DE102022203212A1 - Method for operating an electrical machine - Google Patents

Abstract

The invention relates to a method for operating an electrical machine (2), having a brushless electric motor (4), which is controlled by means of field-oriented control in a d-q coordinate system, with the orientation for a d-axis of the d-q coordinate system being determined, with a direct current signal being impressed on the specific d-axis, which increases an inductance difference between the motor inductances, with the increased inductance difference being used to determine a deviation or a deviation direction between the specific d-axis and the actual d-axis is determined, and wherein the orientation of the determined d-axis is adjusted and/or regulated based on the deviation or direction of deviation.

Description

The invention relates to a method for operating an electrical machine, having a brushless electric motor, which is controlled using field-oriented control in a d-q coordinate system. The invention also relates to an electrical machine and software on a data carrier.

Adjustment systems powered or operated by electric motors as motor vehicle components, such as window lifters, seat adjusters, door and sunroof drives or radiator fan drives, as well as pumps and interior fans, typically have an electric drive with a controlled electric motor. So-called brushless electric motors (brushless DC motors, BLDC motors) are increasingly being used for such electromotive drives, in which the wear-prone brush elements of a rigid (mechanical) commutator are replaced by electronic commutation of the motor current.

Electromotive drives for motor vehicles are usually fed by a (high-voltage) battery as an on-board energy store, from which the electric motor is supplied with electrical energy in the form of a direct current (direct current). In order to convert the direct current into the motor current, a power converter (inverter) is suitably connected between the energy store and the electric motor. The power converter has a bridge circuit, which is supplied with the direct current or direct voltage of the energy store via an electrical intermediate circuit. The motor current is generated as a multi-phase output current by a pulse width modulated (PWM) control or regulation of semiconductor switches of the bridge circuit. The pulses of the PWM signals switch the semiconductor switches between a conducting and a blocking state in a clocked manner.

During operation, the bridge circuit feeds the electric motor current (three-phase current) into the stator coils of the electric motor, which subsequently generates a rotating magnetic field with respect to the stator. In this case, the rotor of the electric motor suitably has a number of permanent magnets, the interaction of the permanent magnets with the rotary field producing a resulting torque which causes the rotor to rotate.

The phases of the three-phase current generated by the bridge circuit and the associated rotating field are referred to as (motor) phases. In a figurative sense, this also includes the stator coils (phase winding) assigned to such a phase with the associated connecting lines (phase end). In this case, the phases are connected to one another, for example, in a star point of a star connection.

For efficient operation, it is necessary that the phases are supplied with power at the right time. This requires an exact determination of the relative position of the rotor and stator for motor control/regulation.

The rotor position for determining the position is determined, for example, by means of additional rotary sensors, such as a Hall sensor. However, such rotation sensors or encoders are expensive, which is why a position determination should preferably be carried out without sensors.

The sensorless position determination is based, for example, on the detection of induced current and/or voltage signals due to the counter-electromotive force (counter-EMF, back-EMF), which induces the rotating permanent magnets in the phase windings. The induced back EMF signals are proportional to the rotor speed, which disadvantageously provides little or no information for position determination for the motor control at low speeds or when the electric motor is stationary. In particular, the signal-to-noise ratio is reduced at low speeds. Such a limitation also exists for flow-based sensorless measurement methods. As a result, it is often not possible to determine or recognize a position below a threshold speed, which disadvantageously impedes safe and reliable operation of the electric motor, particularly when starting from a standstill or during operation at a low speed.

In order to reach and/or exceed the threshold speed, it is possible, for example, to align the drive or the rotor without knowing the exact rotor position and then to accelerate it in step mode using an acceleration ramp. A voltage vector is usually used for alignment, which rotates the rotor to a specified position (starting position). For this purpose, for example, one phase is connected to a reference potential, such as a ground, and the other phases are supplied with a pulse width modulated control signal. The magnetic field generated in this way then aligns the rotor so that the rotor is transferred to a defined starting position.

The disadvantage of this method is that it requires comparatively high motor or phase currents. Furthermore, the electric motor or the rotor is accelerated comparatively slowly, so that there is a long starting or run-up time. There is also the risk of oscillations and loss of the synchronous field. As a result of the oscillations and high motor currents, the acoustics of a drive operated in this way also deteriorate disadvantageously.

Another possibility for position detection is the evaluation of anisotropic properties of the drive, such as a rotor position-dependent inductance of the phase windings. Advantageously, this method for position detection also works at low speeds and when the rotor is at a standstill. For example, position detection using a high-frequency signal is known from the doctoral thesis “Sensorless Control of IPM Synchronous Motors for Entire Speed Range Including Start-Up” by Ing. Roman Filka (March 17, 2008). Here, along a suspected d-axis, for example, a sinusoidal voltage with z. B. 500 Hz is impressed, and the reaction of the drive or the electric motor is measured in the q-axis. However, equal shares are not taken into account here. The system response of the electric motor changes depending on the deviation between the presumed and actual rotor position, with the presumed rotor position being able to be adapted to the actual rotor position as a result.

Disadvantageously, this method can only be used in drives that have appropriate properties, such as a sufficiently high dependence of the inductance on the rotor position. In addition, it is the case that a position determination based on the inductance alone is not unambiguous and there is therefore a risk of a positioning error of 180°.

The invention is based on the object of specifying a particularly suitable method for operating an electrical machine. In particular, a method is to be specified by means of which the difference between the inductances is increased, so that a particularly reliable position detection is ensured. The invention is also based on the object of specifying a particularly suitable electrical machine and particularly suitable software.

With regard to the method, the object is achieved with the features of claim 1 and with regard to the electrical machine with the features of claim 5 and with regard to the software with the features of claim 6. Advantageous refinements and developments are the subject of the dependent claims.

Insofar as method steps are described below, advantageous configurations for the electrical machine result in particular from the fact that it is designed to carry out one or more of these method steps.

The method according to the invention is provided for the operation of an electrical machine and is suitable and designed for this.

In this case, the electric machine has an electric motor drive in the form of a brushless electric motor, which is designed, for example, as a synchronous motor. In this case, the electric motor has a stator with a multi-phase rotary field winding and a rotor with permanent magnets mounted rotatably therein. The phases or phase windings of the rotary field winding are wound around stator teeth of the stator, for example as coils or coil pairs.

The electric motor is controlled using field-oriented control in a rotor-fixed d-q coordinate system. This means that the multi-phase, for example three-phase, operating state variables of the electric motor or stator (phase currents, phase voltages) are converted into a two-axis coordinate system by means of a d-q or Park transformation and are regulated there. The control or manipulated variable of the regulation is correspondingly back-transformed and used, for example, for a pulse width modulated control of the electric motor.

The electric motor is designed without sensors, for example, so there is no position sensor for detecting a rotor position or position. This means that the position detection or position determination for the field-oriented control takes place without sensors. The method according to the invention is intended here in particular for operation at low speeds or when starting from a standstill, in which case there is insufficient counter-EMF available. The rotational speed during the process is therefore less than or equal to a minimum speed, for example less than or equal to 300 revolutions per minute (300 RPM).

The method is based on the detection of differences between the inductances Ld and Lq, i.e. the motor inductances effective in the dq coordinate system. In this case, the inductances Ld and Lq are of different magnitudes, in other words the inductances are position-dependent, ie dependent on the relative position or alignment direction of the rotor to the stator. In this case, the inductance Ld corresponds to the inductance acting along the d-direction. The inductance Lq corresponds to the inductance acting along the q-direction.

At the beginning of the method, the rotor position or orientation is essentially unknown. According to the method, the orientation for the d-axis or the d-direction of the d-q coordinate system is first determined, in particular estimated. In other words, the orientation or orientation of the rotor-fixed d-q coordinate system is estimated. Here and in the following, "estimate" or "estimate" means an approximate determination of the axis orientation, for example by means of pre-characterized measurements, stored tables or characteristic curves, or by means of statistical-mathematical methods. The initial value for the d-axis or d-direction can, for example, also be stored in the form of a (fixed) value. The initial value can therefore be specified essentially independently of the rotor position, so that the initial error can be up to ±180°. Alternatively, the orientation of the d-axis can be derived from an estimate or determination of the rotor position, for example by performing an initial position procedure (e.g. test pulses with high current values) or rotor alignment using a voltage vector.

According to the invention, a preferably non-torque-forming first direct current signal is impressed on the estimated or determined d-axis. The first direct current signal is preferably positive (Id>0) and dimensioned beyond the MTPA (Most Torque per Amper) of the electric motor. Due to the reluctance, the direct current signal in the d-axis can also generate torque, with this preferably being compensated for by a control and/or regulation. In the following, the first direct current signal is therefore understood to mean in particular a non-torque-forming direct current. By introducing the (direct) current, which preferably does not generate torque, the electric motor is brought into (partial) saturation. This saturation results in a reduction in inductance in this direction, so the Ld inductance is reduced.

This increases the inductance difference between the inductances Ld and Lq. Based on this, an operationally safe and reliable position detection can be implemented.

According to the method, this increased inductance difference according to the invention is used for improved sensorless position detection of the rotor position. For this purpose, for example, an alternating current or an alternating voltage, ie a signal with a predefined or definable signal frequency, for example 500 Hz (Hertz), is fed in in addition to the first direct current signal along the estimated d-direction. The alternating signal and the first direct current signal are thus generated along the estimated d-direction. For example, the resulting electric motor response is captured along the (estimated or determined) q-axis of the d-q coordinate system. For example, the reaction of the electric motor along the q-direction is monitored for the direct current and alternating signals acting in the d-direction. In this case, the answer or reaction is in particular a changed current along the q-axis, which can be monitored, for example, by means of an ammeter for detecting the phase currents (for example a shunt resistor). For example, a deviation or direction of deviation between the estimated d-axis and the actual d-axis is determined on the basis of the response or reaction, the orientation of the estimated d-axis being set and/or regulated using the deviation or direction of deviation. A particularly suitable method for operating an electrical machine is thereby implemented. In particular, the increase in the inductance difference according to the invention increases the validity of conventional/classic position detection methods or makes their use possible in the first place. The method can thus be used to determine the orientation of the d-q coordinate system and thus indirectly the rotor position, in particular a position offset and a direction/speed of rotation of the rotor.

The conjunction “and/or” is to be understood here and in the following in such a way that the features linked by means of this conjunction can be designed both together and as alternatives to one another.

The additional direct current and the resulting saturation of the electric motor enables a particularly precise position detection. At the same time, a large current in the estimated d-direction prevents the drive from accelerating to an undesired extent. As a result, critical position estimation errors are avoided in an advantageous and simple manner. The method thus improves or enables sensorless position determination on the basis of inductance. The method thus further reduces unintended accelerations. For example, if the drive accelerates faster than the position detection estimates, the result is that the additionally applied (first) direct current is not applied in the d-direction as assumed, but in the actual negative q-direction. This has a reduction in acceleration tion and thus stabilizes the drive or engine operation.

In an advantageous embodiment, a field-amplifying or field-weakening first direct current signal is impressed. In other words, the first direct current signal has a field-enhancing or field-weakening effect.

For a field-enhancing DC signal in the d-direction, a positive DC current is applied in the estimated d-direction (Id > 0). The field applied by the permanent magnets is subsequently amplified by the stator current in the d-direction. The saturation effect reduces the d-inductance and enables or improves position detection.

In some electric motors, the Lq inductance is smaller than the Ld inductance. In this case it can be advantageous to increase the inductance in the d-direction. For this purpose, a negative direct current is applied in the estimated d direction (Id < 0). The field generated by the permanent magnets of the rotor is weakened by the current in the d-direction. The reduced saturation effect increases the Ld inductance and enables or improves position detection.

In a suitable development, a field-enhancing or field-weakening first direct current is impressed depending on an operating situation of the electric motor. In particular, depending on the operating situation, a field-strengthening and field-weakening first direct current is impressed in alternation. Depending on the operating situation, it can be advantageous to weaken or strengthen the magnetic field in the d-direction. In this case, the operating situation is monitored in particular by means of the response or reaction of the electric motor, ie for example by means of the resulting q current. It can be the case, for example, that in the case of q currents of small magnitude, Ld < Lq. Here it makes sense to strengthen the field in the d-direction. With high absolute q-currents, it can then happen that the inductance in the q-direction falls due to saturation and can even be smaller than Ld. In this case, switching to field-weakening operation can be beneficial.

Optionally, the additional torque-generating component can be compensated here. This is particularly advantageous at the moment of changing from field-enhancing to field-weakening and vice versa.

In one possible configuration, a second direct current is impressed along the q-axis. In this case, the second direct current has a particularly field-weakening effect in the q-direction. In order to avoid unwanted torque due to reluctance, an additional (second) q-direct current can be applied in addition to the (first) d-direct current. In this case, the second direct current is preferably selected in such a way that it compensates for the (rotational) moment due to the reluctance. This q-current also has an influence on the inductance. However, the second direct current preferably has a small amplitude compared to the first direct current. In particular, the second direct current is dimensioned in such a way that the influence on the inductance compared to the first direct current can be accepted. Alternatively or additionally, a second direct current can be impressed along the d-axis to compensate for the torque of the first direct current.

The electric machine according to the invention is provided for a motor vehicle and is suitable and set up for it. The advantages and configurations given with regard to the method can also be transferred to the electrical machine and vice versa.

The electrical machine has a brushless electric motor with a rotatable rotor and a stator provided with a multi-phase rotary field winding. The motor current provided for operating the electric motor is generated, for example, by means of a converter (inverter). The converter is part of the motor electronics. The converter is coupled to a controller (that is, a control unit), which is preferably also part of the motor electronics.

In this case, the controller has a control unit for, in particular, field-oriented control of the motor operation or the motor current, which is coupled to the controller or is integrated into it. During operation, the control unit generates a control variable for the electric motor.

In this case, the controller is generally set up—in terms of program and/or circuitry—to carry out the method according to the invention described above. The controller is thus specifically set up to estimate the orientation of a d-axis or a d-q coordinate system and to impress an alternating signal and a non-torque-forming first direct current signal on the estimated d-axis. The controller is further configured to detect a resulting response of the electric motor along a q-axis, determine a deviation between the estimated d-axis and the actual d-axis based on the response, and the orientation of the estimated d-axis based on the deviation set and/or regulate.

In a preferred embodiment, the controller is formed, at least in its core, by a microcontroller with a processor and a data memory, in which the functionality for carrying out the method according to the invention is implemented programmatically in the form of operating software (firmware), so that the method - optionally in interaction with a machine user - is carried out automatically when the operating software is executed in the microcontroller. Alternatively, within the scope of the invention, the controller can also be formed by a non-programmable electronic component, such as an application-specific integrated circuit (ASIC), in which the functionality for carrying out the method according to the invention is implemented with circuitry means.

An additional or further aspect of the invention provides software on a medium or data carrier for carrying out or executing the method described above. This means that the software is stored on a data medium and is provided for executing the method described above, and is suitable and designed for this when the software runs on a computer or a calculator. As a result, particularly suitable software for the operation of an electrical machine is implemented, with which the functionality for carrying out the method according to the invention is implemented in terms of programming. The software is thus in particular operating software (firmware), with the data carrier being, for example, a data memory of the controller, and with the computer being in particular a processor of the controller. The explanations in connection with the method and/or the electrical machine also apply to the software and vice versa.

• 1 eine elektrische Maschine mit einer Stromquelle und mit einem Elektromotor sowie mit einem dazwischen verschalteten Stromrichter,
• 2 drei Phasenwicklungen eines dreiphasigen Elektromotors der Maschine in Sternschaltung,
• 3 ein Brückenmodul einer Brückenschaltung des Stromrichters zur An-steuerung einer Phasenwicklung des Elektromotors,
• 4 ein Ersatzschaltbild für die Stromquelle, und
• 5 ein Flussdiagramm für ein Verfahren zum Betrieb der elektrischen Maschine.

Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. It shows in schematic and simplified representations:

• 1 an electrical machine with a power source and with an electric motor and with a power converter connected in between,
• 2 three phase windings of a three-phase machine electric motor in star connection,
• 3 a bridge module of a bridge circuit of the power converter for controlling a phase winding of the electric motor,
• 4 an equivalent circuit for the current source, and
• 5 a flowchart for a method for operating the electric machine.

Corresponding parts and sizes are always provided with the same reference symbols in all figures.

The invention is explained below using a three-phase star connection as an example. However, the invention can also be transferred to multi-phase systems and/or delta circuits without restricting the generality.

The 1 shows an electric machine 2 for an electric motor drive of a motor vehicle, not shown in detail, for example for a refrigerant compressor or for a seat adjustment. In this embodiment, the electrical machine 2 comprises a three-phase brushless electric motor 4 which is connected to a power source (voltage supply) 8 by means of a power converter (converter, inverter) 6 . In this exemplary embodiment, the power source 8 comprises a vehicle-internal energy store in the form of a (vehicle) battery 10 and a (DC voltage) intermediate circuit 12 connected thereto, which extends at least partially into the power converter 6 .

The intermediate circuit 12 is essentially formed by a forward line 12a and a return line 12b, by means of which the power converter 6 is connected to the battery 10. The lines 12a and 12b are at least partially routed into the power converter 6, in which an intermediate circuit capacitor 14 and a bridge circuit 16 are connected between them.

During operation of the electrical machine 2, an input current I _E ( 4 ) is converted into a three-phase output current (motor current, three-phase current) I _U , I _V , I _W for the three phases U, V, W of the electric motor 4 . The output currents lu, Iv, Iw, also referred to below as phase currents, are fed to the corresponding phase (windings) U, V, W ( 2 ) out of a stator, not shown.

In the 2 a star connection 18 of the three phase windings U, V, W is shown. The phase windings U, V and W are each connected to a (phase) end 22, 24, 26 to a respective bridge module 20 ( 3 ) of the bridge circuit 16 out, and connected to each other with the respective opposite end in a star point 28 as a common connection terminal.

In the representation of 2 are the phase windings U, V and W each by means of an equivalent circuit diagram in the form of an inductor 30 and a Ohmic resistance 32 and a respective voltage drop 34, 36, 38 shown. The respectively across the phase winding U, V, W dropping voltage 34, 36, 38 is represented schematically by arrows and results from the sum of the voltage drops across the inductance 30 and the ohmic resistance 32 and the induced voltage 40. The movement of a Rotor of the electric motor 4 induced voltage 40 (electromagnetic force, EMF, EMF) is in the 2 represented by a circle.

The star circuit 18 is controlled by means of the bridge circuit 16. The bridge circuit 16 is designed with the bridge modules 20 in particular as a B6 circuit. In this embodiment, during operation, each of the phase windings U, V, W is switched at a high switching frequency between a high (DC) voltage level of the supply line 12a and a low voltage level of the return line 12b. In this case, the high voltage level is in particular an intermediate circuit voltage U _ZK of the intermediate circuit 12, the low voltage level preferably being a ground or ground potential U _G . This clocked control is available as a - in 1 PWM control, illustrated by arrows, is carried out by a controller 42, with which control and/or regulation of the speed, the power and the direction of rotation of the electric motor 4 is possible.

The bridge modules 20 each include two semiconductor switches 44 and 46, which in the 2 are shown only schematically and as an example for the W phase. The bridge module 20 is connected on the one hand with a potential connection 48 to the supply line 12a and thus to the intermediate circuit voltage U _ZK . On the other hand, the bridge module 20 is contacted with a second potential connection 50 to the return line 12b and thus to the ground potential U _G . The respective phase end 22, 24, 26 of phase U, V, W can be connected via the semiconductor switches 44, 46 either to the intermediate circuit voltage U _ZK or to the ground potential U _G . If the semiconductor switch 44 is closed (conductive) and the semiconductor switch 46 is opened (nonconductive, blocking), then the phase end 22, 24, 26 is connected to the potential of the intermediate circuit voltage U _ZK . Correspondingly, when the semiconductor switch 44 opens and the semiconductor switch 46 closes, the phase U, V, W is in contact with the ground potential U _G . This makes it possible to apply two different voltage levels to each phase winding U, V, W using PWM control.

In the 3 a single bridge module 20 is shown in simplified form. In this exemplary embodiment, the semiconductor switches 44 and 46 are implemented, for example, as MOSFETs (metal-oxide semiconductor field-effect transistors), which each switch clocked by means of PWM control between an on state and an off state. For this purpose, the respective gate connections are routed to corresponding control voltage inputs 52, 54, by means of which the signals of the PWM control of the controller 42 are transmitted.

The 4 shows an equivalent circuit diagram for the current source 8. During operation, the battery 10 generates a battery power P _Bat ( 5 ), A battery voltage U _Bat and a corresponding battery current I _Bat for operating the power converter 6. In the 4 the internal resistance of the battery 10 is shown as an ohmic resistance 56 and an inherent inductance of the battery 10 as an inductance 58 . A shunt resistor 60, across which the intermediate circuit voltage U _ZK drops, is connected in the return line 12b.

Depending on the switching states of the (power) semiconductor switches 44, 46, the phase current Iu, Iv, Iw flows through the shunt resistor 60. The voltage drop across the shunt resistor 60 is amplified and evaluated. The phase currents Iu, Iv, Iw are reconstructed by the controller 42 using measurements and the state of knowledge of the switching states of the semiconductor switches 44, 46. Other measurement methods can also be used to determine the motor currents (e.g. direct phase current measurement). The phase voltages Uu, Uv, Uw and the phase currents Iu, Iv, Iw are available to the controller 42 together with the measured and/or calculated phase voltages Uu, Uv, Uw.

The controller 42 is provided for the field-oriented regulation of the electric motor 4 and is suitable and set up for this. The controller 42 has a control unit that is not shown in detail.

The following is based on the 5 an inventive method for operating the electrical machine 2 is explained in more detail.

The electric motor 4 is designed without sensors, so there is no position sensor for detecting a rotor position or position. This means that the position detection or position determination for the field-oriented control takes place without sensors. The method according to the invention is intended for operation at low speeds or when starting from a standstill, in which case there is insufficient voltage 40 available due to the counter-EMF.

In the course of the field-oriented regulation, the electric motor 4 is regulated in a rotor-fixed dq coordinate system. This means that the three-phase operating state variables of the electric motor 4 or stator, in particular the phase currents I _U , I _V , I _W and/or the phase voltages Uu, Uv, Uw are converted into a two-axis coordinate system by means of a dq or Park transformation and regulated there become. In this case, the control or manipulated variable of the regulation is correspondingly inverse-transformed and used, for example, for the pulse-width-modulated activation of the bridge circuit 16 .

The method is started with a method start 62, for example when the electric motor 4 is started up from a standstill. At the beginning of the method, the rotor position or orientation is essentially unknown.

According to the method, the orientation for the d-axis or the d-direction of the d-q coordinate system is therefore determined in a first method step 64 . In method step 64, the orientation of the d-axis is first estimated.

In a subsequent method step 66, both an alternating signal and a non-torque-forming first direct current signal are impressed on the estimated d-axis. The alternating signal is, for example, an alternating current or an alternating voltage, ie a signal with a predetermined or predeterminable signal frequency, for example 500 Hz (Hertz). The alternating signal and the first direct current signal are thus generated along the estimated d-direction. For this purpose, the alternating signal and the first direct current signal are added to the manipulated variable for the Id current, for example, before the inverse transformation into the three-phase system for driving the bridge circuit 16 takes place. Alternatively, the alternating signal and the first direct current signal can, for example, also be added to the command variable or the setpoint value of the Id current.

The introduction of an additional, preferably non-torque-generating, (direct) current brings the electric motor into (partial) saturation. This saturation results in a reduction in inductance in that direction
As a result, the Ld inductance of the electric motor 4 is reduced. This increases the inductance difference between the inductances Ld and Lq. This increased difference in inductance is then used for sensorless position detection of the rotor position.

For this purpose, in a method step 68 the resulting response of the electric motor 4 is recorded along the (estimated) q-axis of the d-q coordinate system. In this case, a changed current along the q-axis results in particular as a response or reaction. To detect the q current, the phase currents Iu, Iv, Iw detected by the shunt resistor 60 are converted to the d-q coordinate system, and the change in the amplitude of the Iq current is monitored.

A deviation between the estimated d-axis and the actual d-axis is determined in a method step 70 on the basis of the answer or reaction. In a method step 72, this deviation is used to correct the orientation of the estimated d-axis. This is done, for example, as part of a regulation. The orientation of the d-axis is the controlled variable, with the deviation representing the control difference. In method step 66, the orientation of the d-axis is re-determined or re-estimated based on the deviation, so that an iterative or successive approximation to the actual orientation of the d-q coordinate system, and thus a position detection of the rotor position, is realized. The method is ended, for example, when a sufficiently high engine speed is reached with a sufficient back EMF.

The direct current signal introduced in method step 66 in the d-direction has a field-enhancing or field-weakening effect, for example. In particular, depending on an operating situation of the electric motor 4, a field-enhancing or field-weakening direct current is impressed. Optionally, the additional torque-generating component can be compensated here. This is particularly advantageous at the moment of changing from field-enhancing to field-weakening and vice versa.

In a possible embodiment, in method step 66, a second direct current is impressed along the q-axis. In this case, the second direct current has a particularly field-weakening effect in the q-direction. This avoids unwanted torque due to reluctance.

The claimed invention is not limited to the embodiments described above. Rather, other variants of the invention can also be derived from this by the person skilled in the art within the scope of the disclosed claims without departing from the subject matter of the claimed invention. In particular, all of the individual features described in connection with the various exemplary embodiments can also be combined in other ways within the scope of the disclosed claims, without departing from the subject matter of the claimed invention.

Reference List

2

electric machine

4

electric motor

6

Power converters/inverters

8th

power source

10

energy storage

12

intermediate circuit

12a

direction

12b

return line

14

intermediate circuit capacitor

16

bridge circuit

18

star connection

20

bridge module

22,24,26

phase end

28

star point

30

inductance

32

Resistance

34, 36, 38

voltage drop

40

Tension

42

controllers

44, 46

semiconductor switch

48, 50

potential connection

52, 54

control voltage input

56

Resistance

58

inductance

60

shunt resistance

72

start of proceedings

64, 66, 68, 70, 72

process step

AND MANY MORE

phase/phase winding

IU, IV, IW

phase current/output current

ie

input current

UCC

intermediate circuit voltage

UG

earth potential

IBat

battery power

UBat

battery voltage

Claims (6)

Method for operating an electrical machine (2), having a brushless electric motor (4), which is controlled by means of field-oriented control in a d-q coordinate system, - where the orientation is determined for a d-axis of the d-q coordinate system, - wherein a first direct current signal is impressed on the determined d-axis, which increases an inductance difference between the motor inductances, - wherein a deviation or a direction of deviation between the determined d-axis and the actual d-axis is determined on the basis of the increased inductance difference, and - wherein the orientation of the determined d-axis is set and/or regulated on the basis of the deviation or direction of deviation. procedure after claim 1 , characterized in that a field-amplifying or field-weakening first DC signal is impressed. procedure after claim 1 or 2 , characterized in that depending on an operating situation of the electric motor (4) a field-amplifying or field-weakening first DC signal is impressed. Procedure according to one of Claims 1 until 3 , characterized in that a second direct current signal is impressed along the q-axis. Electrical machine (2) for a motor vehicle, having a brushless electric motor (4) and an energy store (10) and an inverter (6) connected between them, which is controlled or regulated by means of a control unit for field-oriented regulation, and a controller (42) for Carrying out a method according to one of Claims 1 until 4 . Software on a data carrier for carrying out a method according to one of Claims 1 until 4 , if the software runs on a computer.

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