JP2582751Y2 - Power supply for arc machining - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION The present invention takes a commercial AC power source as input, rectifies and converts it to DC, smoothes the obtained DC output by a smoothing circuit, converts it to high-frequency AC by an inverter circuit, and then performs arc machining. The present invention relates to an inexpensive arc processing power supply device of a type that converts the output into an output having characteristics suitable for the device, in which the capacitance of the capacitor of the smoothing circuit is reduced.

[0002]

2. Description of the Related Art (Prior Art 1) FIG. 1 shows a conventional example of a power supply device for arc processing which receives a commercial AC power supply, converts it to high-frequency AC by an inverter circuit after rectification and smoothing, and further obtains an output suitable for an arc processing method. This shows an example of a constant current type DC power supply device having a full-bridge type inverter circuit.

In FIG. 1, 1a to 1c are input terminals connected to a three-phase AC power supply, 2 is a power switch, 3
Reference numerals a to 3f denote rectifier diodes, which constitute the three-phase bridge type rectifier circuit 3. 4a is a current limiting resistor,
Reference numeral 4b denotes a smoothing capacitor, and the smoothing circuit 4 is formed by the resistor 4a and the capacitor 4b. 5a ~
5d is a switching transistor, and a rectifier circuit 3
And an inverter circuit 5 for inversely converting the DC output obtained by the smoothing circuit 4 into a high-frequency AC. Reference numeral 6 denotes a transformer, which converts an output voltage of the inverter circuit 5 into a voltage suitable for arc machining. Reference numeral 7 denotes a rectifier circuit, 8 denotes a DC reactor, 9 denotes an arc load, which comprises an electrode 9a, a workpiece 9b and an arc 9c. 10 is an output current detector, 11 is an output current setter, 12 is a set value I of the output current setter 11
The error amplifier 13 receives r and the output If of the output current detector 10 as inputs, and outputs a difference signal ΔI = Ir−If. The conduction of the switching elements 5 a to 5 d of the inverter circuit 5 depends on the output signal ΔI of the error amplifier 12. This is a pulse width control type inverter control circuit for controlling a time width.

In the apparatus shown in FIG. 1, a three-phase AC power is rectified by a rectifier circuit 3, smoothed by a smoothing circuit 4 and supplied to an inverter circuit 5. In the inverter circuit 5, this DC output is converted into a high-frequency AC, and is converted into a predetermined voltage in the transformer 6. The output of the transformer 6 is supplied to an arc load 9 through a DC reactor 8 after being smoothed by a rectifier circuit 7. This output current is supplied to the detector 10
The detection signal If is detected by the
The difference signal ΔI = Ir−If is compared with the set value Ir of the output current setter 11 at 2 and is supplied to the inverter control circuit 13. In the inverter control circuit 13, a pulse signal having a pulse width corresponding to the input signal ΔI and a predetermined constant frequency is generated. And outputs signals s1 and s2 for simultaneously turning on each set of transistors simultaneously. As a result, the output current is maintained at a constant current according to the set value of the output current setting unit 11.

(Prior Art 2) FIG. 2 shows another example of a circuit configuration of the prior art.
3 shows an example in which the capacitance of the smoothing circuit 4 is reduced.

In FIG. 2, the only difference from the conventional apparatus shown in FIG. 1 is the smoothing circuit 4, and the other parts are completely the same. In FIG. 2, the smoothing circuit 4 includes a circuit in which a capacitor C1 is connected in series to a parallel circuit of a resistor R and a diode DR, and a capacitor C2 connected in parallel to this circuit.

Here, as the capacitor C2, a film capacitor or the like having good frequency characteristics is used. As the capacitor C1, an electrolytic capacitor is generally used. Resistor R
Is used to discharge the charge of the capacitor C1 and has a relatively large resistance value of several tens of ohms.

[0008]

In the prior art 1, since the capacity of the electrolytic capacitor 4b as a smoothing capacitor needs to be larger than the actually required capacity, the apparatus becomes large and furthermore. Cost is up.

That is, in the smoothing capacitor, a combined current of a high-frequency discharge current intermittently flowing due to switching of the inverter circuit and a charging current from the commercial frequency power supply flows as a ripple current. An electrolytic capacitor used as a smoothing capacitor has a relatively large equivalent internal resistance value, so that the heat generated by the ripple current cannot be ignored and appears as an increase in the temperature of the electrolytic capacitor. The life of an electrolytic capacitor is closely related to the temperature, as it is said that the life rises by half when the temperature rises by 10 degrees C. Therefore, as a method of reducing the equivalent internal resistance value of the electrolytic capacitor, a method of connecting several electrolytic capacitors in parallel is used. as a result,
The capacity of the electrolytic capacitor used in the device will increase more than necessary. For example, a capacitor of about 1000 μF may be used only for reducing the ripple rate, but at present, an electrolytic capacitor of about 10,000 μF is used in order to secure a required life.

Problems when the smoothing capacitor has a large capacity can be divided into the following two problems. First, there is a problem of an inrush current. When the power switch is turned on, the inrush current becomes excessively large, which causes problems such as welding of a primary-side switch and fusing of a fuse. Was needed. In the current limiting resistor 4a, the loss due to resistance heating is excessive during the normal operation of the device, so that the efficiency of the device is reduced and the generated heat is treated. There is also a method of solving this problem by providing a switch in parallel with the resistor 4a and closing the switch during normal operation of the apparatus. However, a large-capacity switch is required.

Second, as shown in FIG. 3, the input current I during normal operation of the device is not a sine wave but an intermittent current waveform. This means that the peak value becomes large, the effective value of the input current becomes large, and the power factor is deteriorated.

Further, in the prior art 2, since the capacity of the smoothing capacitor can be reduced, the peak value of the input current is reduced and the effective value of the input current is reduced, so that the rush current limitation of the capacitor C1 is improved although the power factor is improved. Since there is no resistance, the inrush current is large, which causes switch welding,
Problems such as blown fuses remain.

Further, the diode DR requires a diode having a large capacity to withstand the rush current, and is not an inexpensive device.

[0014]

The apparatus of the present invention takes a commercial AC power supply as input, rectifies and converts it to DC, smoothes the obtained DC output by a smoothing circuit, and converts it to high-frequency AC by an inverter circuit. In a power supply device for arc processing, which converts the output into a characteristic suitable for arc processing later, the smoothing circuit impairs the electrolytic capacitor for charging / discharging the commercial frequency current and absorbing the low frequency surge voltage, and the above-described operation. A series circuit consisting of resistors
From the electrolytic capacitor connected in parallel to the series circuit
Also arc machining power supply apparatus configured from a film capacitor having a small capacity.

[0015]

In the device of the present invention, since the smoothing circuit is constructed as described above, the electrolytic capacitor is used to absorb the low-frequency surge voltage mixed from the commercial power supply line without impairing the smoothing action of the smoothing capacitor. The low resistor which works effectively and is connected in series with the electrolytic capacitor realizes the function of the electrolytic capacitor with an electrolytic capacitor having a minimum necessary capacity. In addition, the film capacitor effectively acts to absorb a high-frequency surge voltage generated at the time of high-speed switching of the inverter circuit.

[0016]

FIG. 4 shows an embodiment of the present invention. 1 differs from the conventional apparatus shown in FIG. 1 only in the smoothing circuit 4, and the other parts are completely the same. The smoothing circuit 4 includes a series circuit of a resistor Ra and a capacitor C1a, and a capacitor C2a connected in parallel to the series circuit.

Here, the capacitor C2a is a capacitor that bears a high-frequency ripple current supplied to the inverter circuit and absorbs a high-frequency surge voltage generated during the switching operation. The capacity of the capacitor C2a corresponds to the output current of the device. Although it depends on the magnitude of the ripple current flowing through the capacitor C2a during the switching operation, when the operating frequency of the inverter circuit is a high frequency of several tens of kHz, several tens of μm are used.
It may be about F. The capacitor C2a bears a high-frequency ripple current and uses a film capacitor having good frequency characteristics to absorb a high-frequency surge voltage.

This film capacitor is arranged as close as possible to a switching element constituting the inverter circuit to shorten the wiring as much as possible in order to supply a high-frequency current to the inverter circuit and to absorb a surge voltage generated during switching. deep. Further, the capacitor C1a is an electrolytic capacitor for smoothing the output obtained by rectifying the commercial frequency and at the same time absorbing the low-frequency surge voltage mixed in from the commercial power supply line, and its capacity depends on the impedance of the commercial power supply line. It may be about 1000 μF. further,
The resistor Ra satisfies the above-described operation of the capacitor C1a, and eliminates the resonance generated by the inductance of the capacitors C1a and C2a and the wiring, and has an appropriate resistance value within a range in which an unnecessary ripple current does not flow.

Here, when the power is turned on, the low-frequency surge voltage mixed from the commercial power supply line appears most remarkably.

[0020] FIG. 5 (a) shows an equivalent circuit of only the input portion of the device having a smoothing circuit in the prior art 1 in Fig.

Assuming that the power supply voltage is E, its peak value is (2) ^1/2 · E, so that the maximum value of the input voltage of the device can be regarded as (2) ^1/2 · E DC voltage. L1 and R1 are the inductance and resistance of the primary side wiring. S is a main power switch, and C3 is a smoothing capacitor.

FIG. 5 (a) is a construction of a well-known LCR series resonant circuit, the voltage of the capacitor C3 at the main power switch S is turned over to the C3 becomes oscillatory when the condition of Formula (1) It turns out that it is charged.

[0023]

(Equation 1)

Therefore, it can be seen that if the capacitance of the capacitor C3 is too small compared to the inductance L1 of the primary side wiring, this oscillation becomes remarkable and the overcharged voltage becomes high.

FIG. 5 (b) shows an equivalent circuit of the input section of the present invention. A series circuit of a capacitor C4 and a resistor R4 is added in parallel with a capacitor C3 to form a capacitor C.
3, the apparent capacity is increased to prevent vibration when the main power switch S is turned on, thereby suppressing overcharging.

Here, the capacity of the capacitor C4 is sufficient as long as it does not become oscillating when the main power switch is turned on. The larger the resistor R4 is within the range in which the action of the capacitor C4 can be maintained, the larger the ripple current flowing through the capacitor C4 becomes. It can be suppressed to a necessary minimum capacity.

Here, as a specific example, for a power supply device having a capacity of about 20 kVA, respective constants were obtained by experiments.

In the experiment, the capacity of the capacitor C3 having a good frequency characteristic disposed near the switching element depends on the magnitude of the high-frequency ripple current to the inverter circuit which is substantially proportional to the output current during the operation of the power supply device. In the embodiment, it is set to 60 μF.

Also, the inductance L of the primary side power supply equipment
Assuming that L1 = 1 mH and R1 = 0.01Ω as a considerably poor condition of the primary side power supply equipment, 1 and the resistance R1 are simulated as L1 = 1mH and R1 = 0.01Ω on the input side of the power supply device.
And the capacitor C4 and the resistor R
Table 1 shows the results of measuring the charging voltage of the capacitor C3 when the main power switch was turned on while changing the constant of 4 in various ways.

[0030]

[Table 1]

From these results, it can be seen that assuming the impedance of the primary side power supply equipment as described above, the lower limit of the capacitance of the capacitor C4 is about 1500 μF, and the upper limit of the resistor R4 is about 3Ω.

FIG. 5 (c) shows a portion around the smoothing circuit of the embodiment of FIG. In the drawing, during operation, charge and discharge currents flow through the capacitors C1a and C2a, respectively, so that the closed loop formed inside the dotted line is L
Since the CR resonance circuit is formed, the resistor Ra has the function of the damping resistor. Therefore the resistor R
a needs to satisfy the relational expression of Expression (2).

[0033]

(Equation 2) However,

(Equation 3)

Here, assuming that the inductance of the closed loop wiring is L = 0.1 μH, the resistance is calculated by the equation (2).
Calculating the resistance of the vessel Ra

(Equation 4) The resistance value of the resistor Ra needs to be larger than 0.1Ω.

Therefore, it can be said that the appropriate value of the resistor Ra is Ra = 0.1Ω to 3Ω. The appropriate value of the capacitor C1a is about C1a = 1500 μF.

The effects of the power supply device for arc machining of about 20 kVA embodying the present invention can be summarized by using a capacitor C2a = 60 μF and a resistor Ra = 1.0Ω.

In comparison with the prior art 1, the capacitance of the smoothing capacitor 10000 μF becomes 1500 μF, the power factor 0.8 becomes 0.9 and the inrush current peak value 1000 A becomes 300 A.

Each improved. Also, the charging voltage of the smoothing capacitor when the main power switch is turned on is 280 V in the prior art 1 even when the primary power supply is L = 1 mH and R = 0.01 Ω. It was never charged.

It is needless to say that the constants of the capacitors C1a and C2a and the resistor Ra vary depending on the inductance and resistance of the primary power supply equipment, the capacity of the applied device, and the like.

Further, the present invention is not limited to the embodiment shown in FIG. 4, but may be a half-bridge type or a forward converter type as an inverter circuit. The present invention can be applied to, for example, a device in which a polarity switching circuit using a switching element is provided to enable both AC output and DC output.

[0041]

[Effect of the Invention] The device of the present invention uses an electrolytic capacitor for the smoothing circuit.
A series circuit consisting of the capacitors and resistors, by configuring the a film capacitor having a small capacity than the electrolytic capacitor connected in parallel to said series circuit, a high-frequency surge voltage generated during switching operation of the inverter circuit An inexpensive smoothing circuit that not only absorbs but also smoothes the rectified output of the commercial frequency and absorbs the low-frequency surge voltage mixed in from the commercial power supply line can be realized.

Further, since the capacitance of the capacitor of the entire smoothing circuit can be reduced, the peak value of the input current decreases, and the effective value of the input current also decreases, thereby improving the power factor of the power supply device. Further, the rush current when the main power switch is turned on is also reduced, so that the welding of the switch and the blowing of the fuse can be prevented.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing a configuration of a conventional technique 1.

FIG. 2 is a connection diagram showing a configuration of a conventional technique 2.

3 is a diagram showing waveforms of an input voltage and a current in a smoothing circuit 4. FIG.

FIG. 4 is a connection diagram showing an embodiment of the present invention.

5 (a) is a diagram showing an equivalent circuit of the smoothing circuit portion in the prior art 1, (b) is a diagram showing an equivalent circuit of the smoothing circuit part in the embodiment of FIG. 4, (c 4 ) is a diagram showing an equivalent circuit in which a smoothing circuit portion in the embodiment of FIG. 4 is detailed.

[Explanation of symbols]

 1a, 1b, 1c Input terminal 2 Power switch 3 Rectifier circuit 4 Smoothing circuit 5 Inverter circuit 6 Transformer 7 Rectifier circuit 9 DC reactor 10 Arc load 11 Output current detector 12 Output current setting device 13 Error amplifier 14 Inverter control circuit Ra resistor Piler C1a Electrolytic capacitor C2a Film capacitor L1 Inductance on power supply side R1 Resistance value on power supply side

Claims (1)

(57) [Scope of request for utility model registration] 1. A commercial AC power supply is input, rectified and converted to DC, the obtained DC output is smoothed by a smoothing circuit, then converted to high-frequency AC by an inverter circuit, and then output having characteristics suitable for arc machining. in arc machining power supply apparatus of a type to be converted to, electrolytic said smoothing circuit
An arc processing power supply device comprising: a series circuit including a capacitor and a resistor; and a film capacitor connected in parallel to the series circuit and having a smaller capacity than the electrolytic capacitor .