JPH0424145B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter type arc welding power source, and more specifically, a welding power source control method that can suppress noise during the arcing period and stably control the inverter current during the short circuit period. Regarding.

Figures 1 and 2 are block diagrams showing examples of the configuration of a conventional arc welding power source. Figure 1 shows the configuration of a phase controlled current type power supply device, and Figure 2 shows the configuration of a DC chopper type power supply device. It is. In these figures, 1 is a main transformer that transforms (steps down) the AC voltage supplied from a three-phase AC power supply 2 via a switch 3, 4 is a smoothing reactor for removing ripples, and 5 is a wire 6. a contactor that supplies direct current to
7 is a motor for feeding out the wire 6; 8 is a welding base material; 9 is an arc; 10 is the wire 6 and the welding base material 8
11 is an amplifier that detects the voltage between (welding voltage) Va and outputs a feedback voltage Vf;
A shunt resistor 12 detects the feedback current If from the voltage across the shunt resistor, and also connects the set voltage Vs of the arc voltage setter 13 to the feedback voltage Vf and the welding current setter 14. This is a control circuit that compares the set current Is with the feedback current If and outputs a control pulse Pc. In addition, in Fig. 1, 15 is a control pulse Pc
16 is a rectifier;
17 is a switching element turned on/off by control pulse Pc, 18 is an electrolytic capacitor, 19
is a diode.

In these configurations, the phase control rectification type power supply device shown in FIG. 1 controls the firing angle of the forward converter 15, and the DC chopper type power supply device shown in FIG. 2 controls the on period of the switching element 17. By doing so, arc voltage Va and welding current I
and to maintain the set values.

On the other hand, in recent years, inverter-type welding power supply apparatuses have become popular, which use a high-frequency inverter and install a transformer in a high-frequency AC circuit to significantly reduce the size of the transformer.

FIG. 3 is a block diagram showing an example of the configuration of this type of welding power supply device. In the figure, Figure 1, Figure 2
Components corresponding to those in the figure are given the same reference numerals.

The feature of this welding power supply device is that the output (DC) of the rectifier 16 is converted into high frequency alternating current (e.g.
6KHz), then transformed by a transformer 22, rectified again by a rectifier 23, and supplied to the welding machine. In this case, the welding voltage Va and the welding current I are adjusted by controlling the on-period To of the switching element constituting the inverter 21.

According to such a configuration, the transformer 22 can be made smaller than the conventional main transformer 1. That is, if the number of windings and the primary and secondary voltages of the main transformer 1 and the transformer 22 are constant, the magnetic flux density used is Φ, and the frequency is set, then Φ∝1/...(1) holds true. Therefore, the frequency of commercial power supply 2 is set to 60Hz,
If the switching frequency (inverter frequency) of the inverter 21 is 6KHz, the inverter system requires a transformer with a core cross-sectional area of 1/100.
However, in reality, it is necessary to keep the magnetic flux density Φ low in order to lower the permissible limit of the number of turns due to the decrease in the core outer diameter and to suppress core loss due to the increase in frequency. The weight will be reduced by about 5%. Furthermore, the cross-sectional area of the iron core of the smooth reactor 4 can also be reduced in weight to 1/10.

In this way, inverter-type welding power supplies can be made extremely small and lightweight;
The drawback was that the arc generated high-frequency vibration noise, which significantly worsened the working environment. This is the ripple component of the welding current I (2 of the inverter frequency).
This is because the high-frequency components) appear as arc pulsating pressure. In order to eliminate this drawback, the only way is to set the inverter frequency to 8KHz or higher and remove the frequency of the ripple component from the audible frequency band, or to reduce the ripple component by increasing the value of reactor 4 to a very large value. There is no way.

By the way, the method of increasing the value of the reactor 4 not only loses the long-awaited weight reduction effect, but also reduces the powerful advantages of the inverter system, such as decreasing control response time. Therefore, the only solution can be considered to be to set the inverter frequency to 7.5 KHz or higher and to make the high-frequency vibration sound 15 KHz or higher so that it is almost inaudible to human ears.

However, increasing the inverter frequency also creates new problems. This problem will be explained below. FIG. 4 is a block diagram showing the configuration of the main parts of the inverter type welding power supply device shown in FIG. 3, and FIG. 5 is a waveform chart showing waveforms of each part of the device. In these figures, when the switching elements S1 and S2 of the inverter 21 are turned on, a pulsed current flows into the primary winding of the transformer 22 from terminal b and flows from terminal a (Fig. 5A).
As a result, a welding current I flows into the secondary winding from terminal C and flows into terminal d through diode 23a → reactor 4 → contact 5 → wire 6 → arc 9 → welding base metal 8. flows. (Figure 5 d). Furthermore, when the switching elements S3 and S4 are turned on, a current flows in the primary winding in the opposite direction to the above (FIG. 5b), which flows into the secondary winding from terminal e and causes diode 23b to flow into the secondary winding. The welding current I flows from the reactor 4 through the same path as above and flows into the terminal d (FIG. 5D). Further, the voltage (secondary voltage) Vac between both terminals ce and e of the secondary winding of the transformer 22 is an alternating current voltage with positive and negative sides symmetrical, as shown in FIG. 5C.

Here, the number of turns of the primary winding is _n1 , the winding between terminals c-d and e-d of the secondary winding is _n2 , the primary voltage is E, the resistance of the welding circuit is R, and the flow through it is The welding current is I,
Assuming that the arc voltage is Va, the switching period of the inverter 21 is 2T, and the on period of the switching element is To (see FIG. 5), the equation at steady state is as follows.

n ₂ /n ₁ E×T ₀ /T=IR+Va...(2) Also, in this type of power supply, the arc voltage Va is 15V.
, and the circuit resistance R is
Since it is about 10mΩ, the welding current I = 100A,
If the primary voltage E = 300V and n ₂ /n ₁ = 1/5, then from equation (2), 60 × T ₀ /T = 100 × 10 ^-2 + 15 = 16 ... (3), and at this time T ₀ /T=0.27. And if the inverter frequency (=1/2T) is 8KHz,
Since T = 62.5 μS, the on period T ₀ is approximately 17 μS (=
62.5×0.27).

Now, using large capacity transistors for the switching elements S1 to S4 is an important factor that leads to lower cost of the device, but the storage time of this type of transistor (the time from when the on signal is removed until the element turns off) ) is usually 5 μS or more. Therefore, if about 17 μS is the minimum value of the on-period T ₀ , variations in the on-periods of the switching elements S1 to S4 due to variations in storage time will not be a problem.

However, in this type of power supply device,
The melting of the electrode (wire 6) progresses in the steps shown in Fig. 6 A to F, and at a frequency of about 20 to 100 Hz, the melting progresses in the steps shown in Fig.
It is normal for the short circuit shown in (d) to occur.

Now, a problem occurs during this short circuit. That is, in equation (2), if the arc voltage Va = 0 with the welding current I = 100A, T ₀ /T = 1/60 ... (4), and when T = 62.5μS, T ₀ ≒ 1μS become.
In reality, due to voltage drop in the rectifier 23, etc.
T ₀ = about 2 μS may be sufficient, but this value is still within the storage time of the transistor. Even if this on-period T ₀ can be achieved, there will be extremely large variations, and the transformer 22 shown in Fig.
The positive and negative sides of the secondary voltage Vac become asymmetrical, causing biased magnetization of the transformer 22. Furthermore, even if the on-pulse is instantaneously generated, if the on-period T ₀ is greater than 2 μS, the on/off operation of the inverter 21 may be in a state of inactivity. That is, the switching element S of the inverter 21
1. When S2 is turned on and its on period T ₀ becomes greater than 2 μS, the welding current I increases. Therefore, the third
The illustrated control circuit 12 acts to reduce the welding current I, which may prevent the switching elements S3 and S4 from turning on again. In this case, for example, the positive half cycle (switching elements S1, S
2 ON) occurs continuously, and it becomes necessary to increase the saturation tolerance of the transformer 22. thus,
The minimum value of the on-period T ₀ must be set to a value that is sufficiently larger than the storage time of the transistor, and the influence of variations in storage time can be ignored.

In view of the above circumstances, the present invention provides a welding power source control method capable of suppressing noise during the arc period and ensuring a sufficient control range of the inverter current during the short circuit period. detecting an arc voltage applied to a pair of electrodes having a voltage and comparing the arc voltage with a predetermined reference voltage;
When the arc voltage exceeds the reference voltage, it is determined that the arc period is in progress, and the switching period of the switching element is controlled to increase the inverter frequency of the welding power source to a value that is twice as high as the above-mentioned reference voltage. and when the arc voltage falls below the reference voltage, it is determined that a short circuit period is in progress, and the switching period of the switching element is controlled to reduce the inverter frequency of the welding power source. do. In addition, since there is no arc 9 during the short circuit period, no air vibration occurs,
No noise is generated. Therefore, the inverter frequency may be lowered during this time, thereby allowing the use of slower switching elements.
As a result, this method is significantly advantageous in terms of reliability and cost compared to the conventional method of using high-speed switching elements in parallel.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 7 is a block diagram showing the configuration of an embodiment of the present invention, in which parts corresponding to those in FIGS. 3 and 4 are given the same reference numerals. In this figure, 31 is an amplifier that amplifies the voltage across the shunt resistor 11 and outputs a feedback current If, and 32 is an amplifier that amplifies the voltage across the shunt resistor 11 and outputs a feedback current If, and 32 is an amplifier that amplifies the voltage across the shunt resistor 11 and outputs a feedback current If.
This is an integrating circuit that integrates the sum If-Is with Is and outputs a signal Sa. Also, 33 is the feedback voltage Vf
34 is a comparator that compares the reference voltage Es and outputs a signal Sb of "H" level when Vf<Es and "L" level when Vf>Es.
This is a triangular wave generator that outputs a triangular wave Dw with a frequency of ₀ when the signal is at the "L" level and a frequency of ₀ /n when the signal is on the "H" level. Furthermore, 35 is an integration circuit 32
Compare the output Sa and the triangular wave DW (Fig. 8 A),
A comparator 36 inverts the output of the comparator 35 (FIG. 8B), which outputs "H" level when DW>Sa and "L" level when DW<Sa.
This is an inverter that outputs a control signal Sc that turns on/off switching elements S1 to S4. (Figure 8c). Here, the control signal Sc is “L” when DW>Sa
Since the level is "H" when DW<Sa, the lower the level of the signal Sa, the wider the "L" level width of the control signal Sc becomes, and the narrower the "H" level width becomes. Furthermore, since the on-period _T0 of the switching elements S1 to S4 almost matches the "H" level width of the control signal Sc, the on-period _T0 becomes shorter as the feedback current If increases and the level of the signal Sa decreases. controlled in direction.

In such a configuration, when the welding current I increases and the feedback current If becomes larger than the set current Is, the on-period T ₀ is short-circuited in the above-mentioned process, and the welding current I decreases. On the other hand, when the welding current I decreases, the on-period T ₀
increases, and the welding current I increases. In this way, welding current I is maintained at a predetermined value.

Next, when the wire 6 and the weld base metal 8 are separated and an arc 9 exists (arc period; 6th
In Figures A, B, H, and F), since the arc voltage Va is larger than a certain value, the feedback voltage Vf is also larger than the reference voltage Es. Therefore, the output Sb of the comparator 33 becomes "L" level, and the triangular wave generator 34 outputs a triangular wave with a frequency of ₀ (>7.5 KHz).
DW is output, and the above-mentioned current control is performed using this triangular wave DW. Therefore, the frequency ₂₀ of the ripple component of the welding current I is 15 KHz or more, and as a result, the high frequency vibration sound generated from the arc 9 becomes almost inaudible to human ears.

On the other hand, during the short-circuit period when the wire 6 and the welding base metal 8 are short-circuited and the arc 9 is not present (Fig. 6 C, D), the arc voltage Va becomes 0, so (2)~
As explained in equation (4), the welding current I is set to the set current Is
In order to hold the switching elements S1 to S
The on-period T ₀ of 4 must be made extremely short with respect to the switching period 2T. Therefore, in this embodiment, the switching period 2T is lengthened instead of shortening the on-period _T0 . Even in this case, no high-frequency vibration sound is generated during the short-circuit period, so no noise is generated.

Now, a short circuit occurs and the feedback voltage Vf<
When it comes to the reference voltage Es, the output of the comparator 33
Sb goes to the "H" level, and the triangular wave generator 34 outputs a low frequency triangular wave DW with a frequency of ₀ /n, and the above-described current control is performed by this triangular wave DW. In this case, the frequency ₀ /n is determined as follows.

(1) Switching elements (transistors) S1 to S
Considering the storage time of 4, determine the minimum on-period T ₀ min that can be realized with the switching element used.

(2) Next, use equation (4) to find the time T so that the on-period T ₀ when outputting the minimum welding current I is greater than or equal to the minimum value T ₀ min, and from this calculate the frequency ₀ / n Find (=1/2T).

By controlling the switching elements S1 to S4 using the frequency ₀ /n thus obtained, stable current control can be performed during the short circuit period.

As explained above, in the present invention, an arc voltage applied to a pair of electrodes having a predetermined interval is detected, the arc voltage is compared with a predetermined reference voltage, and the arc voltage is higher than the reference voltage. When you cross it,
It is determined that the arcing period is in progress, and the switching period of the switching element is controlled to set the inverter frequency of the welding power source to a value such that twice the inverter frequency is equal to or higher than the audible frequency band, and the arc voltage is adjusted to the reference level. When the voltage drops below the voltage, it is determined that a short-circuit period is occurring, and the switching period of the switching element is controlled to reduce the inverter frequency of the welding power source so that the inverter current can be stably controlled, thereby reducing ripples in the welding current. It is possible to make high-frequency vibration noise caused by the components inaudible to the human ear, and it is also possible to use slower switching elements for the inverter.
It is possible to improve reliability and reduce costs.

[Brief explanation of drawings]

Figure 1 shows a conventional phase-controlled current type power supply device.
Figure 2 is a block diagram showing the configuration of a conventional DC chopper type power supply, Figure 3 is a block diagram showing the configuration of a conventional inverter type welding power supply, and Figure 4 is a block diagram showing the configuration of a conventional inverter type welding power supply.
The figure is a block diagram showing the configuration of the main parts of the welding power supply, Figures 5A to 5D are waveform diagrams showing the waveforms of each part of the welding power supply, and Figure 6 explains the arc period and short circuit period in the welding process. This is a diagram for
B, E, and F are diagrams showing the arc period, C and D of the same figure are diagrams showing the short-circuit period, FIG. 7 is a block diagram showing the configuration of an embodiment of the present invention, and FIGS. FIG. 21... Inverter, S1 to S4... Switching element, ₀ , ₀ /n... Inverter frequency, T ₀
...On period.

Claims (1)

[Scope of Claims] 1. A welding power source control method using an inverter method in which the arc welding current and voltage are controlled by the switching period of a predetermined switching element when performing arc welding accompanied by a short circuit, comprising: Detecting the arc voltage applied to a pair of electrodes having The switching period of the switching element is controlled to set the inverter frequency of the welding power source to a value that doubles the inverter frequency and exceeds the audible frequency band, and when the arc voltage falls below the reference voltage, during the short circuit period. A welding power source control method, characterized in that the inverter frequency of the welding power source is reduced by determining that the switching period of the switching element is . 2. The welding power source control method according to claim 1, wherein during the short-circuit period, the on-period of the switching element is set to be equal to or longer than the minimum on-period value of the switching element.