Control method for position sensorless operation of a drive unit, drive unit and vehicle
Patent Information
- Application Number
- DE102023127451
- Authority / Receiving Office
- DE · DE
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-10-09
- Publication Date
- 2025-04-10
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
The invention relates to a control method for the position-sensor-free operation of a drive unit, a drive unit and a vehicle.For a proper control of an electric motor, for example a synchronous machine, the angular position of the rotor is decisive. Therefore, a position sensor fixed to the shaft is generally used. However, in order to reduce the system costs, to save the required installation space for the sensor and to improve the reliability of the control of the electric motor, the position-sensor-free (position-sensor-free) control is becoming increasingly important in automotive applications.In the medium and high speed range of corresponding electric motors, model-based methods are one of the most frequently used methods for estimating the rotor position. A model-based observer generally consists of a state observer for estimating the position-related system states, e.g. back electromotive forces (back EMFs) and a speed and position estimator. Generally, there are various state monitors based on the flux linkages and / or current equations of the underlying electric motor, such as a Luenberger observer, a sliding regime observer, an extended Kalman filter, and sliding horizon estimates. The estimation of the rotational speed and the position (angular position) of the rotor is usually carried out by a phase-locked loop (PLL).In previous approaches, the magnetic flux is assumed to be linear with the phase currents occurring in the electric motor. In addition, magnetic saturation is typically neglected. However, in externally excited synchronous machines (also: electrically excited synchronous machines, EESM) used in automotive applications, the flux linkages are non-linear due to the higher magnetic density, magnetic saturation and cross coupling.In a non-linear flux electric motor, the inductances used in the observer are normally stored in look-up tables (LUTs) and read out according to the estimated (d,q) axis currents. However, in the event of deviations or due to errors in the position estimate of the rotor relative to the stator, the estimated (d,q) axis currents are likewise distorted. The estimated distorted values of the (d,q) axis currents continue to propagate and also cause errors in the inductances determined on the basis of the conversion tables, which in turn leads to further inaccuracies and adversely affects the position estimate (angular position) of the rotor. This limits the achievable precision of known control methods, in particular if non-linearities of the dependence between the magnetic flux and the phase currents cannot be underturned on account of the machine type.The object of the invention is to eliminate or at least reduce the disadvantages of the prior art. In particular, it is desirable to provide a control method with which increased precision of the control (increased control quality) of an electric motor is made possible.The object is achieved by the subject matters of the independent claims. Advantageous embodiments are specified in the dependent patent claims and the following description, each of which can represent aspects of the invention individually or in (sub)combination. Some features are explained with respect to methods and others with respect to devices. However, the aspects are to be transferred respectively in mutually corresponding fashion.According to one aspect, a control method for the position-sensor-free operation of a drive unit is provided. The drive unit comprises a converter and an electric motor assigned to the converter. The inverter includes a control device. The control method has at least the steps:A reference torque to be provided by the electric motor is received by the control device.A reference rotational speed of a rotor of the electric motor is determined by the control device based at least on the reference torque.A reference current of a stator of the electric motor is determined by the control device based at least on the reference torque and the reference rotational speed.A reference value of a counter-voltage induced by a counter-electromotive force is determined by the control device based at least on the received reference torque and the determined reference current.An inductance deviation with respect to an estimation inductance determined during the current control of the converter is determined by the control device based on a difference of the reference value of the induced back voltage and an estimated value of the induced back voltage.The inductance deviation is taken into account in a current regulation of the converter by a current regulator of the control device.The invention uses the approach that the counter voltage induced during operation of the electric motor can be determined in a reverse direction on the basis of the setpoint torque (reference torque) to be provided by the electric motor. On the basis of the induced countervoltage to be expected, the inductance actually to be expected can then be determined, even in the case of a nonlinear relationship between the inductance and the phase currents arising in the electric motor. The inductance to be expected is thus determined on the basis of a reverse approach-starting from the target of the reference torque to be ensured.The expected induced back voltage may be related to the induced back voltage estimate determined in a "usual" manner using a forward approach. As a result, an additional control mechanism can be provided which utilizes the deviation of these values in order to equalize the differently determined values of the counter voltage by a corresponding current control in subsequent control intervals. This allows the precision of the current control to be improved without the need for an angular position sensor or position sensor for detecting the rotor position relative to the stator. The increase in precision can also be considered an increase in the control quality of the control of the electric motor. In effect, the power losses caused during the regulation of the electric motor can thereby be reduced. In addition, the required installation space can be reduced by saving the position sensor and a weight saving can be achieved. Corresponding devices, for example vehicles, which have such a drive unit, can then have a longer range with the same amount of energy.In addition, sensors such as position sensors can always only achieve finite accuracy and also have the finite risk of a defect or failure. In this case, redundant sensors must then be stored, as a result of which the installation space is additionally reduced. The finite accuracy of the position sensors also impair the achievable precision of the control method for operating the electric motor. In the present case, a deterministic approach is presented which is fundamentally unlimited in the precision that can be achieved. Therefore, the robustness of the control method for operating the drive unit is increased compared to previous position sensor-free control methods and also compared to position sensor-based approaches.The electric motor can preferably comprise a separately excited synchronous machine (EESM). In particular in the case of EESMs, the relationship between the magnetic flux and the phase currents arising in the EESM is nonlinear on account of the higher magnetic density. In addition, magnetic saturation in EESMs cannot be neglected. The control method can then ensure a high, previously unachieved control precision, in particular for EESMs.Optionally, the reference torque may be based on a torque request to be operated by the electric motor. For example, the torque request can be made by a superordinate control device, for example a driving control system. By way of example, the torque request may be based on a driver pedal position or driving functionality exerted by the driving control system.In some embodiments, the inductance deviation is used within the current regulation of the inverter to correct an estimate of an angular position of the rotor of the electric motor. This means that the "conventionally" determined value of the angular position of the rotor relative to the stator of the electric motor can be corrected on the basis of the control method. As a result, the error propagation outlined at the beginning is broken through or at least reduced. Thus, the corrected angular position can be used to determine, on the basis of conversion tables, a more appropriate value of the (d,q) axis currents with respect to the real situation and thus also of the estimation inductance.Optionally, the current controller comprises a state estimator and a position and speed estimator. The state estimator is configured to determine the estimate value of the induced counter voltage based on position-dependent system states of the drive unit determined by the state estimator. The position-dependent system states have an influence on the (d,q) axis currents. The estimation inductance is in turn dependent on the axis currents, which in turn has an influence on the induced counter voltage. The state estimator can take these relationships into account, for example on the basis of corresponding conversion tables.Optionally, the conversion tables can also be taken into account in a control stage which is separate from the state estimator.In some embodiments, the state estimator may determine an estimate of the induced back voltage based on the estimate inductance. In this case, corresponding conversion tables can be taken into account by the state estimator.The state estimator is preferably configured to determine the estimate value of the induced counter voltage on the basis of a nonlinear relationship between the magnetic flux and a phase current of the electric motor. The state estimator is then configured in particular for the regulation of EESMs.In some embodiments, the state estimator receives as input variables at least one estimated rotational speed of the rotor of the electric motor, which estimated rotational speed is ascertained by the position and rotational speed estimator, the estimated inductance, phase voltages and phase currents of current phases of the electric motor.As a result, the determination of the estimated value of the induced countervoltage can be carried out with particularly high precision.Optionally, the inductance deviation is determined based on a proportional / integral (PI) regulator. As a result, the amplitude of the manipulated variable, which is determined on the basis of the inductance deviation, can be matched to the respective inductance deviation. As a result, the adaptation of the estimate of the induced back voltage to the reference value of the induced back voltage is accelerated. Any deviations can thus be compensated within shorter time intervals.The PI controller can preferably also have a differential element and thus form a PID controller.In some embodiments, the inductance deviation is taken into account in the state estimator. This increases the precision in determining the estimate of the induced back voltage. Thus, the inductance deviation for subsequent control intervals can be reduced.Optionally, the regulation method is designed as a computer-implemented method. This means that the essential control mechanisms can be executed with the aid of one or more data processing devices.According to a further aspect, the disclosure also relates to a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to execute the control method as described herein. The advantages achieved by the control method described herein are also achieved in a corresponding manner by the computer program product.In an additional aspect, the disclosure also relates to a computer readable storage medium comprising instructions which, when the program is executed by a computer, cause the computer to execute the control method as described herein. The advantages achieved by the control method described herein are also achieved in a corresponding manner by the computer-readable storage medium.According to a further aspect, a drive unit is also provided. The drive unit is configured for a vehicle. The drive unit has a converter and an electric motor assigned to the converter. The inverter includes a control device. The control device is configured to execute the control method as described hereinbefore. The advantages achieved by the control method described herein are also achieved in a corresponding manner by the drive unit.The control device preferably comprises a current regulator with a state estimator. The state estimator is designed in the manner of a Luenberger observer and takes into account a non-linear relationship between a magnetic flux and a phase current of the electric motor. As a result, the state estimator is advantageously configured in particular for use with regard to externally excited synchronous machines (EESMs). Thus, a high control quality can be achieved by the drive unit for EESMs, i.e. a high precision in the current control. As a result, the power losses caused are reduced compared to previous approaches.According to a further aspect, a vehicle is also provided. The vehicle has, in particular, a drive unit as described above. Thereby, the operation efficiency of the vehicle can be increased. On the one hand, installation space is saved since no position sensor is required. In addition, the robustness of the vehicle control can be increased since a position sensor always has tolerances compared to a deterministic control method, which tolerances reduce the control quality. In addition, the control method cannot be influenced by a defective position sensor. Furthermore, the sensor saving leads to a weight reduction. The weight reduction and / or the reduced power loss ensured by the control method has the result that the vehicle can also have a longer range with the same amount of energy.Optionally, the vehicle may be a motor vehicle. For the purposes of the present invention, vehicles (motor vehicles) can comprise, in particular, land vehicles having an electric machine, specifically, inter alia, tricycles, trikes, quads, off-road and road vehicles such as passenger cars, buses, trucks, tractors and other commercial vehicles. The vehicles may preferably have at least one electric machine serving for the propulsion of the vehicle. Vehicles may be manned or unmanned. In addition to pure electric vehicles (BEV), plug-in hybrids (PHEV) and fuel cell vehicles (FCEV) may also be included.Alternatively, motor vehicles can also comprise vehicles with an internal combustion engine which have at least one drive unit as described above.The invention and further advantageous embodiments and developments thereof are described and explained in more detail below with reference to the examples illustrated in the drawings. The features to be gathered from the description and the drawings can be used according to the invention individually or together in any combination. The following are shown:FIG. 1 shows a schematic illustration of a drive unit according to the invention having a converter and an electric motor,FIG. 2 shows schematic representations of parts of the control circuit for operating the drive unit according to the invention,FIG. 3 shows a schematic illustration of the control method according to the invention for operating the drive unit, andFIG. 4 shows a schematic illustration of a vehicle according to the invention having a drive unit.All features disclosed below with respect to the embodiments and / or the accompanying figures may be combined alone or in any sub-combination with features of the aspects of the present disclosure, including features of preferred embodiments, provided the resulting combination of features is appropriate to a person skilled in the art.FIG. 1 shows a schematic illustration of a drive unit 8 according to the invention having a converter 10 and an electric motor 12.The electric motor 12 is configured here as a separately excited synchronous motor.According to this embodiment, the converter 10 comprises a B6 bridge 14 with three half bridges 16.Each half bridge 16 comprises in the present case a first power switch 18, which is designed here in the form of a transistor (n-channel MOSFET) and acts as a high-side switch, and a second power switch 20, which is likewise designed in the form of a transistor (likewise n-channel MOSFET) and acts as a low-side switch. Between the first power switch 18 and the second power switch 20, each half bridge 16 comprises a center tap 22 for providing a phase voltage U, V, W for the electric motor 12, by means of which a phase current is driven or is set in each case (for example based on the machine parameters of the electric motor 12).The three half bridges 16 apply three corresponding phase voltages to the electric motor 12, U, V and W. However, other topologies, for example a six-phase electric motor 12, are likewise possible, which then require corresponding modifications of the converter 10.The respective half bridges 16 are coupled via lines 24, for example a busbar structure, to a DC power source 26, for example a high-voltage accumulator, the electrical energy of which is converted into kinetic energy by means of the electric motor 12. The electric motor 12 can serve, for example, for driving a vehicle. In this case, a high-voltage HV of 800 V can be provided.Each power switch 18, 20 is usually assigned a driver circuit 28, which can also be referred to as a gate driver. The respective driver circuit 28 controls the associated power switch 18, 20.Depending on the switching positions of the power switches 18, 20, corresponding commutation cells are formed in the converter 10 when the high-voltage is applied.In addition, the inverter 10 includes a controller 30 coupled to the driver circuits 28. For reasons of better clarity, the respective connection of the control device 30 only to the driver circuits 28 of the first half bridge 16 is shown continuously. The other connections between the control device 30 and the driver circuits 28 are merely indicated.The driving circuits 28 receive driving signals from the controller 30 to control the switching positions of the power switches 18, 20.The control device 30 is configured to provide corresponding (digital) switching signals indirectly for the power switches 18, 20, which are transmitted to the driver circuits 28, which generate the drive signals for the power switches 18, 20 on the basis of the switching signals. Based on the received switching signals, the driver circuits 28 provide control voltages to affect the switching positions of the power switches 18, 20.The converter 10 comprises output current rails 32, which are coupled on the one hand to the center taps 22 of the half bridges 16 and on the other hand to the electric motor 12. The electric powers are output from the converter 10 to the electric motor 12 by means of the output current rails 32.In the embodiment shown, the drive unit 8 includes phase current sensors 34 disposed in the output current rails 32. The phase current sensors 34 detect the phase currents occurring in each case as a result of the output phase voltages U, V and W, that is to say the actual values of the phase currents, and transmit the corresponding values to the control device 30. In particular, the control device 30 can determine how to adapt a duty cycle of a control signal for the circuit breaker 18, 20 as required for a subsequent control interval, so that the actual phase current can be adapted to the desired phase current.The setpoint phase current is determined by the control device 30 on the basis of a setpoint torque 36 which the control device 30 receives at an input, for example from a higher-order driving control system, in order to ensure specific driving functionalities. The desired torque 36 represents a torque command to be provided by the electric motor 12 at an output. The torque specification can depend, for example, on a pedal position of the driver.In an alternative, the control device 30 can also receive a setpoint specification with respect to the phase current, i.e. a setpoint phase current.On the basis of a current regulator 38 of the control device, it is then possible to determine, on the basis of the phase voltages detected by means of the phase current sensors 34, with consideration of the rotor position, how to adapt the switching states of the power switches 18, 20 in order that the setpoint torque 36 can be provided at the output of the electric motor 12.As a result, the current regulator 38 determines a control variable which is transmitted to the pulse width modulator 40 (PWM unit), which, on the basis of the received control variable, adjusts the output digital switching signals for the driver circuits 28 in order to ensure an adaptation of the actual phase current to the desired phase current.FIG. 2 shows schematic representations 42 of parts of the control loop for operating the drive unit 8 according to the invention.The illustration 42 shows the basic structure of the underlying control loop 44. the control loop 44 is set up in the control device 30, and in particular in the current regulator 38 thereof.At an input, the control circuit 44 receives the torque specification (setpoint torque 36), which is denoted here by m m,ref the phase voltages u dc output by the converter 10, and the estimated value of the rotational speed ω̂ p of the electric motor 12 from the preceding control interval.On the basis of conversion tables 46, a setpoint specification for the phase current to be achieved is determined therefrom.A current regulating unit 47 is then used to determine corresponding setpoint specifications for the phase voltages on the basis of the phase current to be achieved, which specifications are required in order for the phase current to be achieved to be established in the electric motor 12.For this determination, the current control unit 47 additionally receives the estimates of the inductance and the phase current that are adjusted taking into account the intrinsic system parameters.The estimated values are transformed into corresponding coordinate systems based on corresponding Park transformations 48 dqe→αβe,αβe→abce, applied to the modeled properties of pulse width modulator 40, converter 10 and electric motor 12 and then transformed back. The Park transforms are additionally used to determine an estimate of the angular position of the rotor φ̂ p.As a result, the estimated value of the phase current can be determined. On the basis of further conversion tables 50, the estimated value of the inductance can be determined therefrom.The control circuit 44 has a state estimator 52. The state estimator 52 receives the estimated value of the inductance, the transformed target specifications of the phase voltages and the phase current resulting taking into account the system parametersThe state estimator 52 determines therefrom the position-dependent system states of the drive unit 8 and in particular an estimated value for the induced countervoltage resulting from the inductance on the basis of the system states.The control circuit 44 has a feedback with respect to the determined estimated values of the rotational speed ω̂ p of the electric motor 12 and the angular position of the rotor φ̂ p to the state estimator 52.It is therefore immediately apparent that an incorrectly determined value of the angular position of the rotor has a direct influence on the determination of the estimates of the inductance and the induced countervoltage, which in turn propagates in the determination of the angular position.This effect has a particularly pronounced effect if there is a non-linear dependence between the magnetic flux within the electric motor 12 and the phase currents arising therein.Therefore, plot 56 shows a compensation mechanism 58 for the deviation between the induced back voltage reference value and the induced back voltage estimateThe compensation mechanism 58 is explained in more detail on the basis of the schematic illustration, shown in FIG. 3, of the control method 70 according to the invention for operating the drive unit 8.The control method 70 first comprises the step 72, in which a reference torque m m,ref to be provided by the electric motor 12 is received by the control device 30.In the subsequent step 74 of the control method 70, a reference rotational speed ω p,ref of a rotor of the electric motor 12 is determined by the control device 30 on the basis of at least the reference torque m m,ref. Generally, the relationship between the rotational speed of the rotor of the electric motor 12 and the torque provided at the output of the electric motor 12 is known. On the basis of this relationship, the required rotational speed for ensuring the reference torque m m,ref can be determined.In the further step 76 of the control method 70, a reference current of a stator of the electric motor 12 is then determined by the control device 30 on the basis of at least the reference torque m m,ref and the reference rotational speed ω p,ref. In this case, a forward regulator with an optimum value regulating function can be used. Alternatively or cumulatively, conversion tables can optionally also be used for determining the reference current.In the subsequent step 78 of the control method 70, a reference value of a countervoltage induced by a counterelectromotive force can then be determined by the control device 30 on the basis of at least the received reference torque m m,ref and the determined reference current.The control method 70 takes advantage here of the fact that the torque m m output by the electric motor 12 (actually) can be described as follows:In this case, n p describes the number of poles and describe the absolute inductances with respect to the phase currents in accordance with the (d,q) axis system. describes the absolute mutual inductance between the stator and the externally excited rotor. and describe the stator currents in accordance with the (d,q) axis system and describes the rotor current.The curved bracket in the above figure indicates that the corresponding term indicates the magnetic flux ψ active "active" at a certain time.The counter electromotive force induced voltage can be expressed by utilizing the principle of active flux as:Here, φ p describes the angular position of the rotor relative to the stator of the electric motor 12.The absolute value of the countervoltage induced by the counterelectromotive force is given as:From the different expressions for the magnetic flux ψ active, "active" at a certain point in time, the absolute value of the reference value of the counter-voltage induced by the counter-electromotive force can be determined as:Knowing the received reference torque m m,ref( step 72) and the reference speed ω p,ref( step 74) and the reference current determined based thereon (step 76), therefore, the absolute value of the reference value of the induced back voltage can be determined (step 78).In the compensation mechanism 58, this is ensured by the counter-voltage element 60, which for this purpose receives the reference torque m m,ref and at least the reference current as input variables.The absolute value of the reference value of the countervoltage induced by the counterelectromotive force is then transmitted to the comparator 62.Therefore, in the subsequent step 80 of the control method 70, an inductance deviation with respect to an estimation inductance determined during the current control of the converter 10 can be determined by the control device 30 on the basis of a difference of the reference value of the induced back voltage and an estimated value of the induced back voltage.In the steady state, the median of the induced countervoltage is given as:Here, J denotes the system variables of the drive unit 8 comprising the converter 10 and the electric motor 12 in connection with the Luenberger observer of the control circuit 44 used here.On the basis of the median of the induced countervoltage, the absolute error of the inductance is proportional to the counterelectromotive force and results in: the following considerations result from this. If it holds, the following results for the absolute error of the counter electromotive force:This means that the difference between the absolute value of the estimate of the induced back voltage and the absolute value of the reference value of the induced back voltage is then negative.On the other hand, if it is determined that the absolute value of the counter electromotive force is the difference between the absolute value of the counter induced voltage estimation value and the absolute value of the counter induced voltage reference value is positive.In this case, the conditions for the absolute counter electromotive force error are reversed accordingly.As a result, it is immediately apparent that a necessary stability criterion can be fulfilled. As a result, a controller, such as a proportional / integral (PI) controller, may be used to estimate the inductance offset in step 80 as follows:Here, k p and k i denote the coupling parameters of the proportional part and the integral part of the PI controller.In the compensation mechanism 58, the comparison element 62 uses this relationship. In addition to the absolute value of the reference value of the countervoltage induced by the counterelectromotive force, it also receives from the state estimator 52 the estimate value of the induced countervoltage On the basis of these variables, the inductance deviation is then determined by the comparison element 62, as explained above.The control method 70 can be further developed in that in step 80 position-dependent system states are optionally taken into account, for example on the basis of the state estimator 52.The inductance deviation thus determined is fed back at least to the state estimator 52. Consequently, the control method 70 also comprises the step 84 in which the inductance deviation is taken into account in the current control of the converter 10 by a current regulator 38 of the control device 30. Since the state estimator 52 determines corresponding variables, as explained with reference to the control loop 44, the precision of the current control by means of the current regulator 38 for the electric motor 12 is improved.According to optional step 86 of control method 70, the estimated value of the angular position of the rotor relative to the stator of electric motor 12 may be corrected on the basis of the inductance deviation received from comparator 62, and thus correspond more precisely to the actual angular position. In other words, deviations can thereby be compensated at least proportionally, so that the power losses are reduced. The control method 70 is applicable in particular to electric motors 12 which have a non-linear relationship between the magnetic flux and the phase currents arising in the electric motor 12 and in which the magnetic saturation is not negligible.The control method 70 may be used to improve robustness of the position sensorless control, which may save cost for a position sensor and its cable.This creates a current control that manages without a position sensor for detecting the angular position of the rotor with respect to the stator of the electric motor 12. Nevertheless, a high control quality can be achieved.FIG. 4 shows a schematic illustration of a vehicle 88 according to the invention with a drive unit 8.The vehicle 88 has wheels 90, which are driven in the present case by the electric motor 12 of the drive unit 8.In the present application, amounts and numbers may be referred to. Unless expressly stated, such amounts and numbers are not to be considered as limiting, but as examples of the possible amounts or numbers in connection with the present application. In this context, the term "plurality" may also be used in the present application to refer to a quantity or number. In this context, the term "plurality" means any number greater than one, e.g., two, three, four, five, etc. The terms "about", "about", "near", etc. mean plus or minus 5% of the stated value.
Claims
Control method (70) for the position-sensor-free operation of a drive unit (8) having an inverter (10) and an electric motor (12) assigned to the inverter (10), wherein the inverter (10) has a control device (30), wherein the control method (70) has at least the steps of: - receiving a reference torque to be provided by the electric motor (12) from the control device (30), - determining a reference rotational speed of a rotor of the electric motor (12) on the basis of at least the reference torque by the control device (30), - determining a reference current of a stator of the electric motor (12) on the basis of at least the reference torque and the reference rotational speed by the control device (30), - determining a reference value of a countervoltage induced by a counterelectromotive force on the basis of at least the received reference torque and the determined reference current by the control device (30), determining an inductance deviation with respect to an estimated inductance determined during the current control of the converter (10) based on a difference of the reference value of the induced counter voltage and an estimated value of the induced counter voltage by the control device (30), and taking the inductance deviation into account during a current control of the converter (10) by a current controller (38) of the control device (30).Control method (70) according to Claim 1, characterized in that the inductance deviation within the current control of the converter (10) is used to correct an estimated value of an angular position of the rotor of the electric motor (12).Control method (70) according to Claim 1 or 2, characterized in that the current regulator (38) has a state estimator (52) and a position and rotational speed estimator (54), wherein the state estimator (52) is configured to determine the estimate value of the induced countervoltage on the basis of position-dependent system states of the drive unit (8) determined by the state estimator (52).Control method (70) according to Claim 4, characterized in that the state estimator (52) is configured to determine the estimate value of the induced countervoltage on the basis of a nonlinear relationship between the magnetic flux and a phase current of the electric motor (12).Control method (70) according to Claim 3 or 4, characterized in that the state estimator (52) receives as input variables at least one estimated rotational speed of the rotor determined by the position and rotational speed estimator, the estimated inductance, phase voltages and phase currents of current phases of the electric motor (12).Control method (70) according to one of the preceding claims, characterized in that the inductance deviation is determined on the basis of a proportional / integral regulator.Control method (70) according to one of Claims 3 to 6, characterized in that the inductance deviation is taken into account in the state estimator (52).Drive unit (8) for a vehicle (88), wherein the drive unit (8) has an inverter (10) and an electric motor (12) assigned to the inverter (10), wherein the inverter (10) has a control device (30), and wherein the control device (30) is configured to execute the control method (70) according to one of Claims 1 to 7.Drive unit (8) according to Claim 8, characterized in that the control device (30) has a current regulator (38) with a state estimator (52) which is designed in the manner of a Luenberger observer and takes into account a non-linear relationship between a magnetic flux and a phase current of the electric motor (12).Vehicle (88) having a drive unit (8) according to Claim 8 or 9.