JP4464175B2 - Output control method of inverter controlled welding power source for pulse arc welding - Google Patents

Description

  The present invention relates to inverter frequency control in an output control method for an inverter-controlled welding power source for pulse arc welding in which a consumable electrode is fed to perform pulse welding.

  FIG. 7 is an electrical connection diagram of a power supply device for carrying out an output control method of an inverter-controlled welding power source for pulse arc welding of the prior art. In FIG. 7, an inverter type main power supply circuit PS converts a primary rectifier circuit that rectifies a commercial power supply (not shown), a smoothing circuit that smoothes a rectified rippled voltage, and a smoothed DC voltage into a high-frequency AC. Formed from an inverter circuit, a main transformer that converts high-frequency alternating current into a voltage suitable for arc load, a secondary rectifier circuit that rectifies the converted voltage again, and a direct current reactor that smoothes the rectified rippled direct current Has been.

  The output control circuit performs pulse width modulation control on the inverter circuit at a predetermined inverter frequency, and controls a plurality of sets of power transistors forming the inverter circuit to perform output control.

  In the above-mentioned inverter-controlled welding power source, even if welding is performed at the same average output current, for example, 350 A, in pulse mag and mig welding, the output voltage is about 35 V when there is no pulse, and when there is a pulse, it is output during the peak current conduction period. The change in current increases, and the effective output current of the peak current reaches about 600 A with respect to the average output current 350 A, and about 50 V with respect to the output voltage. As described above, since a high output voltage is required during the energization period of the peak current, the prior art has ensured a high output voltage by increasing the number of secondary windings of the main transformer. Further, a power transistor having a large capacity is used for the increase in the primary current that occurs when the number of windings of the secondary winding is increased.

  Prior art document 1 discloses a technique for increasing the inverter frequency of the inverter circuit during the arc period and lowering the inverter frequency during the short circuit period to stably control the inverter current, thereby reducing high-frequency vibration due to the ripple component of the output current. Has been.

Japanese Patent Publication No. 4-24145

  In pulse arc welding, when welding is performed with the average output current set to 350 A, the peak current during the peak current conduction period is about 600 A, and the output voltage is also required to be high, and the high output voltage is ensured. Therefore, the number of windings on the secondary side of the main transformer was increased. As a result, the main transformer becomes large. Further, by increasing the number of secondary windings, the primary current of the main transformer increases, and the capacity of the power transistor that constitutes the inverter circuit is required, which increases the cost.

In order to solve the above-described problems, the present invention uses an inverter-controlled welding power source that controls output by pulse width modulation control at a predetermined inverter frequency, and supplies a consumable electrode with a peak current and a base current. In an output control method of an inverter-controlled welding power source for pulse arc welding that performs pulse arc welding with a welding current consisting of:
The peak current and the base current are alternately energized at a predetermined cycle according to a current control set value, the current control set value is compared with a reference current set value, and the current control set value is the reference current set value. When the value is equal to or higher than the value, the inverter frequency during the peak current conduction period is set to a predetermined low triangular wave frequency,
Inverter for pulse arc welding, wherein when the current control set value is less than the reference current set value, the inverter frequency of the peak current energizing period and the base current energizing period is set to a predetermined high triangular wave frequency This is an output control method for a controlled welding power source.

  According to the first aspect of the present invention, since the inverter frequency of the inverter circuit is lowered and the pulse width modulation control is performed in the peak current energizing period in which a large current is energized, the number of windings on the secondary side of the main transformer is not increased. Even a high output voltage can be obtained. As a result, an increase in the size of the main transformer can be prevented. Furthermore, by lowering the inverter frequency of the inverter circuit, the switching loss of a plurality of sets of power transistors constituting the inverter circuit is reduced, and a power transistor having a small capacity can be used.

  According to the second aspect of the present invention, in the peak current energizing period, when the peak current is larger than the reference current, the frequency of the inverter circuit is lowered, and when the peak current is smaller, the frequency is raised, so that more accurate inverter frequency switching control is performed. As a result, stable pulse arc welding can be realized.

[Embodiment 1]
FIG. 1 is an electrical connection diagram of a power supply apparatus that implements an output control method of an inverter-controlled welding power supply for pulse arc welding according to Embodiment 1 of the present invention. In the figure, an inverter type main power supply circuit PS performs output control with a commercial power supply as an input, and supplies an output suitable for an arc load.

  The output voltage detection circuit VD detects the output voltage of the inverter type main power supply circuit PS, averages it, and outputs it as an output voltage detection signal Vd. The voltage setting circuit VS sets a predetermined output voltage value and outputs it as a voltage setting signal Vs. The voltage error amplification circuit EV amplifies an error between the output voltage detection signal Vd that is a feedback signal and the voltage setting signal Vs that is a target value, and outputs the amplified voltage error signal Ev.

  The V / F conversion circuit VF receives the voltage error amplification signal Ev, performs V / F conversion, and outputs a V / F conversion signal Vf. The peak current conduction time setting circuit TP sets a predetermined peak current conduction time and outputs it as a peak current conduction time setting signal Tp. The mono multivibrator MM is triggered by the change of the V / F conversion signal Vf from the Low level to the High level as a trigger, and the pulse period signal Tf that becomes the High level for the time set by the peak current conduction time setting signal Tp. Is output. The modulation circuit MC is formed by the voltage error amplification circuit EV, the V / F conversion circuit VF, the peak current conduction time setting circuit TP, and the mono multivibrator MM. The modulation circuit MC receives the output voltage detection signal Vd and the voltage setting signal Vs as inputs, and outputs the pulse period signal Tf by pulse frequency modulation control based on an error between these signals.

  The peak current setting circuit IP outputs a preset peak current setting signal Ip. The base current setting circuit IB outputs a preset base current setting signal Ib. The peak base switching circuit SW is connected to the a side when the pulse cycle signal Tf is at a high level and outputs the peak current setting signal Ip as a current control setting signal Isc. When the pulse cycle signal Tf is at a low level, Is connected to the b side and outputs the base current setting signal Ib as the current control setting signal Isc.

  The output control circuit SC is formed by the current error amplifier circuit EI, the triangular wave generation circuit OSC, and the pulse width modulation control circuit PWM shown in FIG. The current error amplifier circuit EI amplifies an error between the output current detection signal Id as a feedback signal and the current control setting signal Isc as a target value, and outputs the amplified current error signal Ei. The triangular wave generation circuit OSC outputs a triangular wave having a predetermined low frequency when the pulse period signal Tf is at a high level, and outputs a triangular wave having a predetermined high frequency when the pulse period signal Tf is at a low level. The pulse width modulation control circuit PWM compares the current error amplification signal Ei with the selected triangular wave generation signal Osc, and outputs an output control signal Sc based on the result.

  The feed speed setting circuit WS sets a feed speed and outputs it as a feed speed setting signal Ws. The feed control circuit WC receives the feed speed setting signal Ws and outputs a feed control signal Wc. The wire feeder WR controls the feeding of the wire according to the feeding control signal Wc.

  FIG. 3 is a timing chart for explaining the operation of the power supply device shown in FIG. The waveform of FIG. 3A shows the pulse period signal Tf, the waveform of FIG. 3B shows the triangular wave generation signal Osc (carrier signal), and FIG. 3C shows the output current detection signal Id. .

  FIG. 4 shows the external characteristics of the power supply device shown in FIG. The inductance existing in each wiring of the power supply device causes a voltage drop in proportion to the inverter frequency. When the inverter frequency increases, the output voltage decreases as shown in FIG. 4, and conversely, when the inverter frequency decreases, the output voltage decreases. Will rise.

  At time t = t1 shown in FIG. 3, when the pulse cycle signal Tf becomes High level, the peak base switching circuit SW is connected to the a side and outputs the peak current setting signal Ip as the current control setting signal Isc. The current error amplifier circuit EI amplifies an error between the output current detection signal Id that is a feedback signal and the current control setting signal Isc that is a target value, and outputs the amplified current error signal Ei.

  The triangular wave generation circuit OSC outputs a triangular wave having a low frequency shown in FIG. 3B when the pulse period signal Tf is at a high level. The pulse width modulation control circuit PWM compares the current error amplification signal Ei and the triangular wave generation signal Osc, performs pulse width modulation control based on the result, and outputs an output control signal Sc (not shown). At this time, during the peak current conduction period Tp shown in FIG. 3 (C), the inverter frequency of the inverter circuit is lowered and the above-mentioned lowering results in a higher output voltage shown in FIG. Prevent voltage drop due to influence.

  At time t = t2, when the pulse cycle signal Tf becomes low level, the peak base switching circuit SW is connected to the b side and outputs the base current setting signal Ib as the current control setting signal Isc. The current error amplifier circuit EI amplifies an error between the output current detection signal Id that is a feedback signal and the current control setting signal Isc that is a target value, and outputs the amplified current error signal Ei.

  The triangular wave generation circuit OSC outputs a triangular wave with a high frequency shown in FIG. 3B when the pulse period signal Tf becomes Low level. The pulse width modulation control circuit PWM compares the current error amplification signal Ei and the triangular wave generation signal Osc, performs pulse width modulation control based on the result, and outputs an output control signal Sc (not shown). At this time, during the base current energization period Tb shown in FIG. 3C, the inverter frequency of the inverter circuit is increased, so that the output voltage is lowered as shown in FIG. 4 due to the influence of the inductance of the power cable or the like. However, since the high output voltage is not required during the base current energization period, there is no influence of the decrease in the output voltage. Furthermore, since the inverter frequency of the inverter circuit is increased, the current ripple of the output current is reduced and the arc during the base period becomes more stable. In addition, after time t = t3, the same operation as described above is repeated, and the description of the operation is omitted.

[Embodiment 2]
FIG. 5 is an electrical connection diagram of the power supply device according to the second embodiment. In FIG. 5, the same reference numerals as those in the electrical connection diagram of the power supply device for carrying out the output control method of the inverter control welding power source for pulse arc welding according to the first embodiment of the present invention shown in FIG. The description will be omitted and different operations will be described.

  The peak current corresponding output control circuit SCP is formed by a current error amplification circuit EI, a triangular wave generation circuit OSC, a pulse width modulation control circuit PWM, a comparison circuit CP, and a reference current setting circuit IR. The comparison circuit CP compares the current control setting signal Isc with the reference current setting signal Ir output from the reference current setting circuit IR, and compares the current control setting signal Isc with the reference current setting signal Ir. The signal Cp is set to High level, and when it is small, it is set to Low level.

  The triangular wave generation circuit OSC outputs a triangular wave having a low frequency when the pulse period signal Tf and the comparison signal Cp are at a high level, and outputs a triangular wave having a high frequency when the pulse period signal Tf or the comparison signal Cp is at a low level. To do.

  At time t = t1 shown in FIG. 6, when the pulse cycle signal Tf becomes High level, the peak base switching circuit SW is connected to the a side and outputs the peak current setting signal Ip as the current control setting signal Isc. The current error amplifier circuit EI amplifies an error between the output current detection signal Id that is a feedback signal and the current control setting signal Isc that is a target value, and outputs the amplified current error signal Ei. The comparison circuit CP compares the current control setting signal Isc and the reference current setting signal Ir, and sets the comparison signal Cp to the high level because the current control setting signal Isc is larger than the reference current setting signal Ir. The triangular wave generation circuit OSC outputs a triangular wave having a low frequency when the pulse period signal Tf and the comparison signal Cp are at a high level. At this time, during the peak current energizing time Tp shown in FIG. 6C, the inverter frequency of the inverter circuit is lowered, so that the output voltage is high as shown in FIG. 4 due to the influence of each inductance such as the power cable. Voltage drop can be improved.

  At time t = t2, when the pulse cycle signal Tf becomes low level, the peak base switching circuit SW is connected to the b side and outputs the base current setting signal Ib as the current control setting signal Isc. The comparison circuit CP compares the current control setting signal Isc with the reference current setting signal Ir, and sets the comparison signal Cp to the low level because the current control setting signal Isc is smaller than the reference current setting signal Ir. The triangular wave generation circuit OSC outputs a high-frequency triangular wave when the pulse period signal Tf and the comparison signal Cp are at a low level.

At time t = t3, when the pulse period signal Tf becomes High level again, the peak base switching circuit SW is connected to the a side and outputs the peak current setting signal Ip as the current control setting signal Isc. At this time, the comparison circuit CP compares the current control setting signal Isc with the reference current setting signal Ir, and sets the comparison signal Cp to the low level because the current control setting signal Isc is smaller than the reference current setting signal Ir. The triangular wave generation circuit OSC outputs a triangular wave having a high frequency when the comparison signal Cp becomes a low level.

  By the way, the prior art document 1 discloses a technique for reducing the high-frequency vibration due to the ripple component of the output current by stably controlling the inverter current by lowering the inverter frequency during the short circuit period. There is no disclosure of a technique for increasing the output voltage on the secondary side of the main transformer by lowering the inverter frequency of the inverter circuit during the peak current conduction period. Further, of course, a technique for switching the inverter frequency to a predetermined frequency during the energization period of the peak current and the energization period of the base current is not disclosed.

It is an electrical connection diagram of the power supply device for implementing the output control method of the inverter control welding power supply for pulse arc welding of Embodiment 1 of this invention. FIG. 2 is a detailed diagram of an output control circuit SC shown in FIG. FIG. 2 is a timing diagram illustrating an operation of the power supply device illustrated in FIG. 1. The external characteristic of the power supply device shown in FIG. 1 is shown. FIG. 6 is an electrical connection diagram of a power supply device according to a second embodiment. FIG. 6 is a detailed diagram of the output control circuit SC shown in FIG. 5. FIG. 6 is an electrical connection diagram of a power supply device for carrying out an output control method of an inverter-controlled welding power supply for pulse arc welding of the prior art.

Explanation of symbols

EI Current error amplifier circuit EV Voltage error amplifier circuit IB Base current setting circuit ID Output current detection circuit IP Peak current setting circuit M Workpiece MM Mono multivibrator OSC Triangle wave generation circuit PS Inverter type main power supply circuit PWM Pulse width modulation control circuit SC Output control circuit SCP Peak current corresponding output control circuit SW Peak base switching circuit TH Welding torch TP Peak current energizing time setting circuit VD Output voltage detection circuit VF V / F conversion circuit VS Voltage setting circuit WC Feed control circuit WR Wire feed device WS Feeding speed setting circuit Ei Current error amplification signal Ev Voltage error amplification signal Ib Base current setting signal Id Output current detection signal Isc Current control setting signal Ip Peak current setting signal Osc Triangular wave generation signal Sc Output control signal Tf Pulse cycle signal Tb Base Current conduction time Tp Peak current conduction time setting signal Vd Output voltage detection signal Vf V / F conversion signal Vs Voltage setting signal Wc Feed control signal Ws Feed speed setting signal

Claims (1)

Pulse arc welding that uses an inverter-controlled welding power source that controls output by pulse width modulation control at a predetermined inverter frequency, and performs pulse arc welding with a welding current consisting of energization of peak current and base current to the consumable electrode In an inverter control welding power supply output control method for
The peak current and the base current are alternately energized at a predetermined cycle according to a current control set value, the current control set value is compared with a reference current set value, and the current control set value is the reference current set value. When the value is equal to or higher than the value, the inverter frequency during the peak current conduction period is set to a predetermined low triangular wave frequency,
Inverter for pulse arc welding, wherein when the current control set value is less than the reference current set value, the inverter frequency of the peak current energizing period and the base current energizing period is set to a predetermined high triangular wave frequency Control welding power supply output control method.

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