JPH08308239A - Controller for welding machine - Google Patents

Abstract

PURPOSE: To improve the accuracy at a high speed and to weld with high quality by correcting the error amount of the current control by a dither signal via a modulation factor obtained from a pulse width modulation signal directly or through a function. CONSTITUTION: An adder 15 adds the output of an amplifier 14 to an effective value reference Irms*, adds it to the input of the adder 15 as a correction signal in the direction for reducing the error of the amplifier 14, outputs a new current reference I*, and outputs the reference I* to an adder 16. On the other hand, the output of a pulse generator 27 is input to a dither circuit 28, which outputs a triangular waveform gradually increasing or decreasing at each modulation synchronization, and inputs it to a comparator 26. A modulation factor detector 32 inputs the PWM signal of the output of a flip-flop 29 to detect the modulation factor. The detected factor is input to a functional circuit 33, and input to the adder 26 as the obtained current accuracy correction input.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding machine controller.

[0002]

2. Description of the Related Art FIG. 13 shows a first example (inverter system) of a control device for a conventional resistance welding machine, which is constructed as follows. The AC voltage of the AC power supply 1 is converted into DC by the rectifier 2, smoothed by the capacitor 3, and then converted into high-frequency AC of about 1 kHz by an inverter composed of switching elements such as IGBTs (insulated gate bipolar transistors) 41 to 44. After being converted into a low AC voltage by the transformer 5, the DC current is converted by the rectifier 7 and a DC welding current can be supplied to the welding electrode 9. A stray inductance 8 is present in the wiring portion to the welding electrode 9 and effectively acts on smoothing the DC welding current.

The magnitude of the welding current is controlled by the current reference I ^* . That is, the welding current, after detecting the primary current of the transformer 5 through the current transformer 6, simulates the DC welding current by the welding current simulator circuit 12 (the primary side of the transformer 5 is the rectifier 7 of the welding current). The circulating current does not flow), the current is detected and compared with the current reference I ^*, and the current controller 63 outputs the current control signal a so as to reduce the error.

The current control signal a is compared by the comparator 65 with the triangular wave b output from the carrier generator 64, and the PWM
It becomes the signal c. The carrier generator 64 outputs a signal d synchronized with the cycle of the triangular wave b, and the distribution circuit 66 activates one of the output signals e and f according to the signal d. As a result, the PWM signal c is alternately applied to the drive circuits 21 and 22 via the AND circuits 67 and 68.

On the other hand, when the drive signal g is input from the start-up circuit 19, the timer 20 operates and the energization signal h is output only for the set time, and the switching signals j and k are set by putting the drive circuits 21 and 22 into the operating state. Are output alternately, I
A group of IGBT41 and IGBT44, and an IGBT43
And the group of IGBTs 42 are alternately turned on, a high-frequency AC voltage is applied to the primary side of the transformer 5, and welding current and welding time are controlled.

FIG. 14 shows a second example (thyristor system) of a conventional controller for a resistance welding machine, in which the AC voltage from the AC power source 1 to the ignition phase control by the thyristor 70 is changed to the primary voltage of the transformer 5. Is supplied to the side of the transformer 5, and the voltage on the secondary side of the transformer 5 is used as an alternating current for the welding electrode 9.

[0007]

Both the first example (inverter system) and the second example (thyristor system) described above have the following problems. The inverter system of FIG. 13 has a quicker response than the thyristor system of FIG. 14, and the current control is highly accurate by proportional-plus-integral (PI) control. However, the power loss of the rectifier 7 that rectifies a current of tens of thousands of amperes occurs. However, the problems are the low efficiency and the increase in the amount of cooling water.

Since the thyristor system can control only every half cycle of the commercial power source, the current control response is slow and there is a non-energized period, so that the heat fluctuation is large and the welding quality is poor.

Further, in the thyristor system, the ON timing can be controlled, but the OFF timing cannot be controlled. Therefore, it is difficult to finely control the saturation prevention of the transformer. Therefore, it is necessary to design the magnetic flux density of the iron core to be low.

An object of the present invention is to provide a controller for a welding machine that enables high quality welding, performs saturation prevention control of a transformer, and can utilize a high magnetic flux density of an iron core.

[0011]

In order to achieve the above object, the invention according to claim 1 controls the load current flowing in the welding machine by shaping the DC power from the DC power supply by pulse width modulation control. A power converter, a control means for comparing the load current with a current reference and outputting a control signal for reducing a deviation thereof, and a pulse width modulation signal for conduction at a constant modulation cycle, and the control signal and the A pulse width modulation control means for outputting a non-conducting pulse width modulation signal according to a comparison result with a load current, and a calculation means for adding a dither signal to the current reference or the load current, the dither signal being gradually increased or decreased in each modulation cycle, A welding machine control device comprising a correction means for correcting the current reference or the load current directly or through a function of a modulation rate obtained from the pulse width modulation signal.

In order to achieve the above object, in the invention according to claim 2, the modulation rate is obtained by averaging a pulse width modulated signal or an inverted signal of the pulse width modulated signal through a filter. It is a control device for a welding machine according to Item 1.

In order to achieve the above object, in the invention according to claim 3, the DC power from the DC power supply is converted into AC power by pulse width modulation control, and the AC power is supplied to the primary side of the transformer. An inverter that supplies AC power obtained from the secondary side to the welding machine, current control means that controls the current by comparing the output current of this inverter with the current reference, and reverses the direction of the output current of the inverter according to the frequency reference. And an inversion control means for alternately comparing the current change rate during the period of the final pulse width modulation conduction signal in the positive cycle of the alternating current and the final pulse width modulation conduction signal in the negative cycle of the alternating current. Comparing means, first adjusting means for adjusting a positive cycle and a negative cycle based on a comparison result obtained by the comparing means, and a positive cycle and a negative cycle of the alternating current A control device for welding machine provided with the second adjusting means for adjusting adjusted.

In order to achieve the above object, in the invention corresponding to claim 4, the frequency of the inverter is set higher than the steady frequency only during a half cycle to several cycles of starting energization. It is a device.

In order to achieve the above-mentioned object, in the invention corresponding to claim 5, DC power from a DC power supply is converted into AC power by pulse width modulation control, and the AC power is supplied to the primary side of the transformer. An inverter that supplies AC power obtained from the secondary side to the welding machine, a detection means that detects the polarity and conduction width of the final half cycle at the end of energization of this inverter, and the final half cycle at the end of energization. Whether the energization width is wider or narrower than the set value is detected.If the energization width is narrow, energization starts from the same direction as the last half cycle at the start of the next energization, and if wide, the last half cycle at the start of the next energization It is a control device of a welding machine provided with a means for determining the start of energization from the opposite direction.

In order to achieve the above object, in the invention according to claim 6, DC power from a DC power supply is converted into AC power by pulse width modulation control, the AC power is supplied to the primary side of the transformer, and the An inverter that supplies AC power obtained from the secondary side to the welding machine, a detection unit that detects the AC current value and the modulation factor of the pulse width modulation control, and a positive half cycle and a negative half cycle of the AC current. Comparing the AC current and the modulation rate at the time of the final pulse width modulation control respectively, means for changing at least one of the positive and negative magnitude of the AC current and the conduction width of the AC current in a direction in which this value is balanced. It is a control device of the welding machine provided.

In order to achieve the above object, the invention according to claim 7 is provided with means for manually adjusting the frequency of the alternating current of the inverter. This is the control device for the welding machine.

[0018]

According to the invention corresponding to claim 1, the error rate of the current control by the dither signal is corrected directly or through the function of the modulation rate obtained from the pulse width modulation signal, thereby improving the accuracy at high speed. , Which enables high quality welding.

According to the invention corresponding to claim 2, there is a delay by averaging the pulse width modulated signals, but the average modulation rate can be easily obtained. According to the invention corresponding to claim 3, the current change rate of the conduction period of the final pulse width modulation of the positive side current of the transformer primary side, and the conduction of the final pulse width modulation of the negative side primary side cycle of the transformer. By comparing the change rates of the currents during the periods, the direction of magnetic bias can be found, and based on the result, the current value of the positive cycle and the current value of the negative cycle can be finely adjusted to prevent magnetic bias.

According to the invention according to claim 4, transient inverter magnetization is prevented by transiently increasing the inverter frequency only in the initial section of energization that is easily biased, thereby lowering the magnetic flux density of the transformer. it can.

According to the invention corresponding to claim 5, starting from the polarity of the final energization and the energizing width, the energizing direction at the next start is selected so that the magnetic flux density of the transformer core is lower. According to the invention corresponding to claim 6, the bias magnetism can be prevented by comparing the bias magnetism detection mainly with the modulation rate of the final pulse width modulation control and correcting when the current value changes.

According to the invention corresponding to claim 7, by manually lowering the frequency of the alternating current of the square wave circuit below the commercial frequency, the stray inductance of the variable welding electrode circuit portion becomes large and the waveform ratio deteriorates. However, the power factor does not deteriorate.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. The same portions as those in FIG. 13 are designated by the same reference numerals and the description thereof will be omitted. <First Embodiment> (Configuration) The first embodiment is configured as shown in FIG. That is, the effective value circuit 13 detects the primary current of the transformer 5 by the current transformer 6, and the detected alternating current is converted into the direct current Id by the rectifier circuit 11, from which the effective value Irms is calculated.
Ask for.

The amplifier circuit 14 amplifies the error between the effective value Irms and the effective value reference (Irms ^* ). The adder circuit 15
The output of the amplifier circuit 14 and the effective value reference Irms ^* are added, and added as a correction signal to the input of the adder circuit 15 so that the error of the amplifier circuit 14 decreases, and a new current reference I ^* is output. The current reference I ^* is output to the adder circuit 16.

The adder circuit 16 adds the current reference I ^* , the output V35 from the current correction circuit 35 described later, and the output of the function generation circuit 33 described later, and outputs the output V16, that is, the final current reference.

The comparator circuit 26 outputs the output V16 of the adder circuit 16.
And the direct current Id which is the output of the rectifier circuit 11 are compared,
This deviation output is the reset terminal R of the flip-flop 29.
A signal from a pulse generator 27, which will be described later, is input to the set terminal S of the flip-flop 29.

The pulse generator 27 generates a modulation frequency, and at the rising edge thereof, the set terminal S of the flip-flop 29.
To the output of the flip-flop 29 to turn on the IGBT of the inverter bridge.

From the output V16 of the adder circuit 16, the rectifier circuit 11
When the output Id of the flip-flop 29 becomes large, the output of the flip-flop 29 becomes "0". That is, the output of the flip-flop 29 becomes the PWM signal.

On the other hand, the output of the pulse generator 27 is input to the dither circuit 28, and the dither circuit 28 outputs a triangular waveform that gradually increases or decreases at each modulation synchronization, and this is input to the comparison circuit 26. With the above configuration,
A PWM signal that is strong against noise and the like can be output.

The modulation rate (M rate) detection circuit 32 is obtained by inputting the PWM signal output from the flip-flop 29, detecting the modulation rate, and inputting the detected modulation rate to the function circuit 33. It is input to the adder circuit 16 as a current accuracy correction input.

The PWM signal output from the flip-flop 29 and the AC current polarity signal F from the energization width selection circuit 39, which will be described later, are input to the distribution circuit 31.
The PWM signal is distributed to the drive circuits 21 and 22 that drive the IGBT of the inverter (inverter bridge) 4.

The starting circuit 19 outputs a signal for starting the timer 20 and operates the drive circuits 21 and 22 only during the energization time of the timer 20. In addition to the above-described configuration, a configuration for preventing biased magnetism of the transformer 5 is provided. That is, the sample signal circuit 34 inputs the AC current polarity signal F and the PWM signal from the energization width selection circuit 39, which will be described later, and outputs the sample signals Sa and Sb.

The differentiating circuit 17 detects the current change rate V17 of the DC detection current Id rectified by the rectifying circuit 11.
The sampling and holding circuit 18 includes the sampling signal circuit 3
4 to the sample signal Sa and the current change rate V of the differentiating circuit 17
17 is input, the current change rate at the final PWM of the half cycle of the alternating current is sampled and held, and the output A is output.

Further, the sampling and holding circuit 23 is
The sample signal Sb and the current change rate V17 of the differentiating circuit 17 are input from the sample signal circuit 34, the current change rate at the final PWM of the half cycle of the alternating current is sampled and held, and the output B is output.

The comparison circuit 24 compares the levels of the outputs A and B of the sampling and holding circuits 18 and 23, outputs 0 when A and B are substantially equal, and B> A + α (window width of the comparison circuit 24). In case of, P is output and B <
In the case of A-α (window width of the comparison circuit 24), N is output.

The latch circuit 25 discriminates the result of level comparison in the comparison circuit 24 into three levels of plus (P), zero (0) and minus (N) by a latch signal L from a signal circuit 37 described later.

The current correction circuit 35 receives the AC current polarity signal F from the energization width selection circuit 39, which will be described later, and corrects the current value according to the outputs P, 0, N from the latch circuit 25 (correction of DC component). And output V35.

The square wave circuit 36 inputs a signal from a transient frequency raising circuit 40, which will be described later, and determines an inverter output frequency f. The signal circuit 37 inputs the inverter output frequency f from the square wave circuit 36 and outputs three kinds of energization width signals W1, W2, W3.

The energization width selection circuit 39 receives the outputs P, 0, N from the latch circuit 25 and three kinds of energization width signals W1.
, W2, W3 outputs one alternating current polarity signal F to the sump signal circuit 34 and the distribution circuit 31.

The transient frequency raising circuit 40 receives the output V19 from the starting circuit 19 and raises the frequency only during the first fixed period of starting. (Operation) The operation and effect of the first embodiment configured as described above will be described with reference to FIGS. First, the output waveform of the signal circuit 37 will be described with reference to FIG. The output signal f of the square wave circuit 36 is a signal that determines the frequency of the inverter output current, and the pulse widths T1 and T2 are equal. W2 is a signal slightly delayed from the output signal f and has the same pulse width. W3 has a narrower "1" section than W2.
1 has a wider "1" section than W2.

The latch signal L rises when the output signal f changes, and the latch circuit 25 latches the data at the time when L rises. The energization width selection circuit 39 selects one of the energization width signals W1, W2, W3 from the signal circuit 37 according to the outputs P, 0, N of the latch circuit 25 and outputs it.

Next, the bias magnetic direction detection operation will be described with reference to FIG. When there is currently no magnetic bias and the latch circuit 25 outputs 0, the energization width selection circuit 39 selects the energization width W of FIG.
Select 2 to output F. That is, it is assumed that the positive and negative energization widths of the inverter outputs are equalized.

The inverter output current iAC is rectified by the rectifying circuit 11 to become Id, and the IGBT in the section "1" of the PWM signal is turned on, so that the current is increased and the IGBT is turned off in the section "0" of the PWM signal. Therefore, the current decreases.

Upon receiving the PWM waveform and the F signal, Sa and Sb are output from the sampling signal circuit 34, and the current differential value V17 for each half cycle of the alternating current is sampled and held to obtain outputs A and B.

At time t1, V17 is held and output A
And At time t2, V17 is held to be the output B, the rising point of L is compared, and the output of the latch circuit 25 is output at three levels. At time t2, 0 is output when A and B are substantially equal, and P output is output when B> A + α (window width of the comparison circuit 24).

That is, the fact that (dId) / (dt) is large in the direction of the period when the F signal is "0" means that the transformer 5 is demagnetized and the exciting current is increased. By shortening the period of "0", magnetic bias can be prevented.

Therefore, the energization width selection circuit 39 shortens the period of "0" of the F signal by switching from W2 to W1 at time t2 when P is output. B <A-α
In the case of (the window width of the comparison circuit 24), the output is N, and when F is "1", the magnetic field is biased in the saturation direction. Therefore, it is sufficient to select W3 and output the F. This selection is done every half cycle.

Next, the current correction circuit 35 will be described with reference to FIG. That is, when the latch circuit 25 outputs P output at time t2, F is "0" as described in FIG.
Since the transformer 5 is in the saturation direction during the period, the bias current can be prevented by decreasing the current value in this section and increasing the current value in the section where F is "1". This is because the output of the current correction circuit 35 is V35.

At time t2, the latch circuit 25 becomes "0".
When the current is output, the current correction circuit 35 outputs V350, that is, zero output, and the current correction is not performed. Further, when the latch circuit 25 outputs N at time t2, similarly, the output of the current correction circuit 35 outputs V35, and the current in the section where F is "1" is reduced, so that the bias of the transformer 5 is reduced. It can prevent magnetism.

The current correction circuit 35 and the energization width selection circuit 39 are provided on both sides as shown in FIG. 1, and the operation is almost the same even if either one is provided, but the frequency of the alternating current is varied. If the frequency increases,
The energization selection circuit 39 becomes strong, and when the frequency is low, the current correction circuit 35 becomes strong.

Next, the operation of the transient frequency raising circuit 40 will be described with reference to FIG. Immediately before the energization of the transformer 5, the magnetic flux density of the iron core is affected by the residual magnetic flux,
There is a deviation in the direction of the final magnetic flux of the previous energization to a position slightly higher than zero.

Therefore, when the frequency of the energized AC is selected from the beginning of energization, the iron core is easily saturated. However, in the DC system of the conventional thyristor and the inverter, the energization width was narrowly started at a constant frequency, but in this embodiment, the 180-degree energization system (to improve the welding performance) cannot be used.

From the above, as shown in FIG.
It is devised to avoid saturation of the iron core by increasing the frequency of the first portion (1 cycle in FIG. 5) when the activation signal V19 is turned on.

This first part is a few cycles from a few cycles
The shorter the cycle, the better the waveform ratio, so that the magnetic flux density of the transformer 5 can be effectively used without deteriorating the welding quality. That is, the first half cycle of startup is controlled by paying attention to the fact that the magnetic flux change width can be used only about 50%.

Next, the improvement of the current accuracy by the dither correction will be described with reference to FIG. At each modulation cycle, the set signal S from the pulse generator 27 is input, the PWM signal is turned on, and the output V16 of the adder circuit 16 is output.
The comparison circuit 26 compares the final current reference and the detected current Id, and when the detected current Id becomes larger than the final current reference,
The PWM signal is switched to "0" and "OFF".
Comparing circuit 2 is a sawtooth wave that is synchronized with the modulation frequency.
6 (in FIG. 6, in addition to the same polarity as the detected current), so that stable pulse width modulation (PWM) resistant to noise can be performed,
A dither signal having a peak of several% to 5% of the maximum value of the detected current is added.

However, due to this dither signal, the current accuracy is maximum and deteriorates by the peak value of the dither signal.
Dither circuit 2 for performing this current control at high speed and with high accuracy
Reference numeral 8 is correction of the current reference by the modulation rate detection circuit 32 and the function generator 33 of FIG.

In FIG. 6, at time t1, the current reference- (detection current + dither) <0 and the PWM signal changes from "1" to "0", so that it is known that the current control error is only h. The magnitude of h depends on the modulation factor M, that is, T2 /
If T1 is calculated and the current reference is increased by that much, the next PW
Since it is corrected at the M signal point, it is possible to obtain an extremely fast response. The modulation rate can be corrected by calculating T2 / T1 by a microprocessor or the like, but it can be corrected with a delay of 2 to 3 pulses by simply averaging the PWM signal through a filter.

It should be noted that in the case of the system in which the dither signal is added to the current reference side with the reverse slope shown in FIG. 7, it can be seen that the inverted PWM signal is obtained and M = (1-inverted PWM signal). Further, when the dither signal is non-linear as shown in FIG. 8, it is easy to correct the non-linearity by the function circuit 33 of FIG.

(Effect) According to the first embodiment described above,
To prevent the saturation of the iron core of the transformer 5 by transiently increasing the frequency of the alternating current at the time of start-up, detect the bias direction by comparing the rate of change of the current ripple, and finely adjust the current value and conduction width. As a result, the magnetic flux density of the transformer 5 can be used to its limit, and as a result, downsizing can be achieved.
It is economical.

Moreover, by controlling the current at high speed and with high accuracy, it is possible to provide a control device for a welding machine which enables high quality welding. <Second Embodiment> As shown in FIG. 9, an energization width memory 51, a direction determining circuit 52, and a starting direction circuit 53 are newly added to the embodiment of FIG. The energization width of the alternating current polarity signal F at the time when the timer 20 outputs the stop signal is obtained by the energization memory 51, and from the result, the direction determination circuit 52 which determines the energization direction at the next activation is activated by the activation signal V19 from the activation circuit 19. In response to this, the activation direction circuit 53 presets the energization direction to start the square wave circuit 36. This is extremely effective when the alternating current frequency is used below the commercial frequency.

As shown in FIG. 10, the energizing direction at the time of stopping energization and the energizing width T3 are latched to determine the energizing direction of the next starting cycle, and energization is started from the direction in which the transformer 5 is not saturated. In brief, when the energization width T3 is 50% or less, the magnetic flux is in the range in which the magnetic flux is moving in the zero direction, so that the next start causes the current to flow in the same direction. Current width T3 is 50%
In the above case, the magnetic flux is passing through zero and is increasing, so at the next startup, the current flows in the opposite polarity and the transformer 5
The iron core of can be effectively used.

To be precise, since there is voltage forcing, it is desirable to determine the next start direction with the point at which the conduction width T3 is less than 50% as the boundary. <Modifications> 1) In the embodiment of FIG. 1, the bias magnetism of the transformer 5 was obtained from the change in the ripple current on the primary side of the transformer 5, but when high-speed current control is performed as shown in FIG. Even if 5 is saturated, the inverter output is lowered so that the current Id hardly increases. Therefore, by detecting and comparing the modulation factors M at the times t1 and t2, it is possible to detect the magnetic bias.

Further, when the current increases due to the saturation of the transformer 5 as shown in FIG. 11, the saturation is further expanded by comparing (Id-M) at the times t1 and t2. You can catch it.

2) The high-speed current control with high current accuracy described with reference to FIG. 1 does not use the inverter 4 of FIG. 1 but I shown in FIG.
It goes without saying that the same can be applied to the chopper circuit including the GBT 4 ′, the diode 50, the reactor 8 and the load 5 ′ such as the laser oscillator. The circuit of FIG. 12 is used for a small capacity welding machine, a pulse welding machine, or the like.

3) In the embodiment of FIG. 1, the output V of the adder circuit 16
Although 16 is a direct current reference and the frequency is separately given from the pulse generator 27, an alternating current reference is made by the output V16 of the adder circuit 16 and the frequency, and this and the alternating current detected by the current transformer 6 are used. The drive circuits 21 and 22 may be directly driven by the PWM signal output by comparing with iAC in the comparison circuit 26. Even with this method, it is possible to obtain the same effect as that of the embodiment of FIG. In this case, the current component control for bias correction is performed by sampling outputs A and B.
The difference can be added to the AC current reference.

4) Of the control device (circuits other than the main circuit) of the embodiment shown in FIG. 1, the rectifying circuit 11, the differentiating circuit 17, the sampling and holding circuits 18, 23, the driving circuits 21, 22,
All circuits except the starting circuit 19 can be easily realized by a microcomputer.

5) In FIG. 1, the comparison circuit 24 operates the current correction circuit 35 and the energization width selection circuit 39 at the three levels according to the determination of the three levels (P, 0, N).
Needless to say, even if the levels are omitted and two levels are provided, the operation is substantially the same.

6) In the embodiment of FIG. 1, when the stray inductance 8 of the welding electrode circuit portion becomes large, the waveform ratio deteriorates. Therefore, if a circuit in which the frequency of the square wave circuit 36 can be manually set and changed is provided, the inductance will be reduced. Is large and the power factor is poor, it is possible to improve the power factor by lowering the frequency in a circuit where power cannot be injected. In this case, the transformer 5 needs to be replaced with a low frequency one.

[0069]

According to the present invention, it is possible to provide a welding machine control device that enables high quality welding, performs saturation prevention control of a transformer, and can use a high magnetic flux density of an iron core.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining a first embodiment of a control device for a welding machine according to the present invention.

FIG. 2 is a diagram for explaining a signal circuit 37 of FIG.

FIG. 3 is a diagram for explaining a magnetic bias direction detection operation of the embodiment of FIG.

FIG. 4 is a diagram for explaining a current correction circuit 35 of the embodiment of FIG.

5 is a diagram for explaining a transient frequency raising circuit 40 of the embodiment of FIG.

FIG. 6 is a diagram for explaining a dither circuit 28 of the embodiment of FIG.

FIG. 7 is a diagram for explaining a dither circuit 28 of the embodiment of FIG.

FIG. 8 is a diagram for explaining a dither circuit 28 of the embodiment of FIG.

FIG. 9 is a block diagram for explaining a second embodiment of the control device for the welding machine of the present invention.

FIG. 10 is a diagram for explaining the operation of the embodiment of FIG.

FIG. 11 is a diagram for explaining a modified example of the control device for the welding machine of the present invention.

FIG. 12 is a view for explaining a modified example of the control device for the welding machine of the present invention.

FIG. 13 is a diagram for explaining a first example of a conventional controller for a welding machine.

FIG. 14 is a view for explaining a second example of the conventional controller for the welding machine.

[Explanation of symbols]

1 ... AC power supply, 2 ... Rectifier, 3 ... Capacitor, 4 ... Inverter, 4 '... IGBT, 5 ... Transformer, 5' ... Load, 6
... current transformer, 7 ... rectifier, 8 ... stray inductance, 9 ...
Welding electrode, 11 ... Rectifier circuit, 12 ... Effective value reference, 13 ...
Effective value circuit, 14 ... Amplification circuit, 15, 16 ... Addition circuit,
17 ... Differentiation circuit, 18, 23 ... Sampling hold circuit, 19 ... Start-up circuit, 20 ... Timer, 21, 22 ... Driving circuit, 24 ... Comparison circuit, 25 ... Latch circuit, 26 ... Comparison circuit, 27 ... Pulse generator, 28 ... Dither circuit, 29
... Flip-flop circuit, 31 ... Distribution circuit, 32 ... Modulation rate detection circuit, 33 ... Function circuit, 34 ... Sample signal circuit, 35 ... Current correction circuit, 36 ... Square wave circuit, 37 ... Signal circuit, 39 ... Energization width selection Circuit, 40 ... Transient frequency increasing circuit, 51 ... Energization width memory, 52 ... Direction determining circuit, 5
3 ... Starting direction circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H02M 7/537 9181-5H H02M 7/537 D

Claims (7)

[Claims] 1. A power converter for shaping a waveform of DC power from a DC power supply by pulse width modulation control to control a load current flowing to a welding machine, and comparing the load current with a current reference to reduce a deviation thereof. Control means for outputting a control signal, and a pulse for outputting a pulse width modulation signal with conduction at a constant modulation cycle and outputting a pulse width modulation signal with non-conduction according to the result of comparison between the control signal and the load current. Width modulation control means, arithmetic means for adding a dither signal that gradually increases or decreases in each modulation cycle to the current reference or load current, and a modulation factor obtained from the pulse width modulation signal directly or through a function to the current reference Or a control device for a welding machine, comprising a correction means for correcting the load current. 2. The control apparatus for a welding machine according to claim 1, wherein the modulation rate averages a pulse width modulation signal or an inversion signal of the pulse width modulation signal through a filter. 3. The DC power from the DC power supply is converted into AC power by pulse width modulation control and supplied to the primary side of the transformer, and the AC power obtained from the secondary side of the transformer is supplied to the welding machine. An inverter, a current control means for comparing the output current of this inverter with a current reference to control the current, an inversion control means for inverting the direction of the output current of the inverter according to a frequency reference, and a positive cycle of the alternating current Comparison means for alternately comparing the current change rate during the period of the final pulse width modulation conduction signal and the final pulse width modulation conduction signal of the negative cycle of the alternating current, and a positive result by the comparison result obtained by the comparison means. The first and second adjustment means for adjusting the positive and negative cycles of the alternating current, and the second adjustment means for adjusting the time of the positive and negative cycles of the alternating current. Machine of the control device. 4. The control device for a welding machine according to claim 3, wherein the frequency of the inverter is set higher than the steady frequency only during a half cycle to a few cycles of starting energization. 5. The DC power from the DC power supply is converted into AC power by pulse width modulation control and supplied to the primary side of the transformer, and the AC power obtained from the secondary side of the transformer is supplied to the welding machine. An inverter, and a detection means for detecting the polarity and energization width of the final half cycle at the end of energization of the inverter, and detecting whether the energization width of the final half cycle at the end of energization is wider or narrower than a set value, If it is narrow, the welding is equipped with a means for starting energization in the same direction as the last half cycle at the start of the next energization, and for a wide start of energization in the opposite direction for the last half cycle at the start of the next energization. Machine control device. 6. The DC power from the DC power supply is converted into AC power by pulse width modulation control and supplied to the primary side of the transformer, and the AC power obtained from the secondary side of the transformer is supplied to the welding machine. An inverter, a detection unit that detects the AC current value and the modulation factor of the pulse width modulation control, and the AC current at the time of the final pulse width modulation control of the positive half cycle and the negative half cycle of the AC current, respectively. A controller for a welding machine, comprising means for comparing the modulation rates and changing at least one of a positive and negative magnitude of the alternating current and a conduction width of the alternating current in a direction in which the values are balanced. 7. The control device for a welding machine according to claim 5, further comprising means for manually adjusting the frequency of the alternating current of the inverter.