Welding power supply device

Abstract

To solve the problem that in switching polarities of a plurality of welding power supply devices connected in parallel, the polarities need to be switched at the same timing because when an output current of any one welding power supply device falls below a switching current, and when the polarity switching is performed ahead, a lateral flow in which currents flow into the welding power supply device whose polarities are not switched occurs, so that the output current of the welding power supply device whose polarities are not switched do not falls below the switching current and the polity switching fails.SOLUTION: At a time point when an output current of a welding power supply device falls below a switching current, a permission signal Pm is transmitted to perform polarity switching. The polarity switching is performed to the welding power supply device whose output current does not fall below the switching current at a time point when the permission signal Pm is received.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] It relates to the polarity switching of a welding power supply device.

Background Art

[0002] Multiple welding power supply devices may be connected in parallel to increase the output capacity. In Patent Document 1, when multiple welding power supply devices are operated in parallel, if the polarity timings of the welding power supply devices are not aligned, in order to prevent a cross current in which current flows from a welding power supply device whose polarity has already switched to a welding power supply device whose polarity has not yet switched, it is disclosed to transmit a synchronization signal that instructs the polarity timings of multiple welding power supply devices by high-speed communication.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] A welding power supply device is disclosed in Prior Art Document 2, which converts a DC power supply into a high-frequency power supply by an inverter circuit, converts it into a desired voltage by a transformer, and obtains welding currents of both positive and negative polarities by a switching element connected in series to the output of the DC power obtained by rectification. As described in Prior Art Document 2, in order to prevent an excessive induced voltage generated by an external inductance from being applied to the switching element, when switching polarities, both of the switching elements connected in series are turned on, the current flowing through the external inductance is decreased to a predetermined value, and then one of the switching elements is turned off to perform polarity switching. As described in Prior Art Document 1, even if a synchronization signal is transmitted in high-speed communication and a plurality of AC power supplies connected in parallel align the start timing of polarity switching, in the welding power supply device described in Prior Art Document 2, since the timing of performing polarity switching is when the current flowing through each welding power supply device becomes a value equal to or less than a predetermined value, the timings of polarity switching are not aligned due to variations in the external inductance, and there is a problem that a cross current occurs in which current flows from a welding power supply device whose polarity has been switched earlier to a welding power supply device whose polarity has not been switched yet.

[0005] The present disclosure has been conceived in view of the above circumstances, and provides a welding power supply device capable of aligning the polarity switching timings of a plurality of welding power supply devices connected in parallel.

Means for Solving the Problem

[0006] In order to solve the above-described problems, the invention according to claim 1 is an inverter circuit that converts DC power into high-frequency power, a transformer that applies the high-frequency power generated by the inverter circuit to a primary winding and converts it into a predetermined voltage, a rectifier circuit that converts the high-frequency power generated in a secondary winding of the transformer into DC power, a polarity switching circuit that switches the output of the rectifier circuit into welding currents of both positive and negative polarities by switching elements connected in series, a current detector that detects the welding output current, a control circuit that drives the inverter circuit and the polarity switching circuit, A communication line that receives a synchronization signal instructing the timing of polarity switching from a control device at high speed communication, A second communication line that transmits a permission signal issued by the control circuit when the absolute value of the output of the current detector becomes equal to or less than a predetermined value during a polarity switching period in which the control circuit stops the inverter circuit and turns on both of the switching elements connected in series to the polarity switching circuit, In a welding system in which a plurality of welding power supply devices provided with the above are connected in parallel, The control circuit turns off one of the switching elements and operates the inverter circuit to perform polarity switching when the absolute value of the output of the current detector becomes equal to or less than the predetermined value or when the permission signal is received via the second communication line, A welding system characterized by the above.

[0007] The invention of claim 2 is, The control circuit turns off one of the switching elements and operates the inverter circuit to perform polarity switching when the absolute value of the output of the current detector is equal to or less than the predetermined value and the permission signal is received from all of the welding power supply devices connected in parallel other than the own device via the second communication line, The welding system according to claim 1, characterized by the above.

[0008] The invention of claim 3 is, The control circuit turns off one of the switching elements and operates the inverter circuit to perform polarity switching when a predetermined time has elapsed from the synchronization signal, The welding system according to claim 2, characterized by the above.

[0009] The invention of claim 4 is, When the control circuit turns off one of the switching elements and operates the inverter circuit to perform polarity switching when a predetermined time has elapsed from the synchronization signal, a warning is given by a notification device, The welding system according to claim 3, characterized by the above.

Effect of the Invention

[0010] According to the welding power supply device of the present disclosure, in a welding system in which a plurality of welding power supply devices are connected in parallel, the timing of polarity switching of the welding power supply device can be made to coincide.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0013] 〔Embodiment 1〕 FIG. 1 is a diagram showing a welding system according to Embodiment 1 of the present invention. Hereinafter, the operation of the system will be described with reference to the same figure.

[0014] The welding system A1 in Fig. 1 is a welding system for performing submerged arc welding. The welding system A1 includes a control device 1, welding power supply devices 2a, 2b, 2c, communication lines 31, 32, 33, a carriage 4, a wire feeding roll 5, a welding wire 6, and an electrode 7. The welding system A1 performs welding by generating an arc 8 between the tip of the welding wire 6 and the workpiece W while moving the carriage 4 along the weld line of the workpiece W and supplying the welding wire 6 to the tip of the electrode 8 by the wire feeding device 5. The arc 8 is shielded from the atmosphere by a flux 9. The welding power supply devices 2a, 2b, 2c convert the AC power supplied from the commercial power supply P into AC power of a desired frequency and output it to generate an arc 8 between the tip of the welding wire 6 and the workpiece W. Instead of using the carriage 4, the workpiece W may be moved or rotated.

[0015] The control device 1 performs various controls of the welding system A1. The control device 1 may be a general-purpose computer installed with a program for performing various controls of the welding system A1, or may be a dedicated device for controlling the welding system A1. The control device 1 moves the carriage 4 at a predetermined moving speed. The moving speed is set according to the material and thickness of the workpiece W, etc. The control device 1 instructs the wire feeding device 5 to start and stop the feeding of the welding wire. Also, the feeding speed of the welding wire 6 is instructed. The feeding speed is set according to the set welding current, etc.

[0016] The control device 1 instructs the welding power supply devices 2a, 2b, 2c to start and stop the output. Also, the control device 1 transmits a current command value for setting the output current, the number of parallel-connected welding power supply devices of the welding system A1, and a synchronization signal which is the timing of switching the positive and negative of the output AC current.

[0017] The communication line 31 is a communication line that connects the control device 1 and the welding power supply devices 2a, 2b, and 2c, and is wired in a bus-type wiring form. The control device 1 and the welding power supply devices 2a, 2b, and 2c communicate with each other via the communication line 31, for example, by fieldbus communication. The control device 1 can transmit different signals to the welding power supply devices 2a, 2b, and 2c respectively. On the other hand, since the control device 1 divides the utilization time of the communication line 31 and transmits signals to each welding power supply device 2a, 2b, and 2c, the communication speed on the communication line 31 becomes slower according to the amount of information to be communicated, and is about 1.2 kbps to 10 Mbps. In the first embodiment, it is about 500 kbps. The control device 1 transmits a command signal for instructing the start and stop of the output to the welding power supply devices 2a, 2b, and 2c via the communication line 31. In addition, the control device 1 transmits the current command value and the number of welding power supply devices connected in parallel in the welding system A1 to the welding power supply devices 2a, 2b, and 2c via the communication line 31. Note that the communication standard between the control device 1 and the welding power supply devices 2a, 2b, and 2c via the communication line 31 is not limited to fieldbus communication. Also, the wiring form of the communication line 31 is not limited either.

[0018] The communication line 32 is a communication line that connects the control device 1 and the welding power supply devices 2a, 2b, and 2c, and is wired in a bus-type wiring form. The control device 1 and the welding power supply devices 2a, 2b, and 2c communicate with each other via the communication line 32 in accordance with, for example, the HCI (Host Control Interface) communication standard. The HCI communication standard is a communication standard developed for high-speed communication between the control device 1 and the welding power supply devices 2a, 2b, and 2c. In the HCI communication standard, the amount of the head of communication data is made less than or equal to half of the amount of the head of fieldbus communication, and the data amount of the communication data to be transmitted is reduced. The communication speed on the communication line 32 according to the HCI communication standard is faster than the communication speed on the communication line 31 and is about 25 Mbps to 100 Mbps. In this case, it is about 50 Mbps. The control device 1 transmits a synchronization signal instructing the start of polarity switching to the welding power supply devices 2a, 2b, and 2c via the communication line 32. Since the communication line 32 only transmits the synchronization signal and does not transmit or receive other signals, the communication speed does not become too slow. Note that the communication standard by which the control device 1 and the welding power supply devices 2a, 2b, and 2c communicate via the communication line 32 is not limited to the HCI communication standard, as long as the synchronization signal can be transmitted with almost no delay. Also, the wiring form of the communication line 32 is not limited. Further, the communication line 32 may be a dedicated line that transmits a pulse signal in which the high level and the low level are switched as a synchronization signal from the control device 1 to the welding power supply devices 2a, 2b, and 2c. Also in this case, the communication line 32 can perform high-speed communication compared to the communication line 31 and transmit the synchronization signal with almost no delay.

[0019] That is, the control device 1 and the welding power supply devices 2a, 2b, and 2c are connected by two communication lines, namely, the communication line 32 for high-speed communication of only the synchronization signal and the communication line 31 for transmitting other signals.

[0020] The communication line 33 is a dedicated line for transmitting the permission signal pm, which will be described later, as a high-level pulse signal, and is connected between the welding power supply devices 2a, 2b, and 2c connected in parallel. Since the permission signal Pm needs to be mutually transmitted between the welding power supply devices 2a, 2b, and 2c connected in parallel at a high transmission speed, the communication line 33 may use wired communication or optical communication using an optical fiber, but the communication method is not limited.

[0021] Figure 2 is a block diagram of each function of the welding power supply device according to Embodiment 1 of the present invention. Hereinafter, each block will be described with reference to the figure.

[0022] The rectifying and smoothing circuit 21 converts the AC power input from the commercial power supply P into DC power and outputs it. The rectifying and smoothing circuit 21 includes a rectifying circuit DR1 that rectifies the AC current and a smoothing capacitor C1 that smooths it. Note that the configuration of the rectifying and smoothing circuit 21 is not limited.

[0023] The inverter circuit 22 is, for example, a single-phase full-bridge type PWM control inverter and includes four switching elements TR1 to TR4. The inverter circuit 22 converts the DC power input from the rectifying and smoothing circuit 21 into high-frequency power and outputs it by switching the switching elements according to the output control drive signal Idr input from the control circuit 27. Note that the inverter circuit 22 only needs to convert DC power into high-frequency power, and may be, for example, a half-bridge type or an inverter circuit with other configurations.

[0024] Transformer 23 transforms the high-frequency voltage output by the inverter circuit 22 and outputs it to the rectifier circuit 24. Transformer 23 includes a primary winding 23a and a secondary winding 23b. Each input terminal of the primary winding 23a is connected to each output terminal of the inverter circuit 22 respectively. Each output terminal of the secondary winding 23b is connected to each input terminal of the rectifier circuit 24 respectively. The output voltage of the inverter circuit 22 is transformed according to the turns ratio of the primary winding 23a and the secondary winding 23b and input to the rectifier circuit 24. Since the secondary winding 23b is insulated from the primary winding 23a, it is possible to prevent the current input from the commercial power supply P from flowing into the secondary-side circuit. Also, since transformer 23 transforms the high-frequency voltage output by the inverter circuit 22, it is smaller and lighter compared to a transformer that transforms the AC voltage of the commercial power supply P.

[0025] Rectifier circuit 24 includes a rectifier circuit DR2 and a DC reactor DCL that smooths the current. It converts the high-frequency power input from transformer 23 into DC power with a smoothed current and outputs it to the polarity switching circuit 25. Note that the configuration of the rectifier circuit 24 is not limited.

[0026] Polarity switching circuit 25 is, for example, a single-phase full-bridge type PWM control inverter, and includes four switching elements TR5 to TR8 that form an H-type bridge circuit composed of two pairs of arms in which two switching elements are connected in series. Inverter circuit 25 switches the switching elements according to the polarity switching signal Pdr input from the control circuit 27, thereby converting the DC power input from the rectifier circuit 24 into AC power and outputting it. Inverter circuit 25 alternately switches between a reverse polarity (EP) in which the potential of the output terminal 28 (connected to electrode 7) is higher than the potential of the output terminal 29 (connected to the workpiece W) and a positive polarity (EN) in which the potential of the output terminal 28 is lower than the potential of the output terminal 29. Note that the polarity switching circuit 25 may be any circuit that converts DC power into AC power, for example, a half-bridge type or an inverter circuit with other configurations.

[0027] The output terminal 28 is connected to the electrode 7, and the output terminal 29 is connected to the workpiece W. An arc 8 is generated between the tip of the welding wire 6 and the workpiece W by the output of the welding power source device 2, melting the tip of the welding wire 6 and the workpiece W, and welding is performed by feeding the welding wire 6 with the wire feeding device 5. The arc 8 is covered with the flux 9 to cut off the atmosphere. Note that there is an external inductance Lx due to wiring between the welding power source device 2, the electrode 7, and the workpiece W.

[0028] The current detector CT detects the output current Io of the welding power source device 2. In the first embodiment, it is arranged on the connection line connecting the output terminal 29 from the polarity switching circuit 25. The current detector CT inputs a current value signal Id corresponding to the detected output current Io to the control circuit 27. Note that the configuration of the current detector CT is not limited as long as it can detect the output current from the connection line. The location where the current detector CT is arranged is not limited. For example, the current detector CT may be arranged on the connection line connecting the other output terminal of the polarity switching circuit 25 and the output terminal 28.

[0029] The control circuit 27 is a circuit for controlling the welding power source device 2 and is realized by, for example, a microcomputer or the like. The control circuit 27 receives the current value signal Id from the current detector CT, receives a command signal and a current command value via communication 31, receives a synchronization signal via the communication line 32, and inputs and outputs a permission signal Pm via the communication line 33. Then, the control circuit 27 outputs an output control drive signal Idr and a polarity switching signal Pdr, which are drive signals, to the inverter circuit 22 and the polarity switching circuit 25, respectively.

[0030] When the control circuit 27 receives a command signal instructing the start of output from the control device 1, it starts the output of the output control drive signal Idr and the polarity switching signal Pdr, which are the respective drive signals, to the inverter circuit 22 and the polarity switching circuit 25, thereby starting the power output. Also, when the control circuit 27 receives a command signal instructing the stop of power output from the control device 1, it stops the output of the output control drive signal Idr and the polarity switching signal Pdr, thereby stopping the power output.

[0031] Further, the control circuit 27 calculates the effective current value from the current value signal Id input from the current detector CT. Then, based on the effective current value and the current command value input from the control device 1, the control circuit 27 generates an output control drive signal Idr for controlling the switching elements TR1 to 4 of the inverter circuit 22 and outputs it to the inverter circuit 22. That is, the control circuit 27 performs feedback control so that the effective current value matches the current command value.

[0032] Also, during the polarity switching period, the control circuit 27 calculates the absolute value of the current value signal Id, transmits or receives a permission signal Pm (described later) to / from the control line 33, and generates a polarity switching signal Pdr for controlling the switching elements TR5 to 8 of the polarity switching circuit 25 and outputs it to the polarity switching circuit 25.

[0033] The control circuit 27 performs positive / negative polarity switching in the following procedure at the timing of the synchronization signal input from the control device 1. When switching from the reverse polarity (EP) to the positive polarity (EN), the control circuit 27 stops the operation of the inverter circuit 22 by the synchronization signal input from the control device 1, and drives and switches TR7 and TR6, which were in the off state of the polarity switching circuit 25, to the on state. Then, the welding current Iw flowing through the external inductance Lx is divided and shunted through two paths: external inductance Lx → electrode 7 → arc 8 → work W → output terminal 29 → body diode of switching element TR7 → TR5 and external inductance Lx → electrode 7 → arc 8 → work W → output terminal 29 → switching element TR8 → body diode of switching element TR6. The energy stored in the external inductance Lx is consumed by the arc 8, and the welding current Iw and the output current Io also gradually decrease. During this period, all of the switching elements TR5 to TR8 are on, and the current flowing through the DC reactor DCL is in a short-circuited state by the switching elements TR5, TR6 and the rectifier DR2, and the switching elements TR7, TR8 and the rectifier DR2, and is not supplied to the arc 8 through the output terminals 28 and 29.

[0034] When the absolute value of the current value signal Id becomes equal to or less than a predetermined value (100 A), the control circuit 27 transmits a permission signal Pm, which is a high-level pulse signal, to the control line 33, turns off the switching elements TR5 and TR8, and starts the inverter circuit 22 that has been stopped. Then, the current flowing through the DC reactor DCL flows through the path of the switching element TR7 → current detector CT → output terminal 29 → workpiece W → arc 8 → electrode 7 → output terminal 28 → switching element TR6 → rectifier diode DR2, so the polarity switches to the positive polarity (EN). Note that the predetermined value is not limited to 100 A, and any current value that can suppress the induced voltage of the external inductance Lx to an allowable value may be used. Even when the absolute value of the current value signal Id does not reach the predetermined value (100 A) or less, if the control circuit 27 receives the permission signal Pm from the control line 33, it turns off the switching elements TR5 and TR8, starts the inverter circuit 22 that has been stopped, and switches to the positive polarity (EN).

[0035] Figure 3 is a diagram showing the welding current Iw output in the welding system A1 according to Embodiment 1 of the present invention. Hereinafter, the operation of the welding system A1 will be described with reference to this figure. Note that in the figure, (a) is the synchronization signal, (b) is the permission signal Pm, (c) is the welding current Iw, (d) is the output control drive signal Idr, (e) is the on / off state of the switching elements TR5 and TR8 of the polarity switching circuit 25, and (f) is the on / off state of the switching elements TR6 and TR7 of the polarity switching circuit 25.

[0036] A rectangular wave current setting command of 500 A welding current is transmitted from the control device 1 to the welding power supply devices 2a, 2b, and 2c via the signal line 31. Also, as shown in (a) of the figure, a synchronization signal with a frequency of 50 Hz is transmitted from the control device 1 via the signal line 32. The welding power supply devices 2a, 2b, and 2c are the same welding power supply devices shown in the block diagram of FIG. 2, and the outputs of the welding power supply devices 2a, 2b, and 2c are connected in parallel. Therefore, the welding current Iw becomes an AC rectangular wave with a frequency of 50 Hz and a welding current of ±1500 A as shown in (c) of the figure.

[0037] Time t0: At time t0, a synchronization signal is input to the welding power supply devices 2a, 2b, and 2c via the signal line 32, and there is an instruction to switch from the reverse polarity (EP) to the positive polarity (EN). Since the signal line 32 is a high-speed communication line with little delay in transmission time, the control circuits 27 of the welding power supply devices 2a, 2b, and 2c start the polarity switching operation simultaneously according to the following procedure. (1) As shown in Fig. (d) of the same figure, the control circuit 27 switches the output control drive signal Idr to stop and stops the inverter circuit 22. (2) As shown in Fig. (f) of the same figure, the switching elements TR6 and TR7 of the polarity switching circuit 25 are turned on. The operations (1) and (2) are maintained until the absolute value of the current value signal Id becomes equal to or less than a predetermined value (100 A), preventing the switching elements of the polarity switching circuit 25 from failing due to the induced voltage of the external inductance Lx.

[0038] Time t1: At time t1, since the output currents Ioa, Iob, and Ioc of the welding power supply devices 2a, 2b, and 2c become equal to or less than a predetermined value (100 A), the control circuits 27 of the welding power supply devices 2a, 2b, and 2c perform polarity switching simultaneously according to the following procedure. (1) As shown in Fig. (b) of the same figure, a pulse signal of High level is transmitted as the permission signal Pm. (2) As shown in Fig. (e) of the same figure, the switching elements TR5 and TR8 of the polarity switching circuit 25 are turned off. (3) As shown in Fig. (c) of the same figure, the control circuit 27 switches the output control drive signal Idr to start and starts the inverter circuit 22. As a result, as shown in Fig. (b) of the same figure, the welding current Iw switches its polarity from the reverse polarity (EP) to the positive polarity (EN) at time t1 and gradually decreases to -1500 A.

[0039] Time t2: At time t2, a synchronization signal is input to the welding power supply devices 2a, 2b, and 2c via the signal line 32, and there is an instruction to switch from the positive polarity (EN) to the reverse polarity (EP). The control circuits 27 of the welding power supply devices 2a, 2b, and 2c start the polarity switching operation simultaneously according to the following procedure. (1) As shown in Fig. (d), the control circuit 27 switches the output control drive signal Idr to stop and stops the inverter circuit 22. (2) As shown in Fig. (e), the switching elements T5 and TR8 of the polarity switching circuit 25 are turned on. The operations (1) and (2) are maintained until the absolute value of the current value signal Id becomes equal to or less than a predetermined value (100 A), preventing the switching elements of the polarity switching circuit 25 from failing due to the induced voltage from the external inductance.

[0040] Time t3: At time t3, since the output currents Ioa, Iob, and Ioc of the welding power supply devices 2a, 2b, and 2c become equal to or less than a predetermined value (100 A), the control circuits 27 of the welding power supply devices 2a, 2b, and 2c perform polarity switching simultaneously in the following procedure. (1) As shown in Fig. (b), a pulse signal of High level is transmitted as the permission signal Pm. (2) As shown in Fig. (f), the switching elements TR6 and TR7 of the polarity switching circuit 25 are turned off. (3) As shown in Fig. (c), the control circuit 27 switches the output control drive signal Idr to start and starts the inverter circuit 22. Thereby, as shown in Fig. (b), the welding current Iw switches from the positive polarity (EN) to the reverse polarity (EP) at time t3 and gradually increases to the set value of 1500 A.

[0041] By the above operations, as shown in Fig. (b), the welding current Iw becomes an AC rectangular wave with a frequency of 50 Hz and ±1500 A. However, since there are variations in the external inductance Lx connected to the welding power supply devices 2a, 2b, and 2c, and the time points when the absolute value of the current value signal Id becomes equal to or less than a predetermined value (100 A) are different, it is difficult to align the polarity switching times t1 and t3 simultaneously for all the welding power supply devices 2a, 2b, and 2c.

[0042] FIG. 4 is a block diagram considering external inductances connected to the welding power supply devices 2a, 2b, and 2c in the welding system A1 according to Embodiment 1 of the present invention. It is assumed that the magnitude relationship of the inductances of the external inductances Lxa, Lxb, and Lxc is Lxa < Lxb < Lxc. Note that the block diagrams and operations of the welding power supply devices 2a, 2b, and 2c are the same as those in FIG. 2 and are omitted.

[0043] FIG. 5 is a timing chart of the polarity switching operation when the inductances of the external inductances Lxa, Lxb, and Lxc connected to the welding power supply devices 2a, 2b, and 2c in the welding system A1 according to Embodiment 1 of the present invention shown in FIG. 4 are different (Lxa < Lxb < Lxc). In the figure, (a) shows the synchronization signal, (b) shows the permission signal Pm, (c) shows the welding current Iw, (d) shows the output current Ioa of the welding power supply device 2a, (e) shows the output current Iob of the welding power supply device 2b, and (f) shows the output current Ioc of the welding power supply device 2c. Hereinafter, with reference to this figure, it will be explained that even when the external inductances are different, the timing of the polarity switching of the welding power supply devices 2a, 2b, and 2c can be made the same according to Embodiment 1.

[0044] Time t10: At time t10, as shown in FIG. (a), a synchronization signal is input to the welding power supply devices 2a, 2b, and 2c through the signal line 32, and there is an instruction to switch from the reverse polarity (EP) to the positive polarity (EN). The control circuits 27 of the welding power supply devices 2a, 2b, and 2c stop the inverter circuits 22 and turn on the switching elements TR5 to TR8 of the polarity switching circuit 25. Then, the output currents Ioa, Iob, and Ioc flowing through the welding power supply devices 2a, 2b, and 2c decrease as shown in FIGS. (d) to (f). However, due to the difference in the inductances of the external inductances Lxa, Lxb, and Lxc (Lxa < Lxb < Lxc), the reduction rates are different. The reduction rate of the output current Ioa of the welding power supply device 2a with the smallest connected external inductance is the largest, and the reduction rate of the output current Ioc of the welding power supply device 2c with the largest connected external inductance is the smallest.

[0045] Time t11: At time t11, as shown in Fig. (d), when the output current Ioa of the welding power supply device 2a with the largest rate of decrease in the output current becomes equal to or less than a predetermined value (100 A), the control circuit 27 of the welding power supply device 2a transmits a high-level pulse signal as a permission signal Pm to the signal line 33 as shown in Fig. (b), turns off the switching elements TR5 and TR8 of the polarity switching circuit 25, activates the inverter circuit 22, and switches the polarity to the positive polarity (EN). At time t11, as shown in Figs. (e) and (f), the output currents Iob and Ioc of the welding power supply devices 2b and 2c have not yet reached the predetermined value (100 A). However, the control circuits 27 of the welding power supply devices 2b and 2c that have received the permission signal Pm transmitted by the welding power supply device 2a turn off the switching elements TR5 and TR8 of the polarity switching circuit 25, activate the inverter circuit 22, and switch the polarity to the positive polarity (EN), thereby enabling the timing of the polarity switching of the welding power supply devices 2a, 2b, and 2c to be aligned.

[0046] According to Embodiment 1, although the output current Ioa of the welding power supply device 2a is equal to or less than the predetermined value (100 A), the output currents Iob and Ioc of the welding power supply devices 2b and 2c have not yet reached the predetermined value (100 A). Therefore, there is a risk that the switching elements of the polarity switching circuit 25 of the welding power supply devices 2b and 2c may malfunction during polarity switching. Therefore, in Embodiment 2, a method for solving this problem will be described.

[0047] 〔Embodiment 2〕 In Embodiment 2, polarity switching is performed when the output currents Io of all the welding power supply devices connected in parallel to the welding system A1 transmitted from the control device 1 become equal to or less than a predetermined value (100 A). Therefore, the control circuit 27 performs polarity switching when it confirms that the permission signal Pm has been transmitted to the communication line 33 from all of the parallel-connected welding power supply devices other than its own device based on the number data of the parallel-connected welding power supply devices of the welding system A1 transmitted from the control device 1.

[0048] FIG. 6 is a timing chart for explaining the polarity switching operation in the welding system A1 according to the second embodiment of the present invention. Hereinafter, the operation at the time of polarity switching will be described with reference to the same figure. Note that also in the second embodiment, the configurations and block diagrams of the welding system A1 and the welding power supply devices 2a, 2b, and 2c are the same as those in the first embodiment of this form.

[0049] The control circuit 27 of the welding power supply devices 2a, 2b, and 2c determines from the number-of-units data of the welding power supply devices connected in parallel to the welding system A1 transmitted via the communication line 31 from the control device 1 that there are three welding power supply devices connected in parallel including its own unit, and is set to parallel connection number = 3.

[0050] Time t10: At time t10, as shown in FIG. (a) of the same figure, a synchronization signal is input to the welding power supply devices 2a, 2b, and 2c via the signal line 32, and there is an instruction to switch from reverse polarity (EP) to positive polarity (EN). The control circuit 27 of the welding power supply devices 2a, 2b, and 2c resets the number of permission signal transmissions and receptions to zero, stops the inverter circuit 22, and turns on the switching elements TR5 to TR8 of the polarity switching circuit 25.

[0051] Time t11: At time t11, as shown in FIG. (d) of the same figure, when the output current Ioa of the welding power supply device 2a with the largest rate of decrease in output current becomes equal to or less than a predetermined value (100 A), that is, when the absolute value of the current value signal Id of the welding power supply device 2a becomes equal to or less than the predetermined value (100 A), the control circuit 27 of the welding power supply device 2a transmits a high-level pulse signal as a permission signal Pm to the signal line 33 as shown in FIG. (b) of the same figure, and sets the number of permission signal transmissions and receptions to 1. At this point, since the number of permission signal transmissions and receptions of the control circuit 27 of the welding power supply device 2a has not reached 3, the parallel connection number, the inverter circuit 22 is stopped without performing polarity switching, and the on-state of the switching elements TR5 to TR8 of the polarity switching circuit 25 is maintained. The control circuits 27 of the welding power supply devices 2b and 2c receive the permission signal Pm from the welding power supply device 2a and count up the number of permission signal transmissions and receptions to 1.

[0052] Time t12: At time t12, as shown in Fig. (e), the output current Iob of the welding power supply device 2b becomes equal to or less than a predetermined value (100 A). As shown in Fig. (b), the control circuit 27 of the welding power supply device 2b transmits a high-level pulse signal as a permission signal Pm to the signal line 33, and counts up the permission signal transmission / reception count to 2. At this point, since the permission signal transmission / reception count has not reached 3, which is the number of parallel connection units, in the control circuit 27 of the welding power supply device 2b, the inverter circuit 22 is stopped, and the on-state of the switching elements TR5 to TR8 of the polarity switching circuit 25 is maintained. The control circuits 27 of the welding power supply devices 2a and 2c receive the permission signal Pm from the welding power supply device 2b and count up the permission signal transmission / reception count to 2.

[0053] Time t13: At time t13, as shown in Fig. (f), the output current Ioc of the welding power supply device 2c, which has the smallest rate of decrease in the output current, becomes equal to or less than a predetermined value (100 A). As shown in Fig. (b), the control circuit 27 of the welding power supply device 2c transmits a high-level pulse signal as a permission signal Pm to the signal line 33, and counts up the permission signal transmission / reception count to 3. Since the permission signal transmission / reception count has reached 3, which is the number of parallel connection units, in the control circuit 27 of the welding power supply device 2c, the switching elements TR5 to TR8 of the polarity switching circuit 25 are turned off, the inverter circuit 22 is activated, and the polarity is switched to the positive polarity (EN). When the control circuits 27 of the welding power supply devices 2a and 2b receive the permission signal Pm from the welding power supply device 2c and count up the permission signal transmission / reception count to 3, since the permission signal transmission / reception count has reached 3, which is the number of parallel connection units, the switching elements TR5 to TR8 of the polarity switching circuit 25 are turned off, the inverter circuit 22 is activated, and the welding power supply devices 2a and 2b also switch the polarity to the positive polarity (EN) simultaneously.

[0054] According to the second embodiment, since the polarity switching is performed when the output currents Ioa, Iob, and Ioc of the welding power supply devices 2a, 2b, and 2c all become equal to or less than a predetermined value (100 A), there is no need to worry about the failure of the switching element of the polarity switching circuit 25. On the other hand, as shown in FIGS. (d) and (e), during the polarity switching period (t10 to t13), the output currents Ioa and Iob of the welding power supply devices 2a and 2b may become 0 A. Even at the polarity switching time t13, a welding current Iw of about 100 A flows through the arc 8, and further at the time t13, the current flowing through the DC reactor DCL of the welding power supply devices 2a, 2b, and 2c is supplied to the arc 8, so the welding current Iw does not become 100 A or less, and the arc generation can be sustained.

[0055] In the second embodiment, a welding system A1 capable of outputting an amplitude of ±1500 A by connecting three 500 A-class welding power supply devices in parallel has been described. The normal welding system A1 is a welding system capable of outputting an AC welding current with a frequency of 10 to 100 Hz and an amplitude of about ±4500 A, and is configured by connecting nine 500 A-class welding power supply devices in parallel or three 1500 A-class welding power supply devices in parallel. In order to output an AC welding current up to a frequency of 100 Hz, the polarity switching period (the period of t10 to t13) for performing polarity switching from the synchronization signal needs to be within 10% of the half-cycle period, and needs to be within (1 / 100 Hz) × 1 / 2 × 0.1 = 0.5 mS. Therefore, when the welding current is increased by connecting nine 500 A-class welding power supply devices in parallel or three 1500 A-class welding power supply devices in parallel, it is conceivable that the output currents of all the welding power supply devices do not become equal to or less than the predetermined value within 0.5 mS and the desired frequency cannot be obtained. Therefore, the control circuit 27 may be set to perform polarity switching when a predetermined time has elapsed from the synchronization signal even if the number of permission signal transmissions and receptions has not reached the number of parallel connections. The predetermined time may be set as a default in the control circuit 27 in advance, or the value transmitted from the control device 1 via the communication line 31 may be used.

[0056] If the output current does not fall below a predetermined value and the polarity is switched after a predetermined time has elapsed from the synchronization signal, the welding power source device can facilitate troubleshooting by notifying the operator via a notification device to check the wiring between output terminals 28 and electrode 7 and between output terminals 29 and non-welded object W. The notification device can be implemented by, for example, lighting a warning indicator light, but is not limited thereto.

Explanation of Signs

[0057] 1 Control device 2, 2a - 2c Welding power source device 4 Trolley 5 Wire feeding device 6 Welding wire 7 Electrode 8 Arc 9 Flux 21 Rectifier smoothing circuit 22 Inverter circuit 23 Transformer 23a Primary winding 23b Secondary winding 24 Rectifier circuit 25 Polarity switching circuit 27 Control circuit 28, 29 Output terminals 31 - 33 Communication lines A1 Welding system C1 Smoothing capacitor CT Current detector DCL DC reactor DR1, 2 Rectifiers P Commercial power supply Pdr Polarity switching signal Pm Permission signal Lx, Lxa - c External inductance TR1 - 4, TR5 - 8 Switching elements Id Current value signal Idr Output control drive signal Io, Ioa - c Output current Iw Welding current W Welded object

Claims

1. An inverter circuit that converts DC power into high-frequency power, A transformer that applies the high-frequency power generated by the inverter circuit to a primary winding and converts it into a predetermined voltage, A rectifier circuit that converts the high-frequency power generated in the secondary winding of the transformer into DC power, A polarity switching circuit that switches the output of the rectifier circuit to welding currents of both positive and negative polarities by switching elements connected in series, A current detector that detects the welding output current, A control circuit that drives the inverter circuit and the polarity switching circuit, A communication line that receives a synchronization signal instructing the timing of polarity switching from a control device via high-speed communication, A second communication line that transmits a permission signal issued by the control circuit when the absolute value of the output of the current detector becomes equal to or less than a predetermined value during a polarity switching period in which the control circuit stops the inverter circuit and turns on both of the switching elements connected in series to the polarity switching circuit, In a welding system in which a plurality of welding power supply devices provided with the above are connected in parallel, The control circuit turns off one of the switching elements and operates the inverter circuit to perform polarity switching when the absolute value of the output of the current detector becomes equal to or less than the predetermined value or when the permission signal is received via the second communication line, A welding system characterized by the above.

2. The control circuit turns off one of the switching elements and operates the inverter circuit to perform polarity switching when the absolute value of the output of the current detector is equal to or less than the predetermined value and the permission signal is received from all of the welding power supply devices connected in parallel other than its own device via the second communication line, The welding system according to claim 1, characterized by the above.

3. The control circuit turns off one of the switching elements and operates the inverter circuit to perform polarity switching when a predetermined time has elapsed from the synchronization signal, The welding system according to claim 2, characterized by the above.

4. When the control circuit turns off one of the switching elements and operates the inverter circuit to perform polarity switching when a predetermined time has elapsed from the synchronization signal, a warning is given by a notification device, The welding system according to claim 3, characterized by the above.

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