JP2685547B2 - Control device for arc welding power supply - 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 device.

[Conventional technology]

In recent years, an AC / DC dual-purpose arc welding power source has been put into practical use, which has been made smaller and lighter by adopting inverter control. FIG. 7 shows the circuit configuration, and FIG. 8 shows the operation waveform.

In FIG. 7, the AC voltage applied from the commercial power source to the input terminal 1 is converted into a direct current by the input side rectification unit 2, and this is converted into a high frequency AC (for example, 20 kHz) by the input side inverter unit 3 to convert it into a main transformer. 4 is applied.

The AC voltage stepped down to a voltage suitable for welding by the main transformer 4 is made smooth via the current detector 5 by the output side rectification section 6, the reactor 7, and the capacitor 8, and the output side inverter section 9 again makes this smooth DC. It is converted into alternating current and supplied from an 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. 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. In addition, the output side inverter unit 9 includes an inversion transistor as shown in FIG.
T ₁ through T _4, the diode D ₁ to D ₄ is configured by Buritsuji connection, 2 of T _1, T ₂ and T _3, T ₄ in synchronization with the rise and fall of the reference square wave signal as described above If a pair of transistors is turned on and off alternately, the output will be AC, and if the output of the rectangular wave generator 16 is kept at "0" or "1" and one of the transistors is kept on, the output will be DC. Becomes

[Problems to be solved by the invention]

In Fig. 7, 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 decrease in the load current causes a transient voltage in the reactor 7 of the output circuit, and the magnitude of the transient voltage is equal to the inductance value of the reactor 7. It is determined by the current value flowing at the time of polarity reversal. In the circuit of FIG. 7, the current value at the time of polarity reversal changes over a wide range from 300 A to 100 A or less, for example, and the transient voltage generated in the reactor 7 at the time of polarity reversal also changes over a wide range.
Therefore, when the excessive voltage is excessive, the capacitor 8 having a large capacity for absorbing the excessive voltage to prevent the destruction of the transistor or the like of the output side inverter unit 9 and the transient voltage being too small to re-ignite the voltage of the capacitor 8 If the voltage is not reached, a large-capacity ignition auxiliary circuit 25 that supplies the voltage (approximately 200 V or more) necessary for re-ignition of the arc is required, which makes the device expensive. Also,
In order to avoid the generation of excessive transient voltage, the inductance value of the reactor 7 is limited, the current ripple cannot be sufficiently smoothed, and the response of output control is impaired by increasing the capacity of the capacitor 8. There is also.

An object of the present invention is to provide an economical inverter-controlled power source for arc welding, which can perform a stable and reliable polarity reversal operation from a small current to a large current without generating an excessive transient voltage and which is economical. .

[Means for solving the problem]

A first invention of the present application is a means for generating two control rectangular wave signals having a predetermined phase difference, a first current setting device for setting a steady output current value, and an output current value at the time of polarity reversal. And a second current setting device for setting the output current setting value of the current control system in synchronization with the rising and falling of the rectangular wave signal of the leading phase of the both rectangular wave signals. A current control circuit for shifting the set value to the set value of the second current setter, and an inversion operation of the output side inverter unit in synchronization with the rising and falling of the rectangular wave signal of the delay phase of the two rectangular wave signals. When the first current setting value is lower than the second current setting value, the driving circuit for
Control of the arc welding power supply, characterized in that the current is increased from the current setter of No. 2 to the second current setter and the current is increased, and the value of the first current setter is reversed during the reverse polarity period. It is a device.

A second invention is, in addition to the constituent elements of the first invention, a third current setting device for setting an upper limit current value at the time of polarity reversal higher than a setting value of the second current setting device; The delay phase is provided on the condition that the signal indicating that the delay time corresponding to the phase difference between the two rectangular wave signals has elapsed and the signal indicating that the output current value is less than or equal to the set value of the third current setting device are matched. A polarity reversal restricting unit that generates a rectangular wave signal and enables the polarity reversal of the output current is provided, and the polarity reversal is not performed unless the output current value is less than or equal to the upper limit current value set by the third current setting device. This is a control device for a power source for arc welding.

[Action]

The arc welding power source 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. It occurs in the reactor.

In the first invention, two rectangular wave signals having a predetermined phase difference are used, and the output current setting 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 the two rectangular wave signals gives sufficient time for the change in the output current value immediately before the inversion.
As a result, the output current value can be smoothly shifted from the steady output current setting value to the current setting value at the time of polarity reversal within the delay time according to a predetermined time constant.

Therefore, by changing the output current value immediately before the polarity reversal of the output current and performing the polarity reversal at an almost predetermined current value, the transient voltage generated at the time of the polarity reversal is leveled and becomes excessive when welding large currents. A stable arc is achieved by charging the output circuit capacitor to the re-ignition voltage or higher with the transient voltage at the time of polarity reversal even when welding a small current, and applying that voltage to the arc load without generating a large transient current. Can be sustained.

At this time, at the moment when the welding current reverses from the reverse polarity to the positive polarity, the arc can be easily maintained without a high voltage.

In the second generation, the upper limit current value at the time of polarity reversal is further set, and the delay time corresponding to the phase difference between both rectangular wave signals elapses from the rising / falling of the rectangular wave signal of the leading phase by the polarity reversal restricting means. When the output current value at this time is less than or equal to the upper limit current value at the time of polarity reversal, a rectangular wave signal with a delayed phase is generated and the output side inverter section is inverted. In this way, when the current suddenly increases transiently due to a change in the arc length or the like, the reversal operation is not performed until it returns to the steady state, and it is possible to avoid generating an excessive transient voltage even in the non-steady state as described above. To be

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

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 the current value at the time of polarity reversal (hereinafter referred to as the reversal current value), and the set value is determined according to the specifications of the welding machine. It is a current value (for example, 100A) and does not need to be variable. The set values of the 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 rectangular wave generator 16, a rectangular wave signal of a lead phase 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 (hereinafter,
The reference rectangular wave signal) is generated. This square wave generator
Reference numeral 16 is a well-known 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.
In addition, 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 / falling of the reference rectangular wave signal, and a signal indicating that the delay time t _D has elapsed is output from this delay circuit 21. When output, the rectangular wave generator 23 receives the signal and outputs a rectangular wave signal with a delayed phase (hereinafter, referred to as a delayed rectangular wave signal). The rectangular wave generator 23 is composed of a flip-flop or the like that is set and reset by the 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 section 9 shown in FIG. , Reverses the polarity of the output current. The set value comparison circuit 26 compares the values set in the current setters 14 and 15 and transmits the result to the current control circuit 13.

The positive polarity detector 27 detects the falling edge of the reference rectangular wave signal generated by the rectangular wave generator 16 and transmits it to the current control circuit 13. The current control circuit 13 receives the operation signal of the drive circuit 24 and returns the output current setting value compared with the detection value of the current detector 5 to the setting value of the first current detector 14.

FIG. 3 shows a configuration example of the current control circuit 13. This circuit is
Set when the reference rectangular wave signal rises and falls, and when the drive circuit 24 is operating (when the slow rectangular wave signal rises and falls)
Flip-flop 30 reset to 0, analog switch 3 turned on / off by Q output of flip-flop 30
1. It is composed of analog switches 32 and 33, resistors 34 and 35, and a capacitor 36 which are turned on and off by the Q output of the flip-flop 30, and the analog switch 31 is turned on and the analog switch 32 is turned on and off when the reference rectangular wave signal rises and falls.
By turning off 33, the voltage corresponding to the setting value of the first current setting device 14 is changed to the voltage corresponding to the setting value of the second current setting device 15 according to the time constants of the resistor 34 and the capacitor 36. The changing voltage is output as a signal corresponding to the output current set value through the resistor 35, and the analog switches 32 and 33 are turned on and the analog switch 31 is turned off during the operation of the drive circuit 24, whereby the resistors 34 and 35, The capacitor 36 is short-circuited, and the output current setting value immediately returns to the setting value of the first current setting device 14.

The operation of the embodiment described above is illustrated in FIG. 4. In the figure, the solid line of the output current waveform indicates that the steady output current set value is larger than the reversal current value, and the dotted line indicates that the steady output current set value is reversed. The case where it is smaller than the current value is shown. In any case, the transient voltage generated in the reactor 7 during the reversing operation is almost the same, and the capacitor 8 can be charged to the voltage required for re-ignition, and the capacitor 8 is transiently charged to output the inverter unit 9 on the output side. It does not destroy the transistor, etc.

When the current value set in the first current setting device 14 is smaller than the current value set in the second current setting device 15,
If the current control circuit 13 is operated only at the falling edge when the reference rectangular wave signal shifts from the positive pole to the reverse pole, the output current waveform as shown in FIG. 5 can be obtained.

In the above description, the case where the output current values of the positive polarity and the reverse polarity are equal is described, but it is easy to change the output current value depending on the polarity and by switching the output current set value returned when the drive circuit 24 operates. Can be realized. Moreover, if both outputs of the rectangular wave generators 16 and 23 are kept at “0” or “1”,
The output from the output terminal 10 is DC. That is, the arc welding power source shown in FIG. 1 can be used as an AC / DC power source.

FIG. 6 is a block diagram showing a circuit configuration of an embodiment embodying the second invention. In the figure, portions corresponding to those in FIG. 1 are designated by the same reference numerals, and duplicated description will be omitted. .

In FIG. 6, the upper limit reverse current value higher than the reverse current set value of the second current setter 15 is set in the third current setter 19, and the comparator 20 sets the set upper limit reverse current value. And the detected value of the current detector 5 are compared, and when the detected current value is less than or equal to the upper limit inversion current value, a signal of "1" 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. Square wave generator only when the output signal of the generator 20 matches
The signal is sent to 23 to generate a slow-phase rectangular wave signal. As a result, it becomes possible to invert the output side inverter unit 9 via the drive circuit 24 as described in the explanation of FIG. Due to the action of the polarity reversal control 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 be avoided.

When the current value set in the first current setting device 14 is smaller than the current value set in the second current setting device 15,
If the current control circuit 13 is operated only during the positive polarity period of the reference rectangular wave signal, the average current can be reduced.

〔The invention's effect〕

The first and second aspects of the invention each have the following unique effects.

That is, according to the first aspect of the invention, (1) it is possible to perform stable and reliable polarity reversal of the output current without generating an excessive transient voltage. According to experiments, a rated current of about 300A and a reverse current value of about 100A are sufficient, and the transient voltage generated is halved.

(2) When the steady output current setting value is larger than the reversing current value, the current change width at the time of reversing the polarity becomes small, so that the rapid change in the arc pressure is suppressed and the arc becomes more 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 increased and the capacitance of the capacitor can be reduced as compared with 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. 7 can be eliminated, and the price, size and weight of the welding power source can be reduced.

(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 transition of the output current set value to the reversal current value can be performed smoothly.

According to the second aspect of the invention, further, (7) polarity reversal is not performed unless the actual current flowing in the welding circuit is less than or equal to a predetermined value, and an unexpected state occurs in an unsteady state such as a rapid current due to a change in arc length. It is possible to prevent the destruction of the circuit element due to the transient voltage.

(8) When the output current setting value is smaller than the reversing current value, the current increases only when the polarity is reversed from the positive polarity. Therefore, when the average current on the output side is lowered, the setting value of the output current is significantly reduced. The desired average current can be obtained without increasing the stability of the arc at a small current.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the first 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 circuit configuration of a current control circuit in FIG. FIGS. 4 and 5 are block diagrams showing an embodiment of the second invention of the present application, FIG. 7 is a block diagram of a conventional example, and FIG. 8 is a conventional diagram. It is an operation | movement waveform diagram of an 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, 26 ... Set value comparator, 27 ... Positive polarity detector.

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 an arc welding power source for controlling an output current in a section, a means for generating two control rectangular wave signals having a predetermined phase difference, a first current setting device for setting a steady output current value, and a polarity reversal A second current setting device for setting an output current value at the time, and an output current setting value of the current control system for the output current setting value of the first control device in synchronization with rising and falling of a rectangular wave signal of a lead phase of the rectangular wave signals. Current control circuit for shifting from the setting value of the current setting device to the setting value of the second current setting device, and the output side in synchronization with the rising and falling of the rectangular wave signal of the delayed phase of the both rectangular wave signals. Invert the inverter When the first current setting value is lower than the second current setting value, a drive circuit for operating is provided, and the current is shifted from the first current setting device to the second current setting device only during the positive polarity period. A control device for a power source for arc welding, which is increased and reversed during a period of reverse polarity with a value of a first current setting device. 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. In an arc welding power source for controlling an output current in a section, a means for generating two control rectangular wave signals having a predetermined phase difference, a first current setting device for setting a steady output current value, and a polarity reversal A second current setting device for setting an output current value at the time of
A current setting device for setting an upper limit current value at the time of polarity reversal that is higher than the setting value of the current setting device, and the current in synchronization with the rising and falling edges of the rectangular wave signal of the leading phase of the two rectangular wave signals. A current control circuit for shifting the output current set value of the control system from the set value of the first current setter to the set value of the second current setter, and a rectangular wave signal of a delayed phase of the two rectangular wave signals. Drive circuit for inverting the output-side inverter section in synchronism with the rising and falling edges of the signal, a signal indicating that a delay time corresponding to the phase difference between the rectangular wave signals has elapsed, and the output current value is the third current value. A polarity reversal restricting means for generating the lagging rectangular wave signal on condition that the signal is equal to or less than the upper limit current value set by the current setting device, and reversing the polarity of the output current; The current setting value of 1 is the second
When it is lower than the current setting value of, the current is transferred from the first current setting device to the second current setting device only for the positive polarity period to perform the reversing operation, and the reverse polarity period is inverted by the value of the first current setting device. A control device for an arc welding power source characterized by being operated.