JPH02112881A - Power source for arc welding and cutting - Google Patents

Abstract

PURPOSE:To reduce the size and weight over the entire part of the power source device for arc welding and cutting by controlling the output of an inverter by a current control means in such a manner as to increase or decrease the output current to a load in synchronization with the momentary increase or decrease of an AC input voltage. CONSTITUTION:The AC input from a single-phase AC power source 1 is subjected to current rectification by a full-wave current rectifying circuit 2. The current rectified output is converted to high-frequency AC by an inverter main circuit 4 and after this current is dropped by a voltage transformer 5, the secondary output of the transformer is subjected again to the current rectification in a full-wave current rectifying circuit 6. This output is supplied via a DC reactor 7 to the arc load 8. The output of the inverter main circuit 4 is so controlled by the current control means as to be increased or decreased in nearly synchronization with the increase or decrease of the momentary value of the AC input voltage. The size and weight over the entire part of the power source device for arc welding and cutting are reduced in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an inverter-controlled arc welding and cutting power source, and is particularly suitable for use with a small-capacity AC input such as single-phase 100 V human power. Regarding arc welding and cutting power supplies.

[Conventional technology]

Conventionally, in a single-phase input arc welding and cutting power supply controlled by an inverter, the output current is set by dividing the constant voltage output 21 of the control DC power supply 20 by a current setting device 11, as shown in FIG. was.

A commercial frequency AC input from the single-phase AC power R1 is converted to DC by a full-wave rectifier circuit 2 and a large-capacity smoothing capacitor 3, and then converted from DC to high-frequency AC by an inverter main circuit 4. After this high frequency AC output is stepped down by a transformer 5, it is again converted to DC by a full wave rectifier circuit 6, and is supplied to an arc load 8 via a DC reactor 7. A feedback signal 23 of the output current value detected by the current detector 12 and a reference voltage 22 from the current setter 11 are compared in a comparator amplifier 13, and the output of the comparator amplifier 13 is applied to an inverter drive circuit 14.
And PWM Ill? 11 signals and configure the inverter main circuit 4. 6z<' MOS FET etc. An output current corresponding to the setting value of the current setting device 11 is caused to flow by causing the element to operate rapidly.

[Problem to be solved by the invention]

In the above conventional technology, the relationships among the output current to the arc load, the AC input voltage, the DC input voltage obtained by rectifying and smoothing the AC input voltage, and the input current flowing through the smoothing capacitor 3 are shown in FIGS. 3(a) to (d). As shown, since the input current (d) has a pulse-like waveform, the power factor with respect to the input power source is very poor, and is usually about 60%. Therefore, single phase 10
0■ When using a power supply with limited input capacity, such as a power supply, it is difficult to obtain a large output current due to the poor power factor.
Therefore, welding machines and cutting machines with a single-phase 100μ input were not able to make full use of their capabilities.

An object of the present invention is to provide a power source for arc welding and cutting that can obtain a sufficiently large output current with a single-phase input having a limited capacity by improving the power factor of the input current.

[Means to solve the problem]

To achieve the above object, the present invention rectifies single-phase AC input, converts the rectified output into high-frequency AC using an inverter, and applies it to the primary side of the transformer, and rectifies the secondary output of the transformer again to supply the load. The arc welding and cutting power source supplied includes current control means for controlling the output of the inverter so that the output current to the load increases or decreases substantially in synchronization with the increase or decrease in the instantaneous value of the AC input voltage. do.

[Effect]

Conventional inverter-controlled single-phase input arc welding and cutting power supplies have an input current power factor of about 60%, which is about 20% lower than that of three-phase input power supplies.

If this can be made into the 90% range, the output current can be increased by 1.5 times. On the other hand, in TIG welding, shielded arc welding, plasma arc cutting, etc., there are few performance problems even if the output current is not a complete direct current but a pulsating current.

The present invention has been made with attention to these points, and as shown in FIG. The DC input current (d) also has a waveform that increases and decreases almost in synchronization with the increase and decrease in the instantaneous value of the AC input voltage (a), and the power factor is significantly improved compared to the conventional input current waveform shown in Figure 3 (d). be done. As a result, a sufficiently large output current can be obtained with the same human power capacity, and the capacity of a single-phase 100-input arc welding and cutting power source can be improved to about 1.5 times that of the conventional one.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

A commercial frequency AC input from a single-phase AC power supply 1 is rectified by a full-wave rectifier circuit 2, and then partially smoothed by a smoothing capacitor 3. Since the output current has a pulsating waveform that is approximately synchronized with the AC input voltage, the DC input voltage does not need to be completely DC, but may be partially smoothed to the extent that arc breakage does not occur at the zero point of the AC input voltage. Therefore, the capacitance of the smoothing capacitor 3 may be smaller than that of a conventional device having the same input capacitance.

The partially smoothed DC input voltage is converted into high-frequency AC (for example, 20 kHz) by the inverter main circuit 4, and this is stepped down to an appropriate voltage by the transformer 5.The secondary output of the transformer is then converted again by the full-wave rectifier circuit 6. It is rectified and supplied to an arc load 8 via a DC reactor 7.

The current control means is constructed as follows. After the AC input voltage from the single-phase AC power supply 1 is stepped down by the control transformer 9, it is rectified by the full-wave rectifier circuit 10, and the output voltage 16 is applied without smoothing to the current setting device 11 for voltage division. Therefore, the output voltage of the current setting device 11 has a value that increases or decreases in synchronization with the increase or decrease in the instantaneous value of the AC input voltage. A constant DC bias 17 from a bias power supply 15 is added to the output voltage of this current setting device 11 to obtain a reference voltage 18 corresponding to the setting value of the current setting device 11. Feedback signal 19 of the output current value detected by the current detector 12 such as a shunt resistor
and the reference voltage 18 in a comparator amplifier 13, the output of the comparator amplifier 13 is converted into a PWM control signal in an inverter drive circuit 14, and elements such as power MOSFETs constituting the inverter main circuit 4 are operated to switch. , so that an output current according to the setting value of the current setting device 11 flows to the arc load 8.

According to the above configuration, the relationship between the output current to the arc load, the AC input voltage, the DC input voltage obtained by rectifying and smoothing the AC input voltage, and the input terminal flowing to the smoothing capacitor 3 is as shown in FIGS. 4(a) to (d). As shown in , the output current (a) increases and decreases almost in synchronization with the increase and decrease of the instantaneous value of the AC input voltage (b), so if the capacity of the smoothing capacitor 3 is appropriately selected, The waveform also increases and decreases almost in synchronization with the increase and decrease in the instantaneous value of the AC input voltage (b), and its power factor is significantly improved compared to the conventional one.

Here, if the capacitance of the smoothing capacitor 3 is too small or if the current setting value at the zero point of the AC input voltage is set to zero, there is a risk of arc breakage. By adding a DC bias to the minimum current value (Imin) required for arc stabilization,
can be held. Furthermore, in order to prevent arc breakage, there is also a method of adding a current corresponding to Ill1in from another DC power source (not shown) at the output end to the arc load.

〔Effect of the invention〕

According to the present invention, in a single-phase input arc welding and cutting power source controlled by an inverter, the power factor of the input terminal, which was conventionally as low as 60%, can be significantly improved, resulting in a single-phase 10% power factor.
When the input capacity is limited such as 0V input, the output current can be made sufficiently large, and the welding and cutting ability can be improved.

Furthermore, as an additional effect, power contract charges are reduced by improving the power factor, and since the capacitance of the smoothing capacitor may be small, the power supply device as a whole becomes smaller, lighter, and cheaper.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram of an embodiment of the present invention, FIG. 2 is a circuit block diagram of a conventional example, FIG. 3 is a voltage and current waveform diagram of each part of FIG. 2, and FIG. It is a voltage and current waveform diagram of each part. 1-Single-phase AC power supply, 2-Full-wave rectifier circuit, 3-Smoothing capacitor, 4--Inverter main circuit, 5--Transformer,
6-・Full-wave rectifier circuit, 7-・DC reactor, 8-arc load, 9-・Control transformer, 10-・Full-wave rectifier circuit,
11 - current setter, 12 - current detector, 13 comparison amplifier, 14 - inverter drive circuit, 15 - bias power supply.

Claims (1)

[Claims] 1. Arc welding that rectifies single-phase AC input, converts the rectified output into high-frequency AC using an inverter, applies it to the primary side of the transformer, rectifies the secondary output of the transformer again, and supplies it to the load;
Arc welding, characterized in that the cutting power source is equipped with a current control means for controlling the output of the inverter so that the output current to the load is increased or decreased substantially in synchronization with the increase or decrease in the instantaneous value of the AC input voltage. Power supply for cutting.