JP6444271B2 - AC output inverter welding machine - Google Patents

Description

  The present invention relates to an AC output inverter welding machine. More specifically, PWM (Pulse Width Modulation: pulse width modulation) control of an inverter circuit provided on the primary side of a transformer controls output current flowing through a welding load. The present invention relates to an improved AC output inverter welding machine to be controlled.

  An arc welding machine is a processing device that performs welding by generating an arc between a welding electrode made of a welding material constituting a welding load and a welding base material to be processed. Arc welding is a welding method that utilizes a discharge phenomenon in a gas, and the high temperature caused by the arc melts and integrates the weld base material and the weld material. Also, in an AC welding arc welding machine in which the polarity of the output current flowing through the welding load is periodically reversed, the oxide film on the surface of the base metal is cleaned during a period of reverse polarity where the potential of the welding electrode is higher than that of the weld base metal. Can be removed. For this reason, when welding is performed using a metal that is easily oxidized, such as aluminum, as a welding base material, an AC welding arc welder is used.

  Such an AC output arc welding machine rectifies the AC current supplied from the transformer for stepping down, the inverter circuit for supplying AC current to the primary coil of the transformer, and the secondary coil of the transformer. A rectifier circuit and a polarity switching circuit that periodically switches the output polarity and supplies the direct current to the welding load with respect to the direct current after rectification by the rectifier circuit. In this arc welder, the inverter circuit is controlled by PWM (Pulse Width Modulation) to control the output current flowing through the welding load. The PWM control is performed by controlling the pulse width of the PWM signal based on the difference between the detected value of the output current and the command value of the output current.

  In the conventional AC output inverter welding machine as described above, when the polarity of the output current flowing through the welding load is reversed, the output current is zero-crossed, so the difference between the detected value and the command value changes suddenly, and the pulse of the PWM signal In some cases, the width increased rapidly to the maximum level. For this reason, the temporal change of the magnetic flux passing through the primary coil of the transformer is biased, which may cause saturation of the transformer. If the transformer is saturated, an excessive current flows through the switching element of the inverter circuit, and the switching element may be damaged.

  The magnetic flux that passes through the primary coil of the transformer is proportional to the time integral of the voltage applied to the primary coil. Further, if the switching frequency of the inverter circuit is high, the pulse width of the PWM signal is shortened. Therefore, even if the pulse width increases rapidly, saturation of the transformer hardly occurs. However, when the switching frequency of the inverter circuit is low, as described above, there is a problem that the pulse width rapidly increases when the output polarity is inverted. If the transformer is increased in size, saturation of the transformer can be made difficult even when the switching frequency of the inverter circuit is low, but the manufacturing cost increases.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an AC output inverter welding machine with improved durability. In particular, an object of the present invention is to provide an AC output inverter welding machine that can suppress the saturation of the transformer and the damage of the switching element of the inverter circuit when the polarity of the output current flowing through the welding load is reversed. .

  An AC output inverter welding machine according to a first aspect of the present invention includes a switching element, an inverter circuit that converts a direct current into an alternating current, a transformer in which an output of the inverter circuit is supplied to a primary coil, and the transformer A rectifying circuit for rectifying the alternating current supplied from the secondary coil of the ceramic device, a polarity switching circuit for periodically switching the output polarity to the direct current after rectification by the rectifying circuit and supplying the welding load to the welding load, and the welding An output current detecting means for detecting an output current flowing through a load; a PWM signal generating means for generating a PWM signal for defining an ON time of the switching element based on the output current; and an upper limit of a pulse width of the PWM signal. A pulse width upper limit control means for controlling the pulse width upper limit control means until the predetermined period of time elapses after the output polarity is switched. Monotonically increases the upper limit value of, then, configured to secure the maximum level of the upper limit.

  According to such a configuration, since the pulse width of the PWM signal is limited to an upper limit value that monotonously increases for a certain period from the switching of the output polarity, when the polarity of the output current flowing through the welding load is reversed, It is possible to prevent the pulse width from rapidly increasing. Also, since the upper limit value of the pulse width is monotonously increased during the above-mentioned fixed period, the increase amount of the pulse width at the start and end of the fixed period is suppressed as compared to the case where the upper limit value is not fixed. be able to. Therefore, since it is possible to suppress the occurrence of bias in the temporal change of the magnetic flux passing through the primary coil of the transformer, it is possible to suppress the transformer from being saturated and the switching element of the inverter circuit from being damaged.

  In addition to the above configuration, the AC output inverter welder according to the second aspect of the present invention is configured such that the pulse width upper limit control means increases the upper limit value along a straight line having a constant slope. According to such a configuration, the configuration of the pulse width upper limit control means can be simplified. For example, the pulse width upper limit control means can be configured by a circuit for charging and discharging a capacitor.

  In addition to the above configuration, the AC output inverter welder according to the third aspect of the present invention is configured such that the pulse width upper limit control means increases the upper limit value from a zero level to a maximum level. According to such a configuration, even if the pulse width of the PWM signal is reduced to the zero level before the output polarity is switched, it is possible to prevent the pulse width from rapidly increasing.

  An AC output inverter welder according to a fourth aspect of the present invention includes, in addition to the above configuration, drive signal generation means for generating a drive signal for driving the polarity switching circuit, and timing for switching the output polarity based on the drive signal. Timing signal generating means for generating a timing signal indicating the above, and the pulse width upper limit control means is configured to control the upper limit value based on the timing signal. According to such a configuration, the response of the pulse width upper limit control can be improved as compared with the case where the polarity switching timing is determined by monitoring the output of the polarity switching circuit.

  An AC output inverter welder according to a fifth aspect of the present invention includes, in addition to the above configuration, a DC reactor that smoothes the DC current rectified by the rectifier circuit, and the polarity switching circuit is smoothed by the DC reactor. A direct current is converted into an alternating current, and the output current detecting means is configured to detect the direct current smoothed by the direct current reactor as the output current. According to such a configuration, the detection accuracy of the output current can be improved. Further, the output current when the output polarity is positive and the output current when the output polarity is reverse can be detected by a common detection circuit indicated by a real number of 0 or more.

  ADVANTAGE OF THE INVENTION According to this invention, when the polarity of the output current which flows through a welding load reverses, it can suppress that a transformer is saturated and the switching element of an inverter circuit is damaged, and the alternating current output which improved durability An inverter welder can be provided.

It is the figure which showed one structural example of the alternating current output inverter welding machine 1 by embodiment of this invention. It is the block diagram which showed the structural example of the inverter control part 5 of FIG. Is a diagram illustrating an example of the operation of the AC output inverter welding machine 1 in FIG. 1, the time change and the gate drive signals G _1, G ₂ and the timing signal and the output current is shown. It is the figure which showed the operation | movement of the conventional alternating current output inverter welding machine, and the temporal change of the detected value I of an output current, an error, and a pulse width is shown. It is the figure which showed the operation | movement at the time of the polarity reversal of the alternating current output inverter welding machine 1 of FIG. 1 compared with the comparative example. FIG. 3 is a diagram illustrating a configuration example of a pulse width upper limit control unit 55 in FIG. 2. FIG. 7 is a diagram illustrating an example of the operation of the ramp signal generation circuit 551 in FIG. 6, and shows a characteristic curve that changes with time using a timing signal as a trigger.

<AC output inverter welding machine 1>
FIG. 1 is a diagram showing a configuration example of an AC output inverter welding machine 1 according to an embodiment of the present invention. In the figure, an arc welding machine is shown that generates an arc by using electric power supplied from an AC power source, for example, a commercial power source having a three-phase rated voltage of 400 V and a frequency of 50 Hz or 60 Hz.

  The AC output inverter welding machine 1 includes rectifier circuits 11 and 31, a smoothing capacitor 12, an inverter circuit 13, a transformer 2, a DC reactor 32, a detection circuit 33, a polarity switching circuit 34, an inverter control unit 5, and an output control unit 6. Composed. In this AC output inverter welding machine 1, the output current flowing through the welding load 4 is controlled by PWM (Pulse Width Modulation) control of the inverter circuit 13 provided on the primary side of the transformer 2. The welding load 4 includes a welding electrode 41 called a torch and a welding base material 42 to be processed.

  The rectifier circuit 11 is an input circuit for rectifying an alternating current input from the alternating current power supply via the power supply terminal 10, and is configured by a bridge circuit using a plurality of diodes. The smoothing capacitor 12 is a capacitive element for smoothing the direct current rectified by the rectifying circuit 11.

  The inverter circuit 13 is a conversion device that includes four switching elements 131 to 134 and four free-wheeling diodes 14 and converts a direct current that has been smoothed by the smoothing capacitor 12 into an alternating current. The inverter circuit 13 is configured by a bridge circuit using switching elements 131 to 134.

  The switching elements 131 to 134 are all semiconductor elements that are turned on or off by a drive signal from the inverter control unit 5. These switching elements 131 to 134 include voltage controlled transistors such as IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). Is used.

  The freewheeling diode 14 is a circuit element for preventing a surge current from flowing through the switching elements 131 to 134. The reflux diode 14 is provided for each of the switching elements 131 to 134 and is connected between the collector terminal and the emitter terminal of the switching elements 131 to 134.

  The transformer 2 is a transformer for stepping up or down to a voltage necessary for welding. The transformer 2 includes a primary coil 21 and a secondary coil 22, and an output of the inverter circuit 13 is supplied to the primary coil 21. The rectifier circuit 31 is a converter for rectifying an alternating current supplied from the secondary coil 22 of the transformer 2, and is configured by a bridge circuit using four diodes.

The direct current reactor 32 is an inductive element for smoothing the direct current rectified by the rectifier circuit 31. The detection circuit 33 is a circuit element for detecting an output current flowing through the welding load 4, and outputs a detection value I of the output current to the inverter control unit 5. The detection circuit 33 is placed between the DC reactor 32 and the polarity changeover circuit 34 detects the DC current I ₁ and I ₂ which is smoothed by a DC reactor 32 as an output current. The detection value I is I = (I ₁ + I ₂ ).

  The polarity switching circuit 34 is an inverter that periodically switches the output polarity and supplies the direct current to the welding electrode 41 of the welding load 4 with respect to the direct current that has been rectified by the rectifying circuit 31, and includes two switching elements 341, 342 and two It is constituted by a reflux diode 35. The polarity switching circuit 34 is configured by a bridge circuit using the switching elements 341 and 342, and converts the DC current smoothed by the DC reactor 32 into an AC current having a frequency lower than that of the inverter circuit 13. For example, the inverter circuit 13 generates a high-frequency alternating current of about 1 kHz, whereas the polarity switching circuit 34 generates a low-frequency alternating current of about 100 Hz.

  The switching elements 341 and 342 are both semiconductor elements that are turned on or off by a drive signal from the output control unit 6. For these switching elements 341 and 342, voltage-controlled transistors such as IGBTs and MOSFETs are used. The switching element 341 is a positive-polarity switching element, and makes the potential of the welding electrode 41 lower than that of the welding base material 42 in the ON state. On the other hand, the switching element 342 is a switching element having a reverse polarity, and makes the potential of the welding electrode 41 higher than that of the welding base material 42 in the ON state.

  The freewheeling diode 35 is a circuit element for preventing a surge current from flowing through the switching elements 341 and 342. The reflux diode 35 is provided for each of the switching elements 341 and 342 and is connected between the collector terminal and the emitter terminal of the switching elements 341 and 342.

  The output control unit 6 is a control unit that controls the polarity switching circuit 34 in order to obtain a desired AC output. In the output control unit 6, a drive signal for driving the switching elements 341 and 342 of the polarity switching circuit 34 is generated. The drive signal is input to the gate terminals of the switching elements 341 and 342.

  The inverter control unit 5 is a control unit that performs PWM control of the inverter circuit 13, generates a PWM signal based on the output current flowing through the welding load 4, and outputs the PWM signal to the switching elements 131 to 134 of the inverter circuit 13. The PWM signal is a drive signal whose pulse width defines the ON time of the switching elements 131 to 134, and is input to the gate terminals of the switching elements 131 to 134.

<Inverter control unit 5>
FIG. 2 is a block diagram showing a configuration example of the inverter control unit 5 of FIG. The inverter control unit 5 includes a command value generation unit 51, a comparator 52, a PWM signal generation unit 53, a timing signal generation unit 54, and a pulse width upper limit control unit 55.

The command value generation unit 51 generates a command value I ₀ of the output current and outputs it to the comparator 52. The command value I ₀ is a parameter indicating a target output current in feedback control based on the detection value I.

The comparator 52 compares the detection value I from the detection circuit 33 with the command value I ₀ from the command value generation unit 51, and specifies a pulse width of the PWM signal based on the voltage level based on the comparison result. Is output to the PWM signal generation unit 53. Control signal, the difference between the detected values I and the command value I ₀ and an error is generated based on the error.

  The PWM signal generation unit 53 determines a pulse width based on the control signal from the comparator 52 and generates a PWM signal. The timing signal generation unit 54 generates a timing signal indicating the timing for switching the output polarity based on the drive signal from the output control unit 6, and outputs the timing signal to the pulse width upper limit control unit 55.

  The pulse width upper limit control unit 55 is a control unit that controls the upper limit of the pulse width of the PWM signal based on the timing signal from the timing signal generation unit 54, and includes a ramp signal generation circuit 551 and a diode 552. The pulse width upper limit control unit 55 monotonously increases the upper limit value of the pulse width until the fixed pulse width suppression period Tp elapses after the output polarity is switched, and then fixes the upper limit value to the maximum level. The upper limit value of the pulse width is a value at which the transformer 2 is not saturated and is the maximum value at which the inverter circuit 13 can operate normally.

  For example, the pulse width upper limit control unit 55 increases the upper limit value of the pulse width along a straight line having a constant slope until a predetermined time elapses after the output polarity is switched. Further, the pulse width upper limit control unit 55 fixes the upper limit value of the pulse width to the maximum level from when a certain time has elapsed until the next switching of the output polarity. The maximum level here is the maximum value that can be specified as the pulse width of the PWM signal. Such upper limit control of the pulse width is repeated every time the polarity of the output current is switched.

  The ramp signal generation circuit 551 is a signal generation device that generates a ramp signal whose voltage level increases along a straight line having a constant slope with a timing signal as a trigger, and the ramp signal is generated via the diode 552 during the pulse width suppression period Tp. Is added to the control signal of the comparator 52 to realize the above-described upper limit control of the pulse width. The diode 552 has an anode terminal connected to the wiring connecting the comparator 52 and the PWM signal generation unit 53, and a cathode terminal connected to the output terminal of the ramp signal generation circuit 551.

FIG. 3 is a diagram showing an example of the operation of the AC output inverter welding machine 1 of FIG. 1, and shows gate drive signals G ₁ and G _2, timing signals, and temporal changes in output current. The gate drive signal G ₁ is a rectangular waveform of a drive signal for driving the switching element 341 of the positive polarity, by switching the voltage level, switches between ON and OFF states of the switching elements 341. The switching element 341 is shifted to an ON state by the rising of the gate drive signals G _1, it goes to the off state by the fall of the gate drive signal G _1.

The gate drive signal G ₂ is a rectangular waveform of a drive signal for driving the switching element 342 of opposite polarity, by switching the voltage level, switches between ON and OFF states of the switching elements 342. The switching element 342 is shifted to an ON state by the rising of the gate drive signal G _2, it shifts to the OFF state by the fall of the gate drive signal G _2.

Output current is the welding current flowing through the welding load 4, the switching of the switching elements 341 and 342 based on the gate drive signals G ₁ and G _2, a rectangular wave waveform polarity is periodically reversed.

During the period Ta in which the switching element 341 is in the ON state, the output current is positive and the value of the output current is substantially constant (constant value = a). On the other hand, during the period Tb in which the switching element 342 is in the ON state, the output current has a reverse polarity, and the value of the output current is substantially constant (constant value = −a). In this example, the reverse polarity period Tb is shorter than the period Ta. Timing signal used to limit the control of the pulse width, the pulse-like signal is generated using the gate drive signals G ₁ and G ₂ as described above.

FIG. 4 is a diagram showing the operation of a conventional AC output inverter welder, in which the output current detection value I, error, and pulse width change over time are shown. When the polarity of the output current is reversed, a surge voltage is generated between the collector terminal and the emitter terminal of the switching element 341 or 342 due to the energy stored in the DC reactor 32 or the wiring inductance. Thus to suppress the surge voltage, before a predetermined time than the switching of the output polarity, surge suppression control is performed to decrease the command value I ₀ of the output current.

For example, the period from time t ₁ to time t ₂ showing the switching of the output polarity and surge suppression period Ts, the command value I ₀ during this surge suppression period Ts, is fixed to a constant value b (b <a) . Further, the command value I ₀ is fixed to a constant value a from time t ₂ to the next surge suppression period Ts.

Detection value I of the output current, except for a certain period immediately after the switching of the output polarity, a waveform to follow the command value I _0. In detail, the detection value I, between the time t ₁ of the surge suppression period Ts to the time t _2, and gradually decreases along a curve convex downward, reaching the value b at time t ₂ ing. Detection value I is then, after reaching the zero rapidly decreases, increases rapidly, when the almost constant time has elapsed from the time t _2, the saturated to the value a.

The error represents a difference (I ₀ −I) between the detected value I and the command value I ₀ . This error is in surge suppression period Ts, increasing moderately from a negative value along a convex curve upward, and reaches zero at time t _2. Error, then, after increasing sharply, slowly decreased, when the almost constant time has elapsed from the time t _2, the has reached zero.

The pulse width of the PWM signal is controlled based on the error described above. In the conventional AC output inverter welder, when the output polarity is reversed, the pulse width of the PWM signal may increase rapidly from the zero level to the maximum level. In detail, the pulse width of the PWM signal, between the time t ₁ of the surge suppression period Ts to the time t _2, is fixed to zero level, at time t ₂ to a maximum level p _m increases rapidly Yes. Thereafter, the pulse width, after maintaining the maximum level p _m while, decreases along a downward convex curve, when the almost constant time has elapsed from the time t _2, the value _{p 1 (p 1 <p m} ) Has reached. Thereafter, the pulse width is substantially constant p ₁ until the next surge suppression period Ts. At time t ₂ as in the prior art, the pulse width is increased to abruptly maximum level p _m, deviation occurs in the temporal variation of magnetic flux penetrating the primary coil 21 of the transformer 2, the transformer 2 is I or cause saturation Absent.

  FIG. 5 is a diagram showing the operation of the AC output inverter welding machine 1 of FIG. 1 at the time of polarity reversal in comparison with the comparative example. (A) in the figure shows the case of the AC output inverter welder 1 according to the present invention, and (b) shows the case of the conventional AC output inverter welder.

In AC output inverter welding machine 1 according to this embodiment, the period from time t ₂ showing the switching of the output polarity to time t ₃ a pulse width suppression period Tp, the pulse width suppression period Tp elapses from the switching of the output polarity In the meantime, the pulse width upper limit control for monotonically increasing the pulse width upper limit value is performed.

  During the pulse width suppression period Tp, since the pulse width of the PWM signal is limited to an upper limit value that monotonously increases, it is possible to prevent the pulse width from rapidly increasing when the output polarity is reversed. For this reason, it can suppress that a bias arises in the temporal change of the magnetic flux which penetrates the primary coil 21 of the transformer 2.

<Timing Signal Generation Unit 54 and Ramp Signal Generation Circuit 551>
FIG. 6 is a diagram illustrating a configuration example of the timing signal generation unit 54 and the ramp signal generation circuit 551 in FIG. The timing signal generator 54 includes an amplifier, a pull-up resistor, DC voltage sources V ₁ and V _2, resistance elements, and the like, and a timing signal composed of a one-shot pulse signal using the gate drive signals G ₁ and G _2. Is generated.

  The ramp signal generation circuit 551 includes a switching element 71, a resistance element 72, a capacitor 73, a constant current source 74, and an operational amplifier 75. The voltage level is constant with a timing signal input from the timing signal generation unit 54 as a trigger. A ramp signal that increases along a straight line is generated.

  The switching element 71 is a semiconductor element for controlling charging / discharging of the capacitor 73 and is driven by a timing signal. As the switching element 71, a voltage control type transistor such as an IGBT or a MOSFET is used. The collector terminal of the switching element 71 is connected to the non-inverting input terminal of the operational amplifier 75 via the resistance element 72, and the emitter terminal is grounded. The output terminal of the operational amplifier 75 is connected to the inverting input terminal to output a ramp signal.

Capacitor 73 is a capacitor element of the capacitor C _1, one terminal connected to the non-inverting input terminal of the constant current source 74 and the operational amplifier, the other terminal is grounded. The capacitor 73 is discharged while the switching element 71 is in the on state, and is charged by the current supplied from the constant current source 74 while the switching element 71 is in the off state.

FIG. 7 is a diagram illustrating an example of the operation of the ramp signal generation circuit 551 in FIG. 6, in which a ramp signal whose voltage level changes using a timing signal as a trigger is illustrated. The ramp signal is a line-shaped curve showing the upper limit of the voltage level pulse width, the upper limit value decreases rapidly in synchronization with the rise of the timing signal at time t _2, the transition switching element 71 to the OFF state by the fall time t ₂₁ of the timing signal for, to reach the zero level.

The upper limit of the pulse width, the maximum from the time t ₂₁ until the pulse width suppression period Tp has elapsed, the slope increases monotonically along a predetermined straight line, at a time t ₃ when the pulse width suppression period Tp is completed Level It has reached the p _m. Thereafter, the upper limit of the pulse width, until the next pulse width suppression period Tp, is fixed at the maximum level p _m. In this example, although the maximum value of the ramp signal to match the maximum value p _m of the pulse width, the maximum value of the ramp signal may be any maximum value p _m or more pulse width.

Pulse width suppression period Tp is comprised of a fixed time length defined by the capacitance C ₁ or the like of the capacitor 73. The ramp signal output from the ramp signal generation circuit 551 operates as a limiter due to the action of the diode 552 on the output of the comparator 52. For this reason, it is possible to prevent the pulse width from rapidly increasing for a certain period from the switching of the output polarity.

  According to the present embodiment, since the occurrence of bias in the temporal change of the magnetic flux passing through the primary coil 21 of the transformer 2 is suppressed, the transformer 2 is saturated and the switching elements 131 to 134 of the inverter circuit 13 are saturated. Can be prevented from being damaged.

  In the present embodiment, an example has been described in which the upper limit value of the pulse width is increased along a straight line with a constant slope until a predetermined period elapses after the output polarity is switched. The method for monotonously increasing the upper limit of the width is not limited to this. For example, the upper limit value of the pulse width may be increased along a downwardly convex curve or an upwardly convex curve.

DESCRIPTION OF SYMBOLS 1 AC output inverter welding machine 10 Power supply terminal 11, 31 Rectifier circuit 12 Smoothing capacitor 13 Inverter circuits 131-134, 341, 342 Switching element 14, 35 Reflux diode 2 Transformer 32 DC reactor 33 Detection circuit 34 Polarity switching circuit 4 Welding load 41 Welding electrode 42 Welding base material 5 Inverter control unit 51 Command value generation unit 52 Comparator 53 PWM signal generation unit 54 Timing signal generation unit 55 Pulse width upper limit control unit 551 Ramp signal generation circuit 552 Diode 6 Output control unit

Claims (5)

An inverter circuit having a switching element and converting a direct current into an alternating current;
A transformer in which the output of the inverter circuit is supplied to the primary coil;
A rectifying circuit for rectifying an alternating current supplied from a secondary coil of the transformer;
A polarity switching circuit that periodically switches the output polarity and supplies it to the welding load with respect to the DC current after rectification by the rectifier circuit,
Output current detection means for detecting an output current flowing through the welding load;
PWM signal generating means for generating a PWM signal that defines the on-time of the switching element based on the output current;
Pulse width upper limit control means for controlling the upper limit of the pulse width of the PWM signal,
The pulse width upper limit control means monotonically increases the upper limit value of the pulse width until a predetermined period has elapsed since the switching of the output polarity, and then fixes the upper limit value to a maximum level. AC output inverter welding machine.   2. The AC output inverter welding machine according to claim 1, wherein the pulse width upper limit control means increases the upper limit value along a straight line having a constant slope.   The AC output inverter welding machine according to claim 2, wherein the pulse width upper limit control means increases the upper limit value from a zero level to a maximum level. Drive signal generating means for generating a drive signal for driving the polarity switching circuit;
A timing signal generating means for generating a timing signal indicating a timing for switching the output polarity based on the drive signal;
The AC output inverter welding machine according to any one of claims 1 to 3, wherein the pulse width upper limit control means controls the upper limit value based on the timing signal. A DC reactor for smoothing the DC current rectified by the rectifier circuit;
The polarity switching circuit converts a direct current after smoothing by the direct current reactor into an alternating current,
5. The AC output inverter welding machine according to claim 4, wherein the output current detection unit detects a DC current smoothed by the DC reactor as the output current. 6.

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