JP2778184B2 - Power supply for AC arc welding - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an arc welding power supply, and in particular, to an arc welding power supply that supplies power to a welding part by alternately switching between positive and reverse polarities. It is about.

<Prior Art> A combination of a DC power supply and a switching element for switching polarity is used as a power supply for arc welding, which switches between positive polarity where the electrode side is a negative potential and reverse polarity where the electrode side is a positive potential. It has been proposed as gaining by. (For example, JP-A-60-18275). FIG. 5 is a connection diagram showing an example of this type of conventional device. In FIG.
Reference numeral denotes a known DC power supply, and reference numeral 2 denotes a reactor for smoothing the output of the DC power supply 1. 3a to 3d are bridge-connected switching elements, and 4a to 4d are diodes connected to the switching elements 3a to 3d in anti-parallel, respectively. Reference numeral 5 denotes an electrode; 6, an object to be welded; and 7, a switching element drive circuit for driving the switching elements 3a to 3d. Reference numeral 8 denotes a relatively large-capacity capacitor for smoothing the output of the DC power supply 1 and absorbing a surge voltage generated in the circuit. FIG. 6 is a diagram for explaining the operation of the conventional device of FIG. 5, and shows the relationship between the output signals s1, s2 of the switching element drive circuit 6 and the output voltage Eo with the passage of time. In FIG. 5, when the driving signals s1 and s2 are alternately output from the switching element driving circuit 6, the switching elements 3a and 3b or the switching elements 3c and 3d simultaneously conduct and cut off simultaneously, and the electrode 4 and the electrode 4 are covered. A rectangular wave voltage in which the output voltage of the DC power supply 1 is switched between forward and reverse is supplied to the welding object 5.

<Problems to be Solved by the Invention> In the above-described conventional device, the operation when the drive signal s1 is supplied and disappears, and the drive signal s2 is supplied and the current switches from the positive polarity to the reverse polarity, is described. An example is described. Switching elements 3c and 3d are turned on by the disappearance of signal s1
When the power supply is turned off, the supply of power from the DC power supply 1 is cut off, but the current (positive current) from the work 6 to the electrode 5 immediately becomes zero due to the inductance included in the cable or the like of the output circuit. And diodes 4b, 4a
And the capacitor 8 is charged by this current. The energy for charging the capacitor 8 is the electromagnetic energy stored in the inductance of the cable or the like during the positive polarity period.
, The signal s2 is supplied next, and when the switching elements 3a and 3c are turned on, the voltage is applied between the electrode 5 and the workpiece 6 to fire an arc of opposite polarity (welding arc). Re-ignition).

Therefore, it is necessary that the charging voltage of the capacitor, which is generated at the time of polarity switching, is a value sufficient for re-ignition of the arc and at the same time is lower than the withstand voltage of the switching elements 3a to 3d.

However, this voltage V is determined by the inductance Lc of the output circuit such as a cable and the welding current Ia. If the capacitance of the capacitor 8 is c, Becomes Therefore, if a large-capacity capacitor is used with a large current and a long cable, that is, a charging voltage generated assuming that the inductance Lc is large does not exceed the withstand voltage of the switching element, when the welding current is small, When a short cable is used, the charging voltage becomes insufficient and re-ignition of the arc fails. Conversely, if a small-capacity capacitor is adopted as a device using a small current or a short cable, the charging voltage becomes excessive when a large current or a long cable is used, and the switching element is destroyed.

Further, if the change of the current is abrupt at the time of switching the polarity, a loud arc sound is generated, which deteriorates the working environment.

<Means for Solving the Problems> The present invention provides an AC arc welding power supply that obtains an AC output by switching the output of a DC power supply by a switching element. At the time of a large current, connect an AC reactor that shows a relatively small inductance value at the time of a large current, and a capacitor necessary and sufficient voltage to re-ignite the arc at the time of polarity switching regardless of the current value used or the length of the cable. Is to be charged.

<Example> FIG. 1 shows an example of the present invention. In the drawing, reference numerals 1 to 8 denote the same components having the same functions as those in the embodiment shown in FIG. Reference numeral 9 denotes an AC reactor, which forms a main part of the present invention. FIG. 2 shows an example of the characteristics of the AC reactor used in the present invention. In the figure, the horizontal axis shows the welding current Ia flowing through the AC reactor, and the vertical axis shows how the inductance value La changes with this current. In the figure, if the current value Iao at which the inductance rapidly decreases is set to a low value of about several tens of amps, the AC reactor is effective only during a period when the current is small at the time of polarity switching. Therefore, as shown in FIG. 3, a change in the welding current Ia results in a current waveform that changes in a slope shape in a range of several tens of amperes or less where the inductance value of the AC reactor changes rapidly before and after the polarity is switched. In this case, if the capacitor 8 is set to have a relatively large capacity required when using a long cable with a large current, the inductance of the AC reactor 9 has little effect at the time of a large current, and the voltage generated by the inductance of the cable is almost zero. This voltage is suppressed by the large-capacity capacitor 8 to a value necessary for re-ignition of the arc, and the switching element is not destroyed. Conversely, when welding is performed with a small current, AC reactor 9 exhibits a relatively large inductance value, whereby a voltage sufficient for arc regeneration is induced and capacitor 8 is charged. In any case, the rise of the welding current becomes slow when the polarity is switched, so that the occurrence of arc noise is reduced.

An AC reactor having characteristics as shown in FIG. 2 can be easily obtained by reducing the cross-sectional area of the iron core and setting the magnetic core to be magnetically saturated at about several tens of amperes. In particular, if a grain-oriented silicon steel sheet having a rectangular magnetization characteristic is used as the material of the iron core, a more distinct change in inductance can be obtained.

FIG. 4 is a connection diagram showing another embodiment of the present invention.
In the figure, a DC power supply 1 converts an AC power supply 101 into a direct current by a rectifier circuit 102, and converts the direct current into an alternating current again by an inverter 103 composed of a switching transistor. After converting to a voltage suitable for arc welding in the transformer 104, the rectifiers 105a and 105b convert the voltage to positive and negative polarity, and then smoothing the output terminals a, 106a and 106b and the capacitors 107a and 107b. b, c to obtain positive, negative and zero DC outputs. Here, reactor 106a and
As shown in the figure, 106b uses a core that shares a core and whose winding direction is determined to have a polarity in which magnetic flux in the same direction is generated in the core that is shared by currents flowing through the cores. The positive output terminal (a) of the DC power supply is connected to the switching element 4a.
In addition, the negative output terminal is connected to the switching element 4b, and the other terminals of the switching elements 4a and 4b are commonly connected to each other and serve as one AC output terminal, which is connected to the electrode 5. The zero output terminal C of the DC power supply 1 is the other AC output terminal via an AC reactor 9 having the same characteristics as the embodiment of FIG. 1, and is connected to the workpiece 6.

In the embodiment of FIG. 4, two switching elements 4
AC output is obtained by alternately performing ON-OFF control of a and 4b, and this AC output current changes in a slope shape only during a low current period before and after the polarity is switched by the action of the AC reactor 9 FIG. Has the same waveform as In addition, by using the current-inductance characteristics shown in FIG. 2 as in the embodiment shown in FIG. The voltage for restriking can be obtained safely and reliably.

In the DC power supply 11 used in FIG. 4, the rectifiers 105a, 105
Since the current flowing through 5b has a substantially rectangular waveform, a high-quality DC voltage with little output voltage ripple can be obtained.

If the operating frequency of the inverter circuit 103 is set to a value sufficiently higher than the commercial frequency, the smoothing reactor can be made extremely small.

<Effects of the Invention> Since the present invention is as described above, it is possible to safely and reliably reproduce an arc when switching the polarity, and the rise of current at the time of arc reproduction becomes slow. Therefore, the generation of arc noise is reduced, and the working environment can be improved.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention, FIG. 2 is a diagram for explaining characteristics of an AC reactor used in the present invention,
FIG. 3 is a waveform diagram of a welding current obtained by the power supply of the present invention, FIG. 4 is a connection diagram showing another embodiment of the present invention, FIG. 5 is a connection diagram showing an example of a conventional device, and FIG. FIG. 6 is a waveform diagram of a welding current obtained by the conventional apparatus of FIG. 1 DC power supply 2 DC reactor 3a-3b Switching element 4a-4b Diode 5 Electrode 6 Workpiece 8 Capacitor 9 AC reactor 102… Rectifier circuit, 103… Inverter, 104… Transformer, 105a, 105b …… Rectifier, 106a, 106b …… DC reactor, 107a, 107b …… Capacitor,

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroyuki Ishii 2-1-1-11 Tagawa, Yodogawa-ku, Osaka-shi, Osaka Daihen Co., Ltd. (56) References JP-A-63-165075 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) B23K 9/073

Claims (3)

(57) [Claims] An output of a DC power supply is supplied to DC input terminals of four bridge-connected switching elements, and two opposing elements of said switching elements are paired simultaneously and each pair of elements is connected to each other. In an AC arc welding power supply that alternately turns on and off to obtain an AC output from the AC output terminal of the switching element, a high inductance value is provided between the AC output terminal of the switching element and the arc welding output terminal at a small current. A power supply for AC arc welding in which AC reactors showing a relatively low inductance value at high current are connected in series. 2. A DC power supply having three positive, zero and negative output terminals, and one terminal connected to each of a positive output terminal and a negative output terminal of the DC power supply and the other terminal commonly connected and alternately connected. In an AC arc welding power supply that obtains an AC output from two sets of switching elements that are ON-OFF controlled, a common connection part of the switching elements, and a zero output terminal of the DC power supply, a zero output terminal of the DC power supply or the switching. An AC arc welding power source in which an AC reactor having a high inductance value at a small current and a relatively low inductance value at a large current is connected in series between any of the common connection portions of the elements and the welding output terminal. 3. The DC power supply has a DC reactor in series with a positive output terminal and a negative output terminal, and the DC reactor shares a core and is shared by currents flowing through respective reactor windings. 3. The power supply for AC arc welding according to claim 2, wherein the power supply has a polarity to induce magnetic flux in the same direction.