JPH0756125Y2 - Power supply for arc welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a power source for arc welding, and in particular, an arbitrary frequency from a high frequency to a direct current can be obtained as an output current,
In addition, it proposes a universal power supply whose polarity can be freely and electronically changed during DC output.

<Prior Art> As a power source for arc welding, there is a power source that can arbitrarily obtain a high frequency to a direct current. Conventionally, there is a power source for generating a high frequency alternating current by an inverter and then generating an alternating current of an arbitrary frequency by a frequency down converter. . (For example, Japanese Utility Model Sho 63-9
No. 5830) FIG. 3 is a connection diagram showing an example of a conventional device of this type.
In the figure, 1 is an AC power supply, and 2 is a DC power supply circuit for rectifying and smoothing the output of the AC power supply 1 to obtain DC power, the output of which is adjusted according to a command signal. Reference numeral 3 is an inverter circuit for exchanging the output of the DC power supply circuit 3 for high frequency AC, and outputs a rectangular wave AC of a constant frequency in response to a drive signal from the inverter control circuit 4. 5 is a transformer,
A center tap is provided on the secondary winding. Reference numerals 6a to 6d denote rectifying elements, which are connected as shown so as to perform double-wave rectification on the output of the transformer 5 and obtain two sets of positive and negative DC outputs connected in series with each other. 7a and 7b are reactors, each having a coil wound around a common iron core, and having a polarity that causes a magnetic flux in the same direction to be generated in the common iron core by a current flowing through each coil. Numerals 8a and 8b are switching elements connected in series to the reactors 7a and 7b with the polarities shown in the drawing. Numeral 9 is an electrode and numeral 10 is an object to be welded. 11 is an output current detector, 12 is an output current setting signal source, and 13 is a comparator. The output of the comparator 13 determines the output current of the DC power supply circuit 2. Reference numeral 14 is a polarity switching signal source, and 15 is a drive circuit for controlling opening / closing of the switching elements 8a and 8b. Again 16
Reference numerals a and 16b are diodes for protecting the switching elements 8a and 8b from reverse voltage.

In the device shown in the figure, when the switching element 8a is turned on, a current having a positive polarity in the electrode 9 flows and the switching element 8a
When 8b is brought into conduction, a current having a polarity in which the object to be welded 10 is positive flows.

Now, the output circuit ep of the polarity switching signal source 14 is configured such that the drive circuit 15 outputs a signal that conducts the switching element 8a during a positive period and conducts the switching element 8b during a period when ep is negative. To do. In FIG. 3, the electric power supplied from the AC power supply 1 is converted into DC power by the DC power supply circuit 2 and supplied to the inverter circuit 3. In the inverter circuit 3, the DC input is converted into high-frequency AC according to the drive signal from the inverter control circuit 4 and output to the transformer 5. The output of the transformer 5 is rectified by the two-wave rectifying circuit of positive and negative polarities composed of the rectifying elements 6a to 6d to become a DC output again, and the reactor 7a, the switching element 8a and the reactor 7b and the switching element 8b It is supplied to the electrode 9 and the object to be welded 10 together with the output from the center tap of the secondary winding of the transformer 5 via the two series circuits. At this time, one of the switching elements 8a and 8b becomes conductive by the output of the drive circuit 15 which is determined by the polarity of the output signal ep of the polarity switching signal source 14.
The current supplied to the electrode 9 and the workpiece 10 by the conduction of the switching elements 8a and 8b is detected by the output detector 11 and becomes a signal If, and the set value er of the output current setting signal source 12 and the comparator 13 are set. The difference signals are compared and supplied to the DC power supply 2. The output of the DC power supply 2 is determined by this difference signal, and feedback control is performed so that the output current Ia becomes a value corresponding to the reference signal er.

The operation of the device of FIG. 3 when switching the polarity will be described with reference to FIG. In FIG. 4, (a) is the output voltage waveform of the transformer 5, (b) is the output ep of the polarity switching signal source 14, (c) is the current ia flowing through the switching element 8a, and (d) is the switching element 8b. The flowing currents ib and (e) show the respective waveforms of the output current Ia. As shown in FIG. 4, the high frequency output of the transformer 5 is rectified into both positive and negative polarities and then output from the polarity switching signal source 14.
The welding load is supplied by the switching element 8a or 8b that is selectively turned on / off depending on the polarity of ep. When the conduction signal to the switching element 8a is cut off at the time t = T1 when the polarity is switched, and the conduction signal is supplied to the switching element 8b at the same time, the switching element 8a is rapidly turned off and the switching element 8b is turned on. During this time, the switching elements 8a and 8b are both conductive, but the electromagnetic energy stored in the reactor 7a when the switching element 8a was conductive immediately transfers to the magnetically coupled reactor 7b, This causes current to circulate in the reactors 7a and 7b. Next, when the switching element 8a is completely shut off, the current flowing in the reactor 7a tends to become zero rapidly. For this reason, a high surge voltage is generated in the reactors 7a and 7b, and this voltage acts in a direction to assist the regeneration of the arc that has once disappeared when the polarity of the current is reversed. Further, since the surge voltage generated at this time is in the forward direction with respect to the switching element 8b to which the conduction signal is supplied, it is not destroyed. As a result, switching transistors
The current flowing through 8b rapidly increases and reaches a current value substantially the same as the current ia flowing through the switching element 8b immediately before time t = T1.

<Problems to be solved by the invention> In the above conventional device, when the output current is inverted from positive to negative or from negative to positive, the induced voltage by the reactors 7a and 7b included in the power supply device is Since the reactor is wound around a common iron core and is magnetically tightly coupled, it effectively acts on the polarity in the direction of inversion and is used for arc regeneration. However, there is no problem because the induced voltage is applied in the forward direction to the switching element that tries to conduct when switching the polarity, but it should be applied in the forward direction to the switching element that tries to cut off. become. For this reason, the reverse diode connected in parallel with the switching element is useless, and if this induced voltage exceeds the maximum rating of the element, such as when the welding current is high, they can easily be destroyed. .
Especially when failing to re-ignite the arc once extinguished during polarity disconnection, this induced voltage becomes extremely high and all of the induced voltage is applied to the switching element that is going to be cut off, which is a very dangerous state. Becomes

<Means for Solving the Problem> In the present invention, a third winding is provided on an iron core shared by two series reactors, and the induced voltage generated at the time of polarity switching is forwarded to the third winding. The above-mentioned drawbacks of the conventional device are solved by providing a circuit in which a series circuit composed of a diode that operates and a DC power source having a reverse polarity to the diode is connected.

<Operation> In the device of the present invention, the third core provided on the reactor iron core is used.
The induced voltage of the winding is suppressed by the voltage of the DC power supply connected to the winding, and the maximum value of the induced voltage of each reactor is suppressed.

<Embodiment> FIG. 1 shows an embodiment of the present invention. The device shown in the figure is different from the conventional device shown in FIG. 3 in that an iron core shared by the reactors 7a and 7b is provided with a third winding 7c, and a diode 16 and a DC power source 17 are respectively shown in the third winding 7c. It is connected to the polarity. Then, the third winding 7c induces a forward voltage to the diode 16 when the currents of the reactors 7a and 7b decrease, as indicated by the polarity indicated by-in the figure. Has been set.

FIG. 2 is a diagram for explaining the operation of the apparatus of the embodiment of FIG. 1, and FIG. 2 (a) shows the output of the polarity switching signal source 14.
ep, (b) and (c) are switching elements 8a and 8b
Shows the ON and OFF states, (d) and (e) show the induced voltage of reactors 7a and 7b, and (f) shows the third winding.
The voltage induced in 7c is shown, and (g) shows the change of the output current Ia. In FIG. 2, the time required for polarity switching is exaggerated in order to explain the operation of each part at the moment of polarity switching, and in reality, this polarity switching takes several microseconds or less. It's a very short time.

In the apparatus of FIG. 1, the polarity switching and the output current control are the same as those of the conventional apparatus of FIG. 4, so the description thereof will be omitted and the moment of polarity switching will be described. The switching element 8a is in the conducting state before the time t = T1 in FIG.
It is assumed that the output current Ia is flowing in the direction of the arrow in FIG.
From this state, it is assumed that at time t = T1, the output of the polarity switching signal source 14 is inverted, the drive signal to the switching element 8a is stopped, and the drive signal is simultaneously supplied to the switching element 8b. At this time, even if there is no drive signal, the switching element 8a does not immediately become zero but shuts off after a delay time (turn-off time) Tdf.

On the other hand, the switching element 8b supplied with the drive signal
The delay time (turn-on time) from T1 starts to increase after Tdn. There is a period in which the switching elements 8a and 8b are both in a conductive state in the period between the turn-off time Tdf and the turn-on time Tdn. During this period, the current flows through the circuit of [transformer 5 → reactor 7a → switching element 8a → switching element 8b → reactor 7b → transformer 5].

When the switching element 8a is completely cut off after the turn-off time Tdf, the current flowing through the circulation circuit passing through the reactors 7a and 7b is [the center tap of the transformer 5 → the work piece → the electrode → the switching element 8b → the reactor 7b → The transformer must follow the normal route. While the switching elements 8a, 8b immediately before this are both conducting, the current is flowing through the circulation circuit, so that it is not supplied to the electrode and the workpiece, and therefore the welding arc is extinguished. . For this reason, when the switching element 8a tries to shut off completely, the direction from the workpiece to the electrode (time t =
Since the arc in the direction opposite to that before T1) has not yet occurred, the passage of the current that flows only through the switching element 8b is not actually configured, and the reactors 7a and 7b are designed to maintain the current just before this. A high voltage will be induced in. This voltage is also induced in the winding 7c. Since this induced voltage is in the forward direction with respect to the diode 16, if this voltage tries to exceed the voltage ef of the DC power supply 17, a current flows in the route of [winding 7c → diode 16 → DC power supply 17], The terminal voltage of 7c does not rise above the voltage of the DC power supply 17. For this reason, the voltage induced in the reactors 7a and 7b is also limited to a value according to the winding ratio of the DC power supply 17 and the winding 7c with respect to the reactors 7a and 7b. The maximum voltage Vf induced in the reactors 7a and 7b at this time is (However, Na, Nb, Nc are the number of turns of reactors 7a, 7b and winding 7c respectively, and ef is the voltage of DC power supply 17), so this voltage Vf is higher than the voltage required for arc re-ignition and switching If the voltage is set to the maximum rated voltage of the elements 8a, 8b or less, the switching element can be prevented from being broken.

Further, it is understood that this voltage is determined only by the number of turns and the voltage of the DC power source as described above and is not affected by the current used.

It is needless to say that the DC power source used in the above should have a low internal impedance and a structure capable of passing a current in the opposite direction (charging direction).

Also, the output current has a slightly delayed response when the output of the DC power supply 2 is adjusted, but in order to avoid this, the DC power supply 2 should be an unadjusted power supply consisting only of a rectifying / smoothing circuit, and a comparator
A well-known PWM that inputs the output of 13 to the inverter control circuit 4 and controls the inverter circuit 3 to a pulse width according to the input signal.
A controlled circuit may be used.

Further, in the above description, a method of rectifying a commercial frequency AC power source as a DC power source, converting it into a high frequency AC by an inverter, and converting it into a direct current again by a transformer and a rectifying circuit has been described. The DC power source used in the device of the invention is not limited to this, and any other type of DC power source can be used as long as it can obtain two sets of DC outputs connected in series. Of course.

<Effect of device> Since the device of the present invention is as described above, the maximum value of the surge voltage generated at the time of switching the polarity can be suppressed to an arbitrary value regardless of the output current to be used, so the main circuit for output adjustment. The switching element can be completely protected.

[Brief description of 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, FIG. 3 is a connection diagram showing an example of a conventional device, and FIG. The figure is a diagram for explaining the operation of the conventional apparatus of FIG. 2 ... DC power supply, 3 ... Inverter circuit, 4 ... Inverter control circuit, 5 ... Transformer, 6a to 6d ... Rectifier element, 7a, 7b ... Reactor, 7c ... Third winding, 8a , 8b ...
… Switching elements, 9… Electrodes, 10… Workpieces, 11
…… Output current detector, 12 …… Output current setting signal source, 13…
… Comparator, 14 …… Polarity switching signal source, 15 …… Drive circuit, 16
…… Diode, 17 …… DC power supply

Claims (1)

[Scope of utility model registration request] 1. A reactor comprising a pair of direct current power supplies connected in series and a series circuit composed of a reactor and a switching element connected in series to each of the non-commonly connected output terminals of the direct current power supplies. The other end of the series circuit composed of the switching element and the switching element is commonly connected to serve as one output terminal, the commonly connected output terminal of the two sets of DC power sources serves as the other output terminal, and is shared as each reactor. In the arc welding power supply device having the iron core, and the polarity is determined so that magnetic fluxes in the same direction are generated in the iron core shared by the currents flowing through the reactors by the conduction of the switching elements connected in series, respectively, in the reactor, A third winding is provided on the iron core, and the third winding has a polarity that is a forward direction with respect to a voltage generated when the switching element is cut off. Power supply device for arc welding, comprising a control circuit for connecting a series circuit composed of a diode and a direct current power source having a polarity opposite to that of the diode and controlling the switching elements to open and close without interruption in a predetermined order. .