JPH0413061B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention provides feedback control in which input DC is converted into AC with a frequency higher than the commercial power supply frequency and then used as a welding load power source via a transformer and a rectifier circuit. The present invention relates to a power supply device for an arc welding machine with functions.

[Background of the invention]

In order to reduce the size and weight of the overall configuration of the power supply device for arc welding machines, the power frequency is converted to a frequency higher than the commercial power frequency at the stage before the transformer, and the power is transmitted through the transformer, rectifier, and reactor. There are configurations that supply the load.

FIG. 1 is a circuit diagram showing the overall configuration of a power supply device for an arc welding machine of this type which was previously developed by the present applicant, and this will be explained first.

In the figure, 1 is a rectifier that converts a three-phase AC power supply into a DC power supply, 2 is a smoothing capacitor, and 3 is a bridge connection of transistors T ₁ to T4, with diodes D ₁ to D ₄ connected between their collectors and emitters. An inverter (switching circuit) consists of an inverter (switching circuit) that alternately turns on and off between the pair of transistors T ₁ and T ₄ and the pair of transistors T ₂ and T ₃ , so that the DC current from rectifier 1 is lower than the commercial power frequency. It outputs as AC power at a much higher frequency. 4 is a transformer which inputs the AC output of the inverter 3 and outputs AC at a desired welding voltage.

A rectifier 5 is inserted into the secondary side of the transformer 4 and converts the output of the transformer 4 into direct current, and a reactor 6 is used to stably flow a smoothed direct current to the welding load 7. 8 is a shunt provided between the middle point of the secondary winding of the transformer 4 and the load 7;
Detects the welding current flowing through the The output of the shunt 8 is applied to the − input terminal of a differential amplifier 10 via an amplifier 9. Reference numeral 11 denotes a reference voltage generator for output setting, the output of which is applied to the +input terminal of the differential amplifier 10. The differential amplifier 10 amplifies the difference signal between the output signal of the reference voltage generator 11 and the current detection signal obtained by amplifying the output signal of the shunt 8 with the amplifier 9, and outputs the output control signal V to the comparator 12. It is given as ₁ .

Reference numeral 13 denotes a sawtooth voltage generator, and its output signal (sawtooth wave signal) is input to the - input terminal of the comparator 12, and is also input to the signal distribution circuit 14. The comparator 12 compares the sawtooth wave signal with the output control signal V ₁ of the differential amplifier 10, and when the output control signal V ₁ is smaller, the transistors T ₁ , T ₄ and T ₂ of the inverter 3 Outputs pulse signal _V2 to alternately turn _T3 on and off.

The signal distribution circuit 14 receives the sawtooth wave signal from the sawtooth voltage generator 13 and the output pulse signal from the comparator 12.
V ₂ is input, two types of output pulses V ₃ and V ₄ which are alternately turned on and off are generated, one of which is given to the inverter drive circuit 15 and the other to the inverter drive circuit 16 . Inverter drive circuit 15, 16
creates two-phase pulse signals V _{5 ,} V ₆ ; V ₇ , V ₈ that alternately turn on and off in response to output pulses V 3 , V ₄ , and connects transistors T ₁ , T ₄ and T ₂ , T ₃ to Turn on and off alternately. Note that the inverter drive circuit 15,
Reference numeral 16 includes a transistor whose switching speed is faster than that of transistors T ₁ to T ₄ and a delay circuit, and the switching speed can be arbitrarily adjusted by the function of the delay circuit.

According to the power supply device for an arc welding machine configured in this way, feedback control is performed to stabilize the output, but due to some kind of failure (such as so-called "hand shake" during welding work), the output signal of shunt 8 (feedback control) signal) changes suddenly, pulse signal V ₂
For example, _{the pulse width of the output pulse V 3 ( pulse} signal
V ₅ , V ₆ ) side is the output pulse V ₄ (pulse signal V ₇ , V ₈ )
A state in which the pulse width is wider than the other side continues for several cycles, and as a result, the transformer 4 may become biased.

In addition, hunting occurs due to feedback control, and _the output pulses V ₃ and V ₄ become stable with wide and _narrow pulse widths. ₆ )
The output pulse V ₄ (pulse signals V ₇ , V ₈ ) side is always stabilized in a wider pulse width than the output pulse V 4 (pulse signals V 7 , V 8 ) side, and this also causes biased magnetization.

When such biased magnetization occurs, the transformer 4 becomes saturated, and the switching elements of the inverter 3, here transistors T ₁ , T ₄ ; T ₂ , T ₃ , generate high-frequency alternating current.
An overcurrent flows through these transistors T ₁ , T ₄ ;
T ₂ and T ₃ were sometimes destroyed thermally or by spike voltage caused by overcurrent.

[Purpose of the invention]

The present invention has been made in view of the problems of the prior art described above, and is a method for stable output control that does not cause biased magnetic development in the transformer even when the feedback signal suddenly changes or hunting occurs. It is an object of the present invention to provide a power supply device for an arc welding machine that can obtain pulse V ₂ and, in turn, V ₃ and V ₄ .

[Summary of the invention]

A feature of the present invention is that the shunt is provided at the downstream side of a current detector (shunt) or at the downstream side of a first comparison circuit that compares the output of this current detector with a reference voltage for output setting, and the current detector output A sample hold circuit holds a signal level according to the signal level until receiving a reset pulse and outputs it to the first comparator circuit or second comparator circuit, and the other is a sample hold circuit for driving an inverter from a signal distribution circuit. A reset circuit is provided which provides a reset pulse to the sample and hold circuit in synchronization with the trailing edge of each pulse of either one of _the pulse signals _{V 3 or} V ₄ , and The point is that the pulse widths of the pulse signals V ₃ and V ₄ during the cycle (period) are made the same.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 2 and 3.

FIG. 2 is a circuit diagram showing an embodiment of the power supply device for an arc welding machine according to the present invention. In FIG. 2, the same reference numerals as in FIG. 1 indicate the same or corresponding parts.

In FIG. 2, a signal level corresponding to the output of shunt 8 is maintained between an amplifier 9 that amplifies the output signal (feedback signal) of shunt 8 and a differential amplifier 10 until it receives a reset pulse. A sample and hold circuit 20, which outputs to the differential amplifier 10 and includes a switch circuit 17, a buffer 18, and a capacitor 19, is provided. Further, an off-delay circuit 21 is provided which applies a reset pulse to the sample and hold circuit 20 in synchronization with the trailing edge, here the falling edge, of each pulse of the pulse signal _V4 for driving the inverter from the signal distribution circuit 14.

Next, the operation of the above-mentioned apparatus of the present invention will be explained with reference to FIG. FIG. 3 is a diagram showing the signal waveforms of _each part in FIG. 2. As shown in FIG. (at the falling edge in the illustrated example), the output signal c of the off-delay circuit 21
is output as a reset pulse of the sample and hold circuit 20. Here, the reset pulse c
When is output from the off-delay circuit 21, the switch circuit 17 of the sample-and-hold circuit 20 is turned on, and the voltage b of the capacitor 19 is made to be the voltage corresponding to the output signal level of the shunt 8, here the output voltage a of the amplifier 9. Note that the pulse width of reset pulse c (pulse off point) is the time required to sample and hold the output voltage a as described above (pulse signal
(a time shorter than one cycle of V ₃ and V ₄ ) is set.

Therefore, the output voltage a of the amplifier 9 is as shown in FIG.
When the output voltage b of the capacitor 19 changes as shown in _FIG .
→b ₂ →b ₃ →b ₄ …).

Now, when the signal distribution circuit 14 outputs the pulse signal V ₄ , the inverter drive circuit 16 operates accordingly and outputs the pulse signals V ₇ and V ₈ .
As a result, transistors T ₂ and T ₃ of inverter 3
is on, but when it is off, i.e. the pulse signal
When the pulse V ₄ -0 of V ₄ falls, the off-delay circuit 21 applies a reset pulse c ₁ to the sample and hold circuit 20, and the output voltage a of the amplifier 9 at that time is held in the capacitor 19 as a voltage b ₁ . As a result, immediately after that, the signal distribution circuit 14 for one period is
Pulse signals V ₃ , V ₄ from V ₃ −1, V ₄ −
1 has the same pulse width. When the pulse V ₄ -1 is output from the signal distribution circuit 14, the off-delay circuit 21 applies a reset pulse c ₂ to the sample and hold circuit 20 at the time of its fall, and the output voltage a of the amplifier 9 at that time is applied to the capacitor 19. Hold voltage b as ₂ . As a result, the pulses V ₃ -2 and V ₄ -2 of the pulse signals V ₃ and V ₄ from the signal distribution circuit 14 for one period immediately thereafter have the same pulse width.

The same operation follows, and the pulse widths of the pulse signals V ₃ and V ₄ (pulse signals V ₃ and V ₄ shown respectively surrounded by broken lines in FIG. 3) during each cycle are made the same.
As a result, pulse signals V ₅ , V ₆ and pulse signals V ₇ ,
_V8 also has the same pulse width within each cycle (one cycle).

Therefore, even if the feedback signal suddenly changes or hunting occurs, the pulse signal
V ₃ and V ₄ (pulse signal V ₅ , V ₆ and pulse signal V ₇ ,
There is no longer any possibility that the pulse width of V ₈ ) will change, and transformer 4
is not biased.

In the above-described embodiment, a case has been described in which the sample and hold circuit 20 is inserted before the differential amplifier 10, but a similar configuration may be provided after the differential amplifier 10.

〔Effect of the invention〕

As described above, according to the present invention, each period (1
Since the pulse widths of the pulse signals V ₃ and V ₄ (the pulse signals V ₃ and V ₄ shown respectively surrounded by broken lines in Fig. 3) during the period (period) are made to be the same, it is possible to avoid sudden changes in the feedback signal. Even if hunting occurs, there is no possibility that the pulse widths of the pulse signals V ₃ and V ₄ (pulse signals V ₅ , V ₆ and pulse signals V ₇ , V ₈ ) will change, and the transformer 4 will not be biased. do not have. Therefore, the transformer 4 will no longer be saturated, and an overcurrent will flow through the switching elements of the inverter 3, causing thermal destruction of the elements or destruction of the elements due to spike voltage caused by the overcurrent. It has the effect of preventing

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing the overall configuration of a power supply device for an arc welding machine of this type previously developed by the present applicant, Figure 2 is a circuit diagram showing an embodiment of the device of the present invention, and Figure 3 is the same as above. FIG. 3 is a signal waveform diagram of each part for explaining the operation of the device. 3... Inverter, 4... Transformer, 5... Rectifier (rectifier circuit), 8... Shunt (current detector),
10...Differential amplifier (first comparison circuit), 11...
... Reference voltage generator, 12 ... Comparator (second comparison circuit), 13 ... Sawtooth voltage generator, 14 ... Signal distribution circuit, 15, 16 ... Inverter drive circuit, 17 ... Switch circuit, 18... Buffer circuit, 19... Capacitor, 20... Sample hold circuit, 21... Off-delay circuit (reset circuit).

Claims (1)

[Scope of Claims] 1. An inverter 3 that receives two-phase pulse signals V ₅ , _{V 6 ;} transformer 4, rectifier circuits 5, 5 that convert the output of this transformer into direct current, and a current detector 8 that detects the welding current output from this rectifier circuit.
A first comparison circuit 10 compares this current detector output with a reference voltage for output setting, and compares this first comparison circuit output with a predetermined sawtooth voltage.
a second comparison circuit 12 that outputs a signal whose pulse width is controlled according to the comparison circuit output, and two types of pulse signals V _{3 and} V for driving the inverter in response to the second comparison circuit output. A signal distribution circuit 14 outputs a signal _V4 , and one pulse signal _V3 of two types of pulse signals from this signal distribution circuit is input, and one of the two-phase pulse signals _V5 drives the inverter. , V ₆ and the other of the two types of pulse signals from the signal distribution circuit, V ₄ , is input to drive the inverter. A power supply device for an arc welding machine is provided with a second inverter drive circuit 16, the other of which is V ₇ , V ₈ , which is provided at a subsequent stage of the current detector or the first comparison circuit, and which outputs the current detector. a sample and hold circuit 20 that holds a signal level corresponding to the signal level until receiving a reset pulse and outputs it to the first comparator circuit or second comparator circuit; and two types of pulse signals from the signal distribution circuit. A power source for an arc welding machine characterized by comprising a reset circuit 21 that provides a reset pulse to the sample and hold circuit in synchronization with the trailing edge of each pulse of either one of the pulse signals _V3 or _V4 . Device.