JPH06190562A - Power source for plasma arc - Google Patents

Abstract

PURPOSE:To prevent disturbance of feedback control at the time of transferring from individual operation of a DC power unit to parallel operation of each DC power unit and to stabilize power feeding of arc starting. CONSTITUTION:The power source for the plasma arc is provided with a parallel operation command terminal 26 where a parallel operation command signal is supplied, an integrator 28 to form an integration signal of this terminal 26 signal and an inversion signal formed by inverting this signal, a first multiplier 30 to multiply a reference signal by the inversion signal of the load feeding quantity, an attenuator 29 to attenuate the reference signal to I/N, a second multiplier 31 to multiply the integration signal by an output signal of the attenuator 29 and an adder 32 to add an output signal of the first multiplier 30 and an output signal of the second multiplier 31. A specified output setting signal of the DC power unit is formed by an output signal of the adder 32 and a remaining output setting signal of the DC power unit is formed by the output signal of the second multiplier 31.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma arc power source for operating N DC power source devices in parallel to output a constant current controlled DC power source.

[0002]

2. Description of the Related Art Conventionally, a plasma arc power source used for plasma fusing or plasma welding is formed by a DC power source device having a so-called inverter power source structure in order to reduce the size and weight. This DC power supply device rectifies and smoothes an input AC power supply such as a commercial power supply, converts it into DC, and converts this DC into high-frequency AC by a high-frequency inverter circuit composed of semiconductor switching elements such as IGBT, MOSFET, and bipolar transistor. The high frequency AC is rectified and smoothed through a transformer to form a DC output, and this output is supplied to the torch and the base material of the load.

Further, the operating frequency of the switching circuit is feedback-controlled by the error signal between the detection signal of the output current and the setting signal to constant-current control the load power supply. By the way, since the semiconductor switching element of the switching circuit does not have a large capacity, a plasma arc power supply configured to operate a plurality of (N) DC power supply devices in parallel is used when a large output is required. .

In this case, if the DC power supply devices are always operated in parallel so as to share the output evenly, the following problems will occur at the time of arc start. That is, at the time of arc start,
First, a small-current pilot arc is generated between the nozzle electrode of the torch and the main electrode, and then the torch approaches the base metal, which causes a high-current plasma arc (main arc) between the main electrode and the base metal. Arc).

At this time, if the output of each DC power supply device in the pilot arc is controlled to a very small current output of 1 / N of the current required to generate the pilot arc, the no-load voltage before the pilot arc is generated. It becomes lower and it becomes difficult to start the arc. Therefore, in the case of a configuration in which a plurality of DC power supply devices are operated in parallel, at the time of arc start, first, only a predetermined DC power supply device is operated independently to supply the output necessary for generating a pilot arc to the load from this device. .

In this case, the output current of the predetermined DC power supply device is N times as large as that in the case of parallel operation of N units, and the pilot arc is reliably generated at the no-load voltage based on the output voltage. When the pilot arc is changed to the plasma arc, the individual operation is switched to the parallel operation of the DC power supply devices.

[0007]

In the case of a plasma arc power supply having a configuration in which a plurality of conventional DC power supply devices are operated in parallel, a predetermined DC power supply device is switched from independent operation to parallel operation of each DC power supply device. At this time, since the target value of the feedback control of each DC power supply unit changes in steps, the DC power supply unit that was operating independently becomes a state where the load fluctuates rapidly and the feedback control is disturbed, and its output is greatly disturbed. It takes time to stabilize again, and
It takes time from the start of operation of the remaining DC power supply devices until the feedback control becomes stable.

Therefore, there is a problem that the load power supply at the time of arc start cannot be stabilized and the pilot arc cannot be stably transferred to the plasma arc. It is an object of the present invention to prevent output fluctuation due to a shift from independent operation to parallel operation, and stabilize power supply at arc start.

[0009]

In order to achieve the above object, in the plasma arc power supply of the present invention, a parallel operation command terminal to which a parallel operation command signal is supplied, and an integrated signal of the signal of this terminal are provided. An integrator that forms an inverted signal obtained by inverting the signal, a first multiplier that multiplies the reference signal of the load power supply amount and the inverted signal, and an attenuator that attenuates the reference signal to 1 / N. A second multiplier for multiplying the integrated signal by the output signal of the attenuator; and an adder for adding the output signal of the first multiplier and the output signal of the second multiplier,
The output signal of this adder forms the output setting signal of the predetermined DC power supply device, and the output signal of the second multiplier forms the output setting signal of the remaining DC power supply devices.

[0010]

In the plasma arc power supply of the present invention configured as described above, when the predetermined DC power supply device shifts from the independent operation to the parallel operation, the integrator outputs an integral signal which gradually rises and this signal. An inverted signal which is inverted is formed, and the first multiplier forms a signal which decreases and changes from the level of the reference signal of the load power supply amount by the characteristic of the inverted signal.

Further, the second multiplier forms a signal that rises to a level of 1 / N of the reference signal of the load power supply amount by the characteristic of the integrated signal as an output setting signal of the remaining N-1 DC power supply devices. . Further, the adder has an output signal of the first multiplier,
The output signal of the second multiplier is added, and a signal that drops from the level of the reference signal to the level of 1 / N due to the characteristics of the inverted signal is formed as the output setting signal of the predetermined DC power supply device.

Then, based on the change in the output setting signal of the adder, the predetermined DC power supply device prevents a sudden change in the feedback control, and the output current is reduced from the magnitude corresponding to the reference signal of the load power supply amount to 1 / The output current of the remaining N-1 DC power supply devices smoothly increases to a value corresponding to 1 / N of the reference signal for load power feeding. Therefore, when shifting from the independent operation of a predetermined DC power supply device to the parallel operation of each DC power supply device, the output current of each DC power supply device changes smoothly without disturbance of feedback control and immediately shifts to the parallel operation. Good for plasma fusing and plasma welding.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment will be described with reference to FIGS. FIG. 2 shows an overall configuration in the case of N = 2 in which two DC power supply devices are provided.
The three-phase AC power supply is rectified and smoothed by the input rectifier 2 and the capacitor 3 having a diode rectifier structure and converted into DC, and this DC is supplied to the high frequency inverters 6 and 7 of the two DC power supply units 4 and 5. .

Both high frequency inverters 6 and 7 are IGBT, M
It is formed by a bridge circuit of a plurality of semiconductor switching elements Q such as OSFETs and bipolar transistors, and the switching frequency is controlled by respective drive circuits 8 and 9, and the input direct current is converted into high frequency alternating current to transform the transformers 10 and 11. Supply to the primary side.

The secondary outputs of the transformers 10 and 11 are rectified and smoothed by the output rectifiers 12 and 13 of the diode rectifier and the smoothing reactors 14 and 15 to be converted into direct current, and the direct currents are positive and negative outputs. Power is supplied to the load 16 from the terminals 14p and 14n. This load 16 is output terminal 14
The torch 18 comprises a base material 17 and a torch 18 connected to p. The torch 18 has a main electrode 19 connected to an output terminal 14n,
The nozzle electrode 20 is connected to the pilot output terminal 14p '.

Further, the output currents of the DC power supply units 4 and 5 are detected by the current detectors 21 and 22 provided between the output rectifiers 12 and 13 and the output terminal 14p.
Reference numerals 1 and 22 output the detection signals Sa and Sb to the error amplifiers 23 and 24.
Supply to. The operation signal generating circuit 27, to which the reference power supply 25 for output setting and the parallel operation command terminal 26 are connected, supplies the output setting signals Sα and Sβ of the DC power supply devices 4 and 5 to the error amplifiers 23 and 24, respectively.

The error amplifiers 23 and 24 supply error signals between the output setting signals Sα and Sβ and the detection signals Sa and Sb to the drive circuits 8 and 9 as output control signals, and the DC power supply devices 4 and 5 are connected to each other. Feedback control is performed on the constant current output based on the output setting signals α and β.

By the way, when the arc is started, the DC power supply unit 4 is operated independently to generate a pilot arc between the nozzle electrode 20 and the main electrode 19, so that the DC power supply unit 4 has a switch 28 between the output terminals 14p and 14p '. Current limiting resistor 29,
The high frequency generator 30 is provided in series, the switch 28 is closed by the start of the arc start, and is opened when the pilot arc shifts to the plasma arc between the base material 17 and the main electrode 19.

The operation signal generating circuit 27 is formed by an integrator 28, a 1 / N attenuator 29, first and second multipliers 30 and 31, and an adder 32, as shown in FIG.

Next, the operation of the operation signal generating circuit 27 will be described with reference to FIG. First, the parallel operation command signal K which is logic 1 is supplied to the parallel operation command terminal 26 when the DC power supply devices 4 and 5 are in parallel operation, and the parallel operation command signal K is logic 0 when the DC power supply device 4 is operated independently. is there.

The parallel operation command signal K is supplied to the integrator 28, and the integrator 28 outputs the parallel operation command signal K.
Are integrated to form an integrated signal A and an inverted signal B obtained by inverting the signal A, the integrated signal A is supplied to the second multiplier 31, and the inverted signal B is supplied to the first multiplier 30.

The reference signal R of the level r of the reference power supply 25 is supplied to the first multiplier 30 and the attenuator 29.
The attenuator 29 supplies the reference signal R to 1 in order to equalize the output sharing of the DC power supply devices 4 and 5 during parallel operation.
A signal C attenuated to / 2 (= 1 / N) is formed, and the signal C is supplied to the second multiplier 31.

Then, the first multiplier 30 analog-multiplies the inverted signal B and the reference signal R to start parallel operation ts,
From the end te to the rising and falling of the integrator 28 based on the integration time constant of the start and end of the transient period τs, τe from r to 0,
A signal D whose level changes from 0 to r is formed.

The second multiplier 31 analog-multiplies the integrated signal A and the signal C to set the output so that the level changes from 0 to r / 2 and from r / 2 to 0 during the transient periods τs and τe. Form the signal Sβ. Further, the adder 32 analog-adds the signal D and the output setting signal Sβ to form the output setting signal Sα whose level changes from r to r / 2 and from r / 2 to r during the transient periods τs and τe. .

Next, actual changes in the output currents of the DC power supply devices 4 and 5 and the current flowing through the load 16 will be described with reference to FIG. In FIG. 4, ia and ib represent the output currents of the DC power supply devices 4 and 5, and ic represents the current flowing through the load 16 (load current). First, when the current ic flowing through the load 16 is set to I ₁ , the reference signal R is set to the level r ₁ corresponding to I ₁ .

Since the output setting signal Sα is r ₁ and the output setting signal Sβ is 0 before the arc start, only the DC power supply device 4 operates and the high frequency inverter 6 so that its output current ia becomes I _1. Is driven. However, before the start of the arc, the gap between the base material 17 and the main electrode 19 is large, so that no current flows in the load 16 and a so-called no-load voltage is applied to the load 16.

Next, in order to start the arc, the switch 28 is closed at t ₁ , the torch switch is turned on to drive the high frequency generating circuit 30, and the high frequency voltage of this circuit 30 is applied to the nozzle electrode 20 and the main electrode. When applied between 19 and
A pilot arc is generated between the electrodes 20 and 19, and the output rectifier 12 to the current detector 15, the switch 28, the current limiting resistor 29, the high frequency generating circuit 30, the nozzle electrode 20, the main electrode 1
9. The pilot arc current Ip (<I ₁ ) flows in the loop returning to the output rectifier 12 via the DC reactor 14.

Next, when the torch 18 is brought close to the base material 17, the gap resistance between the base material 17 and the main electrode 19 decreases,
For example, at t ₂ , a plasma arc (main arc) is generated between the base material 17 and the main electrode 19. At this time, the switch 28 is opened and the pilot arc current Ip disappears.

When a plasma arc is generated, the output rectifier 12 to the current detector 21, the base material 17, the main electrode 1
9. The plasma arc current I ₁ flows through the loop returning to the output rectifier 12 via the smoothing reactor 14. This current I
₁ is held at a constant current by the feedback control based on the output setting signal Sα.

Further, when the parallel operation command signal K rises to t ₃ and the parallel operation is started, the transient period τ from t _{3 to} t ₄
to s, the output setting signal Sα is progressively lowered from r ₁ to r _1/2, the output setting signal Sβ gradually increases to r _1/2 0.

Since the transient period τs is set to a period in which the feedback control does not change suddenly,
The output current ia of the DC power supply device 4 is stable and promptly I
Decreased from ₁ to I _1/2, a DC power supply device 5 is the output current i
b is stable and quickly rises from 0 to I _1/2 .

Since the output currents ia and ib of the DC power supply devices 4 and 5 change symmetrically based on the changes of the output setting signals Sα and Sβ, the DC power supply device 4 operates independently of the DC power supply devices 4 and 5. The current ic flowing through the load 16 is stably maintained at I ₁ even after shifting to parallel operation of _{No. 1} , the arc start is stabilized, and the plasma arc is stably maintained.
7 Plasma fusing and plasma welding can be performed well.

Further, the electric current for fusing or welding is changed from I ₁ to I _2.
4, the reference power supply 25 is changed at t ₅ in FIG. 4 to change the level of the reference signal R from r ₁ corresponding to I ₁ to r ₂ corresponding to I _2. based output setting signal Sα in slope characteristics, S [beta rise changes from r _1/2 in r _2/2 both output current stably and rapidly for both direct-current power supply 4, 5 I _1/2 from the I _2/2 , And the current flowing through the load 16 changes smoothly from I ₁ to I ₂ .

Further, when the parallel operation command signal K falls to logic 0 and the parallel operation ends, the output setting signals Sα, S
β gradually rises and falls during the transition period τe, and the DC power supply device 4 returns to the independent operation again.

By the way, when the number of DC power supply devices is N,
One predetermined unit is configured the same as the DC power supply device 4, and the remaining N-1 units are configured the same as the DC power supply device 5. Also,
The operation signal generation circuit supplies the output setting signal Sβ of the second multiplier 31 of FIG. 1 to the remaining N−1 DC power supply devices.

The second multiplier is connected to N for each DC power supply device.
It may be formed by −1 multipliers, and the output setting signal of each multiplier may be supplied to each of the N−1 DC power supply devices.
Further, in the above-mentioned embodiment, when the capacities of the DC power supply devices 4 and 5 are different, it is also possible to adjust the attenuation rate of the attenuator 29 and set the output sharing ratio of both power supply devices in consideration of the capacities. Is.

[0037]

Since the present invention is configured as described above, it has the following effects. When shifting from the independent operation of the predetermined DC power supply device 4 to the parallel operation of the DC power supply devices 4 and 5, the first multiplier 30 decreases from the level of the reference signal R of the load power supply amount by the characteristic of the inversion signal B. Each of the second multipliers 31 forms a changing signal, and each second multiplier 31 raises the signal which rises to the level of 1 / N of the reference signal R of the load power feeding amount by the characteristic of the integrated signal A of the remaining N-1 DC power supply devices. It is formed as an output setting signal.

Further, the adder 32 adds the output signal of the first multiplier 30 and the output signal of the second multiplier 31, and the characteristic of the inverted signal B from the level of the reference signal R is 1 / N thereof. The signal that drops to the level is formed as the output setting signal of the predetermined DC power supply device 4.

Then, based on the change in the output setting signal of the adder 32, the predetermined DC power supply device 4 prevents a sudden change in the feedback control so that the output current changes from the magnitude corresponding to the reference signal of the load power supply amount. The output current of the remaining N-1 DC power supply devices 5 smoothly increases to a value corresponding to 1 / N of the reference signal for load power feeding. Therefore, the predetermined DC power supply device 4
When the pilot arc is operated independently, the output currents of the DC power supply units 4 and 5 change smoothly when the DC power supply units 4 and 5 are moved to the plasma arc in parallel. However, the power supply at the time of arc start is stabilized, and plasma fusing and plasma welding can be performed well.

[Brief description of drawings]

FIG. 1 is a detailed block diagram of a part of one embodiment of a plasma arc power supply of the present invention.

FIG. 2 is a block diagram of the overall configuration of one embodiment of the plasma arc power supply of the present invention.

FIG. 3 is a waveform diagram of each part of FIG.

FIG. 4 is a waveform diagram for explaining the operation of FIG.

[Explanation of symbols]

 4, 5 DC power supply device 25 Reference power supply 26 Parallel operation command terminal 27 Operation signal generation circuit 28 Integrator 29 Attenuator 30 First multiplier 31 Second multiplier 33 Adder

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Haruo Moriguchi 2-3-14 Awaji, Higashiyodogawa-ku, Osaka City Sansha Electric Manufacturing Co., Ltd. (72) Inventor Kunio Kano 2-3-14 Awaji, Higashiyodogawa-ku, Osaka Stock company Sansha Denki Seisakusho

Claims (1)

[Claims] 1. N feedback control of DC power supply devices is performed by an error signal between an output setting signal and an output current detection signal, and only a predetermined DC power supply device is operated to supply a pilot arc current to a load. After that, in the plasma arc power supply for supplying the plasma arc current to the load by operating each DC power supply device in parallel, a parallel operation command terminal to which a parallel operation command signal is supplied, and an integrated signal of the signal of the parallel operation command terminal An integrator that forms an inverted signal of the inverted signal, and a first signal that multiplies the inverted signal by the reference signal of the load power supply amount
A multiplier for attenuating the reference signal to 1 / N, and a second multiplier for multiplying the integrated signal by the output signal of the attenuator.
And an adder for adding the output signal of the first multiplier and the output signal of the second multiplier, the output of the predetermined DC power supply device according to the output signal of the adder. A power supply for plasma arc, wherein a setting signal is formed, and the output setting signal of the remaining DC power supply device is formed by the output signal of the second multiplier.