Power supply device for alternating current welding

Abstract

To simplify a circuit configuration for rectifying and converting high-frequency power that has been transformed.SOLUTION: A power supply unit 100 for alternating current welding includes a direct current 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 10 performs at least one of a positive-side rectification control and a negative side rectification control. The positive-side rectification control is for supplying full-wave positive direct current voltage between a first output terminal 6 and a second output terminal 7 by first and second bidirectional switches 4, 5 rectifying a two-phase alternating voltage output from a secondary winding 32 of a transformer 3. The negative side rectification control is for supplying full-wave negative direct current voltage between the first output terminal 6 and the second output terminal 7 by the first and second bidirectional switches 4, 5 rectifying the two-phase alternating voltage output from the secondary winding 32 of the transformer 3.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an AC welding power supply device. [Background technology]

[0002] Power supply devices for AC welding have been known for some time now. For example, a welding power supply device including 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 torch is known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-089093 A (see, in particular, FIG. 1) Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above welding power supply has two circuits, a rectifier circuit and an inverter circuit, on the secondary side of the transformer, and there is a problem in that the circuit configuration for rectifying and converting the transformed AC power to AC is complex.

[0005] The present invention has been made to solve the above-mentioned problems, and has an object to provide an AC welding power supply device that can simplify the circuit configuration for rectifying and converting transformed AC power to AC. [Means for solving the problem]

[0006] In order to achieve the above object, an AC welding power supply device according to an aspect of the present disclosure includes an inverter connected to a DC power supply and outputting a primary AC voltage including a first half-cycle period and a second half-cycle period of opposite polarity to the first half-cycle period, first and second output terminals supplying a DC voltage for welding to an arc generating section, a primary winding to which the primary AC voltage from the inverter is input, and a secondary winding having a midpoint connected to the first output terminal, and a predetermined potential is applied between the midpoint and one end of the secondary winding with respect to the potential of the midpoint. a two-phase half-wave rectifier transformer having a predetermined voltage and outputting an in-phase secondary side AC voltage having the same phase as the primary side AC voltage, and outputting a negative-phase AC voltage having the predetermined voltage and having a negative phase to the primary side AC voltage between the intermediate point and the other end of the secondary winding; a first bidirectional switch capable of selectively conducting and blocking a current flowing in a positive direction from one end to the other end and a negative direction from the other end to the one end, the first bidirectional switch having one end connected to the one end of the secondary winding of the transformer and the other end connected to the second output terminal; a second bidirectional switch having one end connected to the other end of the secondary winding of the transformer and the other end connected to the second output terminal, a smoothing reactor inserted in a current path passing through the first and second bidirectional switches, and a controller for controlling operations of the first and second bidirectional switches, the controller controlling the first bidirectional switch to a conductive state in the positive direction and the second bidirectional switch to a smoothing reactor in the first half-cycle period of the primary side AC voltage, a positive side rectification control for causing the first bidirectional switch to rectify the in-phase secondary side AC voltage to output an in-phase half-wave positive DC voltage by turning on the first bidirectional switch and turning on the second bidirectional switch and turning on the first bidirectional switch and turning on the second bidirectional switch and turning on the first bidirectional switch and turning on the second bidirectional switch and turning on the second bidirectional switch and turning on the first bidirectional switch and turning on the second bidirectional switch and turning on the second bidirectional switch and turning on the second bidirectional switch and turning on the first bidirectional switch and turning on the second bidirectional switch and turning on the second bidirectional switch and turning on the second bidirectional switch and turning on theand negative side rectification control in which, during the first half-cycle period of the primary side AC voltage, the second bidirectional switch is brought into a conducting state in the negative direction and the first bidirectional switch is brought into a cut-off state, so that the second bidirectional switch rectifies the negative-phase secondary side AC voltage and outputs a negative-phase half-wave negative DC voltage, and, during the second half-cycle period of the primary side AC voltage, the first bidirectional switch is brought into a conducting state in the negative direction and the second bidirectional switch is brought into a cut-off state, so that the first bidirectional switch rectifies the in-phase secondary side AC voltage and outputs an in-phase half-wave negative DC voltage, so that the first and second bidirectional switches supply a full-wave negative DC voltage between the first output terminal and the second output terminal. Effect of the Invention

[0007] The present invention has an effect of providing an AC welding power supply device capable of simplifying the circuit configuration for rectifying and converting transformed AC power to AC. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a circuit diagram showing an example of the configuration of an AC welding power supply device according to a first embodiment of the present disclosure. [Diagram 2] FIG. 2 is a flow chart showing the contents of the rectification and polarity control of the first AC welding by the controller of FIG. [Diagram 3] FIG. 3 is a waveform diagram showing the waveform of an output current and the waveform of a gate signal to a bidirectional switch. [Figure 4] FIG. 4 is a diagram showing the input and output current flows in the circuit of FIG. 1 in the first mode of positive side common-phase rectification. [Diagram 5] FIG. 5 is a diagram showing the flow of input current and output current in the circuit of FIG. 1 in positive side negative phase rectification in the first mode. [Figure 6] FIG. 6 is a diagram showing the flow of the charging current and discharging current in the circuit of FIG. 1 when the polarity is switched from positive to negative in the second mode. [Figure 7]FIG. 7 is a diagram showing the flow of the input current and the output current in the negative side anti-phase rectification of the third mode in the circuit of FIG. [Figure 8] FIG. 8 is a diagram showing the input and output current flows in the circuit of FIG. 1 in the negative side common-phase rectification of the third mode. [Figure 9] FIG. 9 is a diagram showing the flow of the charging current and discharging current in the circuit of FIG. 1 when the polarity is switched from negative to positive in the fourth mode. [Figure 10A] FIG. 10A is a circuit diagram showing an example of the configuration of a first bidirectional switch of an AC welding power supply device according to Embodiment 2 of the present disclosure. [Figure 10B] FIG. 10B is a circuit diagram showing an example of the configuration of the second bidirectional switch of the AC welding power supply device according to the second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] According to one aspect of the present disclosure, there is provided an AC welding power supply device comprising: 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 of opposite polarity to the first half-cycle period; a first output terminal and a second output terminal supplying a DC voltage for welding to an arc generating section; a primary winding to which the primary AC voltage from the inverter is input; and a secondary winding having a midpoint connected to the first output terminal, and a secondary winding having a predetermined voltage between the midpoint and one end of the secondary winding, the secondary winding being in phase with the primary AC voltage, with the potential of the midpoint as a reference. a two-phase half-wave rectifier transformer that outputs an in-phase secondary side AC voltage of the predetermined voltage and outputs an anti-phase AC voltage that is anti-phase to the primary side AC voltage between the intermediate point and the other end of the secondary winding; a first bidirectional switch that is capable of selectively conducting and blocking a current flowing in a positive direction from one end to the other end and a negative direction from the other end to the one end, the first bidirectional switch having one end connected to the one end of the secondary winding of the transformer and the other end connected to the second output terminal; a second bidirectional switch having one end connected to the other end of the secondary winding of the transformer and the other end connected to the second output terminal, a smoothing reactor inserted in a path of a current passing through the first and second bidirectional switches, and a controller for controlling operations of the first and second bidirectional switches, wherein the controller controls the first bidirectional switch to be in a conductive state in the positive direction and the second bidirectional switch to be in a cut-off state during the first half-cycle period of the primary side AC voltage, a positive side rectification control for rectifying the in-phase secondary side AC voltage to output an in-phase half-wave positive DC voltage, and for causing the second bidirectional switch to be in a conductive state in the positive direction and the first bidirectional switch to be in a cut-off state during the second half-cycle period of the primary side AC voltage, thereby causing the second bidirectional switch to rectify the negative-phase secondary side AC voltage to output a negative-phase half-wave positive DC voltage, whereby the first and second bidirectional switches supply a full-wave positive DC voltage between the first output terminal and the second output terminal; andand a negative-side rectification control in which the second bidirectional switch is brought into a conducting state in the negative direction and the first bidirectional switch is brought into a cut-off state, so that the second bidirectional switch rectifies the negative-phase secondary side AC voltage to output a negative-phase half-wave negative DC voltage, and in the second half-cycle period of the primary side AC voltage, the first bidirectional switch is brought into a conducting state in the negative direction and the second bidirectional switch is brought into a cut-off state, so that the first bidirectional switch rectifies the in-phase secondary side AC voltage to output an in-phase half-wave negative DC voltage, thereby causing the first and second bidirectional switches to supply a full-wave negative DC voltage between the first output terminal and the second output terminal. Here, "bringing a bidirectional switch into a conducting state in the positive direction" means that the bidirectional switch is "allowed to allow a current to flow in the positive direction", and "bringing a bidirectional switch into a conducting state in the negative direction" means that the bidirectional switch is "allowed to allow a current to flow in the negative direction".

[0010] According to this configuration, the first and second bidirectional switches perform positive side rectification or negative side rectification of the AC voltage output to the secondary winding of the transformer for each half cycle period of the primary AC voltage. The positive side rectification supplies a positive DC voltage between the first output terminal and the second output terminal, and the negative side rectification supplies a negative DC voltage 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 whether to rectify the in-phase secondary side AC voltage or the negative phase secondary side AC voltage in one half cycle period by one bidirectional switch. Therefore, the rectification of the AC voltage output to the secondary winding of the transformer and the polarity switching of the DC voltage for arc welding can be performed using two bidirectional switches, and the configuration related to the switching can be simplified. Therefore, it is possible to provide an AC welding power supply device capable of simplifying the circuit configuration for rectifying and converting the transformed AC power to AC.

[0011] The first bidirectional switch includes a first pair of switching elements connected in anti-series to each other, capable of selectively conducting and blocking currents flowing in both directions, and a first pair of diodes connected in anti-parallel to the first pair of switching elements, respectively, and connected in anti-series to each other. The second bidirectional switch includes a second pair of switching elements connected in anti-series to each other, capable of selectively conducting and blocking currents flowing in both directions, and a second pair of diodes connected in anti-parallel to the second pair of switching elements, respectively, and connected in anti-series to each other. The controller brings the first pair of switching elements into a conductive state and brings into a cut-off state a switching element of the second pair of switching elements that is parallel to a diode of the second bidirectional switch that is conductive in the positive direction, during the first half-cycle period of the primary side AC voltage, to cause the first bidirectional switch to rectify the in-phase secondary side AC voltage to output an in-phase half-wave positive DC voltage, and controls the second bidirectional switch to output an in-phase half-wave positive DC voltage. a positive-side synchronous rectification control as the positive-side rectification control, in which, during a half-cycle period, the second pair of switching elements are brought into a conductive state, and a switching element of the first pair of switching elements that is parallel to a diode of the first bidirectional switch that is conductive in the positive direction is brought into a cut-off state, so that the second bidirectional switch rectifies the negative-phase secondary side AC voltage and outputs a negative-phase half-wave positive DC voltage, thereby causing the first and second bidirectional switches to supply a full-wave positive DC voltage between the first output terminal and the second output terminal; and during the first half-cycle period of the primary side AC voltage, the second pair of switching elements are brought into a conductive state, and a switching element of the first pair of switching elements that is parallel to a diode of the first bidirectional switch that is conductive in the negative direction is brought into a cut-off state, so that the second bidirectional switch rectifies the negative-phase secondary side AC voltage and outputs an in-phase half-wave negative DC voltage, and during the second half-cycle period of the primary side AC voltage, the first pair of switching elements are brought into a conductive state,The negative-side rectification may be performed by at least one of negative-side synchronous rectification, in which a switching element of the second pair of switching elements that is parallel to a diode of the second bidirectional switch that is conductive in the negative direction is turned off to cause the first bidirectional switch to rectify the in-phase secondary side AC voltage and output an inverse-phase half-wave negative DC voltage, thereby causing the first and second bidirectional switches to supply a full-wave negative DC voltage between the first output terminal and the second output terminal.

[0012] According to this configuration, one pair of switching elements is rendered conductive in synchronization with one half-cycle period of the primary AC voltage, and the other pair of switching elements is rendered conductive in synchronization with the other half-cycle period of the primary AC voltage. Therefore, the voltage drop (voltage across both ends) caused by the rectifying elements when rectifying the secondary AC voltage output from the transformer is the voltage drop of the switching elements alone. Therefore, by selecting, as the pair of switching elements, switching elements whose voltage drop when conductive is smaller than the voltage drop of a diode, it is possible to reduce power loss caused by the rectifying elements and improve the efficiency of the AC welding power supply device.

[0013] The controller may be configured to: further bring the remaining switching elements of the second pair of switching elements into a conductive state when, in the positive-side rectification control, the first bidirectional switch is caused to rectify the in-phase secondary side AC voltage to output an in-phase half-wave positive DC voltage; further bring the remaining switching elements of the first pair of switching elements into a conductive state when, in the positive-side rectification control, the second bidirectional switch is caused to rectify the negative-phase secondary side AC voltage to output a negative-phase half-wave positive DC voltage; and further bring the remaining switching elements of the first pair of switching elements into a conductive state when, in the negative-side synchronous rectification, the second bidirectional switch is caused to rectify the negative-phase secondary side AC voltage to output an in-phase half-wave negative DC voltage; and further bring the remaining switching elements of the first pair of switching elements into a conductive state when, in the negative-side synchronous rectification, the second bidirectional switch is caused to rectify the negative-phase secondary side AC voltage to output an in-phase half-wave negative DC voltage;

[0014] According to this configuration, one of the pair of switching elements of the bidirectional switch is always kept in an on state and only the other is turned on and off, thereby switching between a conductive state and a cut-off state of the bidirectional switch, so that the first bidirectional switch and the second bidirectional switch can be operated at high speed.

[0015] 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. With this configuration, AC welding can be performed.

[0016] The AC welding power supply device includes a first snubber capacitor having one end 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 snubber capacitor, a first discharge switching element having one end connected to the other end of the first snubber capacitor such that a cathode side of a body diode is connected to the other end of the first snubber capacitor, a current limiting resistor having one end connected to the other end of the first discharge switching element and the other end connected to the first output terminal, 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 snubber capacitor having one end connected to the other end of the second bidirectional switch, and 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 snubber capacitor, the first and second bidirectional switches are brought into an interrupted state when the positive side control is switched to the negative side control, and the first discharge switching element is brought into a conductive state during a period before, during, or after the interruption; and the second arc interruption prevention control is performed when the negative side synchronous rectification control is switched to the positive side synchronous rectification control, and the first and second bidirectional switches are brought into an interrupted state when the negative side synchronous rectification control is switched to the positive side synchronous rectification control, and the second discharge switching element is brought into a conductive state during a period before, during, or after the interruption.

[0017] According to this configuration, when the positive side rectification control is switched to the negative side rectification control in the first arc interruption prevention control, if the first and second bidirectional switches are turned off, a surge voltage is generated by the magnetic energy stored in the inductance component of the torch cable of the welding torch, which is the arc generating part, and this surge voltage causes a current to flow from the first output end through the smoothing reactor to the midpoint of the secondary winding of the transformer, where it is divided, one divided current passes through one end of the secondary winding and the first diode to the other end of the first snubber capacitor, and the other divided current passes through the other end of the secondary winding and the second diode to the other end of the first snubber capacitor, where both divided currents join together, and a charging current flows to the first snubber capacitor so that the joined current returns to the arc generating part through the first snubber capacitor and the second output end. Therefore, the charging current caused by this surge voltage stores energy that would conventionally be consumed by a resistor element in the first snubber capacitor. On the other hand, before and after this charging current flows, if the first discharge switching element is turned on, the first snubber capacitor discharges, and the discharge current flows back to the first snubber capacitor through the first discharge switching element, the current limiting resistor, the first output terminal, the arc generating portion, and the second output terminal. Since the direction of this discharge current is opposite to the direction of the charging current caused by the surge voltage, the voltage of the first snubber capacitor is determined by the relationship between the charging current and the discharge current. Therefore, by controlling the conduction period of the first discharge switching element so as to obtain an optimal voltage for preventing arc interruption, the first snubber capacitor can supply a negative voltage for preventing arc interruption to the inductance component of the torch cable and the arc generating portion. In the second arc interruption prevention control, too, a positive voltage for preventing arc interruption can be supplied from the second snubber capacitor to the inductance component of the torch cable and the arc generating portion according to the same principle as in the first arc interruption prevention control.

[0018] A first high-pass filter may be provided in parallel with the first discharge switching element, and a second high-pass filter may be provided in parallel with the second discharge switching element.

[0019] With this configuration, the first high-pass filter can protect the first discharge switching element from a surge voltage caused by turning off the first discharge switching element, and the second high-pass filter can protect the second discharge switching element from a surge voltage caused by turning off the second discharge switching element.

[0020] Hereinafter, specific embodiments of the present disclosure will be described with reference to the drawings. In the following, the same or corresponding elements are denoted by the same reference numerals throughout all the drawings, and their repeated description will be omitted. In addition, since the following drawings are for explaining the present disclosure, elements unrelated to the present disclosure may be omitted, dimensions may be inaccurate due to exaggeration, or may be simplified, and the shapes of corresponding elements in multiple drawings may not match. In addition, the present disclosure is not limited to the following embodiments.

[0021] (Embodiment 1)

[0022] [composition] FIG. 1 is a circuit diagram showing an example of the configuration of an AC welding power supply device 100 according to the first embodiment of the present disclosure.

[0023] 1, the AC welding power supply device 100 includes, as main components, 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. These elements will be described in detail below.

[0024] <DC power supply 1> There are no particular limitations on the DC power supply 1 as long as it outputs a DC voltage. The DC power supply may be, for example, a rectifier that rectifies AC power, various types of batteries or rechargeable batteries, a DC generator, etc.

[0025] <Inverter 2> The inverter 2 is connected to the DC power source 1, and outputs a primary side AC voltage of a square wave including a first half cycle period and a second half cycle period under the control of the controller 10. This primary side AC voltage is a high-frequency voltage having a frequency of, for example, 20 to 100 kHz. The inverter 2 is not particularly limited as long as it generates an AC voltage from the DC power source 1. The inverter 2 may be, for example, a single-phase full-bridge inverter or a single-phase half-bridge inverter.

[0026] The inverter 2 is a single-phase full-bridge inverter, and a pair of arms are connected in parallel to both ends of the DC power source 1. In one arm, a high-side switching element SW21 and a low-side switching element SW22 are connected in series. In the other arm, a high-side switching element SW23 and a low-side switching element SW24 are connected in series. The connection points of the pairs of switching elements in each pair of arms form output terminals 21 and 22 of the inverter. A pair of switching elements SW21 and SW24 and a pair of switching elements SW23 and SW22 are alternately conducted, so that a primary side AC voltage of a rectangular wave is output from the output terminals 21 and 22. This primary side AC voltage includes a first half cycle period and a second half cycle period of mutually opposite polarities. The "polarity" being different between the first and second half-cycle periods means that the potential of one of the output terminals 21, 22 is higher or lower than the potential of the other output terminal when the potential of the other output terminal is used as a reference, and this is different between the first and second half-cycle periods. Here, for convenience, the first and second half-cycle periods of the primary side AC voltage are defined by the direction of the current flowing through the primary winding 31 of the transformer 3, as described later.

[0027] <Transformer 3> The transformer 3 is, for example, a two-phase half-wave rectifier transformer. Specifically, the transformer 3 has a primary winding 31 and a secondary winding 32 having a midpoint 32c. The turn ratio of the primary winding 31 to the secondary winding 32 is determined appropriately. The transformer 3 is, for example, a depolarizing transformer. Note that the transformer 3 may be an additive polarity transformer. In this case, the connection of the secondary winding 32 to the first and second bidirectional switches 4 and 5 may be reversed to that of the depolarizing transformer. Therefore, in the transformer 3, the polarity of the voltage induced between one end 31a and the other end 31b of the primary winding 31 when the potential of the other end 31b is used as a reference, the polarity of the voltage induced between one end 32a and the midpoint 32c of the secondary winding 32 when the potential of the midpoint 32c is used as a reference, and the polarity of the voltage induced between the midpoint 32c and the other end 32b of the secondary winding 32 when the potential of the other end 32b is used as a reference are all the same. Therefore, when the potential of the midpoint 32c is used as a reference, the polarity of the voltage induced between the midpoint 32c and the other end 32b of the secondary winding 32 is opposite to the polarity of the voltage induced between the midpoint 32c and one end 32a of the secondary winding 32.

[0028] 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. Alternatively, one end 31a of the primary winding 31 may be connected to the other output end 22 of the inverter 2 via a capacitor, and the other end 31b of the primary winding 31 may be connected to one output end 21 of the inverter 2. In addition, a midpoint 32c of the secondary winding 32 is connected to the first output end 6 via a smoothing reactor 9.

[0029] When a primary AC voltage is input between both ends 31a, 31b of the primary winding 31 from a pair of output terminals 21, 22 of the inverter 2, the transformer 3 outputs an in-phase secondary AC voltage that has a predetermined voltage corresponding to the winding ratio and is in phase with the primary AC voltage between the midpoint 32c of the secondary winding 32 and one end 32a, with the potential of the midpoint 32c of the secondary winding 32 as a reference, and outputs an anti-phase AC voltage that has a predetermined voltage corresponding to the winding ratio and is in phase with the primary AC voltage between the midpoint 32c and the other end 32b of the secondary winding.

[0030] Here, within one cycle period of the primary side AC voltage, the half-cycle period during which current flows from one end 31a to the other end 31b in the primary winding 31 of the transformer 3 is defined as the first half-cycle period, and the half-cycle period during which current flows from the other end 31b to one end 31a in the primary winding 31 of the transformer 3 is defined as the second half-cycle period.

[0031] <First and second bidirectional switches 4, 5> Both the first and second bidirectional switches 4 and 5 have a function of selectively conducting and blocking a current flowing in both directions, that is, in the positive direction from one end to the other end and the negative direction from the other end to the one end.

[0032] Specifically, the first bidirectional switch 4 includes a first pair of switching elements SW1, SW2 connected in anti-series to each other, and a first pair of diodes 41, 42 connected in anti-parallel to the first pair of switching elements SW1, SW2 and connected in anti-series to each other. Each of the first pair of switching elements SW1, SW2 is called a first switching element SW1 and a second switching 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 switching element SW1 is connected to one end 32a of the secondary winding 32 of the transformer 3, and the other end of the first switching element SW1 is connected to one end of the second switching element SW2. The other end of the second switching element SW2 is connected to the second output terminal 7.

[0033] The second bidirectional switch 5 includes a second pair of switching elements SW3, SW4 connected in anti-series to each other, and a first pair of diodes 51, 52 connected in anti-parallel to the second pair of switching elements SW3, SW4 and connected in anti-series to each other. The individual switching elements of the second pair of switching elements SW3, SW4 are called a third switching element SW3 and a fourth switching element SW4. The second bidirectional switch 5 has one end connected to the other end 32b of the secondary winding 32 of the transformer 3 and the other end connected to the second output terminal 7. Specifically, one end of the third switching 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 switching element SW3 is connected to one end of the fourth switching element SW4. The other end of the fourth switching element SW4 is connected to the second output terminal 7.

[0034] {First to fourth switching elements SW1 to SW4} The first to fourth switching elements SW1 to SW4 may be semiconductor switching elements that can selectively conduct and cut off a current flowing in at least one direction. Examples of semiconductor switching elements that can selectively conduct and cut off only a current flowing in one direction include bipolar transistors and IGBTs (Insulated Gate Bipolar Transistors).

[0035] Examples of switching elements that can selectively conduct and cut off a current flowing in both directions include field effect transistors (FETs), such as MOSFETs, MESFETs, and JFETs.

[0036] <<Inverse series connection of switching elements>> The "anti-series connection" of switching elements means that two switching elements (more precisely, two semiconductor switching elements) are connected in series with each other so that the directions of voltage application between a pair of main terminals are opposite to each other when used alone. Specifically, for bipolar transistors, it means that two bipolar transistors are connected in series with each other so that their emitters or collectors are connected. For FETs, it means that two FETs are connected in series with each other so that their sources or drains are connected. In MOSFETs and MESFETs, the main terminal of a pair of main terminals that is connected (conducting) with the control terminal (gate) is the source. The channel type of MOSFETs and MESFETs may be either N-channel type or P-channel type.

[0037] {Diodes 41, 42, 51, 52} The individual diodes 41, 42, 51, and 52 may be diodes (hereinafter, referred to as external diodes) that are separate from the first to fourth switching elements SW1 to SW4, or may be body diodes formed inside the first to fourth switching elements SW1 to SW4. The body diodes may be parasitic diodes or may be intentionally designed diodes.

[0038] Examples of external diodes include rectifier diodes, switching diodes, fast recovery diodes, and Schottky diodes.

[0039] <Inverse parallel connection of diodes> The "inverse-parallel connection" of a diode to a switching element means that the diode is connected in parallel to the switching element so that the forward direction of the diode is opposite to the direction in which a voltage is applied across a pair of main terminals when the switching element is used alone.

[0040] <<Inverse series connection of diodes>> "Anti-series" diodes means that two diodes are connected in series with each other, with their forward currents reversed.

[0041] {Operation of the first and second bidirectional switches 4, 5} Under the control of the controller 10, the first bidirectional switch 4 rectifies the in-phase secondary side AC voltage output from the transformer 3 during a first half-cycle period of the primary side AC voltage to output an in-phase half-wave positive DC voltage, and rectifies the in-phase secondary side AC voltage output from the transformer 3 during a second half-cycle period of the primary side AC voltage to output an in-phase half-wave negative DC voltage.

[0042] Under the control of the controller 10, the second bidirectional switch 5 rectifies the negative-phase secondary side AC voltage output from the transformer 3 during a first half-cycle period of the primary side AC voltage to output a negative-phase half-wave negative DC voltage, and rectifies the negative-phase secondary side AC voltage output from the transformer 3 during a second half-cycle period of the primary side AC voltage to output a negative-phase half-wave positive DC voltage.

[0043] {Specific configuration examples of the first to fourth switching elements SW1 to SW4} Here, the first to fourth switching elements SW1 to SW4 are switching elements that can selectively conduct and cut off a current that flows in both directions. A configuration in which the first to fourth switching elements SW1 to SW4 are switching elements that can selectively conduct and cut off a current that flows in only one direction will be described in the second embodiment described later.

[0044] The first to fourth switching elements SW1 to SW4 are, for example, composed of MOSFETs. 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. 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 end 7. The diodes 41 and 42 are respectively composed of the body diodes of the first switching element SW1 and the body diodes 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. 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 end 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.

[0045] <First and second output terminals 6, 7> The first and second output terminals 6, 7 are output terminals of the AC welding power supply device 100 for supplying a direct current voltage for welding to the arc generating unit 8. The first output terminal 6 is connected to the workpiece. The base end of a torch cable having a welding torch connected to its tip is connected to the second output terminal 7. Reference character Ls indicates the inductance component of this torch cable. An arc is generated between the workpiece and the welding torch. In other words, the workpiece and the welding torch constitute the arc generating unit 8.

[0046] Specifically, the first and second output terminals 6, 7 supply the full-wave positive DC voltage or full-wave negative DC voltage output from the first and second bidirectional switches 4, 5 to the arc generating unit 8 as a DC voltage for welding.

[0047] <Smoothing reactor 9> The smoothing reactor 9 is inserted in the path of a current passing through the first and second bidirectional switches 4 and 5. The smoothing reactor 9 is inserted, for example, between the midpoint 32c of the secondary winding 32 of the transformer 3 and the first output port 6. Note that 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.

[0048] <Arc interruption prevention circuit> The arc interruption prevention circuit includes a first snubber capacitor Cs1, a second snubber capacitor Cs2, a first discharge switching element SW5, a second discharge switching element SW6, first to fourth diodes D1 to D4, a current limiting resistor R1, and first and second high-pass filters Hf1, Hf2.

[0049] The first snubber capacitor Cs1 has one end connected to the other end of the first bidirectional switch 4. The first diode D1 has an anode connected to the one end of the first bidirectional switch 4 and a cathode connected to the other end of the first snubber capacitor Cs1.

[0050] One end of the first discharge switching element SW5 is connected to the other end of the first snubber capacitor Cs1. In this case, the cathode side of a diode 61 connected in anti-parallel to the first discharge switching element SW5 is connected to the other end of the first snubber capacitor Cs1. The first discharge switching element SW5 may be composed of, for example, a bipolar transistor, an IGBT, or a FET. Here, the first discharge switching element SW5 is composed of an IGBT.

[0051] The current-limiting resistor R1 has one end connected to the other end of the first discharge switching element SW5 and the other end connected to the second output port 7. The second diode D2 has an anode connected to the one end of the second bidirectional switch 5 and a cathode connected to the cathode of the first diode D1. The current-limiting resistor R1 is a resistor for limiting a discharge current Id, which will be described later.

[0052] The second snubber capacitor Cs2 has one end connected to the other end of the second bidirectional switch 5. The third diode D3 has a cathode connected to the one end of the second bidirectional switch 5 and an anode connected to the other end of the second snubber capacitor Cs2.

[0053] The second discharge switching element SW6 has one end connected to the other end of the second snubber capacitor Cs2 and the other end connected to the one end of the current limiting resistor R1. In this case, the anode side of the diode 62 connected in anti-parallel to the second discharge switching element SW6 is connected to the other end of the second snubber capacitor. The second discharge switching element SW6 may be formed of, for example, a bipolar transistor, an IGBT, or a FET. Here, the second discharge switching element SW5 is formed of an IGBT.

[0054] <First and second high-pass filters Hf1, Hf2> The AC welding power supply device 100 further includes first and second high-pass filters Hf1 and Hf2 connected in parallel to the first and second discharge switching elements SW5 and SW6, respectively. The first and second high-pass filters Hf1 and Hf2 are snubber circuits for the first and second discharge switching elements SW5 and SW6, respectively. The first high-pass filter Hf1 is composed of a snubber resistor element R2 and a third snubber capacitor Cs3 connected in series to each other. The second high-pass filter Hf2 is composed of a snubber resistor element R3 and a fourth snubber capacitor Cs4 connected in series to each other.

[0055] <Controller 10> 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-SW24 of the inverter 2, the first to fourth switching elements SW1-SW4 of the first and second bidirectional switches 4, 5, and the first and second discharge switching elements SW5, SW6.

[0056] The controller 10 is configured, for example, by a computing unit having a processor and a memory. Specifically, this computing unit is configured, for example, by 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 configured by a single computing unit that performs centralized control, or may be configured by multiple computing units that perform distributed control.

[0057] In other words, the functions of the controller 10 can be performed using circuits or processing circuitry, including general purpose processors, special purpose processors, integrated circuits, Application Specific Integrated Circuits (ASICs), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. Processors are considered processing circuitry or circuitry because they include transistors and other circuitry.

[0058] The memory stores various control programs including, for example, a welding control program. The processor reads out these control programs from the memory and executes them to control the operation of the AC welding power supply device. AC welding includes a first AC welding mode that starts with positive pole DC welding (first mode) and a second AC welding mode that starts with negative pole DC welding (third mode).

[0059] The controller 10 includes, for example, a user interface. The user interface includes, for example, a first AC welding instruction section for the user to instruct the first AC welding, a second AC welding instruction section for the user to instruct the second AC welding, a positive pole DC welding instruction section for the user to instruct the positive pole DC welding, and a negative pole DC welding instruction section for the user to instruct the negative pole DC welding. The control contents of the controller 10 will be described in detail below as the operation of the AC welding power supply device 100.

[0060] [Operation] Next, a description will be given of the operation of the thus configured AC welding power supply device 100. The operation of the AC welding power supply device 100 is performed under the control of the controller 10.

[0061] Here, the operation of AC welding power supply device 100 when it outputs a voltage for AC welding will be described. In this case, AC welding power supply device 100 has, for example, first to fourth operation modes, and controller 10 performs rectification and polarity control for AC welding. Here, an overview of the control of the first AC welding will be described.

[0062] Fig. 2 is a flowchart showing the contents of the rectification and polarity control of the first AC welding by the controller 10. Referring to Fig. 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 the input of a welding start command (NO in step S1, step S1).

[0063] When a welding start command is input (YES in step S1), controller 10 causes AC welding power supply device 100 to execute the first to fourth modes (steps S2 to S5) in sequence.

[0064] When controller 10 has finished causing AC welding power supply device 100 to execute fourth mode (S5), controller 10 determines whether or not a welding end command has been input (step S6). If a welding end command has not been input (NO in step S6), controller 10 returns to step S2, and thereafter repeats steps S2 to S6 (NO) until a welding end command is input.

[0065] When the welding end command has been input (YES in step S6), controller 10 ends the rectification and polarity control of the first AC welding.

[0066] Next, the rectification and polarity control of the first AC welding will be described in detail for each mode with reference to Figures 3 to 9. Figure 3 is a waveform diagram showing the waveform of the output current and the waveform of the gate signal to the bidirectional switch.

[0067] Specifically, the contents of the waveform diagrams in each row in FIG. 3 are as follows. The top waveform diagram shows the waveform of the output current output from the first and second output terminals 6, 7. The second waveform diagram from the top shows the waveform of the gate signal of the second switching element SW2. The third waveform diagram from the top shows the waveform of the gate signal of the first switching element SW1. The fourth waveform diagram from the top shows the waveform of the gate signal of the fourth switching element SW4. The fifth waveform diagram from the top shows the waveform of the gate signal of the third switching element SW3. The sixth waveform diagram from the top shows the waveform of the gate signal of the first discharge switching element SW5. The seventh waveform diagram from the top (bottom row) shows the waveform of the gate signal of the second discharge switching element SW6.

[0068] 3, a gate signal corresponding to each of the switching elements SW1 to SW6 is input from the controller 10. To be precise, these gate signals are amplified by the gate drive circuits after being sent from the controller 10, and then input to the corresponding switching elements SW1 to SW6. However, for the sake of simplicity, the gate signals are assumed to be input from the controller 10 to the corresponding switching elements SW1 to SW6. In addition, in the gate signal, the high level portion is called an "on signal" and the low level portion is called an "off signal." The same applies to the gate signals to the switching elements SW21 to SW24 of the inverter 2.

[0069] In the gate signals of the first to fourth switching elements SW1 to SW4, the portions represented by vertical lines with small intervals indicate that on signals and off signals are repeatedly sent alternately at equal small time intervals. The repetition frequency of these on signals and off signals is, for example, 20 to 100 kHz. The repetition frequency of these on signals is equal to the frequency of the primary side AC voltage output from the inverter 2. In other words, as will be clear from the description below, the rectification performed by the first and second bidirectional switches 4, 5 is synchronous rectification that is performed in synchronization with the switching of the switching elements SW21 to SW24 of the inverter 2.

[0070] It should be noted that the frequency corresponding to the cycle of the periods of the first to fourth modes, ie, the polarity switching frequency of the voltage (and current) for AC welding, is a low frequency of, for example, 100 to 500 Hz.

[0071] <First mode> Fig. 4 is a diagram showing the flow of the input current Ii and the output current Io in the positive-side in-phase rectification in the first mode in the circuit of Fig. 1. Fig. 5 is a diagram showing the flow of the input current Ii and the output current Io in the positive-side inverse-phase rectification in the first mode in the circuit of Fig. 1. Note that in Figs. 4 to 9, the controller 10 is omitted in order to make the flow of each current easier to see, and reference numerals of other elements are omitted.

[0072] In the first mode, the controller 10 controls the first and second bidirectional switches 4 and 5 to perform positive-side in-phase rectification and positive-side anti-phase rectification, respectively, through positive-side rectification control. Also, in the first mode, the output current Io rises to a high-level current value at the fastest speed in accordance with the time constant (τ=L / R) of the circuit through which the output current Io flows.

[0073] {Positive side common-phase rectification} 1, 3, and 4, the controller 10 causes the inverter 2 to output a primary side AC voltage during AC welding. In the first mode, the controller 10 first puts the first bidirectional switch 4 into a positive conductive state and the second bidirectional switch 5 into a cut-off state during a first half cycle period of the primary side AC voltage. Specifically, the controller 10 sends an ON gate signal to the second switching element SW2 and sends an ON gate signal to the first switching element SW1 throughout the entire period of the first mode. Then, the second switching element SW2 is put into a conductive state and the first switching element SW1 is put into a conductive state throughout the entire period of the first mode, and the first bidirectional switch 4 is put into a positive conductive state. As a result, the first bidirectional switch 4 rectifies the common-phase secondary side AC voltage output from the transformer 3 and outputs a common-phase half-wave positive DC voltage. Here, the "positive conductive state" means "a state in which a current flows in a positive direction."

[0074] On the other hand, the controller 10 sends an OFF gate signal to the fourth switching element SW4. As a result, the fourth switching element SW4 is switched to a cut-off state, and the second bidirectional switch 5 is switched to a cut-off state. As a result, the second bidirectional switch 5 blocks the negative-phase secondary side AC voltage output from the transformer 3. At this time, the controller 10 also sends an ON gate signal to the third switching element SW3 throughout the entire period of the first mode. As a result, the third switching element SW3 is in a conductive state throughout the entire period of the first mode.

[0075] In addition, the controller 10 sends an OFF gate signal to the first discharge switching element SW5 throughout the entire period from the third mode of the previous cycle to the first mode of the current cycle, and sends an OFF gate signal to the second discharge switching element SW6 throughout the entire periods of the first to third modes, so that the first discharge switching element SW5 is in a cut-off state throughout the entire period from the third mode of the previous cycle to the first mode of the current cycle, and the second discharge switching element SW6 is in a cut-off state throughout the entire periods of the first to third modes.

[0076] 4, when AC welding power supply device 100 is in the above state, on the primary side of transformer 3, input current Ii from inverter 2 to transformer 3 flows through primary winding 31 of transformer 3 in a direction from one end 31a to the other end 31b, while on the secondary side of transformer 3, output current Io flows from one end 32a of secondary winding 32 of transformer 3, through first bidirectional switch 4, second output port 7, arc generating unit 8, first output port 6, smoothing reactor 9, and midpoint 32c of secondary winding 32 of transformer 3, returning to one end 32a of secondary winding 32 of transformer 3.

[0077] In addition, the first snubber capacitor Cs1 is charged to a voltage CV1 corresponding to the voltage across the first bidirectional switch 4. However, the other end (the end on the cathode side of the first diode D1) is maintained at the highest potential (positive pole) of the in-phase secondary side AC voltage output from the transformer 3 by the first diode D1.

[0078] In addition, the second snubber capacitor Cs2 is charged to a voltage CV2 corresponding to the voltage across the second bidirectional switch 5. However, the other end (the end on the anode side of the third diode D3) is maintained at the minimum potential (negative pole) of the negative-phase secondary side AC voltage output from the transformer 3 by the third diode D3.

[0079] In this manner, positive side common-phase rectification is performed in AC welding power supply device 100.

[0080] {Positive side negative phase rectification} 1, 3, and 5, when the primary side AC voltage next enters the second half-cycle period, the controller 10 brings the second bidirectional switch 5 into a positive conductive state and brings the first bidirectional switch 4 into a cut-off state. Specifically, the controller 10 sends an ON gate signal to the fourth switching element SW4. Then, since the fourth switching element SW4 enters a conductive state and the third switching element SW3 has already been in a conductive state throughout the entire period of the first mode, the second bidirectional switch 5 rectifies the negative-phase secondary side AC voltage output from the transformer 3 and outputs a negative-phase half-wave positive DC voltage.

[0081] On the other hand, the controller 10 sends an OFF gate signal to the second switching element SW2. Then, the second switching element SW2 is turned off, and the first bidirectional switch 4 is turned off. As a result, the first bidirectional switch 4 blocks the common-phase secondary side AC voltage output from the transformer 3.

[0082] 5, when AC welding power supply device 100 is in the above state, on the primary side of transformer 3, input current Ii from inverter 2 to transformer 3 flows through primary winding 31 of transformer 3 in a direction from the other end 31b to one end 31a, while on the secondary side of transformer 3, output current Io flows from the other end 32b of the secondary winding of transformer 3, through second bidirectional switch 5, second output port 7, arc generating unit 8, first output port 6, smoothing reactor 9, and midpoint 32c of secondary winding 32 of transformer 3, returning to the other end 32b of secondary winding 32 of transformer 3.

[0083] Further, 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. In this manner, positive-side negative-phase rectification is performed in the AC welding power supply device 100.

[0084] In this manner, the first and second bidirectional switches 4, 5 supply a full-wave positive DC voltage between the first output terminal 6 and the second output terminal 7 by the positive-side positive phase rectification and the positive-side negative phase rectification.

[0085] <Second mode> FIG. 6 is a diagram showing the flow of the charging current and discharging current in the circuit of FIG. 1 when the polarity is switched from positive to negative in the second mode.

[0086] In the second mode, the controller 10 performs positive-to-negative polarity switching control of the output voltage and the output current and first arc interruption prevention control.

[0087] 1, 3, and 6, the controller 10 switches the first and second bidirectional switches 4, 5 to the cut-off state at a predetermined timing according to the polarity switching frequency of the voltage (or current) for AC welding. Specifically, the controller 10 sends gate signals that are OFF signals to the first to fourth switching elements SW1 to SW4. Then, the first to fourth switching elements SW1 to SW4 are switched to the cut-off state, and the first and second bidirectional switches 4, 5 are switched to the cut-off state. This starts the second mode.

[0088] Then, as shown by the dashed arrow in FIG. 6, a surge voltage is generated by the magnetic energy stored in the inductance component Ls of the torch cable of the welding torch, which is the arc generating part 8, and the surge voltage flows from the first output end 6 through the smoothing reactor 9 to the midpoint 32c of the secondary winding 32 of the transformer 3, where it is split into two currents, one of which passes through one end 32a of the secondary winding 32 and the first diode D1 to the other end of the first snubber capacitor Cs1, while the other of which passes through the other end 32b of the secondary winding 32 and the second diode D2 to the other end of the first snubber capacitor Cs1, where both currents join together, and a charging current Ic flows to the first snubber capacitor Cs1 so that the joined current returns to the arc generating part 8 through the first snubber capacitor Cs1 and the second output end 7.

[0089] Therefore, the energy that would conventionally be consumed in a resistive element is stored in the first snubber capacitor Cs1 by the charging current Ic due to this surge voltage.

[0090] Meanwhile, before and after this charging current flows, the controller 10 sends an ON gate signal to the first discharging switching element SW5, thereby turning on the first discharging switching element SW5. Then, the first snubber capacitor Cs1 discharges, and as shown by the dotted arrow in Fig. 6, the discharge current Id flows back to the first snubber capacitor Cs1 through the first discharging switching element SW5, the current limiting resistor R1, the first output terminal 6, the arc generating unit 8, and the second output terminal 7. Since the direction of this discharge current Id is opposite to the direction of the charging current Ic due to the surge voltage, the voltage CV1 of the first snubber capacitor Cs1 is determined by the relationship between the charging current Ic and the discharging current Id.

[0091] Here, a conduction period of the first discharge switching element SW5 that provides an optimal voltage for preventing arc interruption (hereinafter referred to as a "first optimum conduction period") is stored in advance in the memory of the controller 10. This "first optimum conduction period" is obtained by simulation, experiment, calculation, etc.

[0092] The controller 10 turns on the first discharge switching element SW5 during the "first optimum conduction period". As a result, a negative DC voltage that prevents arc interruption is supplied from the first snubber capacitor Cs1 to the inductance component Ls of the torch cable and the arc generating unit 8. This will be described in detail with reference to the waveform diagram of the output current at the top of FIG. 3. First, the "output current" will be described. The "output current" refers to the current supplied from 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 stored in the inductance component Ls of the torch cable by the current supplied from the AC welding power supply device 100 to the arc generating unit 8 as their energy source. The two currents flow in opposite directions, and only the current with the larger absolute value is manifested. Therefore, the current with the larger absolute value of the charging current Ic and the discharging current Id corresponds to the "output current".

[0093] Referring to FIG. 3, the "first optimal conduction period" starts, for example, when the second mode starts, and ends when the second mode ends. In the "first optimal conduction period", the charging current Ic is initially larger than the discharging current Id, but the discharging current Id becomes larger than the charging current Ic midway, and at this point, the polarity of the output current Io and the output voltage switches from positive to negative. Then, the current value of the negative output current Io, which is the difference current between the charging current Ic and the discharging current Id, increases with the decrease in the charging current Ic, and when the charging current Ic eventually disappears, the current value of the output current Io becomes the approximately constant current value Id of the discharging current Id, Id=CV1 / R(A) (CV1 is the voltage (V) of the first snubber capacitor Cs1, and R is the resistance value (Ω) of the current-limiting resistor R1). After that, the output current Io maintains the approximately constant current value until the "first optimal conduction period" ends. When the "first optimal conduction period" ends, the first discharge switching element SW5 is turned off. This ends the second mode.

[0094] When transitioning from the second mode to the third mode, the voltage applied to the arc generating unit 8 switches from the negative voltage by the first snubber capacitor Cs1 in the second mode to the negative voltage by the first bidirectional switch 4 or the second bidirectional switch 5 in the third mode, but the output current Io is maintained by the inductance component Ls of the torch cable. Therefore, the polarity of the output voltage and the output current Io is suitably switched from positive to negative while preventing arc interruption.

[0095] When the first discharge switching element SW5 is turned off at the end of the "first optimal conduction period", the resulting surge voltage is bypassed by the first high-pass filter Hf1, thereby protecting the first discharge switching element SW5.

[0096] <Third mode> Fig. 7 is a diagram showing the flow of the input current Ii and the output current Io in the negative side negative phase rectification in the third mode in the circuit of Fig. 1. Fig. 8 is a diagram showing the flow of the input current Ii and the output current Io in the negative side in-phase rectification in the third mode in the circuit of Fig. 1. In the third mode, the controller 10 causes the first and second bidirectional switches 4 and 5 to perform negative side in-phase rectification and negative side negative phase rectification, respectively, by negative side rectification control. In the third mode, the output current Io falls to a low-level current value at the fastest in accordance with the time constant (τ=L / R) of the circuit through which the output current Io flows.

[0097] {Negative side inverted phase rectification} 1, 3, and 7, in the third mode, the controller 10 first makes the second bidirectional switch 5 conductive in the negative direction and makes the first bidirectional switch 4 cut off during the first half cycle period of the primary side AC voltage. Specifically, the controller 10 sends an ON gate signal to the third switching element SW3 and sends an ON gate signal to the fourth switching element SW4 throughout the entire period of the third mode. Then, the third switching element SW3 becomes conductive and the fourth switching element SW4 becomes conductive throughout the entire period of the third mode, and the second bidirectional switch 5 becomes conductive in the negative direction. As a result, the second bidirectional switch 5 rectifies the negative-phase secondary side AC voltage output from the transformer 3 and outputs a negative-phase half-wave negative DC voltage. Here, the "negative conductive state" means "a state in which a current flows in the negative direction."

[0098] On the other hand, the controller 10 sends an OFF gate signal to the first switching element SW1. As a result, the first switching element SW1 is switched to a cut-off state, and the first bidirectional switch 4 is switched to a cut-off state. As a result, the first bidirectional switch 4 blocks the in-phase secondary side AC voltage output from the transformer 3. At this time, the controller 10 also sends an ON gate signal to the second switching element SW2 throughout the entire period of the third mode. As a result, the second switching element SW2 is in a conductive state throughout the entire period of the third mode.

[0099] In addition, the controller 10 sends an OFF gate signal to the first discharge switching element SW5 for the entire period from the third mode to the first mode of the next cycle, so that the first discharge switching element SW5 is in a cut-off state for the entire period from the third mode to the first mode of the next cycle.

[0100] 7, when AC welding power supply device 100 is in the above state, on the primary side of transformer 3, input current Ii from inverter 2 to transformer 3 flows through primary winding 31 of transformer 3 in a direction from one end 31a to the other end 31b, while on the secondary side of transformer 3, output current Io flows from midpoint 32c of secondary winding 32 of transformer 3, through smoothing reactor 9, first output terminal 6, arc generating unit 8, second output terminal, second bidirectional switch 5, and the other end 32b of secondary winding 32 of transformer 3, in this order, to return to midpoint 32c of secondary winding 32 of transformer 3.

[0101] In addition, the second snubber capacitor Cs2 is charged to a voltage CV2 corresponding to the voltage across the second bidirectional switch 5. However, the other end (the end on the anode side of the third diode D3) is maintained at the minimum potential (negative pole) of the negative-phase secondary side AC voltage output from the transformer 3 by the third diode D3.

[0102] In addition, the first snubber capacitor Cs1 is charged to a voltage CV1 corresponding to the voltage across the first bidirectional switch 4. However, the other end (the end on the cathode side of the first diode D1) is maintained at the highest potential (positive pole) of the in-phase secondary side AC voltage output from the transformer 3 by the first diode D1.

[0103] In this manner, negative side negative phase rectification is performed in AC welding power supply device 100.

[0104] {Negative side in-mode rectification} 1, 3, and 8, when the primary side AC voltage next enters the second half-cycle period, the controller 10 brings the first bidirectional switch 4 into a negative conductive state and brings the second bidirectional switch 5 into a cut-off state. Specifically, the controller 10 sends an ON gate signal to the first switching element SW1. Then, since the first switching element SW1 enters a conductive state and the second switching element SW2 has already been in a conductive state throughout the entire period of the third mode, the first bidirectional switch 4 rectifies the in-phase secondary side AC voltage output from the transformer 3 and outputs an in-phase half-wave negative DC voltage.

[0105] On the other hand, the controller 10 sends an OFF gate signal to the third switching element SW3. Then, the third switching element SW3 is turned off, and the second bidirectional switch 5 is turned off. As a result, the second bidirectional switch 5 blocks the negative-phase secondary side AC voltage output from the transformer 3.

[0106] 8, when AC welding power supply device 100 is in the above state, on the primary side of transformer 3, input current Ii from inverter 2 to transformer 3 flows through primary winding 31 of transformer 3 in a direction from the other end 31b to one end 31a, while on the secondary side of transformer 3, output current Io flows from midpoint 32c of secondary winding 32 of transformer 3, through smoothing reactor 9, first output terminal 6, arc generating unit 8, second output terminal 7, first bidirectional switch 4, and one end 32a of secondary winding 32 of transformer 3, in this order, to return to midpoint 32c of secondary winding 32 of transformer 3.

[0107] Further, 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. In this manner, negative side common-phase rectification is performed in the AC welding power supply device 100.

[0108] In this manner, the first and second bidirectional switches 4, 5 supply a full-wave negative DC voltage between the first output terminal 6 and the second output terminal 7 by the negative side antiphase rectification and negative side inphase rectification.

[0109] <Fourth mode> FIG. 9 is a diagram showing the flow of the charging current and discharging current in the circuit of FIG. 1 when the polarity is switched from negative to positive in the fourth mode.

[0110] In the fourth mode, the controller 10 performs negative-to-positive polarity switching control of the output voltage and the output current and second arc interruption prevention control.

[0111] 1, 3, and 9, the controller 10 switches the first and second bidirectional switches 4, 5 to the cut-off state at a predetermined timing according to the polarity switching frequency of the voltage (or current) for AC welding. Specifically, the controller 10 sends gate signals that are OFF signals to the first to fourth switching elements SW1 to SW4. Then, the first to fourth switching elements SW1 to SW4 are switched to the cut-off state, and the first and second bidirectional switches 4, 5 are switched to the cut-off state. This starts the fourth mode.

[0112] Then, as shown by the dashed arrow in FIG. 9, a surge voltage is generated by the magnetic energy stored in the inductance component Ls of the torch cable of the welding torch, which is the arc generating part 8, and this surge voltage causes a current to flow from the second output end 7 through the second snubber capacitor Cs2, where it is divided into two parts, one of which passes through the third diode D3 and the other end 32b of the secondary winding 32 of the transformer 3 to the midpoint 32c of the secondary winding 32, and the other of which passes through the fourth diode D4 and the one end 32a of the secondary winding 32 of the transformer 3 to the midpoint 32c of the secondary winding 32, where both branches join together, and a charging current Ic flows to the second snubber capacitor Cs2 so that the combined flow returns to the arc generating part 8 through the smoothing reactor 9 and the first output end 6.

[0113] Therefore, the energy that would conventionally be consumed in a resistive element is stored in the second snubber capacitor Cs2 by the charging current Ic due to this surge voltage.

[0114] Meanwhile, before and after this charging current flows, the controller 10 sends an ON gate signal to the second discharge switching element SW6, thereby turning on the second discharge switching element SW6. Then, the second snubber capacitor Cs2 discharges, and as shown by the dotted arrow in Fig. 9, the discharge current Id flows back to the second snubber capacitor Cs2 through the second output terminal 7, the arc generating unit 8, the current limiting resistor R1, and the second discharge switching element SW6. Since the direction of this discharge current Id is opposite to the direction of the charging current Ic due to the surge voltage, the voltage CV2 of the second snubber capacitor Cs2 is determined by the relationship between the charging current Ic and the discharging current Id.

[0115] Here, a conduction period of the second discharge switching element SW6 that provides an optimal voltage for preventing arc interruption (hereinafter referred to as the "second optimum conduction period") is stored in advance in the memory of the controller 10. This "second optimum conduction period" is obtained by simulation, experiment, calculation, etc.

[0116] The controller 10 turns on the second discharge switching element SW6 during the "second optimal conduction period". As a result, a positive DC voltage that prevents arc interruption is supplied from the second snubber capacitor Cs2 to the inductance component Ls of the torch cable and the arc generating part 8.

[0117] In this manner, the polarity of the output voltage is switched from negative to positive while preventing arc interruption.

[0118] This will be described in detail with reference to the waveform diagram of the output current at the top of FIG. 3. Referring to FIG. 3, the "second optimal conduction period" starts, for example, when the fourth mode starts, and ends when the fourth mode ends. In the "second optimal conduction period", the charging current Ic is initially larger than the discharging current Id, but the discharging current Id becomes larger than the charging current Ic midway, and at this point, the polarity of the output current Io and the output voltage switches from negative to positive. Then, the current value of the positive output current Io, which is the difference current between the charging current Ic and the discharging current Id, increases with the decrease in the charging current Ic, and when the charging current Ic eventually disappears, the current value of the output current Io becomes the approximately constant current value Id of the discharging current Id, Id=CV2 / R(A) (CV2 is the voltage (V) of the second snubber capacitor Cs2, and R is the resistance value (Ω) of the current limiting resistor R1). After that, the output current Io maintains the approximately constant current value until the "second optimal conduction period" ends. When the "second optimum conduction period" ends, the second discharge switching element SW6 is turned off, thereby ending the fourth mode.

[0119] When transitioning from the fourth mode to the first mode, the voltage applied to the arc generating unit 8 switches from the positive voltage by the second snubber capacitor Cs2 in the fourth mode to the positive voltage by the first bidirectional switch 4 or the second bidirectional switch 5 in the third mode, but the output current Io is maintained by the inductance component Ls of the torch cable. Therefore, the polarity of the output voltage and the output current Io is suitably switched from negative to positive while preventing arc interruption.

[0120] Furthermore, when the second discharge switching element SW6 is turned off at the end of the "second optimal conduction period", the resulting surge voltage is bypassed by the second high-pass filter Hf2, thereby protecting the second discharge switching element SW6.

[0121] <Other actions> When the user inputs a command to instruct 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 execute AC welding from the third mode described above. This allows the second AC welding to be performed. Also, when the user inputs a command to instruct 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 execute the first mode described above. This allows the positive DC welding to be performed. Also, when the user inputs a command to instruct 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 execute the third mode described above. This allows the negative DC welding to be performed.

[0122] [Variations] In this modification, the "first optimal conduction period" does not end in the second mode, but is extended to the rising section of the output voltage in the third mode. For example, the "first optimal conduction period" is extended to the end of the falling section of the output voltage in the third mode. In this case, the second mode ends with the start of the third mode (negative conduction of the first bidirectional switch 4 or the second bidirectional switch 5). The third mode is divided into a sub-mode from when the first discharge switching element SW5 is turned off until the "first optimal conduction period" ends, and a sub-mode for the remaining part. As described above, the length of the "first optimal conduction period" is determined so that the voltage CV1 of the first snubber capacitor Cs1 becomes the "optimum negative voltage that prevents arc interruption" in the relationship between the charging current Ic and the discharging current Id. Therefore, by extending the "first optimal conduction period" until the end of the falling section of the output voltage in the third mode, the "optimum negative voltage for preventing arc interruption" can be suitably set even in cases where the "first optimal conduction period" must be lengthened due to the relationship between the charging current Ic and the discharging current Id.

[0123] In addition, in this modification, the "second optimal conduction period" does not end in the fourth mode, but is extended to the rising section of the output voltage in the first mode of the next cycle. For example, the "second optimal conduction period" is extended to the end of the rising section of the output voltage in the first mode. In this case, the fourth mode ends with the start of the first mode (positive conduction of the first bidirectional switch 4 or the second bidirectional switch 5). The first mode is divided into a sub-mode until the second discharge switching element SW6 is turned off and the "second optimal conduction period" ends, and a sub-mode for the remaining part. As described above, the length of the "second optimal conduction period" is determined so that the voltage CV2 of the second snubber capacitor Cs2 becomes the "optimum positive voltage that prevents arc interruption" in the relationship between the charging current Ic and the discharging current Id. Therefore, by extending the "second optimal conduction period" until the end of the falling section of the output voltage in the first mode of the next cycle, the "optimum positive voltage for preventing arc interruption" can be suitably set even in cases where the "second optimal conduction period" must be lengthened due to the relationship between the charging current Ic and the discharging current Id.

[0124] [Effects] As described above, according to the first embodiment, firstly, the two bidirectional switches 4, 5 can be used to rectify the AC voltage output to the secondary winding 32 of the transformer 3 and to switch the polarity of the DC voltage for arc welding, and the configuration related to this switching can be simplified. Therefore, it is possible to provide an AC welding power supply device 100 that can simplify the circuit configuration for rectifying and converting the transformed AC power to AC.

[0125] Secondly, one pair of switching elements SW1, SW2 is rendered conductive in synchronization with one half-cycle period of the primary AC voltage, and the other pair of switching elements SW3, SW4 is rendered conductive in synchronization with the other half-cycle period of the primary AC voltage. Therefore, the voltage drop (voltage across both ends) caused by the rectifying elements when rectifying the secondary AC voltage output from transformer 3 is the voltage drop of the switching elements alone. Therefore, by selecting, as the pair of switching elements, switching elements whose voltage drop when conductive is smaller than the voltage drop of a diode, it is possible to reduce power loss caused by the rectifying elements and improve the efficiency of AC welding power supply device 100.

[0126] Thirdly, one of the pair of switching elements of the first and second bidirectional switches 4, 5 is always on and only the other is turned on and off, thereby switching between the conductive state and the cut-off state of the first and second bidirectional switches 4, 5, so that the first bidirectional switch 4 and the second bidirectional switch 5 can be operated at high speed.

[0127] Fourth, when switching the polarity of the output voltage, the controller 10 controls the conduction period of the first discharge switching element SW5 or the second discharge switching element SW6 to an optimum voltage for preventing arc interruption, so that a negative or positive voltage for preventing arc interruption can be supplied from the first snubber capacitor Cs1 or the second snubber capacitor Cs2 to the inductance component Ls of the torch cable and the arc generating unit 8. As a result, arc interruption can be suitably prevented when switching the polarity of the output voltage.

[0128] (Embodiment 2) The second embodiment differs from the first embodiment in the following respects, and is otherwise the same as the first embodiment (including the modified examples). The following describes these differences.

[0129] Fig. 10A 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 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.

[0130] 10A, in the second embodiment, the first to fourth switching elements SW1 to SW4 are switching elements that can selectively conduct and cut off only a current flowing in one direction. The first bidirectional switch 4 includes a first pair of switching elements SW1, SW2 connected in anti-series to each other, and a first pair of diodes 41, 42 connected in anti-parallel to the first pair of switching elements SW1, SW2, respectively, and connected in anti-series to each other.

[0131] Referring to FIG. 10B, the second bidirectional switch 5 includes a second pair of switching elements SW3, SW4 connected in anti-series to each other, and a second pair of diodes 51, 52 connected in anti-parallel to the second pair of switching elements SW3, SW4, respectively, and connected in anti-series to each other.

[0132] The first to fourth switching elements SW1 to SW4 are configured, for example, with bipolar transistors, IGBTs, etc. The individual diodes 41, 42, 51, and 52 are external diodes.

[0133] In the second embodiment, similarly to the first embodiment, the first and second bidirectional switches 4 and 5 perform 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 for each half cycle period of the primary AC voltage. However, in the first mode, the first to fourth switching elements SW1 to SW4 are, for example, in such a manner that the first switching element SW1 is in a conductive state throughout the entire period of the first mode, the second switching element SW2 is in a cut-off state throughout the entire period of the first mode, the third switching element SW3 is in a conductive state throughout the entire period of the first mode, and the fourth switching element SW4 is in a cut-off state throughout 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 through the diode 42 connected in anti-parallel to the second switching element SW2. In addition, in {positive-side negative-phase rectification}, the output current Io flows through the diode 52 connected in anti-parallel to the fourth switching element SW4.

[0134] In the third mode, the fourth switching element SW4 is turned on throughout the entire period of the third mode, the third switching element SW3 is turned off throughout the entire period of the third mode, the second switching element SW2 is turned on throughout the entire period of the third mode, and the first switching element SW1 is turned off throughout the entire period of the third mode. That is, synchronous rectification is not performed. In this case, in {negative side reverse phase rectification}, the output current Io flows through the diode 51 connected in anti-parallel to the third switching element SW3. In addition, in {negative side in-phase rectification}, the output current Io flows through the diode 41 connected in anti-parallel to the first switching element SW1.

[0135] The first to fourth switching elements SW1 to SW4 may be on / off controlled in the same manner as in embodiment 1. In this case as well, the output current Io flows in the same manner as described above.

[0136] Unlike the first embodiment, the second embodiment configured as described above cannot improve the efficiency of the AC welding power supply device 100. However, the second embodiment can achieve other effects similar to those of the first embodiment.

[0137] Numerous modifications and other embodiments will be apparent to those skilled in the art in light of the above description, and therefore the above description is to be construed as illustrative only. [Industrial Applicability]

[0138] INDUSTRIAL APPLICABILITY The AC welding power supply device of the present invention is useful as an AC welding power supply device capable of simplifying the circuit configuration for rectifying and converting transformed AC power to AC. [Explanation of symbols]

[0139] 1 DC power supply 2 Inverter 3. Transformer 4 First Two-Way Switch 5 Second Two-Way Switch 6 First output terminal 7 2nd output terminal 8 Arc generating part 9. Smoothing reactor 10 Controller 31 Primary Winding 31a one end 31b Other end 32 Secondary Winding 32a one end 32b other end 32c midpoint 41,42,51,52,61,62 Diodes Cs1 to Cs4 First to fourth snubber capacitors D1 to D4 First to fourth diodes Hf1 1st high pass filter Hf2 2nd high pass filter Ls Inductance component SW1 to SW4: First to fourth switching elements SW5 First discharge switching element SW6 Second discharge switching element R1 Current limiting resistor element

Claims

1. An inverter connected to a DC power supply and outputting a primary AC voltage including a first half-cycle period and a second half-cycle period with the opposite polarity to the first half-cycle period, First output terminal and second output terminal that supply a DC voltage for welding to the arc generating unit, A two-phase half-wave rectifier transformer 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, with the potential of the intermediate point as a reference, it outputs a secondary AC voltage that has a predetermined voltage and is in phase with the primary AC voltage between the intermediate point and one end of the secondary winding, and outputs a reverse-phase AC voltage that has the predetermined voltage and is in phase with the primary AC voltage between the intermediate point and the other end of the secondary winding, A first bidirectional switch capable of selectively conducting and interrupting current flowing in both the positive direction from one end to the other and the negative direction from the other end to the one end, wherein one end is connected to the one end of the secondary winding of the transformer and the other end is connected to the second output terminal, A second bidirectional switch is capable of selectively conducting and interrupting current flowing in both the positive direction from one end to the other and the negative direction from the other end to the one end, with one end connected to the other end of the secondary winding of the transformer and the other end connected to the second output terminal, A smoothing reactor is interposed in the current path passing through the first and second bidirectional switches, A controller that controls the operation of the first and second bidirectional switches, A first snubber capacitor, one end of which is connected to the other end of the first bidirectional switch, A first diode whose anode is connected to one end of the first bidirectional switch and whose cathode is connected to the other end of the first snubber capacitor, A first discharge switching element is connected to the other end of the first snubber capacitor such that one end of the body diode's cathode 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 switching element and the other end of which is connected to the first output terminal, A second diode whose anode is connected to one end of the second bidirectional switch and whose cathode is connected to the cathode of the first diode, A second snubber capacitor, one end of which is connected to the other end of the second bidirectional switch, A third diode whose cathode is connected to one end of the second bidirectional switch and whose anode is connected to the other end of the second snubber capacitor, A second discharge switching element, one end of which is connected to the other end of the second snubber capacitor such that the anode side of the body diode is connected to the other end of the second snubber capacitor, and the other end of which is connected to the one end of the current-limiting resistor element, A fourth diode is provided, the cathode of which is connected to one end of the first bidirectional switch and the anode of which is connected to the anode of the third diode. The controller is, During the first half-cycle period of the primary AC voltage, the first bidirectional switch is set to conduct in the positive direction and the second bidirectional switch is set to disconnect, causing the first bidirectional switch to rectify the in-phase secondary AC voltage and output an in-phase half-wave positive DC voltage; and during the second half-cycle period of the primary AC voltage, the second bidirectional switch is set to conduct in the positive direction and the first bidirectional switch is set to disconnect, causing the second bidirectional switch to rectify the reverse-phase secondary AC voltage and output 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 of the first and second bidirectional switches, thus providing positive-side rectification control. The system is configured to perform at least one of the following: during the first half-cycle period of the primary AC voltage, the second bidirectional switch is made conductive in the negative direction and the first bidirectional switch is made disconnected, causing the second bidirectional switch to rectify the inverse-phase secondary AC voltage and output an inverse-phase half-wave negative DC voltage; and during the second half-cycle period of the primary AC voltage, the first bidirectional switch is made conductive in the negative direction and the second bidirectional switch is made disconnected, causing the first bidirectional switch to rectify the in-phase secondary AC voltage and output an in-phase half-wave negative DC voltage, thereby supplying a full-wave negative DC voltage between the first output terminal and the second output terminal of the first and second bidirectional switches; and AC welding power supply device, configured to perform at least one of the following: a first arc interruption prevention control that, when switching from positive-side rectification control to negative-side rectification control, shuts off the first and second bidirectional switches and makes the first discharge switching element conductive for a period before and after the shutdown; and a second arc interruption prevention control that, when switching from negative-side rectification control to positive-side rectification control, shuts off the first and second bidirectional switches and makes the second discharge switching element conductive for a period before and after the shutdown.

2. The first bidirectional switch includes a first pair of switching elements connected in reverse series to each other, which are capable of selectively conducting and interrupting the current flowing in both directions, and a first pair of diodes connected in reverse parallel to each of the first pair of switching elements and also connected in reverse series to each other. The second bidirectional switch includes a second pair of switching elements connected in reverse series to each other, which are capable of selectively conducting and interrupting the current flowing in both directions, and a second pair of diodes connected in reverse parallel to each of the second pair of switching elements and also connected in reverse series to each other. The controller is, During the first half-cycle period of the primary AC voltage, the first pair of switching elements are made conductive, and the switching element in parallel with the diode conducting in the positive direction of the second bidirectional switch among the second pair of switching elements is made disconnected, causing the first bidirectional switch to rectify the in-phase secondary AC voltage and output an in-phase half-wave positive DC voltage. Furthermore, during the second half-cycle period of the primary AC voltage, the second pair of switching elements are made conductive, and the switching element in parallel with the diode conducting in the positive direction of the first bidirectional switch among the first pair of switching elements is made disconnected, causing the second bidirectional switch to rectify the reverse-phase secondary AC voltage and output 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 of the first and second bidirectional switches. This is the positive-side synchronous rectification control as positive-side rectification control. AC welding power supply device according to claim 1, configured to perform at least one of the negative side synchronous rectification control, which is negative side rectification control, wherein during the first half-cycle period of the primary AC voltage, the second pair of switching elements are made conductive, and the switching element in parallel with the diode that conducts in the negative direction of the first bidirectional switch among the first pair of switching elements is made disconnected, causing the second bidirectional switch to rectify the inverse-phase secondary AC voltage and output an in-phase half-wave negative DC voltage, and during the second half-cycle period of the primary AC voltage, the first pair of switching elements are made conductive, and the switching element in parallel with the diode that conducts in the negative direction of the second bidirectional switch among the second pair of switching elements is made disconnected, causing the first bidirectional switch to rectify the in-phase secondary AC voltage and output an inverse-phase half-wave negative DC voltage, thereby supplying a full-wave negative DC voltage between the first output terminal and the second output terminal of the first and second bidirectional switches.

3. The controller is, In the positive-side synchronous rectification control described above, when the first bidirectional switch rectifies the common-phase secondary AC voltage to output a common-phase half-wave positive DC voltage, the remaining switching element of the second pair of switching elements is further made conductive, and when the second bidirectional switch rectifies the reverse-phase secondary AC voltage to output a reverse-phase half-wave positive DC voltage, the remaining switching element of the first pair of switching elements is further made conductive, and The AC welding power supply device according to claim 2, wherein, in the negative side synchronous rectification, when the second bidirectional switch rectifies the inverse-phase secondary AC voltage to output a common-phase half-wave negative electrode DC voltage, the remaining switching element of the first pair of switching elements is made conductive, and when the first bidirectional switch rectifies the common-phase secondary AC voltage to output a reverse-phase half-wave negative electrode DC voltage, the remaining switching element of the second pair of switching elements is made conductive.

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 the frequency of the primary-side AC voltage.

5. The AC welding power supply device according to claim 1, wherein a first high-pass filter is provided in parallel with the first discharge switching element, and a second high-pass filter is provided in parallel with the second discharge switching element.

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