JP2770454B2 - Power supply for arc machining - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an improvement in an arc processing power supply device used for arc welding, cutting, heating, plasma arc welding, cutting, and the like.

<Conventional technology> A DC / AC converter using a switching element converts DC power into high-frequency AC, then converts it back to DC and supplies it to the arc load. By increasing the frequency, the output transformer can be reduced in size and weight, and the output can be controlled precisely, so that various types of excellent devices have been developed in recent years.

FIG. 10 shows a connection diagram of a typical example of this type of conventional apparatus. In FIG. 1, reference numeral 1 denotes an AC power supply, which is usually a commercial frequency three-phase or single-phase AC power supply. Reference numeral 2 denotes a rectifier circuit, and reference numerals 3a and 3b denote capacitors connected in series, which divide the output voltage of the rectifier circuit 2 into two. 4a and 4b are switching elements connected in series, and self-extinguishing elements such as transistors are used. Reference numerals 5a and 5b denote rectifying elements connected in parallel to the switching elements 4a and 4b, respectively, with opposite polarities, for protection to prevent application of a reverse voltage to the switching elements 4a and 4b. 6a and 6b are capacitors connected in parallel to the switching elements 4a and 4b, for absorbing surge voltage. Reference numeral 7 denotes an output transformer whose primary winding is connected between the connection point of the capacitors 3a and 3b and the connection point of the switching elements 4a and 4b.
The output of the next winding is rectified by a rectifier circuit 8 and then smoothed by a DC reactor 9 to be DC, and supplied to an arc load composed of an electrode 10, an arc 11 and a workpiece 12. 13
An output current detector, the output setting circuit 14, comparator 15 which compares the output signal I _f the output signal e _r output setting circuit 14 outputs the current detector, to obtain a difference signal Δv = e _r -I _f And 16 is a pulse width control (PWM) that alternately supplies a drive signal having a pulse width corresponding to the output signal Δv of the comparator 15 to the switching elements 4a and 4b.
Control) circuit.

In the device shown in the figure, the switching elements 4a and 4b are turned on alternately by the drive signal from the pulse width control circuit 16, whereby the transformer 7 is supplied with substantially rectangular wave AC power. After this current is rectified by the rectifier circuit 9,
It is smoothed by the DC reactor 9 and supplied to the welding load. The output current detector 13 is converted into a voltage signal I _f is compared with the output setting signal e _r in the comparator 15 at and difference signals Δv becomes, the drive signal is a pulse width control of a pulse width determined by the difference signal Control is performed so that the value is generated by the circuit 16 and corresponds to the set value of the output current. At this time, the pulse width of the drive pulse generated by the pulse width control circuit 16 is determined by the error signal Δv, and the frequency is a predetermined constant frequency.

<Problems to be Solved by the Invention> In the above-mentioned conventional device, each switching element has almost no reactance in its output circuit, so that it operates so that a substantially rectangular current flows with respect to a rectangular drive signal. I do.

However, the switching element cannot make a complete step change with respect to the step drive signal,
The target value is reached after a period of a slight slope change. For this reason, a large power loss occurs at the start of conduction and at the start of interruption (at the time of switching) in which the voltage and current change in a slope shape. Since this loss occurs every time switching is performed, the heat generated by the element becomes large, so that the operating frequency cannot be increased sufficiently, and the necessary control of the definition cannot be obtained. In addition, the cooling mechanism for releasing this large amount of heat becomes large, and high-frequency DC / A
The effect of trying to reduce the size using the C conversion circuit is offset. In addition, the current during switching
Since the voltage changes rapidly, the generation of noise due to electromagnetic induction becomes large, and a large amount of cost is required for measures for preventing noise disturbance not only in the control system itself but also in other devices.

<Means for Solving the Problems> The present invention provides an LC resonance circuit at the output terminal of a DC / AC conversion circuit using a switching element, and drives the switching element at a frequency higher than the resonance frequency of the LC resonance circuit. In addition, the above problem is solved by extracting output power from a part of the LC resonance circuit through a transformer. The pulse width control (PWM control) that determines the LC resonance circuit is performed, and when the current of the LC resonance circuit becomes substantially zero after one of the switching elements is cut off, the LC resonance circuit conducts the switching element of the opposite polarity. The switching circuit is synchronized by the current zero point detection signal of the circuit.

<Operation> In the present invention, by supplying the output of the DC / AC conversion circuit to the LC resonance circuit, the change in the current flowing through the switching element is approximated to a sine wave to prevent a sudden change in the current, and the DC / AC conversion circuit By adjusting the operating frequency of the LC resonance circuit to a higher frequency than the resonance frequency of the LC resonance circuit, it is possible to adjust the output, and by switching the polarity to the zero point of the current of the LC resonance circuit, zero current switching is realized. is there.

<Embodiment> FIG. 1 shows a connection diagram of an embodiment of the present invention. In this figure, reference numerals 1 to 12 denote elements having the same functions as those of the conventional apparatus shown in FIG. An output detector 17 detects an output voltage in the case of FIG. Reference numeral 18 denotes an output setting circuit, which uses an output voltage detector as the output detector 17, and uses an output voltage setting circuit for setting the output voltage. 19 is a comparator, compares the set value e _r output setting circuit 18 and the output signal V _f output detector, and outputs a difference signal Δv = e _r -V _f. 20 is a reactor, 21 is a capacitor, and reactor 20 and a capacitor
21 and an LC resonance circuit, and the output transformer 7
The primary winding obtains power from both ends of the capacitor 21 of the LC resonance circuit. 22 resonance current detector for detecting a current I _L flowing through the LC resonance circuit, 23 is zero-current setting circuit is set to a relatively small value, 24 the output Iz of zero current setting circuit 23 of the resonant current detector 22 compares the absolute value of the output I _L | I _L | <Iz
A zero-phase detection circuit that generates a pulse signal p when the following condition is satisfied; 25, an oscillator that generates a sawtooth wave s synchronized with the output p of the zero-phase detection circuit 24; 26, an output s of the sawtooth wave oscillator 25 and a comparator 19; And a comparator 27 which receives the output Δv of the comparator as an input and obtains a signal d having a constant amplitude that is continuous during the period Δv> s. The output circuit 27 alternately divides the output d of the comparator circuit 26 for each pulse into d ₂ and d ₂ . This is a two-phase separation circuit that distributes to the switching elements 4a and 4b. Here, the sawtooth wave oscillator 25, the comparison circuit 26, and the two-phase separation circuit 27 are, together with the comparator 19, the switching elements 4a and 4b.
A pulse generation circuit for driving the pulse width control circuit is configured to synchronize and follow the phase and operating frequency of an output feedback type pulse width control (PWM control) circuit with the output pulse of the zero phase detection circuit 24.

FIG. 2 is a diagram showing changes in signals of respective sections over time for explaining the operation of the embodiment of FIG.

In the same figure, (a) and (b) show changes in terminal voltages of the switching elements 4a and 4b, and (c) shows currents I _4a , I _5a and I _5a flowing through the switching element 4a, the rectifying element 5a and the capacitor 6a, respectively. The change in I _6a is shown with the arrow direction shown as the positive direction, and (d) shows the switching element 4b
b and the currents I _4b , I _5b , I
The change in _6b is also shown. (E) current flows in the LC resonance circuit I _L, (f) the absolute value of the current I _L | a relationship between a zero setting signal Iz current setting circuit 23, (g) is | | I _L I _L | <I
The output p of the zero-phase detection circuit 24 corresponding to the period of z is
(H) shows the relationship between the error signal Δv and the output s of the sawtooth wave oscillator 25, respectively. (I) shows the comparison circuit 26
(J) and (k) show drive signals d ₁ and d ₂ of the switching elements 4a and 4b, respectively, obtained by separating the signal d into two phases. The (l) is the output voltage V _P to be supplied to the transformer 7.

In FIGS. 1 and 2, the signal d ₁ at time t = t ₁ is being output, the switching element 4a is conductive. At this time, the current flows in the direction of [rectifier circuit 2 → switching element 4a → capacitor 21 → reactor 20] as shown by the arrow in the figure. This current _IL is shown in FIG.
As shown in (2), it changes in a sine wave shape corresponding to the resonance frequency of the resonance circuit formed by the reactor 20 and the capacitor 21. At this time, the transformer 7 receives the terminal voltage of the capacitor 21 and generates a sinusoidal output voltage.
Is converted to DC by the DC reactor 9 and the electrode 10
The arc 11 is supplied between the workpiece and the workpiece 12 to generate an arc 11.
This output voltage becomes a detection signal _Vf by the output detector 17, and
It is compared with the output e _r output setting circuit 18 in the comparator 19 with the error signal Δv = e _r -V _f. The error signal Δv is compared with the output s of the sawtooth wave generation circuit 25 by the comparison circuit 26, and the switching element 4a is continuously turned on while Δv> s.

Next, when Δv <s at time t = t ₂ , the comparison circuit 2
The output d of 6 becomes zero, which causes
a shuts off. And tries to continue to flow a current I _L by energy switching element 4a is accumulated in the resonant circuit current which has been flowing in until immediately before shut off,
In this case, [Capacitor 3a → Capacitor 6a → Capacitor 21
→ Reactor 20] circuit and [Capacitor 3b → Capacitor
6b → capacitor 21 → reactor 20]. Immediately before this time t = t ₂ , the terminal voltage of the capacitor 6a is substantially zero because the switching element 4a is conducting, and the terminal voltage of the capacitor 6b is charged to a voltage substantially equal to the output voltage of the rectifier circuit 2. I have. When the switching element 4a is cut off, the capacitor 6a starts charging, and the capacitor 6b starts discharging. Completed in approximately the same time t _c is the charge and discharge current and discharge current are both 1/2 · I _L and the charge for both capacitor, the terminal voltage of the capacitor 6a is raised to the supply voltage, the capacitor 6b is a switching element The power supply voltage charged during the conduction period of 4a drops to zero. Therefore, the signal d is applied to the switching element 4a.
Immediately after ₁ disappears, current stops flowing.

When the terminal voltage of the capacitor 6b becomes zero, the rectifying element 5b conducts, and the current I _L that has been divided and passed through the capacitors 6a and 6b flows only through the rectifying element 5b.
During this time, the current I flowing through the reactor 20 and the capacitor 21
_L decreases like a sine wave corresponding to the resonance frequency from time t = t ₂ . The absolute value of the current I _L is zero current setting circuit 23
At time t = t ₃ , which is smaller than the set value Iz, the output p of the zero phase detection circuit 24 is generated, and the sawtooth wave oscillator 25 is reset. As a result, Δv> s is satisfied, and the comparison circuit 26 outputs the high-level signal d again.
Switching element 4b becomes the signal d ₂ by phase separation circuit 27
Supplied to In this case the reactor 20 and the resonant circuit composed of a capacitor 21. and also flows while still above the current in the same direction is reduced, thus the forward voltage of the rectifier also signal d ₂ is supplied to the switching element 5b element 5b It does not conduct because it is reverse biased by the fall. Next, when the current I _L becomes zero at time t = t _4, already the polarity of the current I _L of the resonant circuit continuity signal d ₂ is a current starts to flow in the switching element 4b, which is supplied previously it reverses.

When the switching element 4a is conducting, this current similarly changes in a sine wave shape corresponding to the resonance frequency of the resonance circuit, and only the polarity of the current is reversed. Thereafter, the switching element 4b continues to conduct until the output s of the sawtooth wave oscillator 25 becomes larger than the output signal Δv of the comparison circuit 26, and Δv
It shuts off at the time of <s. Subsequent operations are performed at the previous time t.
= From t ₂ is the same as the operation between leading to t _4, this time the capacitor 6a and 6b, the switching elements 4a and 4b, a rectifying element 5a
5b are opposite to each other, and the direction of the current _IL is also opposite to the direction of the arrow in FIG.

Alternating current flows through the resonance circuit by repeating the above operation, the capacitor 21 becomes a voltage Vp obtained by integrating the current I _L is obtained, the primary input voltage of the transformer 7
Vp is obtained.

The diagram shown in FIG. 2 shows a state where the error signal Δv is large and the switching element is conducting for a relatively long time. For this reason, the state of flowing to the resonance circuit is shown. For this reason, the current flowing through the resonance circuit has a period of almost half a sine wave. However, when the error signal Δv is small, the conduction period of the switching element is short, whereas the resonance frequency of the resonance circuit remains unchanged, so that the switching element is cut off relatively early in the sine wave,
Since decrease in current from the moment of the cut-off begins, it varies a state of the current I _L flowing in the resonant circuit. FIG. 3 is a diagram showing the situation at this time, and FIGS.
Correspond to (a) to (l) of FIG. 2, respectively. Current I _L of the resonant circuit as shown in the figure distortion is increased, the primary voltage of the transformer is a waveform obtained by integrating the also slight distortion occurs. However, since the switching elements are turned on and off in exactly the same manner as in FIG. 2, no switching loss occurs in either of FIGS. 2 and 3.

Here, the conduction drive signal for each switching element is
It is important that the operation be completed within a half cycle of the resonance frequency of the resonance circuit. If the drive signal is supplied beyond the half cycle of the resonance frequency, the current becomes an oscillating current according to the constant of the resonance circuit while the conduction signal is supplied. In this case, during the period of the current having the polarity opposite to the conduction direction of the switching element to which the conduction signal is supplied, the current flows through the rectifying element connected in parallel with the other switching element. Is not supplied, but only the energy stored in the resonance circuit is released. Therefore, the output during this period is small, the sign of the output becomes unbalanced, and the pulsation of the output becomes extremely large. Further, when the oscillating current ends when the polarity of the oscillating current is opposite to the conducting polarity of the switching element, that is, when the oscillating current is flowing through the rectifying element connected in parallel with the switching element of the opposite polarity, the current decreases, thereby | After I _L | <Iz, a conduction signal is supplied to the next switching element, so that a current having the same polarity as the last half wave of the previous conduction period flows out. As a result, the half-wave in the same direction continues twice each time switching is performed, which not only promotes output pulsation, but also causes magnetic saturation of the output transformer, lowers the output, and further reduces the voltage. This can lead to accidents in which devices and switching elements are destroyed.

Next, how to determine the set value Iz of the zero current setting circuit 23 will be described. Apparatus as described above of the present invention, current I _L of the resonant circuit so on are changed sinusoidally, | I _L | <conduct signals to the switching elements for supplying the next polarity of the current when it becomes Iz Is to supply. At this point, it is an essential condition that the current of the original polarity continues to flow through the rectifying elements connected in antiparallel. Therefore, the signal Iz is not zero and a relatively large current is set to, for example, about 5 to 10% of the maximum value of the resonance current. However, if this set value is set to an excessively large value, the output adjustment range is narrowed accordingly, so that it should be kept to the minimum necessary.

In the embodiment of FIG. 1, earlier than the end of the half-wave of the resonance frequency of the resonance circuit, to be precise, Δv <s with respect to the normal error voltage Δv within | I _L |> Iz. An example when the conduction period of the switching element ends is shown. In this case, the changing speed (gradient) of the output voltage of the sawtooth wave oscillator 25 is determined so as to satisfy the above condition with respect to the resonance frequency.

Next, the situation when the output setting signal is suddenly changed or the load condition is suddenly changed in the embodiment of FIG. 1 will be described with reference to the diagram of FIG. At this time, as shown in FIG. 4, the error voltage becomes excessive, and a half-wave of the resonance frequency ends before Δv <s. In this case, before reaching Δv <s, the absolute value | I _L | of the current I _L decreases in accordance with the sine wave, and at time t = t ₀ in FIG. 4, | I _L | <Iz
As a result, the output signal p of the zero-phase detection circuit 24 becomes high level, resets the sawtooth wave generation circuit 25, thereby cutting off the drive signal for the conducting switching element, and immediately thereafter, the driving signal for the other switching element. And the switching cycle is determined by a cycle shorter than a half-wave of the resonance cycle of the resonance circuit by a period determined by the zero current set value Iz.

In this case, unless the parallel capacitors 6a and 6b of FIG. 1 are provided, | I _L | <Iz and the switching element 4a
Immediately after the drive signal for (or 4b) disappears, the rectifying element 5b (or 5a) conducts, and a current substantially equal to the current immediately after that, that is, | I _L | = Iz, flows, and the resonance circuit passes over time. Is reduced by the arc load, and when _IL becomes zero, a current starts to flow through the switching element 4b (or 4a) to which the conduction signal is already supplied.

However, when there are capacitors 6a and 6b connected in parallel as shown in FIG. 1, the charges charged in these capacitors are shown at "a" in FIG. 4 at the moment when the conduction signal is supplied to the switching element. As described above, discharge is performed only through the switching element. For this reason, a large loss occurs in the switching element in which conduction is newly started.

In order to prevent the above phenomenon, in the connection diagram of FIG. 1, the set value Iz is set slightly higher, and | I _L | <Iz with respect to this set value Iz so that the zero-phase detection circuit 24 It is sufficient to provide a timed circuit for prohibiting the output of the next switching element drive signal d for a certain period from when the output p becomes high level.

FIG. 5 shows a mono-multivibrator 3 for generating a high-level signal m for a certain period of time in response to the rise of the output p of the zero-phase detecting circuit 24 in the embodiment of FIG.
0 shows another embodiment of the present invention in which an inverter 31 for inverting the output of the monomultivibrator 30 and an analog switch 32 provided between the comparator 19 and the comparison circuit 26 for opening and closing the error signal Δv are added. FIG.

Figure 6 is a diagram for explaining the operation of the embodiment of FIG. 5, (a) represents the absolute value of the current I _L of the resonance circuit | I _L | shows changes in, (b) is zero The output p of the phase detection circuit 24,
(C) shows the relationship between the output m of the monomultivibrator 30, (d) shows the relationship between the output s of the sawtooth wave oscillator 25 and the error signal Δv, and (e) shows the outputs d, (f) and (g) of the comparison circuit 26. () Shows how the outputs d ₁ and d ₂ of the two-phase separation circuit 27 change.

In FIGS. 5 and 6, when the error signal Δv becomes excessively large and the half cycle of the resonance current I _L ends while being larger than the sawtooth wave s, the time t at which | I _L | <Iz is satisfied = T ₁ , the signal p goes to high level, thereby resetting the sawtooth wave oscillator 25 and the drive signal d ₁ for the switching element 4a goes to low level. At the same time, the mono-multivibrator is triggered at the rising edge of the signal p and outputs a high-level signal m for a fixed time Tm. This signal m is converted by the inverter 31 into a signal which becomes low level only during the time Tm from the rise of the signal p, and this signal causes the analog switch 32 to open only during the time Tm and close during the other periods. .
As a result, the error signal Δv becomes the time t = t _{1 when} | I _L | <Iz.
To Tm, the comparison circuit 26 has Δv of the input signal of zero, so that s> Δv holds, and the signal d is at the low level during the period of Tm. As a result, the switching element 4b operates at time t = t ₂ , which is Tm after time t = t _1.
, A high-level drive signal d ₂ is supplied. Therefore, if the time limit Tm of the multivibrator 30 is set to a time slightly longer than the time required for charging and discharging the capacitors 6a and 6b (the time _{Tc in} FIG. 2), then the drive signal d is transmitted to the switching element 4b. _{When 2} is given, no discharge current is generated from the capacitor 6b.

Further, as described in the embodiment of FIG. 1, when the drive signal is supplied to the switching element for flowing the current of the next polarity, the current of the previous polarity continues to flow through the rectifying element connected in parallel. Since this is an essential condition for the current of the next polarity to start flowing from zero to the switching element, the set value Iz of the zero current setting circuit 23 needs to be set relatively high.

Next, when the analog switch 32 is closed due to the disappearance of the output m of the monomultivibrator 30, the sawtooth wave s has a low value before, so that Δv> s holds, and the comparison circuit 26 outputs the high-level signal d. output, whereby the signal d ₂ becomes high level, is supplied with continuity signal to the switching element 4b. At this time, if Iz and Tm are determined so that the resonance current I _L has not yet become zero, the current I _L continues to flow through the rectifying element 5b.
4b is reverse biased and does not actually conduct current. At time t = t ₃ when the current decreases to zero, the current starts to flow through the switching element 4b, and the polarity is inverted.

FIG. 7 shows that switching loss does not occur even when a parallel capacitor is provided in the switching element.
FIG. 10 is a connection diagram showing still another embodiment. In the figure,
DC / AC with switching elements 4a to 4d assembled in a bridge
It constitutes a conversion circuit. Therefore, the rectifier and capacitor connected in parallel to each switching element also
Four sets of 5a to 5d and 6a to 6d are provided. The first figure as the output detector 17, using a current detector which outputs a fifth view of an embodiment with different detecting an output current signal I _f, as the output setting circuit 18 the output current setting signal e _r An example in which constant current control is performed by using an output device is shown. Moreover compared to the current setting circuit 28 defined slightly higher Ir than the set value Iz of zero-current setting circuit 23, the output I _r of the current setting circuit 28 and the detection signal I _L of the resonant current detector 22, A comparison circuit 29 for outputting a high-level signal when | I _L <I _r is provided. Comparison circuit 29
Outputs a high-level signal p ₂ when | I _L | <I _r ,
The output Δv of the comparison circuit 19 is supplied to the pulse generation circuit 33 together with the output Δv. The pulse generating circuit 33 includes an oscillator of the sawtooth wave s ₁ reset by the signal p _{1 of} | I _L | <Iz, and a high level Δv <s ₁ from the time of resetting the sawtooth wave.
Or a circuit that outputs a signal d that goes low when | I _L | <I _r.
Each time an input signal arrives, the signal is alternately separated into high-level signals d ₁ and d ₂ by a phase separation circuit 27, and the switching elements 4a and 4d
Preparative to the signal d ₁ is also the signal d ₂ is supplied to the switching element 4b and 4c, conducting each set of the switching elements at the same time, is blocked controlled. Other parts having the same functions as those in the embodiment of FIG.

FIG. 8 shows a specific embodiment of the pulse generation circuit 33 used in the embodiment of FIG. In the figure, FF1 is a flip-flop circuit, and a comparison circuit is connected to a clock input terminal CK.
29 outputs p ₂ is, also is supplied with the output p ₁ of the zero-phase detection circuit 24 to clear input terminal CL, Q terminal output at the rising of the signal p ₂ becomes high level, is reset at the rising edge of the signal p ₁ As a result, the Q terminal output returns to a low level. Amp1 is an operational amplifier, the resistance R1 and the capacitor C1 integrates the voltage of the DC power supply E1, constitute a sawtooth oscillator which is reset by an analog switch AW1 close by signals p _1, the signal p ₁ Generates a synchronized sawtooth wave. Comp1 is a comparator, compares the output s ₁ of the error signal Delta] v and the sawtooth oscillator, and outputs a signal s ₂ to be between high-level Delta] v> s _1. NOR1 is NOR gate, only a high level when the output signal s ₃ and the output signal s ₂ are both low level of the comparator Comp1 of the flip-flop circuit FF1, high in one input signal of the signal s _2, s ₃ When the signal is a level signal, the signal d becomes a low level.
Is output. The signal d is a signal d ₁ is supplied to the 2-phase separation circuit 27 of Figure 7 as an output signal of the pulse generating circuit 30, d ₂
Becomes

The operation of the embodiment of FIG. 7 when the pulse generating circuit of FIG. 8 is used will be described with reference to the diagram of FIG. In FIG. 8, when the error signal Δv becomes larger than the output s ₁ of the sawtooth wave generating circuit within the half-wave period of the resonance frequency of the resonance circuit, the same operation as in the embodiment of FIG. 1 is performed. For example, when the cut off becomes ninth view of the time t = .DELTA.c from a state in which the switching elements 4a and 4d are a current flows in the arrow direction of FIG. 7 and not conduct at t ₁ <s, the current is [ Reactor 20 → Capacitor 21 → Capacitor 6b → Capacitor 6a]
Circuit and [Reactor 20 → Capacitor 21 → Capacitor
6d → capacitor 6c]. Thereby, the capacitors 6a and 6d are charged, and the capacitors 6b and 6c are discharged. When charging / discharging of the capacitors 6a to 6d is completed, the current is changed to [reactor 20 → capacitor 21 → rectifier 5b
→ rectifier circuit 2 → rectifier element 5c]. During this time, as the energy stored in the resonance circuit is consumed by the arc load via the transformer 7, the current flowing through the circuit decreases. When | I _L | <I _R at time t = t ₂ , the signal p ₂ goes high, and the rising of the signal p ₂ sets the flip-flop circuit FF1 of FIG.
The pin output goes high. However, since Δv <s at t = t ₁ , the NOR gate NOR1 is already at the low level, and the output d of the pulse generation circuit 33 remains at the low level at the time t = t ₁ and does not change. This state continues, further current I _L is reached at time t = t ₃ decreases | becomes <Iz become the signal p ₁ is high level, | I _L
Sawtooth wave s ₁ are short-circuited capacitor C1 eighth diagram is reset to zero and is reset at the same time by the rise of the flip-flop circuit FF1 also signals p _1. As a result, the signals s ₂ and s ₃ are both at a low level, and the signal d is at a high level. Signal d is separated by 2-phase separation circuit 27 signals d ₂ becomes high level, the switching element 4b, is supplied as a drive signal to 4c. At this time, the current _IL has decreased but is not yet zero, and the rectifying element
As it continues to flow through 5b and 5c, switching element 4
b and 4c are in a reverse bias state and do not conduct. Next, when the current decreases and reaches zero at time t = t ₄ , the conduction signal d ₂
, The current starts to flow through the switching elements 4b and 4c to which the current IL is applied, whereby the current _IL is inverted.

After the polarity of the current I _L is inverted in this way, at the time t
= Error signal Delta] v becomes excessive output set value and a load as shown in t ₅ is suddenly changed, when not in Delta] v <s ₁ within a half wave of the resonant frequency of the resonant circuit, | a <Ir | I _L At time t = t ₆ , the signal p ₂ goes to a high level, the output s ₃ of the flip-flop circuit FF 1 goes to a high level, and the signal d, that is, the signal d ₂ , despite the fact that Δv> s ₁ still holds.
To low level. As a result, the switching elements 4b, 4
c and cut off, the current I _L continues to flow through capacitors 6a, 6b and 6c, the 6d, so that upon completion of charging and discharging flow through the rectifying element 5a, the 5d. When the current I _L further decreases and | I _L | <Iz, the signal p ₁ goes to a high level, the sawtooth wave s ₁ is reset, and the flip-flop circuit FF 1 is also reset, so that the signals s ₂ and s ₃ are both low. signal d becomes high level again become level, the switching elements 4a and the signal d is a signal d ₁ at 2-phase separation circuit 27, it is supplied to 4d. Thereafter, the current further switching element 4a when reduced to I _L becomes zero, the polarity of the current I _L a current begins to flow to 4d is reversed.

Since the embodiment of FIG. 7 operates as described above, than the signal Iz signal I _r even when the error signal Δv during the half-wave is not lower than the output signal s ₁ of excessive sawtooth wave oscillator By setting a slightly higher appropriate value, the polarity is switched at regular intervals. As a result,
Even when having a capacitor in parallel with the switching element,
The charge of this capacitor is not discharged in a short-circuit state through the switching element, and the switching is always performed at zero current. Therefore, a capacitor having a sufficient capacity for absorbing surge can be connected in parallel to each switching element.

In the embodiment of FIG. 7, it is possible to apply a DC / AC conversion circuit of another system as shown in the embodiments of FIGS. 1 and 5, and an output setting circuit and an output detection circuit. It is a matter of course that the constant voltage control may be performed by using a device for setting and detecting the output voltage instead of the output current for each device.

<Effect of the Invention> As described above, in the present invention, by switching in a state where the current flowing through the switching element is always zero, and the rise of the current at the start of conduction becomes a sine wave,
Since the occurrence of switching loss becomes almost zero because of the gradual rise, the operating frequency of the DC / AC conversion circuit can be set high. In addition, since the voltage and current of the circuit do not change suddenly, the generation of electromagnetic noise is extremely reduced as compared with the conventional device in which a rectangular current flows.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention, FIG. 2 is a diagram for explaining the operation of the embodiment of FIG. 1, and FIG. 3 is a diagram in which the error signal is small in the embodiment of FIG. FIG. 4 is a diagram for explaining the operation when the error signal is excessive, FIG. 5 is a connection diagram showing another embodiment of the present invention, and FIG. Is a diagram for explaining the operation of the embodiment of FIG. 5, FIG. 7 is a connection diagram showing still another embodiment of the present invention, and FIG. 8 is a diagram of a pulse generating circuit used in the embodiment of FIG. FIG. 9 is a connection diagram showing a specific embodiment, FIG. 9 is a diagram for explaining the operation of the embodiment of FIG. 7, and FIG. 10 is a connection diagram showing an example of a conventional apparatus. 2 ... Rectifier circuit, 3a, 3b ... Capacitor, 4a-4d ... Switching element, 5a-5d ... Rectifier element, 6a-6d ... Capacitor, 7 ... Transformer, 8 ... Rectifier circuit, 9 ... ... DC reactor, 8 ... Output detector, 18 ... Output setting circuit, 19
…… Comparison circuit, 20… Reactor, 21 …… Capacitor,
22 ... Resonant current detector, 23 ... Zero current setting circuit, 24 ...
Zero phase detection circuit, 25 ... sawtooth wave oscillator, 26 ... comparison circuit, 27 ... two-phase separation circuit, 28 ... current setting circuit, 29 ...
... Comparison circuit, 30 ... Pulse generation circuit, FF1 ... Flip-flop circuit, NOR1 ... Nor gate, Comp1 ... Comparator, Amp1 ... Operational amplifier, AW1 ... Analog switch

Claims (4)

(57) [Claims] A DC power supply; a DC / AC conversion circuit for converting an output of the DC power supply into a high-frequency AC by a switching element; an LC resonance circuit connected to an output terminal of the DC / AC conversion circuit; A transformer for extracting a part of the energy stored in the resonance circuit, an AC / DC conversion circuit for converting the output of the transformer into DC and supplying the DC to a load, and the LC / LC conversion circuit A switching element control circuit for driving at a frequency higher than the resonance frequency of the switching element and a switching element for returning the current flowing through the resonance circuit when the switching element is cut off are connected in parallel with opposite polarities. An arc machining power supply device comprising a rectifying element. Wherein said switching element control circuit includes a zero-phase detector circuit for generating a pulse p when the absolute value of the current I _L flowing through the LC resonance circuit becomes a predetermined value or less Iz close to zero, the output setting circuit An output detection circuit that detects an output of the AC / DC conversion circuit, a comparison circuit that compares an output signal of the output setting circuit with an output signal of the output detection circuit to obtain a difference signal Δv, The pulse width is determined according to the output signal Δv, and the switching element driving pulse generation circuit that generates a pulse synchronized with the output signal p of the zero-phase detection circuit is connected to the switching element in parallel with the opposite polarity, respectively. And a rectifying element.
The power supply device for arc processing according to claim 1. 3. The pulse generation circuit compares an oscillator that generates a sawtooth wave s synchronized with an output of the zero-phase detection circuit, an output signal Δv of the comparison circuit, and an output s of the sawtooth wave oscillator. 3. The power supply device for arc machining according to claim 2, further comprising a comparator that generates a pulse having a constant amplitude during a period of s. 4. An oscillator for generating a sawtooth wave s synchronized with an output of the zero-phase detection circuit;
A first comparator for generating a signal when the output signal Δv and by comparing the output signal s of the sawtooth oscillator delta _v> s of the comparator circuit, the LC absolute current I _L flowing in the resonant circuit and Hassururu second comparator signal when the value is smaller than the second reference value I _r stipulated in large becomes a value by a predetermined amount than the reference value Iz of the zero-phase detector circuit, said first 1
And the output of the second comparator as an input and a period from when Δv> s to Δv <s or | I _L | <I _r
3. The power supply device for arc machining according to claim 2, further comprising a comparator that generates a pulse having a constant amplitude during a period until the power supply reaches the following condition.