JP2018192477A - Electric power unit for welding and method for controlling output of electric power unit for welding - Google Patents

Abstract

To provide an electric power unit for welding and so on which is adaptable to a steep change in an output current while suppressing increase of a non-load voltage.SOLUTION: An electric power unit 50 for welding has: a primary rectifier circuit 51 which rectifies a commercial AC power source 5; a DC voltage conversion circuit 52 which converts an output of the primary rectifier circuit 51 into direct current; an inverter circuit 53 which converts an output of the DC voltage conversion circuit 52 into alternating current; a transformer 54 which transforms an output of the inverter circuit 53; a secondary rectifier circuit 55 which rectifies an output of the transformer 54; an output current detection circuit 56 which detects an output current output from the secondary rectifier circuit 55; and a control circuit 57 which controls the inverter circuit 53 so that an output current value detected by the output current detection circuit 56 approaches an output current target value, and increases an output of the DC voltage conversion circuit 52 when a difference between the output current target value and the output current value is large.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a welding power supply apparatus and an output control method for the welding power supply apparatus.

  As a power supply device used in arc welding equipment, etc., a primary side conversion circuit that rectifies a commercial power supply (three-phase AC power supply) and converts it into a DC voltage, and a DC voltage that is input from the primary conversion circuit, includes a plurality of switching elements. An inverter circuit that converts a high frequency AC voltage into a high voltage AC voltage, a welding transformer that converts a high frequency AC voltage input from the inverter circuit into a lower voltage AC voltage, and a low voltage AC voltage input from the welding transformer is rectified into a DC voltage. And a secondary conversion circuit for converting and outputting to a welding torch and a welding object, and adjusting the magnitude of the welding current flowing from the electrode of the welding torch to the welding object by switching control of an inverter circuit is known. (See Patent Document 1). Patent Document 1 describes that a reactor for stabilizing the welding current and the arc plasma is provided on the output side of the secondary side conversion circuit by generating a counter electromotive force so as to prevent a change in the welding current. Has been.

JP2015-228773A

  In arc welding, it is required to output a desired current value for a target value of a very large output current. For this reason, in a power supply device used in an arc welding apparatus or the like, a reactor of about several μH to several tens μH is often installed. The reactor has a property of generating a counter electromotive force so as to prevent a change in current due to its inductance, and the output current and the arc plasma are stabilized using this property. This inductance value varies depending on the material and wire diameter of the welding wire used, the current range used for welding, and the like.

  In the welding environment, the power supply device is installed and fixed at a specific location, the welding torch equipped with the electrode that generates the arc is moved to the welding location, and the welding device is welded between the welding device and the welding torch. Tied by cable. As a matter of course, the length of this welding cable varies depending on the construction environment in which the welding cable is installed, and generally, a length of several m to several tens of m is connected. This long cable also has an inductance component, but its size varies greatly depending on the length and wiring path.

  On the other hand, for example, a technique called electronic reactor control is known. Electronic reactor control is to reproduce output characteristics as if an appropriate reactor is mounted by utilizing the fact that output characteristics can be arbitrarily controlled by digital inverter control.

  By the way, if the inductance value of the load increases, it becomes easier to prevent a change in current, and thus a steep current change becomes difficult. In order to overcome this, it is necessary to lower the inductance value of the load or to apply a voltage exceeding the counter electromotive force generated by the inductance and the current change. The former can be realized to some extent, for example, by removing a fixed reactor, but when a long cable must be connected, it is difficult to reduce the inductance value. In the latter case, the maximum voltage that can be output is determined by the transformation ratio of the mounted transformer. It is possible to cope by changing the transformation ratio, but on the other hand, the no-load voltage increases, which is not preferable for safety.

  It is an object of the present invention to provide a welding power supply apparatus and the like that can cope with a sudden change in output current while suppressing an increase in no-load voltage.

The welding power supply device of the present invention includes a primary rectifier circuit that rectifies a commercial AC power supply and outputs a DC voltage, a DC voltage conversion circuit that converts the magnitude of the DC voltage output from the primary rectifier circuit, and the DC From the inverter circuit that converts the DC voltage output from the voltage conversion circuit into an AC voltage having a frequency higher than that of the commercial AC power source, the transformer that converts the magnitude of the AC voltage output from the inverter circuit, and the transformer A secondary rectifier circuit that rectifies an output AC voltage and outputs a DC voltage, a current detection circuit that detects a magnitude of a welding current flowing from the secondary rectifier circuit via a welding wire, and the current detection circuit The inverter circuit is controlled so that the detected value of the welding current approaches the target value of the welding current, and the direct current that is output according to the difference between the target value and the detected value And a control circuit for controlling the DC voltage converter to change the magnitude of the pressure.
From another point of view, the welding power source apparatus of the present invention converts a magnitude of the DC voltage output from the primary rectifier circuit that rectifies a commercial AC power source and outputs a DC voltage, and the primary rectifier circuit. A DC voltage conversion circuit, an inverter circuit that converts a DC voltage output from the DC voltage conversion circuit to an AC voltage having a frequency higher than that of the commercial AC power supply, and a magnitude of the AC voltage output from the inverter circuit A transformer, a secondary rectifier circuit that outputs a DC voltage by rectifying an AC voltage output from the transformer, and a current that detects a magnitude of a welding current flowing from the secondary rectifier circuit via a welding wire And a control circuit for controlling the inverter circuit so that a detected value of the welding current by the current detection circuit approaches a target value of the welding current, and the target value of the current control cycle According to the difference between the target value before the control period, and a control circuit for controlling the DC voltage converter to change the magnitude of the output DC voltage.
In these welding power supply apparatuses, the control circuit may set the voltage after the voltage rise of the DC voltage conversion circuit to a constant value.
The control circuit may be characterized in that when performing control to increase the output voltage of the DC voltage conversion circuit, the voltage increase width of the DC voltage conversion circuit per control cycle is set to a constant value. .
Furthermore, the control circuit may be characterized in that, when performing control to increase the output voltage of the DC voltage conversion circuit, the voltage increase width of the DC voltage conversion circuit per control cycle is variable.
From another point of view, the output control method of the welding power supply apparatus of the present invention uses a primary rectifier circuit to rectify a commercial AC power supply and output a DC voltage, and uses a DC voltage conversion circuit. The DC voltage output from the primary rectifier circuit is converted, and an inverter circuit is used to convert the DC voltage output from the DC voltage converter circuit into an AC voltage having a frequency higher than that of the commercial AC power source. Using a transformer, the AC voltage output from the inverter circuit is converted, and a secondary rectifier circuit is used to rectify the AC voltage output from the transformer to output a DC voltage to detect current. A circuit is used to detect the magnitude of the welding current flowing from the secondary rectifier circuit through the welding wire, and the inverter is adjusted so that the detected value of the welding current by the current detection circuit approaches the target value of the welding current. It controls the motor circuit, according to the difference between the target value and the detected value, is characterized by controlling the DC voltage converter to change the magnitude of the output DC voltage.
From another point of view, the output control method of the welding power supply apparatus of the present invention uses a primary rectifier circuit to rectify a commercial AC power supply and output a DC voltage, and uses a DC voltage conversion circuit. The DC voltage output from the primary rectifier circuit is converted, and an inverter circuit is used to convert the DC voltage output from the DC voltage converter circuit into an AC voltage having a frequency higher than that of the commercial AC power source. Using a transformer, the AC voltage output from the inverter circuit is converted, and a secondary rectifier circuit is used to rectify the AC voltage output from the transformer to output a DC voltage to detect current. A circuit is used to detect the magnitude of the welding current flowing from the secondary rectifier circuit through the welding wire, and the inverter is adjusted so that the detected value of the welding current by the current detection circuit approaches the target value of the welding current. And controlling the DC voltage conversion circuit so as to change the magnitude of the DC voltage to be output according to the difference between the target value of the current control cycle and the target value of the previous control cycle. It is characterized by.

  ADVANTAGE OF THE INVENTION According to this invention, the power supply device for welding etc. which can respond to the steep change of output current can be provided, suppressing the raise of a no-load voltage.

It is a figure showing a schematic structure of a welding system concerning an embodiment of the invention. It is a figure which shows schematic structure of the welding power supply device in a welding system. It is a figure which shows schematic structure of a control circuit. 3 is a flowchart for explaining the operation of the control circuit according to the first embodiment. (A)-(c) is a figure for demonstrating the setting method of the target voltage correction value of a DC voltage converter. 6 is a flowchart for explaining the operation of the control circuit of the second embodiment.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
<Embodiment 1>
[Configuration of welding system]
FIG. 1 is a diagram showing a schematic configuration of a welding system 1 according to an embodiment of the present invention. The welding system 1 performs welding of an 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 that welds a workpiece 200 using a welding wire 100, and a robot arm 20 that holds the welding torch 10 and sets the position and orientation of the welding torch 10. The welding system 1 also 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 shielding gas (for example, carbon dioxide gas) to the welding torch 10. Further, the welding system 1 supplies a welding current 100 to the welding wire 100 and the workpiece 200 via the welding torch 10 and controls a welding power source device 50 that controls the welding current, and a robot that controls the robot arm 20. And a 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.

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

  The welding power supply device 50 converts the three-phase AC power supplied from the commercial AC power supply 5 into DC power by performing various processes, and supplies the DC power to the welding torch 10 and the workpiece 200 (see FIG. 1). . During this time, the welding power supply device 50 adjusts the voltage (DC voltage) and current (DC current) of the DC power output to the outside by performing various power conversions. The welding power supply device 50 according to the present embodiment includes a primary rectifier circuit 51, a DC voltage conversion circuit 52, an inverter circuit 53, a transformer 54, a secondary rectifier circuit 55, and an output current detection circuit 56. And a control circuit 57.

(Primary rectifier circuit)
The primary rectifier circuit 51 has an input side connected to the commercial AC power supply 5 and an output side connected to the DC voltage conversion circuit 52. The primary rectifier circuit 51 converts a three-phase AC voltage (for example, three-phase 200 V: 60 Hz) input from the commercial AC power supply 5 into a DC voltage (for example, 300 V) by rectifying and smoothing. The primary rectifier circuit 51 can be composed of a three-phase full-wave rectifier circuit or the like. Moreover, you may connect a smoothing capacitor in parallel with the output side of the primary rectifier circuit 51 as needed.

(DC voltage conversion circuit)
The DC voltage conversion circuit 52 has an input side connected to the primary rectifier circuit 51 and an output side connected to the inverter circuit 53. The DC voltage conversion circuit 52 converts the DC voltage input from the primary rectification circuit 51 into a DC voltage having a higher voltage value. However, the DC voltage conversion circuit 52 can output the DC voltage input from the primary rectifier circuit 51 as it is (with the same voltage value) as necessary. The DC voltage conversion circuit 52 can be composed of various chopper circuits including switching elements such as power transistors, and DC / DC converters including a transformer.

(Inverter circuit)
The inverter circuit 53 has an input side connected to the DC voltage conversion circuit 52 and an output side connected to the transformer 54. The inverter circuit 53 converts the DC voltage input from the DC voltage conversion circuit 52 into an AC voltage having a frequency higher than that of the commercial AC power supply 5. The inverter circuit 53 can be composed of various inverters including switching elements such as power transistors. Further, the inverter circuit 53 according to the present embodiment operates by, for example, PWM (Pulse Width Modulation) control.

(Transformer)
The transformer 54 has an input side connected to the inverter circuit 53 and an output side connected to the secondary rectifier circuit 55. The input side (left side in the figure) is the primary side when viewed from the transformer 54, and the output side (right side in the figure) is the secondary side when viewed from the transformer 54. The transformer 54 converts the AC voltage (primary side voltage) input from the inverter circuit 53 into an AC voltage (secondary side voltage) having a lower voltage value. The transformer 54 can be composed of a single-phase transformer or the like.

(Secondary rectifier circuit)
The secondary rectifier circuit 55 has an input side connected to the transformer 54, an output side positive electrode connected to the welding torch 10 (see FIG. 1), and an output side negative electrode connected to the output current detection circuit 56. . The secondary rectifier circuit 55 converts the AC voltage input from the transformer 54 into a DC voltage by rectifying and smoothing. The secondary rectifier circuit 55 can be constituted by a center tap type full-wave rectifier circuit or the like using a secondary side center tap (not shown) in the transformer 54. Further, a DC reactor may be connected in series to the positive electrode on the output side of the secondary rectifier circuit 55 as necessary.

(Output current detection circuit)
The output current detection circuit 56 has an input side connected to the secondary rectifier circuit 55 and an output side connected to the workpiece 200 (see FIG. 1). The output current detection circuit 56 is an output current value I _o as an example of a detection value that is the magnitude of the welding current (output current) that flows from the welding torch 10 to the workpiece 200 via the welding wire 100 and the arc. Is detected.

(Control circuit)
The control circuit 57 controls the operations of the DC voltage conversion circuit 52 and the inverter circuit 53 based on the output current value I _o detected by the output current detection circuit 56.

[Configuration of control circuit]
FIG. 3 is a diagram showing a schematic configuration of the control circuit 57.
The control circuit 57 includes a current calculation unit 571, a boost flag setting unit 572, a voltage determination unit 573, a control command value output unit 574, and a storage unit 575.

(Current calculation unit)
The current calculation unit 571 uses the output current value I _o input from the output current detection circuit 56 to perform a calculation process on the output current target value I _ref that is an example of the target value of the output current, and the obtained calculation The result is output to the boost flag setting unit 572.

(Boost flag setting part)
The boost flag setting unit 572 is based on a calculation result input from the current calculation unit 571, and serves as a reference flag for determining whether or not to boost the output voltage (DC voltage) of the DC voltage conversion circuit 52 (boost boost). (Referred to as a flag) is set, and the result is written in the storage unit 575. Further, the boost flag setting unit 572 reads the boost flag written in the storage unit 575. Here, in the present embodiment, “ON (1)” is set as the boost flag when boosting is to be performed, and “OFF (0)” is set when boosting is not to be performed. Yes.

(Voltage determination unit)
The voltage determination unit 573 determines an output voltage target value V _ref that is a target value of the output voltage (DC voltage) of the DC voltage conversion circuit 52 based on the state of the boost flag input from the boost flag setting unit 572.

(Control command value output section)
The control command value output unit 574 creates control command values for each of the DC voltage conversion circuit 52 and the inverter circuit 53 based on the output voltage target value V _ref input from the voltage determination unit 573, and the DC voltage conversion circuit. Each control command value is output to 52 and the inverter circuit 53.

(Storage section)
The storage unit 575 stores various parameters used in the current calculation unit 571 and the voltage determination unit 573, various calculation results, and the like. The storage unit 575 stores the boost flag set by the boost flag setting unit 572.

[Operation of control circuit]
FIG. 4 is a flowchart for explaining the operation of the control circuit 57 of the present embodiment.
In the initial state, it is assumed that the target value of the output current (DC current) of the secondary rectifier circuit 55 is set to the output current target value I _ref . In the initial state, the output voltage target value V _ref that is the target value of the output voltage (DC voltage) of the DC voltage conversion circuit 52 is set to the initial output voltage target value V _t . Here, the initial output voltage target value V _t is determined based on the output current target value I _ref . The output current target value I _ref and the initial output voltage target value V _t are stored in the storage unit 575 as parameters. In the initial state, it is assumed that the boost flag stored in the storage unit 575 is set to “OFF”.

The welding is started in the welding system 1, a current calculation unit 571 reads the output current I _o inputted from the output current detection circuit 56 (step 101). Subsequently, the current calculation unit 571 has a difference ΔI ₁ (= I _ref) which is a difference between the output current target value I _ref read from the storage unit 575 and the output current value I _o input from the output current detection circuit 56. -I _o) is calculated (step 102).

Next, the boost flag setting unit 572 determines whether or not the difference ΔI ₁ calculated in step 102 is equal to or _larger than a predetermined second threshold I _th2 (ΔI ₁ ≧ I _th2 ) (step S1). 103). Here, the second threshold value I _th2 is a predetermined numerical value and is stored in the storage unit 575 as a parameter.

When an affirmative determination (YES) is made in step 103, that is, when the difference ΔI ₁ is greater than or equal to the second threshold value I _th2 , the boost flag setting unit 572 reads the boost flag from the storage unit 575, It is determined whether or not the read boosting flag is “OFF” (step 104). If a negative determination (NO) is made in step 104, that is, if the boost flag is “ON”, the routine proceeds to step 107 described later.

On the other hand, when an affirmative determination (YES) is made in step 104, that is, when the boost flag is “OFF”, the boost flag setting unit 572 determines the difference ΔI ₁ calculated in step 102 in advance. It is then determined whether or not it is equal to or greater than the first threshold value I _th1 (ΔI ₁ ≧ I _th1 ) (step 105). Here, the first threshold value I _th1 is a predetermined numerical value and is stored in the storage unit 575 as a parameter. Further, the first threshold value I _th1 has a relationship that is larger than the second threshold value I _th2 used in step 103 (I _th1 > I _th2 ). If a negative determination (NO) is made in step 105, that is, if the difference ΔI ₁ is less than the first threshold value I _th1 , the process proceeds to step 109 described later.

In contrast, in the case of performing a positive determination (YES) in step 105, i.e., when the difference [Delta] I ₁ was the first threshold value I _th1 or more, the step-up flag setting unit 572, a step-up flag to "ON" It is set (step 106) and stored in the storage unit 575.

In addition, when a negative determination (NO) is made in step 104 and when the boost flag is set to “ON” in step 106, in other words, in the state where the boost flag is “ON”, the voltage The determining unit 573 sets the output voltage target value V _ref of the DC voltage conversion circuit 52 to the sum (V _ref = V _t + V _a ) of the initial output voltage target value V _t and the target correction voltage value V _a (step) 107). And it progresses to step 110 mentioned later. The target correction voltage value Va takes _a positive value, and the determination method will be described later.

On the other hand, when a negative determination (NO) is made in step 103, that is, when the difference ΔI ₁ is less than the second threshold value I _th2 , the boost flag setting unit 572 sets the boost flag to “OFF”. (Step 108), and stored in the storage unit 575.

Further, when a negative determination (NO) is made at step 105, that is, when the difference ΔI ₁ is less than the first threshold I _th1 and when the boosting flag is set to “OFF” at step 108, In other words, in a state where the boost flag is “OFF”, the voltage determination unit 573 converts the output voltage target value V _ref of the DC voltage conversion circuit 52 to the initial output voltage target value V _t (V _ref = V _t ) Is set (step 109). And it progresses to step 110 mentioned later.

Then, the control command value output unit 574 creates a control command value for the DC voltage conversion circuit 52 based on the output voltage target value V _ref determined in step 107 or step 109 input from the voltage determination unit 573. And output to the DC voltage conversion circuit 52 (step 110). At this time, the control command value output unit 574 creates a control command value for the DC voltage conversion circuit 52 so that the output voltage of the DC voltage conversion circuit 52 becomes the output voltage target value V _ref . The control command value for the DC voltage conversion circuit 52 includes data (duty ratio, etc.) for ON / OFF control of switching elements (here, power transistors) that constitute the DC voltage conversion circuit 52.

Further, the control command value output unit 574 creates a control command value for the inverter circuit 53 based on the output voltage target value V _ref and outputs it to the inverter circuit 53 (step 111). At this time, the control command value output unit 574 creates a control command value for the inverter circuit 53 in accordance with the adjustment of the output voltage of the DC voltage conversion circuit 52 in step 110. The control command value for the inverter circuit 53 includes data (duty ratio or the like) for on / off control of the switching elements (in this case, IGBT) constituting the inverter circuit 53.

Then, the control command value output unit 574 updates the output current target value I _ref based on the output voltage target value V _ref (step 112) and writes it in the storage unit 575.

  Thereafter, it is determined whether or not the welding in the welding system 1 has been completed (step 113). If a negative determination (NO) is made, the process returns to step 101 to continue the process, and an affirmative determination (YES) is made. If so, a series of processing is completed. In the present embodiment, while welding is performed in the welding system 1, the processing from step 101 to step 113 is repeatedly executed at a constant cycle. In the present embodiment, the time taken for processing from step 101 to step 113 is referred to as a control cycle T.

[Target voltage correction value setting method]
_Now , _a method for setting the target voltage correction value V _a used for calculation of the output voltage target value V _ref of the DC voltage conversion circuit 52 in step 107 shown in FIG. 4 will be described.
FIG. 5 is a diagram for explaining a method for setting the target voltage correction value V _a of the DC voltage conversion circuit 52. Here, FIG. 5A is a diagram for explaining the first setting method, FIG. 5B is a diagram for explaining the second setting method, and FIG. FIG. 3 is a diagram for explaining a setting method 3; In each of FIGS. 5A to 5C, the horizontal axis represents the elapsed time t, and the vertical axis represents the output voltage target value _Vref . In addition, the horizontal axis of each of FIGS. 5A to 5C also shows the control cycle T (for 5 cycles). In each of FIGS. 5A to 5C, the initial output voltage target value V _ref is the initial output voltage target value V _t .

(First method)
A first approach is to fix the magnitude of the target voltage correction value V _a. In this case, the magnitude (= V _t + V _a ) of the output voltage target value V _ref determined in step 107 is always a constant value. For example, in the example shown in FIG. 5A, the output voltage target value V _ref in the first and fourth control periods T is the initial output voltage target value V _t , whereas the second, third, and 5 The output voltage target value V _ref in the second control cycle T is the sum of the initial output voltage target value V _t and the target correction voltage value V _a . Thus, in the first method, the output voltage target value V _ref is binary.

(Second method)
The second approach is the magnitude of the target voltage correction value V _a is variable, is intended to fix the rise of the output voltage target value V _ref for one control period T. In this case, the magnitude (= V _t + V _a ) of the output voltage target value V _ref determined in step 107 can vary. For example, in the example shown in FIG. 5B, the output voltage target value V _ref in the first and fifth control periods T is the initial output voltage target value V _t , whereas the second to fourth controls. The output voltage target value V _ref in the cycle T is the sum of the initial output voltage target value V _t and the target correction voltage value V _a . However, unlike the above-described first method, the increase range of the output voltage target value V _ref per one control cycle T is fixed, so that the first control cycle T and the second control cycle T are Increase range of the output voltage target value V _ref between the second control cycle T and the third control cycle T, the increase range of the output voltage target value V _ref between the second control cycle T and the third control cycle T The increase range of the output voltage target value V _ref with the fourth control cycle T is the same. Thus, in the second method, the output voltage target value V _ref is multivalued.

(Third method)
Furthermore, a third approach, the magnitude of the target voltage correction value V _a is variable, rise of the output voltage target value V _ref for one control period T is also intended to be variable. In this case, the magnitude (= V _t + V _a ) of the output voltage target value V _ref determined in step 107 can vary. For example, in the example shown in FIG. 5C, the output voltage target value V _ref in the first and third control periods T is the initial output voltage target value V _t , whereas the second, fourth, and 5 The output voltage target value V _ref in the second control cycle T is the sum of the initial output voltage target value V _t and the target correction voltage value V _a . However, unlike the above-described second method, the increase width of the output voltage target value V _ref per one control cycle T is not fixed, so that the first control cycle T and the second control cycle T and rise of the output voltage target value V _ref between are different and rise of the output voltage target value V _ref between the third control cycle T and fourth control period T. Thus, in the third method, the output voltage target value V _ref is multivalued.

(Upper limit of output voltage target value)
When the output voltage target value V _ref is set to the sum of the initial output voltage target value V _t and the target correction voltage value V _a (V _ref = V _t + V _a ) in step 107 shown in FIG. The magnitude of V _ref is desirably determined in consideration of the withstand voltage of each element constituting the DC voltage conversion circuit 52 and the inverter circuit 53. As a measure of the magnitude of the output voltage target value V _ref , it is 75% or less of the withstand voltage of the switching element provided in each of the DC voltage conversion circuit 52 and the inverter circuit 53 and 90% of the withstand voltage of the capacitor provided in each. It is desirable that the degree. However, it is not limited to these numerical values.

[Effects of the present embodiment]
In the conventional power supply apparatus that does not have the DC voltage conversion circuit 52, the upper limit of the output current value I _o that actually flows through the workpiece 200 is determined by the function of the inverter circuit 53. For this reason, even when the output current value _Io is insufficient with respect to the output current target value _Iref , it may be difficult to supply further current.

On the other hand, in the present embodiment, a DC voltage conversion circuit 52 is provided between the primary rectifier circuit 51 and the inverter circuit 53 so that the voltage can be output exceeding the limit value in the current control in the inverter circuit 53. . Thereby, for example, even if the inductance value of the load is large, it is possible to realize a current change with sufficient responsiveness. In addition, since the output voltage (DC voltage) of the DC voltage conversion circuit 52 is increased only when the output current value _Io is desired to be increased to a certain degree or more, an increase in no-load voltage in the welding power supply device 50 is suppressed. Can do.

<Embodiment 2>
In the first embodiment, the output voltage target value V _ref of the DC voltage conversion circuit 52 is determined based on the actually measured output current value I _o of the welding power source device 50. On the other hand, in the present embodiment, the output voltage target value V _ref of the DC voltage conversion circuit 52 is determined based on the output current target value I _ref of the welding power supply device 50 determined every control cycle T. It is a thing. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

[Operation of control circuit]
FIG. 6 is a flowchart for explaining the operation of the control circuit 57 of the present embodiment.
In the initial state, it is assumed that the target value of the output current (DC current) of the secondary rectifier circuit 55 is set to the output current target value I _ref . However, in this embodiment, the current to be output current target value I _ref of (n control period th to) "This output current target value I _{ref (n)",} the current one control cycle before n It is assumed that “previous output current target value I _{ref (n−1)} ”, which is the output current target value I _ref in the −1 control cycle, exists and is stored as a parameter in the storage unit 575. Here, the former “current output current target value I _{ref (n)} ” is an example of the current target value, and the latter “previous output current target value I _{ref (n−1)} ” is the previous target value. It is an example of a value.

When welding is started in the welding system 1, the current calculation unit 571 reads the current output current target value I _{ref (n)} and the previous output current target value I _{ref (n−1)} read from the storage unit 575. A difference ΔI ₂ (= I _{ref (n)} −I _{ref (n−1)} ), which is a difference between the _two , is calculated (step 201).

Next, the boost flag setting unit 572 determines whether or not the difference ΔI ₂ calculated in step 201 is equal to or greater than a predetermined fourth threshold I _th4 (ΔI ₂ ≧ I _th4 ) (step 202). Here, the fourth threshold value I _th4 is a predetermined numerical value and is stored in the storage unit 575 as a parameter.

When an affirmative determination (YES) is made in step 202, that is, when the difference ΔI ₂ is equal to or greater than the fourth threshold value I _th4 , the boost flag setting unit 572 reads the boost flag from the storage unit 575, and It is determined whether or not the read boosting flag is “OFF” (step 203). If a negative determination (NO) is made in step 203, that is, if the boost flag is “ON”, the process proceeds to step 206 described later.

On the other hand, when an affirmative determination (YES) is made in step 203, that is, when the boost flag is “OFF”, the boost flag setting unit 572 determines the difference ΔI ₂ calculated in step 201 in advance. It is then determined whether or not the threshold value is greater than or equal to the third threshold value I _th3 (ΔI ₂ ≧ I _th3 ) (step 204). Here, the third threshold value I _th3 is a predetermined numerical value and is stored in the storage unit 575 as a parameter. The third threshold value I _th3 has a relationship that is larger than the fourth threshold value I _th4 used in step 202 (I _th3 > I _th4 ). If you make negative determination of (NO) in step 204, i.e., if the difference delta ₂ is less than the third threshold I _th3, the process proceeds to step 208 which will be described later.

On the other hand, when a positive determination (YES) is made in step 204, that is, when the difference ΔI ₂ is equal to or greater than the third threshold value I _th3 , the boost flag setting unit 572 sets the boost flag to “ON”. It is set (step 205) and stored in the storage unit 575.

Further, when a negative determination (NO) is made in step 203 and when the boost flag is set to “ON” in step 205, in other words, in the state where the boost flag is “ON”, the voltage The determining unit 573 sets the output voltage target value V _ref of the DC voltage conversion circuit 52 to the sum (V _ref = V _t + V _b ) of the initial output voltage target value V _t and the target correction voltage value V _b (step) 206). And it progresses to step 209 mentioned later. The target correction voltage value V _b takes a positive value, and the determination method will be described later.

On the other hand, when a negative determination (NO) is made in step 202, that is, when the difference ΔI ₂ is less than the fourth threshold value I _th4 , the boost flag setting unit 572 sets the boost flag to “OFF”. (Step 207) and stored in the storage unit 575.

If a negative determination (NO) is made in step 204, that is, if the difference ΔI ₂ is less than the third threshold I _th3 and if the boosting flag is set to “OFF” in step 207, In other words, in a state where the boost flag is “OFF”, the voltage determination unit 573 converts the output voltage target value V _ref of the DC voltage conversion circuit 52 to the initial output voltage target value V _t (V _ref = V _t (Step 208). And it progresses to step 209 mentioned later.

Then, the control command value output unit 574 creates a control command value for the DC voltage conversion circuit 52 based on the output voltage target value V _ref determined in step 206 or step 208 input from the voltage determination unit 573. Then, it is output to the DC voltage conversion circuit 52 (step 209). At this time, the control command value output unit 574 creates a control command value for the DC voltage conversion circuit 52 so that the output voltage of the DC voltage conversion circuit 52 becomes the output voltage target value V _ref . The control command value for the DC voltage conversion circuit 52 includes data (duty ratio, etc.) for ON / OFF control of switching elements (here, power transistors) that constitute the DC voltage conversion circuit 52.

Further, the control command value output unit 574 creates a control command value for the inverter circuit 53 based on the output voltage target value V _ref and outputs it to the inverter circuit 53 (step 210). At this time, the control command value output unit 574 creates a control command value for the inverter circuit 53 in accordance with the adjustment of the output voltage of the DC voltage conversion circuit 52 in step 209. The control command value for the inverter circuit 53 includes data (duty ratio or the like) for on / off control of the switching elements (in this case, IGBT) constituting the inverter circuit 53.

Then, the control command value output unit 574 updates the output current target value I _ref based on the output voltage target value V _ref (step 211) and writes it in the storage unit 575. At this time, what was used as the current output current target value I _{ref (n)} in step 201 is updated as the previous output current target value I _{ref (n-1)} , and the newly created current current target value I _{ref (n-1)} The output current target value I _{ref (n)} is updated.

  Thereafter, it is determined whether or not the welding in the welding system 1 has been completed (step 212). If a negative determination (NO) is made, the process returns to step 201 to continue the process, and an affirmative determination (YES) is made. If so, a series of processing is completed. In the present embodiment, while welding is performed in the welding system 1, the processing from step 201 to step 212 is repeatedly executed at a constant cycle. In the present embodiment, the time required for the processing from step 201 to step 212 is the control cycle T.

[Target voltage correction value setting method]
The method for setting the target voltage correction value V _b in the present embodiment is basically the same as the method for setting the target voltage correction value V _{a in} the first embodiment. Therefore, any of the three methods shown in FIGS. 5A to 5C (first method to third method: “V _a ” shown in FIG. 5 is replaced with “V _b ”) Can be adopted.

[Effects of the present embodiment]
In the first embodiment, the DC voltage conversion circuit 52 and the like are controlled based on the output current value I _o that actually flows through the workpiece 200. In this case, control for satisfying the output current value _Io cannot be performed unless a state in which the output current value _Io is insufficient occurs.

On the other hand, in the present embodiment, the prediction control is performed using the history of the output current target value I _ref . As a result, it is possible to output the voltage in advance exceeding the limit value in the current control in the inverter circuit 53 without waiting for actually detecting the shortage of the output current value _Io .

DESCRIPTION OF SYMBOLS 1 ... Welding system, 5 ... Commercial alternating current power supply, 10 ... Welding torch, 20 ... Robot arm, 30 ... Wire feeding apparatus, 40 ... Shield gas supply apparatus, 50 ... Power supply apparatus for welding, 51 ... Primary rectifier circuit, 52 ... DC voltage conversion circuit, 53 ... inverter circuit, 54 ... transformer, 55 ... secondary rectifier circuit, 56 ... output current detection circuit, 57 ... control circuit, 60 ... robot controller, 100 ... welding wire, 200 ... workpiece

Claims (7)

A primary rectifier circuit that rectifies commercial AC power and outputs a DC voltage;
A DC voltage conversion circuit for converting the magnitude of the DC voltage output from the primary rectifier circuit;
An inverter circuit for converting a DC voltage output from the DC voltage conversion circuit into an AC voltage having a frequency higher than that of the commercial AC power supply;
A transformer for converting the magnitude of the AC voltage output from the inverter circuit;
A secondary rectifier circuit that outputs a DC voltage by rectifying an AC voltage output from the transformer;
A current detection circuit for detecting the magnitude of a welding current flowing from the secondary rectifier circuit via a welding wire;
The inverter circuit is controlled so that the detected value of the welding current by the current detection circuit approaches the target value of the welding current, and the output DC voltage is large in accordance with the difference between the target value and the detected value. And a control circuit for controlling the DC voltage conversion circuit so as to change the length. A primary rectifier circuit that rectifies commercial AC power and outputs a DC voltage;
A DC voltage conversion circuit for converting the magnitude of the DC voltage output from the primary rectifier circuit;
An inverter circuit for converting a DC voltage output from the DC voltage conversion circuit into an AC voltage having a frequency higher than that of the commercial AC power supply;
A transformer for converting the magnitude of the AC voltage output from the inverter circuit;
A secondary rectifier circuit that outputs a DC voltage by rectifying an AC voltage output from the transformer;
A current detection circuit for detecting the magnitude of a welding current flowing from the secondary rectifier circuit via a welding wire;
The inverter circuit is controlled so that the detected value of the welding current by the current detection circuit approaches the target value of the welding current, and according to the difference between the target value of the current control period and the target value of the previous control period And a control circuit for controlling the DC voltage conversion circuit so as to change the magnitude of the DC voltage to be output.   The welding power supply device according to claim 1, wherein the control circuit sets the voltage after the voltage rise of the DC voltage conversion circuit to a constant value.   3. The control circuit according to claim 1, wherein when the control circuit performs control to increase the output voltage of the DC voltage conversion circuit, the voltage increase width of the DC voltage conversion circuit per control cycle is set to a constant value. The power supply apparatus for welding as described.   3. The control circuit according to claim 1, wherein when the control circuit performs control to increase the output voltage of the DC voltage conversion circuit, the voltage increase width of the DC voltage conversion circuit per control cycle is variable. Power supply for welding. Using a primary rectifier circuit, rectify commercial AC power and output DC voltage,
Using a DC voltage conversion circuit, the magnitude of the DC voltage output from the primary rectifier circuit is converted,
Using an inverter circuit, the DC voltage output from the DC voltage conversion circuit is converted into an AC voltage having a higher frequency than the commercial AC power supply,
Using a transformer, convert the AC voltage output from the inverter circuit,
Using a secondary rectifier circuit, rectify the AC voltage output from the transformer to output a DC voltage,
Using a current detection circuit, detect the magnitude of the welding current flowing from the secondary rectifier circuit through the welding wire,
The inverter circuit is controlled so that the detected value of the welding current by the current detection circuit approaches the target value of the welding current, and the output DC voltage is large in accordance with the difference between the target value and the detected value. An output control method for a welding power supply apparatus, wherein the DC voltage conversion circuit is controlled to change the length. Using a primary rectifier circuit, rectify commercial AC power and output DC voltage,
Using a DC voltage conversion circuit, the magnitude of the DC voltage output from the primary rectifier circuit is converted,
Using an inverter circuit, the DC voltage output from the DC voltage conversion circuit is converted into an AC voltage having a higher frequency than the commercial AC power supply,
Using a transformer, convert the AC voltage output from the inverter circuit,
Using a secondary rectifier circuit, rectify the AC voltage output from the transformer to output a DC voltage,
Using a current detection circuit, detect the magnitude of the welding current flowing from the secondary rectifier circuit through the welding wire,
The inverter circuit is controlled so that the detected value of the welding current by the current detection circuit approaches the target value of the welding current, and according to the difference between the target value of the current control period and the target value of the previous control period And controlling the direct-current voltage conversion circuit so as to change the magnitude of the direct-current voltage to be output.

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