Method for limiting welding power of a welding device

Abstract

In order to enable a stable welding process, the welding device (1) is supplied with electrical supply power (P1) by an energy source (2) and at least a part of the electrical supply power (P1) is converted into welding power (P2) in order to generate a welding arc, wherein the welding power (P2) is regulated by a predetermined welding current (I2). For this purpose, an electrical supply voltage (U1) is determined and a maximum electrical supply current (I 1,max ) is predetermined, which can be output by the energy source (2) to the welding device (1). A maximum electrical supply power (P 1,max ) is calculated using the electrical supply voltage (U1) and the maximum electrical supply current (I 1,max ). A maximum welding power (P 2,max ) is determined from the maximum electrical supply power (P 1,max ), which can be output by the welding device (1); and the welding power (P2) is limited to the maximum welding power (P 2,max ) which can be output.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for operating a welding device, wherein the welding device is supplied with supply power by an energy source and at least a part of the supply power is converted into welding power for generating a welding arc, the welding power is adjusted by a predetermined welding current, and a supply voltage is determined. Furthermore, the invention relates to a welding device for generating a welding arc by converting supply power into welding power, wherein the welding device is designed to adjust the welding power by means of a predetermined welding current. BACKGROUND

[0002] The welding device generates a welding voltage and a welding current at the electrode during the welding process, that is to say during the ignition and combustion of the welding arc. Here, the welding device outputs welding power by means of the welding arc, which in turn consists of the product of welding voltage and welding current. The welding device is supplied with supply power by an energy source, wherein, for example, a power supply network or a generator can be provided as energy source. In order to supply the welding device with power by means of the energy source, a voltage converter (inverter, rectifier, converter, etc.) can of course also be provided between the energy source and the welding device. The conversion of the supply power into welding power is effected by means of a power piece, wherein the welding device adjusts the welding power by means of a predetermined welding current. The welding current can be adjusted, for example, to a predetermined theoretical value. The welding voltage can be set manually, for example, by means of the length of the welding arc.

[0003] Methods for limiting the output welding power are known. The document DE 35 23 879 A1 discloses a method for limiting the welding power in order to prevent spatter in welding. This is achieved in that the welding power is measured by means of the welding current and the welding voltage and is furthermore limited to a pre-determined limit value.

[0004] A power supply for a welding device having functionality for dynamic power limitation is known from the document US 2018 / 0056428 A1. For this purpose, the control module of the power supply is supplied with static and dynamic parameters of the power supply (for example information about maximum loss power, maximum useful power, temperature or power reduction, actual input and output voltage values, actual input and output current values, etc.) by a further module of the power supply. The maximum output power or loss power and the maximum permissible output power or loss power as a dynamic output framework condition is then determined by the control module on the basis of the static and / or dynamic parameters, and the output parameters (that is to say output voltage, output current and / or output power) are adapted on the basis thereof.

[0005] Furthermore, a welding system and a method associated therewith are known from document US 2009 / 0277893 Al, in which the output power characteristic is determined on the basis of inputtable configuration parameters, such as wire diameter, material thickness, etc. The current input voltage or input power is then monitored and compared with the ideal input voltage or input power, for example, in the absence of fluctuations, etc. In the event of a deviation of the current input power from the ideal input power, the output power is then adapted in accordance with the determined output characteristic. SUMMARY

[0006] It is the task of the present application to propose a method and a welding device which enable a stable welding process.

[0007] This task is solved according to the application by a method in which the maximum supply current which can be output by the energy source to the welding device is predetermined; the maximum supply power is calculated using the supply voltage and the maximum supply current; the maximum welding power which is output by the welding device is determined from the maximum supply power; and the welding power is limited to the maximum welding power which can be output.

[0008] Furthermore, this task is solved by a welding device in which a calculation unit is provided which is designed to calculate the maximum supply power from the supply voltage of the welding device and the maximum supply current which can be output by the energy source to the welding device and to determine the maximum welding power which is output by the welding device from the maximum supply power; and a limiting unit is provided which is designed to limit the output welding power to the maximum welding power which can be output. The maximum welding power which can be output is thus taken into account when the welding power is regulated.

[0009] The limitation of the welding power is thus not based on a previously known limit value but on the current maximum supply power, which in turn arises using the current supply voltage. From the current maximum supply power, the current maximum welding power can in turn be determined, on the basis of which the welding power to be output is limited. It is thus prevented that the welding device attempts to regulate a welding power which cannot be output at all, however. An undesirable interruption of the welding process due to an undesirable interruption of the welding arc can thus be prevented. In particular, fluctuations in the supply voltage can occur due to long feed lines between the energy source and the welding device or in the case of the use of a generator as the energy source.

[0010] It is advantageous if a measurement unit is provided which is designed to measure the supply voltage. It can thus be ensured that the current supply voltage is known. It is of course also conceivable that the supply voltage is predetermined by other means and methods, for example if the welding device is connected to an energy source which has another supply voltage.

[0011] Advantageously, the welding power is limited by limiting the welding current. To this end, the limiting unit can be designed to limit the welding current in order to limit the output welding power to the maximum welding power that can be output. This can be achieved in the case that a current regulator is present in order to regulate the welding power by means of the welding current, in that the limiting unit limits the setpoint value of the current regulator, i.e. the setpoint current, and / or the adjustment variable. If the adjustment variable is limited, it is advantageous to implement an anti-windup measure in order to prevent the current regulator from trying to adjust the limited adjustment variable. Anti-windup measures are basically known and are therefore not further discussed here.

[0012] It is advantageous if the maximum supply current that can be output by the energy source to the welding device or that can be received by the welding device is predetermined, preferably by a user or by an automated recognition, and the maximum supply power is calculated from the supply voltage and the maximum supply current. The maximum supply current can correspond to the tripping current of an overcurrent protection. In contrast to the assumption of a variable supply voltage, the maximum supply current is fixedly predetermined. Here, it is assumed that the supply current does not exceed the maximum supply current.

[0013] Preferably, the maximum welding power output by the welding device is determined from the maximum supply power that can be output by the energy source to the welding device, taking into account the operating power. In this case, the supply power is used not only to output the welding power but also to supply the operating power for the further operation of the welding device. The maximum welding power is therefore limited by the supply power minus the operating power. This means that the maximum welding power corresponds to the maximum supply power minus the operating power.

[0014] The limiting unit can be designed to be activatable and deactivatable. Thereby, for example, a user can decide whether the welding power is to be limited or whether such an intervention is not desired when the power variable changes. In particular, if the supply voltage is to be expected not to change, it can be advantageous to deactivate the limiting unit. BRIEF DESCRIPTION OF DRAWINGS

[0015] The application is explained below with reference to the attached Figures 1 to 6c The application is further illustrated by the attached drawings, which show by way of example, schematically and non-limitingly, advantageous design embodiments of the application. In the drawings:

[0016] Figure 1 a schematic welding device is shown;

[0017] Figure 2 a schematic welding device with a welding power component is shown;

[0018] Figure 3 a welding device with a calculation unit and a limiting unit is shown;

[0019] Figure 4a a, b, c show time curves of the supply voltage, the supply current, the welding power, the welding voltage and the welding current;

[0020] Figure 5a a, b, c show detailed curves of the supply voltage, the supply current, the welding power, the welding voltage and the welding current at a reduction of the supply voltage;

[0021] Figure 6a a, b, c show detailed curves of the supply voltage, the supply current, the welding power, the welding voltage and the welding current at a limitation according to the application. DETAILED DESCRIPTION

[0022] An exemplary welding device 1 is shown in Figure 1 which is supplied with a supply power P1 by an energy source 2. To this end, the energy source 2 provides the welding device 1 with a supply voltage U1 and a supply current I1, wherein the supply power P1 can be represented as the product of the supply voltage U1 and the supply current I1: P1 = U1 · I1.

[0023] During the welding process, the welding device 1 generates a welding arc arc at the electrode by outputting a welding power P2. The welding power P2 can be represented as the product of a welding current I2 and a welding voltage U2: P2 = U2 · I2. Thus, during the welding process, i.e. in the case of a burning welding arc arc, the welding current I2 flowing through the electrode is generated by the welding device 1, i.e. ignited and kept active, while the welding voltage U2 occurs at the electrode. The welding voltage U2 is known, for example, by measurement.

[0024] Furthermore, a welding regulator 10 is provided in order to regulate the welding power P2. In the shown figures, as welding regulator 10 a current regulator is provided, which regulates the welding current I2 in order to regulate the welding power P2 in turn. The welding regulator 10 obtains a theoretical quantity, for example predetermined by a user, in order to regulate the welding power P2. In the shown current regulator, a theoretical current I 2,soll is predetermined in order to regulate the welding current I2. During the output of the welding current I2, the welding voltage U2 occurs, which can be influenced, for example, by adjusting the length of the welding arc arc, for example by changing the distance of the welding torch / electrode from the workpiece. This means that the welding power P2 is predetermined on the one hand by the welding current I2, which is regulated in accordance with the set theoretical current I 2,soll and on the other hand by the welding voltage U2.

[0025] As in Figure 2As shown, the welding equipment 1 may also include a voltage converter 14 (i.e., an AC-to-DC voltage converter or a DC-to-DC voltage converter and a welding power unit 13 connected to the voltage converter 14), wherein the voltage converter 14 converts the supply voltage U1 into an intermediate circuit voltage U applied to the capacitive intermediate circuit Z. z Thus, the power supply P1 is temporarily stored in the intermediate circuit Z. The welding power unit 13 is fed by the intermediate circuit Z and outputs welding current I2 and thus welding power P2 during the welding process according to the predetermined parameters of the welding regulator 10. Different basic construction possibilities of the welding equipment 1 are known, and therefore will not be discussed further here.

[0026] exist Figure 3 Use Figure 1 The general welding equipment 1 is used to illustrate the present invention. Of course, the present invention can also be applied to [the following]: Figure 2 Welding equipment 1 or other types of welding equipment 1.

[0027] According to the present invention, a calculation unit 12 is provided, which is designed to calculate the maximum power supply P that the energy source 2 can output to the welding equipment 1. 1,max Advantageously, the maximum power supply P 1,max From the supply voltage U1—which is currently assumed to be constant—and the maximum supply current I that can be output by energy source 1. 1,max To calculate: P 1,max =U1·I 1,max The supply voltage U1 is preferably determined by means of the measuring unit 13.

[0028] Maximum supply current I 1,max The overcurrent protection circuit breaker current can be predetermined and, for example, manually set or pre-set by the user on the welding equipment 1 or by automatically identifying the type of energy source 2.

[0029] The maximum welding power P that welding equipment 1 can output 2,max This basically corresponds to the maximum power supply P received by welding equipment 1 (and thus output by energy source 2). 1,max However, an operating power P can also be set. b The operating power is required for the operation of welding equipment 1 (e.g., for the temporary storage of intermediate energy in intermediate circuit Z). If the operating power P b Similarly, the power is obtained from the power supply P1, so the maximum welding power P is determined. 2,max The operating power P will be used at that time. b Subtract P from the power supply. 2,max =P 1,max –Pb .

[0030] Operating power P b It can also be expressed as supply voltage U1 and operating current I. b The product of these two factors determines the maximum welding power P. 2,max It can also be represented as P 2,max =U1(I 1,max -I b ).

[0031] The following situation may occur: when the welding regulator 10 adjusts the welding current I2, the resulting welding voltage U2 will cause the welding power P2 to exceed the maximum welding power P. 2,max This could occur, for example, when the maximum welding power P that can be output is reached. 2,max For example, the reduced supply voltage U1 or the increased welding voltage U2.

[0032] To ensure that the actual welding power P2 does not exceed the maximum welding power P 2,max Then the welding current I2 was adjusted to the predetermined theoretical value I. 2,soll This ensures that the product of the welding current I2 and the welding voltage U2 does not exceed the current welding power P. 2,max If the welding power P2 is not limited, the welding arc arc may drop below the critical supply voltage U due to excessively high increased supply current I1 (and corresponding overcurrent protection shutdown) and / or excessively strong current. 1,min The power supply is interrupted when the voltage U1 (below which welding is impossible) is reached. Therefore, according to the present invention, the welding power P2 is limited by the limiting unit 11 to the maximum welding power P. 2,max .

[0033] Preferably, this is achieved by limiting the welding current I2, which in turn can be achieved by limiting the theoretical parameter I of the regulated welding current I2. 2,soll To achieve, as in Figure 3 As shown in the diagram. However, it is also possible to limit the adjustment parameters of the welding regulator 10. By limiting the welding current I2, it can be ensured that the welding voltage U2 can be maintained when the welding power P2 decreases.

[0034] The following example describes the limitation of the welding current I2 (i.e., the adjustment parameter). The welding power difference ΔP2 is determined at the current moment, which ranges from the maximum welding power P. 2,max The difference between the output welding power P2 and the output welding power P2 is: ΔP2 = P 2,max -P2.

[0035] In order to limit the welding power P used in the current adjustment step 2,i It can be filtered (P)2,i = filtered (P 2,max b ) or unfiltered using the welding power P 2,i .

[0036] Furthermore, if the loss power P loss is taken into account, the resulting welding power is P 2,i = P 2,max - P b - P loss or the filtered welding power P 2,i = filtered (P 2,max - P b - P loss ). The loss power P loss is preferably described in the switching and conduction losses in the semiconductor switches (transistors) and the ohmic losses, for example, in lines, transformers, etc. In contrast, the power temporarily stored in the intermediate circuit Z is included in the operating power P b .

[0037] Furthermore, the welding current I 2,i for the current regulation step can be determined from the quotient of the welding power P 2,i at the current time and the welding voltage U2 currently occurring Thus, the theoretical current I 2,soll can be adapted accordingly. As a result, the welding current I2 is limited in the current regulation step, which in turn limits the welding power P2. It can be achieved here that the welding voltage U2 and thus the welding arc arc are maintained.

[0038] Correspondingly, in Figure 4a , 4b , 4c, the curves of the supply voltage U1, the welding current I2 and the welding voltage U2 are shown.

[0039] In Figure 4a , exemplary curves of the supply voltage U1 and the supply current I1 are shown. The supply current I1 is constant in Figure 4a . The supply voltage U1 is at a first voltage value until the first time t1, falls to a reduced supply voltage U 10 after the first time t1 until the second time t2 and rises again to the original first voltage value after the second time t2. The supply voltage U1 jumps from the constant first voltage value to the constant reduced supply voltage U 10 ​and then jumps up again to a constant first voltage value only for a more simple representation and thus only to be regarded as exemplary. The drop of the supply voltage Ui can be generated, for example, due to an overload, a fault, etc. of the energy source 2 and / or of the feed line from the energy source 2 to the welding device 1. Since the supply current Ii is constant, the curve (not explicitly shown) of the supply power Pi corresponds to the curve of the supply voltage Ui in the case shown.

[0040] Figure 4b the curve representing the welding power P2, and Figure 4c the curve representing the welding current I2 in the case of use of the method according to the application. The welding current I2 is adjusted to the constant theoretical current I 2,soll from the first time instant ti up to the second time instant t2. The welding power P2 is generated as the product of the welding current I2 and the welding voltage U2.

[0041] From the first time instant ti, the supply voltage Ui drops to a reduced supply voltage U 10 , as described above. Thereby, from the first time instant ti, the maximum supply power P 1,max is also reduced, since the predetermined maximum supply current I 1,max is constant.

[0042] Thereby, from the first time instant ti, the welding power P2 is also reduced to a now reduced maximum welding power P 2,max , which is generated from the maximum supply power P 1,max . If the welding current I2 is continued to be adjusted to the constant theoretical current I 2,soll from the first time instant ti (without restriction), an increase of the supply current Ii would occur, as described below with reference to Figure 5a , b, c.

[0043] Therefore, it is advantageous to limit the welding current I2 Figure 4c from the first time instant ti, which can be achieved by intervening in the theoretical current I 2,soll or in the adjustment parameters of the welding regulator 10. The welding power P2, which is thereby limited, is generated from the predetermined welding voltage U2, which is only exemplarily constant, and the adjusted welding current I2, which is limited here, between the first time instant ti and the second time instant t2. The Figure 4b and the welding current I2 in Figure 4c are shown extremely and only for a better understanding of the application.

[0044] The limitation of the welding power P2, as in Figure 4a, b, c it is visible - of course not instantaneously, because the welding regulator 10 must first react to the new theoretical or adjusted value. Basically it is advantageous if the limitation of the welding current I2 is not achieved in jumps, because this can lead to audible disturbing noises.

[0045] Figure 5a , b, c show in the case that the regulation / limiting according to the application is deactivated or not set, in Figure 4a , b, c the detailed curves of the supply parameters (i.e. supply voltage U1 and supply current I1) and of the welding parameters (i.e. welding voltage U2 and welding current I2) at the first time t1. Figure 4a The first time t1 shown in, b, c is here shown in such detail that individual detailed times t3, t4, t5 are shown. The duration between the detailed times t3 and t5 can for example be 5 ms to 5 s, wherein a duration of 200 ms preferably occurs between the detailed times t3 and t5.

[0046] In Figure 5a , for example at the detailed time t3, the supply voltage U1 drops for example due to external influences (grid fluctuations). In this case the value of the supply voltage U1 drops so far that at the detailed time t4 the critical supply voltage U 1,min is reached. Until the critical supply voltage U 1,min (which can differ depending on the energy source 2) the energy source 2 can also provide a continued constant welding current I2. In the case that at the time t4 the critical supply voltage U 1,min is reached (or fallen below), the welding device 1 is switched off. Thus the supply current I1 drops to the value 0 A Figure 5a . After the supply current I1 has dropped to 0 A, the supply voltage U1 rises again to a value which is lower than the supply voltage U1 at the time t3.

[0047] Because the welding device 1 is already switched off at the time t4, no welding current I2 and welding voltage U2 Figure 5c occur, so that the welding arc arc is interrupted. Because the supply current I1 drops to 0 A at the time t4, the supply power P1 drops to the value 0 W at the time t4, as can also be seen in Figure 5b .

[0048] Figure 6a , b, c are similar to Figure 5a , b, c show the detailed curves of the supply parameters and of the welding parameters at the time t1, wherein the detailed times t3, t4, t5 are shown. Unlike Figure 5a , b, c, in Figure 6aLimitations according to the invention are included in sections b and c, wherein, for the sake of simplicity, the welding current I2 is immediately reduced once the supply voltage U1 decreases, thereby compared to Figure 4b and 4c There is no time delay, rise time, overshoot, or undershoot in the welding power P2 and welding current I2. Furthermore, therefore, starting from the detailed time t3, for example due to external influences, the supply voltage U1 ( Figure 6a The welding current I2 is reduced. However, because the welding current I2 is reduced by the limitation according to the invention, the supply current I1 can remain constant. Therefore, the supply voltage U1 does not reach or falls below the critical supply voltage U. 1,min Thus, welding equipment 1 maintains the welding arc arc. By means of the method according to the invention, the supply voltage U1 can be prevented from dropping too quickly by reducing the welding current I2, thereby preventing it from reaching or falling below the critical supply voltage U. 1,min And welding equipment 1 is not turned off. From time t5, the supply voltage U1 decreases to a reduced supply voltage U. 10 And maintain this supply voltage, see Figure 4a .

[0049] The curve for the power supply P1 corresponds to the curve for the power supply voltage U1 due to the constant power supply current I1 (caused by limiting the welding power P2). Figure 6b The output power P1 and welding power P2 can be seen in the graph. The distance between the curves of power supply P1 and welding power P2 represents the power loss P of the welding system. loss .

[0050] The computing unit 12 and / or the limiting unit 11 may include microprocessor-based hardware (e.g., a computer or digital signal processor (DSP)) on which corresponding software executes to implement the corresponding functions. The computing unit 12 and / or the limiting unit 11 may also include integrated circuits (e.g., application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or configurable programmable logic devices (CPLDs)) and / or be monitored by a microprocessor in parallel thereon. However, the computing unit 12 and / or the limiting unit 11 may also include analog circuitry or an analog computer. Hybrid forms are also conceivable. It is also possible to implement different functions on the same hardware and / or different hardware components. A particularly advantageous hybrid form is one in which the individual units are implemented not only in hardware but also in software.

Claims

1. Method for operating a welding device (1), wherein The welding device (1) is supplied with supply power (P1) by an energy source (2) and converts at least a part of the supply power (P1) into welding power (P2) for generating a welding arc (arc), the welding power (P2) is adjusted by a predetermined welding current (I2), a supply voltage (U1) is determined, characterized in that a maximum supply current (I 1,max ) is predetermined, which can be output by the energy source (2) to the welding device (1); a maximum supply power (P 1,max ) is calculated from the supply voltage (U1) and the maximum supply current (I 1,max ); a maximum welding power (P 2,max ) is determined from the maximum supply power (P 1,max ), which can be output by the welding device (1); and the welding power (P2) is limited to the maximum welding power (P 2,max ) which can be output.

2. The method of claim 1, wherein, The welding power (P2) is limited by limiting the welding current (I2).

3. The method according to claim 1 or 2, characterized in that, In consideration of the operating power (P b ), the maximum welding power (P 2,max ) output by the welding device (1) is determined from the maximum supply power (P 1,max ) that can be output by the energy source (2) to the welding device (1).

4. Welding device (1) for generating a welding arc (arc) by converting supply power (P1) into welding power (P2), wherein, The welding device (1) is designed to adjust the welding power (P2) by means of a predetermined welding current (I2), characterized in that a calculation unit (12) is provided, which is designed to calculate the maximum supply power (P 1,max ) from the supply voltage (U1) of the welding device (1) and the maximum supply current (I 1,max ) which can be output to the welding device (1) by the energy source (2) and to determine the maximum welding power (P 2,max ) which can be output by the welding device (1) from the maximum supply power (P 1,max ); and a limiting unit (11) is provided, which is designed to limit the output welding power (P2) to the maximum welding power (P 2,max ) which can be output.

5. The welding apparatus (1) according to claim 4, characterized in that A measuring unit (13) is provided, which is designed to measure the supply voltage (U1).

6. The welding apparatus (1) according to claim 4 or 5, characterized in that The limiting unit (11) is designed to limit the welding current (I2) so as to limit the output welding power (P2) to the maximum welding power (P 2,max ) that can be output.

7. The welding apparatus (1) according to claim 4 or 5, characterized in that The limiting unit (11) is designed to be activatable and deactivatable.

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