JPH0822458B2 - AC arc welding machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an arc welding machine that supplies alternating current power to an arc welding load composed of a welding torch and a workpiece by switching the polarity of a direct current power supply with a switching element. Is.

[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 with a negative potential on the electrode side and reverse polarity with a positive potential on the electrode side. Proposed as what you get by. (For example, JP-A-60-18275). FIG. 2 is a connection diagram showing an example of this type of conventional device. In the figure, 1 is a known DC power supply, and 2 is a reactor for smoothing the output of the DC power supply 1. 3a to 3d are switching elements connected in a bridge, 4 is an electrode, 5 is an object to be welded, 6
Is a switching element drive circuit for driving the switching elements 3a to 3d. 7a to 7d are capacitors, 8a to 8d are resistors, and these are switching elements.
This is a surge absorption circuit for absorbing the surge voltage generated in the circuit when 3a to 3d is cut off. In the device of FIG. 2, when the drive signals s1 and s2 are alternately output from the switching element drive circuit 6, the switching elements 3a and 3b are simultaneously turned on and off or the switching elements 3c and 3d are turned on and off at the same time, DC power supply 1 between 4 and workpiece 5
The rectangular wave AC power whose output voltage is switched between forward and reverse is supplied.

[Problems to be Solved by the Invention] In the above conventional device, when switching the polarity, the current of the reactor 2 suddenly changes when the switching element is cut off, and a high surge voltage is generated. All of this surge voltage will be applied to the switching element, so to prevent the switching element from being destroyed by this voltage, capacitors 7a to 7d and resistor 8a
It is essential to provide a surge absorption circuit consisting of 8d to 8d.

By the way, when the output current is large, the surge voltage generated in the DC reactor also becomes large.Therefore, in order to control this large surge voltage, the capacitors 7a to 7d should have a large capacitance, and the resistors 8a to 8d should have a low resistance value. It is necessary to make it one. However, in this way, when the output current is small, the magnetic energy stored in the DC reactor is small, and this energy is stored in the capacitor.
There is a possibility that the ratio of being absorbed by 7a to 7d becomes too large and re-ignition of the arc after the polarity switching fails (that is, the arc is interrupted).

Also, if a non-linear voltage absorbing element such as a varistor is used instead of the capacitor, the problem of the above capacitor can be solved, but these elements have a relatively short life and are combined with a transistor used as a switching element for a long period of time. Not suitable for use.

[Means for Solving Problems] In the present invention, a circuit for regenerating the surge voltage generated by the DC reactor to the power supply side through the secondary winding is provided in place of the surge voltage absorbing means of the conventional device. It controls the surge voltage generated by the DC reactor.

[Embodiment] FIG. 1 is a connection diagram showing an embodiment of the present invention. In the figure, reference numeral 1 denotes a DC power supply, which is a first rectifier circuit 101 that receives power from commercial AC and converts it to DC, and an inverter circuit 102 that converts the output of the first rectifier circuit 101 into high-frequency AC by switching. , A transformer 103 for converting the output of the inverter circuit 102 into a voltage suitable for arc welding,
The second rectifier circuit 104 is configured to rectify the output of the transformer 103 to obtain a DC output. Reference numeral 2 is a reactor for smoothing the output of the DC power source 1, which has a secondary winding 21 magnetically and tightly coupled, and the series circuit of the secondary winding 21 and the rectifying element 11 is the first rectifier. It is connected to the output terminal of the circuit 101 with the same polarity. Here, the secondary winding 21 of the reactor 2 and the rectifying element 11 constitute a voltage regeneration circuit of the DC reactor 2.
Further, 3a to 3d are switching elements bridge-connected, 4 is an electrode, 5 is an object to be welded, and 6 is a switching element 3a.
3 to 3d are switching element drive circuits.

Next, the operation of the embodiment shown in FIG. 1 will be described. DC power supply 1
Is a commercial alternating current 14 which is converted into a direct current by the first rectifying circuit 101, the output of the first rectifying circuit 101 is converted into a high frequency alternating current by the inverter circuit 102, and then a voltage suitable for arc welding is obtained by the transformer 103. Convert the output of this transformer 103 to a second
Is rectified again by the rectifier circuit 104 to generate a direct current. The output of the DC power supply 1 is supplied via a DC reactor 2 to a polarity switching circuit composed of switching elements 3a to 3d bridge-connected. According to the drive signals s1 and s2 from the switching element drive circuit 6, the switching elements 3a, 3b or 3c, 3d alternately repeat conduction and interruption, respectively, and a rectangular wave power is generated between the electrode 4 and the workpiece 5. Supplied. During this period, switching element 3a
The voltage generated in the secondary winding 21 of the reactor 2 is lower than the output voltage of the first rectifying circuit 101 of the DC power supply 1 while any of the elements 3 to 3d is conducting, so that the rectifying element 11 is reverse-biased. No current flows. Next, when the pair of switching elements which are conducting are cut off and the pair of switching elements of opposite polarities are conducting, the current flowing through the DC reactor 2 once tries to become zero. A surge voltage having a polarity corresponding to the forward direction of the switching elements 3a to 3d is generated in order to prevent the sudden decrease. Here, in the embodiment of FIG. 1, since the secondary winding 21 and the rectifying element 11 of the DC reactor 2 have the illustrated polarities, this occurs when the welding current suddenly decreases due to the interruption of the switching elements 3a to 3d. The surge voltage that occurs is positive on the side marked with a. When this voltage exceeds the output voltage of the first rectifying circuit 101, it is regenerated by the DC power supply 1 through the rectifying element 11.
As a result, the surge voltage generated by the reactor 2 is limited to the voltage at this time. Therefore, if the winding ratio of the DC reactor 2 is appropriately determined, it is possible to easily set the voltage at the time of regeneration to be slightly higher than the voltage required for arc regeneration.

EFFECTS OF THE INVENTION Since the present invention is as described above, it is possible to suppress the surge voltage generated by the DC reactor irrespective of the current flowing before the polarity switching, so that the arc of the arc after the polarity switching is suppressed. There is no risk of adversely affecting playback.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention, and FIG. 2 is a connection diagram of a conventional device. 1 ... DC power supply, 2 ... DC reactor 3a to 3d ... Switching element 4 ... Electrode, 5 ... Workpiece, 11 ... Rectifier element 21 ... Secondary winding 101 provided on DC reactor 2 ... … First rectifier circuit, 102 …… Inverter circuit 103 …… Transformer, 104 …… Second rectifier circuit

Claims (1)

[Claims] 1. A first rectifier circuit for rectifying commercial AC into DC, an inverter circuit for exchanging the output of the first rectifier circuit for high-frequency AC by a high-frequency switching circuit, and an output of the inverter circuit. To a voltage suitable for welding, a second rectifier circuit for converting the output of the transformer into DC, and an arc welding load by switching the polarity of the output of the second rectifier circuit with a switching element. A polarity switching circuit for supplying, a series reactor provided in series between the second rectifier circuit and the polarity switching circuit, and a series circuit of a secondary winding and a rectifying element provided in the DC reactor. An AC arc welding machine, comprising: a voltage regeneration circuit connected to the output terminal of the first rectifier circuit with the same polarity.