JPS61289975A - Welding power unit - Google Patents

Abstract

PURPOSE:To prevent the breakdown of the transistor forming an inverter by arranging a magnetoelectric converting element in the iron core of a transformer and by stopping totally or partially the motion of the inverter according to the output of the magnetoelectric converting element. CONSTITUTION:A DC deflected magnetism is generated on the iron core 3a of a transformer 3 by the unevenness in the property of the transistor 2a-2d forming an inverter 2. When it exceeds the prescribed value, the magnetic flux detected by the Hall element 21 inside the iron core 3a increases abnormally and the output amplified by an amplifier circuit 22 exceeds the prescribed value as well. Therefore when the magnetic flux inside the iron core 3a approaches the magnetic saturation and the output of the Hall element 21 amplified by the amplifier circuit 22 exceeds the output signal of a setter 23, the output to the inverter control circuit 6 is caused with actuation of a comparator 24. The inverter control circuit thus stops the motion of the inverter 2 and prevents the breakdown of the transistor 2a-2d.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a welding power source having an inverter for converting direct current to high frequency alternating current, and in particular to protection of transistors forming the inverter.

[Conventional technology]

FIG. 5 is a circuit diagram showing a conventional welding power source. In the figure, numeral 1 is a rectifier circuit that converts input AC into DC and outputs it, and 2 is an inverter to which the output of the rectifier circuit is supplied. The inverters are Tiger, Jistar 2a, 2b, 2c.
, 2d. The transistors 2m and 2b are connected in series, and the transistors 2C and 2d
are connected in series, and the series-connected transistors 2a and 2b and transistors 2c and 2d are connected in parallel. 3 is a transformer to which the output alternating current from the inverter 2 is supplied, 4 is a rectifier connected to the secondary side of the transformer and rectifies the alternating current from the transformer, and 5 is rectified by the rectifier. This is a reactor to which DC current is supplied. Reference numeral 6 denotes an inverter control circuit, which outputs a control signal to the inverter 2 described above.

Next, the operation will be explained. At the start of welding, a commercial frequency alternating current is rectified by the rectifier circuit 1, and the rectified direct current is converted into an alternating current by an inverter 2. This converted alternating current is input to the transformer 6, and is insulated and transformed by the transformer. This transformed alternating current is rectified by a rectifier 4 and converted into direct current again, and this converted direct current is smoothed by an axle 5 and output as a power supply current for welding.

The frequency of the alternating current obtained from the above-mentioned inverter 2 is normally a high frequency of several Klh 11 or more, and if the transformer 3 is to be made smaller and lighter, it is necessary to further increase the frequency.

Here, the operation of generating an alternating current as described above by the inverter 2 will be explained. In response to the signal from the inverter control circuit 6 described above, the transistors 2a and 2d are first switched on simultaneously for a certain period of time, and a current flows through the transformer 6 in a certain direction (in direction in FIG. 4). Next, transistor 2a.

2d is switched off and after a certain time period transistor 2b
, 2c are switched on for a certain period of time, and a current flows through the transformer 3 in a direction opposite to the above-described certain direction (direction B in FIG. 6). In this way, high-frequency alternating current is generated by repeating the switching on and off operations of the transistors 2a, 2b, 2c, and 2d at high speed based on the signal from the inverter control circuit 6. FIG. 6 shows the output current waveform of the inverter 2 generated by the above-described operation. A transistor 2a to be formed.

If the characteristics of the inverter 2b, 2c, and 2d are uneven, a DC component may be generated in the output of the inverter 2.

FIG. 7 shows the output current waveform of the inverter 2 where the above DC component is generated. In FIG.

It can be seen that the current in the direction of the arrow is larger than the current in the B direction, and a direct current component is generated.

As described above, when the output of the inverter 2, that is, the input of the transformer 30 contains a DC component, the iron core of the transformer 3 is biased by the DC current. In this way, when the iron core of the transformer 60 is strongly biased by direct current, magnetic saturation occurs in the iron core, and the magnetic flux in the iron core no longer increases beyond a certain value.

As a result, the excitation inductance rapidly decreases VC.

For this reason, an excessive current flows through the primary side VCVi of transformer B.
That is, an excessive current flows through the transistors 2a, 2d-j and the transistors 2b, 2eK of the inverter 2, and the transistors 2a, 2b, 2c, and 2d may be damaged.

This invention was made to solve the above-mentioned problems, and even if magnetic saturation occurs in the iron core of a transformer,
It is an object of the present invention to obtain a welding power source equipped with a protection means capable of preventing damage to transistors forming an inverter.

[Means for solving problems]

The welding power source according to the present invention converts DC power supply current into AC using an inverter, insulates and converts the converted AC using a transformer, converts the voltage, and converts the voltage-converted AC into DC for welding. In a welding power source designed to obtain a DC power supply current of

A magnetoelectric transducer is disposed in the iron core of the transformer, and the operation of the inverter is stopped according to the output of the magnetoelectric transducer.

[Effect]

In the welding power source according to the present invention, a magnetic flux generated in the iron core is detected by a magnetoelectric conversion element disposed in the iron core of the transformer, and the detected magnetic flux is set to a predetermined value close to the saturation magnetic flux of the iron core. The inverter stops operating when the value reaches .

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, the same reference numerals as in FIG. 5 indicate the same or corresponding parts. Reference numeral 21 denotes a Hall element (magnetoelectric conversion element), which is placed in the iron core 6a of the transformer 6 and detects the magnetic flux passing through the iron core, as shown schematically in FIG. be. 22 is an amplifier circuit;
It amplifies the signal from the Hall element 21 described above. 25 is a setting device that outputs a certain set value, and the output of this setting device is higher than the signal value output from the amplifier circuit 22 when the iron core 6a is magnetically saturated.

A constant value is set to a low value. A comparator 24 compares the output of the amplifier circuit 22 and the output of the setting device 23. The output of this comparator 24 is input to the inverter control circuit 6 mentioned above.

Note that the reference numeral 6b in FIG. 2 indicates a primary winding, and the reference numeral 3c indicates a secondary winding.

Next, the operation of the welding power source configured as described above will be explained. At the start of welding, a commercial frequency alternating current is rectified by the rectifier circuit 1, and the rectified direct current is converted into an alternating current by an inverter 2. This converted alternating current is manually supplied to the transformer 6, and is insulated and transformed by the transformer. This transformed alternating current is rectified by a rectifier 4 and converted into a restarting direct current, and the converted direct current is smoothed by an axle 5 and outputted to the outside as a welding power supply current.

As is well known, the Hall element 21 provides an output proportional to the detected magnetic flux. Therefore, the iron core 3a of the transformer 6
The magnetic flux in the iron core 6a is constantly detected by the Hall element 21 disposed therein, and an output proportional to the detected magnetic flux is supplied to the amplifier circuit 22.

Transistors 2a, 2. forming the above-mentioned inverter 2;
b, 2c, 2d, etc. As mentioned above, DC bias occurs in the iron core 6a of the transformer 6, and when this exceeds a predetermined value, the Hall element 21 in the iron core 3a The detected magnetic flux becomes abnormally large, and the output amplified by the amplifier circuit 22 also exceeds a predetermined value.

Therefore, when the magnetic flux in the iron ILJ 5a approaches magnetic saturation and the output of the Hall element 21 amplified by the amplifier circuit 22 exceeds the output signal value of the setting device 23, the comparator 24 is activated and the inverter Produces an output to control circuit 6. As a result, the inverter control circuit controls the inverter 2.
The operation of the transistors 2a and 2 is thereby stopped.
b, 2c, and 2d are prevented from being damaged.

In the above embodiment, the operation of the inverter 2 is completely stopped by the output of the comparator 24.
There is no need to completely stop the operation. For example, as shown in FIG. 6, a phase determination circuit 25 to which the output of the Hall element 21 is supplied
is provided, determines the phase of the magnetic flux detected by the Hall element, and inputs a determination signal indicating the determination result to the inverter control circuit 6, and the inverter control circuit determines the direction of the biased magnetism from the determination signal. However, in accordance with this determination result, that is, the determination signal output from the phase determination circuit 25, the magnetic flux in the iron core 3a approaches magnetic saturation as described above, and the amplifier circuit 2
2, the output of the Hall element 21 exceeds the output signal value of the setting device 26.

As a result, when the comparator 24 operates, it outputs a control signal to the inverter 2 and stops only one of the positive side and negative side of the output of the inverter, that is, increases the magnetic flux due to DC bias magnetization. Alternatively, only the current in the direction that is intended to increase the magnetic flux in that direction may be cut off.

In this way, when the biased magnetization increases, it is not necessarily necessary to completely stop the operation of the inverter 2, and it is also possible to continue outputting the welding output.

FIG. 4 shows the output current waveform of the inverter 2 when the phase determination circuit 25 is used as described above and a control signal is output to the inverter 2 by the output of the phase determination circuit via the inverter control circuit 6. It is something. Since biased magnetism exceeding a predetermined value occurred at the time indicated by the symbol A1, and this persisted until the next time indicated by the symbol A2, it was determined that flowing the current in the direction of the arrow would further increase the biased magnetism. The current that is supposed to flow at time A2 is prevented from flowing because the inverter 2 is stopped.

〔Effect of the invention〕

As explained above, this invention converts DC power supply current into AC using an inverter, insulates and converts the converted AC using a transformer, converts the voltage, and converts the voltage-converted AC into DC for welding. In a welding power source configured to obtain a direct current power supply current, a magnetoelectric conversion element is disposed in the iron core of the transformer] 7. The operation of the inverter is completely or partially stopped depending on the output of the magnetoelectric conversion element. Therefore, even if DC bias magnetization occurs and the excitation inductance of the transformer is about to drop suddenly, the operation of the inverter is completely or partially stopped, thereby preventing damage to the transistors forming the inverter. It has the effect of

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a welding power source showing an embodiment of the present invention;
FIG. 2 is a schematic perspective view showing the main parts of one embodiment, FIG. 6 is a circuit diagram showing another embodiment of the invention, and FIG. 4 is a waveform for explaining the operation of the one shown in FIG. 3. 5 are circuit diagrams showing a conventional welding power source, and FIGS. 6 and 7 are waveform diagrams for explaining the operation of the conventional welding power source. 1: Rectifier circuit, 2: Inverter, 2a, 2b. 2e, 2d:) transistor, 6: transformer, 3a: iron core,
4: rectifier, 5: reactor, 6: inverter control circuit, 21: Hall element, 22: amplifier circuit, 23 setting device,
24: Comparator, 25: Phase determination circuit. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Patent Attorney Tadashi Sato Figure 3 Figure 4 Figure I A2: 1 Figure 5 Figure 6 Figure 7

Claims (3)

[Claims] (1) It has an inverter that converts DC power supply current to AC, and a transformer that insulates this converted AC and converts it into voltage. In the welding computer that obtains the power supply current,
A welding power source comprising: a magnetoelectric conversion element disposed in an iron core of the transformer; and a protection means for stopping operation of the inverter in accordance with the output of the magnetoelectric conversion element. (2) The protection means includes a setting device that outputs a predetermined value, a comparator that receives the output of the magnetoelectric conversion element and the output of the setting device and compares the magnitude of these outputs, and the comparator. The welding power source according to claim 1, further comprising means for stopping the operation of the inverter according to the output of the inverter. (3) The protection means includes a setting device that outputs a predetermined value, a comparator that receives the output of the magneto-electric conversion element and the output of the setting device and compares the magnitude of these outputs, and the magneto-electric conversion element. a phase determination circuit that determines the phase of the output of the conversion element to determine the direction of biased magnetism; and either the positive side or the negative side of the output of the inverter depending on the output of the phase determination circuit and the output of the comparator. The welding power source according to claim 1, further comprising means for stopping only one of the welding power sources.