A dc-dc converter for a welding device and a method for operating a dc-dc converter for a welding device

Abstract

According to the invention, in order to reduce the energy consumption of a welding device (1) in an idle mode (L) and to achieve a very good and controlled start of a welding phase (X), wherein a DC-DC converter (2) of the welding device (1) converts a DC input voltage (Ue) applied at input terminals (Ue+) into a DC output voltage (Ua) applied at output terminals (Ua+), wherein at least one switching element (S1) of one branch (A) of the DC-DC converter (2) is switched at a switching frequency (f1), wherein the welding device (1) is provided with a welding phase (X) during which the switching frequency (f1) corresponds to a normal switching frequency (f1x), the welding device (1) is provided with an idle phase (L) during which the at least one switching element (S1) is switched at a switching frequency (f1) corresponding to an idle switching frequency (f1L), which is smaller than the normal switching frequency (f1x).

Description

Technical Field

[0001] This invention relates to a method for operating a welding apparatus, wherein a DC-DC converter of the welding apparatus converts a DC input voltage at an input terminal to a DC output voltage at an output terminal, wherein at least one switching element of the DC-DC converter is switched at a switching frequency, and wherein a welding stage is provided for the welding apparatus, during which the switching frequency corresponds to a normal switching frequency. Furthermore, the invention relates to a DC-DC converter for a welding apparatus, wherein the DC-DC converter is configured to convert a DC input voltage at an input terminal to a DC output voltage at an output terminal, wherein the DC-DC converter includes at least one switching element in a branch and includes an adjustment unit configured to switch the switching element at a switching frequency corresponding to the normal switching frequency during the welding stage of the welding apparatus. Furthermore, the invention relates to a welding apparatus comprising a DC-DC converter and a welding power component configured to adjust the DC output voltage to a welding voltage during the welding stage. Background Technology

[0002] A DC-DC converter transforms a DC input voltage on the input side into a DC output voltage on the output side. In a boost converter (also known as a step-up inverter), the DC output voltage is higher than the DC input voltage, while in a buck converter (also known as a step-down inverter), the DC output voltage is lower than the DC input voltage. Boost converters are particularly used in the field of welding technology.

[0003] Therefore, in welding apparatus, a boost converter is used, for example, as a DC-DC converter, which converts the DC input voltage on the input side into a higher DC output voltage on the output side. Here, during the welding process, energy is transferred from the input side to the output side during a welding phase, which begins from arc ignition. A parallel intermediate circuit capacitor can be provided on the output side of the DC-DC converter, thereby creating or applying a DC output voltage across this capacitor. Specifically, to provide sufficient welding voltage for the welding process during the welding phase, a welding power component is connected downstream of the output side of the DC-DC converter, i.e., downstream of the intermediate circuit capacitor. This welding power component adjusts the DC output voltage to a suitable, preferably potential-separated welding voltage and / or a welding current, wherein the welding voltage / current can be output in a pulsed and / or continuous manner according to the desired welding process. Such a welding apparatus is disclosed, for example, in EP 2850725 B1.

[0004] However, during the operation of the welding apparatus, the welding phase is interrupted by an idle phase where welding is not performed. During this idle phase, a small amount of energy is still transferred by the DC-DC converter to the welding power components connected to the output, such as the control electronics, adjustment units, and displays within the welding apparatus. Because there is no arc combustion during the idle phase, the energy is lower. However, the DC-DC converter operates both during the welding phase and the idle phase of the welding apparatus, and naturally, even during the idle phase, a significant amount of energy is still lost within the DC-DC converter. Summary of the Invention

[0005] Therefore, the object of the present invention is to provide a DC-DC converter for a welding apparatus that allows for the excellent and controlled initiation of the welding phase.

[0006] According to the present invention, this objective is achieved by a method in which an idle phase is provided for the welding apparatus, during which the switching element is switched at a switching frequency corresponding to an idle switching frequency lower than the normal switching frequency. Furthermore, this objective is also achieved by a DC-DC converter, wherein an regulating element is configured to switch the switching element at a switching frequency corresponding to an idle switching frequency lower than the normal switching frequency during the idle phase of the welding apparatus. Additionally, this objective is also achieved by a welding apparatus comprising the DC-DC converter of the present invention and a welding power component configured to regulate the DC output voltage to a welding voltage during the welding phase. During the welding phase, energy is transferred from the input of the DC-DC converter to the output of the DC-DC converter. Of course, regulating to a welding voltage is merely exemplary; naturally, the DC output voltage can be regulated such that a welding current is generated, or both a welding voltage and a welding current are generated. In this regard, constant-voltage regulation / constant-current regulation is involved.

[0007] Since the switching element of the DC-DC converter is not stopped operating during the no-load phase of the welding apparatus, but only its switching frequency is reduced to the no-load switching frequency, the desired DC output voltage for the welding phase is maintained at the output terminals during the no-load phase of the welding apparatus. This DC output voltage is sufficient to sustain the operation of the welding apparatus during the no-load phase (e.g., powering the control electronics, adjustment unit, display, etc.). Unlike when the switching element operates continuously at its normal switching frequency (also during the no-load phase), the energy consumption during the no-load phase is significantly reduced when the no-load switching frequency is applied.

[0008] Furthermore, by maintaining the necessary level of DC output voltage at the output terminals even during the no-load phase, it is ensured that the soldering process begins in a controlled and optimal manner at the start of the soldering phase.

[0009] Preferably, during the welding stage, the DC output voltage is regulated to a welding voltage by a welding power component, wherein the welding voltage is provided to the load.

[0010] The preferred branch includes an induction coil and a freewheeling diode, wherein a first coil terminal of the induction coil is connected to an input terminal, and a second coil terminal of the induction coil is connected to a first switching terminal of a switching element and the anode of the freewheeling diode, wherein a second switching terminal of the switching element is connected to ground, and the cathode of the freewheeling diode is connected to an output terminal.

[0011] This configuration describes a boost converter, but the invention can also be applied to boost converters with other configurations. Of course, the method of the invention can also be considered for application to other types of DC-DC converters (buck converters, boost-buck converters, etc.).

[0012] Preferably, at least one additional switching element of at least one additional branch of the DC-DC converter is switched at at least one additional switching frequency, wherein during the soldering phase, the at least one additional switching frequency corresponds to an additional normal switching frequency. Therefore, the method of the present invention can also be applied to DC-DC converters having multiple switching elements.

[0013] The DC-DC converter may include at least one additional branch with at least one additional switching element, at least one additional induction coil, and at least one additional freewheeling diode. In the at least one additional branch, the first coil terminals of the at least one additional induction coil are respectively connected to the input voltage, and the second coil terminals of the at least one additional induction coil are respectively connected to the corresponding first switching terminal of the at least one additional switching element and to the corresponding anode of the at least one additional freewheeling diode. The second switching terminals of the at least one additional switching element are respectively connected to ground, and the cathodes of the at least one freewheeling diode are respectively connected to the output terminal. The regulating unit is configured to switch the at least one additional switching element at at least one additional switching frequency corresponding to an additional normal switching frequency during the welding phase of the welding apparatus.

[0014] This describes a multi-branch boost converter, which can of course also be configured as different types of multi-branch boost converters, buck converters, or generally DC-DC converters, all of which include the regulation unit of the present invention.

[0015] The additional normal switching frequency can correspond to the normal switching frequency. Therefore, the switching element can be manipulated particularly easily by the adjustment unit during the welding stage. It is particularly advantageous if the switching element of the branch is switched with a phase shift. Thus, in a converter comprising n branches, the i-th branch (where 1≤i≤n) is turned on with a time shift relative to the first branch, the time shift being (T*(i-1)) / n, where T corresponds to the period. This method is called "interleaved operating mode".

[0016] Preferably, during the no-load phase, the at least one additional switching frequency is switched at an additional no-load switching frequency that is lower than the additional normal switching frequency.

[0017] The adjustment unit can be configured accordingly to switch the at least one additional switching element at an additional no-load switching frequency, which is less than the additional normal switching frequency, during the no-load phase.

[0018] If the DC-DC converter has at least one additional switching element, some, preferably all, of these switching elements can be switched at an idle switching frequency lower than the additional normal switching frequency to further reduce idle power consumption.

[0019] The at least one additional no-load switching frequency can correspond to the no-load switching frequency, so the switching element can be manipulated particularly easily by the adjustment unit during the no-load phase.

[0020] Preferably, the at least one additional switching element is deactivated during the no-load phase. The regulating unit can be configured accordingly to deactivate the at least one additional switching element during the no-load phase.

[0021] Therefore, in the presence of multiple switching elements, all but one of them can be deactivated to minimize no-load power consumption during the no-load phase. Simultaneously, at least one switching element is operated at the no-load switching frequency to prevent a drop in DC output voltage during the no-load phase and to ensure a rapid start to the welding process at the beginning of the welding phase. If the DC-DC converter has three branches, each with one switching element, and the first switching element of the first branch is operated at a 2kHz no-load switching frequency during the no-load phase of the welding apparatus, while the corresponding remaining switching elements of the second and third branches are deactivated, the no-load power consumption can be reduced from 43W to 2W.

[0022] A control signal (preferably transmitted via an interface, such as an RS-485 bus) can facilitate the switching of the DC-DC converter from the welding stage to the no-load stage and / or from the no-load stage to the welding stage.

[0023] The control signal can be generated by operating a switch or button (e.g., located on the welding nozzle of the welding apparatus) to start or stop welding as specified. The control signal can also be triggered in other ways to signal the start or end of a welding phase.

[0024] Furthermore, the parameters specified in the welding apparatus can facilitate the transition from the welding stage to the no-load stage and / or from the no-load stage to the welding stage. Of course, control signals can also be triggered by these parameters.

[0025] For example, specified parameters on the output side, such as altered (i.e., decreased or increased) welding voltage and / or specified parameters, such as decreased / increased current, can be used. This allows for the identification of transition requirements into or out of the no-load phase. Transitions into or out of the no-load phase can also be controlled based on events, where, for example, a short circuit during the welding process can be considered an event.

[0026] The parameters can be identified and / or processed, for example, by a welding device regulator or controller. Attached Figure Description

[0027] The following will refer to the appendix. Figures 1 to 7 The invention is described in detail below, and the accompanying drawings illustrate, in a illustrative, schematic, and non-limiting manner, advantageous structural designs of the invention. Wherein:

[0028] Figure 1 This illustrates a DC-DC converter;

[0029] Figure 2 A welding apparatus is shown, which has a DC-DC converter and a welding power assembly;

[0030] Figure 3 A single-branch boost converter is shown as a DC-DC converter;

[0031] Figure 4 A multi-branch boost converter is shown as a DC-DC converter;

[0032] Figure 5 A welding apparatus is shown, which includes a rectifier, a multiphase boost converter, and a welding power assembly.

[0033] Figure 6 The curves show the switching states of the switching elements;

[0034] Figure 7The curve of the DC output voltage is shown. Detailed Implementation

[0035] Figure 1 A schematic DC-DC converter 2 is shown. A DC-DC converter 2 converts a DC input voltage Ue to a DC output voltage Ua, where the DC input voltage Ue is applied to an input terminal Ue+, and the DC output voltage Ua is applied to an output terminal Ua+. More precisely, the DC input voltage Ue is applied between the input terminal Ue+ and ground U-, and the DC output voltage Ue is applied between the output terminal Ue- and ground U-. Typically, a common ground U- is used in the DC-DC converter 2; however, different grounds U- can be used for the input and output sides, for example, by employing a suitable circuit topology. This can be achieved through potential isolation, for example, via a transformer.

[0036] As in Figure 2 As schematically shown, a DC-DC converter 2 can be used in the welding apparatus 1. The DC-DC converter 2 generates a DC output voltage Ua at the output terminal Ua+. Furthermore, the welding apparatus 1 includes a welding power component 5, which has a power component input terminal and a power component output terminal. During welding phase X, the welding power component adjusts the DC output voltage Ua applied to the power component input terminal to a welding voltage Ua' applied to the power component output terminal. This welding voltage Ua' can be continuous or pulsed. During the no-load phase L, a DC output voltage Ua is present / applied at the power component input terminal of the welding power component 5. Here, adjustment to the welding voltage Ua' is merely an example. Similarly, adjustment to the welding current or alternating adjustment to the welding current and welding voltage can also be performed. This adjustment is coordinated accordingly with the welding process.

[0037] During welding stage X, the DC-DC converter 2 is operated by an adjustment unit 3, which can be configured as analog or digital, at a switching frequency f1 corresponding to the normal switching frequency f1x. This means that the switching element S1 of the DC-DC converter 2 is switched at a switching frequency f1. According to the invention, the switching frequency f1 is divided into a normal switching frequency f1x corresponding to the stage and an idle switching frequency f1L, and is switched accordingly.

[0038] After welding stage X, the welding apparatus 1 is switched to an unloaded stage L. According to existing technology, during this unloaded stage L, the DC-DC converter 2 continues to operate at the normal switching frequency f1x and corresponding losses. However, in contrast, according to the present invention, the DC-DC converter 2 operates at an unloaded switching frequency f1L, which is lower than the normal switching frequency f1x, during the unloaded stage L of the welding apparatus 1. Therefore, losses are kept to a minimum, and the DC output voltage Ua does not decrease during the unloaded stage L. Thus, it is possible to start the welding process immediately after the end of the unloaded stage L and at the beginning of the welding stage X.

[0039] During welding stage X, a load Z (in...) Figure 2 (Drawn in dashed lines) - During welding, the electric arc - is connected to the output terminal Ua+ or the power component output terminal of welding power component 5, thereby transferring energy from the input side to the output side. During welding stage X, the electric arc ignites at least with the start of welding stage X. In the no-load stage L, the load is not connected to the output terminal Ua+ or welding power component 5, therefore there is no energy output on the output side and no electric arc burns.

[0040] The switching loss generated during the no-load phase L according to the invention is smaller than that during the welding phase X, because the switching element S1 switches very infrequently due to the smaller no-load switching frequency f1L. The DC-DC converter 2 still provides a sufficiently high DC output voltage Ua to the welding apparatus 1 to power the control electronics, adjustment unit, display, etc., present in the welding apparatus 1.

[0041] exist Figure 3 A simple single-branch boost converter is shown as DC-DC converter 2. This boost converter includes a single branch A with an induction coil L1, a freewheeling diode D1, and a switching element S1. The induction coil L1 and the freewheeling diode D1 are connected in series. The first coil terminal of the induction coil L1 is connected to the input terminal Ue+, and the second coil terminal of the induction coil L1 is connected in series with the anode of the freewheeling diode D1. The cathode of the freewheeling diode D1 is connected to the output terminal Ua+. Furthermore, the DC-DC converter 2 connects its output terminal Ua+ to the first capacitor terminal of an intermediate circuit capacitor Ca, while the second capacitor terminal of the intermediate circuit capacitor Ca is connected to ground U-. Therefore, a DC output voltage Ua exists across the intermediate circuit capacitor Ca.

[0042] The second coil terminal of the induction coil L1 (and therefore the anode of the freewheeling diode D1) is thus connected to ground U- via a switching element S1 (e.g., a MOSFET, a gate turn-off thyristor, a bipolar transistor, etc.). The switching element S1 is opened and closed at a switching frequency f1, wherein an adjustment unit 3 is provided to control the switching frequency f1. Typical switching frequencies f1 are from 20 kHz to 150 kHz, with even higher switching frequencies f1 possible, particularly when using advanced semiconductor technology. The duty cycle of the switching element S1 is, for example, from 0 to 95%.

[0043] Therefore, when the switching element S1 is closed, the anode of the freewheeling diode D1 is connected to the ground U-, while when the switching element S1 is open, it is separated from the ground U-.

[0044] If the switching element S1 is closed (conduction phase), the second coil terminal of the induction coil L1 is connected to the ground U-, resulting in an input voltage Ue on the induction coil L1. Therefore, a coil current iL, increasing from the initial point in time when the switching element S1 is closed, flows through the induction coil L. Energy is (temporarily) stored in the induction coil L through this coil current iL. Since the anode of the freewheeling diode D1 is also connected to the ground U- through the closed switching element S1, the freewheeling diode D1 is interrupted.

[0045] If the switching element S1 is then disconnected (blocking phase), the coil current iL is maintained by the induction coil L1. Therefore, the potential at the second terminal of the induction coil L1 rises, and consequently, the potential at the anode of the freewheeling diode D1 also rises. Once the potential at the anode of the freewheeling diode D1 exceeds the voltage at the cathode of the freewheeling diode D1 above its critical voltage, the freewheeling diode D1 is switched on. The coil current iL flows through the freewheeling diode D1 and the intermediate circuit capacitor Ca to the ground U-, thereby charging the intermediate circuit capacitor Ca. Simultaneously, at least part of the energy stored in the magnetic field of the induction coil L1 and the energy provided by the DC input voltage Ue are transferred to the intermediate circuit capacitor Ca. The intermediate circuit capacitor Ca is thus charged, while the current in the induction coil L1 decreases, where a DC output voltage Ua exists across the intermediate circuit capacitor Ca.

[0046] If the switching element S1 is closed again after the blocking phase (conduction phase), the DC output voltage Ua applied or acting on the intermediate circuit capacitor Ca is first maintained at its value by the intermediate current capacitor Ca. During the conduction phase, there is no direct energy flow from the input side to the output side; however, the induction coil L is recharged.

[0047] During welding phase X, switching element S1 is switched by an adjustment unit 3 at a switching frequency f1 corresponding to the normal switching frequency f1x. This normal switching frequency f1x and the associated duty cycle are designed to prevent the DC output voltage Ua from dropping during the conduction phase of switching element S1.

[0048] According to the invention, during the no-load phase L, the switching element is switched at a switching frequency f1, which corresponds to an no-load switching frequency f1L that is less than the normal switching frequency f1x. Preferably, the regulating unit 3 undertakes this switching. This significantly reduces losses and prevents the DC output voltage Ua from dropping to a small value during the no-load phase L, ensuring that the welding process can begin immediately after the end of the no-load phase L and the start of the welding phase X. Of course, for this purpose, the no-load switching frequency f1L and the associated duty cycle should be designed accordingly to prevent the DC output voltage Ua from dropping during the conduction phase of the switching element S1, even during the no-load phase L.

[0049] Figure 4 A multi-branch boost converter is shown as a DC-DC converter 2. Its structure, besides having not only one branch A, but also at least one additional branch B and C, is similar to... Figure 3 The DC-DC converter 2 shown is identical. Therefore, there are a total of multiple parallel branches A, B, C, in this case three branches A, B, C – namely, two additional branches B, C. Each branch A, B, C includes an induction coil L1, L2, L3, a switching element S1, S2, S3, and a freewheeling diode D1, D2, D3, which are interconnected in the corresponding branch A, B, C similarly to the single-branch DC-DC converter 2 described above. The first coil terminals of the induction coils L1, L2, L3 are connected together to the input terminal Ue, while the cathode of the freewheeling diode D1 is connected together to the first capacitor terminal of the intermediate circuit capacitor Ca, and thus to the output terminal Ua. Alternatively, each branch A, B, C may have its own independent intermediate circuit capacitor Ca (not shown), in which these intermediate circuit capacitors Ca are connected in parallel.

[0050] The second terminals of the switching elements S1, S2, and S3 are respectively connected to the ground wire U-, and are controlled by the adjustment unit 3 at a switching frequency f1, f2, and f3, respectively, i.e., closed and opened.

[0051] To control the switching frequencies f1, f2, and f3, an adjustment unit 3 is provided. Due to the design of multiple branches A, B, and C, the power that can be generated on the output side is higher than when one branch A, B, and C (with the same design size) is activated individually. However, in the no-load phase, higher no-load power consumption also occurs due to the switching losses of the larger number of switching elements S1, S2, and S3 and the induction coils L1, L2, and L3.

[0052] During the welding stage X, the other switching elements S2 and S3 are switched at another switching frequency f2 and f3, which correspond to a normal switching frequency f2x and f3x, respectively, wherein the normal switching frequency f2x and f3x may correspond to the normal switching frequency f1x.

[0053] According to the present invention, during the no-load phase L, the additional switching elements S2 and S3 are switched at alternative switching frequencies f2 and f3, respectively. These alternative switching frequencies correspond to alternative no-load switching frequencies f2L and f3L, which are lower than the alternative normal switching frequencies f2x and f3x. The alternative no-load switching frequencies f2L and f3L may correspond to the no-load switching frequency f1L. During the no-load phase L, one or more of the additional switching elements S2 and S3 may also be deactivated. However, during this period, at least one switching element S1 is switched at the no-load switching frequency f1L.

[0054] Alternatively, the other switching elements S2 and S3 can be switched using different no-load switching frequencies f2L and f3L, respectively, which are lower than the normal switching frequencies f2x and f3x. Therefore, the switching losses of the other switching elements S2 and S3 are also lower, because the number of switching times of these switching elements is also less than that in the welding stage X.

[0055] Preferably, during the no-load phase L, all switching elements S1, S2, and S3 are switched at no-load switching frequencies f1L, f2L, and f3L that are less than the corresponding normal switching frequencies f1x, f2x, and f3x, wherein the no-load switching frequencies f1L, f2L, and f3L are preferably the same.

[0056] However, it is particularly advantageous that during the no-load phase L, one switching element S1 of branch A is switched at a no-load switching frequency f1L, which is less than the normal switching frequency f1x, and the other switching elements S2 and S3 of the other branches B and C are stopped (blocking phase), which means that the other switching elements S2 and S3 are continuously disconnected. Therefore, particularly low no-load power consumption can be achieved.

[0057] Figure 5A welding apparatus 1 is schematically shown, which includes, for example, a multi-branch boost converter as a DC-DC converter 2. Of course, a welding apparatus 1 with a single-branch boost converter, a single-branch buck converter, or a multi-branch buck converter can also be considered. The number of branches A, B, and C is only three as an example; any number of branches A, B, and C can be considered. In principle, other topologies can also be used for the DC-DC converter 2.

[0058] In addition, the welding device 1 also includes a rectifier stage 4 on the input side. This rectifier stage 4 is connected to three AC grid phases P1, P2, and P3. Each grid phase P1, P2, and P3 includes a lower rectifier diode Du1, Du2, and Du3, and an upper rectifier diode Do1, Do2, and Do3. Alternatively, the rectifier diodes Du1, Du2, Du3, Do1, Do2, and Do3 can be configured using switching elements. The anodes of the lower rectifier diodes Du1, Du2, and Du3 are connected to ground U-, while their cathodes are connected to the corresponding grid phases P1, P2, and P3. Similarly, the anodes of the upper rectifier diodes Do1, Do2, and Do3 are connected to the corresponding grid phases P1, P2, and P3, while their cathodes are connected to the input terminal Ue+ of the DC-DC converter 2. In addition, a filter capacitor Ce is provided in rectifier stage 4, which connects the cathodes of the upper rectifier diodes Do1, Do2, and Do3 to the anodes of the lower rectifier diodes Du1, Du2, and Du3. The operating principle of rectifier stage 4 is well known, so it will not be described in detail here.

[0059] The rectifier stage 4 can be considered optional. Alternatively, a welding apparatus 1 can be provided that does not include the rectifier stage 4 and operates, for example, in an alternating mode.

[0060] The DC-DC converter 2 of welding device 1 has been referenced. Figure 3 and 4 It operates as described. An adjustment unit 3 is provided to control the switching frequencies f1, f2, and f3. During welding stage X, the switching frequencies f1, f2, and f3 correspond to the normal switching frequencies f1x, f2x, and f3x, for example, 35 kHz. During welding stage X of the welding apparatus 1, a load Z (in...) Figure 5 (Drawn in dashed line) It is connected to the output side of DC-DC converter 2 via welding power component 5. During the no-load phase L, there is no energy output to the load Z on the output side.

[0061] During the no-load phase L of the welding apparatus 1, at least one switching element S1 switches at a no-load switching frequency f1L, which is less than the normal switching frequency f1x. The DC output voltage Ua on the intermediate circuit capacitor Ca is thus maintained during the no-load phase L.

[0062] The control signal S (preferably transmitted via an interface) and / or the parameter P specified in the welding apparatus 1 can cause the DC-DC converter 2 to switch from welding stage X to no-load stage L and / or from no-load stage L to welding stage X. For example, in Figure 5 As shown, this can be achieved by providing control signals S and / or parameters P to the adjustment unit 3.

[0063] Figure 6 An exemplary diagram illustrates the switching modes of switching elements S1, S2, and S3 of a three-branch DC-DC converter 2. The switching elements S1, S2, and S3 are correspondingly phase-shifted during the welding phase X. As can be seen, during the no-load phase L, switching element S1 switches at an no-load switching frequency f1L, which is less than the normal switching frequency f1x. Advantageously, during the no-load phase L, the other switching elements S2 and S3 are deactivated (as shown).

[0064] According to existing technology, during the no-load phase, all switching elements S1, S2, and S3 of L still operate at their corresponding normal switching frequencies f1x, f2x, and f3x, thus resulting in energy loss.

[0065] To prevent energy loss during the no-load phase L, the DC-DC converter 2 can also be shut down, i.e., turned off, during the no-load phase of the welding apparatus. This is achieved by no longer operating the switching elements S1, S2, and S3, thus keeping them in the off state. However, this causes the DC output voltage Ua to drop because the intermediate circuit capacitor Ca on the output side releases energy during the no-load phase L and is no longer supplied with energy from the input side. Therefore, there may be a situation where the welding apparatus 1 does not have enough voltage to operate the control electronics unit, adjustment unit, display, etc., and thus additional energy must be supplied to them.

[0066] Furthermore, the cessation of operation of the DC-DC converter 2 during the no-load phase L of welding apparatus 1 causes the following problem: For the welding apparatus to continue its welding phase after the no-load phase L, the DC-DC converter 2 must first reach a suitable operating state again to provide the necessary energy or DC output voltage Ua on the output side. This suitable operating state may take some time, resulting in a delay of, for example, tv within the range of 50 milliseconds, until welding apparatus 1 is ready for further welding. Therefore, in the case of switching elements S1, S2, S3 and thus the DC-DC converter 2 ceasing operation during the no-load phase L of welding apparatus 1, the actual welding process, i.e., arc ignition, cannot be restarted in a controlled or timely manner, causing a delayed start to the stable welding phase or making arc ignition difficult or impossible. (The welding phase begins from arc ignition). Figure 7 The dashed line shows the DC output voltage Ua when all branches cease operation during the no-load phase L. As can be seen, in the boost converter, the DC output voltage Ua drops to the DC input voltage Ue during the no-load phase L. After switching back to the welding phase X, there is a certain delay tv, here 50 milliseconds, before the DC output voltage Ua reaches its full value again; therefore, the welding process can only begin after this time delay.

[0067] In contrast, Figure 7 The DC output voltage Ua is shown in solid lines when one or more switching elements S1, S2, S3 are switched during the no-load phase L according to the present invention. Since at least one switching element S1, S2, S3 still switches at a no-load switching frequency f1L, f2L, f3L, the DC output voltage Ua is maintained even during the no-load phase L. Because the DC-DC converter 2 continuously provides the necessary DC output voltage Ua, the welding process can begin immediately after the end of the no-load phase L and the start of the welding phase X. The DC-DC converter 2 thus continuously provides the welding power component 5 with the DC output voltage Ua required for the optimal start of the welding phase X. The already sufficiently high DC output voltage Ua at the DC voltage output terminal Ua+ prevents a delay between the planned start of the welding process and the actual transition from the DC-DC converter 2 to the welding phase X. Therefore, the welding process begins immediately after the no-load phase L when the welding phase X begins. Here, the losses of the DC-DC converter 2 are minimized.

Claims

1. A method for operating a welding apparatus (1), wherein a DC-DC converter (2) of the welding apparatus (1) converts a DC input voltage (Ue) applied to an input terminal (Ue+) into a DC output voltage (Ua) applied to an output terminal (Ua+), the DC output voltage being applied to a power component input terminal of a welding power component (5) of the welding apparatus (1), wherein at least one switching element (S1) of a branch (A) of the DC-DC converter (2) is switched at a switching frequency (f1), wherein a welding stage (X) is provided for the welding apparatus (1), during which the switching frequency (f1) corresponds to a normal switching frequency (f1x), and the welding power component (5) adjusts the DC output voltage (Ua) applied to the power component input terminal to a welding voltage (Ua') applied to the power component output terminal during the welding stage (X), characterized in that: The welding apparatus (1) is provided with an unloaded stage (L) in which no electric arc burns. During this unloaded stage, at least one switching element (S1) is switched at a switching frequency (f1) corresponding to the unloaded switching frequency (f1L), which is less than the normal switching frequency (f1x). The transmitted control signal (S) and / or the parameter (P) specified in the welding apparatus (1) facilitate the transition from the welding stage (X) to the unloaded stage (L) and / or from the unloaded stage (L) to the welding stage (X). The DC output voltage (Ua) is maintained during the no-load phase (L) in order to provide the welding power assembly (5) with the DC output voltage (Ua) required for the optimal start welding phase (X).

2. The method according to claim 1, characterized in that: At least one additional switching element (S2, S3) of at least one additional branch (B, C) of the DC-DC converter is switched at at least one additional switching frequency (f2, f3), wherein the at least one additional switching frequency (f2, f3) in the welding stage (X) corresponds to an additional normal switching frequency (f2x, f3x) in order to transfer energy from the input terminal (Ue+) to the output terminal (Ua+).

3. The method according to claim 2, characterized in that: The other normal switching frequencies (f2x, f3x) correspond to the normal switching frequency (f1x).

4. The method according to claim 2 or 3, characterized in that: During the no-load phase (L), the at least one additional switching frequency (f2, f3) is switched at an additional no-load switching frequency (f2L, f3L) that is less than the additional normal switching frequency (f2x, f3x).

5. The method according to claim 4, characterized in that: The at least one additional no-load switching frequency (f2L, f3L) corresponds to the no-load switching frequency (f1L).

6. The method according to claim 2 or 3, characterized in that: During the no-load phase (L), at least one of the switching elements (S1) and / or at least one of the other switching elements (S2, S3) are stopped from operating.

7. The method according to claim 1, characterized in that: The control signal (S) is generated by operating a switch or button to start or stop welding as specified.

8. The method according to claim 1, characterized in that: The parameter (P) is given by decreasing or increasing the welding voltage and / or decreasing / increasing the current on the output side.

9. The method according to claim 1, characterized in that: The control signal (S) is transmitted via an interface.

10. A welding apparatus (1) comprising a DC-DC converter (2) and a welding power component (5), the DC-DC converter (2) being configured to convert a DC input voltage (Ue) applied to an input terminal (Ue+) into a DC output voltage (Ua) applied to an output terminal (Ua+), the DC output voltage being applied to the power component input terminal of the welding power component (5) of the welding apparatus (1), the DC-DC converter (2) comprising at least one switching element (S1) in a branch (A) and comprising an adjustment unit (3) configured to switch the switching element (S1) at a switching frequency (f1) corresponding to a normal switching frequency (f1x) in a welding stage (X) of the welding apparatus (1), and the welding power component (5) being configured to adjust the DC output voltage (Ua) applied to the power component input terminal to a welding voltage (Ua') applied to the power component output terminal in the welding stage (X), characterized in that: The adjustment unit (3) is configured to switch at least one switching element (S1) at a switching frequency (f1) corresponding to the no-load switching frequency (f1L) in the no-load phase (L) of the welding apparatus (1), the no-load switching frequency being less than the normal switching frequency (f1x), in which there is no arc combustion, and to set the transmitted control signal (S) and / or the parameter (P) specified in the welding apparatus (1) to facilitate the transition from the welding phase (X) to the no-load phase (L) and / or from the no-load phase (L) to the welding phase (X), and The regulating unit (3) is configured to maintain the DC output voltage (Ua) during the no-load phase (L) so as to provide the welding power assembly (5) with the DC output voltage (Ua) required for the optimal start welding phase (X).

11. The welding apparatus (1) according to claim 10, characterized in that: The branch (A) includes an induction coil (L1) and a freewheeling diode (D1), wherein the first coil terminal of the induction coil (L1) is connected to the input terminal (Ue+), and the second coil terminal of the induction coil (L1) is connected to the first switching terminal of the switching element (S1) and the anode of the freewheeling diode (D1), the second switching terminal of the switching element (S1) is connected to the ground wire (U-), and the cathode of the freewheeling diode (D1) is connected to the output terminal (Ua+).

12. The welding apparatus (1) according to claim 11, characterized in that: The DC-DC converter (2) includes at least one additional branch (B, C), which has at least one additional switching element (S2, S3), at least one additional induction coil, and at least one additional freewheeling diode (D). In the at least one additional branch (B, C), the first coil terminals of the at least one additional induction coil are respectively connected to the input voltage (Ue), and the second coil terminals of the at least one additional induction coil are respectively connected to the corresponding first switching terminals of the at least one additional switching element (S2, S3) and the at least one additional freewheeling diode (D). The corresponding anode of the diode (D2) is connected, wherein the second switching terminal of the at least one additional switching element (S2, S3) is connected to the ground (U-), and the cathode of the at least one freewheeling diode (D) is connected to the output terminal (Ua+), and the adjustment unit (3) is configured to switch the at least one additional switching element (S2, S3) at at least one additional switching frequency (f2, f3) during the welding stage (X) of the welding apparatus (1), the at least one additional switching frequency corresponding to an additional normal switching frequency (f2x, f3x).

13. The welding apparatus (1) according to claim 12, characterized in that: The adjustment unit (3) is configured to switch the at least one additional switching element (S2, S3) at an additional no-load switching frequency (f2L, f3L) less than the additional normal switching frequency (f2x, f3x) during the no-load phase (L) of the welding apparatus (1).

14. The welding apparatus (1) according to claim 12 or 13, characterized in that: The adjustment unit (3) is configured to stop the operation of at least one switching element (S1) and / or at least one of the other switching elements (S2, S3) during the no-load phase (L) of the welding apparatus (1).

15. The welding apparatus (1) according to claim 10, characterized in that: The control signal (S) is transmitted via an interface.

16. The welding apparatus (1) according to claim 13, characterized in that: The additional no-load switching frequency corresponds to the no-load switching frequency (f1L).

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