JPH0241777A - Power unit for arc machining - Google Patents

Abstract

PURPOSE:To suppress the voltage impressed on a switching element by regenerating the voltage to the DC power source side when the voltage impressed on the switching element increases at the time of changing over the polarity. CONSTITUTION:A power regenerative circuit 15 is connected to an output line of a rectifier circuit 2 and when the voltage between input terminals 15a and 15b increases higher than a set value, the input voltage is converted into the voltage higher than the output voltage of the rectifier circuit 2 and regenerated from output terminals 15c and 15d to the rectifier circuit 2. A DC/DC converter and a circuit named as an inverter circuit commonly named as a flyback system can be used as the power regenerative circuit 15. By this method, the characteristic at the time of changing over the polarity is prevented from being deteriorated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement of a power supply device for arc machining whose output polarity can be switched between alternating current, positive, and negative.

[Conventional technology]

FIG. 4 shows an example of a conventional arc machining power supply device. In the figure, reference numeral 1 denotes an AC power supply, and usually a single-phase or three-phase commercial AC source is used. Sensor 2 is a rectifier circuit and includes a simple smoothing circuit. 3 is an inverter circuit that converts the DC output of the rectifier circuit 2 into high frequency AC, and 4 is a high frequency transformer that converts the output of the inverter circuit 3 into a voltage suitable for processing.

5 is a rectifier circuit, 6a to 6d are bridge-connected switching transistors, 7a to 78 are electrodes for arc processing, 9 is a workpiece, 10 is a switching transistor 6af, and 6a and 6b of the insulator 6d. Alternatively, 6c and 6d are each set as one set, and a polarity switching control circuit for supplying a signal to alternately turn on and off for each set of transistors, 11 is an output current setting circuit, 12 is an output current detector, and 13 is an output current The output Ir of the setting circuit and the output If of the output current detector 12 are compared and a difference signal (Ir-If
), and 14 is a PWMilil that adjusts the output pulse width of the inverter circuit 3 according to the output of the comparator 13.
This is a Jat1 type inverter control circuit. In addition, C shown in the figure shows the stray capacitance of the circuit, and L shows the electrode 8 from the output terminal.
and the inductance of the electric cable up to the workpiece 9.

In the apparatus shown in FIG. 4, the output of AC type #1 is converted into DC in a rectifier circuit 2, and then inversely converted into high frequency AC in an inverter circuit 3. In this inverter circuit 3, the output Ir of the output current setter 11 is detected by the output current detector 12.
The comparator 13 compares the output If with the difference signal △I=1
．． -If, the inverter control circuit 14 determines the output pulse width and performs feedback control to maintain the output current at the set value. The output of inverter circuit 3 is transferred to transformer 4
The voltage is converted into a voltage suitable for arc machining, and the rectifier circuit 5 converts the voltage into direct current again. This DC output is supplied to the DC terminals of a bridge circuit consisting of transistors 6a to 6d, and the AC terminals of the bridge circuit are connected to output terminals a and b, which are connected to the electrode 8 and the workpiece 9, respectively, by power cables. . Further, the transistors 6afl to 6d are controlled by one word from the polarity switching control circuit 10 so that the transistors 6a and 6b and the transistors 6C and 6d each form one set and the transistors of each set are made conductive alternately. As a result, by adjusting the output of the polarity switching control circuit 10, the load consisting of the electrode 8 and the workpiece 9 can be supplied with rectangular wave alternating current of any frequency from positive and negative direct current to high frequency alternating current.

[Apex while the invention is trying to solve]

In the conventional device described above, the switching of the output polarity and the control of the output current are performed completely independently, which causes the following problems.

Transistors 6a and 6b are now conducting, and electrode 8
■ is a positive polarity current. Suppose that is flowing.

From this state, when the base current to the transistors 6a and 6b is cut off and the base current is simultaneously supplied to the transistors 6c and 6d in order to switch the polarity of the output current, all of the transistors 6a fX to 6d become conductive for a short transition time. become. At this time, the output current of the rectifier circuit 5 is about to increase rapidly, or because the inverter circuit 3 is under constant current control as described above, it operates in a direction to suppress this.

In addition, the current supply from the rectifier circuit 5 to the electrode 8 and the workpiece 9 is stopped, and the electromagnetic energy (1/2・LI%) stored in the inductance of the electric cable is reduced.
Therefore, the current continues to flow in the same direction as before, and the arc continues. This current flows through a circuit including electrode 8 - arc - workpiece 9 - diode 7C - rectifier circuit 5 and stray capacitance C - diode 7d - electrode 8. When the transistors 6a and 6b are completely cut off after the transition time, the circulating current due to the energy stored in the inductance L charges the stray capacitance C together with the output of the rectifier circuit 5.

After an oscillation period determined by the inductance L and stray capacitance C, the circulating current stops when it passes through the zero point, and at this time, the current flows from the rectifier circuit 5 in the opposite direction by the transistors 6c and 6d, which have already been supplied with a conduction signal. A voltage in the opposite direction is applied to the electrode 8 and the workpiece 9 in the direction in which a current flows in the direction that makes the electrode 8 a negative potential. As a result, arc discharge is regenerated between the electrode 8 and the workpiece 9, and current begins to flow again.

Since the polarity switching of the device of FIG. 4 follows the above-described process, the stray capacitance C will be charged to a considerably high voltage just before arc regeneration in the reverse direction.

This charging voltage is effective for destroying the insulation that is developing between the electrode 8 and the workpiece 9 during arc regeneration, but on the other hand, the transistor (
In the above case, since the transistors 6C and 6d become conductive, the transistors 6a and 6b) are also applied in parallel with the processed part, so if this voltage exceeds the forward breakdown voltage of the transistors 6a and 6b, It will lead to destruction. Moreover, since this voltage is naturally applied to the rectifier elements constituting the rectifier circuit 5 which are connected in parallel, it may lead to destruction of these elements.

The charging voltage of the stray capacitance generated during the above polarity switching increases in proportion to the electromagnetic energy stored in the power cable. Therefore, when the machining current is large, or when the power cable is long even if the current is relatively small, the generated voltage will be much higher than the voltage required for arc regeneration, and there is a danger that the elements that make up the circuit will be destroyed. There is sex. In order to prevent the generation of such a high voltage, it is conceivable to proactively increase the stray capacitance shown in the figure. For this purpose, a capacitor can be connected between the output terminals of the rectifier circuit, but if a capacitor with too large a capacitance is connected, the regeneration of the arc will deteriorate due to the charging of this capacitor, and a delay will occur in the control of the output current. This will lead to the opposite effect.

Therefore, in reality, the device has no choice but to use a device with a high withstand voltage several times higher than the withstand voltage required for the circuit voltage, resulting in an expensive device.

[Means to solve the problem]

In order to solve the problems of the conventional device described above, the present invention regenerates the voltage applied to the switching element to the DC power source when the voltage becomes high during polarity switching.

[Effect]

In the present invention, when an abnormally high voltage is generated when switching the polarity, it is regenerated to the DC power supply side beyond the output adjustment circuit, so that the electromagnetic voltage stored in the inductance of the power cable is Even when energy is large, the voltage applied to the switching element can be suppressed.

〔Example〕

FIG. 1 shows an embodiment of the present invention. In the same figure, numerals 1 to 14 indicate the same reference numerals and the same functions as those in the conventional device shown in FIG. 15 is a power regeneration circuit connected to the output line of the rectifier circuit 5, and when the voltage between the input terminals 15a and 15b exceeds a set value, the input voltage is transferred to the rectifier circuit 2.
is converted to a voltage higher than the output voltage of the output terminals 15c, 1.
5d is a connection diagram showing an example of a DC/DC converter including a rectifier.

In the figure, 151 is an oscillator, which generates a high frequency rectangular wave pulse with a duty of 50% or less when the input voltage exceeds a set value. 152 is a transformer diode.

Input terminals 15a, 15 in the power regeneration circuit with the second sprout
While the voltage across b is lower than the set value, the oscillator 151 does not generate an output pulse, so the switching transistor 153 remains cut off and no power is regenerated. When the input voltage exceeds the set value, the oscillator 151 generates a high-frequency pulse, which causes no current to flow if the switching transistor 153 is ON-FF, but normally when rectifying a commercial frequency AC power source. Since a smoothing capacitor is connected in parallel to the output terminal, the recovered power will be stored in this capacitor. Since the output of the rectifier circuit 2 is adjusted by the inverter circuit 3, even if the rectifier circuit 2 includes a smoothing capacitor of large capacity, it does not affect the response speed or integration of output control. Therefore, if a capacitor of sufficient capacity is connected in parallel to the output section of the rectifier circuit 2, the regenerated power can be sufficiently stored and the voltage will not become so high.

In addition, as the oscillation start setting voltage of the oscillation circuit 151, the voltage D
The C/DC converter operates and output terminals 15c and 15d
generates high DC voltage. This voltage is the rectifier circuit 2
When the output voltage becomes higher than the output voltage of the input terminals 15a and 15b,
The DC power supplied to the output terminals 15c and 15d
It will flow from there toward the rectifier circuit 2. Here, the rectifier circuit 27 has only the rectifier with a set voltage of 2
The value may be selected such that the next output voltage is higher than the output voltage of the rectifier circuit 2.

Therefore, it is sufficient to set the frequency to several 10 KHz to several 100 KHz. In addition, the switching transistor 153 is desirably one with a switching speed of 1 μs or less, and is not limited to a MOS transistor manufactured by IXYS in the United States. For example, a DC/DC conversion circuit may be used as long as it performs DC/DC conversion using a known inverter, and then converts it to a predetermined voltage using a transformer and rectifies it to DC. Alternatively, a step-up switching regulator that boosts the voltage using a series coil may be used.

FIG. 2(b) is an example of a step-up switching regulator, in which the input voltage is stepped up by the ON-oFF of the transistor 153 and the series reactor 157 and regenerated to the DC power supply side.

Furthermore, the present invention is not limited to the configuration shown in FIG. 1, but may have other configurations.

For example, instead of obtaining a DC output regulated by an inverter circuit 3, a transformer 4, and a rectifier circuit 5, a transformer is provided in front of the rectifier circuit 2 to output a DC voltage of a predetermined voltage to the rectifier circuit 2.
A switching or analog series regulator may be constructed by configuring the DC power supply section so as to be obtained from the inverter circuit 3 and the rectifier circuit 5, and connecting series transistors in place of the inverter circuit 3 and the rectifier circuit 5. In this case as well, the output of the power regeneration circuit 15 may be supplied to the output side of the rectifier circuit 2 as in the case of FIG.

Furthermore, the polarity switching circuit also has a center-tapped winding as shown in Figure 1, and the output of this secondary winding is converted into two DC outputs, positive and negative, using diodes, and the output is connected to a series transistor, respectively. The polarity may be switched by ON-OFF control. FIG. 3 shows another embodiment of the present invention. In the figure, the transformer 4 has a center tap in the secondary winding, and diodes 16a to 16d provide positive and negative polarities, respectively.
The DC outputs of these two systems are guided to the electrode 8 and the workpiece 9 by series-connected transistors 17a and 17b that are alternately controlled to turn ON and OFF, respectively, as shown in FIG. The same effect as the example is obtained. In this case, the stray capacitance that is charged to a high voltage during polarity switching and directly affects polarity switching transistors 17a and 17b is between the common connection point of diodes 16a and 16b and the common connection point of diodes 16c and 16d. Therefore, the input to the power regeneration circuit 15 can be taken from this part as shown in the figure.

In the same figure, 18a and 18b are transistor protection diodes, and the other components having the same functions as those in FIG. 1 are given the same reference numerals and their explanation will be omitted.

〔Effect of the invention〕

Since the device of the present invention operates as described above, even if a high voltage is induced during polarity switching, this is immediately regenerated to the power supply side, so that an abnormally high voltage will not occur. Therefore, arc regeneration and the rising speed of the output current after regeneration are not impaired unlike when surge absorption is performed by a simple capacitor as in the past. therefore,
Since a transistor with a low withstand voltage is used without impairing the characteristics during polarity switching, the device can be made inexpensive.

[Brief explanation of the drawing]

FIG. 3 is a connection diagram showing another embodiment of the present invention, and FIG. 4 is a connection diagram showing an example of conventional IT. 2... Rectifier circuit, 3... Inverter circuit, 4.15
2... Transformer, 5... Rectifier circuit, 6a to 6d,
16a, 16b, 153 .) - transistors, 7a to 7d. 16a to 16d, 17a, 17b, 15$, 156
- Diode, 8... Electrode, 9... Workpiece, 10
... Polarity switching control circuit, 11... Output current setting circuit, 12... Output current detector, 13... Comparator, 14
... Inverter control circuit, 15 ... Power regeneration circuit,
151... Oscillator agent Patent attorney Nakai
Hiroshi (Yoshi) (Shi)

Claims (1)

[Claims] 1. A DC power supply, an output adjustment circuit that adjusts the output of the DC power supply to a desired voltage or current using a switching element, and a switching circuit that switches the output of the output adjustment circuit to positive and negative polarity and supplies it to a load. , for arc processing, comprising a power regeneration circuit whose input terminal is connected to the output terminal of the output adjustment circuit in parallel with the switching circuit, and regenerates input power to the DC power supply when the input voltage exceeds a predetermined value. power supply.