JP3825870B2 - Arc machining power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a power supply device for arc machining used for arc welding, cutting, plasma arc machining, etc., in which a direct current power source is converted into high frequency alternating current by an inverter circuit and then rectified again to be direct current.
[0002]
[Prior art]
Conventionally, as a power supply device for arc machining, a DC power source is converted into a high frequency alternating current of several KHz to several tens of KHz by an inverter circuit and then rectified again to obtain a DC output for the purpose of miniaturization, weight reduction and high precision output control. It is produced as.
FIG. 12 is a connection diagram showing an example of a DC output arc machining power supply apparatus as described above. In the figure, reference numeral 1 denotes an AC power source, and a single-phase commercial AC power source or a three-phase commercial AC power source is used. Reference numeral 2 denotes a thyristor-controlled primary rectifier circuit that rectifies power from the AC power source 1 and converts it into DC, and its output is controlled by a control signal from a pulse generation circuit 19 described later. The primary rectifier circuit 2 may include a simple smoothing circuit. Reference numerals 3 to 6 denote bridge-connected switching elements, and reference numerals 7 to 10 denote diodes connected in parallel to the switching elements 3 to 6 in reverse polarity, and a reverse voltage is applied to the switching elements 3 to 6. It is provided to prevent this. Reference numeral 51 denotes a capacitor, 52 denotes a reactor, and a resonant inverter that converts the output of the primary rectifier circuit 2 into a high-frequency substantially sinusoidal alternating current by the switching elements 3 to 6, the diodes 7 to 10, the capacitor 51, and the reactor 52. A circuit 43 is configured. An output transformer 11 converts the output voltage of the resonant inverter circuit into a voltage suitable for arc machining. 12 is a secondary rectifier circuit that rectifies the output of the output transformer 11 again to make it a direct current, 13 is a DC reactor connected in series between the secondary rectifier circuit 12 and the output terminal (a), and 14 is an output terminal. An arc machining electrode connected to (a), 15 is a workpiece connected to the output terminal (b). 16 is an output current detector, 17 is a comparator that compares the output signal Ir of the output current setter 18 and the output signal If of the output current detector 16 and outputs a difference signal ΔI = Ir−If, and 19 is a comparator. 17 is a pulse generation circuit having a voltage controlled oscillator in which the phase of an output pulse is determined in accordance with an output signal ΔI of 17, which outputs a phase control signal to the primary rectifier circuit 2, and 20 is a switching element 3, 4 and switching It is an inverter control circuit for outputting a drive signal for alternately turning on the elements 5 and 6 at the resonance frequency.
[0003]
In the conventional apparatus of FIG. 12, the electric power from the AC power source 1 is rectified and smoothed by the primary rectifier circuit 2 to become DC, and is constituted by the switching elements 3 to 6, the diodes 7 to 10, the capacitor 51, and the reactor 52. The resonance type inverter circuit 43 converts the high frequency alternating current. The output becomes a sinusoidal output voltage corresponding to the resonance frequency in the resonance circuit constituted by the capacitor 51 and the reactor 52, and becomes a predetermined voltage in the output transformer 11. The output voltage of the output transformer 11 is converted again into a direct current by the secondary rectifier circuit 12 and supplied to the arc machining electrode 14 and the workpiece 15 from the output terminals (a) and (b) through the direct current reactor 13. As a result, a machining arc is generated between the two. This output current is detected by the output current detector 16 and compared with the set value of the output current setter 18 to calculate the difference signal ΔI. The pulse generation circuit 19 controls the phase control signal output to the primary rectifier circuit 2 in the direction in which the input signal decreases with the difference signal ΔI as an input. As a result, the output current is kept at a constant value corresponding to the set value.
[0004]
[Problems to be solved by the invention]
In the above conventional device, the output of the resonant inverter circuit is a sinusoidal output voltage corresponding to the resonant frequency, and the output supplied to the load is phase-controlled by the thyristor of the primary rectifier circuit. Control is based on half the frequency of commercial AC power supply frequency. When the input commercial power supply is single-phase, it is about every 10 [ms] and even 3 phases are about 3 [ms] units. there were.
[0010]
[Means for Solving the Problems]
The present invention is to solve the above-described problems of the conventional device, and the arc machining power supply device according to claim 1 is configured such that the switching frequency of the resonance type inverter circuit is set according to the output setting signal with respect to the resonance frequency. The present invention proposes a device that adjusts the output by increasing and decreasing the control.
[0011]
The arc machining power supply device according to claim 2, wherein the switching frequency is made higher than the resonance frequency, and two switching elements facing each other out of four switching elements are used as a pair, and each pair of switching elements is alternately arranged. Proposed a device that adjusts the output by providing a period in which all four switching elements are non-conductive only during a period inversely proportional to the difference signal between the output current and the output current setting signal after being turned ON-OFF a predetermined number of times. Is.
[0012]
A power supply device for arc machining according to claim 3 or 4 is proposed in which the switching frequency is controlled to be constant at a frequency slightly lower than the resonance frequency, and the output is adjusted by pulse width control or phase shift control of the switching element. It is a thing.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a connection diagram showing an example of an embodiment of the present invention. In the figure, reference numeral 21 denotes a rectifier circuit composed of a diode that rectifies the electric power from the AC power source 1 and converts it into DC, and may include a simple smoothing circuit. Reference numeral 22 denotes a first pulse generation circuit that generates a rectangular wave pulse with a duty of 50 [%], and includes a voltage-controlled oscillator that determines the period of the output pulse according to the output signal ΔI of the comparator 17. The drive signal P1 for making the switching elements 3 and 4 conductive is output, and the inverter gate 23 inverts the polarity of the drive signal P1 and outputs the drive signal P2 to make the switching elements 5 and 6 conductive. As a result, the output to the load is adjusted by controlling the switching frequency to be increased or decreased from the resonance frequency in accordance with the difference signal ΔI. Other components having the same functions as those in the conventional apparatus shown in FIG. The output current setting unit 18, the comparator 17, the first pulse generating circuit 22, and the inverter target 23 constitute an inverter control circuit.
[0014]
In the apparatus of FIG. 1, the power from the AC power source 1 is rectified and smoothed by a rectifier circuit 21 to become DC, and is a resonance type composed of switching elements 3 to 6, diodes 7 to 10, a capacitor 51, and a reactor 52. The inverter circuit 43 converts it to high frequency alternating current. The output becomes a sinusoidal output voltage corresponding to the resonance frequency in the resonance circuit constituted by the capacitor 51 and the reactor 52, and becomes a predetermined voltage in the output transformer 11. The output voltage of the output transformer 11 is converted again into a direct current by the secondary rectifier circuit 12 and supplied to the arc machining electrode 14 and the workpiece 15 from the output terminals (a) and (b) through the direct current reactor 13. As a result, a machining arc is generated between the two. This output current is detected by the output current detector 16 and compared with the set value of the output current setter 18 to calculate the difference signal ΔI.
[0015]
FIG. 2 is a diagram for explaining the operation of the apparatus of FIG. 1 and shows a case where the switching frequency is increased in proportion to the difference signal in inverse proportion to the difference signal. In the figure, (a) is the output signal P1 of the first pulse generation circuit 22, (b) is a signal P2 obtained by inverting the polarity of the drive signal P1 by the inverter circuit 23, (c) is the voltage of the capacitor 51, and (d) is DC. Reactor 13 current, (e), shows the output voltage appearing between the output terminals (a), (b), respectively, over time.
[0016]
In FIG. 2, the period between times t2 and t3 and between t4 and t5 is a period in which the current flowing through the DC reactor 13 increases and power is stored in the DC reactor 13, and is hereinafter referred to as a current increase period. Further, the period between the times t1 and t2 and the period between t3 and t4 is a period in which the secondary rectifier circuit 12 functions as a flywheel diode, and is hereinafter referred to as a flywheel operation period. When the switching frequency is higher than the resonance frequency, when the drive signal P1 is turned on at time t1, the flywheel operation period is first followed by the current increase period at time t2.
[0017]
When the difference signal ΔI is input and the output current is large, the first pulse generation circuit 22 shortens the cycle of the drive signals P1 and P2 to shorten the switching cycle, for example, between the times t1 and t2 and the time t3. By shortening the flywheel operating period between t4 and t4, the charging voltage of the capacitor 51 is lowered, and as a result, the output current can be reduced. Conversely, when the output current is small, the output current can be increased by increasing the period of the drive signals P1 and P2. That is, the output current can be kept at the set value by adjusting the output frequency of the first pulse generation circuit 22 in inverse proportion to the difference signal ΔI.
[0018]
FIG. 3 is a diagram for explaining the operation of the apparatus of FIG. 1, and shows a case where the switching frequency is decreased below the resonance frequency in accordance with the difference signal ΔI. In the figure, (a) is the output signal P1 of the first pulse generating circuit 22, (b) is a signal P2 obtained by reversing the polarity of the drive signal P1 by the inverter 23, (c) is the voltage of the capacitor 51, (d ) Shows the current of the DC reactor 13, and (e) shows the output voltage appearing between the output terminals (a) and (b) with the passage of time.
[0019]
In FIG. 3, the current increase period is between times t1 and t2 and between t3 and t4, and the flywheel operation period is between times t2 and t3 and between t4 and t5. When the switching frequency is lower than the resonance frequency, when the drive signal P1 is turned on at time t1, the current increases first, and then the flywheel operation period at time t2.
[0020]
When the switching frequency is lower than the resonance frequency, the first pulse generating circuit 22 shown in FIG. 1 takes the difference signal ΔI as an input, and when the output current is large, the period of the drive signals P1 and P2 is lengthened to increase the switching period. By lengthening the output current, the output current can be reduced. Conversely, when the output current is small, the output current can be increased by shortening the cycle of the drive signals P1 and P2. That is, the output current can be kept at the set value by adjusting the output frequency of the first pulse generation circuit 22 in direct proportion to the difference signal ΔI.
[0021]
In the apparatus of FIG. 1, since the switching period must utilize the characteristics of the resonant circuit, the maximum period is limited to several tens [%]. Therefore, if an OFF period is provided between each set of drive signals and the OFF period is adjusted, a minimum output smaller than that of the apparatus shown in FIG. 1 can be obtained.
[0022]
FIG. 4 is a connection diagram showing an example of another embodiment of the present invention as described above. In the figure, 24 is a second pulse generating circuit, 25 and 26 are mono multivibrators, and the mono multivibrator 25 generates a pulse having a certain time width in synchronization with the rising of the input signal. 26 generates a pulse having a certain time width in synchronization with the fall of the input signal. The other components having the same functions as those of the apparatus shown in FIG. The output current setting device 18, the comparator 17, the second pulse generation circuit 24, and the mono multivibrators 25 and 26 constitute an inverter control circuit.
[0030]
FIG. 5 is a diagram for explaining the operation of the apparatus of FIG. In the figure, (a) is the output of the second pulse generating circuit 24, (b) is the output of the mono multivibrator 25 and the drive signal P3, (c) is the output of the mono multivibrator 26 and the drive signal P4, (d). Shows the output voltage appearing between the output terminals (a) and (b) with the passage of time.
[0031]
In FIG. 4, the second pulse generation circuit 24 inputs the difference signal ΔI and outputs a synchronization pulse, and the mono multivibrator 25 outputs a pulse in synchronization with the rise of the output signal of the second pulse generation circuit 24. The mono multivibrator 26 outputs a pulse in synchronization with the fall of the output signal of the mono multivibrator 25. Thereafter, the pulse output is interrupted until the second pulse generation circuit 24 outputs the next pulse. As a result, the switching elements 3 and 4 and the switching elements 5 and 6 receive a set of drive signals P3 and P4, respectively, are turned on once, and then shut off until a set of drive signals P3 and P4 are input again. It will keep the cut-off state. In the apparatus of FIG. 4, the output pulse width T0 of the mono multivibrators 25 and 26 is made equal to or slightly shorter than the resonance period of the resonant inverter circuit, and the output period T of the second pulse generation circuit 24 is inversely proportional to the difference signal ΔI. Thus, the output can be controlled to be kept at the set value by changing under the condition of T ≧ 2T0.
[0032]
FIG. 6 is a connection diagram showing an example of another embodiment according to the present invention, in which an OFF period is provided after the switching elements 3 to 6 of the resonant inverter circuit 43 are turned on and off twice in succession. An example of when. In the figure, reference numeral 24 denotes a second pulse generation circuit, and reference numerals 25 to 28 denote mono multivibrators. The mono multivibrator 25 outputs a pulse having a certain time width in synchronization with the rising of the input signal, and the mono multivibrator. Nos. 26 to 28 output pulses having a certain time width in synchronization with the fall of the input signal. 29 and 30 are OR gates. The other components having the same functions as those of the apparatus shown in FIG. The output current setting unit 18, the comparator 17, the second pulse generation circuit 24, the mono multivibrators 25 to 28, and the OR gates 29 and 30 constitute an inverter control circuit.
[0033]
FIG. 7 is a diagram for explaining the operation of the apparatus of FIG. In the same figure, (a) is the output of the second pulse generating circuit 24, (b) is the output of the mono multivibrator 25, (c) is the output of the mono multivibrator 26, (d) is the output of the mono multivibrator 27, (E) is the output of the mono multivibrator 28, (f) is the drive signal P5, (g) is the drive signal P6, (h) is the output voltage appearing between the output terminals (a) and (b), respectively. It is shown together.
[0034]
In FIG. 6, the second pulse generation circuit 24 receives the difference signal ΔI and outputs a synchronization pulse having a period inversely proportional to the magnitude of the input signal. The mono multivibrator 25 outputs a pulse in synchronization with the rise of the output of the second pulse generation circuit 24, and the mono multivibrator 26 outputs a pulse in synchronization with the fall of the output signal of the mono multivibrator 25, The mono multivibrator 27 outputs a pulse in synchronization with the falling edge of the output signal of the mono multivibrator 26, and the mono multivibrator 28 outputs a pulse in synchronization with the falling edge of the output signal of the mono multivibrator 27. Here, the mono multivibrators 25 to 28 are set so that the output pulse width T 0 is slightly shorter than the period corresponding to the resonance frequency of the resonance type inverter circuit 43. The OR gate 29 outputs the drive signal P5 when either the output signal of the mono multivibrator 27 or the output signal of the mono multivibrator 25 is ON. The OR gate 30 outputs the drive signal P6 when either the output signal of the mono multivibrator 28 or the output signal of the mono multivibrator 26 is ON. Thereafter, until the second pulse generation circuit 24 outputs the next pulse, the switching elements 3 to 6 become non-conductive. As a result, the switching elements 3 to 6 are provided with an OFF period that is inversely proportional to the difference signal ΔI after the ON / OFF is alternately repeated twice by the two sets of drive signals P5 and P6.
[0035]
Similar to the apparatus shown in FIG. 6, by connecting N stages of mono-multivibrators, the switching elements 3 to 6 change the difference signal ΔI between N sets of drive signals and the next N sets of drive signals. A signal having an inversely proportional OFF period can be input.
[0036]
FIG. 8 is a connection diagram showing an example of still another embodiment of the present invention. In the figure, 31 is a third pulse generating circuit, 32 is a sawtooth wave generating circuit, 33 is a second comparator, 34 is a flip-flop circuit, and 35 and 36 are AND gates. The other components having the same functions as those of the apparatus shown in FIG. The output current setting unit 18, the comparator 17, the third pulse generation circuit 31, the sawtooth wave generation circuit 32, the second comparator 33, the flip-flop circuit 34, and the AND gates 35 and 36 constitute an inverter control circuit.
[0037]
FIG. 9 is a diagram for explaining the operation of the apparatus of FIG. In the figure, (a) is the output of the third pulse generation circuit 31, (b) is the output of the sawtooth wave generation circuit 32, (c) is the output of the flip-flop circuit 34, and (d) is the output of the second comparator 33. (E) is the drive signal P7, (f) is the drive signal P8, (g) is the output of the output transformer 11, (h) is the output voltage appearing between the output terminals (a) and (b), respectively. It is shown with the progress of.
[0041]
In FIG. 8, the third pulse generation circuit 31 outputs a synchronization pulse having a frequency slightly lower than the resonance frequency of the resonant inverter circuit, and the sawtooth wave generation circuit 32 synchronizes with the output of the third pulse generation circuit 31. Is output. The second comparator 33 compares the output of the sawtooth wave generating circuit 32 with the difference signal ΔI, and when the output of the sawtooth wave generating circuit is smaller than the difference signal ΔI, a positive signal is sent to the AND gates 35 and 36. Output. The flip-flop circuit 34 outputs the outputs Q and Q bar to the AND gates 35 and 36 in synchronization with the fall of the output of the third pulse generating circuit 31, respectively. The AND gates 35 and 36 receive the output of the second comparator 33 and the output of the flip-flop circuit 34, and output drive signals P7 and P8 to the switching elements 3, 4 and 5, 6 respectively. In the figure, since the switching frequency is the output frequency of the third pulse generating circuit 31, this frequency is controlled to be constant at a frequency smaller than the resonant frequency of the resonant inverter circuit and close to the resonant frequency, and the switching elements 3 to 6 are controlled. By controlling the pulse width corresponding to the difference signal ΔI, the output current is controlled to be kept at the set value.
[0042]
FIG. 10 is a connection diagram showing an example of still another embodiment of the present invention. In the figure, 31 is a third pulse generating circuit, which determines the switching frequency. Reference numeral 37 denotes a phase comparator, and a known phase comparator such as a multiplier type, a digital type, or a phase frequency comparator that outputs a voltage signal corresponding to the phase difference between two input signals is used. Reference numeral 38 denotes a low-pass filter that removes high-frequency components from the output of the phase comparator 37. 39 is an adder, 40 is a voltage controlled oscillator, and 41 and 42 are inverter gates. The other components having the same functions as those of the apparatus shown in FIG. The output current setting unit 18, the comparator 17, the third pulse generating circuit 31, the phase comparator 37, the low pass filter 38, the adder 39, the voltage controlled oscillator 40, and the inverter gates 41 and 42 constitute an inverter control circuit.
[0043]
FIG. 11 is a diagram for explaining the operation of the apparatus of FIG. In the figure, (a) is the output of the third pulse generating circuit 31 and the drive signal P9, (b) is the drive signal P10, (c) is the drive signal P11, (d) is the drive signal P12, and (e) is the output. The output of the transformer 11, (f) shows the output voltage appearing between the output terminals (a) and (b) with the passage of time.
[0044]
In the apparatus of FIG. 10, the output of the third pulse generating circuit 31 is output to the switching element 3 as the drive signal P9, and the polarity is inverted by the inverter circuit 42 and output to the switching element 5 as the drive signal P11. Further, the output of the third pulse generating circuit 31 is compared with the output signal of the voltage controlled oscillator 40 by the phase comparator 37, and a voltage corresponding to the phase difference between the two input signals is calculated. A high-frequency component is removed from the output of the phase comparator 37 by the low-pass filter 38 and is input to the adder 39. On the other hand, the set value Ir of the output current setter 18 is compared with the output signal If of the output current detector 16 by the comparator 17 to become a difference signal ΔI, which is the other input of the adder 39. In the adder 39, the output of the low-pass filter 38 and the output of the comparator 17 are added and input to the voltage controlled oscillator 40. The voltage controlled oscillator 40 outputs a pulse signal having a frequency corresponding to the input voltage. The output signal of the voltage controlled oscillator 40 is output to the switching element 4 as the drive signal P10 after the polarity is inverted by the inverter gate 41. The output of the voltage controlled oscillator 40 is fed back to the phase comparator 37 and also output to the switching element 6 as a drive signal P12.
[0045]
Here, the phase comparator 37, the low-pass filter 38, and the voltage controlled oscillator 40 constitute a known PLL circuit, and the control circuit of FIG. 10 is an adder that adds a difference signal ΔI in the middle of the known PLL circuit. 39 is added. Therefore, the voltage controlled oscillator 40 outputs a pulse signal having a waveform having the same frequency as the output frequency of the third pulse generating circuit 31 and having a phase shifted by an amount corresponding to the difference signal ΔI. As a result, the drive signals P9 and P10 and the drive signals P11 and P12 have waveforms shifted in phase by α corresponding to the difference signal ΔI, and the drive signals P9 and P11 and the drive signals P10 and P12 are opposite to each other. It becomes a phase. In the figure, when the switching frequency is controlled to be constant at a frequency smaller than the resonance frequency and close to the resonance frequency, the conduction time of each switching element is determined in proportion to the phase difference α of the drive signal, that is, the difference signal ΔI. Is controlled to be kept at the set value.
[0046]
In the embodiment shown in FIGS. 4 and 6, if control for increasing or decreasing the output pulse width of the mono multivibrators 25 to 28 is added, a wider range of output control is possible. Further, in the embodiment shown in FIG. 8 and FIG. 10, if a control for increasing / decreasing the output frequency of the third pulse generating circuit 31 with respect to the resonant frequency of the resonant inverter circuit 43 is added, a wider range of output control is possible. It becomes.
[0047]
In the embodiments shown in FIGS. 1, 4, 6 and 8, the resonant inverter circuit 43 is a full-bridge type circuit, but the present invention is replaced with a half-bridge type circuit. A circuit may be used. In any of the above-described embodiments, the output current is fed back and the set value is compared to maintain the output current at a constant value, but the present invention detects the output voltage instead of the output current, This can be applied to a device that keeps the output voltage constant by comparing it with a set value.
[0050]
【The invention's effect】
As described above, the arc machining power supply device according to the present invention adjusts the output by changing the switching frequency of the switching element of the resonance type inverter circuit with respect to the resonance frequency. On the other hand, there is an effect of good responsiveness. Further, the switching frequency is increased from the resonance frequency, and two switching elements facing each other among the four switching elements are taken as a pair, and each pair of switching elements is alternately and continuously turned ON / OFF a predetermined number of times, and then the difference signal. By providing a period in which all four switching elements are non-conductive for a period inversely proportional to the minimum output, the minimum output can be made smaller and the controllable output range can be expanded. In addition, by controlling the switching frequency at a constant frequency slightly lower than the resonance frequency and controlling the pulse width or phase shift of the switching element, it maintains the responsiveness to fluctuations in the output to the load while maintaining the low output range. The control range can be expanded.
[Brief description of the drawings]
FIG. 1 is a connection diagram illustrating an example of an embodiment of the present invention.
FIG. 2 is a diagram for explaining the operation of the apparatus of FIG. 1, and shows a case where the switching frequency is increased above the resonance frequency.
FIG. 3 is a diagram for explaining the operation of the apparatus shown in FIG. 1, and shows a case where the switching frequency is decreased below the resonance frequency.
FIG. 4 is a connection diagram showing an example of another embodiment of the present invention.
5 is a diagram for explaining the operation of the apparatus of FIG. 4;
FIG. 6 is a connection diagram showing still another example of the embodiment of the present invention.
FIG. 7 is a diagram for explaining the operation of the apparatus of FIG. 6;
FIG. 8 is a connection diagram illustrating another example of the embodiment of the present invention.
9 is a diagram for explaining the operation of the apparatus of FIG.
FIG. 10 is a connection diagram illustrating another example of the embodiment of the present invention.
11 is a diagram for explaining the operation of the apparatus shown in FIG. 10;
FIG. 12 is a connection diagram illustrating an example of a conventional apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 AC power supply 2 Primary rectifier circuit 3 Switching element 4 Switching element 5 Switching element 6 Switching element 7 Diode 8 Diode 9 Diode 10 Diode 11 Output transformer 12 Secondary rectifier circuit 13 DC reactor 14 Arc processing electrode 15 Workpiece 16 Output Current detector 17 Comparator 18 Output current setting device 19 Pulse generation circuit 20 Inverter control circuit 21 Rectifier circuit 22 First pulse generation circuit 23 Inverter gate 24 Second pulse generation circuit 25 Mono multivibrator 26 Mono multivibrator 27 Mono multivibrator 28 Mono multivibrator 29 OR gate 30 OR gate 31 Third pulse generator circuit 32 Sawtooth wave generator circuit 33 Second comparator 34 Flip-flop circuit 35 AND gate 36 AND gate 37 Phase Comparator 38 Low pass filter 39 Adder 40 Voltage controlled oscillator 41 Inverter gate 42 Inverter gate 43 Resonant inverter circuit

Claims (4)

A primary rectifier circuit that rectifies an AC power source to obtain DC power, a resonant inverter circuit that converts the output of the primary rectifier circuit into a high-frequency substantially sinusoidal AC, and an output of the resonant inverter circuit that converts the output to a predetermined voltage An output transformer, a secondary rectifier circuit that rectifies the output of the output transformer to make a direct current, and a switching frequency of the resonant inverter circuit according to a difference signal between an output current and an output current setting signal. An arc machining power supply device comprising an inverter control circuit that changes the resonance frequency. A primary rectifier circuit that rectifies an AC power source to obtain DC power, a resonant inverter circuit that includes four switching elements connected in a bridge that converts the output of the primary rectifier circuit into a high-frequency substantially sinusoidal AC, and the resonance An output transformer that converts the output of the inverter circuit into a predetermined voltage, a secondary rectifier circuit that rectifies the output of the output transformer into a direct current, and a difference signal between the output current and the output current setting signal Accordingly, the switching frequency of the resonance type inverter circuit is increased above the resonance frequency, and two switching elements facing each other out of the four switching elements are taken as a pair, and each pair of switching elements is alternately and continuously set. An inverter control circuit provided with a period in which all of the four switching elements are non-conductive for a period inversely proportional to the difference signal after being turned on and off a number of times; Arc machining power supply apparatus having. A primary rectifier circuit that rectifies an AC power source to obtain DC power, a resonant inverter circuit that includes four switching elements connected in a bridge that converts the output of the primary rectifier circuit into a high-frequency substantially sinusoidal AC, and the resonance An output transformer that converts the output of the inverter circuit into a predetermined voltage, a secondary rectifier circuit that rectifies the output of the output transformer into a direct current, and a difference signal between the output current and the output current setting signal Accordingly, the switching frequency of the resonant inverter circuit is controlled at a constant frequency slightly lower than the resonant frequency, and two switching elements facing each other among the four switching elements are defined as one pair, and each pair of switching elements is set. An inverter control circuit that controls ON / OFF alternately and controls the output by changing the conduction time rate of each pair of switching elements. Arc machining power supply apparatus. A primary rectifier circuit that rectifies an AC power source to obtain DC power, a resonant inverter circuit that includes four switching elements connected in a bridge that converts the output of the primary rectifier circuit into a high-frequency substantially sinusoidal AC, and the resonance An output transformer that converts the output of the inverter circuit into a predetermined voltage, a secondary rectifier circuit that rectifies the output of the output transformer into a direct current, and a difference signal between the output current and the output current setting signal Accordingly, the switching frequency of the resonance type inverter circuit is controlled at a constant frequency slightly lower than the resonance frequency, and the drive signals of each of the two switching elements connected in series among the four switching elements are transmitted every half cycle. The ON / OFF control is alternately performed to change the phase difference between the drive signals of the two switching elements facing each other among the four switching elements. Arc machining power supply apparatus comprising an inverter control circuit for controlling the output by the.

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