JPH07115180B2 - AC arc welding power supply - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a power supply for AC arc welding having an inverter circuit.

2. Description of the Related Art In the prior art, in the inverter circuit as shown in FIG. 4, the conduction period of the switching element that performs S1 chopping is synchronized with the conduction period of the switching element that flows the free wheel current of S3, and the chopping of S2 is performed. Since the conduction period of the switching element for carrying out S4 is synchronized with the conduction period of the switching element for flowing the free wheel current of S4, the timing at which the conduction period of S1, S2 ends is shown in FIG.
The timing is the same as the timing at which the conduction period of S3 and S4 ends as shown in FIG. 3, or a little earlier than the timing shown in FIG. 3b.

Problems to be Solved by the Invention Although there is no problem with the switching timing as shown in FIG. 3b, when the control circuit controls the switching timing as shown in FIG. Therefore, the conduction period of S3 may end earlier than the conduction period of S1. In that case, the counter electromotive force due to the energy stored in the reactor of the inverter circuit shown in FIG. 1 is applied to S1 when S1 is off, and the voltage due to the counter electromotive force exceeds the breakdown voltage of the switching element of S1. In that case, the switching element S1 is destroyed. Or S4
The conduction period of may end earlier than the conduction period of S2. In that case, the counter electromotive force due to the energy stored in the reactor of the inverter circuit shown in FIG.
When turned off, the switching element S2 will be destroyed if the withstand voltage of the switching element of S2 exceeds the withstand voltage of S2.

Means for Solving the Problems In order to solve the above problems, the present invention is a chopping system in which a first DC power supply and a second DC power supply are connected in series with additive polarity, and the two DC power supplies are respectively connected in series. Circuit in which an arc load and a smoothing reactor are connected in series between a common connection point of a series power supply and a common connection point of two switching elements that perform chopping, and a rectifying element and a switching element. In an AC arc welding power supply having an inverter circuit composed of a circuit in which two sets of free wheel circuits connected in series are connected in parallel to the series connection circuit of the arc load and the smoothing reactor, a positive polarity in which a current flows from a base metal to an electrode After the conduction period of the switching device that performs chopping that operates during the period ends, the switching device of the free wheel circuit The switching element of the free wheel circuit is delayed for a certain period after the conduction period of the synchronous delay circuit that delays the current for a certain period and turns off, and the switching element that performs chopping that operates during the reverse polarity period when the current flows from the electrode to the base material ends. And a synchronous delay circuit for turning off.

Action According to the switching timing of the present invention, as shown in FIG. 3c, when the switching element S1 or S2 for chopping is turned off, the switching element S3 or S4 for flowing the free wheel current is always turned on. Therefore, the back electromotive force due to the reactor is almost absorbed by the free wheel circuit. As a result, the back electromotive force of the reactor is not applied to the switching elements S1 and S2 that perform chopping, and the breakdown of S1 and S2 due to the reverse bias is eliminated.

Example Hereinafter, one example of the present invention will be described in detail. FIG. 2 shows a control circuit for realizing the switching timing of the present invention. 1 is an inverter, 2 is OR, 3 is AND, 4
Is a timer IC that outputs a HIGH signal for a certain period by a rising signal, and 5 is a timer IC that outputs a LOW signal for a certain period by a rising signal. FIG. 4 shows a timing chart of each part of the control circuit shown in FIG. g is the conduction period of the reverse polarity free wheel switching element, h is the conduction period of the reverse polarity chopping switching element, i is the conduction period of the positive polarity free wheel element, and j is the positive polarity chopping This is the period during which the switching element can be conducted. a is LOW during the reverse polarity period and H during the positive polarity period
A signal which becomes IGH and b is its inverted signal. c outputs the HIGH signal of T1 for a certain period due to the rise of a, and the signal becomes the conduction extension period of the reverse polarity free wheel switching element as shown in FIG. 4g. Next, f outputs T2 and LOW signal for a certain period by the rising signal of a,
The period of T1 is T3, and the period becomes a dead time from the reverse polarity conduction period to the positive polarity conduction period as shown in FIG. Similarly, T4 is the extension period of the positive polarity free wheel period, and the T6 period of T5-T4 is the dead time from the positive polarity conduction period to the positive polarity conduction period. The current flowing at this switching timing will be described with reference to FIG.
Reference numeral 1A is a first DC power supply that supplies a reverse polarity current, and 2A is a second DC power supply that supplies a positive polarity current. S1 is a switching element that controls on / off of reverse polarity current, S3 is a switching element that conducts freewheel current when reverse polarity, S2 is a switching element that controls on / off of positive polarity current, S4 is a conduction of freewheel current when positive polarity It is a switching element.

For reverse polarity operation, when S1 is turned on, reverse polarity side DC power supply 1A +
From S1 → smoothing reactor 5 → electrode 2 → arc 4 → base metal 3 → reverse polarity side DC power supply 1A-current flows, and when S1 is turned off, the magnetic energy of the smoothing reactor 5 causes
Smoothing reactor 5 → Electrode 2 → Arc 4 → Base material 3 → S3 →
A freewheel current on the reverse polarity side flows through the path from D6 to the smoothing reactor 5. Next, when the arc current is switched from the reverse polarity side current to the positive polarity side current, after switching off the switching element S1 which was controlling the conduction of the previous reverse polarity side current, the fourth
S3 is turned off by flowing a free wheel current for a certain period shown in FIG. T1, and a dead time period shown in FIG. Turn on the energized S4.

For positive polarity operation, when S2 is turned on, positive polarity side DC power supply 1B +
From base material 3 → arc 4 → electrode 2 → smoothing reactor 5 →
Current flows in the path of S2 → positive polarity side DC power supply 1B-, and when S2 is turned off, the magnetic energy of the smoothing reactor 5 causes
A positive-side freewheel current flows through the path of smoothing reactor 5 → D5 → S4 → base material 3 → arc 4 → electrode 2 → smoothing reactor 5. Next, when the arc current is switched from the positive polarity side current to the reverse polarity side current, after switching off the switching element S2 that was controlling the conduction of the previous positive polarity side current,
S4 is turned off by flowing a free wheel current for a certain period shown in Fig. T4, and a dead time period shown in T6 of Fig. 4 is provided. Turn on the energized S3.

As described above, the energy stored in the smoothing reactor is removed by delaying the conduction period of the switching element that conducts the free wheel current by a certain period relative to the conduction period of the switching element that performs chopping and turning off the energy. Absorb in the circuit. Then, by preventing the counter electromotive force of the smoothing reactor from being applied to the switching element that performs chopping, it is possible to prevent the switching element from being destroyed.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a general AC arc welding power source, FIG. 2 is a synchronous delay circuit diagram for realizing switching timing according to an embodiment of the present invention, and FIG. 3 is a time chart showing switching according to a conventional example. 4 is a timing chart of this embodiment shown in FIG. 1A: DC power supply for reverse polarity, 1B: DC power supply for positive polarity, D1
-D4: Freewheel diode with a built-in switching element, D5, D6: Rectifier diode that constitutes the freewheel circuit.

Claims (1)

[Claims] 1. A first DC power supply and a second DC power supply are connected in series with polarity, and switching elements for chopping that are respectively connected in series to the two DC power supplies are connected to each other, and a series power supply is connected. Between the common point and the connection common point of the switching elements that perform two choppings, a circuit in which an arc load and a smoothing reactor are connected in series and two sets of free wheel circuits in which a rectifying element and a switching element are connected in series are provided in the arc. In an AC arc welding power source having an inverter circuit composed of a circuit connected in parallel with a series connection circuit of a load and a smoothing reactor, the conduction period of a switching element that performs chopping that operates during the positive polarity period when current flows from the base metal to the electrode A synchronous delay circuit that delays the switching element of the free wheel circuit for a certain period after turning off and turns off, AC arc welding equipped with a synchronous delay circuit that delays the switching element of the free wheel circuit for a certain period and turns off after the conduction period of the switching element that performs chopping that operates during the reverse polarity period when the flow flows from the electrode to the base material ends Power supply.