signal rises: The analog switch 31 turns on and the analog switches 32 and 33 turn off due to the fall of the reference rectangular wave signal.

From the rising edge of the reference rectangular wave signal to the rising edge of the delayed rectangular wave signal: As in the case of, the voltage charged in the capacitor 36 via the resistor 35 changes as a voltage that changes according to a predetermined time constant determined by the resistor 34 and the capacitor 36. As a result of being output and the signal voltage being output as a signal corresponding to the output current setting value, the output current gradually switches to the setting value of the second current setting device 15.

Slow rectangular wave signal rises.

T ₁ and T ₂ of the output side inverter unit 9 shown in FIG. ₂ are turned on,
T _3, T ₄ is turned off, the direction of the current flowing through the weld is inverted.

 The above steps are repeated until the welding is completed.

In FIG. 5, the solid line of the output current waveform shows the operation when the steady output current set value is larger than the reversal current value. The dotted line of the output current waveform shows the case where the steady output current set value is smaller than the reversal current value.
In either case, the transient voltage generated in the reactor 7 during the reversing operation is almost the same, the capacitor 8 can be charged to the voltage required for re-ignition, and the capacitor and the like in the output side inverter unit 9 are destroyed. It does not overcharge the 8.

In the above description, the case where the output current values of the positive polarity and the reverse polarity are equal to each other has been described, but it is possible to easily change the output current value depending on the polarity by switching the output current set value during the operation of the drive circuit 24. . Further, if the outputs of the rectangular wave generators 16 and 23 are both kept at "0" or "1", the output from the output terminal 10 becomes DC. That is, the arc welding power source shown in FIG. 1 can be used as an AC / DC power source.

FIG. 4 is a block diagram showing a circuit configuration of another embodiment of the second invention. In the figure, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and duplicated description will be omitted. In FIG. 4, the upper limit reversal current value higher than the reversal current value of the second current setter 15 is set in the third current setter 19, and the comparator 20 sets the upper limit reversal current value to the set upper limit reversal current value. Current detector 5
When the current detection value is less than or equal to the upper limit reversal current value, a "1" signal is output. The gate circuit 22 compares the output signal of the delay circuit 21 indicating that a predetermined delay time t _D has elapsed from the rising and falling edges of the reference rectangular wave signal with the current detection value being equal to or less than the upper limit inversion current value. The signal is sent to the rectangular wave generator 23 only when the output signal of the device 20 matches, and the delayed rectangular wave signal is generated. As a result, it becomes possible to invert the output side inverter section 9 via the drive circuit 24 as described in the explanation of FIG. Due to the action of the polarity reversal restricting means composed of the comparator 20 and the gate circuit 22, excessive transient voltage is generated when polarity reversal is performed in an unsteady state in which a large current exceeding the upper limit reversal current value is flowing. can avoid.

〔The invention's effect〕

The first and second inventions have unique effects as described below.

That is, according to the first aspect of the invention, (1) since the transient voltage at the time of polarity reversal can be set to a predetermined magnitude, stable and reliable polarity reversal of the output current can be performed without generating an excessive transient voltage. You can According to experiments, a rated current of 300 A and a reverse current value of about 100 A are sufficient, and the transient voltage generated is halved.

(2) When the steady output current set value is smaller than the predetermined current value, the welding current is once increased before the polarity reversal, and as a result, the temperature of the space between the electrode and the base metal rises and the space between the electrode and the base metal rises. The number of the ions in the field increases, and the polarity is reversed immediately, that is, without providing the rest period, so that the re-ignition becomes easy and the arc becomes stable.

(3) The selection range of the reactor and the capacitor to be inserted in the output circuit is widened, and the inductance value of the reactor can be made larger and the capacitance of the capacitor can be made smaller than the conventional example, so that the smoothing function of the current ripple and the control response are improved. To do.

(4) The re-ignition auxiliary circuit 25 shown in FIG. 6 can be dispensed with, and the price, size and weight of the welding power source can be reduced.

According to the second invention, (5) the function of the first invention can be realized by a device having a simple circuit configuration, high reliability, and low cost.

(6) A sufficient delay time can be taken for the change of the output current value, and the steady change of the output current setting value to the reversal current value can be performed smoothly.

Further, according to another embodiment of the second invention, (7) the polarity reversal is not performed unless the actual current flowing in the welding circuit is equal to or less than a predetermined value, and a non-steady state such as a current surge due to a change in arc length. It is possible to prevent the breakdown of the circuit element due to the unexpected transient voltage.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment embodying the second invention of the present application, FIG. 2 is a circuit configuration diagram of an output side inverter section in FIG. 1, and FIG. 3 is a current control circuit in FIG. Circuit configuration diagram of
FIG. 4 is a block diagram of another embodiment of the second invention of the present application,
FIG. 5 is an operation waveform diagram of the embodiment of FIGS. 1 and 4, FIG. 6 is a block diagram of a conventional example, and FIG. 7 is an operation waveform diagram of the conventional example. 3 ... Input side inverter section, 4 ... Main transformer, 6 ... Output side rectification section, 7 ... Reactor, 8 ... Capacitor, 9 ... Output side inverter section 5, 11, 12 ... Current control system , 13 ... current control circuit, 14 ... first current setting device, 15 ... second current setting device, 16, 21, 23 ... rectangular wave signal generating means, 19 ... third current setting device , 20, 22 …… Polarity reversal control means, 24 …… Drive circuit.

Continuation of front page (56) References JP-A-58-112657 (JP, A)

Claims (2)

(57) [Claims] 1. A high-frequency AC output of an input-side inverter section is stepped down, rectified, and smoothed by a reactor and a capacitor. The polarity of the direct-current is inverted by the output-side inverter section, converted into AC again, and supplied to an arc load. In the arc welding power source that controls the output current at a constant current, the current setting value of the current control system is switched from the steady output current value to the output current value at the time of polarity reversal immediately before the polarity reversal of the output current. A method for controlling a power source for arc welding, which is characterized in that: 2. A high-frequency AC output of an input-side inverter section is stepped down, rectified, and smoothed by a reactor and a capacitor, and then the output-side inverter section inverts the polarity of the direct-current again to convert it into an alternating current and supplies it to an arc load. Means for generating two control rectangular wave signals having a predetermined phase difference in a power source for arc welding whose output current is controlled by a constant current,
A first current setting device for setting a steady output current value, a second current setting device for setting an output current value at the time of polarity reversal, and a rising edge of a rectangular wave signal of a lead phase of the two rectangular wave signals.
A current control circuit that shifts the output current setting value of the current control system from the setting value of the first current setting device to the setting value of the second current setting device in synchronization with the fall; A drive circuit for inverting the output side inverter unit in synchronism with the rising and falling edges of the rectangular wave signal of the delay phase is provided, and the output current is output when the output current value reaches the setting value of the second current setting device. A power supply control device for arc welding, characterized in that the polarity is reversed.