JPS589768A - Electric power source device for arc welding machine - Google Patents

Abstract

PURPOSE:To provide a device of a low cost and a small size by executing driving and switching of switching elements by high frequencies and switching elements by low frequencies in parallel thereby obtaining stable square wave currents of desired sizes in the output of a transformer. CONSTITUTION:The DC output of a DC electric power source part consisting of a rectifier 2 and a smoothing circuit 3 is inputted to an inverter device 4. The device 4 consists of a transformer 5 having a neutral point in the primary winding and two windings on the secondary side, transistors (TRs) 6, 7 connected to the primary winding of the transformer and a control circuit 8 which drives and controls the TRs 6, 7. The circuit 8 includes a part of a feedback control section. The secondary voltage of the transformer 5 is half-wave rectified by diodes 9, 10 respectively, and is supplied through an AC-DC switch 11 and a current detector 12 to load 13. The detector 12 detects the output current and transmits the same to the circuit 8, that is, said circuit controls the TRs 6, 7 which are switching elements in such a way that part of the output current is fed back and the output current is made constant.

Description

[Detailed description of the invention] This invention relates to a power supply device for an arc welder.

This relates to power source #[K, which is particularly suitable for application to AC arc welding machines.

As is well known, when a sinusoidal load current is used in AC arc welding, maintaining the arc is relatively difficult, especially when welding aluminum materials.

The reason for this is that when the aluminum material is in the -4th position, good electron emission cannot be achieved, and in many cases, the arc fails to re-ignite in the phase where the aluminum material is in the -4th position. do. Conventionally, in order to make the four load currents into a rectangular waveform, the rise and fall of the current waveform were made steeper by thyristor control, and the current and waveform were flattened using a large accelerator as shown in Figure 9. At the same time, the current stop period due to the buoyster control (phase angle control #) fc was eliminated. This technique is disclosed in equity fIB54-30653.

However, such a power supply device has the following drawbacks.

First of all, as mentioned above, it is necessary to increase the capacity of the KFi reactor that eliminates the four-fluid stop period and facilitates the re-ignition of the arc, which makes the heel control device larger and more expensive. Second, when two circuits are installed on the secondary side of a transformer, the positive half-wave and negative half-wave are individually controlled in each circuit, so basically the input on the primary side of the transformer is converted into a three-phase input. I can't, so I put U on this primary side.

If either the V or W phase is used, the load may cause the Fi 3-phase power supply itself to be in a voltage unbalanced state, which may adversely affect other equipment. Thirdly, when the connection state of the two circuits on the secondary side is changed and this device is used as a power supply device for a DC arc welding machine, the current supplied to the load becomes four single-phase rectified currents, so the ripple becomes large. Therefore, when welding with a large flow, the ripple causes the arc to vibrate, making the welding beat uneven.

This invention was made in view of the above, and its primary purpose is to provide a small 4E source device for arc welding machines at low cost. When using a DC arc welding machine, the power supply device is designed to prevent the 3-phase 4# from becoming unbalanced even if In summary, the inverter device includes a DC power supply unit that converts AC input into DC, an inverter device including a transformer and a switching element, and a feedback control unit that sets the output to a constant current of 1!1ll (lit). A switching signal forming means for forming a high frequency switching signal based on the output of the feedback control section and a switching element switching signal forming means for switching the drive of the switching element at a low frequency are provided, and the switching element is switched by high frequency and the switching element by low frequency. Drive switching is performed in parallel to obtain a stable rectangular waveform of a desired magnitude at the transformer output.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of a power supply device according to an embodiment of the present invention.

In the figure, 1 is a commercial three-phase AC power supply, 2 is a rectifier composed of a bridge circuit, etc., and a 3Fi smoothing circuit. Input 4v.

Inverter device 4Fi, a transformer 5 having a neutral point on the secondary winding and two windings on the secondary side, a transistor 6.7 connected to the primary winding of this transformer 5, and this transistor 6
．． The control circuit 8 includes a part of the feed rose 211J as will be described later.

The secondary voltage of the transformer 5 is connected to each diode 9.1O.
The half wave is passed through the AC/DC switch 11 and the current detector 12 to be supplied to the load 13. Current detector 12
is a device for detecting an output current, and a transistor, which is a switching element, is used so that this output Fi is sent to the control circuit, that is, a part of the output #1 current is fed 'packed, and the output current is made into a constant current. 6.7.

FIG. 2 shows a block diagram of the control circuit 8. As shown in FIG. In the figure, reference numeral 8a denotes a comparator amplifier to which the base $1#E and the output of the current detector 12 are connected to the input side. comparison amplifier 8λ
is connected to the high frequency pulse generation circuit 8b-, where a high frequency pulse having a duty ratio corresponding to the output of the comparator amplifier 8a is generated. The Phytopack control section is this comparison amplifier 8a.

It is composed of a reference can source E and a current detector 12.

As shown in FIG. 3, the high frequency pulse generating circuit 8b is composed of a sawtooth wave generating circuit 8 and a cloudy pulse forming circuit 8d, and one quiescent wave is generated by comparing the signal level of the comparison output signal of the comparison amplifier 8 and the sawtooth wave. A method is used to determine the utility ratio. That is, a 1-high signal is generated only when the level of the output signal is lower than the signal level of the sawtooth wave. As a result, the pulse width TFi is inversely proportional to the level of the comparison output signal, and therefore R11jJ is inversely proportional to the output current of the inverter device.

The switching drive circuit 8C receives the output pulse from the high frequency pulse generation circuit 8b and forms a switching signal to be applied to the pace of the transistor 6.7.
Low frequency pulse generation circuit 8
f is connected so that the selection of the transistor to which the switching signal is supplied, that is, the drive switching of the transistors 6 and 7 is performed by this low frequency pulse.

FIG. 545 is a timing chart for clearly explaining the disturbance of the switching drive circuit 8C.

The figure (al is the output pulse of the high-frequency pulse generation circuit in the state in which it is present, +b) is the output pulse of the low-frequency pulse generation circuit, t'L td) is the output signal (switching signal) of the switching drive circuit, In the figure, Ldl indicates the output current (however, the AC/DC switch 11 is set to the AC side).The correspondence between the extraction position and waveform of each signal is shown in both Figures 1.2 and 5. It is indicated by the symbols Ia) to Ie).

As is clear from this figure, the transistor 6Fi, which is the first switching element, is high-frequency switched in a half cycle of one period of the low-frequency pulse, and the transistor 6Fi, which is the second switching element, is high-frequency switched in a half cycle of one period of the low-frequency pulse. #i above half day period off e
On the other hand, it is high frequency switched in the next cow cycle.

If we examine the changes in the four output currents due to the above-mentioned switching operation, we will find that the only factor contributing to the delay in response on the secondary side due to transistor switching is the inductance of the transformer 5.

Since the transformer 5 may be a high frequency transformer, this inductance is relatively small, and therefore the above-mentioned response delay is slight. Therefore, the output current is Fig. 5+e)
As shown in K, there is a slight delay in the rise, and there is a steep change without any rest period at the time of reversal. Furthermore, during the period in which the effective output current flows, the feedback control section maintains a constant current, so that extremely flat characteristics can be obtained. Due to this constant current variation, the small actance of the circuit network, and the fact that the feedback control section is generally composed of semiconductor elements, the control is performed under extremely high-speed response characteristics.

Therefore, -IF is to always maintain a stable arc regardless of the load condition.

In this embodiment, the low frequency pulse generating circuit 8M is fixed, but if it is configured to be variable, there is an advantage that cleaning time during welding can be easily adjusted. Further, although two fi transistors are used as switching elements, four transistors may be used in a full bridge connection. Further, in the above embodiment, if the AC/DC switch 11 is set to the OC side, it is possible to obtain a DC output current, but in this invention, as described above, the output current is made constant by feedback control. Since the welding is performed with high precision in each section, a stable arc can be obtained with little current ripple, and a uniform welding beat can therefore be achieved.

As described above, according to the present invention, there is no need to use a reactor at all, and a small transformer for high frequency can be used, so it is possible to obtain a low-grade and small power supply device. Moreover, it is possible to easily form a rectangular wave output smoke flow with no rest period, which is suitable for performing AC arc welding.
Since there is no large fi 4 inductance component such as a reactor, the response characteristics can be made very excellent, and a flat four-flow waveform with little ripple can be obtained, which has the advantage of making the welding beat uniform. Since the nail can be made into three-phase agFi by one person, there is also the advantage that there is no phase imbalance like in conventional equipment.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a 4# device which is an embodiment of this invention, Figure 2 is a block diagram of a control circuit, Figure 3 is a block diagram of a high frequency pulse generation circuit, and Figure 4 is a high frequency pulse generation circuit. 5 shows a timing chart for explaining the operation of the switching drive circuit. FIG. 5 shows a timing chart for explaining the operation of the switching drive circuit. 4... Inverter device, 5... Transformer, 6.7...
- Transistor, 82... Comparison amplifier, 8b... High frequency pulse generation circuit, 8C... Switching drive circuit, 8f... Low frequency pulse generation circuit, 12... Current detector, E.- - Standard 4 sources. Applicant Sansha Co., Ltd. - Ki Seisakusho Agent Patent Attorney Hisashi Komori Inu 13 Hth Figure 5

Claims (1)

[Claims] an inverter device including a DC heel source, a transformer, and at least one pair of switching elements connected to the primary side of the transformer; a feedback control section for current control (and a switching signal forming means for forming a high-frequency switching signal based on the output of the inverter device and the pre-H L feedback control section; A power supply device for an arc welding machine.