JPH05318113A - Power unit for arc welding - Google Patents

Abstract

PURPOSE:To reduce the generation of spatter by detecting the instantaneous value of the output voltage interrupted through a switching element, comparing it with the set value of the output voltage and driving ON/OFF of the switching element. CONSTITUTION:An AC power source 1 is rectified by a rectifier circuit 2, made a prescribed voltage by turning on and off the switching element 3 and supplied to a welding electrode 6. An unsmoothed output voltage immediately after the switching element 3 is detected by a detector 18 for output voltage. The detected value of the voltage detector 18 is integrated by an integrating circuit 15. The output of the detector 18 and of the integrating circuit 15 are compared, and the ON/OFF of the switching element 3 is controlled. As the phase compensation circuit of an error amplifier is not required, no delay element is contained in a signal transmission system, a high-speed response is made possible against change in the output setting signal, and simultaneously a stable operation is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an arc welding power supply device of a system in which a commercial AC power supply is once rectified into a direct current and this direct current is intermittently controlled by a switching element to control an output voltage to a desired value. It is a thing.

[0002]

2. Description of the Related Art A power source apparatus for arc welding in which a DC power source is intermittently switched by a switching element to obtain a desired output voltage generally compares the output of an output setter with the output of an output voltage detector and switches by a difference signal. A device that controls the conductivity of elements is used. FIG. 1 is a connection diagram showing an example of a power supply device for arc welding as an example of such a general device. In the figure, reference numeral 1 is an AC power supply, and a commercial AC is usually used. 2 is a rectifier circuit that rectifies and smoothes the power of the AC power source 1 to obtain DC, 3 is a switching element,
For example, it is a switching transistor, 4 is a DC reactor for smoothing output, 5 is a flywheel diode, and DC reactor 4 and flywheel diode 5
The output is smoothed by and. A welding electrode 6 is a welding electrode wire which is fed at a predetermined speed. 7 is an object to be welded, 8 is an output voltage setter, 9 is an output voltage detector for detecting a smoothed output voltage, and 10 is an output s of the output voltage setter.
1 and the output s2 of the output voltage detector are input, and the difference signal s1
An error amplifier circuit for outputting a signal s3 corresponding to −s2, 11
Is a PWM that determines the conduction time width of the switching element 3
(Pulse width control) circuit, 12 is an oscillator that generates a sawtooth wave of a constant frequency for determining the operation cycle of the PWM circuit, and 13 is a driver circuit that amplifies the output of the PWM circuit and uses it as a drive signal for the switching element 3. is there. Here, the error amplification circuit 10 includes resistors R1 to R4 and a capacitor C1.
And an operational amplifier OP1. The output signal s1 of the output voltage setting device 8 and the output signal s2 of the output voltage detector 9 are added in mutually opposite polarities to generate a signal s3 corresponding to the difference signal s1 -s2. It has gained. Capacitor C1 and resistor R4
Is a phase compensator for compensating the phase shift between input and output. By providing this phase compensator, it is possible to reduce the gain in the high frequency region and improve the operation stability.

[0003]

In the above conventional device, stable operation can be obtained by providing the error amplifier circuit 10 with the phase compensator including the capacitor C1 and the resistor R4. However, since the gain in the high frequency region is lowered by the capacitor C1, a transmission delay with respect to a sudden change occurs, and even if the output setting signal s1 suddenly changes, there is a delay in the change of the output signal s3. This delay in the signal transmission speed makes the feedback control system unstable, and it was necessary to set the response speed relatively slow in order to stabilize the entire system. On the other hand, in arc welding using a consumable electrode wire, it has been known that the generation of spatter can be reduced by rapidly reducing the output current value at the moment when the tip of the wire short-circuits with the workpiece. However, in the conventional apparatus shown in FIG. 1, even if the short circuit between the wire and the workpiece is detected and the output voltage setting signal s1 is suddenly decreased by this, the output voltage is still decreased due to the existence of the phase compensating capacitor C1 as described above. However, it was difficult to suppress the generation of spatter.

[0004]

In order to solve the above-mentioned problems of the conventional device, the present invention detects a voltage immediately after the DC power supply is interrupted by a switching element and before smoothing, and integrates the detected voltage, The integrated value is compared with the set value of the output voltage setting device, and the switching element is turned on from the output time of the pulse oscillator that determines the reference period until the integrated value exceeds the set value, and the integrated value depends on the output of the next pulse oscillator. By resetting, the phase compensation for ensuring the operation stability is not necessary and the response speed is increased.

[0005]

FIG. 2 is a connection diagram showing an embodiment of the present invention. In the figure, 1 to 8 and 13 have the same functions as those of the conventional device of FIG.
Reference numeral 18 denotes an output voltage detector, which is different from the conventional device in the present invention and detects the unsmoothed output voltage immediately after the switching element as its instantaneous value. A pulse oscillator 14 generates a pulse s4 having a short time width with a predetermined cycle. Reference numeral 15 is an integrating circuit for integrating the output signal s2 of the output voltage detector 18, which is an analog switch for short-circuiting the resistor R5, the operational amplifier OP2, the capacitor C2 and the capacitor C2 for the duration of the pulse width of the output pulse s4 of the pulse oscillator 14. It is composed of SW1. Reference numeral 16 is a comparison circuit, which compares the output signal s1 of the output voltage setting unit 8 and the output s5 of the integration circuit 15 to obtain s5 ≥s
When it becomes 1, a pulse s6 having a short time width is generated. 1
Reference numeral 7 is a flip-flop circuit, which is set at the rising edge of the output pulse s4 of the pulse oscillator 14 to bring the output signal s7 to a high level and reset at the leading edge of the output signal s6 of the comparator circuit 16 to a low level. FIG. 3 is a diagram showing changes in signals at various portions of the embodiment of FIG. 2 with the passage of time. The operation of the embodiment of FIG. 2 will be described with reference to the diagram of FIG. The analog switch SW1 is closed by the output s4 of the pulse oscillator 14, the capacitor C2 is short-circuited during the duration of the pulse signal s4, the integrating circuit 15 is reset, and the output signal s5 becomes zero. Further, the flip-flop circuit 17 is set by the rise of the signal s4, the output signal s7 becomes high level, and the driver circuit 13 amplifies this high level signal to make the switching element 3 conductive. The output of the rectifier circuit 2 is supplied to the DC reactor 4, the electrode wire 6, and the object to be welded 7 by the conduction of the switching element 3, and the output voltage is detected by the output voltage detection circuit 18 and has a waveform signal corresponding to its instantaneous value. It becomes s2. This signal s2 is integrated by the integration circuit 15 after the end of the duration of the output signal s4 of the pulse oscillator 14. At this time, the output voltage due to the conduction of the switching element 3 is smoothed by the DC reactor 4 to form a welding arc. When the integration proceeds in this state, the output signal s5 of the integrating circuit 15 increases and becomes larger than the output signal s1 of the output voltage setting device 8 (s5 ≥s1), the comparison circuit 16 causes the pulse signal of a constant time width. generate s6. This pulse signal s6
The flip-flop circuit 17 is reset and the output s7 of the flip-flop circuit 17 becomes low level. As a result, the switching element 3 is cut off, and the output of the rectifier circuit 2 is no longer transmitted to the DC reactor 4 side. At this time, the current continues to flow through the path of the wire electrode 6, the object to be welded, and the flywheel diode 5 due to the electromagnetic energy held in the reactor 4 in accordance with the current flowing in the reactor 4. Next, one cycle T of the pulse oscillator 14 ends,
When the next pulse s4 is output, the integration circuit is reset by this, the flip-flop circuit 17 is set, the output signal s7 is inverted to the high level, and the switching element 3 becomes conductive again. By repeating the above operation, the average value Vo of the output voltage is maintained at a value corresponding to the set value of the output voltage setter 8. Here, even when the output voltage setting signal s1 suddenly changes as shown at time t = t1 or t = t2 in FIG. 3, there is no delay element in the feedback loop, so there is no response delay, and Since there is no element that destabilizes the control system, it operates stably even if the response speed of the entire control system is set sufficiently high. FIG. 4 is a connection diagram showing another embodiment of the present invention, in which DC voltage is converted into AC by an inverter circuit,
An example in which the present invention is applied to an example of a system in which the voltage is converted into a desired voltage by a transformer and then rectified to be a direct current is shown.
In the figure, the switching element is composed of switching transistors 3a to 3d connected in a bridge,
The transistors 3a and 3b are connected to the driver circuit 13a, and the transistors 3c and 3d are connected to the driver circuit 13a.
driven by b. The primary winding 19p of the transformer 19 is connected to the AC terminals of the bridge-connected transistors 3a to 3d. The transformer 19 has an output secondary winding 19s1 and an auxiliary winding 19s2, and the outputs of the respective windings are double-wave rectified by the diodes 21a and 21b and the diodes 181 and 182 to become a direct current.
Here, the auxiliary winding 19s2 and the diodes 181, 182 constitute the output voltage detection circuit 18. The output signal s7 of the flip-flop circuit 17 is alternately distributed by the two-phase separation circuit 20 to the driver circuits 13a and 13b every time it is output, so that the transistors 3a and 3b are turned on at the same time or the transistors 3c and 3d are turned on. Are alternately conducted at the same time, and the second output of the rectifier circuit is supplied to the primary winding 19p of the transformer 19 by switching between positive and reverse polarities. The two-phase separation circuit 20 is composed of a flip-flop circuit 201 and AND circuits 202 and 203, which are connected as shown. The other components in the figure have the same functions as those of the apparatus of FIG. 1 or 2, and the same reference numerals are given to omit the details. In the figure, each time the output signal s4 of the pulse oscillator 14 is output, the flip-flop circuit 20
The output of 1 is inverted, and the outputs of the two output terminals change complementarily. Both output signals s21 and s22 of the flip-flop circuit 201 and the output s7 of the flip-flop circuit 17
Are supplied to AND circuits 202 and 203, respectively,
The signal s7 is alternately output as the signals s71 and s72. The output signals s71 and s72 enable the driver circuits 13a and 1
3b operate alternately to alternately turn on the combination of the transistors 3a and 3b or the combination of the transistors 3c and 3d. The operation of the other parts is exactly the same as the embodiment of FIG. The present invention is not limited to the embodiment shown in FIGS. 2 and 4, but may be an arc welding power source of a system in which the output of a DC power source is adjusted by a switching element to obtain a desired output. The present invention can be applied to a structure that forms a bridge inverter, a structure that forms a forward converter, or a structure that rectifies the outputs of these inverters and then switches the polarity again by switching to make a low-frequency alternating current. Further, in any of these cases, the output voltage may be detected before smoothing, for example, as shown in FIG.
In place of the auxiliary winding, the diode 21a,
The voltage may be extracted between the common connection point of 21b and the center tap of the secondary winding 19s1.

[0006]

As described above, the present invention eliminates the need for the phase compensation circuit of the error amplifier, which was indispensable in the past, in the feedback control system, so that the signal transfer system does not include a delay element and the output setting signal is not included. It becomes possible to respond quickly to changes in, and stable operation can be obtained. As a result, in arc welding using a consumable electrode wire, when the wire and the workpiece are short-circuited, this is detected and control is performed to switch the output setting signal to a low value so as to reduce the output voltage. By applying the invention, the generation of spatter can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an example of a conventional device.

FIG. 2 is a connection diagram showing an embodiment of the present invention.

FIG. 3 is a diagram for explaining the operation of the embodiment of FIG.

FIG. 4 is a connection diagram showing another embodiment of the present invention.

[Explanation of symbols]

 1 AC power supply 2 Rectifier circuit 3, 3a, 3b, 3c, 3d Switching element 4 DC reactor 5 Flywheel diode 6 Electrode 7 Welding object 8 Output voltage setter 9, 18 Output voltage detector 13, 13a, 13b Driver Circuit 14 Pulse oscillator 15 Integrator circuit 16 Comparison circuit 17 Flip-flop circuit 19 Transformer 19s2 Auxiliary winding 181,182,21a, 21b Diode 20 Two-phase separation circuit R1, R2, R3, R4, R5 Resistor C1, C2 Capacitor OP1 , OP2 operational amplifier SW1 analog switch

Claims (4)

[Claims] 1. An arc welding power supply device of the type in which the output of a DC power supply is intermittently controlled by a switching element to adjust the output, and an output voltage setting device and an instantaneous value of the output voltage intermittently controlled by the switching element are detected. An output voltage detector and an oscillator that generates a pulse at a fixed cycle,
When the output of the output voltage detector is integrated and reset by the output pulse of the oscillator, the output s1 of the output voltage setting device and the output s5 of the integration circuit are input, and s1 ≤s5 is satisfied. A comparison circuit that outputs a pulse signal with a constant time width, a flip-flop circuit that is set by the output pulse of the oscillator and reset by the output pulse of the comparison circuit, and the switching element is turned on with the output of the flip-flop circuit as an input.
A power supply device for arc welding, which includes a switching element drive circuit that turns off. 2. The switching element is a switching transistor that forms a chopper circuit that turns on and off the DC power supply, and the switching element drive circuit amplifies an output of the flip-flop circuit to generate a base current of the switching transistor. The power supply device for arc welding according to claim 1, which is a supply circuit. 3. The switching element constitutes an inverter circuit that converts the output of the DC power supply into AC,
The switching element control circuit is a circuit for separating a phase of the output of the flip-flop circuit into two phases and outputting a two-phase signal for alternately connecting the switching elements carrying the positive and negative half waves of the inverter circuit. A power supply device for arc welding as described in. 4. The circuit according to claim 3, wherein the inverter circuit is a circuit that takes out an output through a transformer, and the output voltage detection circuit is a circuit that obtains a voltage signal from an auxiliary winding provided in the transformer. Power supply device for arc welding as described.