Power supply device for welding and control method thereof

Abstract

In the welding power supply device (10), input current detection parts (13a, 13b), overcurrent judgment circuits (30a, 30b) and inverter drive circuits (40a, 40b) are respectively arranged for inverter circuits (12a, 12b). Input current detection units (13a, 13b) for detecting the input current of the inverter circuits (12a, 12b), respectively; an overcurrent determination circuit (30a, 30b) that determines the presence or absence of an overcurrent on the basis of whether or not the current detected by the input current detection unit (13a, 13b) is equal to or greater than a threshold current; when the at least one overcurrent determination circuit (30a, 30b) determines that there is an overcurrent, the inverter drive circuits (40a, 40b) stop the two inverter circuits (12a, 12b). On the basis of a plurality of currents detected by a plurality of input current detection units (13a, 13b), a control device (50) determines the presence or absence of an abnormality relating to the balance of the plurality of currents. When it is determined that there is an abnormality, the inverter circuits (12a, 12b) are stopped.

Description

Technical Field

[0001] The present disclosure relates to a welding power supply device that generates a welding current flowing into a welding wire for arc welding using a plurality of alternating current voltages output by a plurality of inverter circuits. Background Art

[0002] Patent document 1 discloses a welding power supply device, which includes a pair of inverter circuits, a welding current generating circuit, and a control device. The pair of inverter circuits each have a plurality of switching elements, and convert a DC voltage into an AC voltage by turning the plurality of switching elements on and off; the welding current generating circuit uses the plurality of AC voltages output by the pair of inverter circuits to generate a welding current flowing into a welding wire for arc welding; the control device generates a control signal, and the control signal controls the plurality of switching elements of the plurality of inverter circuits so that the welding current reaches a predetermined target current value. The welding power supply device is provided with an abnormality judgment unit, which judges whether there is an abnormality based on the induced current flowing in the current transformer, and one output wire of each pair of inverter circuits is inserted into the current transformer.

[0003] Patent Document 1: International Publication No. 2019 / 146247 Summary of the invention

[0004] -Technical problem to be solved by the invention 1

[0005] However, in the above-mentioned Patent Document 1, since only the difference in the current value flowing in the output wires of a pair of inverter circuits is detected, when an overcurrent flows through both inverter circuits at the same time, the abnormality determination unit cannot determine that an abnormality exists. Therefore, appropriate processing such as stopping the inverter circuit cannot be performed, which may cause damage to the inverter circuit or shorten the service life.

[0006] The present disclosure is made to solve the above-mentioned technical problems, and its purpose is to suppress the damage of the inverter circuit and the shortening of its service life caused by overcurrent.

[0007] -Technical solution 1 for solving technical problems

[0008] In order to achieve the above-mentioned purpose, the present disclosure provides a welding power supply device, which includes multiple inverter circuits, a welding current generating circuit and a control device, each of the multiple inverter circuits has multiple switching elements, and a DC voltage is converted into an AC voltage by switching the multiple switching elements. The welding current generating circuit uses the multiple AC voltages output by the multiple inverter circuits to generate a welding current flowing into a welding wire for arc welding, and the control device generates a control signal, and the control signal controls the multiple switching elements of the multiple inverter circuits so that the welding current reaches a specified target current value. It is characterized in that: the welding power supply device also includes an input current detection unit, an overcurrent judgment circuit and a logic circuit, and the input current detection unit is set for each of the multiple inverter circuits to respectively detect the corresponding inverter circuit input current, the overcurrent judgment circuit is provided for each of the plurality of inverter circuits, and judges whether there is overcurrent according to whether the current detected by the corresponding input current detection unit is above a threshold current. When any one of the overcurrent judgment circuits judges that there is no overcurrent, the logic circuit sends the control signal generated by the control device to the plurality of inverter circuits. On the other hand, when at least one of the overcurrent judgment circuits judges that there is overcurrent, the logic circuit stops the plurality of inverter circuits. The control device judges whether there is an abnormality related to the balance of the plurality of currents based on the plurality of currents detected by the plurality of input current detection units. When the control device judges that there is an abnormality, the control device stops the plurality of inverter circuits or changes the duty cycle of the control signal to eliminate the abnormality.

[0009] In this way, when an overcurrent flows through at least one inverter circuit, the corresponding overcurrent judgment circuit judges that an overcurrent exists, and the logic circuit stops the plurality of inverter circuits. Therefore, when an overcurrent flows through a plurality of inverter circuits at the same time, the plurality of inverter circuits can be stopped, thereby suppressing damage to the inverter circuit and shortening of its service life caused by the overcurrent.

[0010] -Effects of the Invention-

[0011] According to the present disclosure, it is possible to suppress damage to the inverter circuit and shortening of its service life due to overcurrent. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a schematic diagram showing the structure of an arc welding device according to an embodiment of the present disclosure;

[0013] Figure 2 is a circuit diagram showing the structure of an inverter circuit;

[0014] Figure 3 is a circuit diagram showing the structure of an overcurrent determination circuit, a logical product circuit, and an inverter drive circuit;

[0015] Figure 4 This is an explanatory diagram showing an example of a display screen indicating that there is an abnormality in the balance of input currents of two inverter circuits;

[0016] Figure 5 1 is a timing diagram showing input currents of two inverter circuits when no overcurrent is generated;

[0017] Figure 6 It is equivalent to the case where an overcurrent occurs in an inverter circuit. Figure 5 's picture;

[0018] Figure 7 The second embodiment is equivalent to Figure 1 's picture;

[0019] Figure 8 is a variant equivalent to Figure 4 . DETAILED DESCRIPTION

[0020] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0021] The following description of the preferred embodiments is merely illustrative in nature and is not intended to limit the present invention, its applications, or its uses.

[0022] (First Embodiment)

[0023] Figure 1 An arc welding device 1 is shown. The arc welding device 1 performs arc welding while feeding a welding wire 3 held by a welding gun 2 toward a workpiece W. The arc welding device 1 includes a welding power supply device 10 according to a first embodiment of the present disclosure. The welding power supply device 10 uses power from a power system 100 to pass a welding current through the welding wire 3. In this way, a welding voltage is applied between the workpiece W and the welding wire 3.

[0024] The welding power supply device 10 includes an input-side rectifier circuit 11, a pair (plurality) of inverter circuits 12a, 12b, a welding current generating circuit 20, a pair of input current detecting units 13a, 13b, a welding current detecting unit 14, a pair of overcurrent judging circuits 30a, 30b, a logical product circuit 60, a pair of inverter driving circuits 40a, 40b, a setting device 15, a control device 50, a display 16, a smoothing reactor 17, and an output terminal 18.

[0025] The input-side rectifier circuit 11 converts a three-phase AC voltage of 200 V supplied from the power system 100 into a DC voltage of approximately 280 V.

[0026] like Figure 2 As shown, each inverter circuit 12a, 12b has a plurality of switch elements S1 to S4. Each inverter circuit 12a, 12b converts the DC voltage output by the input side rectifier circuit 11 into a first AC voltage having a predetermined frequency between 20kHz and 100kHz by turning on and off the plurality of switch elements S1 to S4. In the first embodiment, a full-bridge inverter circuit is used as each inverter circuit 12a, 12b, but a half-bridge inverter circuit may also be used. A freewheeling diode RD is connected in parallel to each switch element S1 to S4.

[0027] Welding current generating circuit 20 uses a pair of (plural) first AC voltages outputted by a pair of inverter circuits 12a and 12b to generate welding current flowing into welding wire 3. Specifically, welding current generating circuit 20 includes a pair of transformer circuits 21a and 21b and a pair of output-side rectifier circuits 22a and 22b.

[0028] The voltage conversion circuit 21a is provided for the inverter circuit 12a; the voltage conversion circuit 21b is provided for the inverter circuit 12b. Each of the voltage conversion circuits 21a and 21b reduces the first AC voltage output by the corresponding inverter circuit 12a and 12b and converts it into a second AC voltage. Each of the voltage conversion circuits 21a and 21b has a primary coil 23 and a secondary coil 24. The voltage of the primary coil 23 becomes the first AC voltage, and the voltage of the secondary coil 24 becomes the second AC voltage.

[0029] The output side rectifier circuit 22a is also provided for the inverter circuit 12a (for each transformer circuit), and the output side rectifier circuit 22b is also provided for the inverter circuit 12b (for each transformer circuit). Each output side rectifier circuit 22a, 22b converts the second AC voltage output by the corresponding transformer circuit 21a, 21b into a DC voltage of 10V to 60V. Each output side rectifier circuit 22a, 22b has a first diode 25 and a second diode 26. The anode of the first diode 25 is connected to one end of the secondary coil 24, and the anode of the second diode 26 is connected to the other end of the secondary coil 24. The cathode of the first diode 25 and the cathode of the second diode 26 of the output side rectifier circuit 22a are connected to a common output node N1, and the cathode of the first diode 25 and the cathode of the second diode 26 of the output side rectifier circuit 22b are connected to a common output node N2. The currents output to the output nodes N1 and N2 of the two output-side rectifying circuits 22a and 22b merge at a merging node N3 and are output as a welding current.

[0030] The input current detection unit 13a is provided for the inverter circuit 12a, and the input current detection unit 13b is provided for the inverter circuit 12b. The input current detection units 13a and 13b detect the input current of the corresponding inverter circuits 12a and 12b, respectively.

[0031] Welding current detection unit 14 detects the welding current generated by welding current generation circuit 20 .

[0032] The overcurrent judgment circuit 30a is provided for the inverter circuit 12a; the overcurrent judgment circuit 30b is provided for the inverter circuit 12b. Each overcurrent judgment circuit 30a, 30b judges whether there is an overcurrent based on whether the current detected by the corresponding input current detection unit 13a, 13b is above the threshold current. When the current detected by the corresponding input current detection unit 13a, 13b is above the threshold current, it is judged that there is an overcurrent. On the other hand, when the current detected by the corresponding input current detection unit 13a, 13b is less than the threshold current, it is judged that there is no overcurrent. In this embodiment, the threshold current is set to 100A. Specifically, if Figure 3 As shown, each of the overcurrent determination circuits 30a and 30b includes a comparison circuit 31 and a filter circuit 32.

[0033] When the input current detected by the corresponding input current detection unit 13a, 13b is above the specified threshold current, the comparison circuit 31 outputs a low-level signal. On the other hand, when the input current detected by the corresponding input current detection unit 13a, 13b is less than the specified threshold current, the comparison circuit 31 outputs a high-level signal.

[0034] The filter circuit 32 removes high-frequency noise components from the signal output from the comparison circuit 31 , and outputs the signal from which the noise components have been removed as a signal indicating a determination result.

[0035] The logical product circuit 60 is a logic circuit that outputs the logical product of the outputs of the two overcurrent judgment circuits 30a and 30b. That is, when the input current detected by the two input current detection units 13a and 13b is less than a predetermined threshold current, the logical product circuit 60 outputs a high-level signal, and on the other hand, when the input current detected by at least one of the input current detection units 13a and 13b is greater than a predetermined threshold current, the logical product circuit 60 outputs a low-level signal.

[0036] The inverter drive circuit 40a is provided for each inverter circuit 12a; the inverter drive circuit 40b is provided for each inverter circuit 12b. When any one of the overcurrent judgment circuits 30a and 30b also judges that there is no overcurrent, the inverter drive circuits 40a and 40b send the control signal (described later) generated by the control device 50 to the corresponding inverter circuits 12a and 12b. On the other hand, when at least one (one) of the overcurrent judgment circuits 30a and 30b judges that there is an overcurrent, the two inverter drive circuits 40a and 40b stop the corresponding inverter circuits 12a and 12b respectively. Each inverter drive circuit 40a and 40b has a control signal (described later) according to each bit of the control signal (described later). Figure 3 The three-state buffer 41 shown. When the signal output by the logical product circuit 60 is at a high level, each three-state buffer 41 directly transmits (sends) a control signal (described later) generated by the control device 50 to the corresponding inverter circuit 12a, 12b. On the other hand, when the signal output by the logical product circuit 60 is at a low level, each three-state buffer 41 does not transmit the control signal (described later) to the corresponding inverter circuit 12a, 12b, and outputs a high impedance.

[0037] Setting device 15 sets a target current value as a target value of the welding current in accordance with an input operation by a user.

[0038] The control device 50 includes an abnormality determination unit 51 , an inverter control unit 52 , and a display instruction unit 53 .

[0039] The abnormality determination unit 51 determines whether there is an abnormality related to the balance of the two currents based on the two currents (multiple currents) detected by the two input current detection units 13a and 13b. Specifically, the abnormality determination unit 51 compares the size of the difference between the multiple currents detected by the two input current detection units 13a and 13b with the size of a prescribed reference value that is a reference value of the difference between the currents. In addition, when the difference between the currents detected by the two input current detection units 13a and 13b is greater than the prescribed reference value, the abnormality determination unit 51 determines that there is an abnormality. On the other hand, when the difference between the currents detected by the two input current detection units 13a and 13b is less than the prescribed reference value, the abnormality determination unit 51 determines that there is no abnormality.

[0040] The abnormality determination unit 51 determines the reference value based on the target current value set by the setting device 15. Specifically, when the target value is less than the specified value, the reference value is set lower than when the target value is greater than the specified value. Specifically, in the first embodiment, when the target current value of the welding current is greater than 100A, the abnormality determination unit 51 sets the reference value of the difference between the multiple currents detected by the input current detection units 13a and 13b to 10A, and when the target current value is less than 100A, the abnormality determination unit 51 sets the reference value to 20A. It should be noted that the reference value of the current difference may also be set to other values ​​according to the target current value.

[0041] The abnormality determination unit 51 receives the determination results of the two overcurrent determination circuits 30a and 30b. The abnormality determination unit 51 outputs a display indication in the following cases: based on whether the difference of the currents detected by the input current detection units 13a and 13b is above a predetermined reference value, it is determined that an abnormality exists when the difference is above the reference value; and based on whether the current detected by the input current detection units 13a and 13b corresponding to at least one overcurrent determination circuit 30a and 30b is above a threshold current, the at least one overcurrent determination circuit 30a and 30b determines that an overcurrent exists.

[0042] The inverter control unit 52 generates a control signal that controls a plurality of switching elements S1 to S4 of a pair of inverter circuits 12a and 12b so that the welding current reaches the target current value set by the setting device 15. Specifically, the inverter control unit 52 calculates the control value by performing PID control (feedback control), which is performed based on the difference between the current detected by the welding current detection unit 14 and the target current value, its differential value, and the integral value. It should be noted that the control value is not limited to being calculated by PID control, and can also be calculated by P control, PI control, or PD control. In addition, the inverter control unit 52 generates a control signal based on the calculated control value using PWM (Pulse Width Modulation) control. In normal operation, the inverter control unit 52 provides a common control signal to the two inverter circuits 12a and 12b.

[0043] When the abnormality determination unit 51 determines that an abnormality exists, the inverter control unit 52 stops the two inverter circuits 12a and 12b.

[0044] The display instruction unit 53 causes the display 16 to display a display screen indicating that there is an abnormality in the balance of the input currents of the two inverter circuits 12a and 12b when the abnormality determination unit 51 outputs a display instruction. In addition to indicating the abnormality in the balance, the display screen may display at least one of information identifying the inverter circuit 12a and 12b with a larger input current, information indicating the difference in the input currents of the two inverter circuits 12a and 12b, and information identifying the inverter circuit 12a and 12b with an overcurrent input current. Figure 4 The display screen is shown. Figure 4 An example of a display screen (Inverter unbalance abnormality, please perform maintenance on the upper inverter circuit (inverter circuit 12a)). A statement urging maintenance of one of the two inverter circuits 12a and 12b (in this example, maintenance of the upper inverter circuit (inverter circuit 12a)) is displayed.

[0045] The display 16 displays a display screen in accordance with an instruction from the display instruction unit 53 .

[0046] Smoothing reactor 17 smoothes the welding current output to merging node N3.

[0047] Output terminal 18 outputs the welding current smoothed by smoothing reactor 17 to welding wire 3 .

[0048] Next, an operation example of welding power supply device 10 configured as described above will be described.

[0049] First, an example is described in which the target current value set by the setting device 15 is 350A, and a current of 45A is input to each of the two inverter circuits 12a and 12b. In this example, since the target current value of the welding current is 350A, the abnormality determination unit 51 sets the reference value of the difference between the currents detected by the input current detection units 13a and 13b to 10A. The overcurrent determination circuits 30a and 30b set the threshold current of the input current of the inverter circuits 12a and 12b to 100A. Since the detection values ​​of the two input current detection units 13a and 13b are 45A respectively, the two overcurrent determination circuits 30a and 30b determine that there is no overcurrent. Therefore, the output of the logical product circuit 60 becomes a high level. In addition, the two inverter drive circuits 40a and 40b directly send the control signal generated by the inverter control unit 52 to the corresponding two inverter circuits 12a and 12b. Since the difference between the detection values ​​of the two input current detection units 13a and 13b is 0, the abnormality determination unit 51 determines that there is no abnormality and does not output a display instruction. As a result, the inverter control unit 52 does not stop the operation of the two inverter circuits 12a and 12b. The display 16 does not display a display screen indicating that there is an abnormality in the balance of the input currents of the two inverter circuits 12a and 12b.

[0050] On the other hand, due to the variation of the switching elements S1 to S4 constituting the inverter circuits 12a and 12b or the change of impedance due to the aging of the wiring, the currents flowing through the two inverter circuits 12a and 12b may be different even if the same control signal is provided. As an example of this case, the target current value of the welding current is 350A, and a current of 30A is input to one inverter circuit 12a and a current of 60A is input to the other inverter circuit 12b. In this example, the detection value of one input current detection unit 13a is 30A, and the detection value of the other input current detection unit 13b is 60A, so the two overcurrent judgment circuits 30a and 30b judge that there is no overcurrent. Therefore, since the input currents detected by the two input current detection units 13a and 13b are less than the predetermined threshold current (100A), the output of the logical product circuit 60 becomes a high level. Furthermore, the two inverter drive circuits 40a and 40b directly send the control signal generated by the inverter control unit 52 to the corresponding two inverter circuits 12a and 12b. Since the difference between the detection values ​​of the two input current detection units 13a and 13b is 30A, the abnormality determination unit 51 refers to the reference value 10A of the current difference, determines that there is an abnormality, and outputs a display indication. Correspondingly, Figure 4 As shown, the display instruction unit 53 displays a display screen indicating that there is an abnormality in the balance of the input currents of the two inverter circuits 12a and 12b on the display 16. Since the abnormality determination unit 51 determines that there is an abnormality, the inverter control unit 52 stops the two inverter circuits 12a and 12b.

[0051] exist Figure 5 In the example, the input currents of the two inverter circuits 12a and 12b are less than the threshold current 100A and are equal to each other. In this example, the two overcurrent judgment circuits 30a and 30b continue to judge that there is no overcurrent, and the abnormality judgment unit 51 also continues to judge that there is no abnormality. Therefore, the two inverter circuits 12a and 12b do not stop and continue to work. The display 16 does not display the display screen indicating that there is an abnormality in the balance of the input currents of the two inverter circuits 12a and 12b.

[0052] On the other hand, Figure 6In the example, at a specified time T, the input current of an inverter circuit 12a exceeds 100A, and an overcurrent judgment circuit 30a corresponding to the inverter circuit 12a refers to the threshold current 100A of the input current of the inverter circuits 12a and 12b to judge that there is an overcurrent. The input current detected by at least one of the input current detection units 13a and 13b that respectively detect the input current of the corresponding inverter circuits 12a and 12b is above the specified threshold current (100A), so the output of the logical product circuit 60 becomes a low level. Therefore, regardless of whether the difference between the two input currents exceeds the reference value 10A, the two inverter drive circuits 40a and 40b stop sending control signals to the corresponding inverter circuits 12a and 12b respectively. In this way, the two inverter circuits 12a and 12b stop. Figure 6 In the example, the current of the waveform indicated by the two-dot chain line no longer flows. In addition, the abnormality determination unit 51 outputs a display instruction, and the display 16 displays a display screen indicating that there is an abnormality in the balance of the input currents of the two inverter circuits 12a and 12b.

[0053] When an overcurrent exceeding 100A flows through the two inverter circuits 12a and 12b at the same time, the two overcurrent judgment circuits 30a and 30b judge that there is an overcurrent, and the output of the logical product circuit 60 becomes a low level. Therefore, regardless of whether the difference between the two input currents exceeds the reference value 10A, the two inverter drive circuits 40a and 40b stop sending control signals to the corresponding inverter circuits 12a and 12b. In this way, when an overcurrent flows through at least one of the inverter circuits 12a and 12b, the two inverter circuits 12a and 12b can be stopped, so that the damage and shortening of the service life of the inverter circuits 12a and 12b caused by the overcurrent can be suppressed.

[0054] Therefore, according to the first embodiment, when the target current value of the welding current is less than 100A (prescribed value), the reference value of the difference of the plurality of currents detected by the input current detection units 13a and 13b, which detect the input currents of the corresponding inverter circuits 12a and 12b, is set higher than when the target current value is 100A or more, so that it is not easy to be judged as abnormal. In this way, when the input currents of the two inverter circuits 12a and 12b are small and the difference between the input currents of the two inverter circuits 12a and 12b is unlikely to affect the service life of the inverter circuits 12a and 12b, the generation of the welding current is not stopped unnecessarily. Therefore, the production efficiency can be improved.

[0055] In the case where the functions of the overcurrent judgment circuits 30a, 30b, the logical product circuit 60, and the inverter drive circuits 40a, 40b are realized by executing a program in a microcomputer, it takes time from the generation of the overcurrent to the stop of the inverter circuits 12a, 12b, and the damage to the components included in the inverter circuits 12a, 12b caused by the overcurrent will be expanded. In contrast, in the first embodiment, since the overcurrent judgment circuits 30a, 30b, the logical product circuit 60, and the inverter drive circuits 40a, 40b are configured in a compact and simple circuit using a logic circuit and a filter circuit, the time from the generation of the overcurrent to the stop of the inverter circuits 12a, 12b can be shortened. Therefore, the damage to the components included in the inverter circuits 12a, 12b caused by the overcurrent can be more reliably suppressed.

[0056] (Second Embodiment)

[0057] Figure 7 The second embodiment is equivalent to Figure 1 In the second embodiment, the abnormality determination unit 51 determines the reference value of the difference of the currents of the input current detection units 13a and 13b based on the welding current detected by the welding current detection unit 14, instead of the target current value set by the setting device 15, wherein the input current detection units 13a and 13b detect the input currents of the corresponding inverter circuits 12a and 12b, respectively. Specifically, for example, the abnormality determination unit 51 sets the reference value of the difference of the currents to 10A when the welding current is 100A or more, and sets the reference value of the difference of the currents to 20A when the welding current is less than 100A. It should be noted that the reference value of the difference of the currents may also be set to other values ​​depending on the welding current.

[0058] The other structures and operations are the same as those of the first embodiment, and thus the same structures are denoted by the same reference numerals and their detailed descriptions are omitted.

[0059] It should be noted that in the first and second embodiments, the abnormality determination unit 51 determines whether there is an abnormality based on whether the difference between a pair of currents detected by a pair of input current detection units 13a and 13b is greater than a predetermined reference value. However, the abnormality determination unit 51 may also determine whether there is an abnormality based on the ratio of a pair of currents detected by a pair of input current detection units 13a and 13b. In detail, it may also be determined that there is an abnormality when at least one of the ratio of a pair of currents detected by the input current detection units 13a and 13b and the inverse of the ratio is greater than a predetermined reference value. Specifically, it may also be determined that there is an abnormality when the reference value of the current ratio is set to S, the detection value of one input current detection unit 13a is set to A1, and the detection value of the other input current detection unit 13b is set to A2. When at least one of A1 / A2≥S and A2 / A1≥S is established, it may be determined that there is an abnormality, and when neither A1 / A2≥S nor A2 / A1≥S is established, it may be determined that there is no abnormality. The reference value of the current ratio here may also be determined based on the target current value or the welding current. Specifically, when the target current value or the welding current is less than a predetermined value, the reference value may be set larger than when the target current value or the welding current is greater than a predetermined value. For example, when the target current value of the welding current or the detected welding current is greater than 100A, the reference value of the current ratio may be set to 2, and when the target current value or the welding current is less than 100A, the reference value of the current ratio may be set to 4.

[0060] In the first and second embodiments, when the target current value of the welding current or the welding current detected by the welding current detection unit 14 is less than the current threshold value of 100A, the abnormality determination unit 51 sets the reference value of the current difference to 20A, which is a value higher than when the target current value or the welding current detected by the welding current detection unit 14 is greater than the current threshold value. However, when the target current value of the welding current or the welding current detected by the welding current detection unit 14 is less than the current threshold value of 100A, the abnormality determination unit 51 may always determine that there is no abnormality. Even in such a case, when the input current of the two inverter circuits 12a and 12b is small and the difference in the input current of the two inverter circuits 12a and 12b is unlikely to affect the service life of the two inverter circuits 12a and 12b, the generation of the welding current is not stopped unnecessarily, so that the production efficiency can be improved.

[0061] In the first and second embodiments, when the abnormality determination unit 51 determines that an abnormality exists, the inverter control unit 52 stops the two inverter circuits 12a and 12b. However, when the abnormality determination unit 51 determines that an abnormality exists, the inverter control unit 52 may change the duty ratio of the control signal provided to at least one inverter circuit 12a and 12b to eliminate the abnormality. For example, when the abnormality determination unit 51 determines that an abnormality exists, the inverter control unit 52 may change the duty ratios (the ratio in one cycle during which the output voltage of the inverter circuit becomes high level) of the two inverter circuits 12a and 12b from being equal to each other to a state in which the duty ratio of the inverter circuit 12a with a larger input current is larger than the duty ratio of the inverter circuit 12b with a smaller input current (for example, to about 110% of the duty ratio of the inverter circuit 12b with a smaller input current) so as to continue to output the welding current. By achieving a balance between the input currents of the two inverter circuits 12a and 12b in this manner, welding can be continued without stopping the output of the welding current.

[0062] In the first and second embodiments described above, the display screen displays a message urging maintenance of one of the two inverter circuits 12a and 12b, but it may be replaced by a message such as Figure 8 As shown in FIG. 1 , a predetermined error number is displayed as an inverter unbalance abnormality. Thus, the display area on the display screen can be reduced.

[0063] In the above-described first embodiment and second embodiment, a pair of inverter circuits 12 a and 12 b are provided, but the present invention is also applicable to a case where three or more inverter circuits are provided.

[0064] -Industrial Applicability-

[0065] The welding power supply device of the present disclosure can suppress damage to the inverter circuit and shortening of its service life due to overcurrent, and is useful as a welding power supply device that generates welding current flowing into an arc welding wire using multiple AC voltages output by multiple inverter circuits.

[0066] -Explanation of symbols-

[0067] 10Welding power supply device

[0068] 12a, 12b inverter circuit

[0069] 13a, 13b Input current detection unit

[0070] 14 Welding current detection unit

[0071] 15 Setting device

[0072] 20 Welding current generation circuit

[0073] 30a, 30b Overcurrent judgment circuit

[0074] 40a, 40b inverter drive circuit (logic circuit)

[0075] 51 Abnormality Judgment Unit

[0076] 52 Inverter control unit

[0077] 60 Logical product circuit (logic circuit)

[0078] S1~S4 switching elements.

Claims

1. A welding power supply device, comprising a plurality of inverter circuits, a welding current generating circuit, and a control device, wherein each of the plurality of inverter circuits has a plurality of switching elements, and a DC voltage is converted into an AC voltage by turning on and off the plurality of switching elements, and the welding current generating circuit uses the plurality of AC voltages output by the plurality of inverter circuits to generate a welding current flowing into a welding wire for arc welding, and the control device generates a control signal, and the control signal controls the plurality of switching elements of the plurality of inverter circuits so that the welding current reaches a predetermined target current value, characterized in that: The welding power supply device further includes an input current detection unit, an overcurrent judgment circuit, and a logic circuit. The input current detection unit is provided for each of the plurality of inverter circuits to detect the input current of the corresponding inverter circuit. The overcurrent determination circuit is provided for each of the plurality of inverter circuits, and determines whether an overcurrent exists based on whether the current detected by the corresponding input current detection unit is greater than a threshold current. When any one of the overcurrent judgment circuits judges that there is no overcurrent, the logic circuit sends the control signal generated by the control device to the plurality of inverter circuits. On the other hand, when at least one of the overcurrent judgment circuits judges that there is an overcurrent, the logic circuit stops the plurality of inverter circuits. The control device determines whether there is an abnormality related to the balance of the multiple currents based on the multiple currents detected by the multiple input current detection units. When the control device determines that there is an abnormality, the control device stops the multiple inverter circuits or changes the duty cycle of the control signal to eliminate the abnormality.

2. The welding power supply device according to claim 1, characterized in that: The control device determines the presence or absence of the abnormality by comparing the magnitude of the difference between the plurality of currents detected by the plurality of input current detection units with the magnitude of a predetermined reference value.

3. The welding power supply device according to claim 2, characterized in that: The welding power supply device further includes a setting device for setting the target current value. The control device determines the reference value based on the target current value set by the setting device.

4. The welding power supply device according to claim 2, characterized in that: The welding power supply device further includes a welding current detection unit for detecting the welding current. The control device determines the reference value based on the current detected by the welding current detection unit.

5. The welding power supply device according to claim 1, characterized in that: The welding power supply device further includes a setting device for setting the target current value. When the target current value set by the setting device is smaller than a predetermined current threshold value, the control device determines that the abnormality is always absent.

6. The welding power supply device according to claim 1, characterized in that: The control device determines the presence or absence of the abnormality based on a ratio of a plurality of currents detected by the plurality of input current detection units.

7. The welding power supply device according to claim 1, characterized in that: The welding power supply device also includes a display, When the control device determines that an abnormality exists in the determination of the presence or absence of the abnormality, the control device causes the display to display a predetermined display screen.

8. A control method for a welding power supply device, the welding power supply device comprising a plurality of inverter circuits and a welding current generating circuit, each of the plurality of inverter circuits having a plurality of switching elements, and converting a DC voltage into an AC voltage by turning the plurality of switching elements on and off, the welding current generating circuit using the plurality of AC voltages output by the plurality of inverter circuits to generate a welding current flowing into a welding wire for arc welding, wherein a control signal is generated in the welding power supply device under the control method, the control signal controls the plurality of switching elements of the plurality of inverter circuits so that the welding current reaches a predetermined target current value, characterized in that: The welding power supply device further includes an input current detection unit, an overcurrent judgment circuit, and a logic circuit. The input current detection unit is provided for each of the plurality of inverter circuits to detect the input current of the corresponding inverter circuit. The overcurrent determination circuit is provided for each of the plurality of inverter circuits, and determines whether an overcurrent exists based on whether the current detected by the corresponding input current detection unit is greater than a threshold current. When any one of the overcurrent judgment circuits judges that there is no overcurrent, the logic circuit sends the control signal to the plurality of inverter circuits. On the other hand, when at least one of the overcurrent judgment circuits judges that there is an overcurrent, the logic circuit stops the plurality of inverter circuits. The control method determines whether there is an abnormality related to the balance of multiple currents based on multiple currents detected by the multiple input current detection units. If it is determined that there is an abnormality, the multiple inverter circuits are stopped or the duty cycle of the control signal is changed to eliminate the abnormality.

9. The control method of the welding power supply device according to claim 8, characterized in that: In this control method, the presence or absence of the abnormality is determined based on the magnitude of the difference between the plurality of currents detected by the plurality of input current detection units or the ratio between the plurality of currents detected by the plurality of input current detection units.

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