JPH0518762U - Power supply for arc processing - Google Patents

Abstract

(57) [Abstract] [Purpose] Once the commercial AC power supply has been rectified into DC, it is converted into high-frequency AC by an inverter circuit, and then converted into a voltage suitable for arc machining by a transformer, and then rectified, polarity switched, etc. Concerning the improvement of the power supply device for arc machining of the method that performs the following: [Composition] A rectification circuit that rectifies a commercial AC power supply to obtain a DC current An inverter circuit for converting, a transformer that receives the output of the inverter circuit as an input to obtain a secondary output suitable for arc machining, and a switching circuit that adjusts the output of the secondary winding of the transformer to a predetermined voltage-current characteristic. And an arc machining power supply which is provided with one or more auxiliary windings for supplying control power to another auxiliary circuit including the switching circuit in the transformer. Source device.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention is a method in which a commercial AC power supply is once rectified into DC, converted into high-frequency AC by an inverter circuit, then converted into a voltage suitable for arc machining by a transformer, and then rectified, polarity switched, etc. The present invention relates to a power supply device for arc machining.

[0002]

[Prior Art]

 In an arc processing power supply device used for arc welding, plasma arc welding, cutting, etc., in which an inverter circuit is used to obtain an alternating current with a frequency higher than the commercial frequency and this is converted into a predetermined voltage by a transformer. In the past, the output was adjusted by the inverter circuit on the primary side of the transformer, and the polarity of the machining output was switched by the switching circuit on the secondary side of the transformer.

FIG. 1 is a connection diagram showing an outline of a conventional device having such a configuration. In the figure, 1 is an AC power supply, and a commercial AC power supply is normally used. 2 is a rectifier circuit that regulates and smoothes the output of the AC power supply 1, 3 is a primary inverter circuit that converts the output of the rectifier circuit 2 into high-frequency AC, and 4 is the arc processing such as welding and cutting that is the output of the primary inverter circuit. A transformer for converting to a suitable voltage, 5 is a rectifier circuit that rectifies the output of the transformer 4 again to form a direct current, and 6 is a polarity of the direct current output of the rectifier circuit 5, which is positive, reverse or alternating current of a predetermined frequency. Is a secondary inverter circuit for. Reference numeral 7 denotes an arc processing load, and in the case of the figure, an example is shown when performing arc welding in which the consumable electrode 7a is fed toward the workpiece 7b. Reference numeral 8 denotes a feed roller for feeding the consumable electrode 7a, which is rotationally driven by a drive motor 9 at a predetermined speed. Reference numeral 10 is an auxiliary transformer for control power supply, which receives power from the alternating current power supply 1. Reference numeral 11 denotes an inverter control circuit for the primary inverter circuit 3, which compares the output Ir of the output current setting circuit 13 with the output If of the output current detector 12 to the arc processing load 7 to obtain a difference signal ΔI = Ir. The output ΔI of the comparator 14 that obtains −If is input, and the output of the primary inverter circuit 3 is changed in the direction in which the input signal decreases. Reference numeral 15 denotes an inverter control circuit for the secondary inverter circuit 6, which sets a pair of switching elements 6a, 6b or 6c, 6d of the secondary inverter circuit 6 according to the sign of the output signal so of the reference signal generator 16, respectively. To conduct. Reference numeral 17 denotes a motor control circuit for a drive motor 9 that drives the roller 8 for feeding the consumable electrode 7a, and rotates the drive motor 9 at a predetermined speed. In the apparatus shown in the figure, the welding current, that is, the output current is detected by the detector 12 and becomes the feedback signal If, and this feedback signal If is compared with the output Ir of the output current setting circuit 13 by the comparator 14, and the difference is detected. A signal ΔI = Ir−If is obtained, and the output of the primary inverter circuit 3 is controlled by this difference signal, so that the arc machining load 7 always receives a constant current corresponding to the value set by the output current setting device 13. Will be supplied by adjusting the output of. On the other hand, the secondary inverter circuit 6 has only the function of switching the output of the rectifier circuit 5 to the polarity according to the sign and the period of the reference signal so. Further, in the apparatus shown in the figure, since the output current is adjusted so as to have a constant current characteristic, the welding voltage is determined according to the feed rate of the consumable electrode 7a. A control power source for the primary and secondary inverter control circuits 11 and 15 and the motor control circuit 17 is supplied from the auxiliary voltage transformer 10.

[0004]

[Problems to be solved by the device]

 In the conventional device as described above, the transformer 4 for converting the processing power can be made compact and lightweight by increasing the operating frequency of the primary inverter circuit 3, but an auxiliary transformer for supplying the power for the control circuit. No. 10 cannot be miniaturized because it receives power from the AC power supply 1 of commercial frequency. Among these control circuits, the control power for the inverter control circuits 11 and 15, the output setting circuit 13, the reference signal generator 16 and the like has a relatively small capacity and is about 10 to 20 VA at most, but the motor control circuit 17 has a capacity of several tens of VA to several hundreds of VA depending on the capacity of the drive motor. For this reason, not only is the auxiliary transformer 10 bulky if all of the power for these control circuits is borne by the auxiliary transformer 10, but normally the output of this auxiliary transformer 10 is rectified to each control circuit. Since the smoothing circuit is used as a direct current, a large smoothing circuit that can sufficiently reduce the ripple when rectifying the commercial frequency alternating current is required, and the main power supply circuit is a high frequency by the primary inverter circuit 3 and is small and lightweight. However, there was a problem in that the advantages that were realized were not fully utilized.

[0005]

[Means for Solving the Problems]

 In the present invention, in order to solve the above-mentioned problems of the conventional apparatus, when a commercial AC power source is rectified and then converted into a high frequency AC, an output of a substantially constant voltage is always generated regardless of the load condition. The primary inverter circuit is controlled independently of the load, and the output of this primary inverter circuit is appropriately transformed by a transformer, after which the desired output voltage / current characteristics suitable for arc machining and the desired polarity output can be obtained. In addition to providing a switching circuit that adjusts as described above, the power supply for the control circuit other than the primary inverter circuit is obtained from another output winding provided in the transformer that transforms the output of the primary inverter.

[0006]

【Example】

 FIG. 2 shows an embodiment of the present invention. In the figure, 21 is a commercial AC power source, 22 is a rectifier circuit, 23 is an inverter circuit, 24 is a transformer, and 25 is a transformer 24 having a center tap. Controlled rectifiers 25a and 25b for adjusting the output, for example, a switching circuit using a thyristor, 26 is a DC reactor, 27 is an arc machining load composed of a consumable electrode 27a and a workpiece 27b, and 28 is a transmission circuit for feeding the consumable electrode. Reference numeral 29 is a supply roll, and 29 is a drive motor for driving the supply roll 28. An auxiliary transformer 30 supplies electric power to the inverter control circuit 31 for the inverter circuit 23. Reference numeral 32 denotes a comparator, which compares the output Er of the reference voltage setting circuit 33 with the output voltage Ef of the third winding 24s2 of the transformer 24 constituting the output voltage detector of the inverter circuit 23 to obtain a difference voltage ΔE = Er -Ef is supplied to the inverter control circuit 31. Reference numeral 34 is another comparator which receives the output signal Ir of the output current setting circuit 35 and the output signal If of the output current detector 36 and outputs a difference signal ΔI = Ir −If. Reference numeral 37 is a control circuit for the switching circuit 25, which supplies electric power from the fourth winding 24s3 of the transformer 24 to output a control signal to the switching circuit 25 in a direction in which the output signal ΔI of the comparator 34 decreases. Supply. Here, when the switching circuit 25 is constituted by a full-wave control rectification circuit using a thyristor as shown in the figure, the control circuit is ignited in synchronization with the output voltage phase of the transformer 24 and having a control phase angle corresponding to the difference signal ΔI. The signals s3 and s4 are supplied. A control circuit 38 for the drive motor 29 receives electric power from the fourth winding 24s3 of the transformer 24 and rotates the drive motor 29 at a speed according to a reference signal (not shown).

In the embodiment shown in FIG. 1, the output of the AC power supply 1 is converted into DC by the rectifier circuit 22 and supplied to the inverter circuit 23. When the starting switch TS is closed in this state, the inverter control circuit receiving power from the auxiliary transformer 30 is started, and the inverter circuit 23 controls the DC output of the rectifier circuit 22 by the output signals s1 and s2. The high-frequency alternating current having the frequency and the waveform is converted and supplied to the primary winding 24p 1 of the transformer 24. In the transformer 24, when the output voltage of the inverter circuit 23 is supplied to the primary winding 24p1, a voltage proportional to the input voltage is induced in the third winding 24s2, and this induced voltage Ef is applied to the reference voltage setting circuit in the comparator 32. 33, the inverter control circuit 31 operates in a direction in which the difference signal ΔE = Er−Ef decreases in comparison with the setting signal Er, and the output voltage of the inverter circuit 23 is adjusted by adjusting the output inverter drive signals s1 and s2. To the set value. Also, the switching control circuit 37 is activated at the same time as the closing of the start switch TS or with a slight delay, and supplies the conduction command signals s3, s4 to the thyristors 25a, 25b of the switching circuit 25, whereby the second of the transformer 24 is supplied. The output of the winding 24s1 is phase-controlled and rectified and supplied to the load 27 via the DC reactor 26. On the other hand, the motor control circuit 38 is also activated by the output of the fourth winding 24s3 of the transformer 24, and the drive motor 29 is rotated by a predetermined acceleration pattern and speed. The consumable electrode 27a is sent toward the workpiece 27b by the rotation of the drive motor 29, and when the both are short-circuited, the output of the switching circuit 25 causes a short-circuit current to flow. This short-circuit current causes the tip of the consumable electrode to heat and melt and scatter, thereby generating an arc and starting machining. When a current starts to flow in the output circuit, this current is detected by the output current detector 36 and becomes a signal If, which is compared with the setting signal Ir of the output current setting circuit 35 by the comparator 34 and the difference signal ΔI = Ir − If is output. This difference signal ΔI is supplied to the switching control circuit 37, and the switching control circuit 37 operates so as to maintain the output current at the set value by adjusting the phases of the phase control signals s3 and s4 in the direction in which the difference signal decreases. To do.

Since the embodiment of FIG. 2 operates as described above, most of the auxiliary power supply for the control circuit is maintained at a constant output, and the auxiliary winding of the main transformer receives the output of the inverter circuit as an input. Will be taken out from. As a result, the power supplies for these control circuits can be made small, as only a few additional windings are required on the main transformer operating at high frequency. Of the auxiliary power supplies, only the power supply for controlling the inverter circuit 23 requires the auxiliary transformer 30 that receives power from the commercial AC power supply 21, but the power required for the inverter control circuit 31 is about 10 VA. Therefore, the auxiliary transformer 30 may have a very small size even if it receives commercial AC as an input.

FIG. 3 shows another embodiment of the present invention, in which the polarity of the output voltage can be switched between positive, reverse and alternating current. In the figure, 25 is a switching circuit composed of four thyristors 25a to 25d connected to the second winding 24s1 of the transformer 24. As shown in the figure, thyristors 25a and 25b, and thyristors 25c and 25d are respectively The two windings 24s1 of the transformer 24 having opposite polarities are connected to the output terminals at both ends of the second winding 24s1 to form a double-wave rectifying circuit having both positive and negative polarities. A reactor 39 has two windings 39a and 39b wound around a common magnetic core, and has one terminal at each common connection point of the thyristors 25a and 25c and the thyristors 25b and 25d, as shown in the figure. Are connected, and the other ends are commonly connected. In addition, the polarities of both windings are, as shown by the symbols in the figure, the polarities in which magnetic fluxes in the same direction are generated in the magnetic core shared by the current that flows when the thyristors connected in series are conducting. The winding direction is defined. Reference numeral 40 is a comparator which receives the output signal er of the output voltage setting circuit 41 and the output ef of the output voltage detector 42 as an input and outputs a difference signal Δe = er −ef. Reference numeral 43 denotes a feeding speed setting circuit for setting the feeding speed of the consumable electrode 27a, which is a reference signal setting circuit for supplying the reference signal ir to the motor control circuit 38. Further, the switching control circuit 37 has a selection switch 37a for switching the output polarity between positive, reverse and alternating current, and setting devices 37b and 37c for determining the positive polarity period Ts and the reverse polarity period Tr at the time of alternating current output, A time-limit circuit is incorporated inside which repeats the positive polarity period Ts and the reverse polarity period Tr when the selection switch 37a is set to AC. In FIG. 3, other than the above, those having the same functions as those of the embodiment shown in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted.

In the embodiment of FIG. 3, description will be made on the case where the selection switch 37a is set to (positive) to obtain a positive output, that is, the consumable electrode 27a has a negative DC output and the workpiece 27b has a positive DC output. In this case, the switching circuit 25 uses only the thyristors 25b and 25d, and the thyristors 25a and 25c remain disconnected. When the starting switch TS is closed, the inverter control circuit 31 starts its operation, and the inverter circuit 23 converts the output of the rectifier circuit 22 into a high-frequency alternating current having a constant waveform by the drive signals s1 and s2 from the inverter control circuit 31. .. At this time, the output voltage is inverter controlled by a signal obtained by comparing the output voltage Ef of the third winding 24s2 of the transformer 24 and the set value Er of the reference voltage setting circuit 33 with the comparator 32 as in the embodiment of FIG. It is maintained at the set value when the circuit operates. The control circuit 37 of the switching circuit 25 is activated at the same time as or slightly after the closing of the activation switch TS. In this case, if the selection switch 37a is set to (positive) as described above, only the thyristors 25b and 25d of the four thyristors of the switching circuit 25 operate and the thyristors 25a and 25c are shut off. In order to remain as it is, the switching control circuit 37 outputs only the signals s4 and S6 alternately in a predetermined phase in synchronization with the output voltage of the transformer 24. When the thyristors 25b and 25d are alternately fired by the signals s4 and s6, a positive output in which the workpiece 27b side is positive and the consumable electrode 27a side is negative is generated via the reactor 39b. This output voltage is detected by the output voltage detector 42 and becomes a signal ef, which is compared by the comparator 40 with the setting signal er of the output voltage setting circuit 41. The comparator 40 calculates a difference signal Δe = er −ef between the two input signals and supplies it to the switching control circuit 37 as a command signal. The switching control circuit 37 adjusts the phases of the signals s4 and s6 in the direction in which the input signal .DELTA.e decreases to ignite the thyristors 25b and 25d, and as a result, the thyristors 25b and 25d are supplied to the arc machining load 27. Feedback control is performed so that the output voltage is maintained at a value corresponding to the set value er of the output voltage setting circuit 41.

On the other hand, the motor control circuit 38 is activated after a short delay time from the closing of the activation switch TS and the activation of the switching control circuit 37, and the drive motor 29 is driven at a speed corresponding to the setting signal ir of the reference signal setting circuit 43. Rotates, which causes the consumable electrode 27a to be fed toward the workpiece 27b. When the tip of the consumable electrode 27a is short-circuited to the workpiece 27b, a short-circuit current flows due to the output of the switching circuit 25, and the tip of the consumable electrode 27a is heated and melted and scattered to generate an arc. At this time, the switching control circuit 37 operates so as to maintain the voltage supplied to the arc processing load 27 at the set value of the output voltage setting circuit 41, and adjusts the firing phase of the thyristors 25b and 25d. When feeding at a constant speed according to the output signal ir of the reference signal setting circuit 43, the arc machining current, that is, the welding current is set to a value corresponding to this feeding speed. Therefore, in the case of the embodiment of FIG. 3, the output signal ir of the reference signal setting circuit 43 which determines the feeding speed of the consumable electrode 27a becomes the machining current setting signal.

Next, when the direct current reverse polarity, that is, the consumable electrode 27a obtains a positive output, the selection switch 37a is set to the (reverse) position to control the conduction of the thyristors 25a and 25c instead of the thyristors 25b and 25d. The signals s3 and s5 are phase-adjusted so that the signals s4 and s6 are cut off.

Further, when an alternating current output of alternating positive and reverse polarities with a predetermined cycle and duration is to be set, the selection switch 37a is set to (AC) to set a period of a predetermined wave number of the output of the inverter circuit 23. The signals s4 and s6 are alternately output for Ts, and the signals s3 and s6 are alternately output for a period Tr continuously after this period. This state is repeated in sequence.

FIG. 4 shows the output voltage waveform of the inverter circuit 23, the output signals s3 to s6 of the switching control circuit 37, the output voltage eo supplied to the arc machining load, and the output current io at the time of the AC output. It is the diagram which showed the relationship. 3 and 4, signals s4 and s6 are alternately output during the period Ts from time t = t1 to t2, and signals s3 and s5 are alternated during the period Tr from time t2 to t3. Is output to. As a result, during the period of Ts, the thyristors 25b and 25d are alternately conducted to become a positive output period in the direction from the workpiece 27a to the consumable electrode 27b, and during the period T r, the thyristors 25a and 25c alternate. Then, a period of reverse polarity output from the consumable electrode 27b to the workpiece 27a is reached. Such periods Ts and Tr are alternately repeated to obtain an AC output. At this time, the peak value of the output voltage is determined by the set value of the output voltage setting circuit 41 as before. Therefore, by switching the polarity and simultaneously changing the set value of the output voltage setting circuit to the signals er1 and er2. , And the desired output voltage value can be set in each of the forward and reverse periods. Further, the lengths of the polar periods Ts and Tr can be independently adjusted by the setters 37b and 37c.

Here, the operation when the polarity of the output voltage is reversed will be described. In FIG. 4, immediately before time t2, the thyristor 25b or 25d is ignited by the signal s4 or s6, and a current flowing from the workpiece 27b toward the consumable electrode 27a flows through the reactor 39b. electromagnetic energy determined by the inductance Lb of Ia and the reactor _{39b (1/2 · L a · I} a 2) is stored in the reactor 39 b. In this state, when the period Ts ends at time t2 and the output of the signal s3 or s5 starts, the thyristor 25a or 25c fires. At this time, the electromagnetic energy stored in the reactor 39b up to that time is immediately transferred to the reactor 39a which is tightly coupled by the shared magnetic core. At this time, if the inductance La of the reactor 39a is made equal to the inductance Lb of the reactor 39b, the electric current flowing in the circuit due to the ignition of the thyristor 25a or 25c will not change rapidly because the electromagnetic energy stored in the reactors 39a, 39b cannot change. The currents have the same high value and opposite polarities. As a result, the change in the output current becomes a current in which the polarity sharply reverses when the thyristor having the opposite polarity is ignited immediately after time t2, as shown in FIG. Therefore, in the embodiment of FIG. 3, the reactors 39a and 39b serve as a smoothing circuit for the output current in the form of one of them being connected to the circuit at the time of direct current output, and both at the time of alternating current output. It acts to play a role of abruptly reversing the polarity of the output current, and has the effect of improving the regeneration of arcs that disappear once when the current polarity is reversed.

In FIG. 3, the output adjustment is shown as the phase control of the output voltage of the transformer 24 for each waveform, but the output adjustment is not limited to this, and the output waveform of the transformer remains unchanged. The average value of the output may be adjusted by limiting the number of waves output at. FIGS. 5 and 6 show the state of such a case with the waveforms of the respective portions as in FIG.

FIG. 5 shows how the output is adjusted by limiting the output wave number of the transformer during positive output. In the figure, an example is shown in which the signals s3 and s5 are output for about 60% during the period of To of the output of the transformer, that is, the output of the inverter 23, and the rest of 40% is stopped. .. In this case, the output voltage eo and the output current Io are direct currents with a slight pulsation as shown in (f) and (g) in the figure, and their average values are output as signals s3 and s5 respectively. It depends on the ratio of the period of time. The pulsation can be reduced by shortening the repetition cycle of the signals s3 and s5.

FIG. 6 is a diagram showing how an AC output is obtained by the same control method. In this case as well, the cycle between the period during which the signals s3 to s6 are output and the period during which they are stopped should be shortened. This can reduce the pulsation.

In the embodiments of FIGS. 2 and 3, the inverter circuit 23 used is a full-bridge type inverter circuit in which four switching transistors are combined as shown in FIG. As shown in the drawing, the DC voltage is divided into two by two series capacitors, and any known type of inverter circuit such as a half-bridge type inverter circuit using two switching transistors can be used. Further, in controlling the inverter circuit, the output voltage is fed back and compared with a set value as in each of the above-described embodiments to obtain a constant voltage output, and in addition, a drive signal having a constant frequency and waveform is used for operation. It may be a non-stabilized inverter.

Further, as the arc processing load, the present invention can be applied to any load such as TIG welding, plasma arc welding, plasma arc cutting, arc gouging in addition to arc welding using a consumable electrode. Also, the output control may be performed by a switching circuit provided on the output side of the transformer.This switching circuit uses a rectifier circuit and a switching circuit in addition to the thyristor as shown in the previous example. It may be configured by a combination with a transistor for use. In these cases, the output adjustment is to keep the output current constant, to keep the output voltage constant, to obtain either positive or reverse polarity, to be able to switch to normal or reverse, or to a predetermined value. It does not matter whether the alternating current output is one in which the forward and reverse cycles are repeated depending on the duration and cycle.

Furthermore, as an auxiliary power source to be taken out from the transformer that receives the output of the inverter circuit, when it is rectified and then reconverted to the commercial frequency AC through the low frequency inverter circuit, it is a general commercial frequency. The conventional control circuit that uses alternating current as a power source can be used as it is.

[0022]

【The invention's effect】

 As described above, in the present invention, an inverter circuit that operates with a constant output or an unadjusted output is provided on the primary side of the transformer, and the output of this transformer is adjusted to the desired characteristics and the auxiliary winding is applied to the transformer. Since a line is provided to take out the auxiliary power supply for control, the auxiliary power supply circuit can be made compact and lightweight, and it is suitable for making the main power supply circuit compact and lightweight, which can be achieved by converting the main circuit to an inverter. The size and weight of can be further promoted.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an example of a conventional device.

FIG. 2 is a connection diagram showing an embodiment of the present invention.

FIG. 3 is a connection diagram showing another embodiment of the present invention.

FIG. 4 is a diagram for explaining the operation of the embodiment of FIG. 3 during AC output.

FIG. 5 is a diagram for explaining another operation of the embodiment of FIG.

6 is a diagram for explaining still another operation of the embodiment of FIG.

[Explanation of symbols]

 22 Rectifier circuit 23 Inverter circuit 24 Transformer 25 Switching circuit 27 Arc processing load 28 Feed roll 29 Drive motor 30 Auxiliary transformer 31 Inverter control circuit 32, 34, 40 Comparator 33 Reference voltage setting circuit 35 Output current setting circuit 37 Switching Circuit control circuit 38 Motor control circuit 39 Reactor 40 Comparator 41 Output voltage setting circuit 42 Output voltage setting circuit 43 Reference signal setting circuit

Claims (4)

[Scope of utility model registration request] 1. A rectifier circuit for rectifying a commercial AC power source to obtain a direct current, an inverter circuit for converting an output of the rectifier circuit into an alternating current having a frequency higher than the frequency of the commercial AC power source, and the inverter circuit. A transformer that obtains a secondary output suitable for arc machining by inputting the output to the primary winding, and a switching circuit that adjusts the output of the secondary winding of the transformer to a predetermined voltage-current characteristic are provided, and A power supply device for arc machining, wherein a transformer is provided with one or more auxiliary windings for supplying control power to other auxiliary circuits including the switching circuit. 2. The arc machining power supply device according to claim 1, wherein the inverter circuit is an inverter circuit having a constant voltage characteristic in which the output voltage is controlled so as to be maintained at a constant voltage according to a set value. 3. The arc machining according to claim 1, wherein the switching circuit is a circuit for phase-controlled rectifying the output of the transformer to obtain an output having a desired polarity and voltage / current characteristics. Power supply. 4. The polarity switching circuit, wherein the switching circuit is a polarity switching circuit that adjusts the output of the transformer and switches the polarity of the output voltage to an alternating current having a positive / reverse or a predetermined forward / reverse ratio and frequency. The power supply device for arc machining according to any one of claims.