Method for operating grid-connected converter, converter, computer program and computer readable medium

Abstract

The invention relates to a method for operating a grid-connected converter (1) connected to an electric machine (3), in which during the power generation operation of the converter (1), at least one power switch (4) of the converter (1) is switched on at an ignition angle [alpha] zu suitable for [alpha] zu180 DEG-[alpha] ab + [alpha] cab, where [alpha] ab is an angle, and during the motor operation of the converter (1), the at least one power switch (4) of the converter (1) is switched on at an ignition angle [alpha] zu, which is suitable for [alpha] zu180 DEG-[alpha] ab + [alpha] cab. The at least one power switch (4) of the converter (1) is switched off at an angle at which the line current (imot) drops to zero last within a half cycle, and wherein the acab is a constant angle, and wherein the at least one power switch (4) of the converter (1) is switched off at a flameout angle # imgabs0 #, which is suitable for # imgabs1 #, where aan is an angle at which the line current (imot) drops to zero last within a half cycle before the aab angle drops to zero, and wherein the acab is a constant angle, and wherein the at least one power switch (4) of the converter (1) is switched off at a flameout angle # imgabs0 #, which is suitable for # imgabs1 #. The line current (imot) increases from zero at the last time when the motor of the converter (1) is operated, and wherein [alpha] can is a constant angle.

Description

Technical Field

[0001] The invention relates to a method for operating a grid-connected converter connected to an electrical machine. The invention also relates to a converter, a computer program and a computer-readable medium. Background Art

[0002] Converters (also called "power converters") are used to convert direct voltage into alternating voltage. Converters connected to the public low-voltage supply network must meet various requirements. The relevant standard DIN EN 61000:2011 "Electromagnetic Compatibility (EMC)" plays a role in this regard. The limit values ​​for THC (Total Harmonic Content / Current) and PWHC (Partial Weighted Harmonic Content / Current) are specified in DIN EN 61000-3-12:2011 (Part 3-12: Limit values ​​- Limit values ​​for harmonic currents caused by equipment and devices connected to the public low-voltage network with an input current >16 A and ≤75 A per phase (IEC 61000-3-12:2011).

[0003] There is a problem that the converter partially does not meet the requirements, for example, in all operations. In particular, the problem can arise that the requirements for THC and PWHC can be met in motor operation, but not in generator operation. This is particularly because in generator operation, the current has a square shape due to the switching pattern of the converter being synchronized with the line voltage.

[0004] In motor operation, current flows from a grid connected to the converter through the converter to a motor likewise connected to the converter, in particular a connected motor, and in generator operation, current flows in the opposite direction, namely from the motor through the converter to the grid.

[0005] In generating operation, there is the problem that the requirements for THC and PWHC are not met, for example, for grid-connected converters with a topology having a two-stage rectifier switching at the base frequency (50 Hz in Germany), in combination with a line choke and in particular a large DC intermediate circuit. "Large" here is understood to mean a dimension that is large enough to maintain a constant voltage.

[0006] From the publication "Pre-ignition of rectifiers with intelligent power supply" Siemens AG, Prior Art Publishing GmbH, Manfred-von-Richthofen-Str. 9, 12101 Berlin, volume www.priorartregister.com, May 14, 2020, pages 1-14, XP007023195, a method for operating a rectifier is disclosed, in which an overlap region is formed by pre-ignition of the switches to be commutated in the generator operation and by timely disconnection of the switches to be commutated, which region has a quasi-natural commutation process similar to motor operation. As a result, the current growth rate of the line current can be reduced to the order of magnitude of motor operation.

[0007] A power conversion device is disclosed from EP 2 913 915 A1, to which a three-level power conversion circuit is adopted to generate three voltage levels, and the device can accurately compensate for a conduction voltage drop when a current flows through a semiconductor switching element or a flyback diode.

[0008] DE 27 46 940 A1 discloses a circuit arrangement for starting a statistical converter with forced commutation.

[0009] JP H09 163753 A describes a control voltage correction device for a power converter. The control voltage correction device is particularly useful if it is applied to inverter devices and chopper devices, which form devices with variable speed for induction motors and DC motors.

[0010] The applicant knows a method to deal with the above mentioned problem. In this case, the converter starts switching before the line voltage commutates, in order to reduce the current drop rate and thus reduce resonance in the grid due to high current velocities.

[0011] Although this approach is proven in principle, a suitable solution is still needed. Summary of the invention

[0012] It is therefore an object of the present invention to provide a method for operating a converter which allows optimized power generation operation.

[0013] This object is achieved by a method according to claim 1 .

[0014] A method for operating a grid-connected converter connected to a motor is disclosed, wherein in the generating operation of the converter, at least one power switch of the converter is switched at a firing angle α. zü This ignition angle is suitable for

[0015] α zü =180°-αab +α c_ab ,

[0016] Among them, α ab is the angle at which the line current drops to zero for the last time within half a cycle in motor operation of the converter, and where α c_ab is a constant angle, which is in particular between 0° and + / -2°, preferably between 0° and + / -1°, and wherein at least one power switch of the converter is at a shut-off angle The ignition angle is suitable for

[0017]

[0018] Among them, α an is the angle at which the line current ab The angle is at the last time it increases from zero in the motor operation of the inverter before falling to zero, and wherein α c_an is a constant angle which is in particular between 0° and + / - 2°, preferably between 0° and + / - 1°.

[0019] In other words, the invention is based on the recognition that in the generator operation, a shape can be obtained that is a mirror image of the current shape (in particular the waveform) in the motor operation. According to the invention, in the generator operation, one or more power switches are switched on and off at defined times (related to the motor operation). This is based on when the line current starts to increase or decrease in the motor operation. At the angle, the current drops to zero or the current increases from zero, and the angle is used to achieve an optimized, grid-friendly generator operation. These angles are reversed from the motor operation by subtracting them from 180°. This is also called mirroring half a cycle.

[0020] In an expedient manner, a constant (positive or negative) angle value is also added to improve the accuracy. In particular, since in motor operation there is a voltage drop via one or more diodes of the inverter, this does not apply to one or more power switches in generator operation. In a preferred embodiment of the method according to the invention, it is accordingly provided that the angle α c_ab is suitable for compensating for a voltage drop across at least one diode of the converter during motor operation of the converter, and / or an angle α c_an Suitable for compensating the voltage drop present via at least one diode of the inverter during motor operation of the inverter. Typically, the constant angle is small, having a value in the single digit range, in particular between 0° and + / -2°, preferably between 0° and + / -1°.

[0021] In a further preferred embodiment, α c_ab and α c_anIn other words, to obtain the (corresponding) ignition angle for switching on in generating operation, a constant value different (positive or negative) from the extinction angle for switching off is preferably added. In a particularly preferred embodiment, α c_ab has a negative sign and α c_an has a positive sign. In other words, α c_ab is subtracted and α c_an was added.

[0022] For α c_ab and α c_an The value of can be selected or determined depending on the structural embodiment of the converter and in particular the entire arrangement comprising the converter. It is conveniently applicable for constant correction angles, ie the correction angles are the same for all operating points, ie they do not change.

[0023] The angle value resulting from the reversal and advantageous addition of the constant angle is used according to the invention as the ignition angle or the extinction angle in the generating operation. The ignition angle or the extinction angle is to be understood as the angle at which one or more corresponding power switches are switched on or off. It is pointed out that in principle the term "pre-ignition angle" can also be used instead of the term "ignition angle", since the switching on occurs before the "ignition" (here the increase in current), and in a similar manner the name "pre-extinguishing angle" can also be used for the "extinguishing angle", since the switching off occurs before the "extinguishing" (here the current drops to zero). However, in the present application the short names "ignition angle" and "extinguishing angle" are used.

[0024] The electric machine can be, for example, a motor. Other examples of electric machines can be batteries, fuel cells or any DC power source or current source or another power electrical system, for example, another AC-DC (alternating current-direct current) converter or DC-DC (direct current-direct current) converter. It should be emphasized that this list is not exhaustive.

[0025] Furthermore, it should be noted that the angle usually corresponds to time, since the cycle length is known as the frequency. For example, in Germany, the frequency of the public power grid is 50 Hz, which corresponds to a cycle length of 20 milliseconds for 360°.

[0026] According to the invention, the (first) ignition angle for the generator operation is determined based on the angle at which the current curve drops to zero at the end in the motor operation (if a half period of 180° is considered).

[0027] It should be noted that, in particular in the continuous operation of the converter, the line current in the motor operation increases from zero in the usual manner exactly once within a half period of 180° and then drops to zero again exactly once. According to the mirror image of the invention, for the generating operation then there is exactly one firing angle and exactly one flameout angle, wherein the flameout angle corresponds to the angle of the mirror image which was increased at the beginning.

[0028] In contrast, in intermittent operation, in the usual manner not only one increase from zero and one decrease to zero occur, but at least two increases and at least two decreases occur.

[0029] Therefore, according to the invention, during intermittent operation of the converter, at least one power switch is switched at the firing angle α. zü After switching on and at the ignition off angle After disconnection, once again at the second ignition angle α zü2 and then at the second shut-off angle The second ignition angle α zü2 Applies to

[0030] α zü2 =180°-α ab2 +α c2_ab ,

[0031] Among them, α ab2 is the angle at which the line current in the motor operation of the converter is at an angle α an When it drops to zero for the last time before increasing from zero, and where α c2_ab is a constant angle, which is in particular between 0° and + / -2°, preferably between 0° and + / -1°, and wherein the second extinction angle Applies to

[0032]

[0033] Among them, α an2 is the angle at which the line current in the motor operation of the converter is at an angle α ab2 The last time it increases from zero before it drops to zero, and where α c2_an is a constant angle which is in particular between 0° and + / - 2°, preferably between 0° and + / - 1°.

[0034] Therefore, in intermittent operation, zü , α zü2 as well as Connect and disconnect at four angles.

[0035] In other words, further increases and further decreases in motor operation are also taken into account. Overall, in particular the last decrease to zero angle, the last increase from zero angle, the second-to-last decrease to zero angle and the second-to-last increase from zero angle in motor operation are taken into account and (in this order) for the first switch-on, the first switch-off, the second switch-on and the second switch-off in generator operation, each of which is reversed and conveniently supplemented with a constant angle value.

[0036] It should be noted that preferably α c2_ab and α c2_an can differ from one another, more precisely, can differ in value and / or with respect to their sign. c2_ab With α c_ab Preferably consistent and / or α c2_an With α c_an Preferably consistent. However, it cannot be excluded that α c2_ab With α c_ab Inconsistency and / or alpha c2_an With α c_an In a further particularly preferred embodiment, α c2_ab has a negative sign and α c2_an Has a positive sign.

[0037] In particular, in the transition region between continuous operation and intermittent operation, the current in the motor operation can even increase from zero more than twice and decrease to zero more than twice, in particular increase three times and decrease three times. In this case, depending on the first current increase and first current decrease (within half a cycle) in the motor operation, further, earlier current increases from zero or current decreases to zero (within half a cycle) in the motor operation can be ignored in the case of a triple increase and decrease. Therefore, in this case, only the angle of the last decrease to zero, the angle of the last increase from zero, the second-to-last decrease to zero and the second-to-last increase from zero in the motor operation can also be taken into account and (in this order) for the first connection, the first disconnection, the second connection and the second disconnection in the generator operation, i.e., each angle is inverted and corrected in a convenient manner by a constant correction angle value.

[0038] However, it cannot be excluded that further, earlier current increases from zero or current decreases to zero (within a half cycle) are taken into account during motor operation and that a different ignition angle α is determined for generator operation. züi and flameout angle (with i=3, 4, ...), and thus switched on and off with more than four ignition / extinguishing angles. In the case of triple increase and decrease, there is correspondingly a third ignition angle α zü3 and the third flameout angle Here, each can then proceed in a completely analogous manner to obtain a first ignition angle and a first extinction angle and a second ignition angle and a second extinction angle. The associated correction angle α ci_ab and α ci_an (with i=3, 4, . . . ) in particular also between 0° and + / -2°, preferably between 0° and + / -1°.

[0039] It is understood that the converter can be implemented as a multiphase converter with a plurality of power switches. Then, in a convenient manner, a power switch is switched at the firing angle α. zü At the ignition off angle and optionally at a second ignition angle α zü2 The ignition angle is switched on and the second ignition angle is switched on. and even possibly other flameout angles, and at least one further circuit breaker is switched on and off at the ignition angle and flameout angle shifted with respect to these angles by a predetermined shift value. By way of pure example, it should be provided that the converter is three-phase and comprises at least three circuit breakers. The first circuit breaker (first phase) can then be switched on and off at, for example, the ignition angle α. zü and flameout angle and optionally α zü2 and (and possibly even other firing and flameout angles) is switched on and off, the second power switch (second phase) can be switched on and off, for example, at the firing angle or the flameout angle, α zü -120° (or +240°) and (or +240°) and optionally α zü2 +120° (or +240°) and (or +240°), and the third power switch (third phase) can be turned on and off at the ignition angle or the flameout angle, α zü +240° (or -120°) and (or -120°) and optionally α zü2 +240° (or -120°) and (or -120°) and disconnected.

[0040] Angle α ab and α an and an optional angle α ab2 and α an2 , and possibly other ignition angles and extinction angles are determined in an expedient manner. In principle, a number of possibilities are provided for this.

[0041] It can be provided that the motor operation of the converter is simulated, in particular using a physical simulation model, and that the angle α is determined by means of the simulation, in particular from the simulation results. ab and αan , and optionally an angle α ab2 and α an2 Preferably, a simulation model is used which describes or represents the drive train, i.e. the converter and the connected electric machine, in particular the connected motor. In other words, in this embodiment, the simulation of the motor operation provides a definition for the angle of the generating operation. The simulation can output, for example, a current curve of the motor operation, from which the angle α can then be determined or inferred. ab , α an , and optionally an angle α ab2 and α an2 If a simulation is used, it also enables the possible introduction of a constant angle and the subsequent reversal, so that the firing angle and the flameout angle for generating operation are obtained as output. A corresponding simulation or analysis can be performed before commissioning and also for different grid parameters. Different grid parameters can be provided, in particular by standards that the converter must meet.

[0042] Alternatively or additionally, the angle α is determined based on measurements being recorded or already recorded during normal operation of the converter. ab and α an , and optionally an angle α ab2 and α an2 In other words, the converter can be operated (at least temporarily) in a conventional manner in order to detect the current curve during motor operation and based on this the ignition angle and the flameout angle can be determined for the generator operation according to the invention.

[0043] Other embodiments are also characterized in that the angle α ab and α an and an optional angle α ab2 and α an2 The determination is based on measurement data which are being recorded or have been recorded during commissioning of the converter when the converter is connected to the grid but the motor is not yet in operation. This is particularly the case if the grid-connected converter is operated in motor mode during commissioning and in generator mode the intermediate circuit is briefly charged without significantly reducing the intermediate circuit voltage.

[0044] The method of the invention can be used for any type of converter, also for existing, conventional converters. For example, the ignition angle and the extinction angle obtained according to the invention can be set in existing, conventional converters, for example, after these angles have been obtained by carrying out suitable simulations. Purely by way of example, it is provided that the determined ignition angle and the extinction angle are entered into the software of an existing converter, possibly also into the software of a conventional converter.

[0045] The subject of the invention is a converter comprising:

[0046] - processor, and

[0047] A data storage device on which a computer-executable program code is stored, which, when executed by a processor, causes the processor to perform the steps of the method according to the invention.

[0048] A correspondingly configured converter is suitable for carrying out the method according to the invention.

[0049] The converter according to the invention or the converter operated in the manner according to the invention expediently comprises a line choke and an intermediate circuit.

[0050] The subject of the invention is a computer program comprising program code means which, when executed on at least one computer, cause the at least one computer to execute the steps of the method of the invention.

[0051] The invention also relates to a computer-readable medium comprising instructions which, when executed on at least one computer, cause the at least one computer to execute the steps of the method according to the invention.

[0052] The computer readable medium can be, for example, a CD-ROM or a DVD or a USB or a flash memory. It should be noted that the computer readable medium should be understood not only as a physical medium, but also as a medium that exists in the form of a data stream and / or a signal representing a data stream. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Further features and advantages of the present invention will be clearly shown by the following description of embodiments according to the present invention in conjunction with the accompanying drawings. In the accompanying drawings:

[0054] Figure 1 A purely schematic diagram showing a grid-connected converter connected to a motor,

[0055] Figure 2 Shown from Figure 1 Especially the voltage and current diagram of the inverter motor when running,

[0056] Figure 3 Shown from Figure 1 The diagram of the voltage and current of the converter in the power generation operation is shown in FIG.

[0057] Figure 4 Shown from Figure 1 The harmonic spectrum of the converter line current,

[0058] Figure 5shows a diagram showing, in particular, voltages and currents for motor operation and generator operation of a converter after carrying out an exemplary embodiment of the method according to the invention (below rated current, continuous operation),

[0059] Figure 6 Graph showing, in particular, voltage and current for motor operation and generator operation of a converter after carrying out an exemplary embodiment of the method according to the invention (below rated current, continuous operation)

[0060] Figure 7 Graphs showing, in particular, voltages and currents for motor operation and generator operation of a converter after carrying out an embodiment of the method according to the invention (below rated current, intermittent operation), and

[0061] Figure 8 The diagram shows, in particular, voltage and current for motor operation and generator operation of a converter (below rated current, intermittent operation) after carrying out an exemplary embodiment of the method according to the invention. DETAILED DESCRIPTION

[0062] Figure 1 A purely schematic illustration shows a converter 1 which is connected to a public grid 2 and an electrical machine 3 in the form of a motor. In the example shown here, the motor 3 for its part includes the converter, which is not shown in the highly simplified diagram. Figure 1 Shown in.

[0063] As an alternative to the motor 3 , the electric machine can also be, for example, a battery, a fuel cell or any other DC power source or current source or another power electrical system, for example, another AC-DC converter or a DC-DC converter.

[0064] The converter 1 is multiphase and has a plurality of power switches 4. In addition, the converter has a line choke 5 and an intermediate circuit 6. The line choke 5 serves in particular to suppress harmonics. The line choke limits the increase in current and can thus achieve less interference in the line current. It should be noted that in the highly simplified Figure 1 In the embodiment, the internal wiring of the converter 1 and the multi-phase connection to the public grid 2 are not shown. In addition, it should be noted that, except for Figure 1 In addition to the three power switches 4 shown in the figure, the three-phase converter 1 can also have or have three further power switches 4, which are operated or switched alternately (in other words negatively) with the three power switches 4 shown in the figure. Each pair of two negatively operated power switches 4 forms a half bridge in a known manner. The three further power switches 4 are not additionally provided in the circuit for reasons of clarity. Figure 1 Shown in.

[0065] The converter 1 can be, for example, a Siemens converter RGD (Regenerative Drive) or SLM (Smart Mode), wherein this is to be understood purely as an example.

[0066] DIN EN 61000-3-12:2011 provides limits for THC (total harmonic current) and PWHC (partial harmonic current), which the converter 1 meets in motor operation, but not in generator operation. In motor operation, the current flows from the grid 2 through the converter 1 to the motor 3, and in generator operation, it flows in the opposite direction, i.e. from the motor 3 through the converter 1 to the grid 2.

[0067] In generating operation, the current has a square shape because the switching pattern of the converter 1 is synchronized with the line voltage.

[0068] exist Figure 2 The operation of the inverter 1 in motor mode is shown in Figure 3 The operation of the converter in generating mode is shown in FIG.

[0069] The variables represented in the figures by angles in degrees and listed in the relevant legends are as follows:

[0070] u a Line voltage in phase a

[0071] u c Line voltage in phase c

[0072] i a Line current in phase a

[0073] i a1 Fundamental wave of current in phase a

[0074] i a5 The fifth harmonic of the current in phase a

[0075] V DC Intermediate circuit voltage

[0076] Data 1 Line marking zero point

[0077] Data 2 is a line marking the angle between the line voltage and the 5th harmonic of the line current on phase a.

[0078] Control signal for gate 1 power switch 4.

[0079] The following table compares THC and PWHC for the calculation of the motor operation with the limit values ​​according to DIN EN 61000-3-12 by way of example:

[0080]

[0081] It can be seen that the requirements of DIN EN 61000-3-12 for THC and PWHC are met for motor operation.

[0082] exist Figure 3 It can be seen that in the power generation operation, the current shape (i a ) is square and contains a high di(t) / dt(di a (t) / dt).

[0083] The following table compares THC and PWHC for the calculation of the motor operation with the limit values ​​according to DIN EN 61000-3-12 by way of example:

[0084]

[0085] It can be seen that the extreme value of 46% for PWHC is exceeded at 59.4%.

[0086] Figure 4 The relevant harmonic spectrum is shown, wherein the extreme values ​​according to DIN EN 61000-3-12 are also plotted. In the legend, H stands for harmonics and G stands for the corresponding extreme values ​​according to this standard.

[0087] The above-mentioned problem of exceeding the PWHC limit value during the power generation operation of the converter 1 can be solved by, during the power generation operation of the converter 1, at least one power switch 4 of the converter 1, in the present application, Figure 4 The left power switch 4 in the ignition angle α zü is switched on, this ignition angle is suitable for

[0088] α zü =180°-α ab +α c_ab ,

[0089] Among them, α ab is the angle at which the line current drops to zero for the last time within a half cycle in motor operation of the converter 1, and wherein α c_ab is a constant angle, which is preferably between 0° and 1°, and wherein the power switch 4 of the converter 1 is at the ignition angle The ignition angle is suitable for

[0090]

[0091] Among them, α an is the angle at which the line current flows at angle α abBefore falling to zero at α, it increases from zero for the last time in the motor operation of the inverter 1, and wherein α c_an is a constant angle, which is preferably between 0° and 1°.

[0092] This situation Figure 5 These diagrams show the line current i, especially for the case of motor operation. mot The curve and the line current i for the power generation operation gen The curve is realized by correspondingly switching the switch of the left power switch 4 of the converter 1. In the diagram, the signal in pu (abbreviated S) is each plotted over an angle in degrees (abbreviated A).

[0093] exist Figure 5 In the figure, we draw the angle α ab , α an , α zü as well as Here the constant angle is

[0094] α c_ab =-0.13° and

[0095] α c_an =0.08°.

[0096] They are added to increase the accuracy. Because in motor operation there is a voltage drop across one or more diodes of the converter 1, which does not apply to the power switch 4 in generator operation. c_ab If a value is negative, the value is deducted, that is, subtracted.

[0097] from Figure 5 It can be seen that, in the example shown, the line current i mot During motor operation, it drops to zero at the following angles:

[0098] α ab =157.29°

[0099] The line current also increases to zero at the following angles:

[0100] α an =34.26°

[0101] With two constant angles α c_ab and α c_an Together we get:

[0102] α zü =180°-α ab +α c_ab =180°-157.29°-0.13°=22.58°

[0103]

[0104] Figure 6 shows a completely similar Figure 5 , for the case of motor operation, the line current i mot The curve and the line current i for the power generation operation ge The curve here is the rated current, i.e. 100%.

[0105] The ignition angle and the flameout angle suitable for the generator operation are hereby used as the angle α for the motor mode. ab and α an Function:

[0106] α zü =180°-α ab +α c_ab =180°-165.21°-0.13°=14.66°

[0107]

[0108] When the rated current falls below a certain ratio, the converter 1 switches from continuous operation to intermittent operation. In intermittent operation, in the usual manner, not only does the primary current increase from zero and the primary current decrease to zero occur (see Figure 5 and Figure 6 And the angle α ab and α an together with the corresponding current increase / current decrease), and at least two increases and at least two decreases occur (see Figure 7 and the angle α ab and α an and α ab2 and α an2 together with the corresponding current increase / current decrease).

[0109] In intermittent operation of the converter 1, therefore, at the firing angle α zü At the ignition off angle After the power switch 4 is disconnected at the second ignition angle α zü2 Switch it on again and then also at the second shut-off angle The following applies to the second ignition angle:

[0110] α zü2 =180°-α ab2 +α c2_ab ,

[0111] Among them, α ab2 is the angle at which the line current in the motor operation of the converter is at an angle αan The last time it drops to zero before increasing from zero, and where α c2_ab is a constant angle, which is preferably between 0° and + / - 1°.

[0112] Then, in addition, for the second shut-off angle:

[0113]

[0114] Among them, α an2 is the angle at which the line current in the motor operation of the converter is at an angle α ab2 Before it drops to zero, it increases from zero for the last time, and α c2_an is a constant angle, which is preferably between 0° and + / - 1°.

[0115] In other words, in intermittent operation, preferably at α zü , α zü2 and Connect and disconnect at four angles.

[0116] exist Figure 7 and Figure 8 An example of intermittent operation is shown in FIG.

[0117] For constant angles:

[0118] α c_ab =-0.13

[0119] α c_an =+0.08

[0120] α c2_ab =-0.13

[0121] α c2_an =+0.08

[0122] It can be seen that α c_ab and α c2_ab and α c_an and α c2_an Consistent.

[0123] For Figure 7 The ignition angle and extinction angle in apply:

[0124] α zü =180°-α ab +α c_ab =180°-135.93°-0.13°=43.94

[0125]

[0126] α zü2 =180°-α ab2 +α c2_ab =180°-75.92°-0.13°=103.95°

[0127] For Figure 8 The ignition angle and extinction angle in apply:

[0128] α zü =180°-α ab +α c_ab =180°-157.02°-0.13°=22.85°

[0129]

[0130] α zü2 =180°-α ab2 +α c2_ab =180°-99.72°-0.13°=80.15°

[0131]

[0132] It should be noted that, firstly, in the transition region between continuous operation and intermittent operation, the current can also increase from zero more than twice and can drop to zero more than twice, in particular increase three times and drop three times (see Figure 8 and the angle α ab and α an and α ab2 and α an2 and α ab3 and α an3 In this case, the first current increases (at angle α an3 ) and the first current drop (at angle α ab3 ) can be neglected in the half cycle during motor operation. However, this is not mandatory. For the first increase from zero and the first subsequent decrease to zero, corresponding mirrored ignition angles and extinction angles for generating operation can also be determined and corrected by a constant correction angle, wherein then a completely analogous first ignition angle and a first extinction angle as well as a second ignition angle and a second extinction angle α can occur as described above. zü , α zü2 , In other words, the third ignition angle and the third extinction angle can be determined as: α zü3 =180°-α ab3 +α c3_ab and Constant correction angle α c3_abPreferably with α c_ab and α c2_ab Consistent and constant correction angle α c3_an Preferably with α c_an and α c2_an In principle, for any other feasible ignition angle and extinction angle (α züi and Where i=4, 5, ...), can occur similarly.

[0133] Determined ignition angle and extinction angle α zü and and optionally α zü2 and (and possibly other ignition and flameout angles) can then be input, for example, into the software of an existing, possibly also conventional, converter 1 in order to operate the converter accordingly.

[0134] As people in Figures 5 to 8 As can be seen in FIG. 1 , due to the mirroring of one or more current increase angles and one or more current decrease angles in motor operation and the above-described corresponding switching on and off of the power switch 4 in generator operation, a shape that mirrors the shape (in particular the waveform) of the current in motor operation is obtained. Since the requirements for THC and PWHC are observed in motor operation, the same applies to generator operation with the current curve that is now mirrored.

[0135] It should be emphasized that the other power switches 4 of the multiphase converter, i.e. Figure 1 The center and right power switch 4 in the embodiment are conveniently switched on and off in a phase-shifted manner with respect to the left power switch 4. The ignition angle and the ignition angle α of the center power switch 4 are particularly suitable. zü , α zü2 , This corresponds to the angle -120° (or +240°) calculated above. Figure 1 The right power switches 4 in FIG. 4 are each conveniently reduced by 240° (or +120°). This principle is sufficiently known from the prior art.

[0136] From Figures 5 to 8 The current curve i of the motor operation of the inverter 1 shown in mot The angle α is obtained from ab , α an , α ab2 and α an2, which is described here in an example by simulating the motor operation of the converter 1. In this case, a simulation model is used, which describes or represents the drive train, i.e. the converter and the connected motor, the connected motor, in particular the connected motor. Such a simulation model preferably consists of a plurality of sub-models, which are Figure 1 In the example of , in particular, it consists of the following sub-models: grid model, grid filter model, grid-converter model, intermediate circuit model, motor-converter model and motor model. The characteristics of the model depend on the device and can then be simulated to obtain the angle.

[0137] Alternatively or additionally, data obtained by measurement technology can also be used for the simulation. For example, the converter 1 can first be operated in a conventional manner for at least a period of time, i.e. without switching the power switches on and off in the manner described above, so that a mirrored motor current curve is obtained in the generating mode. The angle α can then be read or determined from the measurement data. ab , α an , α ab2 and α an2 And mirror it.

[0138] It is also possible to use measurement results which are being recorded or have been recorded during commissioning of the converter 1, when the converter is connected to the grid 2, but the motor 3 is not yet in operation. This is in particular if the grid converter 1 is operated in motor operation during commissioning and briefly in generating operation to charge the DC link without significantly discharging the DC link voltage.

[0139] The above steps can be performed by software and using suitable hardware. The hardware conveniently includes a processor and a data storage device and can be an integral part of the inverter 1. However, it can also be hardware separate from the inverter 1. If simulation is used to obtain the current curve i of the motor operation mot , the simulation can also be performed through software.

[0140] Although the present invention has been further illustrated and described in detail through preferred embodiments, the present disclosure is not limited to the disclosed examples and those skilled in the art can derive other variations therefrom without departing from the scope of protection of the present invention.

Claims

1. A method for operating a grid-connected converter (1) connected to a motor (3), in which method: In generating operation of the converter (1), at least one power switch (4) of the converter (1) is switched at a firing angle α. zü For the ignition angle α zü =180°-α ab +α c_ab , in, α ab is the angle at which the line current (i mot ) drops to zero for the last time within half a period, and α c_ab is a constant angle, α c_ab In particular, between 0° and + / -2°, preferably between 0° and + / -1°, and wherein at least one of the power switches (4) of the converter (1) is switched at a flameout angle The ignition cut-off angle is applicable to Among them, α an is the angle at which the line current (i mot )When at angle α ab The last time it increases from zero before it drops to zero, and where α c_an is a constant angle, α c_an In particular between 0° and + / - 2°, preferably between 0° and + / - 1°, And among them, In the intermittent operation of the inverter (1), at least one of the power switches (4) is switched on at the ignition angle α. zü At the ignition angle After disconnection at the second ignition angle α zü2 At the second ignition angle is disconnected again, wherein for the second ignition angle α zü2 Applies to α zü2 ＝180°-α ab2 +α c2_ab ， Among them, α ab2 is the angle at which the line current (i mot )When at angle α an The last time it drops to zero before increasing from zero, and where α c2_ab is a constant angle, α c2_ab In particular between 0° and + / - 2°, preferably between 0° and + / - 1°, And wherein, for the second ignition angle Applies to Among them, α an2 is the angle at which the line current (i mot )When at angle α ab2 The last time it increases from zero before it drops to zero, and where α c2_an is a constant angle, α c2_an In particular, between 0° and + / - 2°, preferably between 0° and + / - 1°.

2. The method according to claim 1, characterized in that: Angle α c_ab Suitable for compensating the voltage drop across at least one diode of the converter (1) during motor operation of the converter (1), and / or the angle α c_an Suitable for compensating a voltage drop existing across at least one diode of the inverter (1) during motor operation of the inverter (1).

3. The method according to claim 1 or 2, characterized in that: α c_ab and α c_an In numerical terms and / or for α c_ab and α c_an The signs are different from each other.

4. The method according to any one of the preceding claims, characterized in that α c2_ab and α c2_an In numerical terms and / or for α c_ab and α c_an have different signs from each other, and / or α c2_ab With α c_ab Consistent and α c2_an With α c_an Consistent.

5. The method according to any one of the preceding claims, characterized in that The converter (1) is implemented as a multiphase converter (1) having a plurality of power switches (4), and a power switch (4) is ignited at an ignition angle α. zü is switched on at the ignition off angle is disconnected at the second ignition angle α zü2 is switched on at the second ignition angle The at least one power switch (4) is switched on and off at an ignition angle and an extinction angle shifted by a predetermined displacement value relative to the ignition angle and the extinction angle.

6. The method according to any one of the preceding claims, characterized in that Determine the angle α ab and α an and optionally determine the angle α ab2 and α an2 .

7. The method according to claim 6, characterized in that In particular, using a physical simulation model, the motor operation of the converter (1) is simulated and, in particular based on the simulation results, the angle α is determined by means of the simulation. ab and α an and optionally determine the angle α ab2 and α an2 .

8. The method according to claim 6 or 7, characterized in that: The angle α is determined based on measurements that are being recorded or have been recorded during normal operation of the converter (1). ab and α an and optionally determine the angle α ab2 and α an2 .

9. The method according to any one of claims 6 to 8, characterized in that When the converter is connected to the grid (2) but the electrical machine (3) is not yet running, the angle α is determined based on measurements that are being recorded or have been recorded during commissioning of the converter (1). ab and α an and optionally determine the angle α ab2 and α an2 .

10. A converter (1), comprising: - processor, and A data storage device having a computer-executable program code stored thereon, which, when executed by the processor, causes the processor to carry out the steps of the method according to any one of claims 1 to 9.

11. A computer program comprising instructions which, when executed on at least one computer, cause at least one computer to carry out the steps of the method according to any one of claims 1 to 9.

12. A computer-readable medium comprising instructions which, when executed on at least one computer, cause at least one computer to implement the steps of the method according to any one of claims 1 to 9.

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