JPH01150470A - Ac arc welding power source - Google Patents

Abstract

PURPOSE:To prevent switching elements from being broken down by arranging constitution to absorb the counter electromotive force by a reactor by a free wheel circuit to prevent the counter electromotive force from being impressed on the switching elements at the time of changing over polarity with AC arc welding. CONSTITUTION:At the time of changing over an arc current from a reversed polarity side current to a straight polarity side current, after the switching element S1 is turned off, a free wheel current is carried for a prescribed period of time and the switching element S3 is then turned off. After this, after an interval of a dead time period, the switching element S2 to control the straight polarity side current and the switching element S4 to apply the straight polarity free wheel current are turned on. By this method, it is prevented that the counter electromotive force is impressed on the switching elements and the switching elements are broken down.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is used in an AC arc welding power source having an inverter circuit.

2. Prior Art In the conventional technology, in an inverter circuit as shown in FIG. 1, the conduction period of the switching element that performs the chopping of Sl is synchronized with the conduction period of the switching element that flows the freewheel current of Ss, and the chopping of S2 Since the conduction period of the switching element that performs this is synchronized with the conduction period of the switching element that conducts the freewheel current of S4, the timing at which the conduction period of Sl, 32 ends is the same as that of Ss, S4, as shown in FIG. 3a. At the same time as the end of the conduction period, or at the third
As shown in the figure, the time is slightly earlier.

Problems to be Solved by the Invention There is no problem with the switching timing as shown in Figure 3 (B), but if the control circuit controls the switching timing as shown in Figure 3 (B), variations in the drive circuit, etc. Therefore, the conduction period of S3 may end earlier than the conduction period of 81. In that case, a back electromotive force due to the energy stored in the inverter circuit shown in FIG. 1 is applied to Sl when 81 is off,
If the voltage due to the back electromotive force exceeds the withstand voltage of the switching element 81, the switching element S1 will be destroyed. Alternatively, the conduction period of S4 may end earlier than the conduction period of 82. In that case, when the back electromotive force due to the energy stored in the inverter circuit accelerator shown in Fig. 1 is applied to S2 when 82 is off, and exceeds the withstand voltage of the switching element of S2, it will destroy the switching element S2. It ends up.

Means for Solving the Problems In order to solve the above problems, the present invention provides a switching system in which a first DC power source and a second DC power source are connected in series with added polarity, and two chopping operations are performed in parallel on the series power source. The elements are connected in series, and between the common connection point of the series power supply and the common connection point of the two switching elements that perform chopping,
A circuit in which an arc load and a smoothing reactor are connected in series,
In an AC arc welding power source having an inverter circuit consisting of a circuit in which two sets of freewheel circuits each having a rectifier element and a switching element connected in series are connected in parallel to the series connection circuit of the arc load and the smoothing reactor, the current flows from the base material. There is a synchronous delay circuit that delays the switching element of the freewheel circuit for a certain period of time and turns it off after the conduction period of the switching element that performs chopping, which operates during the positive polarity period when the current flows to the electrode, and a reverse polarity circuit where the current flows from the electrode to the base material. A synchronous delay circuit is provided to turn off the switching element of the freewheel circuit after a certain period of time after the conduction period of the switching element that operates during the chopping period has ended.

According to the switching timing of the present invention, as shown in FIG. 3C, the switching element Sl or S2 that performs chopping is 0FFj, and sometimes the switching element S3 or S4 that flows the freewheel current is always ON. . Therefore, most of the back electromotive force caused by the reactor is absorbed by the freewheel circuit. As a result, the back electromotive force of the beam handle is not applied to the switching element S1.32 that performs chopping, and destruction of Sl and S2 due to reverse bias is eliminated.

Example An embodiment of the present invention will be described in detail below.

FIG. 2 shows a control circuit for realizing the switching timing of the present invention. 1 is an inverter, 2 is an AND circuit, 4 is a timer IC that outputs a HIGH signal for a certain period of time in response to a rising signal, and 5 is a timer IC that outputs a LOW signal for a certain period of time in response to a rising signal. FIG. 4 shows a timing chart of each part of the control circuit of FIG. 2.

g is the conduction period of the switching element for reverse polarity freewheeling, h is the conduction period of the switching element for reverse polarity chopping, 1 is the conduction period of the positive polarity freewheeling element, and k is the conduction period of the switching element for positive polarity chopping. switch/
This is the period during which the control element can conduct. a is LOW during the reverse polarity period
, a signal that becomes HIGH during the positive polarity period, and b is its inverted signal.

C outputs a HIGH signal of T1 for a certain period upon the rising edge of a, and this signal becomes the conduction extension period of the reverse polarity freewheel switching element as shown in FIG. 4g. Next, f is LOW for a certain period T2 due to the rising signal of a.
output a signal, and set the period of T2-T1 as T3;
This period becomes the dead time between the reverse polarity conduction period and the positive polarity conduction period, as shown in FIG. Similarly, T4 is an extension period of the positive polarity freewheel period, and the T6 period of T5-T4 is a dead time from the positive polarity conduction period to the reverse polarity conduction period. The current that flows depending on this switching timing will be explained with reference to FIG. One person is a first DC power supply that supplies a reverse polarity current, and two people are a second DC power supply that supplies a positive polarity current. SL is a switching element that controls on/off the reverse polarity current, S3 is a switching element that conducts the freewheel current when the polarity is reversed, S2 is a switching element that controls the on/off of the positive polarity current, and S4 is the switching element that conducts the freewheel current when the polarity is positive. It is a switching element that

In the case of reverse polarity, when SL is turned on, the reverse polarity side DC power supply 1 is activated.
Person+ to 81- Smoothing reactor 6 → Electrode 2 → Arc 4
→Base metal 3→Reverse polarity side DC power supply 1 - Current flows in the path, and when Sl is turned off, the magnetic energy of smoothing reactor 6 causes smoothing reactor 6 → electrode 2 → arc 4 → base metal 3 → S3 → A freewheel current on the opposite polarity side flows in the path D6→smoothing reactor 6. Next, when changing the arc current from the reverse polarity side current to the positive polarity side current, after turning off the switching element S1 which previously controlled the conduction of the reverse polarity side current, the switching element S1 is turned off for a certain period of time as shown in Fig. 4 T1. 83 is turned off by passing the foil current, and after a dead time period shown in FIG. 4 T3, the switching element S2, which controls the opposite positive polarity side current, and S4, which conducts the positive polarity freewheel current, are turned on.

For positive polarity operation, when S2 is turned on, the positive polarity side DC power supply 1
A current flows from B+ through the path of base metal 3 → arc 4 → electrode 2 → smoothing reactor 6 → S2 → positive polarity side DC power supply 1B-, and when S2 is turned off, the smoothing reactor 6 is caused by the magnetic energy of the smoothing reactor 6. →D5→S4→Base material 3→
A positive freewheel current flows in the path of arc 4 → electrode 2 → smoothing reactor 6. Next, when changing the arc current from the positive polarity side current to the reverse polarity rt current, after turning off the switching element S2 which previously controlled the positive polarity side current, for a certain period of time shown in T4 in Fig. 4. After passing the freewheel current and turning off 84, there is a dead time period shown in FIG.
Turn on 3.

Effects of the Invention As described above, the energy stored in the smoothing reactor can be released by turning off the conduction period of the switching element that conducts freewheel current by a certain period of time with respect to the conduction period of the switching element that performs chopping. Absorbed by foil circuit. By preventing the back electromotive force of the smoothing reactor from being applied to the switching element that performs chopping, destruction of the switching element can be prevented.

[Brief explanation of the drawing]

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. , FIG. 4 is a timing chart of the present embodiment shown in FIG. 1 person...DC power supply for reverse polarity, 1B...
Positive polarity DC power supply, DI-D4... Freewheel diode with built-in switching element, D6. D6・
・・・・・・Rectifier diode that makes up the freewheel circuit. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] A first DC power supply and a second DC power supply are connected in series with additive polarity, and two switching elements that perform chopping are connected in series in parallel to the series power supply, and the common point of connection of the series power supplies and the two chopping elements are connected in parallel to the series power supply. A circuit in which an arc load and a smoothing reactor are connected in series, and two freewheel circuits in which a rectifying element and a switching element are connected in series are connected between a common point of connection of the switching elements to be connected in series between the arc load and the smoothing reactor. In an AC arc welding power source that has an inverter circuit consisting of a circuit connected in parallel to the connection circuit, the freewheel circuit is activated after the conduction period of the switching element that performs chopping, which operates during the positive polarity period when the current flows from the base metal to the electrode, ends. A synchronous delay circuit that turns off the switching element by delaying it for a certain period of time, and a synchronous delay circuit that turns off the switching element by delaying it for a certain period of time, and a synchronous delay circuit that turns off the switching element for a certain period of time after the conduction period of the switching element that performs chopping that operates during the reverse polarity period when current flows from the electrode to the base material. AC arc welding power source equipped with a synchronous delay circuit that turns off after a delay.