Method for determining an operating parameter of an electrical machine

Abstract

The invention relates to a method for determining a first operating parameter of an electrical machine (1) comprising a multiphase stator with a plurality of phase windings and a rotor with a plurality of permanent magnets, the method comprising determining (S100) a relationship between the first operating parameter of the electrical machine and a second operating parameter of the electrical machine using a model of the electrical machine which describes a dependence of voltages applied to the plurality of phase windings on currents flowing through the plurality of phase windings in a rotor-fixed dq coordinate system using a differential inductance of the plurality of phase windings;a detection (S110) of the second operating parameter, and a determination (S120) of the first operating parameter using the relationship between the first operating parameter and the second operating parameter and the detected second operating parameter, wherein the first and the second operating parameters are selected from at least one voltage applied to one of the plurality of phase windings, at least one current flowing through one of the plurality of phase windings and a torque of the electrical machine.

Description

[0001] The present invention relates to a method for determining a first operating parameter of an electric machine, a computing unit and a computer program for carrying it out, as well as a drive unit comprising an electric machine and a computing unit. Background of the invention

[0002] A permanent magnet synchronous machine (PMSM) conventionally comprises a stator with a plurality of phase windings through which a phase current is passed, and a rotor with a plurality of permanent magnets. The phase current flowing through the phase windings induces a magnetic field that interacts with the magnetic field of the permanent magnets, thus setting the rotor in motion.

[0003] Synchronous machines can be field-oriented controlled (FOC). In this process, a setpoint for the desired torque M is used. solltwo setpoints for the currents i d and i q generated in the rotor-fixed dq coordinate system. These currents are impressed into the phase windings of the stator of the electric machine using a current controller.

[0004] For the design of a controller and the associated simulation of the control loop, a model of the controlled system, i.e. the electrical machine, is helpful, from which the transfer function for the control can be calculated. Disclosure of the invention

[0005] According to the invention, a method for determining a first operating parameter of an electrical machine, as well as a computing unit and a computer program for carrying out this method, are proposed, comprising the features of the independent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0006] The invention relates to an electric machine comprising a stator with a plurality of phase windings and a rotor with a plurality of permanent magnets. The rotor is set in motion by the interaction of the magnetic field of the permanent magnets with a magnetic field induced in the phase windings, which is itself induced by stator currents flowing through the phase windings. For the control and diagnosis of the electric machine, the relationships between the various operating parameters of the electric machine, in particular the torque, the stator currents, and the stator voltages applied to the phase windings, must be known as precisely as possible.

[0007] To create such a model of a three-phase PMSM and to determine the transfer functions, the stator voltages, stator currents and the flux linkage are related according to: u(t)=R⋅i(t)+dΨ(t)dt The equation includes the stator voltage u(t), the stator current i(t), the flux linkage in the phase windings Ψ(t), and the phase winding resistance R. The flux linkage is the magnetic flux generated by the coil and its leads. Bold symbols represent n x n matrices or n-component vectors, where n is the number of phases in the electric machine. The flux linkage is the relationship between the rotor speed and the pole wheel voltage and can be determined, for example, in a no-load test where the electric machine is driven externally at no load.

[0008] For the use of the stator currents instead of the flux linkages in the phase windings as state variables, the following division of the flux linkage can be carried out in a non-inventive approach: Ψ(t)=LS(i(t),φ(t))⋅i(t)+ΨPM(i(t),φ(t)) with the mechanical rotor angle φ(t), the secant inductance L S as a function of the stator current i(t), the mechanical rotor angle φ(t) and the flux linkages Ψ PM The phases are caused by the rotor's permanent magnets as a function of the stator current i(t) and the mechanical rotor angle φ(t). The inductance of a phase winding describes the relationship between the magnetic flux of the phase winding and the stator current flowing through the phase winding. This relationship is non-linear, and the increase in flux decreases with increasing current. The secant inductance describes the slope of the secant through a selected operating point and the zero point (see also Fig. 1, dashed line).

[0009] The following equations can be used to simplify secant inductance and flux linkage: LS(t)=LS(φ(t)) ΨPM(t)=ΨPM(φ(t))

[0010] The dependence of the secant inductance and the flux linkage on the stator current i(t) is neglected.

[0011] The secant inductance L, which depends only on the mechanical rotor angle φ(t) S (φ(t)) can be represented as follows: LS(φ(t))=[LSa(φ(t))−MSab(φ(t))MSac(φ(t))−MSab(φ(t))LSb(φ(t))−MSbc(φ(t))−MSac(φ(t))−MSbc(φ(t))LSc(φ(t))]

[0012] The matrix elements L Sa , L Sb L Sc Here, the secant self-inductance of the coil and the matrix elements M are denoted. Sab , M Sac , M Sbc the secant coupling inductance. The self-inductance L Sa describes the influence of the current in strand a on the coupled flux in the same strand a. The coupling inductance M SabThis describes the influence of the current in strand a on the coupled flux in another strand b. Coupling inductances are typically negative for geometric reasons, therefore a minus sign has been included in the definition.

[0013] The individual elements of the secant inductance, which depend on the electric rotor angle N · φ\(t), have a second-order cosine curve over the rotor angle, i.e., they depend on 2 · N · φ and thus on the second harmonic: LSa(φ(t))=l0+l2⋅cos(2Nφ(t)) LSb(φ(t))=l0+l2⋅cos(2Nφ(t)−4⋅π3) LSb(φ(t))=l0+l2⋅cos(2Nφ(t)−8⋅π3) MSbc(φ(t))=m0+m2⋅cos(2Nφ(t)) MSac(φ(t))=m0+m2⋅cos(2Nφ(t)−4⋅π3) MSab(φ(t))=m0+m2⋅cos(2Nφ(t)−8⋅π3) with the number of pole pairs N of the electric machine.

[0014] The vector of flux linkage caused by the permanent magnets of the stator in the phase windings can be represented as follows: ΨPM(φ(t))=[ΨPMa(φ(t))ΨPMb(φ(t))ΨPMc(φ(t))]

[0015] The elements of the flux chain have a first-order cosine-shaped profile over the rotor angle: ΨPMa(φ(t))=Km⋅cos(Nφ(t)) ΨPMb(φ(t))=Km⋅cos(Nφ(t)−2⋅π3) ΨPMc(φ(t))=Km⋅cos(Nφ(t)−4⋅π3)

[0016] With the simplifications of equations (3), (4), (6) and (8.1) to (8.3), the following equations for the secant inductances and the flux linkages result after the dq transformation into rotor-fixed dq coordinates: LSdq=[LSd00LSq]≠f(φ(t)) ΨPMdq=[Km 0]≠f(φ(t))

[0017] Both equations are no longer dependent on the rotor angle φ(t).

[0018] Applying the dq transformation to equation (1) using the partitioning in equation (2) and the simplifications in equations (9) and (10) yields the following model equations of a non-inventive dq model in the time domain for a three-phase permanent magnet synchronous machine: ud(t)=Rid(t)+LSd⋅did(t)dt−LSq⋅iq(t)⋅N⋅ω uq(t)=Rid(t)+LSq⋅diq(t)dt−LSd⋅id(t)⋅N⋅ω+Km⋅N⋅ω Ψd(t)=LSd⋅id(t)+Km Ψq(t)=LSq⋅iq(t) M(t)=32⋅N⋅(Ψd(t)⋅iq(t)−Ψq(t)⋅iq(t)) =32⋅N⋅(Km+(LSd−LSq)iq(t))⋅iq(t) with the mechanical rotor speed ω and the torque of the electric machine M(t).

[0019] Calculating the parameters L S (t) and Ψ PM(t) can be calculated by performing a finite element simulation of the electric machine and applying the above-mentioned distribution for the flux linkages in equation (2), as well as the described simplifications in equations (3), (4), (6) and (8) for secant inductances and flux linkages through the permanent magnets. The finite element simulation also serves as the reference for the accuracy of the dq model.

[0020] This model is linear and time-invariant due to its constant parameters and can therefore be represented with transfer functions in the frequency domain, or the equations can be transferred into a transfer matrix.

[0021] Saturation effects occurring in the electric machine, however, lead to nonlinear behavior that is not taken into account by this non-inventive model. These saturation effects reduce the accuracy of the model and consequently the accuracy of the specified target voltage. If only steady-state operation at a selected operating point is considered, linearity is usually achieved by parameterizing the system at that point. However, due to the use of secant inductances and the simplifications made above for the secant inductances and the flux linkages through the permanent magnets, there is still a considerable loss of accuracy for the amplitude and ripple of the calculated currents in pulsed operation, as well as for the mean torque, compared to a corresponding finite element simulation model.

[0022] The invention improves upon this by using a differential inductance instead of a secant inductance. By using the differential inductance at the selected operating point, the amplitude and ripple of the calculated currents, as well as the average torque, are described more accurately without sacrificing their advantageous properties: fast computation compared to finite element simulation, and linearity and time invariance, which are prerequisites for use as a transfer function in the frequency domain.

[0023] Specifically, the invention relates to a method for determining a first operating parameter of an electrical machine comprising a multiphase stator with a plurality of phase windings and a rotor with a plurality of permanent magnets. The method includes determining a relationship between the first operating parameter and a second operating parameter of the electrical machine using a model of the electrical machine that describes the dependence of voltages applied to the plurality of phase windings (hereinafter referred to as stator voltages) on currents flowing through the plurality of phase windings (hereinafter referred to as stator currents) in a rotor-fixed dq coordinate system using a differential inductance of the plurality of phase windings.

[0024] For this purpose, the second operating parameter is recorded, for example by measurement or by receiving an external specification (e.g. as a setpoint), and the first operating parameter is then determined using the relationship between the first operating parameter and the second operating parameter and the recorded second operating parameter.

[0025] In other words, a dependence of the stator voltages on the stator currents derived in a special way (namely taking into account the differential inductance of the phase windings) (i.e., the model) is used to determine the first operating parameter from the second operating parameter.

[0026] In one embodiment, the method also includes determining the aforementioned model of the electrical machine. Alternatively, a pre-defined model can be used to determine the relationship and, for example, stored in a computing unit.

[0027] The first and second operating parameters are selected from at least one voltage applied to one of the plurality of phase windings, at least one current flowing through one of the plurality of phase windings, and a torque of the electrical machine.

[0028] In the case that the first and second operating parameters are the stator voltages and the stator currents, the above model simultaneously provides the relationship, i.e., the step of determining the relationship from the model includes the identity.

[0029] By using the differential inductance to determine the model, the accuracy of the determined first operating parameter can be increased, thus improving the subsequent functions that use the first operating parameter.

[0030] For example, the given relationship can be used to determine a current stator current from a current stator voltage. This can be used, for instance, as a substitute for a measured stator current.

[0031] Furthermore, this specific relationship can be used, for example, in the design of a controller for regulating the electric machine, which allows the electric machine to be operated particularly accurately and efficiently.

[0032] Furthermore, the entire procedure can be carried out in a computing unit that is set up to control the electrical machine, i.e., including the determination of the relationship.

[0033] In one embodiment, the model of the electric machine is determined using the motor equations of the electric machine. This allows the dependence of the stator voltages on the stator currents to be represented as accurately as possible.

[0034] In one embodiment, the model of the electric machine is further determined using at least one quantity selected from an offset of a flux linkage induced in the plurality of phase windings, an electrical resistance of the plurality of phase windings, a number of pole pairs of the electric machine, and a mechanical rotor speed of the electric machine. By using these additional quantities, the relationship can be determined more precisely, thus achieving the aforementioned advantages in an improved form.

[0035] In one embodiment, the model of the electric machine is determined under the assumption that the differential inductance is independent of the stator currents through the phase windings of the stator and depends on the mechanical rotor angle. The same is assumed for the offset of the flux linkage induced in the plurality of phase windings when this is used to determine the model of the electric machine.

[0036] In one embodiment, the model of the electric machine is determined by parameterizing the differential inductance with second-order cosine and second-order sine components and / or the flux offset value with first-order cosine and first-order sine components. In particular, the differential inductance and / or the flux offset value, due to their dependence only on the rotor angle and their constants otherwise, can be easily reduced to constants by a dq transformation into a rotor-fixed coordinate system. This reduces the computational effort required to determine the relationship between the operating parameters and allows the first operating parameter to be determined simply and efficiently.

[0037] In one embodiment, the model of the electric machine is defined as a transfer matrix that relates stator voltages and stator currents. This transfer matrix can, for example, be stored in a controller of the electric machine and used to determine a desired relationship between the first and second operating parameters during operation. Alternatively, the control structure of the electric machine can be designed based on the defined transfer matrix, so that it performs the calculation specified by the transfer matrix. For example, a relationship between the stator currents and the stator voltages can be used to determine the stator voltages to be applied to the electric machine based on the stator currents required for a given torque.The relationship between torque and the stator currents required to generate that torque can also be determined, in order to identify the stator current that produces a desired torque. This allows for improved control of the electric machine during operation and more efficient operation of the electric machine.

[0038] In one embodiment, the second operating parameter is a torque of the electric machine and the first operating parameter is at least a stator current, and the method further comprises controlling the electric machine using the at least one stator current.

[0039] In one embodiment, the second operating parameter is a stator current and the first operating parameter is a stator voltage, and the method further comprises controlling the electrical machine using the determined stator voltage. The detected stator current, which is used to determine the stator voltage, can be determined based on the torque and the relationship between the torque and the stator current.

[0040] The specific operating parameters, which are determined based on the relationship, reflect the real situation of the electrical machine very accurately, so that the efficiency of the operation of the electrical machine can be increased.

[0041] In particular, the relationship between torque and stator current and the relationship between stator current and stator voltage can be determined. Subsequently, the stator current is determined based on the torque, which is then used as the second operating parameter for the relationship between stator current and stator voltage in order to determine the stator voltage used to control the electric machine.

[0042] In one embodiment, the second operating parameter is the stator voltage, the first operating parameter is the stator current, and the method further includes diagnosing a current sensor configured to measure a stator current. For diagnosis, in particular, a difference is determined between the current measured by the current sensor and the current of the specified stator current. It is then determined that a fault exists in the current sensor if the absolute value of the difference exceeds a predetermined threshold. This allows the current sensor used to determine the stator current to be accurately checked for faults, so that in the event of a fault, the electric machine is not damaged.

[0043] A computing unit according to the invention, e.g. a control unit of a motor vehicle, is, in particular in terms of programming, equipped to carry out a method according to the invention.

[0044] The invention further relates to a drive unit comprising an electric machine, power electronics configured to supply the electric machine with electrical power, and a computing unit configured to carry out the method according to the invention.

[0045] 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.).

[0046] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0047] In the following, the determination of the model of the electrical machine, which describes a dependence of voltages applied to the multitude of phase windings on currents flowing through the multitude of phase windings in a rotor-fixed dq coordinate system using a differential inductance of the multitude of phase windings, will first be explained in more detail.

[0048] The starting point for the calculations is again equation (1). However, in this embodiment of the invention, currents are used as the state variable instead of flux chains. This results in the following division in contrast to equation (2): Ψ(t)=Ldiff(i(t),φ(t))⋅i(t)+ΨOffset(i(t),φ(t)) with the differential inductance L diff(i(t), φ(t)) as a function of the phase currents and the rotor angle and the offset value term Ψ offset (i(t), φ(t)) for the flux linkages in the phases as a function of the phase currents and the rotor angle.

[0049] For the differential inductances and the offset value term for the flux linkages, the following simplifications can be applied, neglecting the dependencies on the phase currents: Ldiff(t)=Ldiff(φ(t)) ΨOffset(t)=ΨOffset(φ(t))

[0050] The matrices of the differential inductance and the offset value term of the flux linkage can be represented as follows: Ldiff(φ(t))=[Ldiffa(φ(t))−Mdiffab(φ(t))−Mdiffac(φ(t))−Mdiffab(φ(t)) Ldiffb(φ(t))−Mdiffbc(φ(t))−Mdiffac(φ(t))−Mdiffbc(φ(t))Ldiffc(φ(t))] ΨOffset(φ(t))=[ΨOffseta(φ(t))ΨOffsetb(φ(t))ΨOffsetc(φ(t))] with the (self-)inductances of the individual phases L diffa (φ(t)), L diffb(φ(t)) and L diffc (φ(t)) and the coupled inductances (coupling inductances) between the individual phases M diffab (φ(t)), M diffac (φ(t)), M diffbc (φ(t)).

[0051] L diffa (φ(t)) and M diffbc (φ(t)) contain second-order cosine components as well as second-order sine components. For L diffb (φ(t)), L diffc (φ(t)), M diffab (φ(t)) and M diffac The same applies to (φ(t)). Ψ Offseta (φ(t)) contains first-order cosine and first-order sine components. For Ψ Offsetb (φ(t)) and Ψ Offsetc The same applies to (φ(t)).

[0052] After the dq transformation of the parameters L diff (φ(t)) and Ψ Offset (φ(t)) in rotor-fixed dq coordinates yield the following equations: Ldiffdq=[LdiffdLdiff12Ldiff21Ldiffq]≠f(φ(t)) ΨOffsetdq=[ΨOffsetdΨOffsetq]≠f(φ(t))

[0053] Applying the dq transformation to equation (1) using the partitioning of equation (12) and the simplifications of equations (17) and (18) yields, according to one embodiment of the invention, the model equations for the stator voltages and the torque of a dq model in the time domain for a permanent magnet synchronous machine: ud(t)=R⋅id(t)+Ldiffd⋅did(t)dt+Ldiff12⋅diq(t)dt−Ldiffq⋅iq(t)⋅N⋅ω −Ldiff21⋅id(t)⋅N⋅ω−ΨOffsetq⋅N⋅ω uq(t)=R⋅iq(t)+Ldiffq⋅diq(t)dt+Ldiff21⋅did(t)dt+Ldiffd⋅id(t)⋅N⋅ω +Ldiff12⋅iq(t)⋅N⋅ω+ΨOffsetd⋅N⋅ω Ψd(t)=Ldiffd⋅id(t)+Ldiff12⋅iq(t)+ΨOffsetd Ψq(t)=Ldiffq⋅iq(t)+Ldiff12⋅id(t)+ΨOffsetq M(t)=32⋅N⋅(Ψd(t)⋅iq(t)−Ψq(t)⋅id(t))=32⋅N⋅(ΨOffsetd+(Ldiffd−Ldi ffq)⋅id(t))⋅iq(t)−32⋅N⋅(ΨOffsetq⋅id(t)−Ldiff12⋅(iq2(t)−id2(t)))

[0054] The calculation of the differential inductance and the offset term for the flux linkages can be performed by calculating the flux linkages in the three phases using a finite element simulation of the electrical machine and applying the above-mentioned allocation for the flux linkages in equation (12), as well as the simplifications for the inductance and flux linkage of the permanent magnets described in equations (11), (12), (15), and (16). The finite element simulation also serves as the reference for the accuracy of the dq model.

[0055] Due to the constant parameters after the dq transformation, this model is linear and time-invariant and can therefore be represented using transfer functions in the frequency domain.

[0056] Is this dq model applied at the associated operating point (i d , i gWhen parameterized, a significantly higher accuracy for the amplitude and ripple of the currents (when supplied with pulsed voltages) and for the mean value of the torque is achieved near this operating point than when using the previously explained non-inventive dq model compared with finite element simulations.

[0057] The invention is schematically illustrated in the drawing using an exemplary embodiment and is described below with reference to the drawing. Brief description of the drawings Fig. Figure 1 shows the course of the magnetic flux generated by a coil as a function of a current flowing through the coil, as well as the secant inductance and the differential inductance at an operating point. Fig. Figure 2 shows a block diagram of a drive unit designed to carry out an embodiment of the method according to the invention, and Fig. Figure 3 shows a flowchart of an embodiment of the method according to the invention. embodiment of the invention

[0058] Fig. Figure 1 shows a curve 200 of the magnetic flux (y-axis) generated by a coil as a function of a current (x-axis) flowing through the coil, as well as a secant inductance 201 and a differential inductance 202 at an operating point 203. The magnetic flux 200 increases steadily with increasing current up to saturation, with the rate of increase decreasing with increasing current.

[0059] The secant inductance 201 is the slope of a straight line passing through the zero point and the operating point 203.

[0060] The differential inductance 20 is the slope (tangent) of the flux profile at the selected operating point 203.

[0061] It is evident that the two values ​​differ significantly.

[0062] Fig. Figure 2 shows a block diagram of a drive unit designed to carry out an embodiment of the method according to the invention and Fig. Figure 3 shows a flowchart of an embodiment of the method according to the invention. Both figures are described together below.

[0063] The drive unit 100 comprises an electric machine 1, a computing unit 10 which is set up to carry out a proposed method, and power electronics 110.

[0064] For example, electrical machine 1 is a permanent magnet excited synchronous machine and has a stator with a plurality of phase windings and a rotor with a plurality of permanent magnets.

[0065] The phase windings of the stator are supplied with power by the power electronics unit 110. The power electronics unit 110 comprises a converter circuit and a converter circuit control unit for this purpose. The converter circuit has, for example, a half-bridge for each phase of the electric machine 1 that is to be supplied with electrical power. In each half-bridge, a controllable semiconductor switching element is arranged between a first DC voltage terminal and a center terminal of the half-bridge, and another controllable semiconductor switching element is arranged between a second DC voltage terminal and the center terminal. One phase of the electric machine 1 is supplied with electrical power via the center terminal. A power electronics control unit receives specifications or setpoint values ​​for target voltages u from the processing unit 10. d , u qThe power electronics 110 controls the voltages applied to the electric machine 1 in the dq coordinate system such that the specified target voltages are applied to the phase windings of the stator. For this purpose, the power electronics 110 uses, for example, pulse width modulation signals.

[0066] The calculation unit 10 has a function for determining the target voltages u d , u q a target current value determination unit 11 and a target voltage determination unit 13.

[0067] In an optional step S10, which may be part of the procedure or take place independently of the procedure at an earlier time, a model of the electrical machine is determined that describes the dependence of the stator voltages on the stator currents in the dq coordinate system using a differential inductance of the plurality of phase windings, in particular in the form of the aforementioned equations (19.1) and (19.2). This model may, for example, be stored in the computing unit 10.

[0068] In step S100, a relationship between a first operating parameter and a second operating parameter is determined using the model from step S10. In particular, more than one relationship can be determined, i.e., for different first and / or second operating parameters. The first and second operating parameters can be selected from at least one stator voltage (in particular u). d and uq ), at least one stator current (especially i d and i q ) and a torque M of the electric machine. This relationship results from model equations (19.1) to (19.5).

[0069] The following relationships can be advantageously used within the scope of the invention: - Relationship between the torque of the electric machine (second operating parameter) and the stator current required for it (first operating parameter), - Relationship between the stator current (second operating parameter) and the associated stator voltage (first operating parameter) and - Relationship between the stator voltage (second operating parameter) and the resulting stator current (first operating parameter).

[0070] In step S110, a second operating parameter is recorded, for example a target torque M soll, and from this, in step S120, the first operating parameter is determined, here for example a target stator current i d,soll and i q,soll , which is necessary to achieve the target torque.

[0071] The target torque M soll For example, the input can be specified by a driver via an accelerator pedal in a vehicle equipped with the drive unit 100 and / or a driver assistance system, and received, i.e., recorded, by the processing unit 10, in particular the target current determination unit 11. For this purpose, the aforementioned relationship between the torque of the electric machine (second operating parameter) and the required stator current (first operating parameter) can be stored in the target current determination unit 11.

[0072] Simultaneously, in step S110, a further second operating parameter can be recorded, for example the target stator current i. d,soll and i q,soll, and from this, in step S120, another first operating parameter is determined, for example, a target stator voltage u. d,soll and u q,soll , which is necessary to achieve the target stator current. The target stator current i d,soll and i q,soll can be received, i.e., recorded, by the processing unit 10, in particular the target voltage determination unit 13. In particular, the aforementioned relationship between the stator current (second operating parameter) and the associated stator voltage (first operating parameter) can be stored in the target voltage determination unit 13.

[0073] Overall, this means that the target stator voltage can be determined. d,soll and u q,soll to determine which are necessary to achieve the target torque M soll is necessary.

[0074] The electric machine 1 is then controlled in step S130, whereby the target stator voltages u d,soll and u q,sollThe power electronics 110 are output as setpoint values ​​to supply the electric machine 1 with corresponding voltages so that it can produce the setpoint torque M. soll as actual torque. For this purpose, the power electronics 110 continues to use the rotor speed φ(t) received by the electric machine 1.

[0075] Furthermore, in step S110, a second operating parameter can be recorded, for example the target stator voltage u d,soll and u q,soll , and from this, in step S120, a further first operating parameter is determined, for example, the expected actual stator current, which should result from the applied stator voltage. For this purpose, the aforementioned relationship between the stator voltage (second operating parameter) and the resulting stator current (first operating parameter) can be stored in the processing unit 10.

[0076] In step S140, the determined stator current is then used to diagnose a current sensor which is installed in the drive unit 100 and is designed to measure the stator current in at least one of the phases of the electric machine 1.

[0077] In step S141, a difference is determined between the measured stator current and the stator current calculated using the relationship, and then compared with a threshold value. If the difference exceeds the threshold value, step S142 determines that there is a fault in the current sensor.

Claims

[1] Method for determining a first operating parameter of an electrical machine (1) comprising a multiphase stator with a plurality of phase windings and a rotor with a plurality of permanent magnets, the method comprising: Determine (S100) a relationship between the first operating parameter of the electrical machine and a second operating parameter of the electrical machine (1) using a model of the electrical machine (1) which describes a dependence of voltages applied to the plurality of phase windings on currents flowing through the plurality of phase windings in a rotor-fixed dq coordinate system using a differential inductance of the plurality of phase windings; Acquiring (S110) the second operating parameter, and determining (S120) the first operating parameter using the relationship between the first operating parameter and the second operating parameter and the acquired second operating parameter, wherein the first and second operating parameters are selected from at least one voltage applied to one of the plurality of phase windings, at least one current flowing through one of the plurality of phase windings and a torque of the electrical machine. [2] Method according to claim 1, wherein the model of the electric machine is or is determined using motor equations of the electric machine (1) (S10). [3] Method according to claim 1 or 2, wherein the model of the electric machine is further determined or is determined using at least one quantity (S10) selected from an offset of a flux linkage induced in the plurality of phase windings, an electrical resistance of the plurality of phase windings, a pole pair number of the electric machine (1) and a mechanical rotor speed of the electric machine (1). [4] Method according to one of the preceding claims, wherein the model of the electrical machine is or is determined (S10) assuming that the differential inductance and / or, depending on claim 3, the offset of the flux linkage induced in the plurality of phase windings is independent of the currents flowing through the plurality of phase windings and depends on the mechanical rotor angle (φ(t)). [5] Method according to one of the preceding claims, wherein the model of the electrical machine is or is determined (S10) by parameterizing the differential inductance with second-order cosine components and second-order sine components and / or, depending on one of claims 3 or 4, the offset value of the flux linkage with first-order cosine components and first-order sine components. [6] Method according to one of the preceding claims, wherein the model of the electrical machine is or is determined as a transfer matrix (G(s)) (S10) relating the voltages applied to the plurality of phase windings and the currents flowing through the plurality of phase windings. [7] Method according to one of the preceding claims, wherein the second operating parameter is a torque of the electric machine (1) and the first operating parameter is at least a current flowing through the plurality of phase windings and the method further comprises: Control (S130) of the electrical machine using the at least one current flowing through the plurality of phase windings. [8] Method according to one of the preceding claims, wherein the second operating parameter is at least a current flowing through the plurality of phase windings and the first operating parameter is at least a voltage applied to the plurality of phase windings and the method further comprises: Control (S130) of the electrical machine (1) using the voltage applied to the plurality of phase windings. [9] Method according to claim 8 with reference to claim 7, to specify a desired torque of the electric machine (1). [10] A method according to any of the preceding claims, wherein the second operating parameter is at least a voltage applied to the plurality of phase windings and the first operating parameter is at least a current flowing through the plurality of phase windings and the method further comprises: Diagnosing (S140) a current sensor designed to measure the at least one current flowing through the plurality of phase windings, wherein the diagnosing (S140) particularly comprises: Determining (S141) a difference between a current of the stator current measured by the current sensor and a current of the determined at least one current flowing through the plurality of phase windings, Determine (S142) that there is a fault in the current sensor if an absolute value of the difference exceeds a predetermined threshold. [11] Computing unit (10) configured to perform all process steps of a process according to any of the preceding claims. [12] Drive unit (100) comprising an electric machine (1), a power electronics unit (110) configured to supply the electric machine with electrical power, and a computing unit (10) according to claim 11. [13] Computer program that causes a computing unit (10) to perform all the process steps of a method according to any one of claims 1 to 10 when executed on the computing unit. [14] Machine-readable storage medium with a computer program stored thereon according to claim 13.

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