JPH0565265B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an arc welding power source suitable for use in, for example, TIG (tungsten inert gas) welding.

[Prior Art] Fig. 4 is a circuit diagram showing the configuration of a conventional arc welding power source. In the figure, 1 is a DC power source such as a battery (voltage is E), D1, D2 and D3, D.
4 are diodes connected in series in opposite directions to both ends of the power source E, respectively. Each diode D1, D2, D
Switching elements S1, S2, S3, and S4 are interposed between the anodes and cathodes of No. 3 and D4, respectively. In this case, the inverter is activated by the diodes D1 to D4 and the switching elements S1 to S4.
INV is configured. Between the output terminals of this inverter INV, there is a smoothing reactor (including stray inductance in wiring) L, an arc starter AS,
The electrode T, the arc A, and the base material W are inserted in series. Then, a control section (not shown) detects the welding current Iw and appropriately controls on/off of each of the switching elements S1 to S4 so that the average value of the welding current Iw matches the target value. .

FIG. 5 is a diagram showing the relationship between the general on/off control timing of the switching elements S1 to S4 in the above circuit and the welding current Iw. In this figure, a section Ta is a section where the welding current Iw flows in the direction of the arrow shown in FIG. 4, and a section Tb is a section where the welding current Iw flows in the opposite direction (negative direction) to the above-mentioned arrow.
Furthermore, while the switching element S2 is on in the section Ta, energy is stored in the reactor L, and similarly, while the switching element S4 is on in the section Tb, energy is stored in the reactor L in the opposite direction. Can be stored. Sections T ₁ , T ₁ . . . are sections in which the energy stored in the reactor L flows back through the switch S3 and diode D1, and sections T ₂ , T ₂ . . .
The energy stored in the switching element S1,
This is the section where the current flows back through the diode D3.

As can be seen from FIG. 5E, if the above-mentioned switch control is performed, the ripples in the welding current Iw are reduced due to the smoothing effect of the reactor L, and the welding current Iw at a substantially constant level flows alternately in forward and reverse directions.

[Problems to be Solved by the Invention] By the way, in DC TIG welding, it is known that when a high-frequency pulse current is superimposed on the welding current, the electromagnetic pinch effect increases and the stability of the arc is improved. The electromagnetic pinch effect is a property in which the magnetic field generated by the arc current exerts a force in a direction that reduces the diameter of the arc, and is a desirable property for stabilizing the arc. Therefore,
The method of superimposing high-frequency pulsed currents is effective for welding thin plates, which require low current welding and where the arc is likely to become unstable.

On the other hand, in the case of materials that are easily oxidized, such as aluminum, reverse polarity welding or AC welding, which has a cleaning effect to remove the oxide film, is often applied.

However, in the case of an AC welding power source, when welding thin materials, the average value of the welding current must be lowered, which has the disadvantage that the arc becomes unstable. Therefore, it is conceivable to superimpose high-frequency pulses in the same way as in the case of a DC welding power source, but in the conventional AC welding power source shown in FIG. 4, this superimposition is difficult as described below.

That is, in the circuit shown in FIG. 4, since there is a smoothing reactor L, the ripple component is removed from the welding current as shown in FIG. 5, so that high frequency pulses cannot be superimposed.
Therefore, if the reactor L is removed or set to a small value, di/dt can be set to a large value, as shown by the solid line in FIG. In this case, due to the influence of the reactor L and wiring stray inductance, the waveform of the welding current Iw cannot be made into a perfect rectangular wave, but becomes a triangular wave as shown in the figure, but if the value of di/dt is large, A predetermined effect can be achieved.
However, if the reactor L is set to a small value like this, the smoothing effect disappears, so the welding current
If the average value of Iw is small, there will be a section where the welding current Iw is 0, as shown by the dashed line in FIG. 6, resulting in a problem of arc breakage.

This invention was made in view of the above-mentioned circumstances, and it is possible to superimpose a high-frequency pulse current on the welding current in an AC welding power source, and even when the average value of the welding current is set to a small value, arc breakage occurs. The purpose is to provide a welding power source that does not cause any damage.

[Means for Solving the Problems] The present invention was made to solve the above-mentioned problems, and includes a transformer to which the output of an inverter is supplied to the primary side, and a transformer provided on the secondary side of this transformer. The first one supplies current to the load from the positive direction.
a unidirectional switch and a second unidirectional switch that supplies current from the reverse direction, and the load current in the forward direction is circulated through a path different from that of the secondary side and the first unidirectional switch. a third unidirectional switch that changes the load current in the reverse direction to the second unidirectional switch;
and a fourth unidirectional switch that circulates the welding current through a path different from the next side and the second unidirectional switch, and when the welding current falls below a predetermined value, the third and fourth unidirectional switches The directional switch is turned on.

[Function] Since the inverter side and the load (arc side) are connected by a transformer, the arc current can be reduced by regenerating the load current to the power supply via the transformer.
When di/dt becomes large and the current is low, the third
Since the fourth unidirectional switch is turned on, the welding current flows through a bypass path that does not involve a transformer, thereby reducing di/dt and preventing the welding current from becoming zero.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention. In the figure, parts corresponding to those in FIG. 4 described above are given the same reference numerals, and their explanations will be omitted.

In Figure 1, 6 indicates that the primary coil is an inverter.
This is a high frequency transformer connected to the output end of INV, and the cathode of diode 13 is connected to one end of the secondary coil, and the anode of diode 11 is connected via switching element S7. The anode of the diode 13 is connected to the base material W via the switching element 9 and the current detector 15 sequentially, and the cathode of the diode 11 is connected to the cathode of the diode 12 and the current detector 1.
5 and to the anode of a diode 14 via a switching element S10. The other end of the secondary coil of the transformer 6 is connected to the anode of the diode 12 via the switching element S8, and the high frequency transformer 1
It is connected to the electrode T via the secondary coil 6, and also to the cathode of the diode 14. 18 is a control circuit that performs on/off control of switching elements S1 to S4 and switching elements S7 to S10, and drive control of arc starter 17, and controls the welding current detected by current detector 15.
Iw, the peak current setting value ip obtained by integrating the deviation between the average current setting value set by the setting unit 22 and the current feedback, and the lower reference current setting value ib.
On/off control is performed based on. Further, an oscillator is provided in the control circuit 18, and the switching elements are switched on/off based on the period of the output signal (frequency is 15 kHz or more) of this oscillator. In the above configuration, the diode 11 and the switching element S7 constitute a first unidirectional switch, the diode 13 and the switching element S9 constitute a second unidirectional switch, and the diode 12 and the switching element S8 constitute a second unidirectional switch.
A third switch is configured with the diode 14
and switching element S10 constitute a fourth unidirectional switch. Here, a unidirectional switch refers to a switch that allows current to flow in one direction when it is on, and cuts off a circuit when it is off.

Next, the operation of this embodiment with the above configuration will be explained.

First, from the setting section 22, the average current setting value Iwa, the peak current setting value ip, and the lower reference current setting value ib are input.
is supplied to the control circuit 18. And control circuit 1
8 drives the arc starter 17 to generate the arc A, and in the period T11 shown in FIG. 2, the switching element S7 is turned on (all other switching elements are turned off). As a result, on the secondary side of the transformer 6, a current flows along the path of switching element S7→diode D11→current detector 15→base material W→electrode T. Here, transformer 6
The inductance of the secondary wiring is L2, the number of turns of the primary and secondary coils of the transformer 6 is _N1 ,
If N ₂ and the voltage between the electrode and the base metal are Va, the welding current Iw is expressed by the following formula.

Iw=(E×( _N2 / _N1 )−Va)/L2...(1) Then, the control circuit 18 calculates the average value of the welding current Iw detected by the current detector 15 and a predetermined set value. The product obtained by multiplying this integration result by a predetermined constant (hereinafter referred to as integral deviation) and the welding current
Compare with the instantaneous value of Iw. And welding current Iw
exceeds the integral deviation, the switching element S
1. Turn off S4. switching element S1,
When S4 is turned off, the energy stored in the secondary side of transformer 6 causes current to be regenerated to power source 1 through the same path as in period _T11 , and welding current Iw rapidly decreases. That is, it enters period T ₁₂ . The welding current Iw during this period _T12 is expressed by the following formula.

Iw=|ip|-(E×( _N2 / _N1 )+Va)/ _L2 ...(2) Next, the control circuit 18 outputs the welding current Iw detected by the current detector 15 and the lower reference current setting value. When the welding current Iw falls below the lower reference current setting value ib, the switching element S8 is turned on. At this time, even if the switching element S7 remains on,
It may be switched off. When switching elements S7 and S8 are both on, the welding current
Iw is switching element S8, diode D12
, and a part of it excites the secondary side of the transformer 6. This exciting current flows through the primary side of the transformer 6 and the diodes D2 and D3.
It is regenerated to the power supply 1 via. On the other hand, when switching element S7 is off and S8 is on, the welding current Iw is
Reflux through 2. That is, if the switching element S8 is on, all or part of the welding current Iw flows through the switching element S8 and the diode 12, which are bypass paths, in sequence. Therefore, as shown in period T ₁₃ shown in Figure 2,
The value of di/dt becomes significantly small, and the welding current Iw during this period becomes Iw≒|ib| (3) and becomes almost equal to the lower reference current setting value ib. Then, when one cycle of the output signal of the oscillator in the control circuit 18 (frequency is 15kHz or more) is completed, each switching element S1 to S4, S7 to S1
0 is again placed in the same on/off state as in the period _T11 . Thereafter, operations similar to those in periods T ₁₁ , T ₁₂ , and T ₁₃ are performed, and after a series of operations in periods T ₁₁ to _{T 13} have been performed a predetermined number of times, switching elements S3 and S
2 and switch the direction of the welding current Iw.
Then, in the period _T11 , only the switching element S9 is turned on, in the period _T12 , the switching elements S3 and S2 are turned off while the switching element S9 is turned on, and in the period _T13 ', the switching element S9 is turned off. Switching element S10 is turned on by turning it on or off. In this case, switching of the switching elements in each section T ₁₁ ′ to _{T 13} ′ is exactly the same as in the above-described sections T ₁₁ to _{T 13} , only the direction of the welding current Iw is different. That is, the value of the welding current Iw in each section T ₁₁ ′ to T ₁₃ ′ is also expressed by the above-mentioned equations (1) to (3). Further, the operation of the control circuit 18 in the section T ₁₁ ′ to T ₁₃ ′ is also the same as in the above case.

In this embodiment, the above-mentioned periods have the following relationship.

T ₁₁ / (T ₁₁ + T ₁₂ + T ₁₃ ) = T ₁₁ ′ / (T ₁₁ ′ + T ₁₂ ′ + T ₁₃ ′) < (1/2)
...(4) The reason for setting such a relationship is as follows. That is, in period T ₁₁ , E(V) is applied to transformer 6.
E(V) is applied to the transformer 6 during the regeneration periods T ₁₂ and T ₁₃ . In this case, the regeneration period is
If it is shorter than T ₁₁ , biased magnetization will occur in the transformer 6 and it will eventually become saturated, but if the period T ₁₁ is shorter than the regeneration period, the transformer 6 will be energized in the opposite direction by the same amount as it is energized in the forward direction. This is because biased magnetization does not occur, and saturation of the transformer 6 is thereby avoided.

Furthermore, since switching elements S7 and S9 are switched only when switching polarity, and switching elements S8 and S10 forming a bypass path are switched only when low current is present, losses are small in both cases.

Next, FIG. 3 is a circuit diagram showing the configuration of another embodiment of the present invention. This embodiment includes a transformer 6 with a center tap instead of the transformer 6 shown in FIG.
A transformer 6' having a secondary coil is provided.
The primary coil includes switching elements S1,
Excitation control is performed only in S4, and polarity reversal is not performed. In this case, the direction of the welding current Iw is switched by a switching element S provided on the secondary side.
7, performed by S9. The operation of this circuit is
The operation is exactly the same as that of the circuit shown in FIG. 1 described above. In addition, in each of the above embodiments, switching of the switching elements S1 to S4, S7, and S9 is
Since welding is performed at a frequency of 15kHz or higher, there are no hearing problems during welding work.

[Effects of the Invention] As explained above, according to the present invention, the transformer to which the output of the inverter is supplied to the primary side;
A first unidirectional switch that is provided on the secondary side of the transformer and supplies current to the load from the forward direction, a second unidirectional switch that supplies current from the reverse direction, and a load current in the forward direction. a third unidirectional switch that circulates the load current in the reverse direction through a path different from that of the secondary side and the first unidirectional switch;
and a fourth unidirectional switch that causes the flow to flow back through a path different from the unidirectional switch, and turns on the third and fourth unidirectional switches when the welding current falls below a predetermined value. Therefore, it is possible to superimpose a high-frequency pulse current on the welding current, and there is an advantage that arc breakage does not occur even when the average value of the welding current is set small.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a waveform diagram showing the welding current Iw in the same embodiment, and Fig. 3 is a circuit diagram showing the configuration of another embodiment of the invention. , Fig. 4 is a circuit diagram showing the configuration of a conventional welding power source, Fig. 5 is a waveform diagram showing the welding current Iw in the conventional welding power source, and Fig. 6 is a diagram showing the welding current Iw in the conventional welding power source when high-frequency pulse current is superimposed. FIG. 11 to 14... Diodes (first to fourth unidirectional switches), S7 to S10... (first to fourth unidirectional switches).

Claims (1)

[Claims] 1 A transformer to which the output of the inverter is supplied to the primary side, a first unidirectional switch provided on the secondary side of this transformer that supplies current to the load from the positive direction when turned on, and a reverse a second unidirectional switch that supplies current from the direction; and a second unidirectional switch that, when turned on, causes the positive direction load current to circulate through a path different from that of the secondary side and the first unidirectional switch. a third unidirectional switch;
a fourth unidirectional switch that, when turned on, circulates the load current in the reverse direction through a path different from the secondary side and the second unidirectional switch; The third unidirectional switch is turned on when the load current falls below a predetermined value, and the fourth unidirectional switch is turned on when the load current in the reverse direction falls below a predetermined value. An arm welding power source characterized by: