JPH0719668Y2 - DC arc welder - Google Patents

Description

[Detailed description of the device]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC arc welding machine which converts an AC power supply into DC, converts it into a high frequency output by chopper control, converts it into DC again, and supplies this DC to a welding load.

[0002]

2. Description of the Related Art Conventionally, in a DC arc welding machine, in order to stabilize output and improve conversion efficiency against power fluctuations,
There is a method in which a direct current formed by transforming, rectifying, and smoothing an AC power source is converted into a high-frequency output by chopper control, and the high-frequency output is reconverted to a direct current and used for welding. A conventional DC arc welding machine adopting this chopper control is constructed as shown in FIG. 4, in which 1, 2, 3 are terminals of a three-phase AC power source, 4 is contacts 5, 6, 7 of each phase. Is a switch for turning on and closing the power supply, which is opened and closed in cooperation with each other. Reference numeral 8 is a transformer, and primary windings 9, 10, 11 and secondary windings 12, 13, 14 which are Δ-connected.
Have.

Reference numeral 15 denotes a diode rectifier for rectifying the secondary winding output of the transformer 8, which includes diodes 16, 17, ...
It consists of 21 full-wave bridge circuits. Reference numeral 22 is a smoothing capacitor, 23 is a switching transistor 24, a high frequency conversion chopper circuit composed of a control circuit 25 and a flywheel diode 26, 27 is a smoothing reactor as an output circuit, and 28 and 29 are welding load electrodes and mothers. A pair of output terminals to which materials are connected. Then, when the switch 4 is turned on, the three-phase AC power of the terminals 1, 2, 3 is supplied to the primary windings 9, 10, 11 of the transformer 8 via the switch 4.

Further, the secondary windings 12, 13, of the transformer 8 are
After the output of 14 is full-wave rectified by the rectifier 15, it is smoothed by the capacitor 22, and the direct current formed by this smoothing is supplied to the chopper circuit 23. At this time, the transistor 24 performs high-frequency switching at, for example, 20 to 60 KHz by the chopper control of the control circuit 25, and this switching converts DC to a high-frequency output at 20 to 60 KHz.

The high frequency output of the chopper circuit 23 is smoothed by the reactor 27 and returned to direct current, and this direct current is supplied to the welding load via the output terminals 28 and 29.
With this supply, a DC arc is generated and welding is performed.
The energy of the reactor 27 based on the switching of the transistor 24 from ON to OFF is supplied to the welding load via the diode 26.

By the way, in order to supply a sufficient DC power to the welding load, the capacitor 22 is set to a large capacity. Therefore, when the switch 4 is turned on and started, a large rush current flows from the rectifier 15 to the capacitor 22 immediately after the switch 4 is turned on, and the rectifier 15 is damaged.

Therefore, in parallel with the contacts 5, 6 and 7, series circuits of interlocking contacts 31, 32 and 33 of the switch 30 for starting and resistors 34, 35 and 36 for current limiting are connected respectively. At the time of activation, the switch 30 is closed before the switch 4 is closed.
2,33 are interlocked and the three-phase AC power supply is the switch 3
0, primary windings 9, 10, through resistors 34, 35, 36,
11 is supplied.

At this time, due to the current limiting action of the resistors 34, 35, 36, the rush current is suppressed and the capacitor 22 is suppressed.
Is initially charged and the rectifier 15 is protected from the rush current. Then, when the capacitor 22 is charged to some extent, the switch 4 is turned on, and thereafter, the three-phase AC power supply is directly supplied to the primary windings 9, 10, 11 via the switch 4.

When the switch 4 is turned on, the switch 3 is turned on.
0 is released.

[0010]

In the case of the conventional DC arc welding machine of FIG. 4, the switch 30 is provided to protect the rectifier 15 on the secondary side of the transformer 8 from the rush current at the time of starting.
And a large-capacity large-capacity resistor 34, 3 capable of withstanding rush current
Since it is necessary to attach 5, 36, there is a problem that the welding machine becomes large.

An object of the present invention is to prevent the rectifier on the secondary side of the transformer from being damaged by the rush current at the time of start-up without using a switch for start-up and a resistor for current limiting, and to reduce the size. .

[0012]

In order to achieve the above object, a DC arc welding machine according to the present invention comprises:
In the case of the above configuration, a transformer in which a primary winding is connected to a power-on switch, a thyristor rectifier that rectifies the secondary winding output of the transformer, and a switching transistor that smoothes the output of the rectifier A capacitor for supplying a high-frequency converting chopper circuit having a configuration, an output circuit for smoothing the high-frequency output of the chopper circuit and supplying it to a welding load, and an ignition for gradually increasing the conduction angle of the rectifier by closing the switch. And a circuit.

According to the second aspect of the invention, an AC thyristor circuit for power supply adjustment provided between the switch for turning on the power source and the primary winding of the transformer, and the secondary winding of the transformer. A diode rectifier that rectifies the output, a capacitor that smoothes the output of the rectifier and supplies the high-frequency conversion chopper circuit of a switching transistor configuration, and an output circuit that smooths the high-frequency output of the chopper circuit and supplies the welding load.
An ignition circuit for gradually increasing the conduction angle of the AC thyristor circuit when the switch is turned on.

[0014]

In the case of the DC arc welding machine of the present invention constructed as described above, the conventional starting switch and current limiting resistor are not provided, and the starting switch is immediately turned on at the time of starting. It Further, in the structure of claim 1, by controlling the ignition circuit, the conduction angle of the thyristor rectifier on the secondary side of the transformer gradually increases, the current flowing through the rectifier increases due to the soft start characteristic, and the capacitor increases. The inflow of rush current due to the initial charging of the rectifier is suppressed and damage to the rectifier is prevented.

Further, according to the second aspect of the present invention, the conduction angle of the AC thyristor circuit on the primary side of the transformer is gradually increased by the control of the ignition circuit and is supplied to the primary winding of the transformer. The current increases due to the soft start characteristic,
The rush current supplied to the secondary diode rectifier is suppressed, and damage to this rectifier is prevented.

[0016]

EXAMPLES Examples will be described with reference to FIGS. 1 to 3. (First Embodiment) First, the first embodiment will be described with reference to FIGS. In FIG. 1, the same reference numerals as those in FIG. 4 denote the same or corresponding ones.
Is a thyristor rectifier provided in place of the diode rectifier 15 shown in FIG. Reference numeral 37 is a firing circuit for controlling the firing phase of the thyristors 31, 32, 33.

It should be noted that the switch 30 for starting and the resistors 34, 35 and 36 shown in FIG. 4 are not provided. Then, at the time of start-up, the switch 4 is immediately turned on, and the three-phase AC power is supplied to the switch 4
Is directly supplied to the primary windings 9, 10, and 11 of the transformer 8 via.

Further, the ignition circuit 37 is activated by the three-phase AC power source via the switch 4, and the thyristors 31, 32, 33 are gradually changed in control angle from large to small, and the conduction angle is changed. An ignition signal is supplied which gradually increases the value from 0 to a set value or maximum value. Based on this supply, the energizing current of the rectifier 30 that rectifies the secondary winding output of the transformer 8 is
The soft start characteristic gradually increases and is suppressed to an extremely small capacity at the initial stage of startup.

Therefore, when the capacitor 22 is initially charged, the output of the rectifier 30 gradually increases with the soft start characteristic as shown in FIG. 2, and the rush current due to the initial charge is suppressed.

Therefore, the rectifier 30 can be protected from the rush current by using the thyristors 31, 32, 33 and the diodes 34, 35, 36 as the elements having the rated capacity required in the steady state. And the conventional switch 3 for starting
0, large capacity, large resistance 34, 35, 36 can be omitted, and the welding machine can be downsized.

(Second Embodiment) Next, a second embodiment will be described with reference to FIG. In FIG. 3, FIG.
The same reference numerals denote the same or corresponding ones, and 38 denotes an AC thyristor circuit provided between the switch 4 and the primary windings 8, 9, 10 of the transformer 8, and an AC thyristor 39 for each phase. , 40, 41. Reference numeral 42 is a firing circuit for controlling the firing phase of the AC thyristors 39, 40, 41. Also in the case of this embodiment, the switch 3 for starting shown in FIG.
0 and resistors 34, 35 and 36 are not provided.

The switch 4 is immediately turned on at the time of start-up, and the three-phase AC power is supplied to the AC thyristor circuit 38 and the ignition circuit 42 via the switch 4. At this time, the ignition circuit 42 activated by the power supply operates in the same manner as the ignition circuit 37 of FIG. 1, and outputs an ignition signal that gradually increases the conduction angle from 0 to a set value or a maximum value in the AC thyristor 39. ，
Supply to 40 and 41.

By this supply, the current supplied to the primary windings 9, 10, 11 of the transformer 8 via the AC thyristor circuit 38 is gradually increased, and the secondary winding output of the transformer 8 is soft-started. Will gradually increase.

Therefore, when the capacitor 22 is initially charged, the output of the rectifier 15 gradually increases,
The rush current based on the initial charge is suppressed, and the rectifier 15
Is protected from rush current. Further, the AC thyristor circuit 38 and the ignition circuit 42 are provided in place of the switch 30 for starting and the resistors 34, 35, 36 of FIG. 4, so that the welding machine is downsized.

[0025]

Since the present invention is constructed as described above, it has the following effects. First, in the case of the configuration of claim 1, the rectifier on the secondary side of the transformer 8 is the thyristor rectifier 30, and at the time of startup when the switch 4 for turning on the power is turned on, the conduction angle of the rectifier 30 is changed by the ignition circuit 37. Since it is gradually increased, the output of the rectifier 30 is gradually increased, and the rush current based on the initial charge of the capacitor 22 charged by this output is suppressed without adding a conventional switch for starting and a resistor for current limiting. Therefore, the small structure can prevent the rectifier 30 from being damaged by the rush current.

Further, in the case of the structure of claim 2, an AC thyristor circuit 38 is provided between the switch 4 for turning on the power source and the primary windings 9, 10, 11 of the transformer 8, and the switch 4 is turned on. At the time of starting, the AC thyristor circuit 38 is activated by the ignition circuit 42.
Since the conduction angle of the primary winding was gradually increased,
The current supplied to 11 gradually increases, the output of the diode rectifier 15 on the secondary side of the transformer 8 increases, and the rush current based on the initial charging of the capacitor 22 charged by this output is suppressed, The same effect as in the case of the configuration 1 is produced.

[Brief description of drawings]

FIG. 1 is a connection diagram of a first embodiment of a DC arc welding machine of the present invention.

FIG. 2 is an output characteristic diagram of the thyristor rectifier of FIG.

FIG. 3 is a connection diagram of a second embodiment of the present invention.

FIG. 4 is a connection diagram of a conventional example.

[Explanation of symbols]

 4 Switch for turning on power supply 8 Transformer 15 Diode rectifier 22 Capacitor 23 High frequency conversion chopper circuit 27 Reactor 30 Thyristor rectifier 37,42 Firing circuit 38 AC thyristor circuit

Claims (2)

[Scope of utility model registration request] 1. A transformer in which a primary winding is connected to a switch for turning on a power source, a thyristor rectifier for rectifying an output of a secondary winding of the transformer, and a switching transistor for smoothing the output of the rectifier. A capacitor for supplying a high-frequency converting chopper circuit having a configuration, an output circuit for smoothing a high-frequency output of the chopper circuit and supplying it to a welding load, and an ignition for gradually increasing the conduction angle of the rectifier by closing the switch. DC arc welder with circuit. 2. An AC thyristor circuit for adjusting power supply, which is provided between a switch for turning on a power source and a primary winding of a transformer, and a diode rectifier for rectifying an output of a secondary winding of the transformer. A capacitor for smoothing the output of the rectifier and supplying it to a high-frequency conversion chopper circuit of a switching transistor configuration, an output circuit for smoothing the high-frequency output of the chopper circuit and supplying it to a welding load, and the AC by closing the switch. A DC arc welding machine equipped with an ignition circuit that gradually increases the conduction angle of the thyristor circuit.