JPH0768385A - Plasma arc power supply - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent the generation of plasma arc even when the torch is brought close to the base metal while the pilot arc is generated. [Structure] A rectifier 2 and a capacitor 3 rectify and smooth an alternating current, and an inverter 6 converts the direct current voltage into an alternating current, which is transformed by a transformer 70 and rectified by a rectifier 8. Rectifier 8 to opening / closing means 11, high frequency generator 16, nozzle electrode 19, main electrode 18, current detector
12, current flows to the reactor 9, nozzle electrode 19, main electrode
A pilot arc is generated between 18. The error amplifier 13 obtains the difference between the detection output of the detector 12 and the reference signal of the reference power supply 15,
As a result, the driving device 14 controls the inverter 6 to bring the current to a desired value. A circuit from the rectifier 8 to the thyristor 10, the base material 17, the main electrode 18, the detector 12 and the reactor 9 is provided, and when the thyristor 10 is off when the pilot arc is generated, no plasma arc is generated and the thyristor 10 is on. Then, a plasma arc is generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for plasma arc welding and cutting, and more particularly to starting up a power supply device.

[0002]

2. Description of the Related Art Generally, a plasma arc power supply device has
In order to reduce the size and weight, the AC power supply is rectified, smoothed and converted to DC, and then this DC is converted into high frequency AC by an inverter that switches switching elements such as IGBTs and transistors at high frequency, and this high frequency AC is transformed. There is a method in which a direct current obtained by rectifying and smoothing again after voltage transformation is supplied between the nozzle electrode of the plasma load and the base material.
In addition, by detecting the output current supplied to this plasma load,
Constant current control is also performed so that the output current has a constant value.

An example of such a plasma arc power supply device is shown in FIG. This plasma arc power supply device has a DC power supply device 4 to which a DC voltage obtained by rectifying the AC power supplied to the input terminal 1 by the rectifier 2 and smoothing it by the smoothing capacitor 3 is input.

This DC power supply device 4 has an inverter 6 provided with a switching element such as an IGBT or a transistor, and this inverter 6 converts the DC voltage from the smoothing capacitor 3 into a high frequency alternating current. Is applied to the primary winding 7a of the transformer 7. The transformer 7 also has a secondary winding 7b and a tertiary winding 7c, and the high-frequency alternating current induced in the secondary winding 7b is rectified by the rectifier 8a, and the smoothing reactor 9a to the base material 17 and the main electrode 18 are provided. Applied to. Further, the high frequency alternating current induced in the tertiary winding 7c of the transformer 7 is rectified by the rectifier 8p, smoothed by the smoothing reactor 9p, and then opened / closed.
1. Applied to the main electrode 18 and the nozzle electrode 19 via the high frequency generator 16.

A current detector 12 is provided so as to detect a current flowing between the main electrode 18 and the base material 17, or a current flowing between the main electrode 18 and the nozzle electrode 19, and this current detector 12 is provided. Output current is supplied to the error amplifier 13. A reference signal is also supplied from the reference power supply 15 to the error amplifier 13. The error amplifier 13 outputs the difference between the output signal of the current detector 12 and the reference signal, and supplies it to the drive device 14. The driving device 14 controls the inverter 6 so that the current detected by the current detector 12 becomes equal to the reference signal.

Now, it is assumed that the opening / closing means 11 and the high frequency generator 16 are in a non-operating state, the gap between the main electrode 18 and the base material 17 is large, and the gap between the main electrode 18 and the nozzle electrode 19 is small.

In this state, the direct current from the capacitor 3 is converted into high frequency alternating current by the inverter 6, and the transformer 7
High-frequency alternating current is induced in the secondary winding 7b and the tertiary winding 7c. These high-frequency alternating currents are rectified by the rectifiers 8a and 8p and smoothed by the smoothing reactors 9a and 9p.

The direct current from the smoothing reactor 9a is applied between the base material 17 and the main electrode 18, but no current flows because the gap between the main electrode 18 and the base material 17 is wide.

On the other hand, the direct current from the smoothing reactor 9p is applied between the main electrode 18 and the nozzle electrode 19 via the opening / closing means 11 and the high frequency generator 16, but the opening / closing means 11 is opened to generate a high frequency. Since the device 16 is inactive, no current flows between the main electrode 18 and the nozzle electrode 19. Therefore, no current flows in the current detector 12,
Its output is 0. At this time, since the reference signal supplied to the error amplifier 13 is larger than the output of the current detector 12, the output of the error amplifier 13 becomes maximum, and the drive device 14 causes the inverter 6 to generate the maximum output. The inverter 6 is controlled so that

In this state, when the opening / closing means 11 is closed and the high frequency generator 16 is operated, the main electrode 1
8 and a nozzle electrode 19 generate a pilot arc, and a pilot current flows between the main electrode 18 and the nozzle electrode 19. However, since the gap between the main electrode 18 and the base material 17 is large, the main electrode 18 and the base material 19 are large. A plasma arc does not occur between the device 17 and 17, and a plasma current does not flow.

The fact that the pilot current has flown is detected by the current detector 12 and supplied to the error amplifier 13. The error amplifier 13 outputs the difference between the output signal of the current detector 12 and the reference signal, and the drive unit 14 drives the inverter 6 so that the current detected by the current detector 12, that is, the pilot current, becomes equal to the reference signal. To control.

When the torch including the main electrode 18 and the nozzle electrode 19 is brought close to the base material 17 in the state where the pilot arc is generated as described above, a current flows from the rectifier 8a and the reactor 9a to the main electrode 18 and the base material 17. Flows and a plasma arc is generated.

When the plasma arc is generated, the pilot arc is still generated as it is because the loss is large. Therefore, the opening / closing means 11 is opened to extinguish the pilot arc.

[0014]

In such a plasma arc power supply device, a plasma arc is generated immediately when the torch is brought close to the base material in the state where the pilot arc is generated. However, it may be necessary to test drive the torch or position the torch with the pilot arc generated.In such a case, the plasma arc is generated even if the torch is brought close to the base metal. It is desirable not to.

Further, in such a plasma arc power supply device, in order to generate a pilot arc by applying a high no-load voltage between the nozzle electrode 19 and the main electrode 18 at the time of starting, a tertiary winding 7c, a rectifier 8p and a smoothing reactor 9p are provided. Therefore, using the inverter 6,
Despite the miniaturization, the overall size of the device could not be miniaturized, and there was a loss, resulting in low efficiency.

[0016]

In order to solve the above problems, the present invention provides a direct current generating means for converting a direct current power source into an alternating current by an inverter and rectifying and smoothing the alternating current to generate a direct current voltage, and a direct current generating means. Current detection means for detecting the output current of the DC generation means, and control for controlling the inverter based on the difference between the output signal of the current detection means and a preset reference signal to control the output current to a constant value. Means and
Between the direct current generating means, a pilot arc generating means provided in a transmission line extending between the main electrode of the plasma load and the nozzle electrode, and between the direct current generating means and the base material of the plasma load and the main electrode. And a switching means interposed in the transmission line extending to the base plate and generating a plasma arc between the base material and the main electrode in the closed state.

[0017]

According to the present invention, assuming that the pilot arc generating means is in the non-operating state, the switching means is in the open state, and the gap between the nozzle electrode and the main electrode and the base material is large, In this state, even if the DC generating means is operated, the plasma arc is not generated because the switching means is opened. Here, when the pilot arc generating means is actuated, a pilot arc is generated between the main electrode and the nozzle electrode, a current due to the pilot arc flows through the current detector, and the control means drives the inverter so that this becomes a desired value. Control.

In this state, the nozzle electrode and the main electrode are brought close to the base material to reduce the gap between them. In this state, since the switching means is open, no plasma arc is generated. At this time, when the switching means is closed, a plasma arc is generated between the main electrode and the base material, and the control means controls the inverter so that the plasma arc has a desired value.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment of Plasma Arc Power Supply Device According to the Present Invention
Examples of the above are shown in FIGS. 1 and 2. This embodiment is also shown in FIG.
DC power supply 4 as well as the conventional plasma arc power supply device of
Since A is used, the same reference numerals are given to the same portions and the description thereof will be omitted.

The DC power supply device 4A has an inverter 6, a current detector 12, an error amplifier 13, and a drive device 14 as in the conventional DC power supply device 4, but the high frequency AC converted by the inverter 6 is The applied transformer 70 has only the secondary winding 70b other than the primary winding 70a.

The rectifier 8 is connected to the secondary winding 70b. One output side of the rectifier 8 is connected to the nozzle electrode 19 via the opening / closing means 11 and the high frequency generator 16, and the other output side is the smoothing reactor 9 and the current detector 1.
It is connected to the main electrode 18 via 2.

Further, one output side of the rectifier 8 is connected to the base material 17 via the thyristor 10. The thyristor 10 is connected to a polarity in which a current flows from one output side of the rectifier 8 to the base material 17 side. The thyristor 10 is turned on by the gate signal from the drive circuit 21, and the drive circuit 21 is configured to generate the gate signal by operating the plasma starting device 22 such as a switch.

The plasma arc power supply device configured as described above operates as follows. Now, the opening / closing means 11 is opened, the high-frequency generator 16 is inactive, the thyristor 10 is also off, the main electrode 18, the nozzle electrode 1
9 and the base material 17 have a large gap, and the main electrode 18 and the nozzle electrode 19 have a small gap.

In this state, when the drive unit 14 is started at time T1 shown in FIG. 2A, the inverter 6 starts operating as shown in FIG. 2B, and the secondary side of the transformer 70 is started. A high frequency alternating current is induced in the winding 70b. This high frequency alternating current is rectified by the rectifier 8. However, since the thyristor 10 is off, the base material 17 and the main electrode 18 are
Is not applied between the base material 17 and the main electrode 18, and no current flows between the base material 17 and the main electrode 18. Also, the opening / closing means 11 is in the open state,
Since the high frequency generator 16 is inactive, the main electrode 1
8. No current flows between the nozzle electrodes 19.

At this time, the opening / closing means 11 is open, the high frequency generator 16 is inactive, and the thyristor 1
Since 0 is off, no current flows through the current detector 12, and its output is 0. At this time, the error amplifier 13
Since the reference signal supplied from the reference power source 15 is larger than the detection signal of the current detector 12, the output of the error amplifier 13 becomes maximum, and the drive device 14 generates the maximum output of the inverter 6. To control.

As shown in FIG. 2 (c), when the high frequency generator 16 is activated at time T2 and the opening / closing means 11 is turned on, the gap between the main electrode 18 and the nozzle electrode 19 is small, so both A pilot arc is generated between them, and the pilot arc current causes the main electrode 18 and the nozzle electrode 1
It flows between 9. However, since the thyristor 10 is off, the plasma current does not flow.

In this state, when the torch composed of the main electrode 18 and the nozzle electrode 19 is brought closer to the base material 17, the gap between the torch and the base material 17 becomes smaller. However, since the thyristor 10 is off, the plasma current does not flow. In this state, when the plasma starting device 22 is operated at time T3 as shown in FIG.
As shown in, the thyristor 10 is turned on. At this time,
Since the pilot arc has already been generated, the rectifier 8 is connected to the base material 17, the main electrode 18, and the smoothing reactor 9 as shown in FIG.
As shown in (f), a plasma arc current flows and a plasma arc is generated.

When a plasma arc is generated in this way,
The opening / closing means 11 is turned off to extinguish the pilot arc.

In the above embodiment, when the pilot arc current is flowing, the output current of the inverter 6 is detected by the current detector 12, the error between the detected output and the reference signal is amplified by the error amplifier 13, and The error signal is supplied to the driving device 14, and the driving device 14 configures feedback control for controlling the inverter 6, and the output voltage of the inverter 6 becomes lower than the output voltage of the inverter 6 when there is no load. Even if it is turned on, it may be difficult to start. Further, the AC power supply supplied to the input terminal 1 may be two systems, a low voltage system (for example, 200 V) and a high voltage system (for example, 400 V). In order to cope with such a case, it is necessary to use a high withstand voltage switching element for the inverter 6.

The second embodiment shown in FIG. 3 solves the above problem. This embodiment has the same DC power supply device 4A as that of the first embodiment, and further has a DC power supply device 5. The DC power supply device 5 includes an inverter 26, a drive device 34, a transformer 27, a rectifier 28, a reactor 29, a current detector 32, an error amplifier 33, and a thyristor 30. Further, a drive circuit 51 for the thyristor 30 and a plasma starting device 52 are also provided. These are the inverter 6, the driving device 14, the transformer 70, the rectifier 8, the reactor 9, the current detector 12, the error amplifier 13,
Thyristor 10, drive circuit 21, plasma starter 22
Respectively correspond to. However, DC power supply 5
In FIG. 1, the opening / closing means 11 and the high frequency generator 16 are not provided.

Further, instead of the capacitor 3, capacitors 3A and 3B are provided, and these capacitors 3A and 3B are provided.
3B is connected to the input side of the inverters 6 and 26. Further, in the capacitors 3A and 3B, for example, when the voltage applied to the input terminal 1 is a high voltage system (for example, 400 V), the switching contact 23a of the switching means 23 is closed and the contacts 23b and 23c are opened. Are connected in series with each other, and the voltage rectified by the rectifier 2 is applied to the series capacitors 3A and 3B.
The voltage shared by 3B is supplied to the inverters 6 and 26. When the voltage applied to the input terminal 1 is a low voltage system (for example, 200V), the capacitors 3A and 3B are connected.
The switching contacts 23b and 23c of the switching means 23 are closed,
When the contact 23a is opened, they are connected in parallel,
The voltage rectified by the rectifier 2 is the capacitor 3A,
3B in parallel, and these are respectively supplied to the inverters 6 and 26.

Further, the DC power supply devices 4A and 5 supply the reference signals corresponding to them to the error amplifiers 13 and 33 during series operation by the series-parallel operation control device 41, and to the reference signals corresponding thereto during parallel operation. Is supplied to the error amplifiers 13 and 33. The series-parallel operation control device 41 is also provided with a command power supply 42 and a command terminal 43.

The plasma arc power supply device configured as described above operates as follows. Now, the opening / closing means 11 is in an open state, the high frequency generator 16 is in an inactive state, and the thyristor 1
0 is an off state, and the main electrode 18, the gap 19 and the base material 17
Is large, the gap between the main electrode 18 and the nozzle electrode 19 is small, and the reference signal is supplied only from the series-parallel operation control device 41 to the error amplifier 13.

The direct current from the capacitor 3A is converted into a high frequency alternating current by the inverter 6, and the secondary winding 70 of the transformer 70 is converted.
A high frequency alternating current is induced in b. This high-frequency alternating current is rectified by the rectifier 8, but since both the thyristor 10 and the opening / closing means 11 are off, the high-frequency alternating current is applied between the main electrode 18 and the base material 17, and between the main electrode 18 and the nozzle electrode 19. Is not applied.

Therefore, no current flows through the current detector 12 and its output is zero. At this time, since the reference signal supplied to the error amplifier 13 is larger than the output of the current detector 12, the output of the error amplifier 13 becomes maximum, and the driving device 14 controls the inverter 6 to generate the maximum output. To do.

In this state, when the high frequency generator 16 is operated and the opening / closing means 11 is turned on, an arc is generated between the main electrode 18 and the nozzle electrode 19 because the gap between the main electrode 18 and the nozzle electrode 19 is small. Current is the main electrode 1
8, flowing between the nozzle electrodes 19. However, thyristor 1
Since the gate signal is not supplied to 0, no plasma arc is generated between the main electrode 18 and the base material 17, and no plasma current flows.

The fact that the pilot arc current has flowed is detected by the current detector 12 and supplied to the error amplifier 13. The error amplifier 13 outputs the difference between the output signal of the current detector 12 and the reference signal, and the drive unit 14 drives the inverter 6 so that the current detected by the current detector 12, that is, the pilot arc current, becomes equal to the reference signal. To control. Since the control is performed in this manner, the output voltage of the inverter 6 is lower than the output voltage (no-load voltage) before the pilot arc current flows.

On the other hand, in the DC power supply 5, the DC from the capacitor 3B is converted into high frequency AC by the inverter 26, transformed by the transformer 27, and rectified by the rectifier 28. However, since the thyristor 30 is in the off state, no voltage is applied between the main electrode 18 and the nozzle electrode 19. At this time, since the error amplifier 33 is not supplied with the reference signal, the feedback system is not formed, and the drive device 34 controls the inverter 26 to generate its maximum output voltage. Therefore, the rectifier 28 is generating the maximum output voltage (no-load voltage).

In this state, when the torch including the main electrode 18 and the nozzle electrode 19 is brought closer to the base material 17, the gap between the torch and the base material 17 becomes smaller. When the thyristors 10 and 30 are turned on, the gap between the torch and the base material 17 is small, a pilot arc has already occurred, and the output voltage of the DC power supply device 5 is high. A current flows from the base material 17, the main electrode 18, and the smoothing reactor 29 to generate a plasma arc.

When a plasma arc is generated in this way,
The opening / closing means 11 is opened to extinguish the pilot arc.

Then, the series-parallel operation command signal is input to the command terminal 43 of the series-parallel operation controller 41, and the series signals are supplied from the series-parallel operation controller 41 to the error amplifiers 13 and 33, respectively. As a result, plasma current also flows through the rectifier 8, the diode 10, the base material 17, the main electrode 18, and the smoothing reactor 9 of the DC power supply device 4A. In this way, the plasma current also flows through both the DC power supply devices 4A and 5, and the error amplifiers 13 and 33 and the driving devices 14 and 34 include the inverter 6 and the inverter 6 so that the plasma currents have the desired values represented by the reference signals. 26 to control the DC power supply devices 4A, 5
Are operated in parallel or in series.

In each of the above embodiments, when a pilot arc is generated between the main electrode 18 and the nozzle electrode 19 and when a plasma arc is generated between the main electrode 18 and the base material 17, Although the smoothing reactor 9 is provided at a position where the current can be smoothed, the smoothing reactor 9 is provided between one output side of the rectifier 8 and the switching means 11 and between one output side of the rectifier 8 and the thyristor 10, respectively. A smoothing reactor may be provided. Although the thyristor 10 is used in both of the above-mentioned embodiments, other switching elements such as a relay and a transistor may be used. Further, in the second embodiment, two DC power supply devices 4A and 5 are provided,
A plurality of devices having the same configuration as the DC power supply device 5 may be added for serial / parallel operation. Further, in the second embodiment, the thyristors 10 and 3 are provided for each of the DC power supply devices 4A and 5.
Although 0 is provided, only one thyristor may be provided at the position shown by the dotted line in FIG. Also, in the second embodiment,
Although the thyristors 10 and 30 are turned on at the same time, the thyristor 30 connected to the DC power supply 5 may be turned on first and the DC power supplies 4a and 5 may be turned on during parallel operation.

[0043]

As described above, according to the first and second inventions, the switching means is interposed in the transmission path extending from the direct current generating means to the base material of the plasma load and the main electrode. So, with the pilot arc occurring,
Even if the torch is brought close to the base material, the plasma arc does not occur as long as the switching means is opened. Therefore, the test run and the torch can be easily positioned in the state where the pilot arc is generated. Further, according to the second aspect of the present invention, the switching means can switch between a state in which the voltage is applied in series from the direct current power source to each direct current generating means and a state in which the voltage is applied in parallel. Can be applied to both the case of applying a DC voltage and the case of applying a low-voltage DC voltage, and moreover, all the switching elements constituting the inverter of each DC generating means can have a low withstand voltage, which reduces the cost. It can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of a plasma arc DC power supply device according to the present invention.

FIG. 2 is an operation explanatory diagram of the first embodiment.

FIG. 3 is an operation explanatory diagram of the second embodiment.

FIG. 4 is a circuit diagram of a conventional plasma arc DC power supply device.

[Explanation of symbols]

 2 Rectifier (DC power supply) 3 3A, 3B Capacitor (DC power supply) 4A 5 DC power supply device 6 26 Inverter 8 28 Rectifier 10 30 Thyristor (switching means) 11 Switching means (pilot arc generating means) 16 High frequency generator (pilot arc generating) Means) 12 32 Current detector 13 33 Error amplifier (control means) 17 Base material 18 Main electrode 19 Nozzle electrode 23 Switching means 27 70 Transformer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Atsushi Kinoshita 2-14-3 Awaji, Higashiyodogawa-ku, Osaka City, Osaka Prefecture Sansha Electric Manufacturing Co., Ltd. (72) Inventor Kenzo Dangami 2-chome, Awaji, Higashiyodogawa-ku, Osaka City, Osaka Prefecture No.14-3 Sansha Electric Manufacturing Co., Ltd.

Claims (2)

[Claims] 1. A direct current generating means for converting a direct current power source into an alternating current by an inverter, rectifying and smoothing the alternating current to generate a direct current voltage, a current detecting means for detecting an output current of the direct current generating means, and a current detecting means of the current detecting means. Between the control means for controlling the output current to a constant value by controlling the inverter based on the difference between the output signal and the preset reference signal, and between the direct current generating means and the main electrode of the plasma load and the nozzle electrode. Pilot arc generating means provided in the extending transmission line, and interposed in the transmission line extending from the direct current generating means between the base material of the plasma load and the main electrode, and with the base material in the closed state. A plasma arc power supply device comprising: a switching means for generating a plasma arc between the main electrode and the main electrode. 2. A direct current generating means for converting a direct current power source into an alternating current by an inverter, rectifying and smoothing the alternating current to generate a direct current voltage, a current detecting means for detecting an output current of the direct current generating means, and a current detecting means of the current detecting means. Based on a difference between the output signal and a preset reference signal, a plurality of DC power supply devices including a control means for controlling the inverter to control the output current to a constant value, a base material of a plasma load and a main material. In a plasma arc power supply device for supplying a plasma arc current to an electrode, the plasma arc power supply device is provided in a transmission path extending from at least one of the DC power generating devices to the base material and the main electrode. Between the base material and the main electrode from the direct current generating means of the direct current power supply device which does not have the means for generating the pilot arc and at least the pilot arc. A DC power supply provided between the DC power supply and the DC generation means, and a switching means that is interposed in a transmission line extending between the DC power supply and the main electrode in the closed state to generate a plasma arc between the base material and the main electrode. A plasma arc power supply device comprising: switching means for switching the voltage from the DC power generating means to a state in which the voltage is applied in series to each of the DC generating means.