Power supply device for alternating current welding

Abstract

The invention provides a power supply device for AC welding. The power supply device (100) for AC welding comprises a DC power supply (1), an inverter (2), a transformer (3), a first bidirectional switch (4), a second bidirectional switch (5), a first output end (6), a second output end (7), a smoothing reactor (9) and a controller (10). The controller performs at least one of a positive-side rectification control in which the first bidirectional switch and the second bidirectional switch rectify a two-phase AC voltage output from a secondary winding (32) of the transformer and supply a full-wave positive-pole DC voltage between the first output terminal and the second output terminal, and a negative-side rectification control in which the first bidirectional switch and the second bidirectional switch rectify the two-phase AC voltage output from the secondary winding (32) of the transformer and supply the full-wave positive-pole DC voltage between the first output terminal and the second output terminal. In the negative-side rectification control, the first bidirectional switch and the second bidirectional switch rectify a two-phase AC voltage output from the secondary winding of the transformer and supply a full-wave negative DC voltage between the first output terminal and the second output terminal.

Description

Technical Field

[0001] The present invention relates to a power supply device for AC welding. Background Art

[0002] A power supply device for AC welding is conventionally known. As such a power supply device, for example, a welding power supply device is known, which includes: an inverter that generates high-frequency AC power from a DC power supply; a transformer that transforms the generated high-frequency AC power; a rectifier circuit that rectifies the transformed high-frequency AC power into DC power; and an inverter circuit that converts the rectified DC power into AC power and supplies it to a welding gun (for example, see Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Publication No. 2019-089093 (see in particular Figure 1 )

[0004] However, the welding power supply device has two circuits, namely a rectifier circuit and an inverter circuit, on the secondary side of the transformer, and has a problem that the circuit structure for rectifying and converting the transformed AC power is complicated. Summary of the invention

[0005] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an AC welding power supply device having a simplified circuit structure for rectifying and converting transformed AC power.

[0006] In order to achieve the above-mentioned object, an AC welding power supply device according to one aspect of the present disclosure comprises: an inverter connected to a DC power supply, outputting a primary-side AC voltage including a first half-cycle period and a second half-cycle period, wherein the polarity during the second half-cycle period is opposite to the polarity during the first half-cycle period; a first output terminal and a second output terminal, wherein the first output terminal and the second output terminal supply a DC voltage for welding to an arc generating unit; and a transformer for two-phase half-wave rectification, wherein the transformer comprises a primary winding to which the primary-side AC voltage from the inverter is input and a secondary winding having an intermediate point connected to the first output terminal, wherein the transformer for two-phase half-wave rectification outputs a same-phase secondary-side AC voltage having a predetermined voltage and being in phase with the primary-side AC voltage between the intermediate point and one end of the secondary winding, based on a potential of the intermediate point, and outputs a same-phase secondary-side AC voltage having a predetermined voltage and being in phase with the primary-side AC voltage between the intermediate point and one end of the secondary winding, and outputs a same-phase secondary-side AC voltage having a predetermined voltage and being in phase with the primary-side AC voltage between the intermediate point and the other end of the secondary winding. outputting an inverted AC voltage having the prescribed voltage and being in phase with the primary-side AC voltage; a first bidirectional switch capable of selectively conducting and cutting off currents flowing in two directions, namely, a positive direction from one end toward the other end and a negative direction from the other end toward the one end, respectively, wherein the first end of the bidirectional switch is connected to the one end of the secondary winding of the transformer and the other end of the first bidirectional switch is connected to the second output end; a second bidirectional switch capable of selectively conducting and cutting off currents flowing in two directions, namely, a positive direction from one end toward the other end and a negative direction from the other end toward the one end, respectively, wherein the first end of the bidirectional switch is connected to the other end of the secondary winding of the transformer and the other end of the second bidirectional switch is connected to the second output end; a smoothing reactor inserted in a path of current passing through the first bidirectional switch and the second bidirectional switch;and a controller that controls the operation of the first bidirectional switch and the second bidirectional switch, the controller being configured to perform at least one of a positive-side rectification control and a negative-side rectification control, wherein in the positive-side rectification control, during the first half cycle of the primary-side AC voltage, the first bidirectional switch is turned on in the positive direction and the second bidirectional switch is turned off, so that the first bidirectional switch rectifies the same-phase secondary-side AC voltage and outputs a same-phase half-wave positive DC voltage, and, during the second half cycle of the primary-side AC voltage, the second bidirectional switch is turned on in the positive direction and the first bidirectional switch is turned off, so that the second bidirectional switch rectifies the reverse-phase secondary-side AC voltage and outputs a reverse-phase half-wave positive DC voltage, thereby the first bidirectional switch and the second bidirectional switch are connected to each other. The bidirectional switch supplies a full-wave positive DC voltage between the first output terminal and the second output terminal. In the negative side rectification control, during the first half cycle of the primary side AC voltage, the second bidirectional switch is turned on in the negative direction and the first bidirectional switch is turned off, so that the second bidirectional switch rectifies the reverse-phase secondary side AC voltage and outputs a reverse-phase half-wave negative DC voltage. Moreover, during the second half cycle of the primary side AC voltage, the first bidirectional switch is turned on in the negative direction and the second bidirectional switch is turned off, so that the first bidirectional switch rectifies the same-phase secondary side AC voltage and outputs a same-phase half-wave negative DC voltage. Thus, the first bidirectional switch and the second bidirectional switch supply a full-wave negative DC voltage between the first output terminal and the second output terminal. ;

[0007] The present invention has the effect of providing an AC welding power supply device having a simplified circuit structure for rectifying and converting transformed AC power. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a circuit diagram showing an example of the configuration of the AC welding power supply device according to the first embodiment of the present disclosure.

[0009] Figure 2 It shows the use of Figure 1 This is a flow chart showing the contents of rectification and polarity control of AC welding in the first embodiment implemented by a controller.

[0010] Figure 3 1 is a waveform diagram showing the waveform of the output current and the waveform of the gate signal to the bidirectional switch.

[0011] Figure 4 The input current and output current flow in the positive side in-phase rectification of the first mode are Figure 1 The circuit is shown in Fig.

[0012] Figure 5 The input current and output current flow in the positive-side reverse rectification of the first mode are Figure 1 The circuit is shown in Fig.

[0013] Figure 6 The flow of charging current and discharging current when the polarity is switched from positive to negative in the second mode is Figure 1 The circuit is shown in Fig.

[0014] Figure 7 The input current and output current flow in the negative-side inversion rectification of the third mode are Figure 1 The circuit is shown in Fig.

[0015] Figure 8 The input current and output current flow in the negative side same-phase rectification of the third mode are Figure 1 The circuit is shown in Fig.

[0016] Fig. 9 The flow of charging current and discharging current when the polarity is switched from negative to positive in the fourth mode is Figure 1 The circuit is shown in Fig.

[0017] Fig. 10A This is a circuit diagram showing an example of the configuration of a first bidirectional switch of an AC welding power supply device according to a second embodiment of the present disclosure.

[0018] Fig. 10B This is a circuit diagram showing an example of the configuration of a second bidirectional switch of the AC welding power supply device according to Embodiment 2 of the present disclosure.

[0019] Description of symbols

[0020] 1: DC power supply; 2: inverter; 3: transformer; 4: first bidirectional switch; 5: second bidirectional switch; 6: first output terminal; 7: second output terminal; 8: arc generating part; 9: smoothing reactor; 10: controller; 31: primary winding; 31a: one end; 31b: the other end; 32: secondary winding; 32a: one end; 32b: the other end; 32c: middle point; 41, 42, 51, 52, 61, 62: diodes; Cs1~Cs4: first buffer capacitor to fourth buffer capacitor; D1~D4: first diode to fourth diode; Hf1: first high-pass filter; Hf2: second high-pass filter; Ls: inductance component; SW1~SW4: first switch element to fourth switch element; SW5: first discharge switch element; SW6: second discharge switch element; R1: current limiting resistor element. DETAILED DESCRIPTION

[0021] An AC welding power supply device according to one aspect of the present disclosure comprises: an inverter connected to a DC power supply, outputting a primary AC voltage including a first half-cycle period and a second half-cycle period, wherein the polarity of the second half-cycle period is opposite to the polarity of the first half-cycle period; a first output terminal and a second output terminal, wherein the first output terminal and the second output terminal supply a DC voltage for welding to an arc generating unit; and a transformer for two-phase half-wave rectification, comprising a primary winding to which the primary AC voltage from the inverter is input and a secondary winding having an intermediate point connected to the first output terminal, wherein the transformer for two-phase half-wave rectification outputs a same-phase secondary AC voltage having a predetermined voltage and being in phase with the primary AC voltage between the intermediate point and one end of the secondary winding, and outputs a same-phase secondary AC voltage having a predetermined voltage and being in phase with the primary AC voltage between the intermediate point and the other end of the secondary winding, based on the potential of the intermediate point. the prescribed voltage and an inverted AC voltage in phase with the primary-side AC voltage; a first bidirectional switch capable of selectively conducting and cutting off currents flowing in two directions, namely, a positive direction from one end toward the other end and a negative direction from the other end toward the one end, wherein the first end of the first bidirectional switch is connected to the one end of the secondary winding of the transformer and the other end of the first bidirectional switch is connected to the second output end; a second bidirectional switch capable of selectively conducting and cutting off currents flowing in two directions, namely, a positive direction from one end toward the other end and a negative direction from the other end toward the one end, wherein the first end of the second bidirectional switch is connected to the other end of the secondary winding of the transformer and the other end of the second bidirectional switch is connected to the second output end; a smoothing reactor inserted in a path of current passing through the first bidirectional switch and the second bidirectional switch;and a controller that controls the operation of the first bidirectional switch and the second bidirectional switch, the controller being configured to perform at least one of a positive-side rectification control and a negative-side rectification control, wherein in the positive-side rectification control, during the first half cycle of the primary-side AC voltage, the first bidirectional switch is turned on in the positive direction and the second bidirectional switch is turned off, so that the first bidirectional switch rectifies the same-phase secondary-side AC voltage and outputs a same-phase half-wave positive DC voltage, and, during the second half cycle of the primary-side AC voltage, the second bidirectional switch is turned on in the positive direction and the first bidirectional switch is turned off, so that the second bidirectional switch rectifies the reverse-phase secondary-side AC voltage and outputs a reverse-phase half-wave positive DC voltage, thereby the first bidirectional switch and the second bidirectional switch are connected to each other. The bidirectional switch supplies a full-wave positive DC voltage between the first output terminal and the second output terminal. In the negative side rectification control, during the first half cycle of the primary side AC voltage, the second bidirectional switch is turned on in the negative direction and the first bidirectional switch is turned off, so that the second bidirectional switch rectifies the reverse-phase secondary side AC voltage and outputs a reverse-phase half-wave negative DC voltage. Moreover, during the second half cycle of the primary side AC voltage, the first bidirectional switch is turned on in the negative direction and the second bidirectional switch is turned off, so that the first bidirectional switch rectifies the same-phase secondary side AC voltage and outputs a same-phase half-wave negative DC voltage. Thus, the first bidirectional switch and the second bidirectional switch supply a full-wave negative DC voltage between the first output terminal and the second output terminal. ;

[0022] Here, making the bidirectional switch “on in the positive direction” means setting the bidirectional switch to “current flowing in the positive direction”, and making the bidirectional switch “on in the negative direction” means setting the bidirectional switch to “current flowing in the negative direction”.

[0023] According to this structure, the AC voltage output to the secondary winding of the transformer is positively rectified or negatively rectified by the first bidirectional switch and the second bidirectional switch during each half cycle of the primary side AC voltage. By the positive side rectification, a positive DC voltage is supplied between the first output terminal and the second output terminal, and by the negative side rectification, a negative DC voltage is supplied between the first output terminal and the second output terminal. Whether to perform positive side synchronous rectification or negative side synchronous rectification can be determined by causing one bidirectional switch to rectify the same-phase secondary side AC voltage or the opposite-phase secondary side AC voltage during one half cycle. Therefore, the rectification of the AC voltage output to the secondary winding of the transformer and the switching of the polarity of the DC voltage for arc welding can be performed using two bidirectional switches, and the structure for the switching can be simplified. Therefore, it is possible to provide an AC welding power supply device that can simplify the circuit structure of rectifying and alternating the transformed AC power.

[0024] Alternatively, the first bidirectional switch can selectively conduct and cut off the current flowing in the two directions, and the first bidirectional switch includes: a first pair of switch elements connected in series with each other in reverse order; and a first pair of diodes connected in series with each other in reverse order, the first pair of diodes being connected in parallel with the first pair of switch elements, respectively; the second bidirectional switch can selectively conduct and cut off the current flowing in the two directions, and the second bidirectional switch includes: a second pair of switch elements connected in series with each other in reverse order; and a second pair of diodes connected in series with each other in reverse order, the second pair of diodes being connected in parallel with the second pair of switch elements, respectively; and the controller is configured to perform the above At least one of the positive-side synchronous rectification control as the positive-side rectification control and the negative-side synchronous rectification control as the negative-side rectification control, in the positive-side synchronous rectification control as the positive-side rectification control, during the first half cycle of the primary-side AC voltage, the first pair of switch elements are turned on and the switch element in the second pair of switch elements connected in parallel with the diode that conducts in the positive direction of the second bidirectional switch is turned off, so that the first bidirectional switch rectifies the same-phase secondary-side AC voltage and outputs a same-phase half-wave positive DC voltage, and during the second half cycle of the primary-side AC voltage, the second pair of switch elements are turned off. The first pair of switching elements is in a conducting state and the switching element connected in parallel with the diode conducting in the positive direction of the first bidirectional switch is in a cut-off state, so that the second bidirectional switch rectifies the inverted secondary-side AC voltage and outputs an inverted half-wave positive DC voltage, thereby the first bidirectional switch and the second bidirectional switch supply a full-wave positive DC voltage between the first output terminal and the second output terminal, and in the negative-side synchronous rectification control as the negative-side rectification control, during the first half cycle of the primary-side AC voltage, the second pair of switching elements is in a conducting state and the switching element connected in parallel with the diode conducting in the negative direction of the first bidirectional switch is in a cut-off state, so that the second bidirectional switch rectifies the inverted secondary-side AC voltage and outputs an inverted half-wave positive DC voltage, thereby the first bidirectional switch and the second bidirectional switch supply a full-wave positive DC voltage between the first output terminal and the second output terminal, and in the negative-side synchronous rectification control as the negative-side rectification control, during the first half cycle of the primary-side AC voltage, the second pair of switching elements is in a conducting state and the switching element connected in parallel with the diode conducting in the negative direction of the first bidirectional switch is in a cut-off state. The switching element connected in parallel with the diode is in the cut-off state, so that the second bidirectional switch rectifies the inverted secondary-side AC voltage and outputs a half-wave negative DC voltage of the same phase, and, during the second half cycle of the primary-side AC voltage, the first pair of switching elements is in the on state and the switching element in the second pair of switching elements connected in parallel with the diode that conducts in the negative direction of the second bidirectional switch is in the cut-off state, so that the first bidirectional switch rectifies the same-phase secondary-side AC voltage and outputs an inverted half-wave negative DC voltage, thereby supplying a full-wave negative DC voltage between the first output terminal and the second output terminal.

[0025] According to this structure, one pair of switching elements on one side is turned on in synchronization with one half cycle of the primary-side AC voltage, and the other pair of switching elements on the other side is turned on in synchronization with the other half cycle of the primary-side AC voltage. Therefore, the voltage drop of the rectifying elements (voltage across both ends) when rectifying the secondary-side AC voltage output from the transformer is only the voltage drop of the switching elements. Therefore, by selecting switching elements whose voltage drop when turned on is smaller than the voltage drop of the diode as a pair of switching elements, the power loss caused by the rectifying elements can be reduced, and the efficiency of the AC welding power supply device can be improved.

[0026] Alternatively, the controller is configured such that, in the positive side synchronous rectification control, when the first bidirectional switch is caused to rectify the same-phase secondary side AC voltage and output the same-phase half-wave positive DC voltage, the remaining switch elements in the second pair of switch elements are further turned on, and, when the second bidirectional switch is caused to rectify the reversed secondary side AC voltage and output the reversed half-wave positive DC voltage, the remaining switch elements in the first pair of switch elements are further turned on, and, in the negative side synchronous rectification control, when the second bidirectional switch is caused to rectify the reversed secondary side AC voltage and output the same-phase half-wave negative DC voltage, the remaining switch elements in the first pair of switch elements are turned on, and, when the first bidirectional switch is caused to rectify the same-phase secondary side AC voltage and output the reversed half-wave negative DC voltage, the remaining switch elements in the second pair of switch elements are turned on.

[0027] According to this structure, one of a pair of switch elements of the bidirectional switch is always in the on state, and only the other of the pair of switch elements is turned on / off, thereby switching the on state and the off state of the bidirectional switch, so that the first bidirectional switch and the second bidirectional switch can be operated at high speed.

[0028] The controller may be configured to alternately perform the positive-side rectification control and the negative-side rectification control at a frequency lower than a frequency of the primary-side AC voltage. According to this configuration, AC welding can be performed.

[0029] Alternatively, the AC welding power supply device may further include: a first buffer capacitor, one end of which is connected to the other end of the first bidirectional switch; a first diode, an anode of which is connected to the one end of the first bidirectional switch and a cathode of which is connected to the other end of the first buffer capacitor; a first discharge switch element, one end of which is connected to the other end of the first buffer capacitor in a manner such that the cathode side of the body diode is connected to the other end of the first buffer capacitor; a current limiting resistor element, one end of which is connected to the other end of the first discharge switch element and the other end of which is connected to the first output end; a second diode, an anode of which is connected to the one end of the second bidirectional switch and a cathode of which is connected to the cathode of the first diode; a second buffer capacitor, one end of which is connected to the other end of the second bidirectional switch; a third diode, a cathode of which is connected to the one end of the second bidirectional switch and an anode of which is connected to the other end of the second buffer capacitor; a second discharge switch element, one end of which is connected to the other end of the first buffer capacitor in a manner such that the anode side of the body diode is connected to the first output end; the other end of the second snubber capacitor being connected to the other end of the second snubber capacitor and the other end of the second snubber capacitor being connected to the one end of the current limiting resistor; and a fourth diode having a cathode connected to the one end of the first bidirectional switch and an anode connected to the anode of the third diode, the controller being configured to perform at least one of a first arc interruption prevention control and a second arc interruption prevention control, wherein in the first arc interruption prevention control, when the positive side rectification control is switched to the negative side rectification control, the first bidirectional switch and the second bidirectional switch are turned off, and in a period before, after, or after the switching, the first discharge switch element is turned on, and in the second arc interruption prevention control, when the negative side rectification control is switched to the positive side rectification control, the first bidirectional switch and the second bidirectional switch are turned off, and in a period before, after, or after the switching, the second discharge switch element is turned on.

[0030] According to this configuration, in the first arc interruption prevention control, when the positive side rectification control is switched to the negative side rectification control, when the first bidirectional switch and the second bidirectional switch are turned off, a surge voltage is generated by the magnetic energy of the inductance component of the welding gun cable of the welding gun as the arc generating part, and the charging current flowing to the first snubber capacitor by the surge voltage passes from the first output end through the smoothing reactor to the middle point of the secondary winding of the transformer, where it is divided, one of the divided currents passes through one end of the secondary winding and the first diode to the other end of the first snubber capacitor, and the other of the divided currents passes through the other end of the secondary winding and the second diode to the other end of the first snubber capacitor, where the two divided currents merge, and the merged charging current returns to the arc generating part through the first snubber capacitor and the second output end. Therefore, the energy that was previously consumed by the resistance element is accumulated in the first snubber capacitor by the charging current based on the surge voltage. On the other hand, before and after the charging current flows, when the first discharge switch element is turned on, the first buffer capacitor is discharged, and the discharge current flows in a manner that passes through the first discharge switch element, the current limiting resistor element, the first output end, the arc generating unit, and the second output end and returns to the first buffer capacitor. The direction of the discharge current is opposite to the direction of the charging current based on the surge voltage, so the voltage of the first buffer capacitor is determined by the relationship between the charging current and the discharge current. Therefore, the controller controls the conduction period of the first discharge switch element in a manner that becomes the optimal voltage for preventing arc interruption, thereby being able to supply a negative voltage for preventing arc interruption from the first buffer capacitor to the inductance component of the welding gun cable and the arc generating unit. Moreover, in the second arc interruption prevention control, it is also possible to supply a positive voltage for preventing arc interruption from the second buffer capacitor to the inductance component of the welding gun cable and the arc generating unit based on the same principle as the first arc interruption prevention control.

[0031] A first high-pass filter may be provided in parallel with the first discharge switch element, and a second high-pass filter may be provided in parallel with the second discharge switch element.

[0032] According to this configuration, the first discharge switch element can be protected from a surge voltage caused by turning off the first discharge switch element by the first high-pass filter, and the second discharge switch element can be protected from a surge voltage caused by turning off the second discharge switch element by the second high-pass filter.

[0033] Hereinafter, the specific embodiments of the present disclosure will be described with reference to the accompanying drawings. In addition, in all the following drawings, the same reference numerals are used to mark the same or equivalent elements, and their repeated descriptions are omitted. Moreover, the following figures are used to illustrate the present disclosure, so there are cases where elements unrelated to the present disclosure are omitted, the dimensions are inaccurate for the purpose of exaggeration, etc., the cases where simplification is performed, and the forms of elements corresponding to each other in multiple figures are inconsistent. Moreover, the present disclosure is not limited to the following embodiments.

[0034] (Implementation Method 1)

[0035] [structure]

[0036] Figure 1 1 is a circuit diagram showing an example of the configuration of AC welding power supply device 100 according to Embodiment 1 of the present disclosure.

[0037] Reference Figure 1 The AC welding power supply device 100 includes a DC power supply 1, an inverter 2, a transformer 3, a first bidirectional switch 4, a second bidirectional switch 5, a first output terminal 6, a second output terminal 7, a smoothing reactor 9, a controller 10, and an arc interruption prevention circuit as main components. These components are described in detail below.

[0038] <DC power supply 1>

[0039] The DC power source 1 is not particularly limited as long as it outputs a DC voltage. The DC power source may be, for example, a rectifier for rectifying AC power, various batteries or rechargeable batteries, a DC generator, or the like.

[0040] <Inverter 2>

[0041] The inverter 2 is connected to the DC power supply 1, and outputs a primary-side AC voltage including a rectangular wave during the first half cycle and the second half cycle under the control of the controller 10. The primary-side AC voltage is, for example, a high-frequency voltage with a frequency of 20 to 100 kHz. The inverter 2 is not particularly limited as long as it generates an AC voltage from the DC power supply 1. The inverter 2 may be, for example, a single-phase full-bridge inverter or a single-phase half-bridge inverter.

[0042] Here, the inverter 2 is a single-phase full-bridge inverter, and a pair of arms are connected in parallel at both ends of the DC power supply 1. In one arm, the high-side switching element SW21 is connected in series with the low-side switching element SW22. In the other arm, the high-side switching element SW23 is connected in series with the low-side switching element SW24. The connection points of the pair of switching elements of each pair of arms constitute the output terminals 21 and 22 of the inverter. The group of the switching element SW21 and the switching element SW24 and the group of the switching element SW23 and the switching element SW22 are alternately turned on, thereby outputting a primary-side AC voltage of a rectangular wave from the output terminals 21 and 22. The primary-side AC voltage includes a first half-cycle period and a second half-cycle period of different polarities. The difference in "polarity" between the first half-cycle period and the second half-cycle period means that the high or low potential of the output terminal of one of the output terminals 21 and 22 is different between the first half-cycle period and the second half-cycle period when the potential of the output terminal of the other output terminal is used as a reference. Here, as described later, for convenience, the first half cycle period and the second half cycle period of the primary-side AC voltage are defined according to the direction of the current flowing in the primary winding 31 of the transformer 3 .

[0043] <Transformer 3>

[0044] The transformer 3 is, for example, a transformer for two-phase half-wave rectification. Specifically, the transformer 3 has a primary winding 31 and a secondary winding 32, and the secondary winding 32 has an intermediate point 32c. The turns ratio of the primary winding 31 to the secondary winding 32 is determined to be an appropriate ratio. The transformer 3 is, for example, a transformer of a subtractive polarity. In addition, the transformer 3 may also be a transformer of an additive polarity. In this case, it is sufficient to make the connection of the secondary winding 32 with respect to the first bidirectional switch 4 and the second bidirectional switch 5 the opposite connection to the subtractive polarity transformer. Therefore, in the transformer 3, the polarity of the voltage induced between the one end 31a and the other end 31b of the primary winding 31, the polarity of the voltage induced between the one end 32a and the middle point 32c of the secondary winding 32, and the polarity of the voltage induced between the middle point 32c and the other end 32b of the secondary winding 32 are the same when the potential of the middle point 32c is used as a reference. Therefore, the polarity of the voltage induced between the middle point 32c and the other end 32b of the secondary winding 32 is opposite to the polarity of the voltage induced between the middle point 32c and the one end 32a of the secondary winding 32 when the potential of the middle point 32c is used as a reference.

[0045] For example, one end 31a of the primary winding 31 is connected to one output end 21 of the inverter 2, and the other end 31b of the primary winding 31 is connected to the other output end 22 of the inverter 2 via a capacitor. In addition, one end 31a of the primary winding 31 is connected to the other output end 22 of the inverter 2 via a capacitor, and the other end 31b of the primary winding 31 is connected to the one output end 21 of the inverter 2. Furthermore, the middle point 32c of the secondary winding 32 is connected to the first output end 6 via a smoothing reactor 9.

[0046] When a primary-side AC voltage is input between the two ends 31a, 31b of the primary winding 31 from a pair of output terminals 21, 22 of the inverter 2, the transformer 3 uses the potential of the midpoint 32c of the secondary winding 32 as a reference, and outputs a same-phase secondary-side AC voltage having a specified voltage corresponding to the turns ratio and the same phase as the primary-side AC voltage between the midpoint 32c and one end 32a of the secondary winding 32, and outputs an anti-phase AC voltage having a specified voltage corresponding to the turns ratio and an anti-phase AC voltage having an anti-phase with the primary-side AC voltage between the midpoint 32c and the other end 32b of the secondary winding.

[0047] Here, a half-cycle period during one cycle of the primary side AC voltage, in which current flows from one end 31a toward the other end 31b in the primary winding 31 of the transformer 3, is defined as a first half-cycle period, and a half-cycle period during one cycle of the primary side AC voltage, in which current flows from the other end 31b toward one end 31a in the primary winding 31 of the transformer 3, is defined as a second half-cycle period.

[0048] <First Bidirectional Switch 4 and Second Bidirectional Switch 5>

[0049] The first bidirectional switch 4 and the second bidirectional switch 5 both have a function of selectively conducting and blocking currents flowing in two directions, namely, a positive direction from one end toward the other end and a negative direction from the other end toward the one end.

[0050] Specifically, the first bidirectional switch 4 includes a first pair of switch elements SW1, SW2 connected in reverse series to each other and a first pair of diodes 41, 42 connected in reverse series to each other, and the first pair of diodes 41, 42 are connected in reverse parallel to the first pair of switch elements SW1, SW2, respectively. Each switch element of the first pair of switch elements SW1, SW2 is referred to as a first switch element SW1 and a second switch element SW2. One end of the first bidirectional switch 4 is connected to one end 32a of the secondary winding 32 of the transformer 3 and the other end is connected to the second output terminal 7. Specifically, one end of the first switch element SW1 is connected to one end 32a of the secondary winding 32 of the transformer 3, and the other end of the first switch element SW1 is connected to one end of the second switch element SW2. Moreover, the other end of the second switch element SW2 is connected to the second output terminal 7.

[0051] The second bidirectional switch 5 includes a second pair of switch elements SW3, SW4 connected in reverse series to each other and a first pair of diodes 51, 52 connected in reverse series to each other, and the first pair of diodes 51, 52 are connected in reverse parallel to the second pair of switch elements SW3, SW4, respectively. The respective switch elements of the second pair of switch elements SW3, SW4 are referred to as the third switch element SW3 and the fourth switch element SW4. One end of the second bidirectional switch 5 is connected to the other end 32b of the secondary winding 32 of the transformer 3 and the other end is connected to the second output terminal 7. Specifically, one end of the third switch element SW3 is connected to the other end 32b of the secondary winding 32 of the transformer 3, and the other end of the third switch element SW3 is connected to one end of the fourth switch element SW4. Moreover, the other end of the fourth switch element SW4 is connected to the second output terminal 7.

[0052] {1st to 4th switching elements SW1 to SW4}

[0053] The first to fourth switching elements SW1 to SW4 may be semiconductor switching elements that can selectively conduct and cut off current flowing in at least one direction. Examples of semiconductor switching elements that can selectively conduct and cut off current flowing in only one direction include bipolar transistors and IGBTs (Insulated Gate Bipolar Transistors).

[0054] As a switching element capable of selectively turning on and off current flowing in both directions, for example, a field effect transistor (FET) is given. As FET, for example, MOSFET, MESFET, JFET, etc. are given.

[0055] 《Reverse series connection of switching elements》

[0056] The "reverse series connection" of the switching elements means that two switching elements (to be precise, two semiconductor switching elements) are connected in series with each other in such a way that the directions of application of the voltage applied between a pair of main terminals are opposite to each other when used alone. Specifically, in the case of bipolar transistors, it means that two bipolar transistors are connected in series with each other in such a way that the emitters are connected to each other or the collectors are connected to each other. In the case of FETs, it means that two FETs are connected in series with each other in such a way that the sources are connected to each other or the drains are connected to each other. In addition, in MOSFET and MESFET, the main terminal of a pair of main terminals that is connected (conducted) to the control terminal (gate) is the source. The channel type of MOSFET and MESFET can be any one of N-channel type and P-channel type.

[0057] {Diodes 41, 42, 51, 52}

[0058] Each diode 41, 42, 51, 52 may be a diode that is an element different from the first to fourth switching elements SW1 to SW4 (hereinafter referred to as an external diode), or may be a body diode formed inside the first to fourth switching elements SW1 to SW4. The body diode may be a parasitic diode or an intentionally designed diode.

[0059] Examples of the external diode include a rectifier diode, a switching diode, a fast recovery diode, and a Schottky diode.

[0060] 《Reverse-parallel connection of diodes》

[0061] “Antiparallel connection” of a diode and a switching element means connecting the diode and the switching element in parallel so that the forward direction of the diode is opposite to the direction of application of a voltage between a pair of main terminals when the switching element is used alone.

[0062] 《Reverse series connection of diodes》

[0063] The “reverse series connection” of diodes means that two diodes are connected in series with each other in such a manner that their forward directions are opposite to each other.

[0064] {Operation of the first bidirectional switch 4 and the second bidirectional switch 5}

[0065] The first bidirectional switch 4 is controlled by the controller 10. During the first half cycle of the primary side AC voltage, it rectifies the same-phase secondary side AC voltage output from the transformer 3 and outputs a same-phase half-wave positive DC voltage. During the second half cycle of the primary side AC voltage, it rectifies the same-phase secondary side AC voltage output from the transformer 3 and outputs a same-phase half-wave negative DC voltage.

[0066] The second bidirectional switch 5 is controlled by the controller 10. During the first half cycle of the primary side AC voltage, the inverted secondary side AC voltage output from the transformer 3 is rectified and an inverted half-wave negative DC voltage is output. During the second half cycle of the primary side AC voltage, the inverted secondary side AC voltage output from the transformer 3 is rectified and an inverted half-wave positive DC voltage is output.

[0067] {Specific Configuration Example of the First to Fourth Switching Elements SW1 to SW4}

[0068] Here, the first to fourth switch elements SW1 to SW4 are switch elements that can selectively conduct and cut off current flowing in both directions. The structure of the first to fourth switch elements SW1 to SW4 as switch elements that can selectively conduct and cut off current flowing in only one direction will be described in the second embodiment described later.

[0069] The first to fourth switching elements SW1 to SW4 are formed of, for example, MOSFETs.

[0070] In the first bidirectional switch 4, the MOSFET constituting the first switching element SW1 and the MOSFET constituting the second switching element SW2 are connected in series with their sources connected to each other. Furthermore, the drain of the MOSFET constituting the first switching element SW1 is connected to one end 32a of the secondary winding 32 of the transformer 3, and the drain of the MOSFET constituting the second switching element SW2 is connected to the second output terminal 7. The diode 41 and the diode 42 are respectively constituted by the body diode of the first switching element SW1 and the body diode of the second switching element SW2. In the second bidirectional switch 5, the MOSFET constituting the third switching element SW3 and the MOSFET constituting the fourth switching element SW4 are connected in series with their sources connected to each other. Furthermore, the drain of the MOSFET constituting the third switching element SW3 is connected to the other end 32b of the secondary winding 32 of the transformer 3, and the drain of the MOSFET constituting the fourth switching element SW4 is connected to the second output terminal 7. The diode 51 and the diode 52 are respectively constituted by the body diode of the third switching element SW3 and the body diode of the fourth switching element SW4.

[0071] <1st output terminal 6 and 2nd output terminal 7>

[0072] The first output terminal 6 and the second output terminal 7 are output parts of the AC welding power supply device 100 for supplying a DC voltage for welding to the arc generating part 8. The first output terminal 6 is connected to a workpiece. The second output terminal 7 is connected to the base end of a welding gun cable, and the front end of the welding gun cable is connected to a welding gun. Reference symbol Ls represents the inductance component of the welding gun cable. An arc is generated between the workpiece and the welding gun. That is, the workpiece and the welding gun constitute the arc generating part 8.

[0073] Specifically, the first output terminal 6 and the second output terminal 7 supply the full-wave positive DC voltage or the full-wave negative DC voltage output from the first bidirectional switch 4 and the second bidirectional switch 5 to the arc generating unit 8 as the DC voltage for welding.

[0074] <Smoothing reactor 9>

[0075] The smoothing reactor 9 is inserted in the path of the current passing through the first bidirectional switch 4 and the second bidirectional switch 5. The smoothing reactor 9 is inserted, for example, between the middle point 32c of the secondary winding 32 of the transformer 3 and the first output terminal 6. In addition, a pair of smoothing reactors 9 may be inserted between one end 32a of the secondary winding 32 of the transformer 3 and the first bidirectional switch 4 and between the other end 32b of the secondary winding 32 of the transformer 3 and the second bidirectional switch 5, respectively.

[0076] <Arc interruption prevention circuit>

[0077] The arc interruption prevention circuit includes a first snubber capacitor Cs1, a second snubber capacitor Cs2, a first discharge switch element SW5, a second discharge switch element SW6, first to fourth diodes D1 to D4, a current limiting resistor R1, a first high pass filter Hf1, and a second high pass filter Hf2.

[0078] One end of the first snubber capacitor Cs1 is connected to the other end of the first bidirectional switch 4. An anode of the first diode D1 is connected to the one end of the first bidirectional switch 4, and a cathode of the first diode D1 is connected to the other end of the first snubber capacitor Cs1.

[0079] One end of the first discharge switch element SW5 is connected to the other end of the first snubber capacitor Cs1. In this case, the cathode side of the diode 61 connected in reverse parallel to the first discharge switch element SW5 is connected to the other end of the first snubber capacitor Cs1. The first discharge switch element SW5 can be composed of, for example, a bipolar transistor, an IGBT, or a FET. Here, the first discharge switch element SW5 is composed of an IGBT.

[0080] One end of the current limiting resistor element R1 is connected to the other end of the first discharge switch element SW5, and the other end of the current limiting resistor element R1 is connected to the second output terminal 7. The anode of the second diode D2 is connected to the one end of the second bidirectional switch 5, and the cathode of the second diode D2 is connected to the cathode of the first diode D1. The current limiting resistor element R1 is a resistor element for limiting a discharge current Id described later.

[0081] One end of the second snubber capacitor Cs2 is connected to the other end of the second bidirectional switch 5. A cathode of the third diode D3 is connected to the one end of the second bidirectional switch 5, and an anode of the third diode D3 is connected to the other end of the second snubber capacitor Cs2.

[0082] One end of the second discharge switch element SW6 is connected to the other end of the second buffer capacitor Cs2, and the other end of the second discharge switch element SW6 is connected to the one end of the current limiting resistor R1. In this case, the anode side of the diode 62 connected in reverse parallel to the second discharge switch element SW6 is connected to the other end of the second buffer capacitor. The second discharge switch element SW6 can be composed of a bipolar transistor, an IGBT, or a FET, for example. Here, the second discharge switch element SW5 is composed of an IGBT.

[0083] <First High-Pass Filter Hf1 and Second High-Pass Filter Hf2>

[0084] The AC welding power supply device 100 further includes a first high pass filter Hf1 and a second high pass filter Hf2 connected in parallel to the first discharge switch element SW5 and the second discharge switch element SW6, respectively. The first high pass filter Hf1 and the second high pass filter Hf2 are buffer circuits for the first discharge switch element SW5 and the second discharge switch element SW6, respectively. The first high pass filter Hf1 is composed of a buffer resistor element R2 and a third buffer capacitor Cs3 connected in series with each other. The second high pass filter Hf2 is composed of a buffer resistor element R3 and a fourth buffer capacitor Cs4 connected in series with each other.

[0085] <Controller 10>

[0086] The controller 10 controls the overall operation of the AC welding power supply device 100. In particular, the controller 10 controls the operation of the switching elements SW21 to SW24 of the inverter 2, the first to fourth switching elements SW1 to SW4 of the first bidirectional switch 4 and the second bidirectional switch 5, and the first discharge switching element SW5 and the second discharge switching element SW6.

[0087] The controller 10 is composed of, for example, a computing unit having a processor and a memory. Specifically, the computing unit is composed of, for example, a computer, a personal computer, a microcontroller, an MPU, an FPGA (Field Programmable Gate Array), a PLC (Programmable Logic Controller), etc. The controller 10 may be composed of a single computing unit for centralized control or a plurality of computing units for distributed control.

[0088] In other words, the functions of the controller 10 can be performed using circuits or processing circuits including general-purpose processors, special-purpose processors, integrated circuits, ASICs (Application Specific Integrated Circuits), conventional circuits, and / or combinations thereof that are configured or programmed to perform the disclosed functions. The processor includes transistors and other circuits and is therefore considered a processing circuit or circuit.

[0089] The memory stores various control programs including a welding control program, for example. The processor reads out and executes these control programs from the memory, thereby controlling the operation of the AC welding power supply device. Regarding AC welding, there are first AC welding starting from positive DC welding (first mode) and second AC welding starting from negative DC welding (third mode).

[0090] The controller 10 has, for example, a user interface. The user interface includes, for example, a first AC welding instruction unit for the user to instruct the first AC welding, a second AC welding instruction unit for the user to instruct the second AC welding, a positive DC welding instruction unit for the user to instruct the positive DC welding, and a negative DC welding instruction unit for the user to instruct the negative DC welding. Hereinafter, the control content of the controller 10 will be described in detail as the operation of the AC welding power supply device 100.

[0091] [action]

[0092] Next, the operation of AC welding power supply device 100 configured as described above will be described. The operation of AC welding power supply device 100 is performed under the control of controller 10 .

[0093] Here, the operation of the AC welding power supply device 100 when outputting a voltage for AC welding is described. In this case, the AC welding power supply device 100 has, for example, the first operation mode to the fourth operation mode, and the controller 10 performs rectification and polarity control for AC welding. Here, the outline of the control of the first AC welding is described.

[0094] Figure 2 2 is a flowchart showing the contents of rectification and polarity control of the first AC welding performed by the controller 10. Figure 2 When the first AC welding is instructed from the user interface, the controller 10 starts the rectification and polarity control of the first AC welding and waits for input of a welding start instruction ("No" in step S1, step S1).

[0095] When a welding start command is input (YES in step S1 ), controller 10 causes AC welding power supply device 100 to sequentially execute the first mode to the fourth mode (steps S2 to S5 ).

[0096] When the AC welding power supply device 100 completes the fourth mode (S5), the controller 10 determines whether a welding end command is input (step S6). If the welding end command is not input ("No" in step S6), the controller 10 returns to step S2 and then repeats steps S2 to S6 ("No") until a welding end command is input.

[0097] When the welding end command is input (YES in step S6 ), controller 10 ends the rectification and polarity control of the first AC welding.

[0098] Next, refer to Figures 3 to 9 , the rectification and polarity control of the first AC welding will be described in detail for each mode. Figure 3 1 is a waveform diagram showing the waveform of the output current and the waveform of the gate signal to the bidirectional switch.

[0099] Specifically, Figure 3 The contents of the waveform diagrams in each section are as follows. The waveform diagram in the uppermost section shows the waveform of the output current output from the first output terminal 6 and the second output terminal 7. The waveform diagram in the second section from the top shows the waveform of the gate signal of the second switching element SW2. The waveform diagram in the third section from the top shows the waveform of the gate signal of the first switching element SW1. The waveform diagram in the fourth section from the top shows the waveform of the gate signal of the fourth switching element SW4. The waveform diagram in the fifth section from the top shows the waveform of the gate signal of the third switching element SW3. The waveform diagram in the sixth section from the top shows the waveform of the gate signal of the first discharge switching element SW5. The waveform diagram in the seventh section (the bottom section) from the top shows the waveform of the gate signal of the second discharge switching element SW6.

[0100] Reference Figure 3, the controller 10 inputs the corresponding gate signals to each switching element SW1~SW6. To be precise, after being sent from the controller 10, these gate signals are amplified by the gate drive circuit and then input to the corresponding switching elements SW1~SW6, but here, in order to simplify the description, the gate signals are respectively input from the controller 10 to the corresponding switching elements SW1~SW6 for description. Moreover, in the gate signal, the high-level part is called "on signal" and the low-level part is called "off signal". In addition, these situations are the same for the gate signals from the inverter 2 to the switching elements SW21~SW24.

[0101] In the gate signals of the first to fourth switching elements SW1 to SW4, the portion indicated by the vertical lines with small intervals indicates that the on signal and the off signal are sent alternately and repeatedly at small equal time intervals. The repetition frequency of the on signal and the off signal is, for example, 20kHz to 100kHz. The repetition frequency of the on signal is equal to the frequency of the primary side AC voltage output from the inverter 2. That is, as will be understood from the following description, the rectification performed by the first bidirectional switch 4 and the second bidirectional switch 5 is synchronous rectification performed in synchronization with the switching of the switching elements SW21 to SW24 of the inverter 2.

[0102] The frequency corresponding to the period from the first mode to the fourth mode, that is, the polarity switching frequency of the voltage (and current) for AC welding is a low frequency of, for example, 100 Hz to 500 Hz.

[0103] <Mode 1>

[0104] Figure 4 The input current Ii and output current Io in the positive-side in-phase rectification of the first mode are connected in Figure 1 The circuit is shown in Fig. Figure 5 The input current Ii and the output current Io in the positive-side reverse rectification of the first mode are connected in Figure 1 The circuit is shown in the figure. In addition, Figures 4 to 9 In order to facilitate observation of the flow of each current, the controller 10 is omitted, and reference numerals of other elements are omitted.

[0105] In the first mode, the controller 10 controls the positive side rectification to make the first bidirectional switch 4 and the second bidirectional switch 5 perform positive side in-phase rectification and positive side reverse rectification, respectively. In the first mode, the output current Io rises to a high level current value as quickly as possible according to the time constant (τ=L / R) of the circuit through which the output current Io flows.

[0106] {Positive side in-phase rectification}

[0107] Reference Figure 1 , Figure 3 as well as Figure 4 , during AC welding, the controller 10 causes the inverter 2 to output the primary side AC voltage. Moreover, in the first mode, first, during the first half cycle of the primary side AC voltage, the controller 10 causes the first bidirectional switch 4 to be in the on state in the positive direction, and causes the second bidirectional switch 5 to be in the off state. Specifically, the controller 10 sends a gate signal of an on signal to the second switch element SW2, and sends a gate signal of an on signal to the first switch element SW1 during the entire period of the first mode. As a result, the second switch element SW2 becomes in the on state, and the first switch element SW1 becomes in the on state during the entire period of the first mode, and the first bidirectional switch 4 becomes in the on state in the positive direction. As a result, the first bidirectional switch 4 rectifies the same-phase secondary side AC voltage output from the transformer 3 and outputs the same-phase half-wave positive DC voltage. Here, "becoming in the on state in the positive direction" means "a state in which current flows in the positive direction".

[0108] On the other hand, the controller 10 sends a gate signal of an off signal to the fourth switch element SW4. Then, the fourth switch element SW4 is turned off, and the second bidirectional switch 5 is turned off. Thus, the second bidirectional switch 5 blocks the reverse-phase secondary-side AC voltage output from the transformer 3. Moreover, at this time, the controller 10 sends a gate signal of an on signal to the third switch element SW3 during the entire period of the first mode. Then, the third switch element SW3 is turned on during the entire period of the first mode.

[0109] In addition, the controller 10 sends a gate signal of a disconnection signal to the first discharge switch element SW5 during the entire period from the third mode of the previous cycle to the first mode of the current cycle, and sends a gate signal of a disconnection signal to the second discharge switch element SW6 during the entire period from the first mode to the third mode. As a result, the first discharge switch element SW5 is in a disconnected state during the entire period from the third mode of the previous cycle to the first mode of the current cycle, and the second discharge switch element SW6 is in a disconnected state during the entire period from the first mode to the third mode.

[0110] Reference Figure 4When the AC welding power supply device 100 is in the above state, on the primary side of the transformer 3, the input current Ii from the inverter 2 to the transformer 3 flows in the primary winding 31 of the transformer 3 in the direction from the one end 31a to the other end 31b, and on the secondary side of the transformer 3, the output current Io flows from the one end 32a of the secondary winding 32 of the transformer 3, sequentially through the first bidirectional switch 4, the second output terminal 7, the arc generating unit 8, the first output terminal 6, the smoothing reactor 9 and the middle point 32c of the secondary winding 32 of the transformer 3 and returns to the one end 32a of the secondary winding 32 of the transformer 3.

[0111] In addition, the first snubber capacitor Cs1 is charged to a voltage CV1 corresponding to the voltage across the first bidirectional switch 4. The other end of the first snubber capacitor Cs1 (the end on the cathode side of the first diode D1) is maintained at the highest potential (positive electrode) of the in-phase secondary-side AC voltage output from the transformer 3 by the first diode D1.

[0112] In addition, the second snubber capacitor Cs2 is charged to a voltage CV2 corresponding to the voltage across the second bidirectional switch 5. The other end of the second snubber capacitor Cs2 (one end on the anode side of the third diode D3) is maintained at the lowest potential (negative pole) of the reverse-phase secondary-side AC voltage output from the transformer 3 by the third diode D3.

[0113] As described above, in AC welding power supply device 100 , positive-side in-phase rectification is performed.

[0114] {Positive side reverse rectification}

[0115] Reference Figure 1 , Figure 3 as well as Figure 5 Then, when the primary side AC voltage becomes the second half cycle period, the controller 10 turns the second bidirectional switch 5 into the conducting state in the positive direction and turns the first bidirectional switch 4 into the cut-off state. Specifically, the controller 10 sends a gate signal of the on signal to the fourth switch element SW4. Then, the fourth switch element SW4 becomes the conducting state, and the third switch element SW3 has been the conducting state during the entire period of the first mode, so the second bidirectional switch 5 rectifies the reversed secondary side AC voltage output from the transformer 3 and outputs the reversed half-wave positive DC voltage.

[0116] On the other hand, the controller 10 sends a gate signal of an OFF signal to the second switch element SW2 . Then, the second switch element SW2 is turned off, and the first bidirectional switch 4 is turned off. Thus, the first bidirectional switch 4 blocks the in-phase secondary-side AC voltage output from the transformer 3 .

[0117] Reference Figure 5When the AC welding power supply device 100 is in the above state, on the primary side of the transformer 3, the input current Ii flowing from the inverter 2 to the transformer 3 flows in the primary winding 31 of the transformer 3 in the direction from the other end 31b toward the one end 31a, and on the secondary side of the transformer 3, the output current Io flows from the other end 32b of the secondary winding of the transformer 3, sequentially through the second bidirectional switch 5, the second output terminal 7, the arc generating unit 8, the first output terminal 6, the smoothing reactor 9 and the middle point 32c of the secondary winding 32 of the transformer 3 and returns to the other end 32b of the secondary winding 32 of the transformer 3.

[0118] Furthermore, the first snubber capacitor Cs1 is charged to a voltage corresponding to the voltage across the first bidirectional switch 4, and the second snubber capacitor Cs2 is charged to a voltage corresponding to the voltage across the second bidirectional switch 5. As described above, in AC welding power supply device 100, positive-side reverse rectification is performed.

[0119] In this way, the first bidirectional switch 4 and the second bidirectional switch 5 supply a full-wave positive DC voltage between the first output terminal 6 and the second output terminal 7 through the positive side in-phase rectification and the positive side reverse rectification.

[0120] <Mode 2>

[0121] Figure 6 The flow of charging current and discharging current when the polarity is switched from positive to negative in the second mode is Figure 1 The circuit is shown in Fig.

[0122] In the second mode, the controller 10 performs polarity switching control from positive to negative of the output voltage and the output current and the first arc interruption prevention control.

[0123] Reference Figure 1 , Figure 3 as well as Figure 6 At a predetermined timing corresponding to the polarity switching frequency of the voltage (or current) for AC welding, the controller 10 turns the first bidirectional switch 4 and the second bidirectional switch 5 into a disconnected state. Specifically, a gate signal of a disconnection signal is sent to the first to fourth switching elements SW1 to SW4. As a result, the first to fourth switching elements SW1 to SW4 are turned into a disconnected state, and the first bidirectional switch 4 and the second bidirectional switch 5 are turned into a disconnected state. Thus, the second mode starts.

[0124] In this way, Figure 6As shown by the dotted arrow in FIG. 1 , a surge voltage is generated by the magnetic energy accumulated in the inductance component Ls of the welding gun cable of the welding gun as the arc generating unit 8, and the charging current Ic flowing to the first snubber capacitor Cs1 passes from the first output terminal 6 through the smoothing reactor 9 to the middle point 32c of the secondary winding 32 of the transformer 3, where it is divided, one of the divided currents passes through the one end 32a of the secondary winding 32 and the first diode D1 to reach the other end of the first snubber capacitor Cs1, and the other of the divided currents passes through the other end 32b of the secondary winding 32 and the second diode D2 to reach the other end of the first snubber capacitor Cs1, where the two divided currents merge, and the merged charging current passes through the first snubber capacitor Cs1 and the second output terminal 7 and returns to the arc generating unit 8.

[0125] Therefore, the energy that was previously consumed by the resistance element is accumulated in the first snubber capacitor Cs1 by the charging current Ic based on the surge voltage.

[0126] On the other hand, before and after the charging current flows, the controller 10 sends a gate signal of an on signal to the first discharge switch element SW5, thereby turning on the first discharge switch element SW5. Then, the first buffer capacitor Cs1 is discharged. Figure 6 As shown by the dotted arrow in FIG. 1 , the discharge current Id flows through the first discharge switch element SW5, the current limiting resistor element R1, the first output terminal 6, the arc generating unit 8, and the second output terminal 7 and returns to the first snubber capacitor Cs1. The direction of the discharge current Id is opposite to the direction of the charging current Ic based on the surge voltage, so the voltage CV1 of the first snubber capacitor Cs1 is determined by the relationship between the charging current Ic and the discharge current Id.

[0127] Here, the memory of the controller 10 stores in advance the conduction period of the first discharge switch element SW5 that is the optimum voltage for preventing arc interruption (hereinafter referred to as "first optimum conduction period"). The "first optimum conduction period" is obtained by simulation, experiment, calculation, etc.

[0128] During the "first optimal conduction period", the controller 10 turns on the first discharge switch element SW5. As a result, a negative DC voltage for preventing arc interruption is supplied from the first buffer capacitor Cs1 to the inductance component Ls of the welding gun cable and the arc generating unit 8. Figure 3The waveform diagram of the output current at the top of the figure is described in detail. First, the "output current" is described. The "output current" refers to the current supplied by the AC welding power supply device 100 to the arc generating unit 8. The charging current Ic and the discharging current Id use the magnetic energy of the inductance component Ls of the welding gun cable stored in the current supplied by the AC welding power supply device 100 to the arc generating unit 8 as an energy source. Moreover, the flow directions of the two are opposite to each other, and only the one with a larger absolute value becomes obvious. Therefore, the one with a larger absolute value of the charging current Ic and the discharging current Id is equivalent to the "output current".

[0129] Reference Figure 3 The "first optimal conduction period" starts, for example, with the start of the second mode and ends with the end of the second mode. In the "first optimal conduction period", initially, the charging current Ic is larger than the discharging current Id, but halfway through, the discharging current Id becomes larger than the charging current Ic, at which point the polarity of the output current Io and the output voltage is switched from the positive pole to the negative pole. Moreover, the current value of the output current Io at the negative pole, which is the difference current of the discharging current Id relative to the charging current Ic, increases with the decrease of the charging current Ic, and finally when the charging current Ic disappears, the current value of the output current Io becomes the substantially constant current value of the discharging current Id, Id=CV1 / R(A) (CV1 is the voltage (V) of the first buffer capacitor Cs1, and R is the resistance value (Ω) of the current limiting resistor R1). Then, the output current Io maintains this substantially constant current value until the "first optimal conduction period" ends. When the "first optimal conduction period" ends, the first discharge switch element SW5 becomes cut off. Thus, the second mode ends.

[0130] In addition, when the second mode is shifted to the third mode, the voltage applied to the arc generating unit 8 is switched from the negative electrode voltage of the first snubber capacitor Cs1 based on the second mode to the negative electrode voltage of the first bidirectional switch 4 or the second bidirectional switch 5 based on the third mode, but the output current Io is maintained by the inductance component Ls of the welding gun cable. Therefore, the polarity switching from positive to negative of the output voltage and the output current Io is appropriately performed while preventing the arc from being interrupted.

[0131] Furthermore, when the first discharge switch element SW5 is turned off at the end of the “first optimal on period”, a surge voltage generated thereby is bypassed by the first high-pass filter Hf1 , thereby protecting the first discharge switch element SW5 .

[0132] <Mode 3>

[0133] Figure 7 The flow of input current Ii and output current Io in the negative-side inversion rectification of the third mode is Figure 1 The circuit is shown in Fig. Figure 8The flow of input current Ii and output current Io in the negative side in-phase rectification of the third mode is Figure 1 In the third mode, the controller 10 controls the negative side rectification to make the first bidirectional switch 4 and the second bidirectional switch 5 perform negative side in-phase rectification and negative side reverse rectification respectively. In the third mode, the output current Io decreases to a low level current value as quickly as possible according to the time constant (τ=L / R) of the circuit through which the output current Io flows.

[0134] {Negative side reverse rectification}

[0135] Reference Figure 1 , Figure 3 as well as Figure 7 In the third mode, first, during the first half cycle of the primary side AC voltage, the controller 10 turns the second bidirectional switch 5 into a conducting state in the negative direction, and turns the first bidirectional switch 4 into a cut-off state. Specifically, the controller 10 sends a gate signal of an on signal to the third switch element SW3, and sends a gate signal of an on signal to the fourth switch element SW4 during the entire period of the third mode. As a result, the third switch element SW3 becomes a conducting state, and the fourth switch element SW4 becomes a conducting state during the entire period of the third mode, and the second bidirectional switch 5 becomes a conducting state in the negative direction. As a result, the second bidirectional switch 5 rectifies the inverted secondary side AC voltage output from the transformer 3 and outputs an inverted half-wave negative DC voltage. Here, "becoming a conducting state in the negative direction" means "a state in which current flows in the negative direction".

[0136] On the other hand, the controller 10 sends a gate signal of an off signal to the first switch element SW1. Then, the first switch element SW1 is turned off, and the first bidirectional switch 4 is turned off. Thus, the first bidirectional switch 4 blocks the same-phase secondary-side AC voltage output from the transformer 3. Moreover, at this time, the controller 10 sends a gate signal of an on signal to the second switch element SW2 during the entire period of the third mode. Then, the second switch element SW2 is turned on during the entire period of the third mode.

[0137] Furthermore, the controller 10 sends a gate signal of an OFF signal to the first discharge switch element SW5 during the entire period from the third mode to the first mode of the next cycle, thereby the first discharge switch element SW5 is in a cut-off state during the entire period from the third mode to the first mode of the next cycle.

[0138] Reference Figure 7When the AC welding power supply device 100 is in the above state, on the primary side of the transformer 3, the input current Ii flowing from the inverter 2 to the transformer 3 flows in the primary winding 31 of the transformer 3 in the direction from the one end 31a to the other end 31b, and on the secondary side of the transformer 3, the output current Io flows from the middle point 32c of the secondary winding 32 of the transformer 3, sequentially through the smoothing reactor 9, the first output terminal 6, the arc generating unit 8, the second output terminal 7, the second bidirectional switch 5 and the other end 32b of the secondary winding 32 of the transformer 3 and returns to the middle point 32c of the secondary winding 32 of the transformer 3.

[0139] In addition, the second snubber capacitor Cs2 is charged to a voltage CV2 corresponding to the voltage across the second bidirectional switch 5. The other end of the second snubber capacitor Cs2 (one end on the anode side of the third diode D3) is maintained at the lowest potential (negative pole) of the reverse-phase secondary-side AC voltage output from the transformer 3 by the third diode D3.

[0140] In addition, the first snubber capacitor Cs1 is charged to a voltage CV1 corresponding to the voltage across the first bidirectional switch 4. The other end of the first snubber capacitor Cs1 (the end on the cathode side of the first diode D1) is maintained at the highest potential (positive electrode) of the in-phase secondary-side AC voltage output from the transformer 3 by the first diode D1.

[0141] As described above, in AC welding power supply device 100 , negative-side reverse rectification is performed.

[0142] {Negative side in-phase rectification}

[0143] Reference Figure 1 , Figure 3 as well as Figure 8 Then, when the primary side AC voltage becomes the second half cycle period, the controller 10 turns the first bidirectional switch 4 into the conducting state in the negative direction, and turns the second bidirectional switch 5 into the cut-off state. Specifically, the controller 10 sends a gate signal of the on signal to the first switch element SW1. Then, the first switch element SW1 becomes the conducting state, and the second switch element SW2 has been turned into the conducting state during the entire period of the third mode, so the first bidirectional switch 4 rectifies the same-phase secondary side AC voltage output from the transformer 3 and outputs the same-phase half-wave negative DC voltage.

[0144] On the other hand, the controller 10 sends a gate signal of an OFF signal to the third switch element SW3 . Then, the third switch element SW3 is turned off, and the second bidirectional switch 5 is turned off. Thus, the second bidirectional switch 5 blocks the reverse-phase secondary-side AC voltage output from the transformer 3 .

[0145] Reference Figure 8 When the AC welding power supply device 100 is in the above state, on the primary side of the transformer 3, the input current Ii flowing from the inverter 2 to the transformer 3 flows in the primary winding 31 of the transformer 3 in the direction from the other end 31b toward the one end 31a, and on the secondary side of the transformer 3, the output current Io flows from the middle point 32c of the secondary winding 32 of the transformer 3, sequentially through the smoothing reactor 9, the first output terminal 6, the arc generating unit 8, the second output terminal 7, the first bidirectional switch 4, and the one end 32a of the secondary winding 32 of the transformer 3 and returns to the middle point 32c of the secondary winding 32 of the transformer 3.

[0146] Furthermore, the first snubber capacitor Cs1 is charged to a voltage CV1 corresponding to the voltage across the first bidirectional switch 4, and the second snubber capacitor Cs2 is charged to a voltage CV2 corresponding to the voltage across the second bidirectional switch 5. As described above, in the AC welding power supply device 100, negative-side in-phase rectification is performed.

[0147] In this way, the first bidirectional switch 4 and the second bidirectional switch 5 supply a full-wave negative DC voltage between the first output terminal 6 and the second output terminal 7 through the negative side anti-phase rectification and the negative side in-phase rectification.

[0148] <Fourth Mode>

[0149] Fig. 9 The flow of charging current and discharging current when the polarity is switched from negative to positive in the fourth mode is Figure 1 The circuit is shown in Fig.

[0150] In the fourth mode, the controller 10 performs polarity switching control from negative to positive of the output voltage and the output current and second arc interruption prevention control.

[0151] Reference Figure 1 , Figure 3 as well as Fig. 9 At a predetermined timing corresponding to the polarity switching frequency of the voltage (or current) for AC welding, the controller 10 turns the first bidirectional switch 4 and the second bidirectional switch 5 into a disconnected state. Specifically, a gate signal of a disconnection signal is sent to the first to fourth switching elements SW1 to SW4. Then, the first to fourth switching elements SW1 to SW4 are turned into a disconnected state, and the first bidirectional switch 4 and the second bidirectional switch 5 are turned into a disconnected state. Thus, the fourth mode starts.

[0152] In this way, Fig. 9As shown by the dotted arrow in FIG. 1 , a surge voltage is generated by the magnetic energy accumulated in the inductance component Ls of the welding gun cable of the welding gun as the arc generating unit 8. Due to the surge voltage, the charging current Ic flowing to the second buffer capacitor Cs2 passes through the second buffer capacitor Cs2 from the second output terminal 7, and is split here. One side of the split current passes through the third diode D3 and the other end 32b of the secondary winding 32 of the transformer 3 to reach the middle point 32c of the secondary winding 32, and the other side of the split current passes through the fourth diode D4 and the one end 32a of the secondary winding 32 of the transformer 3 to reach the middle point 32c of the secondary winding 32. The two split currents merge here, and the merged charging current passes through the smoothing reactor 9 and the first output terminal 6 and returns to the arc generating unit 8.

[0153] Therefore, the energy that was previously consumed by the resistance element is accumulated in the second snubber capacitor Cs2 by the charging current Ic based on the surge voltage.

[0154] On the other hand, before and after the charging current flows, the controller 10 sends a gate signal of an on signal to the second discharge switch element SW6, thereby turning on the second discharge switch element SW6. Then, the second buffer capacitor Cs2 is discharged. Fig. 9 As shown by the dotted arrow in FIG. 1 , the discharge current Id flows through the second output terminal 7, the arc generating unit 8, the current limiting resistor element R1, and the second discharge switch element SW6, and returns to the second snubber capacitor Cs2. The direction of the discharge current Id is opposite to the direction of the charging current Ic based on the surge voltage, so the voltage CV2 of the second snubber capacitor Cs2 is determined by the relationship between the charging current Ic and the discharge current Id.

[0155] Here, the memory of the controller 10 stores in advance the conduction period of the second discharge switch element SW6 that is the optimum voltage for preventing arc interruption (hereinafter referred to as "second optimum conduction period"). The "second optimum conduction period" is obtained by simulation, experiment, calculation, etc.

[0156] During the "second optimal conduction period", the controller 10 turns on the second discharge switch element SW6. As a result, a positive DC voltage for preventing arc interruption is supplied from the second snubber capacitor Cs2 to the inductance component Ls of the welding gun cable and the arc generating unit 8.

[0157] As described above, arc interruption is prevented and polarity switching of the output voltage from negative to positive is performed.

[0158] For the above content, refer to Figure 3 The waveform diagram of the output current at the top of the diagram is described in detail. Figure 3The "second optimal conduction period" starts, for example, with the start of the fourth mode and ends with the end of the fourth mode. In the "second optimal conduction period", initially, the charging current Ic is larger than the discharging current Id, but halfway through, the discharging current Id becomes larger than the charging current Ic, at which point the polarity of the output current Io and the output voltage is switched from the negative pole to the positive pole. Moreover, the current value of the positive output current Io, which is the difference current of the discharging current Id relative to the charging current Ic, increases with the decrease of the charging current Ic, and finally when the charging current Ic disappears, the current value of the output current Io becomes the substantially constant current value of the discharging current Id, Id=CV2 / R(A) (CV2 is the voltage (V) of the second buffer capacitor Cs2, and R is the resistance value (Ω) of the current limiting resistor R1). Then, the output current Io maintains this substantially constant current value until the "second optimal conduction period" ends. When the "second optimal conduction period" ends, the second discharge switch element SW6 becomes cut off. Thus, the fourth mode ends.

[0159] In addition, when the fourth mode is shifted to the first mode, the voltage applied to the arc generating unit 8 is switched from the positive electrode voltage of the second snubber capacitor Cs2 based on the fourth mode to the positive electrode voltage of the first bidirectional switch 4 or the second bidirectional switch 5 based on the third mode, but the output current Io is maintained by the inductance component Ls of the welding gun cable. Therefore, the polarity switching from negative to positive of the output voltage and the output current Io is appropriately performed while preventing the arc from being interrupted.

[0160] Furthermore, when the second discharge switch element SW6 is turned off at the end of the “second optimal on period”, a surge voltage generated thereby is bypassed by the second high-pass filter Hf2, thereby protecting the second discharge switch element SW6.

[0161] <Other actions>

[0162] When the user inputs a command for the second AC welding from the second AC welding instruction unit of the user interface, the controller 10 causes the AC welding power supply device 100 to perform AC welding from the third mode described above. Thus, the second AC welding can be performed. Furthermore, when the user inputs a command for the positive DC welding from the positive DC welding instruction unit of the user interface, the controller 10 causes the AC welding power supply device 100 to perform the first mode described above. Thus, positive DC welding can be performed. Furthermore, when the user inputs a command for the negative DC welding from the negative DC welding instruction unit of the user interface, the controller 10 causes the AC welding power supply device 100 to perform the third mode described above. Thus, negative DC welding can be performed.

[0163] [Modifications]

[0164] In this modification, the "first optimal conduction period" does not end in the second mode, but is extended to the rising interval of the output voltage of the third mode. For example, the "first optimal conduction period" is extended to the end of the falling interval of the output voltage of the third mode. In this case, the second mode ends by the start of the third mode (the first bidirectional switch 4 or the second bidirectional switch 5 is turned on in the negative direction). In addition, the third mode is divided into a sub-mode until the "first optimal conduction period" ends when the first discharge switch element SW5 becomes cut-off state and the "first optimal conduction period" ends, and a sub-mode of the remaining part. As described above, the length of the "first optimal conduction period" is determined to be a length that the voltage CV1 of the first snubber capacitor Cs1 becomes the "optimal negative voltage to prevent arc interruption" in the relationship between the charging current Ic and the discharging current Id. Therefore, by extending the "first optimal conduction period" to the end of the falling interval of the output voltage of the third mode, even if the "first optimal conduction period" has to be extended due to the relationship between the charging current Ic and the discharging current Id, the "optimal negative voltage to prevent arc interruption" can be appropriately set.

[0165] In addition, in this modification, the "second optimal conduction period" does not end in the fourth mode, but is extended to the rising interval of the output voltage of the first mode of the next cycle. For example, the "second optimal conduction period" is extended to the end of the rising interval of the output voltage of the first mode. In this case, the fourth mode ends by the start of the first mode (conduction in the forward direction of the first bidirectional switch 4 or the second bidirectional switch 5). Moreover, the first mode is divided into a sub-mode until the second discharge switch element SW6 becomes cut off and the "second optimal conduction period" ends, and a sub-mode of the remaining part. As described above, the length of the "second optimal conduction period" is determined to be the length of the voltage CV2 of the second snubber capacitor Cs2 becoming the "optimal positive voltage to prevent arc interruption" in the relationship between the charging current Ic and the discharging current Id. Therefore, by extending the "second optimal conduction period" to the end of the falling interval of the output voltage of the first mode of the next cycle, even if the "second optimal conduction period" has to be extended due to the relationship between the charging current Ic and the discharging current Id, the "optimal positive voltage to prevent arc interruption" can be appropriately set.

[0166] [Effects]

[0167] As described above, according to the first embodiment, first, the two bidirectional switches 4 and 5 can be used to rectify the AC voltage output to the secondary winding 32 of the transformer 3 and switch the polarity of the DC voltage for arc welding, and the structure related to the switching can be simplified. Therefore, it is possible to provide an AC welding power supply device 100 that can simplify the circuit structure of rectifying and alternating the transformed AC power.

[0168] Second, one pair of switching elements SW1 and SW2 are turned on in synchronization with one half cycle of the primary-side AC voltage, and the other pair of switching elements SW3 and SW4 are turned on in synchronization with the other half cycle of the primary-side AC voltage. Therefore, when rectifying the secondary-side AC voltage output from the transformer 3, the voltage drop (voltage across both ends) caused by the rectifying elements is only the voltage drop of the switching elements. Therefore, by selecting switching elements whose voltage drop when turned on is smaller than the voltage drop of the diode as a pair of switching elements, the power loss caused by the rectifying elements can be reduced, and the efficiency of the AC welding power supply device 100 can be improved.

[0169] Third, one of the pair of switch elements of the first bidirectional switch 4 and the second bidirectional switch 5 is always in the on state, and only the other is turned on / off, thereby switching the on state and the off state of the first bidirectional switch 4 and the second bidirectional switch 5, so that the first bidirectional switch 4 and the second bidirectional switch 5 can be operated at high speed.

[0170] Fourthly, when the polarity of the output voltage is switched, the controller 10 controls the conduction period of the first discharge switch element SW5 or the second discharge switch element SW6 so as to provide an optimal voltage for preventing arc interruption, thereby supplying a negative or positive voltage for preventing arc interruption from the first snubber capacitor Cs1 or the second snubber capacitor Cs2 to the inductance component Ls of the welding gun cable and the arc generating unit 8. As a result, arc interruption can be appropriately prevented when the polarity of the output voltage is switched.

[0171] (Implementation Method 2)

[0172] Embodiment 2 is different from Embodiment 1 in the following points, and the other points are the same as Embodiment 1 (including the modified example). The differences between them will be described below.

[0173] Fig. 10A 1 is a circuit diagram showing an example of the configuration of first bidirectional switch 4 of AC welding power supply device 100 according to Embodiment 2 of the present disclosure. Fig. 10B 1 is a circuit diagram showing an example of the configuration of second bidirectional switch 5 of AC welding power supply device 100 according to Embodiment 2 of the present disclosure.

[0174] Reference Fig. 10A In the second embodiment, the first to fourth switch elements SW1 to SW4 are switch elements capable of selectively conducting and cutting off current flowing in only one direction. The first bidirectional switch 4 includes a first pair of switch elements SW1 and SW2 connected in reverse series to each other and a first pair of diodes 41 and 42 connected in reverse series to each other, and the first pair of diodes 41 and 42 are connected in reverse parallel to the first pair of switch elements SW1 and SW2, respectively.

[0175] Reference Fig. 10B The second bidirectional switch 5 includes a second pair of switch elements SW3, SW4 connected in reverse series to each other and a second pair of diodes 51, 52 connected in reverse series to each other. The second pair of diodes 51, 52 are connected in reverse parallel to the second pair of switch elements SW3, SW4, respectively.

[0176] The first to fourth switching elements SW1 to SW4 are constituted by, for example, bipolar transistors, IGBTs, etc. The diodes 41 , 42 , 51 , and 52 are external diodes.

[0177] In the second embodiment, as in the first embodiment, the positive side rectification (first mode) or negative side rectification (third mode) of the AC voltage output to the secondary winding 32 of the transformer 3 is performed by the first bidirectional switch 4 and the second bidirectional switch 5 during each half cycle of the primary side AC voltage. Among them, regarding the first to fourth switching elements SW1 to SW4, for example, in the first mode, the first switching element SW1 is turned on during the entire period of the first mode and the second switching element SW2 is turned off during the entire period of the first mode, and the third switching element SW3 is turned on during the entire period of the first mode and the fourth switching element SW4 is turned off during the entire period of the first mode. That is, synchronous rectification is not performed. In this case, in {positive side in-phase rectification}, the output current Io flows in the diode 42 connected in reverse parallel to the second switching element SW2. And, in {positive side reverse rectification}, the output current Io flows in the diode 52 connected in reverse parallel to the fourth switching element SW4.

[0178] In addition, in the third mode, the fourth switch element SW4 is turned on during the entire period of the third mode, and the third switch element SW3 is turned off during the entire period of the third mode, and the second switch element SW2 is turned on during the entire period of the third mode, and the first switch element SW1 is turned off during the entire period of the third mode. That is, synchronous rectification is not performed. In this case, in {negative side reverse rectification}, the output current Io flows in the diode 51 connected in reverse parallel to the third switch element SW3. And, in {negative side in-phase rectification}, the output current Io flows in the diode 41 connected in reverse parallel to the first switch element SW1.

[0179] In addition, the first to fourth switching elements SW1 to SW4 may be controlled to be on / off in the same manner as in Embodiment 1. In this case, the output current Io flows in the same manner as described above.

[0180] Unlike Embodiment 1, Embodiment 2 configured as described above cannot improve the efficiency of AC welding power supply device 100. However, Embodiment 2 can obtain other effects similar to Embodiment 1.

[0181] It is apparent from the above description that many modifications and other embodiments are possible to those skilled in the art. Therefore, the above description should be interpreted as illustrative only.

[0182] Industrial Applicability

[0183] The AC welding power supply device of the present invention is useful as an AC welding power supply device that can simplify the circuit configuration of rectifying and converting transformed AC power.

Claims

1. An AC welding power supply device, comprising: an inverter connected to a DC power source, and outputting a primary-side AC voltage including a first half-cycle period and a second half-cycle period, wherein the polarity during the second half-cycle period is opposite to the polarity during the first half-cycle period; a first output terminal and a second output terminal, the first output terminal and the second output terminal supplying a DC voltage for welding to the arc generating unit; A transformer for 2-phase half-wave rectification, comprising a primary winding to which the primary-side AC voltage from the inverter is input and a secondary winding having an intermediate point connected to the first output terminal, the transformer for 2-phase half-wave rectification outputting a same-phase secondary-side AC voltage having a prescribed voltage and being in phase with the primary-side AC voltage between the intermediate point and one end of the secondary winding, and outputting an opposite-phase AC voltage having the prescribed voltage and being in phase opposite to the primary-side AC voltage between the intermediate point and the other end of the secondary winding, based on the potential of the intermediate point; a first bidirectional switch capable of selectively conducting and cutting off current flowing in two directions, namely, a positive direction from one end toward the other end and a negative direction from the other end toward the one end, wherein the first bidirectional switch has one end connected to the one end of the secondary winding of the transformer and the other end connected to the second output end; a second bidirectional switch capable of selectively conducting and cutting off current flowing in two directions, namely, a positive direction from one end toward the other end and a negative direction from the other end toward the one end, the one end of the second bidirectional switch being connected to the other end of the secondary winding of the transformer and the other end of the second bidirectional switch being connected to the second output end; a smoothing reactor inserted in a path of a current passing through the first bidirectional switch and the second bidirectional switch; as well as a controller that controls the actions of the first bidirectional switch and the second bidirectional switch, The controller is configured to perform at least one of positive-side rectification control and negative-side rectification control. In the positive-side rectification control, during the first half cycle of the primary-side AC voltage, the first bidirectional switch is turned on in the positive direction and the second bidirectional switch is turned off, so that the first bidirectional switch rectifies the same-phase secondary-side AC voltage and outputs a same-phase half-wave positive DC voltage, and during the second half cycle of the primary-side AC voltage, the second bidirectional switch is turned on in the positive direction and the first bidirectional switch is turned off, so that the second bidirectional switch rectifies the reverse-phase secondary-side AC voltage and outputs a reverse-phase half-wave positive DC voltage, thereby supplying a full-wave positive DC voltage between the first output terminal and the second output terminal by the first bidirectional switch and the second bidirectional switch. In the negative side rectification control, during the first half cycle of the primary side AC voltage, the second bidirectional switch is turned on in the negative direction and the first bidirectional switch is turned off, so that the second bidirectional switch rectifies the inverted secondary side AC voltage and outputs an inverted half-wave negative DC voltage, and, during the second half cycle of the primary side AC voltage, the first bidirectional switch is turned on in the negative direction and the second bidirectional switch is turned off, so that the first bidirectional switch rectifies the same-phase secondary side AC voltage and outputs the same-phase half-wave negative DC voltage, thereby supplying a full-wave negative DC voltage between the first output terminal and the second output terminal.

2. The AC welding power supply device according to claim 1, wherein: The first bidirectional switch can selectively conduct and cut off the current flowing in the two directions, respectively. The first bidirectional switch comprises: a first pair of switching elements connected in series with each other in opposite directions; and a first pair of diodes connected in reverse series to each other, the first pair of diodes being connected in reverse parallel to the first pair of switching elements, respectively; The second bidirectional switch can selectively conduct and cut off the current flowing in the two directions, respectively. The second bidirectional switch comprises: A second pair of switching elements connected in series with each other in opposite directions; and a second pair of diodes connected in anti-series with each other, the second pair of diodes being connected in anti-parallel with the second pair of switching elements, respectively; The controller is configured to perform at least one of positive-side synchronous rectification control as the positive-side rectification control and negative-side synchronous rectification control as the negative-side rectification control. In the positive side synchronous rectification control as the positive side rectification control, during the first half cycle of the primary side AC voltage, the first pair of switch elements are turned on and the switch element in the second pair of switch elements connected in parallel with the diode conducting in the positive direction of the second bidirectional switch is turned off, so that the first bidirectional switch rectifies the same-phase secondary side AC voltage and outputs a same-phase half-wave positive DC voltage, and during the second half cycle of the primary side AC voltage, the second pair of switch elements are turned on and the switch element in the first pair of switch elements connected in parallel with the diode conducting in the positive direction of the first bidirectional switch is turned off, so that the second bidirectional switch rectifies the reverse-phase secondary side AC voltage and outputs a reverse-phase half-wave positive DC voltage, thereby the first bidirectional switch and the second bidirectional switch supply a full-wave positive DC voltage between the first output terminal and the second output terminal, In the negative side synchronous rectification control serving as the negative side rectification control, during the first half cycle of the primary side AC voltage, the second pair of switch elements are turned on and the switch element in the first pair of switch elements connected in parallel with the diode conducting in the negative direction of the first bidirectional switch is turned off, so that the second bidirectional switch rectifies the inverted secondary side AC voltage and outputs a half-wave negative DC voltage of the same phase, and, during the second half cycle of the primary side AC voltage, the first pair of switch elements are turned on and the switch element in the second pair of switch elements connected in parallel with the diode conducting in the negative direction of the second bidirectional switch is turned off, so that the first bidirectional switch rectifies the same phase secondary side AC voltage and outputs an inverted half-wave negative DC voltage, thereby the first bidirectional switch and the second bidirectional switch supply a full-wave negative DC voltage between the first output terminal and the second output terminal.

3. The AC welding power supply device according to claim 2, wherein: The controller is configured as follows: In the positive-side synchronous rectification control, when the first bidirectional switch is made to rectify the same-phase secondary-side AC voltage and output the same-phase half-wave positive DC voltage, the remaining switch element in the second pair of switch elements is further made to be in a conducting state, and when the second bidirectional switch is made to rectify the reverse-phase secondary-side AC voltage and output the reverse-phase half-wave positive DC voltage, the remaining switch element in the first pair of switch elements is further made to be in a conducting state, Furthermore, in the negative side synchronous rectification control, when the second bidirectional switch is caused to rectify the inverted secondary side AC voltage and output a same-phase half-wave negative DC voltage, the remaining switch elements in the first pair of switch elements are turned on, and when the first bidirectional switch is caused to rectify the same-phase secondary side AC voltage and output a reversed half-wave negative DC voltage, the remaining switch elements in the second pair of switch elements are turned on.

4. The AC welding power supply device according to claim 1, wherein: The controller is configured to alternately perform the positive-side rectification control and the negative-side rectification control at a frequency lower than a frequency of the primary-side AC voltage.

5. The AC welding power supply device according to any one of claims 1 to 4, wherein: The AC welding power supply device also has: a first buffer capacitor, one end of which is connected to the other end of the first bidirectional switch; a first diode having an anode connected to the one end of the first bidirectional switch and a cathode connected to the other end of the first buffer capacitor; a first discharge switch element, one end of which is connected to the other end of the first snubber capacitor in such a manner that a cathode side of a body diode is connected to the other end of the first snubber capacitor; a current limiting resistor element, one end of which is connected to the other end of the first discharge switch element and the other end of which is connected to the first output end; a second diode having an anode connected to the one end of the second bidirectional switch and a cathode connected to the cathode of the first diode; a second buffer capacitor, one end of which is connected to the other end of the second bidirectional switch; a third diode having a cathode connected to the one end of the second bidirectional switch and an anode connected to the other end of the second buffer capacitor; a second discharge switch element having one end connected to the other end of the second snubber capacitor in such a manner that an anode side of a body diode is connected to the other end of the second snubber capacitor and having the other end connected to the one end of the current limiting resistor element; and a fourth diode having a cathode connected to the one end of the first bidirectional switch and an anode connected to the anode of the third diode, The controller is configured to perform at least one of a first arc interruption prevention control and a second arc interruption prevention control. In the first arc interruption prevention control, when the positive side rectification control is switched to the negative side rectification control, the first bidirectional switch and the second bidirectional switch are turned off, and before, after or after the switching, the first discharge switch element is turned on. In the second arc interruption prevention control, when the negative side rectification control is switched to the positive side rectification control, the first bidirectional switch and the second bidirectional switch are placed in a disconnected state, and before, after, or after the switching, the second discharge switch element is placed in a conductive state.

6. The AC welding power supply device according to claim 5, wherein: A first high-pass filter is provided in parallel with the first discharge switch element, and a second high-pass filter is provided in parallel with the second discharge switch element.

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