JP7018354B2 - Welding power supply and output control method. - Google Patents

Description

The present invention relates to a welding current output control method and a welding power supply device.

As a power supply device for welding used in an arc welding device, a primary side conversion circuit that rectifies a commercial power source (for example, a three-phase AC power source) and converts it into direct current, and a direct current input from the primary conversion circuit including a plurality of switching elements. Is converted to high-frequency alternating current, a welding transformer (transformer) that converts high-frequency alternating current input from the inverter circuit to lower voltage, and low-voltage alternating current input from the welding transformer is rectified and converted to direct current. Those equipped with a welding torch and a secondary side conversion circuit that outputs to a welding target are known (see Patent Document 1). Further, in Patent Document 1, a full bridge type inverter circuit in which four semiconductor switching elements (transistors, etc.) are arranged in a bridge shape is used, and the magnitude of the welding current flowing from the electrode (welding wire) of the welding torch to the welding target is large. This is adjusted by the switching control of the inverter circuit. More specifically, in the full-bridge type inverter circuit, two diagonally located switching elements are set as one pair, and the pair to be turned on is alternately switched to convert direct current into alternating current. Then, for example, the magnitude of the alternating current output by the inverter circuit is adjusted by using a PWM modulation method that adjusts the period (pulse width) for turning on each pair.

Japanese Unexamined Patent Publication No. 2016-144303

In the case of a welding power supply used in an arc welding device, if the positive and negative are almost balanced in the high frequency alternating current supplied from the inverter circuit to the transformer, there is no particular problem, but it is biased to the positive side or the negative side. If this happens, the transformer may be demagnetized. When the transformer is demagnetized, the switching element may fail due to an excessive current flowing through the switching element.

In particular, in arc welding, control is performed to rapidly increase or decrease the magnitude of the welding current according to the state of droplets formed between the welding wire and the welding target (work) for the purpose of suppressing the generation of spatter. Can be done. When such control is performed, the high frequency alternating current supplied from the inverter circuit to the transformer tends to be biased to the positive side or the negative side.

Here, in Patent Document 1, the on-pulse width for turning on each switching element of the inverter circuit is monitored, and the on-pulse width is corrected to suppress the demagnetization of the transformer. However, it is difficult to suppress the demagnetization of the transformer when the above-mentioned control for rapidly increasing or decreasing the magnitude of the welding current is performed.

An object of the present invention is to suppress demagnetization in a transformer due to an increase or decrease in welding current.

The power supply device for welding of the present invention includes a plurality of switching elements constituting a bridge circuit, an inverter circuit that converts DC into AC, a transformer that transforms AC output from the inverter circuit, and the transformer. It has a rectifying circuit that rectifies the output AC to DC and a control circuit that controls the plurality of switching elements in the inverter circuit, and the control circuit is applied from the inverter circuit to the primary side of the transformer. Based on the cumulative value of the applied voltage on the primary side, the determining means for determining the switching element to be turned on next in the inverter circuit, the output current value flowing from the rectifying circuit to the welding wire, and the target value of the output current value. The means for determining the duty ratio of the predetermined control cycle and the means for creating a duty signal including the duty ratio of the predetermined control cycle are included, and the determining means includes the primary side applied voltage. The result of the calculation of accumulating the ET product, which is the product of the applied time of the primary side applied voltage, is used as the cumulative value, and the applied time is the on-time determined based on the duty signal. Therefore, when the first switching element is turned on and the second switching element is turned off, the inverter circuit supplies a positive current to the primary side of the transformer and turns off the first switching element. Further, when the second switching element is turned on, a negative current is supplied to the primary side of the transformer, and the determining means means that the cumulative value of the applied voltage on the primary side is equal to or less than a predetermined negative threshold value. It is determined that the cumulative value is biased to the negative side based on the existence, and it is determined that the cumulative value is biased to the positive side based on the fact that the cumulative value is equal to or higher than a predetermined positive threshold value. When the cumulative value is biased to the negative side, the switching element to be turned on next in the inverter circuit is determined to be the first switching element, and when the cumulative value is biased to the positive side, the inverter circuit is used. The feature is that the switching element to be turned on next is determined to be the second switching element .
From another point of view, the present invention includes an inverter circuit that includes a plurality of switching elements constituting a bridge circuit and converts DC to AC, and a transformer that transforms AC output from the inverter circuit. This is an output control method for a welding power supply device including a rectifying circuit for rectifying an alternating current output from the transformer to a direct current and a control circuit for controlling the switching operation of the plurality of switching elements, and welding from the rectifying circuit. The value of the output current flowing through the wire is detected , and when the first switching element is turned on and the second switching element is turned off in the inverter circuit, a positive current is supplied to the primary side of the transformer and the current is supplied. When the first switching element is turned off and the second switching element is turned on, a negative current is supplied to the primary side of the transformer, and the output current value and the target of the output current value in the control circuit. Based on the value, the duty ratio of the predetermined control cycle is determined, the duty signal including the duty ratio of the predetermined control cycle is created, the on-time determined based on the duty signal, and the on-time. The ET product, which is the product of the primary side applied voltage applied from the inverter circuit to the primary side of the transformer, is calculated for each control cycle, and the calculated cumulative value of the ET product is calculated, and the cumulative value is calculated. It is determined that the cumulative value is biased to the negative side based on the fact that it is equal to or less than a predetermined negative threshold, and the cumulative value is determined to be equal to or higher than the predetermined positive threshold. When it is determined that the cumulative value is biased to the positive side and the cumulative value is biased to the negative side, the switching element to be turned on next in the inverter circuit is determined to be the first switching element, and the cumulative value is set to the positive side. When the transformer circuit is biased, the switching element to be turned on next in the inverter circuit is determined to be the second switching element, and the plurality of switching elements in the inverter circuit are controlled.

According to the present invention, it is possible to suppress demagnetization in a transformer due to an increase or decrease in welding current.

It is a figure which shows the schematic structure of the welding system which concerns on embodiment of this invention. It is a figure which shows the schematic structure of the power supply device for welding in a welding system. It is a figure which shows the schematic structure of the control circuit in a power supply device for welding. It is a figure which shows an example of the target value of the output current in a short circuit transition. (A) to (c) are diagrams for explaining the operation of the inverter circuit of this embodiment. (A) to (c) are diagrams for explaining the operation (continuation) of the inverter circuit of this embodiment. (A) to (c) are diagrams for explaining the operation (continuation) of the inverter circuit of this embodiment. (A) and (b) are diagrams for explaining the ET product. It is a flowchart for demonstrating control of output current in this Embodiment. It is a figure for demonstrating an example (example) of the time-dependent change of the total ET product when the method of this embodiment is applied. It is a figure for demonstrating an example (comparative example) of the time-dependent change of the total ET product when the method of this embodiment is not applied.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[Welding system configuration]
FIG. 1 is a diagram showing a schematic configuration of a welding system 1 according to an embodiment of the present invention. This welding system 1 welds the object to be welded 200 by a consumable electrode type (melting electrode type) gas shielded arc welding method.

The welding system 1 includes a welding torch 10 for welding an object to be welded 200 using a welding wire 100, and a robot arm 20 for holding the welding torch 10 and setting the position and posture of the welding torch 10. Further, the welding system 1 includes a wire feeding device 30 that feeds the welding wire 100 to the welding torch 10, and a shield gas supply device 40 that supplies a shield gas (for example, carbon dioxide gas) to the welding torch 10. Further, the welding system 1 controls a welding power supply device 50 that supplies a DC welding current to the welding wire 100 and the workpiece 200 via the welding torch 10 and controls the welding current, and a robot arm 20. It is equipped with a robot control device 60. Although not described in detail here, the welding power supply device 50 also controls the welding speed, the feeding speed of the welding wire 100, and the like in addition to the welding current.

[Structure of power supply for welding]
FIG. 2 is a diagram showing a schematic configuration of a welding power supply device 50 in the welding system 1. However, FIG. 2 shows the components related to the supply and control of the welding current extracted from the welding power supply device 50.

The welding power supply device 50 of the present embodiment converts the three-phase AC power supplied from the commercial AC power source 5 into DC power by performing various treatments, and converts the welding torch 10 and the object to be welded 200 (see FIG. 1). ). During this period, the welding power supply device 50 adjusts the DC power (DC voltage and DC current) to be output to the outside by performing various power conversions. In the following description, the welding current output from the welding power supply device 50 to the workpiece 200 (see FIG. 1) via the welding torch 10 and the welding wire 100 may be referred to as an output current. be.

The welding power supply device 50 of the present embodiment includes a primary rectifying circuit 51, an inverter circuit 52, a transformer 53, a secondary rectifying circuit 54, an output reactor 55, an output current detection circuit 56, and a primary side application. It includes a voltage detection circuit 57 and a control circuit 58. Hereinafter, each component of the welding power supply device 50 will be described in order.

(Primary rectifier circuit)
The input side of the primary rectifier circuit 51 is connected to the commercial AC power supply 5, and the output side is connected to the inverter circuit 52. The primary rectifier circuit 51 converts the three-phase alternating current input from the commercial alternating current power supply 5 into direct current by rectifying and smoothing it. Here, the primary rectifier circuit 51 of the present embodiment is configured by a three-phase full-wave rectifier circuit. More specifically, the primary rectifier circuit 51 of the present embodiment includes a primary rectifier diode group 511 provided on the output side of the commercial AC power supply 5 and an input reactor 512 provided on the output side of the primary rectifier diode group 511. It has a smoothing capacitor 513 provided on the output side of the input reactor 512. In this example, the primary rectifying diode group 511 includes six diodes.

(Inverter circuit)
In the inverter circuit 52, the input side is connected to the primary rectifier circuit 51, and the output side is connected to the transformer 53. The inverter circuit 52 converts the direct current input from the primary rectifier circuit 51 into a single-phase alternating current having a higher frequency than that of the commercial alternating current power supply 5 by performing a switching process. Here, the inverter circuit 52 of the present embodiment is configured by a voltage type full bridge inverter. More specifically, the inverter circuit 52 of the present embodiment has an input capacitor 521 provided on the output side of the primary rectifier circuit 51 and a switch element group 522 provided on the output side of the input capacitor 521. There is.

The switch element group 522 of the present embodiment has a plurality of (here, four) switching elements connected in a bridge shape. More specifically, the switch element group 522 of the present embodiment has a first transistor Q1, a second transistor Q2, a third transistor Q3, and a fourth transistor Q4, each of which functions as a switching element. Here, the first transistor Q1 to the fourth transistor Q4 are not particularly limited, but in this example, an IGBT (Insulated Gate Bipolar Transistor) is used. In this embodiment, the first transistor Q1 and the fourth transistor Q4 function as the first switching element, and the second transistor Q2 and the third transistor Q3 function as the second switching element.

In this switch element group 522, the first transistor Q1 and the fourth transistor Q4 are located diagonally on one side of the bridge, and the second transistor Q2 and the third transistor Q3 are located diagonally on the other side of the bridge. ing. The connection portion between the first transistor Q1 and the third transistor Q3 and the connection portion between the second transistor Q2 and the fourth transistor Q4 are on the input side in the switch element group 522. Further, the connection portion between the first transistor Q1 and the second transistor Q2 and the connection portion between the third transistor Q3 and the fourth transistor Q4 are on the output side in the switch element group 522.

Further, the switch element group 522 of the present embodiment includes a first freewheeling diode D1, a second freewheeling diode D2, a third freewheeling diode D3, and a third freewheeling diode D3 connected in parallel to each of the first transistor Q1 to the fourth transistor Q4. It further has a fourth freewheeling diode D4.

(Transformer)
The transformer 53 has an input side connected to an inverter circuit 52 and an output side connected to a secondary rectifier circuit 54. The input side (left side in the figure) is the primary side when viewed from the transformer 53, and the output side (right side in the figure) is the secondary side when viewed from the transformer 53. The transformer 53 converts (transforms) the single-phase alternating current (primary side voltage) input from the inverter circuit 52 into a single-phase alternating current (secondary side voltage) having a lower voltage value. Here, the transformer 53 of the present embodiment has a magnetic core 530, a primary winding 531 and a secondary winding 532, insulates the primary side and the secondary side, and has a secondary winding 532. It consists of a single-phase transformer with a center tap on the side.

(Secondary rectifier circuit)
In the secondary rectifier circuit 54 as an example of the rectifier circuit, the input side is connected to the transformer 53, the output side and the positive electrode side are connected to the output reactor 55, and the output side and the negative electrode side are connected to the output current detection circuit 56, respectively. Has been done. The secondary rectifier circuit 54 converts the single-phase alternating current input from the transformer 53 into a direct current by rectifying it. Here, the secondary rectifier circuit 54 of the present embodiment is configured by a center tap type single-phase full-wave rectifier circuit that utilizes a center tap on the secondary side of the transformer 53. More specifically, the secondary rectifier circuit 54 of the present embodiment has a secondary rectifier diode group 541 provided on the output side of the transformer 53. In this example, the secondary rectifying diode group 541 includes two diodes. Then, these two diodes are connected to one end side and the other end side of the secondary winding 532 provided on the output side of the transformer 53, respectively, and become the output side and the positive electrode side of the secondary rectifier circuit 54. On the other hand, the midpoint of the secondary winding 532 provided on the output side of the transformer 53 is on the output side and the negative electrode side of the secondary rectifier circuit 54.

(Output reactor)
The output reactor 55 has an input side connected to the output side and the positive electrode side of the secondary rectifier circuit 54, and the output side is connected to the welding wire 100 (see FIG. 1) via the welding torch 10. The output reactor 55 smoothes the waveform of the output current, and the flow of the output current when the welding wire 100 is contact-short-circuited to the work piece 200 which is the base material, or when the droplets come into contact with the molten pool. Is passively controlled. However, the output reactor 55 may be connected to the output side and the negative electrode side of the secondary rectifier circuit 54.

(Output current detection circuit)
The input side of the output current detection circuit 56 is connected to the secondary rectifier circuit 54, and the output side is connected to the object to be welded 200 (see FIG. 1). The output current detection circuit 56 detects the welding current value I, which is the magnitude of the output current, flowing from the welding torch 10 to the workpiece 200 via the welding wire 100.

(Primary side applied voltage detection circuit)
The primary side applied voltage detection circuit 57 is provided between the output side of the inverter circuit 52 and the input side of the transformer 53, and detects the voltage (inverter output voltage value) output by the inverter circuit 52. Here, in this example, the inverter output voltage value has the same magnitude as the primary side applied voltage value V applied to the primary winding 531 of the transformer 53.

(Control circuit)
The control circuit 58 as an example of the control means and the determination means is an inverter circuit based on the output current value I detected by the output current detection circuit 56 and the primary side applied voltage value V detected by the primary side applied voltage detection circuit 57. It controls the operation (switching operation) of the first transistor Q1 to the fourth transistor Q4 provided in 52.

[Control circuit configuration]
FIG. 3 is a diagram showing a schematic configuration of a control circuit 58 in a welding power supply device 50. However, FIG. 3 shows an extracted configuration of the control circuit 58 related to the control of the operation of the first transistor Q1 to the fourth transistor Q4. Further, in the following description, among the first transistors Q1 to the fourth transistor Q4 constituting the bridge in the switch element group 522 (see FIG. 2), the first and fourth transistors Q1 and Q4 located diagonally to one of the first transistors Q1 to the fourth transistor Q4. Is referred to as a first element pair P1, and the second and third transistors Q2 and Q3 located diagonally to the other are referred to as a second element pair P2. Then, in the present embodiment, the first transistor Q1 to the fourth transistor Q4 are turned on / off in units of the first element pair P1 and the second element pair P2. In this embodiment, the output of the inverter circuit 52 is controlled by a PWM (Pulse Width Modulation) method that modulates the length (pulse width) of the on period of the first transistor Q1 to the fourth transistor Q4.

The control circuit 58 of the present embodiment has a duty signal creation unit 581, a drive signal creation unit 582, an ET product calculation unit 583, and a total ET product storage unit 584. Hereinafter, each component of the control circuit 58 will be described in order.

(Duty signal creation unit)
The duty signal creation unit 581 determines the duty ratio in PWM control based on the welding current value I input from the output current detection circuit 56 and the target value of the output current (welding current), and creates a duty signal. .. Here, the duty ratio of the present embodiment is determined based on the relationship between the control cycle and the on period in the inverter circuit 52, and the details thereof will be described later.

(Drive signal creation unit)
The drive signal creation unit 582 is based on the duty signal input from the duty signal creation unit 581 and the total ET product input from the total ET product storage unit 584, and the first element pair P1 (first, fourth). A signal for driving the transistors Q1 and Q4) (hereinafter referred to as a first drive signal) and a signal for driving the second element pair P2 (second and third transistors Q2 and Q3) (hereinafter referred to as a second). (Called a drive signal) and.

(ET product calculation unit)
The ET product calculation unit 583 applies the transformer 53 to the primary side based on the duty signal input from the duty signal creation unit 581 and the primary side applied voltage value V input from the primary side applied voltage detection circuit 57. The ET product defined as the product of the voltage value V and the applied time is calculated for each control cycle. Further, the ET product calculation unit 583 performs an operation of adding (cumulating) the ET product newly generated in the current control cycle to the total ET product determined as the cumulative value of the past ET product, and updates the total ET product. do. The details of the ET product will be described later.

(Total ET product storage)
The total ET product storage unit 584 stores the updated total ET product input from the ET product calculation unit 583. Further, the total ET product storage unit 584 outputs the total ET product stored by itself in response to a request from the drive signal creation unit 582 and the ET product calculation unit 583.

[Welding system operation]
Then, the basic operation of the welding system 1 of this embodiment will be described.
The primary rectifier circuit 51 converts three-phase AC (for example, three-phase 220V, 60Hz) input from the commercial AC power supply 5 into direct current (for example, about 300V). At this time, in the primary rectifier circuit 51, the primary rectifier diode group 511 performs three-phase full-wave rectification, and the input reactor 512 and the smoothing capacitor 513 perform smoothing after three-phase full-wave rectification.

Next, the inverter circuit 52 converts the direct current input from the primary rectifier circuit 51 into a single-phase AC (for example, about 10 kHz to 100 kHz) having a higher frequency than the commercial AC power supply 5. At this time, in the inverter circuit 52, the input capacitor 521 stabilizes the voltage, and the first element pair P1 and the second element pair P2 (first transistor Q1 to fourth transistor Q4) are controlled on / off. Performs AC / DC conversion. Further, the first freewheeling diode D1 to the fourth freewheeling diode D4 provided in the inverter circuit 52 serve as an escape route for a current opposite to the applied voltage in the corresponding first transistor Q1 to fourth transistor Q4. Function.

Subsequently, the transformer 53 converts the single-phase alternating current input from the inverter circuit 52 into a lower-voltage single-phase alternating current (for example, about several tens of volts).

Next, the secondary rectifier circuit 54 converts the single-phase alternating current input from the transformer 53 into direct current. At this time, in the secondary rectifier circuit 54, the secondary rectifier diode group 541 performs single-phase full-wave rectification.

Then, the output reactor 55 smoothes the direct current input from the secondary rectifier circuit 54 and outputs it as an output current. Then, the output current output via the output reactor 55 flows to the workpiece 200 via the welding torch 10 and the welding wire 100. At this time, the tip of the welding wire 100 is melted by the arc to form droplets, and the grown droplets are separated from the welding wire 100 and transferred to the work piece 200, and the work piece 200 is welded. become. As a result, a welded object obtained by welding the object to be welded 200 using the welding wire 100 is obtained. During this period, the magnitude of the output current, that is, the welding current value I, is increased or decreased according to the control of the inverter circuit 52.

[Target value of output current]
FIG. 4 is a diagram showing an example of a target value of output current in a short circuit transition. In FIG. 4, the horizontal axis is the time t (sec), and the vertical axis is the magnitude of the target value of the output current, that is, the welding current value I (A). Further, the example shown in FIG. 4 assumes that the feeding speed is constant.

In the case of short-circuit transition, a short-circuit state in which the welding wire 100 and the object to be welded 200 are short-circuited via a droplet formed at the tip of the welding wire 100, and the droplet is separated from the welding wire 100 and the object to be welded 200 By shifting to the side, the arc state in which an arc is generated between the welding wire 100 and the object to be welded 200 is repeated. Here, when the period in which the short-circuit state is maintained is defined as the short-circuit period Tx and the period in which the arc state is maintained is defined as the arc period Ty, the welding cycle Tz is the sum of the short-circuit period Tx and the arc period Ty (Tz = Tx + Ty). Can be expressed as. The welding cycle Tz is about 10 (msec) to 30 (msec), and is repeated about 30 to 100 times per second (about 30 Hz to 100 Hz).

The short-circuit period Tx includes a short-circuit first period Tx1, a short-circuit second period Tx2 following the short-circuit first period Tx1, and a short-circuit third period Tx3 following the short-circuit second period Tx2. Of these, in the short-circuit first period Tx1 in which the welding wire 100 and the object to be welded 200 begin to short-circuit due to the grown droplets, the welding current value I is constant at a low value (however, from the arc second period Ty2 described later). Is a large value), and the target value is set. Further, in the short-circuit second period Tx2 in which the droplets are in a short-circuit state (bridge state) and the formation of a constriction due to an electromagnetic pinch force is promoted, a target value is set so as to rapidly increase the welding current value I. Further, in the third short-circuit period Tx3 where the droplets start to separate after the constriction is formed, the target value is set so as to sharply reduce the welding current value I. In the example shown in FIG. 4, the slope of the target value of the welding current value I is set in two stages in the short circuit second period Tx2.

The arc period Ty includes an arc first period Ty1 following the short circuit third period Tx3 and an arc second period Ty2 following the arc first period Ty1 and continuing to the short circuit first period Tx1. Of these, in the first arc period Ty1 in which the current is increased to prevent re-short circuit after re-ignition of the arc and the growth of droplets is promoted, the target value is set so that the welding current value I is rapidly increased and then gradually decreased. Set. Further, in the arc second period Ty2 for suppressing spatter scattering at the time of a short circuit, a target value is set so that the welding current value I is kept constant in a state of being further lowered.

The target value of the welding current value I in the present embodiment is always set to be a positive value, and basically the same waveform is repeatedly output at the welding cycle Tz. However, strictly speaking, the welding cycle Tz cannot be fixed due to the degree of droplet growth, etc., and the peak value of the current and each of them are maintained while maintaining the basic shape according to the average voltage, the target value of the average current, and the short-circuit state. The width of the period will be adjusted (changed). Here, the target value of the welding current value I is selected from a range in which the minimum value is a number (A) and the maximum value is several hundreds (A), for example, although it depends on the wire diameter of the welding wire 100 and the like. Then, in the present embodiment, by setting the target value of the output current value I in this way, for example, when shifting from the short-circuit period Tx to the arc period Ty, the output current value I becomes excessive. The generation of spatter is suppressed.

[Operation of inverter circuit]
5 to 7 are diagrams for explaining the operation of the inverter circuit 52 of the present embodiment. Here, FIGS. 5A to 5C, FIGS. 6A to 6C, and FIGS. 7A to 7C are the duty signal Sd output by the duty signal creation unit 581 and the drive, respectively. The first drive signal S1 (for the first element vs. P1) and the second drive signal S2 (for the second element vs. P2) output by the signal creation unit 582, and the inverter circuit 52 are output and input to the transformer 53. The relationship with the primary side applied voltage value V is shown. Further, FIGS. 5A to 5C, FIGS. 6A to 6C, and FIGS. 7A to 7C show two consecutive cycles of the control cycle Tc of the inverter circuit 52, respectively. ing. Here, the control cycle Tc of the inverter circuit 52 in the present embodiment is half (half cycle) of the single-phase alternating current cycle (0.01 msec to 0.1 msec when the frequency is 10 kHz to 100 kHz) output by the inverter circuit 52. ). Therefore, it can be said that the control cycle Tc of the inverter circuit 52 is sufficiently smaller than the welding cycle Tz (Tc << Tz).

In general PWM control, positive output and negative output are alternately repeated for each control cycle Tc. On the other hand, in the present embodiment, in addition to alternately performing positive and negative outputs, it is possible to continue positive output and continue negative output. Here, FIGS. 5A to 5C exemplify a case where a positive output and a negative output are performed in two consecutive control cycles Tc. Further, FIGS. 6 (a) to 6 (c) illustrate a case where both positive outputs are performed in two consecutive control cycles Tc. Further, FIGS. 7 (a) to 7 (c) exemplify a case where negative outputs are both performed in two consecutive control cycles Tc.

Further, in general PWM control, the duty ratio (=) is adjusted by adjusting the on-time Ton for turning on the target element pair (first element pair P1 or second element pair P2) in each control cycle Tc. On-time Ton / control cycle Tc) is set. In PWM control, since the control cycle Tc is constant, the output decreases as the on-time Ton decreases, and the output increases as the on-time Ton increases. Here, FIGS. 5 (a), 6 (a), and 7 (a) illustrate a case where outputs of the same magnitude are performed in two consecutive control cycles Tc. Further, FIGS. 5 (b), 6 (b) and 7 (b) illustrate a case where the output is reduced in two consecutive control cycles Tc. Further, FIGS. 5 (c), 6 (c) and 7 (c) illustrate the case where the output is increased in two consecutive control cycles Tc.

Then, in the present embodiment, in the control of the inverter circuit 52, it is described in any of FIGS. 5 (a) to (c), FIGS. 6 (a) to (c), and FIGS. The pattern is used. In this embodiment, when the first element pair P1 is set to on and the second element pair P2 is set to off, the direction of the current flowing through the primary winding 531 of the transformer 53 is determined. Defined as "positive". Further, in the present embodiment, when the first element pair P1 is set to off and the second element pair P2 is set to off, the direction of the current flowing through the primary winding 531 of the transformer 53 is determined. Defined as "negative".

[ET product]
FIG. 8 is a diagram for explaining the ET product. Here, FIG. 8A is a diagram for explaining the ET product when the primary applied voltage value V is positive, and FIG. 8B is a diagram for explaining the ET product when the primary applied voltage value V is negative. It is a figure to do.

The ET product is one of the parameters of the transformer 53, and is the product of the voltage applied to the transformer 53 (here, the primary applied voltage value V) and the applied time (here, on-time Ton) (in the figure). (Indicated by hatching). The ET product corresponds to the magnetic flux density of the transformer 53 (magnetic core 530). When the primary applied voltage value V is positive (see FIG. 8 (a)), the ET product takes a positive value (+), and when the primary applied voltage value V is negative (see FIG. 8 (b)). In addition, the ET product takes a negative value (-).

[Control of output current]
FIG. 9 is a flowchart for explaining the control of the output current (welding current) of the present embodiment. In the initial state, the value of the total ET product stored in the total ET product storage unit 584 is assumed to be "0".

When welding is started in the welding system 1, the duty signal creation unit 581 acquires the output current value I input from the output current detection circuit 56 (step 10). Next, the duty signal creation unit 581 determines the duty ratio of the current control cycle Tc based on the output current value I acquired in step 10 and the target value of the output current value I (see FIG. 4) (step). 20). Then, the duty signal creation unit 581 creates a duty signal Sd including the duty ratio of the current control cycle Tc determined in step 20, and outputs the duty signal Sd to the drive signal creation unit 582 and the ET product calculation unit 583.

Subsequently, the drive signal creation unit 582 reads the total ET product I_ET from the total ET product storage unit 584 (step 30). Then, the drive signal creation unit 582 receives drive signals (first drive signal S1 and second drive signal S2) based on the duty signal Sd input from the duty signal creation unit 581 and the total ET product I_ET read in step 30. ) Is created (step 40). The first drive signal S1 created in step 40 is the first element pair P1 (first and fourth transistors Q1 and Q4), and the second drive signal S2 is the second element pair P2 (second and third). It is output to the transistors Q2 and Q3), respectively.

Here, the specific contents of step 40 will be described.
In step 40, the drive signal creation unit 582 first determines whether or not the total ET product I_ET is equal to or less than the negative threshold value −th (step 41). When a positive determination (Yes) is made in step 41, the drive signal creation unit 582 sets the output destination of the current control cycle Tc to the first element pair P1 (step 42). On the other hand, when a negative determination (No) is made in step 41, the drive signal creation unit 582 next determines whether or not the absolute value of the total ET product I_ET is equal to or less than the positive threshold value + th (. Step 43).

When a positive determination (Yes) is made in step 43, the drive signal creation unit 582 determines whether or not the output destination of the previous control cycle Tc is the second element pair P2 (step 44). When a positive determination (Yes) is made in step 44, the drive signal creation unit 582 proceeds to step 42 and sets the output destination of the current control cycle Tc to the first element pair P1. On the other hand, when a negative determination (No) is made in step 43 or step 44, the drive signal creation unit 582 sets the output destination of the current control cycle Tc to the second element pair P2 (step 45).

Here, when step 42 is selected, the drive signal creation unit 582 sets the first drive signal S1 to ON only for a period (on period Ton) corresponding to the duty signal Sd in the current control cycle Tc, while the first drive signal S1 is set to ON. 2 The drive signal S2 is always set to off. On the other hand, when step 45 is selected, the drive signal creation unit 582 sets the first drive signal S1 to always off in the current control cycle Tc, while the second drive signal S2 corresponds to the duty signal Sd. Set only the period (on period Ton) to on. Then, the process proceeds to the next step 50.

Next, the ET product calculation unit 583 acquires the primary side applied voltage value V input from the primary side applied voltage detection circuit 57 (step 50). Next, the ET product calculation unit 583 calculates the ET product et of the current control cycle Tc based on the duty signal Sd input from the duty signal creation unit 581 and the primary side applied voltage value V acquired in step 50. (Step 60). Further, the ET product calculation unit 583 reads the total ET product I_ET from the total ET product storage unit 584 (step 70). Then, the ET product calculation unit 583 adds the ET product et of the current control cycle Tc calculated in step 60 to the total ET product I_ET read in step 70 (I_ET = I_ET + et: step 80), whereby the total ET Update the product I_ET. After that, the ET product calculation unit 583 writes the total ET product I_ET updated in step 80 to the total ET product storage unit 584 (step 90), so that the total ET product storage unit 584 stores the total ET product I_ET.

Then, it was determined whether or not the welding was completed (step 100), and if a negative determination (No) was made, the process returned to step 10 and the process was continued, and an affirmative determination (Yes) was made. In that case, the process is terminated.

[Concrete example]
FIG. 10 is a diagram for explaining an example (example) of the change with time of the total ET product I_ET when the method of the present embodiment is applied. Here, FIG. 10 shows the relationship between the duty signal Sd, the first drive signal S1, the second drive signal S2, the primary side applied voltage value V, and the total ET product I_ET. Further, in FIG. 10, the horizontal axis indicates the passage of time, and here, 20 continuous control cycles Tc are described. Then, in FIG. 10, for example, the first control cycle Tc is described as [1], and the 20th control cycle Tc is described as [20], for example. It should be noted that these things are the same in FIG. 11 which will be described later.

When the method of the present embodiment is adopted, the output destination, that is, the element to be turned on, depends on the magnitude relationship between the total ET product I_ET and the threshold value (positive threshold value + th, negative threshold value −th) for each control cycle Tc. A pair (first element pair P1 or second element pair P2) is determined.

In the embodiment shown in FIG. 10, basically, the first element pair P1 and the second element pair P2 are alternately selected as output destinations. However, when the total ET product I_ET exceeds the positive threshold value + th or the negative threshold value −th, the first element pair P1 may be continuously selected (see [5] to [6]) depending on the conditions. The second element pair P2 may be continuously selected (see [11] to [13]). Even when the total ET product I_ET exceeds the positive threshold value + th or the negative threshold value −th, the first element pair P1 and the second element pair P2 are alternately selected depending on the conditions ([13] to [15]. ], [16] to [18]).

In the case of the embodiment shown in FIG. 10, the total ET product I_ET may temporarily exceed the positive threshold value + th or the negative threshold value −th, but is subsequently controlled to approach 0. That is, control is performed so that the total ET product I_ET is within the range of the positive threshold value + th and the negative threshold value + th. As a result, the current flowing through the magnetic core 530 of the transformer 53 is less likely to be biased to either positive or negative, so that the demagnetization in the transformer 53 is suppressed. Then, by suppressing the demagnetization in the transformer 53, it is possible to suppress the failure of these switching elements due to the excessive current flowing through the first transistor Q1 to the fourth transistor Q4 constituting the inverter circuit 52. Become.

[Comparison example]
FIG. 11 is a diagram for explaining an example (comparative example) of the change over time in the total ET product I_ET when the method of the present embodiment is not applied. Here, the waveform of the duty signal Sd shown in FIG. 11 is the same as that shown in FIG.

When the method of this embodiment is not adopted, the output destination, that is, the element pair to be turned on (first element pair P1 or second element pair P2) is irrespective of the total ET product I_ET for each control cycle Tc. It will be decided.

In the comparative example shown in FIG. 11, the first element pair P1 and the second element pair P2 are always alternately selected as output destinations. Therefore, as in the embodiment shown in FIG. 10, the first element pair P1 cannot be continuously selected, or the second element pair P2 cannot be continuously selected.

In the case of the comparative example shown in FIG. 11, the total ET product I_ET is biased to the negative side with the passage of time. In this case, the current flowing through the magnetic core 530 of the transformer 53 is negatively biased, so that the demagnetization in the transformer 53 is likely to occur. Further, since demagnetization is likely to occur in the transformer 53, it becomes impossible to suppress the failure of these switching elements due to the excessive current flowing through the first transistor Q1 to the fourth transistor Q4 constituting the inverter circuit 52. ..

[others]
In the present embodiment, the single pulse control that outputs one pulse per control cycle Tc has been described as an example in the PWM control, but the present invention is not limited to this, for example, two or more per control cycle Tc. Multi-pulse control that outputs a pulse may be performed.

Further, in the present embodiment, the case where the inverter circuit 52 is PWM-controlled has been described as an example, but the present invention is not limited to this. For example, a PPM (Pulse Phase Modulation) method may be adopted.

1 ... Welding system, 10 ... Welding torch, 20 ... Robot arm, 30 ... Wire feeding device, 40 ... Shielded gas supply device, 50 ... Welding power supply device, 51 ... Primary rectifying circuit, 52 ... Inverter circuit, 53 ... Transformer Instrument, 54 ... Secondary rectifier circuit, 55 ... Output transistor, 56 ... Output current detection circuit, 57 ... Primary side applied voltage detection circuit, 58 ... Control circuit, 581 ... Duty signal creation unit, 582 ... Drive signal creation unit, 583 ... ET product calculation unit, 584 ... total ET product storage unit, Q1 ... first transistor, Q2 ... second transistor, Q3 ... third transistor, Q4 ... fourth transistor, P1 ... first element pair, P2 ... second element versus

Claims (2)

An inverter circuit that has multiple switching elements that make up a bridge circuit and converts direct current into alternating current,
A transformer that transforms the alternating current output from the inverter circuit,
A rectifier circuit that rectifies alternating current output from the transformer to direct current,
It has a control circuit for controlling the plurality of switching elements in the inverter circuit.
The control circuit is
A determination means for determining the switching element to be turned on next in the inverter circuit based on the cumulative value of the primary side applied voltage applied from the inverter circuit to the primary side of the transformer.
A means for determining the duty ratio of a predetermined control cycle based on the output current value flowing from the rectifier circuit to the welding wire and the target value of the output current value.
The means for creating a duty signal including the duty ratio of the predetermined control cycle is included.
The determination means uses the result of performing an operation for accumulating the ET product, which is the product of the application voltage on the primary side and the application time of the primary side application voltage, as the cumulative value.
The applied time is an on-time determined based on the duty signal .
The inverter circuit supplies a positive current to the primary side of the transformer when the first switching element is turned on and the second switching element is turned off, and at the same time, the first switching element is turned off and the first switching element is turned off. When the second switching element is turned on, a negative current is supplied to the primary side of the transformer.
The determination means determines that the cumulative value is biased to the negative side based on the fact that the cumulative value of the primary side applied voltage is equal to or less than a predetermined negative threshold value, and the cumulative value is predetermined. The switching element to be turned on next in the inverter circuit when it is determined that the cumulative value is biased to the positive side based on the positive threshold value or more and the cumulative value is biased to the negative side is the first. When the switching element of 1 is determined and the cumulative value is biased to the positive side, the switching element to be turned on next in the inverter circuit is determined to be the second switching element.
A power supply for welding that features. An inverter circuit that has multiple switching elements that make up a bridge circuit and converts DC to AC, a transformer that transforms AC output from the inverter circuit, and AC that is output from the transformer is rectified to DC. It is an output control method of a welding power supply device including a rectifying circuit and a control circuit for controlling the switching operation of the plurality of switching elements.
The output current value flowing from the rectifier circuit to the welding wire is detected.
In the inverter circuit, when the first switching element is turned on and the second switching element is turned off, a positive current is supplied to the primary side of the transformer, and the first switching element is turned off and the said. When the second switching element is turned on, a negative current is supplied to the primary side of the transformer.
In the control circuit
Based on the output current value and the target value of the output current value, the duty ratio of the predetermined control cycle is determined.
A duty signal including the duty ratio of the predetermined control cycle is created.
The ET product, which is the product of the on-time determined based on the duty signal and the primary side applied voltage applied from the inverter circuit to the primary side of the transformer, is calculated for each control cycle.
Calculate the cumulative value of the calculated ET product,
Based on the fact that the cumulative value is equal to or less than a predetermined negative threshold value, it is determined that the cumulative value is biased to the negative side, and the cumulative value is equal to or more than a predetermined positive threshold value. When it is determined that the cumulative value is biased to the positive side and the cumulative value is biased to the negative side, the switching element to be turned on next in the inverter circuit is determined to be the first switching element, and the cumulative value is determined. Is biased to the positive side, the switching element to be turned on next in the inverter circuit is determined to be the second switching element.
An output control method comprising controlling the plurality of switching elements in the inverter circuit.

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