Method and control device for charging an intermediate circuit capacitor for a welding machine

Description

[0001] The present invention relates to a method for charging an intermediate circuit capacitor for a welding device, to a control device for charging an intermediate circuit capacitor for a welding device and to a corresponding computer program.

[0002] A resistance welder usually has an intermediate circuit electrolytic capacitor battery. These electrolytic capacitors cannot be connected directly to the power supply; instead, they are first charged with a small current. This pre-charging can be achieved using a series resistor that limits the current. The electrolytic capacitors can also be charged by a power supply, which charges the electrolytic capacitors with a constant current, for example.

[0003] Document US 4 965 860 A discloses a welding power unit with a capacity.

[0004] Document CN 102 130 010 A discloses a method for filling deep trenches with high-quality oxide for semiconductor devices.

[0005] Document US 6 038 155 discloses a 3-phase SCR rectifier bridge with a soft start control IC.

[0006] Against this background, it is the object of the present invention to provide a method for charging an intermediate circuit capacitor for a welding device, a control device for charging an intermediate circuit capacitor for a welding device and a corresponding computer program.

[0007] This object is achieved by a method for charging an intermediate circuit capacitor for a welding device, a control device for charging an intermediate circuit capacitor for a welding device and a corresponding computer program product according to the main claims.

[0008] The present invention is based on the finding that the charging current of an intermediate circuit capacitor can be limited using a phase-cut control or a phase-cut control. The phase cuts or phase cuts become successively larger to increase the electrical voltage at the intermediate circuit capacitor in a controlled manner.

[0009] Advantageously, the intermediate circuit capacitor, or alternatively or additionally the phase-cut control, can be charged with low losses. Furthermore, separate devices for providing a limited charging current are eliminated. This allows for a compact and cost-effective welding system.

[0010] The present invention provides a method for charging an intermediate circuit capacitor for a welding device, the method comprising the steps defined in claim 1.

[0011] The present invention further provides a control device for charging an intermediate circuit capacitor for a welding device, which is designed to carry out or implement the steps of a variant of the method according to the invention in corresponding devices. This embodiment of the invention in the form of a control device also allows the object underlying the invention to be achieved quickly and efficiently.

[0012] In this context, a control unit can be understood as an electrical device that processes sensor or data signals and outputs control and / or data signals depending on them. The control unit can have an interface that can be implemented in hardware and / or software. In a hardware implementation, the interfaces can, for example, be part of a so-called system ASIC, which contains a wide variety of functions of the control unit. However, it is also possible for the interfaces to be separate integrated circuits or to consist at least partially of discrete components. In a software implementation, the interfaces can be software modules that are present, for example, on a microcontroller alongside other software modules.

[0013] Also advantageous is a computer program with program code which can be stored on a machine-readable medium such as a semiconductor memory, a hard disk memory or an optical memory and is used to carry out the method according to one of the embodiments described above when the program is executed on a computer or a device.

[0014] An intermediate circuit capacitor can be understood as an electrolytic capacitor or a film capacitor for smoothing a rectified voltage after a rectifier and before an inverter. A half-wave can be a region of a wave-shaped voltage curve. For example, the half-wave can be a region in which a voltage value of the voltage curve has a positive or negative sign. The half-wave can be limited by two consecutive zero crossings of the voltage curve. The voltage curve can be an alternating voltage. Within the half-wave, the alternating voltage can have phase angles of half a wavelength. At the beginning of the half-wave, the phase angle can be zero. At the end of the half-wave, the phase angle can be 180° or π; likewise, the half-wave can extend between 180° or π and 360° or 2π. 2π can again be considered the zero point.The phase angle can also be considered continuously. A section of the half-wave can be a piece of the half-wave. The section can have a starting point with a starting angle, an initial time, and an initial voltage value, as well as an end point with an end angle, an end time, and an end voltage value. A firing angle (which can also be referred to as a phase-related starting time, as the starting time of a section within a half-wave) can be the starting angle of the section. A phase-related starting time can therefore be understood as a point in time related to the beginning of a half-wave, with the section in question then being defined from the starting time until a voltage of zero volts is reached. The firing angle can correlate with a phase angle of the half-wave that the alternating voltage has at an initial time of the section. The end point can be a zero crossing of the alternating voltage.

[0015] An angle difference between the first firing angle and the second firing angle can be smaller than a maximum angle difference. In other words, a difference between the first phase-related starting time and the second phase-related starting time can be smaller than a maximum specified difference or maximum specified time period. A specified maximum angle difference can limit an excessive voltage rise at the DC link capacitor between the individual feed-in steps. This can also limit the current flow.

[0016] The method may comprise a step of determining the first phase-related starting time, wherein the first phase-related starting time is determined using a maximum permissible current at the intermediate circuit capacitor. Alternatively or additionally, the method may comprise a step of determining the second phase-related starting time, wherein the second phase-related starting time is determined using the maximum permissible current at the intermediate circuit capacitor. A current current at the intermediate circuit capacitor may be determined in a measuring step. The phase-related starting times may be determined such that a current increase during feeding is smaller than a maximum intended current increase that the intermediate circuit capacitor can withstand without suffering a defect.

[0017] The method comprises a step of determining a phase position of the half-wave and a phase position of the subsequent half-wave, wherein the first phase-related starting time and the second phase-related starting time are determined in the feeding steps using the phase positions. For example, the zero crossings or maxima can be determined to determine the phase position. The phase-related starting times can be adjusted relative to the phase position.

[0018] The method may comprise a first step of detecting a voltage of the intermediate circuit capacitor before the first feeding step, wherein the first phase-related starting time is determined using the voltage before the feeding. Alternatively or additionally, the method may comprise a second step of detecting the voltage of the intermediate circuit capacitor after the first feeding step, wherein the second phase-related starting time is determined using the voltage after the first feeding. A voltage of the intermediate circuit capacitor may be an electrical voltage present between the poles of the intermediate circuit capacitor.

[0019] The first phase-related starting time can represent a voltage value of the half-wave that is a predetermined voltage difference greater than the voltage before the first feed-in step. Alternatively or additionally, the second phase-related starting time can represent a voltage value of the subsequent half-wave that is the predetermined voltage difference greater than the voltage after the first feed-in step. This can prevent an excessive increase in the voltage at the intermediate circuit capacitor between two consecutive half-waves.

[0020] The half-wave can represent a portion of a first phase of a multi-phase alternating voltage. The subsequent half-wave can represent a portion of a second phase of the multi-phase alternating voltage, shifted by a phase angle relative to the half-wave. For example, in a three-phase alternating voltage, the phases can have a phase offset of 120° or 2 / 3π. The half-waves can overlap.

[0021] The method may comprise at least one further feeding step in which a voltage of a further section of one of the half-waves or the subsequent half-wave of the alternating voltage is fed into the intermediate circuit capacitor, wherein the further section begins at a further phase-related starting time which is earlier than the second phase-related starting time.

[0022] The at least one further phase-related starting time can be reduced to a predetermined minimum firing angle or minimum phase-related starting time. For example, a maximum effective value of the alternating voltage can be reached at the predetermined minimum firing angle or the minimum phase-related starting time.

[0023] The at least one further phase-related starting time can be reduced until the intermediate circuit capacitor has a specified voltage. The specified voltage can be a target voltage. For example, the specified voltage can be a standby voltage to save energy.

[0024] The present invention further provides a welding device with the following features: an at least semi-controlled rectifier for generating a DC voltage, an intermediate circuit capacitor for smoothing the DC voltage, wherein a positively chargeable contact of the intermediate circuit capacitor is connected to a terminal of the rectifier that outputs a positive voltage, and wherein a negatively chargeable contact of the intermediate circuit capacitor is connected to a terminal of the rectifier that outputs a negative voltage; a control device for charging the intermediate circuit capacitor according to the approach presented here; and a device for generating a welding current, which is connected to the intermediate circuit capacitor in order to consume the DC voltage.

[0025] The invention is explained in more detail below with reference to the accompanying drawings. They show: Fig. 1 a flowchart of a method for charging an intermediate circuit capacitor Fig. 2 a flowchart of part of a method for charging an intermediate circuit capacitor Fig. 3 a graphic representation of voltage curves and sections with decreasing firing angles in different consecutive half-waves Fig. 4 a representation of a welding device Fig. 5 a representation of a voltage curve Fig. 6 a representation of a voltage curve

[0026] Identical or similar elements may be provided with identical or similar reference numerals in the following figures. Furthermore, the figures of the drawings, their description, and the claims contain numerous features in combination. A person skilled in the art will appreciate that these features may also be considered individually or combined to form further combinations not explicitly described here.

[0027] Fig. 1shows a flowchart of a method 100 for charging an intermediate circuit capacitor of a welding device. The method comprises two consecutive feeding steps 102, 104. In the first feeding step 102, a voltage from a first section of a half-wave of an alternating voltage is fed into the intermediate circuit capacitor, the first section beginning at a first phase-related starting time. In the subsequent second feeding step, a voltage from a second section of a subsequent half-wave of the alternating voltage is fed into the intermediate circuit capacitor, the second part beginning at a second phase-related starting time that is earlier than the first phase-related starting time. In terms of the ignition angle, this means that the second phase-related starting time is smaller than the first phase-related starting time.

[0028] Fig. 2shows a flowchart of a part of a method 100 for charging an intermediate circuit capacitor. In this part, the method 100 comprises a step of determining 200, a step of measuring 202, a step of determining 204, a step of feeding 102 and a further step of measuring 202. The steps of the method 100 or a variant thereof can be carried out in the method 100 in Fig. 1be carried out additionally. In the determining step 200, a phase position of the alternating voltage is determined. Here, a frequency and amplitude of the alternating voltage are known, since the alternating voltage is a mains voltage with a mains frequency. If the alternating voltage is unknown, the frequency and amplitude of the alternating voltage can also be recorded in the determining step. The phase position is determined using distinctive, characteristic voltage values ​​of the alternating voltage. For example, zero crossings of the alternating voltage can be detected in order to determine the phase position of the alternating voltage. In the measuring step 202, a voltage is measured at terminals of the intermediate circuit capacitor. In the determining step 204, the first firing angle (phase-related starting time) for a controllable rectifier component is determined.At the firing angle (phase-related starting time), the alternating voltage has a value that is higher by a predetermined difference than the measured voltage at the capacitor so that charge can flow into the capacitor. In the feeding step 102, the rectifier component is switched on when the alternating voltage has the firing angle. The rectifier component remains conductive until the voltage reverses its sign. As long as the instantaneous voltage of the alternating voltage is higher than the instantaneous voltage at the capacitor, charge flows into the capacitor. In the second measuring step, the voltage at the capacitor is measured in order to determine the firing angle in the subsequent step (not shown) of determining the second firing angle so that further charge can flow into the capacitor in the second feeding step (also not shown).The steps of method 100 can be executed until the voltage in the intermediate circuit capacitor corresponds to the effective voltage of the AC voltage. Likewise, the voltage in the intermediate circuit capacitor can be limited to a predetermined value.

[0029] Fig. 3 shows a graphical representation of voltage curves 300 and sections 302 with decreasing (i.e., decreasing) firing angles according to an embodiment of the present invention. Furthermore, the illustration shows an increasing voltage 304 at the intermediate circuit capacitor. The voltages shown here from sections 302a to 302k can be fed into the intermediate circuit capacitor of a welding device using a method according to the approach presented here in order to increase the voltage 304 therein while limiting the current flow at the capacitor.

[0030] The voltage waveforms 300, the sections 302, and the voltage 304 are shown in a diagram that has a phase angle of the voltage waveforms 300 in radians (π) as the abscissa. A voltage value normalized to one from minus one through zero to plus one is plotted on the ordinate. The abscissa begins at 0π and is shown up to beyond 6π. The voltage waveforms 300a, 300b, and 300c represent the three phases L1, L2, and L3 of a three-phase alternating voltage. They have a sinusoidal shape with a wavelength of 2π and an amplitude of 1. The voltage waveforms 300 are offset from one another by 120° or 2 / 3π. All voltage waveforms 300 are shown over three complete wavelengths. A wavelength is divided into a positive half-wave with positive voltage values ​​and a length of 1π and a negative half-wave with negative voltage values ​​and also a length of 1π.In this embodiment, only the positive half-waves are used to feed sections 302. Likewise, the negative half-waves or positive and negative half-waves can be used together.

[0031] In response to a charging signal from a control unit according to an embodiment of the present invention, a first section 302a from a first half-wave of phase 300a is fed into the intermediate circuit capacitor by means of a first switchable component (diode, thyristor, transistor, or similar) of a half-controlled bridge rectifier (i.e., a bridge rectifier in which only one rectifier element is provided for rectifying a positive or negative voltage of the AC voltage). The first section 302a has a first firing angle at which the first component is switched to conduct. The first firing angle is slightly smaller than 1π and lies shortly before the zero crossing of phase 300a. Thus, the first section 302a has a low initial voltage below 0.1. The voltage 304 increases barely noticeably. The second section 302b is fed into the intermediate circuit capacitor from a subsequent first half-wave of phase 300b.The second section 302b has a second firing angle that is smaller than the first firing angle. The second section 302b has an initial voltage below 0.2. The voltage 304 at the intermediate circuit capacitor increases slightly. The third section 302c is fed into the intermediate circuit capacitor from a subsequent first half-wave of phase 300c. The firing angle of the third section 302c is again smaller than the firing angle of the second section 302b. The initial voltage of the third section 302d is therefore below 0.3. The voltage 304 increases noticeably. The fourth section 302d is fed into the intermediate circuit capacitor from a subsequent second half-wave of phase 300a. The firing angle of the fourth section 302d is again smaller than the firing angle of the third section 302c. The initial voltage of the fourth section 302d is therefore below 0.4. The voltage 304 is rising.The fifth section 302e is fed into the intermediate circuit capacitor from a subsequent second half-wave of phase 300b. The firing angle of the fifth section 302e is again smaller than the firing angle of the fourth section 302d. Thus, an initial voltage of the fifth section 302e is below 0.5. The voltage 304 rises to 0.1. The sixth section 302f is fed into the intermediate circuit capacitor from a subsequent second half-wave of phase 300c. The firing angle of the sixth section 302f is again smaller than the firing angle of the fifth section 302e. Thus, an initial voltage of the sixth section 302f is below 0.6. The voltage 304 rises to just below 0.2. The seventh section 302g is fed into the intermediate circuit capacitor from a subsequent third half-wave of phase 300a. The ignition angle of the seventh section 302g is again smaller than the ignition angle of the sixth section 302f.The initial voltage of the seventh section 302g is therefore below 0.7. The voltage 304 rises to just below 0.3. The eighth section 302h is fed into the intermediate circuit capacitor from a subsequent third half-wave of phase 300b. The firing angle of the eighth section 302h is again smaller than the firing angle of the seventh section 302g. The initial voltage of the eighth section 302h is therefore below 0.8. The voltage 304 rises to 0.4. The ninth section 302j is fed into the intermediate circuit capacitor from a subsequent third half-wave of phase 300c. The firing angle of the ninth section 302j is again smaller than the firing angle of the eighth section 302h. The initial voltage of the ninth section 302j is therefore below 0.9. The voltage 304 rises to 0.6. The tenth section 302k is fed into the intermediate circuit capacitor from a subsequent fourth half-wave of phase 300a.The firing angle of the tenth section 302k is again smaller than the firing angle of the ninth section 302j. Thus, the initial voltage of the tenth section 302k is below 1. The voltage 304 rises above 0.9. The intermediate circuit capacitor is now charged.

[0032] According to the invention, a higher-level controller first determines the respective operating state of the system over time. These operating states are: a charging process, generation of a reduced voltage (standby or sleep mode), normal operation with a minimum firing angle, and shutdown. Depending on the respective operating state, the intermediate circuit capacitor can then be charged, so that the intermediate circuit capacitor does not need to be charged in all cases; instead, a different amount of charge is introduced into the intermediate circuit capacitor depending on the operating state (i.e., the intermediate circuit capacitor is charged to a corresponding voltage).

[0033] Fig. 4 shows a representation of a welding device 400 according to an embodiment of the present invention. The welding device is constructed from two separate units, an inverter 402 and a transformer rectifier 404. Both are connected to each other via electrical lines.

[0034] The inverter 402 is connected to a three-phase AC voltage network 406. The three-phase AC voltage network 406 has three phases L1, L2, and L3. The inverter has a semi-controlled bridge rectifier 408, an intermediate circuit capacitor 410, an inverter 412, a control unit 414 according to an embodiment of the present invention, a welding processor 416, and a voltage supply device 418 with a driver 420. The bridge rectifier 408 is connected to the network 406 and is designed to convert the AC voltages of the phases L1, L2, and L3 into a DC voltage. The intermediate circuit capacitor 410 is connected to the bridge rectifier 408 and is designed to reduce a ripple of the DC voltage from the rectifier 408. The inverter 412 is connected to the intermediate circuit capacitor 410 and is designed to convert the DC voltage into a medium-frequency AC voltage.This alternating voltage is conducted via the electrical lines to the transformer rectifier 404. The control unit 414 is connected to the mains 406, the bridge rectifier 408, and the intermediate circuit capacitor 410. The control unit 414 is configured to determine a phase position of the mains 406, to control the feeding of half-wave sections with variable starting times into the intermediate circuit capacitor 410, and to monitor a voltage and / or current flow at the intermediate circuit capacitor 410. The welding processor 416 is connected via a bus system to the voltage supply device 418, the inverter 412, and the transformer rectifier 404. The welding processor 416 is configured to control IGBTs (Insulated Gate Bipolar Transistors) of the inverter 412 in order to provide the medium-frequency alternating voltage to the transformer rectifier 404 as needed.

[0035] The transformer rectifier 404 includes a welding transformer 422, a rectifier 424, and a sensor system 426. The welding transformer 422 is connected to the inverter 412 and is configured to transform a current of the medium-frequency AC voltage into a welding current. The rectifier 424 is connected to the welding transformer 422 and is configured to convert the medium-frequency AC voltage into a medium-frequency DC voltage that can be used for a welding process. The sensor system 426 includes sensors in the welding transformer 422 and the rectifier 424 and is connected to the welding processor 416 for transmitting data.

[0036] The control unit 414 is designed to keep a charging current when charging the intermediate circuit capacitor 410 within a predetermined tolerance by providing an increasing charging voltage by means of a pulse width modulation with increasing pulse width from the half-controlled bridge rectifier 408, as in Fig. 3 is shown.

[0037] In other words, by using a semi-controlled B6 bridge 408 with voltage-dependent control of the thyristors, a charging resistor or charging power supply for charging the intermediate circuit capacitor 410 can be eliminated. By controlling the thyristors from a phase angle of approximately 220° downwards, the precharging function can be fulfilled. System losses can be reduced by using the B6 bridge 408.

[0038] Controlling the thyristors results in a simple and fast charging circuit for the 410 DC link capacitors. Furthermore, this control system can easily implement a standby function with reduced DC link voltage or a sleep mode with the DC link voltage switched off. Nevertheless, it is possible to be ready for welding again quickly.

[0039] According to one embodiment of the present invention, the semi-controlled bridge is controlled using a voltage measurement of the mains voltages. The firing angle of the thyristors is changed based on the voltage measurement per phase. Alternatively, the firing angle can also be changed by a time control. Depending on the difference between the mains voltage and the intermediate circuit voltage, the firing angle can be reduced in uniform steps until the thyristors are then continuously controlled for the required 120°.

[0040] The standby function can be achieved, for example, by regulating the intermediate circuit voltage to half the voltage value. Then, the semi-controlled bridge 408 is fired at the control angle, as during the charging process, only every twentieth mains period, for example. This results in fewer losses due to the loss of firing energy during each mains period. Furthermore, conduction losses of the thyristors are avoided. In addition, significantly fewer losses occur in the symmetry resistances of the electrolytic capacitor battery and due to the lower residual current of the electrolytic capacitors. The standby function can be initiated by a higher-level controller 416, under the boundary condition that the system 400 is ready for welding again, for example, after 50 ms.

[0041] The sleep function can also be activated by the higher-level controller 416. During the sleep function, the semi-controlled bridge 408 is completely blocked, allowing the intermediate circuit 410 to discharge. For welding to resume, the sleep function can then take, for example, one second until the intermediate circuit voltage reaches its setpoint. A delay may also depend on the reactivation of the controller 416, which can also enter sleep mode.

[0042] The Figures 5 and 6 show in principle the effect of advancing the ignition timing according to embodiments of the present invention with approximately sinusoidal alternating voltages.

[0043] Fig. 5 shows a representation of a voltage curve 500 according to an embodiment of the present invention. Analogous to the voltage curves in Fig. 3A three-phase alternating voltage 500 is fed into the intermediate circuit capacitor with a falling edge leading to rising components 502. At the beginning of each component 502, a thyristor in the rectifier is triggered to become conductive. As a result, the intermediate circuit voltage 504 increases approximately linearly in this embodiment.

[0044] Fig. 6 shows a representation of a voltage waveform 600 according to an embodiment of the present invention. As in Fig. 5 The decreasing ignition angles 602 are shown. In contrast to Fig. 5 the voltage curve at the intermediate circuit capacitor is shown as monotonically increasing.

[0045] The embodiments shown are only examples and can be combined with each other. List of reference symbols

[0046] 100 Charging procedure 102 First feeding step 104 Second feeding step 200 Determining step 202 Measuring step 204 Determining step 300 Alternating voltage 302 Section 304 Voltage at the intermediate circuit capacitor 400 Welding machine 402 Inverter 404 Transformer rectifier 406 Three-phase alternating voltage 408 Bridge rectifier 410 Intermediate circuit capacitor 412 Inverter 414 Charging control unit 416 Welding processor 418 Power supply 420 Driver 422 Welding transformer 424 Rectifier 426 Sensors 500 Alternating voltage 502 Section 600 Alternating voltage 602 Firing angle

Claims

1. Method (100) for charging a DC-link capacitor (408) for a welding device (400), wherein the method (100) comprises the following steps: feeding (102) a voltage from a first portion (302a) of a half-cycle of an AC voltage (300a) into the DC-link capacitor (410), wherein the first portion (302a) starts at a first ignition angle; and feeding (104) a voltage from a second portion (302b) of a half-cycle of the AC voltage (300b) that follows the half-cycle into the DC-link capacitor (410), wherein the second portion (302b) starts at a second ignition angle smaller than the first ignition angle, characterized in that first in the chronological sequence of the method (100), one of the following four operating states of a system comprising the DC-link capacitor (408) is determined as being present by means of a superordinate controller: - charging procedure - generating a reduced voltage - normal operation at a reduced ignition angle - switching off and wherein, depending on the operating state, a different amount of charge is introduced into the DC-link capacitor (408).

2. Method (100) according to Claim 1, wherein in the step of feeding in (104) the second portion (302b), a difference between the first ignition angle and the second ignition angle is smaller than a maximum difference.

3. Method (100) according to one of the preceding claims, comprising a step of determining (204) the first ignition angle, wherein the first ignition angle is determined using a maximum permissible current at the DC-link capacitor (410), and / or comprising a step of determining (204) the second ignition angle, wherein the second ignition angle is determined using the maximum permissible current at the DC-link capacitor (410).

4. Method (100) according to one of the preceding claims, comprising a step of determining (200) a phase of the half-cycle and a phase of the half-cycle that follows the half-cycle, wherein the first ignition angle and the second ignition angle are determined in the steps of feeding in (102, 104) using the phases.

5. Method (100) according to one of the preceding claims, comprising a first step of measuring (202) a voltage of the DC-link capacitor (410) before the first step of feeding in (102), wherein the first ignition angle is determined using the voltage before the feeding-in, and / or comprising a second step of measuring (202) the voltage of the DC-link capacitor (108) after the first step of feeding in (102), wherein the second ignition angle is determined using the voltage after the first feeding-in.

6. Method (100) according to Claim 5, wherein the first ignition angle represents a voltage value of the half-cycle that is a predetermined voltage difference greater than the voltage before the feeding-in (104), and / or the second ignition angle represents a voltage value of the subsequent half-cycle that is greater than the voltage after the first feeding-in (102) by the predetermined voltage difference.

7. Method (100) according to one of the preceding claims, wherein in the step of feeding in (102) the voltage from the first portion (302a), the half-cycle represents part of a first phase (300a) of a multiphase AC voltage (406), and wherein in the step of feeding in (104) the voltage from the second portion (302b), the half-cycle that follows the half-cycle represents part of a second phase (300b) of the multiphase AC voltage (406), which is shifted by a phase angle relative to the half-cycle.

8. Method (100) according to one of the preceding claims, comprising at least one further step of feeding in, in which a voltage from a further portion (302) of a half-cycle of the AC voltage (300) that additionally follows the half-cycle or the subsequent half-cycle is fed into the DC-link capacitor (410), wherein the further portion (302) starts at a further ignition angle smaller than the second ignition angle.

9. Control device for charging (414) a DC-link capacitor (410) for a welding device (400), having units which are designed to carry out the steps of a method (100) according to one of Claims 1 to 9.

10. Computer program having program code for carrying out the method (100) according to one of Claims 1 to 9 when the program is executed on an apparatus (414).