Welding power supply device

Abstract

The invention provides a welding power supply device. In the polarity switching of a plurality of welding power supply devices connected in parallel, if the output current of which welding power supply device is less than the switching current, the polarity switching is carried out first, and a transverse flow of the current flowing into the welding power supply device without polarity switching is generated. In the prior art, the output current of a welding power supply device without polarity switching is not less than the switching current, and polarity switching fails, so that polarity switching timing needs to be consistent. When the output current of the welding power supply device is below the switching current, a permission signal (Pm) is sent to perform polarity switching, and when the output current of the welding power supply device is not below the switching current, the polarity switching is performed when the welding power supply device receives the permission signal (Pm).

Description

Technical Field

[0001] The present invention relates to polarity switching of a welding power supply device. Background Art

[0002] Sometimes, multiple welding power supply devices are connected in parallel to increase the output capacity. When multiple welding power supply devices operate in parallel, if the polarities of the welding power supply devices are not synchronized in timing, a cross current will occur in which current flows from a welding power supply device that has switched its polarity earlier into a welding power supply device that has not yet switched its polarity. Patent Document 1 discloses that, in order to prevent such a cross current, a synchronization signal indicating the polarity timing of multiple welding power supply devices is transmitted via high-speed communication.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Documents : Japanese Unexamined Patent Application Publication No. 2021-053695

[0006] Patent Documents : Japanese Unexamined Patent Application Publication No. 2019-221010

[0007] In Patent Document 2, a welding power supply device is disclosed in which a DC power supply is converted into a high-frequency power supply by an inverter circuit, transformed into a desired voltage by a transformer, and positive and negative welding currents are obtained by switch elements connected in series with the output of DC power obtained by rectification. As described in Patent Document 2, in order to prevent an excessive induced voltage generated by an external inductor from being applied to the switch elements, when switching the polarity, both of the switch elements connected in series are turned on, and after reducing the current flowing through the external inductor to a given value, one of the switch elements is turned off to perform polarity switching. There is the following problem: Even if a synchronization signal is transmitted via high-speed communication as described in Patent Document 1 so that the start timing of polarity switching of multiple AC power supplies connected in parallel is the same, in the welding power supply device described in Patent Document 2, since the timing of polarity switching is the timing when the current flowing through each welding power supply device becomes equal to or less than a given value, the timing of switching the polarity will be inconsistent due to the deviation of the external inductor, and a cross current will occur in which current flows from a welding power supply device that has switched its polarity earlier into a welding power supply device that has not yet switched its polarity. Summary of the Invention

[0008] The present disclosure has been conceived in view of the above circumstances, and provides a welding power supply device capable of making the polarity switching timings of multiple welding power supply devices connected in parallel consistent.

[0009] In order to solve the above problems, the invention of Technical Solution 1 is a welding system in which multiple welding power supply devices are connected in parallel. The welding power supply device includes: 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 to convert it into a given 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 positive and negative polarities through series-connected switching elements; a current detector that detects the welding current; a control circuit that drives the inverter circuit and the polarity switching circuit; a communication line that receives a synchronization signal indicating the timing of polarity switching from a control device at high-speed communication; and a second communication line that transmits a permission signal issued by the control circuit at a time point when the absolute value of the output of the current detector becomes equal to or less than a given value during a polarity switching period in which the inverter circuit is stopped and both of the series-connected switching elements of the polarity switching circuit are turned on. The welding system is characterized in that the control circuit disconnects one of the switching elements at a time point when the absolute value of the output of the current detector becomes equal to or less than the given value or at a time point when the permission signal is received through the second communication line, and operates the inverter circuit to perform polarity switching.

[0010] The invention of Technical Solution 2 is based on the welding system described in Technical Solution 1, and is characterized in that the control circuit disconnects one of the switching elements at a time point when the absolute value of the output of the current detector is equal to or less than the given value and when permission signals are received from all of the parallel-connected welding power supply devices other than the local device through the second communication line, and operates the inverter circuit to perform polarity switching.

[0011] The invention of Technical Solution 3 is based on the welding system described in Technical Solution 2, and is characterized in that the control circuit disconnects one of the switching elements when a given time has elapsed since the synchronization signal, and operates the inverter circuit to perform polarity switching.

[0012] The invention of Technical Solution 4 is based on the welding system described in Technical Solution 3, and is characterized in that when a given time has elapsed since the synchronization signal, when one of the switching elements is disconnected, and when polarity switching is performed by operating the inverter circuit, the control circuit issues a warning through a notifier.

[0013] Advantages of the Invention

[0014] According to the welding power supply device of the present disclosure, it is possible to make the timing of polarity switching of the welding power supply device consistent in a welding system in which multiple welding power supply devices are connected in parallel. Description of the Drawings

[0015] Figure 1 It is a diagram showing the welding system according to Embodiment 1 of the present invention.

[0016] Figure 2 It is a block diagram of each function of the welding power supply device according to Embodiment 1 of the present invention.

[0017] Figure 3 It is a diagram showing the welding current of the welding system according to Embodiment 1 of the present invention.

[0018] Figure 4 It is a block diagram of each function of each welding power supply device of the welding system according to Embodiment 1 of the present invention considering external inductance.

[0019] Figure 5 It is a timing diagram showing the operation of polarity switching in the welding system according to Embodiment 1 of the present invention.

[0020] Figure 6 It is a timing diagram showing the operation of polarity switching in the welding system according to Embodiment 2 of the present invention.

[0021] Symbol Explanation

[0022] 1 Control device

[0023] 2, 2a to 2c Welding power supply device

[0024] 4 Trolley

[0025] 5 Wire feeding device

[0026] 6 Welding wire

[0027] 7 Electrode

[0028] 8 Arc

[0029] 9 Flux

[0030] 21 Rectifier smoothing circuit

[0031] 22 Inverter circuit

[0032] 23 Transformer

[0033] 23a Primary winding

[0034] 23b Secondary winding

[0035] 24 Rectifier circuit

[0036] 25 Polarity switching circuit

[0037] 27 Control circuit

[0038] Output terminals 28 and 29

[0039] Communication lines 31 to 33

[0040] Welding system A1

[0041] Smoothing capacitor C1

[0042] Current detector CT

[0043] DC reactor DCL

[0044] Rectifiers DR1 and DR2

[0045] Commercial power supply P

[0046] Polarity switching signal Pdr

[0047] Permission signal Pm

[0048] External inductors Lx, Lxa to Lxc

[0049] Switching elements TR1 to TR4, TR5 to TR8

[0050] Current value signal Id

[0051] Output control drive signal Idr

[0052] Output currents Io, Ioa to Ioc

[0053] Welding current Iw

[0054] Workpiece to be welded W. Detailed implementation mode

[0055] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0056] 〔Embodiment 1〕

[0057] Figure 1 This is a diagram showing the 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.

[0058] Figure 1The welding system A1 is a submerged arc welding system. 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 feed roller 5, a welding wire 6, and an electrode 7. While the welding system A1 moves the carriage 4 along the welding line of the workpiece W, the welding wire 6 is supplied to the tip of the electrode 8 through the wire feeding device 5. At the same time, an arc 8 is generated between the tip of the welding wire 6 and the workpiece W to perform welding. The arc 8 is blocked from the atmosphere by the 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, so as to generate an arc 8 between the tip of the welding wire 6 and the workpiece W. In addition, instead of using the carriage 4, the workpiece W can be moved or rotated.

[0059] The control device 1 performs various controls of the welding system A1. The control device 1 can be a device that installs a program for performing various controls of the welding system A1 in a general-purpose computer, or a dedicated device for controlling the welding system A1. The control device 1 moves the carriage 4 at a given 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. In addition, the feeding speed of the welding wire 6 is also instructed. The feeding speed is set according to the set welding current, etc.

[0060] The control device 1 instructs the welding power supply devices 2a, 2b, 2c to start and stop the output. In addition, the control device 1 sends 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 for switching the positive and negative of the output AC current.

[0061] 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 configuration. The control device 1 and the welding power supply devices 2a, 2b, and 2c communicate via the communication line 31, for example, through fieldbus communication. The control device 1 can send 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 to send signals to each of the welding power supply devices 2a, 2b, and 2c, the communication speed in the communication line 31 slows down according to the amount of information being communicated, and is about 1.2 kbps to 10 Mbps. In the present Embodiment 1, it is about 500 kbps. The control device 1 sends a command signal indicating the start and stop of output to the welding power supply devices 2a, 2b, and 2c via the communication line 31. In addition, the control device 1 sends a current command value and the number of parallel-connected welding power supply devices of the welding system A1 to the welding power supply devices 2a, 2b, and 2c via the communication line 31. Further, 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. In addition, the wiring configuration of the communication line 31 is not limited either.

[0062] 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 pattern. The control device 1 and the welding power supply devices 2a, 2b, and 2c communicate via the communication line 32 according to, 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 header of the communication data is made less than half of the amount of the header of the fieldbus communication, reducing the amount of the communication data to be transmitted. The communication speed in the communication line 32 based on the HCI communication standard is faster than the communication speed in the communication line 31, and is about 25 Mbps to 100 Mbps. In the present Embodiment 1, 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 will not become too slow. In addition, the communication standard for the control device 1 and the welding power supply devices 2a, 2b, and 2c 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. In addition, the wiring pattern of the communication line 32 is not limited either. In addition, the communication line 32 can be a dedicated line that transmits a pulse signal for switching between high level and low level as a synchronization signal from the control device 1 to the welding power supply devices 2a, 2b, and 2c. In this case, the communication line 32 can also perform communication at a higher speed than the communication line 31, and thus transmit the synchronization signal with almost no delay.

[0063] 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 only high-speed communication of the synchronization signal and the communication line 31 for transmitting other signals.

[0064] The communication line 33 is a dedicated line that transmits the permission signal pm described later as a high-level pulse signal, and connects between the parallel-connected welding power supply devices 2a, 2b, and 2c respectively. Since the permission signal Pm needs to be transmitted between the parallel-connected welding power supply devices 2a, 2b, and 2c at a fast transmission speed, it is preferable to use wired communication or optical communication based on optical fiber for the communication line 33, but the communication method is not limited.

[0065] Figure 2 It 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 same figure.

[0066] 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 performs smoothing. Additionally, the structure of the rectifying and smoothing circuit 21 is not limited.

[0067] 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 switches the switching elements by using the output control drive signal Idr input from the control circuit 27, thereby converting the DC power input from the rectifying and smoothing circuit 21 into high-frequency power and outputting it. Additionally, the inverter circuit 22 only needs to convert the DC power into high-frequency power. For example, it can also be a half-bridge type or an inverter circuit with other structures.

[0068] The transformer 23 transforms the high-frequency voltage output by the inverter circuit 22 and outputs it to the rectifying circuit 24. The transformer 23 includes a primary winding 23a and a secondary winding 23b. Each input terminal of the primary winding 23a is respectively connected to each output terminal of the inverter circuit 22. Each output terminal of the secondary winding 23b is respectively connected to each input terminal of the rectifying circuit 24. 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 rectifying circuit 24. Since the secondary winding 23b is insulated from the primary winding 23a, the current input from the commercial power supply P can be prevented from flowing into the secondary-side circuit. In addition, since the transformer 23 transforms the high-frequency voltage output by the inverter circuit 22, it is smaller and lighter in weight compared to a transformer that transforms the AC voltage of the commercial power supply P.

[0069] The rectifying circuit 24 includes: a rectifying circuit DR2; and a DC reactor DCL that smooths the current. The high-frequency power input from the transformer 23 is converted into DC power with a smoothed current and output to the polarity switching circuit 25. Additionally, the structure of the rectifying circuit 24 is not limited.

[0070] The 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 constitute an H-bridge circuit. Among them, the H-bridge circuit is composed of two arms in which two switching elements are connected in series. The inverter circuit 25 converts the DC power input from the rectifier circuit 24 into AC power and outputs it by switching the switching elements by using the polarity switching signal Pdr input from the control circuit 27. The inverter circuit 25 alternately switches between a state where the potential of the output terminal 28 (connected to the electrode 7) is higher than the potential of the output terminal 29 (connected to the workpiece W) (i.e., reverse polarity (EP)), and a state where the potential of the output terminal 28 is lower than the potential of the output terminal 29 (i.e., positive polarity (EN)). In addition, the polarity switching circuit 25 only needs to convert DC power into AC power. For example, it can be a half-bridge type or an inverter circuit with other structures.

[0071] 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 supply device 2, so that the tip of the welding wire 6 and the workpiece W are melted, and the welding wire 6 is fed by the wire feeding device 5 to perform welding. The arc 8 is covered with a flux 9 to block it from the atmosphere. In addition, there is an external inductance Lx caused by wiring between the welding power supply device 2 and the electrode 7 and the workpiece W.

[0072] The current detector CT detects the output current Io of the welding power supply device 2. In the present Embodiment 1, 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. In addition, the structure of the current detector CT is not limited as long as it can detect the output current from the connection line. The arrangement location of the current detector CT is not limited. For example, the current detector CT can also be arranged on the connection line connecting the other output terminal of the polarity switching circuit 25 and the output terminal 28.

[0073] The control circuit 27 is a circuit for controlling the welding power supply device 2, and is realized by, for example, a microcomputer. The control circuit 27 is input with the current value signal Id from the current detector CT, the command signal and the current command value via the communication line 31, the synchronization signal via the communication line 32, and the output 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 as drive signals to the inverter circuit 22 and the polarity switching circuit 25 respectively.

[0074] When the control circuit 27 receives an instruction signal indicating the start of output from the control device 1, it starts the output control of the drive signals Idr and the polarity switching signal Pdr as the respective drive signals for the inverter circuit 22 and the polarity switching circuit 25, thereby starting the power output. In addition, when the control circuit 27 receives an instruction signal indicating the stop of power output from the control device 1, it stops the output control of the drive signals Idr and the polarity switching signal Pdr, thereby stopping the power output.

[0075] In addition, the control circuit 27 calculates the effective current value based on the current value signal Id input from the current detector CT. Then, the control circuit 27 generates an output control drive signal Idr for controlling the switching elements TR1 to 4 of the inverter circuit 22 based on this effective current value and the current command value input from the control device 1, and outputs it to the inverter circuit 22. That is, the control circuit 27 performs feedback control so that the effective current value coincides with the current command value.

[0076] In addition, during the polarity switching, the control circuit 27 calculates the absolute value of the current value signal Id, sends or receives the permission signal Pm described later to the control line 33, 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.

[0077] At the timing of the synchronization signal input from the control device 1, the control circuit 27 performs positive and negative polarity switching according to the following steps. In the case of switching from the reverse polarity (EP) to the positive polarity (EN), the control circuit 27 stops the operation of the inverter circuit 22 using the synchronization signal input from the control device 1, and drives TR7 and TR6 in the off state of the polarity switching circuit 25 to the on state. Then, the welding current Iw flowing through the external inductor Lx is divided into two paths: external inductor Lx → electrode 7 → arc 8 → workpiece W → output terminal 29 → body diode of switching element TR7 → TR5, and external inductor Lx → electrode 7 → arc 8 → workpiece W → output terminal 29 → switching element TR8 → body diode of switching element TR6, and the energy stored in the external inductor Lx is consumed by the arc 8, so that the welding current Iw and the output current Io also gradually decrease. In addition, during this period, all the switching elements TR5 to TR8 are turned on, and the current flowing through the DC reactor DCL is in a short-circuit state through 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 via the output terminals 28 and 29.

[0078] If the control circuit 27 sends a high-level pulse signal, i.e., a permission signal Pm, to the control line 33 at the time point when the absolute value of the current value signal Id becomes equal to or less than a given value (100 A), disconnects the switching elements TR5 and TR8, and starts the stopped inverter circuit 22, the current flowing through the DC reactor DCL flows in the path of 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 is switched to the positive polarity (EN). In addition, the given value is not limited to 100 A, and any current value that suppresses the induced voltage of the external inductor Lx within the allowable value is acceptable. Further, even when the absolute value of the current value signal Id does not reach equal to or less than the given value (100 A), when the control circuit 27 receives the permission signal Pm from the control line 33, it also disconnects the switching elements TR5 and TR8, starts the stopped inverter circuit 22, and switches to the positive polarity (EN).

[0079] Figure 3 It 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 the same figure. In addition, (a) of the same figure represents a synchronization signal, (b) of the same figure represents a permission signal Pm, (c) of the same figure represents a welding current Iw, (d) of the same figure represents an output control drive signal Idr, (e) of the same figure represents the on / off states of the switching elements TR5 and TR8 of the polarity switching circuit 25, and (f) of the same figure represents the on / off states of the switching elements TR6 and TR7 of the polarity switching circuit 25.

[0080] The control device 1 sends a current setting command for a rectangular wave of a welding current of 500 A to the welding power supply devices 2a, 2b, and 2c via the signal line 31. In addition, a synchronization signal with a frequency of 50 Hz is sent from the control device 1 via the signal line 32 as shown in (a) of the same figure. The welding power supply devices 2a, 2b, and 2c are Figure 2 the same welding power supply devices shown in the block diagram. Since the outputs of the welding power supply devices 2a, 2b, and 2c are connected in parallel, 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 same figure.

[0081] Time t0: At time t0, 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). Since the signal line 32 is a high-speed communication line with little time lag in transmission, the control circuits 27 of the welding power supply devices 2a, 2b, and 2c simultaneously start the polarity switching operation according to the following steps.

[0082] (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.

[0083] (2) As shown in Fig. (f), the switching elements TR6 and TR7 of the polarity switching circuit 25 are turned on.

[0084] The operations of (1) and (2) are maintained until the absolute value of the current value signal Id becomes equal to or less than a given value (100 A), preventing the switching elements of the polarity switching circuit 25 from malfunctioning due to the induced voltage caused by the external inductor Lx.

[0085] 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 the given value (100 A), the control circuits 27 of the welding power supply devices 2a, 2b, and 2c simultaneously perform polarity switching according to the following steps.

[0086] (1) As shown in Fig. (b), a high-level pulse signal is sent as the permission signal Pm.

[0087] (2) As shown in Fig. (e), the switching elements TR5 and TR8 of the polarity switching circuit 25 are turned off.

[0088] (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.

[0089] Thus, as shown in Fig. (b), the welding current Iw switches from the reverse polarity (EP) to the positive polarity (EN) at time t1 and slowly decreases to -1500 A.

[0090] Time t2: At time t2, a synchronization signal is input to the welding power supply devices 2a, 2b, and 2c through the signal line 32, indicating a 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 simultaneously start the polarity switching operation according to the following steps.

[0091] (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.

[0092] (2) As shown in Fig. (e), the switching elements T5 and TR8 of the polarity switching circuit 25 are turned on.

[0093] The operations of (1) and (2) are maintained until the absolute value of the current value signal Id becomes equal to or less than a given value (100 A), preventing the switching elements of the polarity switching circuit 25 from malfunctioning due to the induced voltage caused by the external inductor.

[0094] 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 given value (100 A), the control circuits 27 of the welding power supply devices 2a, 2b, and 2c simultaneously perform polarity switching according to the following steps.

[0095] (1) As shown in (b) of the figure, a high-level pulse signal is sent as the permission signal Pm.

[0096] (2) As shown in (f) of the figure, the switching elements TR6 and TR7 of the polarity switching circuit 25 are turned off.

[0097] (3) As shown in (c) of the figure, the control circuit 27 switches the output control drive signal Idr to start and starts the inverter circuit 22.

[0098] As a result, as shown in (b) of the figure, the welding current Iw switches from the positive polarity (EN) to the reverse polarity (EP) at time t3 and slowly rises to the set value of 1500 A.

[0099] Through the above operations, as shown in (b) of the figure, the welding current Iw becomes an AC rectangular wave with a frequency of 50 Hz and ±1500 A. However, due to the deviation of the external inductance Lx connected to the welding power supply devices 2a, 2b, and 2c, the time points at which the absolute value of the current value signal Id becomes equal to or less than the given value (100 A) are different. Therefore, it is difficult for the welding power supply devices 2a, 2b, and 2c to make the polarity switching times t1 and t3 coincide simultaneously.

[0100] Figure 4 It is a block diagram of the welding system A1 according to Embodiment 1 of the present invention, considering the external inductance connected to the welding power supply devices 2a, 2b, and 2c. The magnitude relationship of the inductances of the external inductances Lxa, Lxb, and Lxc is Lxa < Lxb < Lxc. In addition, the block diagrams and operations of the welding power supply devices 2a, 2b, and 2c are the same as Figure 2 and are thus omitted.

[0101] Figure 5 is in Figure 4Timing chart of the polarity switching operation in the case where the inductances of the external inductors 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 are different (Lxa < Lxb < Lxc). (a) of the same figure represents the synchronization signal, (b) of the same figure represents the permission signal Pm, (c) of the same figure represents the welding current Iw, (d) of the same figure represents the output current Ioa of the welding power supply device 2a, (e) of the same figure represents the output current Iob of the welding power supply device 2b, and (f) of the same figure represents the output current Ioc of the welding power supply device 2c. Hereinafter, with reference to the same figure, it will be described that even in the case where the external inductances are different, by Embodiment 1, the timings of the polarity switching of the welding power supply devices 2a, 2b, and 2c can be made consistent.

[0102] Time t10: At time t10, as shown in (a) of the same figure, the 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 make the switching elements TR5 to TR8 of the polarity switching circuit 25 in the on state. Then, the output currents Ioa, Iob, and Ioc flowing through the welding power supply devices 2a, 2b, and 2c decrease as shown in (d) to (f) of the same figure, but due to the differences in the inductances of the external inductors 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 inductor is the largest, and the reduction rate of the output current Ioc of the welding power supply device 2c with the largest connected external inductor is the smallest.

[0103] Time t11: At time t11, as shown in (d) of the same figure, when the output current Ioa of the welding power supply device 2a with the largest reduction rate of the output current becomes below the given value (100 A), the control circuit 27 of the welding power supply device 2a, as shown in (b) of the same figure, sends a high-level pulse signal as the permission signal Pm to the signal line 33, and disconnects the switching elements TR5 and TR8 of the polarity switching circuit 25 and starts the inverter circuit 22, thereby switching the polarity to the positive polarity (EN).

[0104] At time t11, as shown in (e) and (f) of the same figure, the output currents Iob and Ioc of the welding power supply devices 2b and 2c have not reached below the given value (100 A). The control circuits 27 of the welding power supply devices 2b and 2c that receive the permission signal Pm sent by the welding power supply device 2a disconnect the switching elements TR5 and TR8 of the polarity switching circuit 25, start the inverter circuit 22, and switch the polarity to the positive polarity (EN), whereby the timings of the polarity switching of the welding power supply devices 2a, 2b, and 2c can be made consistent.

[0105] According to Embodiment 1, since the output current Ioa of the welding power supply device 2a becomes equal to or less than a given value (100 A), but the output currents Iob and Ioc of the welding power supply devices 2b and 2c have not reached below the given value (100 A), there is a possibility that the switching elements of the polarity switching circuits 25 of the welding power supply devices 2b and 2c may malfunction during polarity switching. Therefore, in the embodiment, a method for solving the problem is described.

[0106] 〔Embodiment 2〕

[0107] In Embodiment 2, polarity switching is performed at the time when the output current Io of all the welding power supply devices connected in parallel with the welding system A1 transmitted from the control device 1 becomes equal to or less than a given value (100 A). Therefore, the control circuit 27 performs polarity switching at the time when it is confirmed, based on the number-of-units data of the welding power supply devices connected in parallel with the welding system A1 transmitted from the control device 1 via the communication line 31, that all the welding power supply devices connected in parallel other than the local device have sent the permission signal Pm to the communication line 33.

[0108] Figure 6 It is a timing chart showing the polarity switching operation in the welding system A1 according to Embodiment 2 of the present invention. Hereinafter, the operation during polarity switching will be described with reference to the same figure. In addition, in Embodiment 2, the structures and block diagrams of the welding system A1 and the welding power supply devices 2a, 2b, and 2c are the same as those in Embodiment 1.

[0109] The control circuits 27 of the welding power supply devices 2a, 2b, and 2c set the number of units connected in parallel = 3, where the number of welding power supply devices connected in parallel including the local device is 3, based on the number-of-units data of the welding power supply devices connected in parallel with the welding system A1 transmitted from the control device 1 via the communication line 31.

[0110] Time t10: At time t10, as shown in (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 the reverse polarity (EP) to the positive polarity (EN). The control circuits 27 of the welding power supply devices 2a, 2b, and 2c reset the permission signal transmission / reception count to zero, stop the inverter circuit 22, and turn on the switching elements TR5 to TR8 of the polarity switching circuit 25.

[0111] Time t11: At time t11, as shown in Fig. (d), it is the time point when the output current Ioa of the welding power supply device 2a with the maximum output current reduction rate becomes below the given value (100 A), that is, it is the time point when the absolute value of the current value signal Id of the welding power supply device 2a becomes below the given value (100 A). The control circuit 27 of the welding power supply device 2a sends a high-level pulse signal to the signal line 33 as the permission signal Pm as shown in Fig. (b), and sets the permission signal reception / transmission count to 1. At this time point, since the permission signal reception / transmission count has not reached 3, which is the number of parallel-connected units, the control circuit 27 of the welding power supply device 2a stops the inverter circuit 22 without performing polarity switching and maintains the on-state of the switching elements TR5 - TR8 of the polarity switching circuit 25. 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 increment the permission signal reception / transmission count by 1.

[0112] Time t12: At time t12, as shown in Fig. (e), the output current Iob of the welding power supply device 2b becomes below the given value (100 A). The control circuit 27 of the welding power supply device 2b sends a high-level pulse signal to the signal line 33 as the permission signal Pm as shown in Fig. (b), and increments the permission signal reception / transmission count to 2. At this time point, in the control circuit 27 of the welding power supply device 2b, since the permission signal reception / transmission count has not reached 3, which is the number of parallel-connected units, the inverter circuit 22 is stopped and the on-state of the switching elements TR5 - 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 increment the permission signal reception / transmission count to 2.

[0113] Time t13: At time t13, as shown in Fig. (f), the output current Ioc of the welding power supply device 2c with the minimum output current reduction rate becomes below the given value (100 A). The control circuit 27 of the welding power supply device 2c sends a high-level pulse signal to the signal line 33 as the permission signal Pm as shown in Fig. (b), and increments the permission signal reception / transmission count to 3. Since the permission signal reception / transmission count has reached 3, which is the number of parallel-connected units, the control circuit 27 of the welding power supply device 2c disconnects the switching elements TR5 - TR8 of the polarity switching circuit 25, starts the inverter circuit 22, and switches the polarity to the positive polarity (EN). 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. If the permission signal reception / transmission count is incremented to 3, then the permission signal reception / transmission count has reached 3, which is the number of parallel-connected units. Therefore, the switching elements TR5 - TR8 of the polarity switching circuit 25 are disconnected, the inverter circuit 22 is started, and the welding power supply devices 2a and 2b also switch the polarity to the positive polarity (EN) simultaneously.

[0114] According to Embodiment 2, since the polarity switching is performed at the time 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 given value (100 A), there is no need to worry about the failure of the switching elements of the polarity switching circuit 25. On the other hand, as shown in FIGS. (d) and (e), there is also a case where the output currents Ioa and Iob of the welding power supply devices 2a and 2b become 0 A during the polarity switching period (t10 to t13). Since the welding current Iw flows at about 100 A in the arc 8 at the polarity switching time point t13, and further, at the time t13, the current flowing into the DC reactor DCL of the welding power supply devices 2a, 2b, and 2c is supplied to the arc 8, the welding current Iw does not become equal to or less than 100 A, and the arc can be continuously generated.

[0115] In Embodiment 2, a welding system A1 that outputs an amplitude of ±1500 A by connecting three 500 A-class welding power supply devices in parallel is described. Usually, the welding system A1 is a welding system that can output 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. Since the AC welding current is output up to a frequency of 100 Hz, the polarity switching period (the period of t10 to t13) for performing polarity switching according to the synchronization signal needs to be within 10% of the half-cycle period, and needs to be set to within (1 / 100 Hz) × 1 / 2 × 0.1 = 0.5 mS. Therefore, it is also considered that in the case of increasing the capacity of the welding current by connecting nine 500 A-class welding power supply devices in parallel or three 1500 A-class welding power supply devices in parallel, the output currents of all the welding power supply devices do not become equal to or less than the given value within 0.5 mS, and the desired frequency cannot be obtained. Therefore, the control circuit 27 can be set so that the polarity switching is performed even when the number of permitted signal transmissions and receptions does not reach the number of parallel-connected units and a given time has elapsed since the synchronization signal. In addition, the given time can be set by default in the control circuit 27 in advance, or a value sent from the control device 1 through the communication line 31 can be used.

[0116] If a welding power supply device that has performed polarity switching after a given time has elapsed since the synchronization signal without the output current becoming equal to or less than the given value notifies an operator through a notification device to recheck the wiring between the output terminals 28 to the electrode 7 and between the output terminals 29 to the non-welded object W, troubleshooting becomes easy. As the notification device, it can be implemented by lighting a warning display lamp or the like, but is not limited thereto.

Claims

1. A welding system in which a plurality of welding power supply devices are connected in parallel, and the welding power supply device includes: 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 to convert it into a given 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 positive and negative polarities through series-connected switching elements; A current detector that detects the welding current; A control circuit that drives the inverter circuit and the polarity switching circuit; A communication line that receives a synchronization signal indicating the timing of polarity switching from a control device at high-speed communication; And A second communication line that transmits a permission signal issued by the control circuit at a time point when the absolute value of the output of the current detector becomes equal to or less than a given value during a polarity switching period in which the control circuit stops the inverter circuit and turns on both of the series-connected switching elements of the polarity switching circuit, The welding system is characterized in that The control circuit disconnects one of the switching elements at a time point when the absolute value of the output of the current detector becomes equal to or less than the given value or at a time point when the permission signal is received through the second communication line, and operates the inverter circuit to perform polarity switching.

2. The welding system according to claim 1, wherein The control circuit disconnects one of the switching elements at a time point when the absolute value of the output of the current detector is equal to or less than the given value and when the permission signal is received from all of the parallel-connected welding power supply devices other than the own device through the second communication line, and operates the inverter circuit to perform polarity switching.

3. The welding system according to claim 2, wherein The control circuit disconnects one of the switching elements when a given time has elapsed from the synchronization signal, and operates the inverter circuit to perform polarity switching.

4. The welding system according to claim 3, wherein When the control circuit disconnects one of the switching elements at a time point when the given time has elapsed from the synchronization signal and operates the inverter circuit to perform polarity switching, a warning is given by a notifier.

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