Method for operating a drive unit and drive unit

Abstract

The invention relates to a method for operating a drive unit (1000) comprising an electric machine (1) and a power converter arrangement (100) for supplying the electric machine with electrical power. The power converter arrangement comprises a first DC voltage terminal (101) and a second DC voltage terminal (102) and at least two half-bridges (110, 120, 130). In each half-bridge, a first and a second semiconductor switch (111, 121, 131, 112, 122, 132) are arranged between the first or second DC voltage terminal (101) and a center terminal (113, 123, 133) of the half-bridge (110, 120, 130). Furthermore, at least two half-bridges include a current sensor (114, 124) which is configured to measure the current strength of a current flowing through the center terminal (113, 123, 133).The procedure determines whether the drive unit (1000) is in a steady state. Subsequently, in a first time interval, the current flowing through the center terminal (113, 123, 133) is measured by each current sensor (114, 124) of the at least two half-bridges (110, 120, 130). The process also determines the field-oriented voltage applied to the phase windings (U, V, W) of the stator, the field-oriented currents flowing through the phase windings (U, V, W) of the stator, and the rotor position angle. A correction factor is then determined for each current sensor based on the measured current, field-oriented voltage, and field-oriented current profiles, as well as the rotor position angle. The drive unit is then operated using these determined correction factors.

Description

[0001] The present invention relates to a method for operating a drive unit and a drive unit with a computing unit and a computer program for carrying out the method. Background of the invention

[0002] In electrical machines, for example, three-phase AC machines, especially permanent magnet synchronous machines, with phases U, V, W, the three-phase stator current can be measured in a power converter (so-called inverter) that supplies the electrical machine with power and regulated to setpoint values ​​by appropriately controlling the power converter. For this purpose, the power converter can have a half-bridge for each phase winding of the electrical machine, in which a first and second semiconductor switch are each arranged between one of the two DC terminals and a center terminal of the half-bridge. The current measurement can be performed by a shunt resistor, which is arranged, for example, between one of the semiconductor switches of the half-bridge and the DC link bus, i.e., one of the DC terminals of the power converter, or the phase winding.If this (hereinafter referred to as the first) semiconductor switch of the corresponding half-bridge is conducting, a corresponding phase current flows through the measuring shunt, and a voltage proportional to the current drops across it. This voltage can be fed via an analog input path with appropriate amplifier stages to the input of an analog-to-digital converter (ADC). A digital current signal can be output from this ADC, which is processed in the control software, for example, in a processing unit of the drive unit. In a three-phase machine, measuring the currents of two phases (e.g., U and V) is sufficient, and the third can be calculated from these measurements.

[0003] In conventional control of the power converter arrangement with pulse width modulation, during each pulse period at least a first semiconductor switch is switched to conducting and the second semiconductor switch of the same half-bridge is switched to blocking, so that at least one time interval is available for current measurement per pulse period.

[0004] Ideally, the digital signals iU,V,W* the real flows i U,V,Wwith a uniform transfer factor (for clarity, in this disclosure, measured quantities are written with * and real quantities without *). However, due to tolerances in the measuring resistor, the analog amplifier, and the A / D converter, the transfer factors up to the digital current signal exhibit a significant tolerance in reality. Furthermore, the measured signals can exhibit offsets, i.e., constant shifts from zero, compared to the actual current waveform. These offsets can be detected by recording the measured signal at a time when no current flows through the shunt resistor, e.g., when the second semiconductor switch of the corresponding branch is conducting and the first semiconductor switch is off.

[0005] If the transfer factors for the half-bridges or phase windings deviate uniformly from their common target value, the output variables of the A / D converters will each exhibit a percentage deviation from the actual currents, but the qualitative current waveforms and the qualitative shape of the current phasor in the three-phase space vector diagram will remain unchanged. However, if the transfer factors of the branches have different values, the measured space vector locus will be distorted compared to the circular shape found in symmetrical three-phase systems. As a result, the field-oriented measured variables i d (so-called longitudinal flow) and i q (so-called cross-flow) in the rotor-oriented d / q coordinate system also exhibits an alternating component and a stationary deviation from its actual value in the steady state, and the determination of the rotor position angle based on the erroneous measured quantities leads to a deviation from the real rotor position angle.

[0006] The current controller attempts to eliminate the non-existent alternating components, thereby causing current and torque pulsations in the electric machine, as it tries to suppress harmonic signals by superimposing opposing current oscillations. While steady-state deviations in the cross-current are compensated for by adjusting the cross-current setpoint in the speed controller, a steady-state deviation of the longitudinal current from its setpoint remains and alters the magnetization state of the machine compared to the desired state.

[0007] With equal current in all three phase windings, the locus of the current phasor in the three-phase space phasor diagram is a circle with a radius corresponding to the current. However, if the currents differ (for example, the current in one phase is increased by 5%, and the current in another phase is decreased by 5%), the locus of the current phasor diagram becomes an ellipse with significant eccentricity instead of a circle.

[0008] A longitudinal axis d (magnetization axis) of an electrical machine operated in this way lies on axis U or a of the space vector diagram at the beginning of the fundamental oscillation period and then rotates once through 360° in the mathematically positive direction during one fundamental oscillation period. The normalized field-oriented currents i should be d , i q Values ​​of i d = 0 and i qAssume = 1. However, due to the correction by the control system, the measured signals of the field-oriented currents exhibit AC components with twice the stator angular frequency ω. S on, whose mean value, depending on a possible offset error, corresponds to the normalized target values. Here, ω S = 2πf s with the stator fundamental frequency fs of the alternating current or three-phase system with which the drive unit is currently being supplied.

[0009] The deviations of the measured values id*,iq* of the real values ​​i d , i q In the control loop for the stator currents, disturbances act as disturbances that couple in at the level of the controlled variables and are compensated for by the stator current controller according to its disturbance transfer function. Any reaction of the longitudinal and transverse voltage setpoints u d,soll , u q,sollHowever, in reality, these disturbances lead to unwanted current components, which, from the controller's perspective, appear necessary to at least partially compensate for the errors in the measured values. From the perspective of the overall system, it would be advantageous in this respect to tune the stator current controller so slowly that it reacts to the AC components in the measurement signals. id*,iq* i d , practically unaffected. However, this leads to low robustness against genuine disturbances and a very slow response to setpoint changes, and is therefore impractical. Furthermore, any deviation of the DC component in the measured value from its setpoint is always compensated for, resulting in a deviation of the actual DC component from its setpoint. This can cause problems, especially with respect to the longitudinal axis d, when operating in the field weakening range.

[0010] Furthermore, the erroneous measurements id*,iq* These errors also affect the machine model used to simulate the rotor position angle, leading to deviations between the simulated and the actual rotor position angle. For example, the current measurement error also results in an angular error in the position of the modeled field-oriented coordinate system relative to the actual field axes of the electric machine. Such an error can further impact the current measurement if the so-called signal injection method is used to determine the rotor position at standstill. Disclosure of the invention

[0011] According to the invention, a method for operating a power converter arrangement, a power converter arrangement itself, a computing unit, and a computer program for carrying out the method, comprising the features of the independent claims, are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0012] The invention relates to a drive unit comprising an electric machine having a stator with a plurality of phase windings and a rotor, and a power converter arrangement for supplying the electric machine with electrical power. The power converter arrangement has a first DC voltage terminal and a second DC voltage terminal, which are configured to be connected to a DC voltage source. Furthermore, the power converter arrangement has at least two half-bridges, each half-bridge having a first semiconductor switch arranged between the first DC voltage terminal and a center terminal, and a second semiconductor switch arranged between the second DC voltage terminal and the center terminal. At least two half-bridges of the power converter arrangement also have a current sensor.The current sensor can, for example, incorporate a shunt resistor and a voltmeter, or be based on a magnetic measurement, such as the Hall effect. The current sensor is designed to measure the current flowing through the center terminal.

[0013] For example, all three half-bridges of a converter arrangement for a three-phase electric machine can have a current sensor. However, it is also conceivable that a current sensor is only installed in two half-bridges, since the sum of the phase currents must always be zero and the third phase current can therefore be calculated from the other two phase currents.

[0014] As described in the introduction, deviations in the measured current values ​​cause the controller of the power converter to attempt to compensate for these deviations. However, if these deviations originate solely from the measurement, no actual current deviations exist, and the compensation by the controller leads to a deterioration in the control of the electric machine.

[0015] Furthermore, a differing current intensity leads to problems in determining the rotor angle.

[0016] In the invention, a correction factor is determined for each current sensor, which compensates for the deviation due to the transmission.

[0017] The invention can be easily integrated into an existing controller concept and requires no design effort.

[0018] The procedure determines whether the drive unit is in a steady state. If a steady state is determined, the procedure records, over a first time interval, the current through each current sensor of the at least two half-bridges, the field-oriented voltages applied to the phase windings of the stator of the electric machine, the field-oriented currents flowing through the phase windings of the stator of the electric machine, and the rotor position angle. This first time interval has, in particular, a length of at least one period of 1 / f. s the stator fundamental frequency f sis covered. Subsequently, a correction factor is determined for each current sensor depending on the recorded current profiles, the recorded field-oriented voltage profiles, the recorded field-oriented current profiles, and the rotor position angle. The drive unit is then operated using these determined correction factors. For the purposes of this disclosure, field-oriented quantities are understood to be those in the rotor-fixed d / q coordinate system.

[0019] This allows the measured currents to be corrected, thus eliminating the aforementioned problems and enabling the electric machine to be operated more efficiently.

[0020] In one embodiment, when determining whether a steady state of the drive unit exists, it is determined that a steady state of the drive unit exists if, in a second time interval that precedes, and in particular directly precedes, the first time interval, one or more of the following conditions are met. A steady state exists if the fluctuation range of the rotor speed n is below a speed threshold value n. Schwell lies and / or a slope dn / dt of a regression line of the rotor speed over the second time interval lies in a rotor speed slope interval defined by a first rotor speed slope threshold (dn / dt) Schwell,1 upwards and a second rotor speed gradient threshold (dn / dt) Schwell,2 is bounded downwards, with the second rotor speed gradient threshold corresponding in particular to the negative of the first rotor speed gradient threshold, i.e. (dn / dt)Schwell,2 = -(dn / dt) Schwell,1 A steady state also exists if, in the second time interval, the fluctuation range of a given torque setpoint of the electric machine remains below a torque threshold value ΔM. Schwell lies and / or a fluctuation range of at least one, in particular each, field-oriented current setpoint below a current threshold value Δi d,soll,Schwell , Δi q,soll,Schwell lies, where in particular the current threshold is the same for each field-oriented current setpoint, i.e. Δi d,soll,Schwell = Δi q,soll,Schwell The range of variation of a quantity can be calculated as the difference between the minimum value and the maximum value in the second time interval.

[0021] This ensures, simply and with minimal computational effort, that the drive unit operates at a constant level at the start of the correction factor determination. Such constant operation is necessary for the procedure to work, as significant changes in the measured operating parameters (voltages and currents) can lead to deviating or incorrect correction factors.

[0022] In one embodiment, operating the drive unit includes determining whether a steady state existed during the first time interval and, if it is determined that a steady state did not exist during the first time interval, discarding the determined correction factors. A steady state of the drive unit is determined if one or more of the aforementioned conditions are met during the first time interval. These conditions are the same ones used to determine the steady state at the beginning of the process. If it is determined that a steady state of the drive unit did not exist, the drive unit is operated with correction factors determined at an earlier time or without the use of correction factors, and the process is repeated at a later time.

[0023] This in turn ensures, in a simple way and with minimal computational effort, that the drive unit was operating at a steady state during the determination of the correction factor(s), so that the correction factors could be determined correctly.

[0024] In one embodiment, determining the correction factor includes determining, for each field-oriented coordinate d, q, a magnitude and a phase angle of a first current alternating component. id,harm*,iq,harm* for each course of the field-oriented flows id*,iq* and an alternating voltage component ud,harm*,uq,harm* for each course of the field-oriented stresses u d , u q depending on a given angular frequency, where the given angular frequency is in particular twice the stator angular frequency ω SThis corresponds to the alternating components. The alternating components can be expressed as complex quantities, since this allows both the magnitude and the phase to be combined into a single quantity. Subsequently, the determined alternating voltage components are calculated for each field-oriented coordinate d, q. ud,harm*,uq,harm* into a second alternating current component i d,harm , i q,harm converted. For this, an impedance matrix can be used, for example. This can be represented as an equation, for instance, as follows: [id,harm,iq,harm]=[ud,harm∗,uq,harm∗]⋅Zharm−1 with Zharm=[RS+2⋅j⋅ωS⋅Ld,diffωSLd−ωsLqRS+2⋅j⋅ωS⋅Lq,diff] with resistor R S the stator winding, the stator angular frequency ω S , the differential longitudinal inductance L d,diff in the present working point, which is caused by dΨ d / di d is determined by the differential transverse inductance L q,diffin the present working point, which is caused by dΨ q / di q is determined by the integral

[0025] Longitudinal inductance L d , which are caused by (Ψ g - Ψ d0 )i d is determined, and the integral transverse inductance L q , which are caused by (Ψ q - Ψ q0 ) / i q is determined.

[0026] Here, Ψ denotes d0 and Ψ q0 the magnetic flux linkage caused by the rotor flux or the permanent magnets in the rotor, i.e. the flux linkage at i d = 0 or i q = 0.

[0027] For each field-oriented coordinate d, q, a deviation between the determined first current alternating components is then calculated. id,harm*,iq,harm* and the specific second current-cycle components i d,harm , i q,harm certain, i.e. Δid,harm=id,harm−id,harm∗ Δiq,harm=iq,harm−iq,harm∗

[0028] The method shown here for converting voltages into currents is merely an example. Similarly, the harmonic first current components could be converted into second voltage components: [ud,harm∗,uq,harm∗]=[id,harm∗,iq,harm∗]⋅Zharm with the same inductance matrix Z harm .

[0029] Subsequently, a deviation between the voltage components and the second voltage components is determined: Δud,harm=ud,harm−ud,harm∗ Δuq,harm=uq,harm−uq,harm∗

[0030] The voltage deviations determined in this way can then be converted into current deviations using the inductance matrix: [Δid,harm,Δiq,harm]=[Δud,harm,Δuq,harm]⋅Zharm−1

[0031] The determined field-oriented current deviations are then converted into stator-oriented deviations Δi U,harm , Δi V,harmThe conversion is performed for at least two phase windings of the electrical machine. The conversion of quantities from the field-oriented coordinate system to a stator-oriented system, e.g., a three-phase system, is well-known and will not be explained further here.

[0032] Furthermore, an amplitude is l^ U*, l^ V* The current waveforms measured by the current sensors are determined. Subsequently, the determined amplitudes are calculated. l^ U*, l^ V* using the specified deviations Δi U,harm , Δi V‚harm The correction is applied to at least the two phase windings. In particular, the correction is additive, i.e., it is additive. l^ U,corr*,l^ U*+ΔiU,harm l^ V,corr*=l^ V*+ΔiV,harm

[0033] From this, a correction factor k is derived for each current sensor. U , k V depending on the corrected amplitude l^ U,corr*,l^ V,corr* The correction factor for each current sensor is determined as the quotient of the corrected amplitude. l^ U,corr*,l^ V,corr* and the amplitude l^ U*, l^ V*, which was determined for each of the current waveforms measured by the current sensors, i.e. kU=l^ U,corr*l^ U* kV=l^ V,corr*l^ V*

[0034] In the following section, the correction factor k will then be used. U multiplicatively on the measured value for the current iU*(t) applied and the correction factor k V multiplicatively on the measured value for the current iV*(t) applied.

[0035] The form of the correction factors given in equations (7.1) and (7.2) is only an example, and the correction factors can also take a different form. The only condition is that the correction factors satisfy the following relationship: kUkV=l^ U,corr*⋅l^ V*l^ U*⋅l^ V,corr*

[0036] This allows the correction factors to be determined easily and with minimal computational effort, and the aforementioned advantages to be achieved particularly efficiently. Since the sum of all currents in the stator is zero, the third current does not need to be corrected but can be calculated from the other two.

[0037] The invention further relates to a drive unit as described above. The drive unit further comprises a computing unit configured to perform all process steps of a method according to the invention. The computing unit, e.g., a control unit of a drive system, is configured, particularly in terms of programming, to perform the method according to the invention.

[0038] Implementing a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, as this incurs particularly low costs, especially if an executing control unit is already available for other tasks. Finally, a machine-readable storage medium is provided with a computer program stored on it as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical, and electrical storage media, such as hard drives, flash memory, EEPROMs, DVDs, etc. Downloading a program via computer networks (Internet, intranet, etc.) is also possible. Such a download can be wired or wireless (e.g., via a WLAN network, a 3G, 4G, 5G, or 6G connection, etc.).

[0039] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0040] The invention is schematically illustrated in the drawing using exemplary embodiments and is described below with reference to the drawing. Brief description of the drawings Fig. Figure 1 shows a block diagram of a drive unit according to an embodiment of the invention, and Fig. Figure 2 shows a flowchart of a process according to an embodiment of the invention. Detailed description

[0041] Fig. Figure 1 shows a block diagram of a drive unit 1000 according to an embodiment of the invention.

[0042] The drive unit 1000 comprises an electric machine 1 and a converter assembly 100, which is configured to supply the electric machine 1 with electrical power. The electric machine 1 in the example shown is a three-phase electric machine and has a rotor and a stator with three phase windings U, V, W. Each of the three phase windings is supplied with electrical power by a half-bridge 110, 120, 130 of the converter assembly 100.

[0043] Each half-bridge 110, 120, 130 of the converter arrangement has a first semiconductor switch 111, 121, 131, which is arranged between the first DC voltage terminal 101 and a center terminal 113, 123, 133 of the respective half-bridge 110, 120, 130. Furthermore, each half-bridge 110, 120, 130 has a second semiconductor switch 112, 122, 132, which is arranged between the second DC voltage terminal 102 and the center terminal 113, 123, 133 of the respective half-bridge 110, 120, 130.

[0044] The converter arrangement 100 has a first and a second DC voltage terminal 101, 102, which are configured to be connected to a DC voltage source, for example, a battery of a vehicle in which the drive unit 1000 is installed. The second DC voltage terminal 101 is specifically a terminal to which potential zero is assigned. The converter arrangement 100 allows either the potential voltage U to be applied to each of the center terminals 113, 123, 133. Batt , which corresponds to the battery voltage, or the potential zero (ground connection) is applied.

[0045] Furthermore, in two of the three half-bridges 110, 120 shown, a current sensor 114, 124 is arranged between the first DC voltage terminal 101 and the first semiconductor switch 111, 121. The current sensors 114, 124 comprise, for example, a shunt resistor 1141, 1241 and a voltmeter 1142, 1242, which measures a voltage drop across the shunt resistor 1141, 1241. The voltage is proportional to the current flowing through the shunt resistor 1141, 1241. The current sensors can also be arranged, for example, between the second DC voltage terminal 102 and the second semiconductor switch 112, 122, 132; between the center terminal 113, 123, 133 and one of the semiconductor switches; or be arranged between the center terminal 113, 123, 133 and the phase winding.

[0046] If one of the first semiconductor switches 111, 121 is switched to a conducting state and the corresponding second semiconductor switch 112, 122 of the same half-bridge is switched to a non-conducting state, the potential at the corresponding center terminal 113, 123 is zero, and a corresponding phase current flows from the first DC voltage terminal 101 via the current sensor 114, 124 and the first semiconductor switch 111, 121 through the phase winding (it is understood that in this case at least one other of the first semiconductor switches is non-conducting and the corresponding first semiconductor switch of the same half-bridge is conducting). Due to the phase current, a voltage (U = R · I) drops across the respective shunt resistor 1141, 1241, which can be measured by the voltmeter 1142, 1242. The measured voltage drop is first fed to analog amplifiers with the gain factors V. U or V VThe signal is fed into a signal converter, the output of which is then converted into a digital value by a downstream analog-to-digital converter (ADC). Each ADC is clocked with a clock signal typically derived from the inverter's PWM clock, so that signal sampling advantageously always occurs in the middle of the period in which the corresponding output potential is zero. This ensures that the instantaneous current value at the sampling time is almost exactly equal to the average current value during the corresponding pulse period.

[0047] The measured current values ​​are then output to a computing unit 10 of the drive unit 1000, which processes them further.

[0048] Fig. Figure 2 shows a flowchart of a process according to an embodiment of the invention.

[0049] In step 200, it is determined whether the drive unit 1000 has reached a steady state. A variety of different criteria can be used for this purpose, either alternatively or in combination.

[0050] For example, a steady state is determined to exist if, in a second time interval preceding a first time interval in which the measured quantities are to be recorded, the rotor speed fluctuation range is below a speed threshold. Further conditions can be seen in the fact that the slope of a regression line of the rotor speed over the second time interval is below a rotor speed slope threshold, and / or that, in the second time interval, the fluctuation range of a torque setpoint is below a torque threshold, and / or that, in the second time interval, the fluctuation range of at least one, in particular each, field-oriented current setpoint is below a current threshold Δi. d,soll,Schwell , Δi q,soll,Schwell lies, where in particular the current threshold is the same for each field-oriented current setpoint, i.e. Δi d,soll,Schwell = Δi q,soll,SchwellThe range of variation of a quantity can be calculated as the difference between the minimum value and the maximum value in the second time interval.

[0051] If it has been determined that a steady state of the drive unit 1000 exists, in a step 210 in the first time interval, which lies after the second time interval, a course of the current intensities of the current flowing through the center terminals 113, 123 through each current sensor 114, 124 of the two half-bridges 110, 120, a course of the field-oriented voltages applied to the phase windings of the stator of the electric machine 1, a course of the field-oriented currents flowing through the phase windings of the stator of the electric machine 1 and a rotor position angle are recorded.

[0052] Subsequently, in a block 220, a correction factor is determined for each current sensor 114, 124 depending on the recorded current profiles, the recorded field-oriented voltage profiles, the recorded field-oriented current profiles and the rotor position angle.

[0053] In step 221, for each field-oriented coordinate, a magnitude and phase angle of a first alternating current component for each field-oriented current profile and an alternating voltage component for each field-oriented voltage profile are determined as a function of a given angular frequency, where the given angular frequency is in particular twice the stator angular frequency ω SThis corresponds to the magnitude and phase angle of the first alternating current component and the alternating voltage component, which can be determined in particular as complex numbers, since both quantities can then be represented by a single complex quantity.

[0054] In step 222, the determined voltage alternating component is then converted into a second current alternating component for each field-oriented coordinate d, q (see Eqs. 1.1, 1.2). Alternatively, the determined first current alternating components can also be converted into second voltage alternating components (see Eq. 3).

[0055] In step 223, for each field-oriented coordinate d, q, a deviation between the determined first current components and the determined second current components is determined (see Eqs. 2.1, 2.2). If, on the other hand, the first current components have been converted into second voltage components, a deviation between the first voltage components and the second voltage components is determined and converted into a current deviation (cf. Eqs. 4.1, 4.2, 5).

[0056] In step 224, the determined field-oriented current deviations are converted into stator-oriented current deviations for at least two phase windings of the electrical machine 1; that is, a transformation from the field-oriented coordinate system to the stator-oriented coordinate system of the individual phases takes place. This transformation is known.

[0057] In step 225, an amplitude is then determined for each of the current waveforms in the phase windings measured by the current sensors 114, 124. For this purpose, for example, half the difference between a measured maximum and a measured minimum of the current can be used.

[0058] In step 226, the determined measured current waveforms are corrected using the determined stator-oriented current deviations for the at least two phase windings, and the corrected current amplitudes are calculated from the corrected current waveforms (see Eqs. 6.1, 6.2).

[0059] In step 227, a correction factor is determined for each current sensor 114, 124 as a function of the corrected amplitudes (see Eqs. 7.1, 7.2, 8). Since the sum of all currents in the stator is zero, the third current does not need to be corrected, but can be calculated from the other two.

[0060] Subsequently, in block 230, the drive unit 1000 is operated using the specified correction factors.

[0061] In step 231, it is determined whether a steady state existed during the first time interval to ensure that at least one correction factor was determined during steady-state operation. A non-steady-state condition may exist, for example, if the vehicle in which the drive unit is installed is on a track with a changing gradient during the first time interval. For this purpose, one or more of the conditions mentioned previously with reference to step 200 can be checked during the first time interval.

[0062] If it is determined that a steady state has existed, the at least one correction factor is applied in a step 232 during operation of the drive unit 1000, in particular multiplicatively or additively, to the respective current strength detected by the two current sensors 114, 124. The current strengths thus corrected are then used for the operation of the drive unit 1000.

[0063] If it is determined that a steady state did not exist during the first time interval, the at least one specified correction factor is discarded in step 233. The operation of the drive unit 1000 is then carried out with a previously determined correction factor or without a correction factor, and a new correction factor can be determined at a later time using the procedure.

Claims

[1] Method for operating a drive unit (1000) comprising an electric machine (1) and a converter arrangement (100) for supplying the electric machine (1) with electrical power, wherein the electric machine (1) comprises a stator with a plurality of phase windings (U, V, W) and a rotor, wherein the power converter arrangement (100) comprises: - a first DC voltage terminal (101) and a second DC voltage terminal (102) which are designed to be connected to a DC voltage source, - at least two half-bridges (110, 120, 130), each half-bridge (110, 120, 130) having: -- a first semiconductor switch (111, 121, 131) arranged between the first DC terminal (101) and a center terminal (113, 123, 133) of the half-bridge (110, 120, 130), -- a second semiconductor switch (112, 122, 132) arranged between the second DC terminal (102) and the center terminal (113, 123, 133) of the half-bridge (110, 120, 130), wherein at least two half-bridges (110, 120, 130) of the converter arrangement have a current sensor (114, 124), wherein the current sensor (114, 124) is configured to measure the current strength of a current flowing through the center terminal (113, 123, 133) of the half-bridge (110, 120, 130), the procedure comprehensively: Determine (200) whether the drive unit (1000) is in a steady state, Detect (210), when it is determined that a steady state of the drive unit (1000) exists, in a first time interval a course of the current intensity of the flowing current through each current sensor (114, 124) of the at least two half-bridges (110, 120, 130), a course of field-oriented voltages applied to the phase windings (U, V, W) of the stator of the electric machine (1), a course of field-oriented currents flowing through the phase windings (U, V, W) of the stator of the electric machine (1) and a rotor position angle, Determining (220) a correction factor for each current sensor (114, 124) depending on the recorded current profiles, the recorded field-oriented voltage profiles, the field-oriented current profiles and the rotor position angle, Operating (230) the drive unit (1000) using the specified correction factors. [2] Method according to claim 1, wherein the first time interval has at least a length by which one period of the stator fundamental frequency is covered. [3] Method according to claim 1 or 2, wherein determining (200) whether a steady state of the drive unit (1000) exists comprises: Determine (200) that a steady state of the drive unit (1000) exists if, in a second time interval preceding the first time interval, a fluctuation range of the rotor speed is below a speed threshold and / or a slope of a regression line of the rotor speed over the second time interval lies within a rotor speed slope interval that is bounded upwards by a first rotor speed slope threshold and downwards by a second rotor speed slope threshold, and / or in the second time interval a fluctuation range of a predetermined torque setpoint of the electric machine (1) is below a torque threshold and / or a fluctuation range of at least one, in particular each, field-oriented current setpoint is below a current threshold, wherein in particular the current threshold is the same for each field-oriented current setpoint. [4] Method according to any of the preceding claims, wherein operating (230) the drive unit (1000) using the specified correction factors comprises: Determine (231) whether a steady state existed during the first time interval, Rejecting (232) the determined correction factors if it is determined that a steady state did not exist during the first time interval. [5] Method according to claim 4, wherein determining (231) whether a steady state existed during the first time interval comprises: Determine that a steady state of the drive unit (1000) exists if, in the first time interval, a fluctuation range of the rotor speed is below a speed threshold value and / or a slope of a regression line of the rotor speed over the first time interval lies in a rotor speed slope interval that is bounded upwards by a first rotor speed slope threshold value and downwards by a second rotor speed slope threshold value, and / or in the first time interval, a fluctuation range of a predetermined torque setpoint of the electric machine (1) is below a torque threshold value and / or a fluctuation range of at least one, in particular each, field-oriented current setpoint is below a current threshold value, wherein in particular the current threshold value is the same for each field-oriented current setpoint. [6] Method according to any of the preceding claims, wherein determining (220) the correction factor for each current sensor (114, 124) comprises: Determine (221) for each field-oriented coordinate, a magnitude and phase of a first alternating current component for each course of the field-oriented currents and an alternating voltage component for each course of the field-oriented voltages as a function of a given angular frequency, wherein the given angular frequency corresponds in particular to twice the stator angular frequency, Converting (222), for each field-oriented coordinate, the determined alternating voltage component into a second alternating current component, Determine (223), for each field-oriented coordinate, a field-oriented current deviation between the determined first current alternating components and the determined second current alternating components, Conversion (224) of the determined field-oriented current deviations into stator-oriented current deviations for at least two phase windings (U, V, W) of the electrical machine (1), Determine (225) an amplitude for each of the current waveforms measured by the current sensors (114, 124), Correcting (226), in particular additively, the determined amplitudes using the determined stator-oriented current deviations for the at least two phase windings (U, V, W), Determine (227), for each current sensor (114, 124), a correction factor as a function of the corrected amplitudes. [7] Method according to claim 6, wherein the correction factor for each current sensor is determined as the quotient of the corrected amplitude and the amplitude determined for each of the current waveforms measured by the current sensors (114, 124). [8] Drive unit (1000) comprising an electric machine (1) and a converter arrangement (100) for supplying the electric machine (1) with electrical power, wherein the electric machine (1) has a stator with a plurality of phase windings (U, V, W) and a rotor wherein the power converter arrangement (100) comprises: - a first DC voltage terminal (101) and a second DC voltage terminal (102) which are designed to be connected to a DC voltage source, - at least two half-bridges (110, 120, 130), each half-bridge (110, 120, 130) having: -- a first semiconductor switch (111, 121, 131) arranged between the first DC terminal (101) and a center terminal (113, 123, 133) of the half-bridge (110, 120, 130), -- a second semiconductor switch (112, 122, 132) arranged between the second DC terminal (102) and the center terminal (113, 123, 133) of the half-bridge (110, 120, 130), wherein at least two half-bridges (110, 120, 130) of the converter arrangement (100) have a current sensor (114, 124), wherein the current sensor (114, 124) is configured to measure the current strength of a current flowing through the center terminal (113, 123, 133) of the half-bridge (110, 120, 130), and a computing unit (10) which is configured to perform all process steps of a process according to any of the preceding claims. [9] Computer program that causes a computing unit (10), in particular the drive unit (1000) according to claim 8, to carry out all process steps of a method according to any one of claims 1 to 7 when executed on the computing unit. [10] Machine-readable storage medium with a computer program stored thereon according to claim 9.

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