JPH0544681B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an arc power supply device used for high frequency TIG welding, plasma arc welding, plasma arc cutting, etc.

[Conventional technology]

Generally, an arc power supply device used for arc welding, arc cutting, etc. is configured as shown in FIG. 3, for example. In the figure, 1 is a connection terminal connected to a commercial power supply, 2 is a transformer whose primary side is connected to terminal 1, and 3 is a rectifier circuit consisting of a diode bridge rectifier circuit, etc. connected to the secondary side of transformer 2. , 4 is a smoothing capacitor connected in parallel to the rectifier circuit 3, 5 is an NPN type transistor whose collector is connected to the positive output terminal of the rectifier circuit 3, and 6 is a smoothing capacitor connected in parallel to the rectifier circuit 3.
is the base material connected to the emitter of transistor 5,
7 is an electrode such as a torch connected to the negative output terminal of the rectifier circuit 3, and the base material 6 and the electrode 7 constitute a load 8.

9 is a starter circuit provided in the current-carrying path between the electrode 7 and the negative output terminal of the rectifier circuit 3 and applies a high frequency high voltage to the load 8 at the time of arc start; A current detector 11 detects a flowing load current and outputs a voltage detection signal proportional to the detected current, and the anode 11 is connected to the negative output terminal of the rectifier circuit 3 and transfers energy due to the inductance of the connecting cable of the electrode 7 to the load 8. 12 is a current-limiting resistor whose both ends are connected to the cathode of diode 11 and the base material 6, 13 is a control circuit whose power supply terminal is connected to terminal 1, and both input terminals are current detectors. 1
0 detection signal output terminal and the reference power supply 14, and its output terminal is connected to the base of the transistor 5, and outputs a switching pulse to the transistor 5 so that the voltage of the detection signal becomes equal to the voltage of the reference power supply 14. Next, the pulse width of the switching pulse to transistor 5 is controlled.

When the commercial power is turned on, the control circuit 13 is activated and outputs a high-level switching pulse as shown in FIG. Direct current obtained by rectification and smoothing by the circuit 3 and capacitor 4 is converted into alternating current by the transistor 5, and the alternating current power is supplied to the load 8.

At this time, there is a delay in the rise and fall of the load current flowing through the load 8 due to the inductance of the connection cable of the electrode 7, and the ON period of the transistor 5, that is, the high level period of the switching pulse shown in FIG. The load current gradually increases as shown in figure b, and during the off period of transistor 5, that is, the low level period of the switching pulse, the load current gradually decreases, and the waveform of the load current becomes as shown in figure b. It becomes serrated.

Next, after the commercial power is turned on, the starter circuit 9 is activated, and the high frequency high voltage generated by the starter circuit 9 is superimposed on the AC voltage generated by the switching of the transistor 5 as described above, and is applied to the load 8. The insulation between 6 is broken and an arc starts.
After the arc starts, the starter circuit 9 stops operating.
Only the AC voltage generated by switching the transistor 5 is applied to the load 8 to maintain the arc, and the control circuit 13 controls the load current flowing through the load 8 to be constant.

Note that during the off-period of the transistor 5, the accumulated energy due to the inductance of the connecting cable of the electrode 7 is circulated to the load 8 via the diode 11 and the resistor 12.

On the other hand, the arc restraint force increases as the load current flowing through the load 8 increases, and furthermore, as shown in Fig. 5, the higher the frequency of the load current, the greater the arc restraint force becomes. This has made it possible to perform good welding and cutting, and the frequency of the load current is usually set to several tens of kilohertz.

By the way, since the connecting cable of the electrode 7 is set to be relatively long, the inductance of the connecting cable becomes large, and as a result, the current ripple of the load current decreases, causing deterioration of arc concentration. The first measure is to place the power supply and the load 8 as close as possible to reduce the inductance of the connection cable for the electrode 7, the second measure is to set the secondary voltage of the transformer 2 high, and the third measure is to increase the resistance. Efforts have been made to increase the ripple of the load current by increasing the resistance value of the resistor 12.

[Problem that the invention seeks to solve]

However, in the case of the first measure, the connecting cable of the electrode 7 cannot be shortened beyond a certain point in practice, and there is a limit;
In order to increase the secondary voltage of the transformer 2, the size of the transformer 2 becomes large, leading to an increase in the size of the entire device.
In the case of the third measure, the current ripple becomes larger and the concentration of the arc improves, but on the other hand, the transistor 5
The problem is that the surge voltage applied to the transistor 5 increases, causing damage to the transistor 5, requiring the use of a transistor 5 with a high withstand voltage, which increases the cost.

Therefore, the technical object of the present invention is to maintain the current ripple of the load current in a large state to prevent a decrease in arc concentration and protect the auxiliary switching element.

[Means for solving problems]

This invention has been made with the above-mentioned points in mind, and includes an input rectifier circuit connected to an AC power source, a main switching element and an output transformer, and connected to both output terminals of the input rectifier circuit. a high-frequency inverter; a control circuit that outputs switching pulses to the control terminal of the main switching element to control the output of the inverter; an output rectifier circuit connected to the secondary side of the output transformer; A load connected to both output terminals of a rectifier circuit, an auxiliary switching element provided in a current-carrying path between the output side rectifier circuit and the load, and a switching element of the auxiliary switching element in synchronization with a switching pulse of the control circuit. This is an arc power supply device characterized by comprising a drive circuit that outputs a switching pulse to a control terminal, and a surge absorbing capacitor provided in parallel with the auxiliary switching element.

[Effect]

Therefore, according to the present invention, the main switching element is switched by the switching pulse from the control circuit to drive the high frequency inverter, and the output DC of the input side rectifier circuit is converted to high frequency by the high frequency inverter, and the output from the control circuit is The auxiliary switching element is switched by the switching pulse output from the drive circuit in synchronization with the switching pulse, and the high frequency generated by the inverter is rectified by the output rectifier circuit, and the resulting DC is converted back into AC by the auxiliary switching element. AC power is supplied to the load.

At this time, when the auxiliary switching element is turned off,
Although the voltage of stored energy due to the inductance of the load connection cable is applied to the auxiliary switching element as a surge voltage, the surge voltage is absorbed by the surge absorbing capacitor and damage to the auxiliary switching element is prevented.

〔Example〕

Next, the present invention will be explained in detail with reference to FIGS. 1 and 2 showing one embodiment thereof.

In Figure 1, 15a, 15b, 15c are 3
1st to 3rd connected to a phase AC power supply (not shown)
Terminals, 16, each input terminal is the first to third terminals 15a
~15c is an input side rectifier circuit consisting of a three-phase diode bridge rectifier circuit connected to 15c, 17 and 18 are two smoothing capacitors connected in series between the positive and negative output terminals of the rectifier circuit 16, and 19 is a collector a first NPN transistor 20 as a main switching element connected to the positive output terminal of the rectifier circuit 16;
is an NPN type second transistor as a main switching element whose collector and emitter are connected to the emitter of the first transistor 19 and the negative output terminal of the rectifier circuit 16, 21 is an output transformer, and both ends of the primary winding 21a are connected to the It is connected to the emitter of one transistor 19 and the connection point of both capacitors 17 and 18, and a high frequency inverter 22 is constituted by both transistors 19 and 20 and an output transformer 21.

23 and 24 are first and second diodes whose anodes are connected to both ends of the secondary winding 21b of the transformer 21 and whose cathodes are connected to each other to form the output rectifier circuit 25; 26 is an emitter connected to the middle of the secondary winding 21b; A third NPN type transistor as an auxiliary switching element connected to tap t, 27 a base material connected to the cathode of the first diode 23, 28
is an electrode connected to the collector of the third transistor 26, and the base material 27 and the electrode 28 constitute a load 29.

30 is a starter circuit provided in the current-carrying path between the electrode 28 and the collector of the third transistor 26 and applies a high frequency high voltage to the load 29 at the time of arc start; 31 is a starter circuit provided in the current-carrying path to the load 29;
A current detector 32 detects the load current flowing through 9 and outputs a voltage detection signal proportional to the detected current, and 32 has an anode connected to the collector of the third transistor 26 and loads energy due to the inductance of the connecting cable of the electrode 28. 29 is a third flywheel diode that circulates current; 33 is a high-resistance current-limiting resistor whose both ends are connected to the cathode of the third diode 32 and the base material 27; 34 is a control circuit; 3 terminals 15b and 15c, both input terminals are connected to the detection signal output terminal of the current detector 31 and the reference power supply 35, and the output terminals are connected to the bases of the first and second transistors 19 and 20. Number K alternately on 19 and 20
A switching pulse of Hz to several tens of kHz is output, and the pulse width of the switching pulse to both transistors 19 and 20 is controlled so that the voltage of the detection signal becomes equal to the voltage of the reference power supply 35. Note that a synchronization pulse obtained by combining the switching pulses to both transistors 19 and 20 is output from the synchronization pulse output terminal of the control circuit 34.

36 is a drive circuit whose synchronous pulse input terminal is connected to the synchronous pulse output terminal of the control circuit 34 and which outputs a switching pulse to the base, which is the control terminal of the third transistor 26, in synchronization with the synchronous pulse; 37 is a primary drive circuit; an auxiliary transformer, 3, in which both ends of the winding 37a are connected to the third and second terminals 15c, 15b;
8 is an anode, a fourth diode for rectification whose cathode is connected to one end of the secondary winding 37b of the transformer 37 and the cathode of the third diode 32, and 39 is a surge absorption capacitor, whose one end is connected to the cathode of the third diode 32. The other end is connected to the other end of the secondary winding 37b and the emitter of the third transistor 26, and a series circuit of the third diode 32 and the capacitor 39 is provided in parallel with the third transistor 26.

Next, the operation of the above embodiment will be explained.

Now, when the three-phase AC power is turned on, the control circuit 34 operates and the transistors 19 and 20 are connected to the second
High-level switching pulses as shown in Figures a and b are output, respectively, and the transistors 19,
20 are turned on alternately, and the three-phase alternating current of the power source is rectified and smoothed by the rectifier circuit 16 and both capacitors 17 and 18, and the resulting direct current is converted into alternating current of several KHz to several tens of KHz by the high frequency inverter 22. A high frequency AC voltage is induced on the secondary side of 21.

On the other hand, from the control circuit 34 to the drive circuit 36, the second
As shown in Figure c, a high-level synchronizing pulse that is a combination of both switching pulses a and b in the figure is input, and a switching pulse similar to the synchronizing pulse is output from the drive circuit 36 to the base of the transistor 26. , transistor 26 is transistor 1
9 and 20, the rectifier circuit 2
Direct current obtained by rectifying the high frequency secondary voltage of the transformer 21 by the transistor 5 is converted back into alternating current by the transistor 26, and AC power is supplied to the load 29.

At this time, as in the case of FIG. 3 described above, there is a delay in the rise and fall of the load current flowing through the load 29 due to the inductance of the connection cable of the electrode 28, and as shown in FIG. During the on period, the load current gradually increases, and during the off period of the transistor 26, the load current gradually decreases, and the waveform of the load current becomes a sawtooth waveform as shown in d of the figure.

In addition, at the time of arc start, the starter circuit 30 is activated and a high frequency high voltage is applied to the load 29 in a superimposed manner to perform the arc start. After the arc start, the control circuit 34 controls the load current flowing through the load 29 to be constant. What is controlled is the same as in the case of FIG. 3 described above.

Then, during the off period of the transistor 26 , the energy accumulated due to the inductance of the connecting cable of the electrode 28 is circulated to the load 29 via the diode 32 and the resistor 33 , and the surge voltage applied to the off-state transistor 26 is transferred via the diode 32 . The voltage is absorbed by the capacitor 39, and damage to the transistor 26 due to surge voltage is prevented.

At this time, the capacitor 39 is charged to a predetermined voltage via the transformer 37 and the diode 38, but when the surge voltage applied to the transistor 26 exceeds the predetermined voltage, a charging current is applied to the capacitor 39 via the diode 32. flows and the surge voltage is absorbed.

Therefore, by setting the charging voltage of the capacitor 39 by the transformer 37 and the diode 38 to the same level as the withstand voltage of the transistor 26, it is possible to exceed the withstand voltage of the transistor 26 without selecting a transistor with a high withstand voltage. The transistor 26 can be protected by absorbing the surge voltage by the capacitor 39.

In addition, since the high frequency inverter 22 was introduced,
It is now possible to set the secondary voltage of the small output transformer 21 high without using a large transformer as in the past, keeping the current ripple of the load current large and reducing arc concentration. It can be prevented.

Note that the third transistor 26 is replaced by the diode 23.
In this case, the diode 32 and the resistor 33 are exchanged and connected, and both ends of the capacitor 39 are connected to the cathode of the diode 23 and the anode of the exchanged diode 32. do it.

〔Effect of the invention〕

As described above, according to the arc power supply device of the present invention, the surge voltage applied to the auxiliary switching element provided in the energization path between the output side rectifier circuit and the load can be absorbed by the surge absorption capacitor, and the surge voltage flowing through the load can be absorbed by the surge absorption capacitor. It is possible to maintain the current ripple of the load current in a large state to prevent a decrease in arc concentration, and it is possible to protect the auxiliary switching element from damage due to surge voltage.

Further, by introducing a high frequency inverter, the output transformer can be made smaller, and the entire device can be made smaller.

[Brief explanation of drawings]

1 and 2 show one embodiment of the arc power supply device of the present invention, FIG. 1 is a wiring diagram, and FIG. 2 is a
~d are various signal waveform diagrams, Figure 3 and the following drawings show conventional examples, Figure 3 is a wiring diagram, Figures 4 a and b are various signal waveform diagrams, and Figure 5 shows the frequency of load current and arc. It is a relationship diagram with binding force. 16... Input side rectifier circuit, 19, 20... First and second transistors, 21... Output transformer,
22... High frequency inverter, 25... Output side rectifier circuit, 26... Third transistor, 29... Load, 34... Control circuit, 36... Drive circuit, 39
...Surge absorption capacitor.

Claims (1)

[Claims] 1. An input rectifier circuit connected to an AC power supply, a high-frequency inverter comprising a main switching element and an output transformer and connected to both output terminals of the input rectifier circuit, and control of the main switching element. a control circuit that outputs switching pulses to terminals to control the output of the inverter; an output rectifier circuit connected to the secondary side of the output transformer; and a control circuit connected to both output terminals of the output rectifier circuit. a load; an auxiliary switching element provided in a current-carrying path between the output side rectifier circuit and the load; and a drive for outputting a switching pulse to a control terminal of the auxiliary switching element in synchronization with a switching pulse of the control circuit. An arc power supply device comprising: a circuit; and a surge absorption capacitor provided in parallel with the auxiliary switching element.