Method for field-oriented current control of motor currents of an electric motor

Abstract

The invention relates to a method for field-oriented current control of motor currents (Id, Iq) of an electric motor, the motor voltage of which is limited by a maximum voltage (Us,max), using a field-weakening controller (9) set up to correct setpoint values of reference variables for the current control if a motor voltage that exceeds the maximum voltage (Us,max) would be required to control the motor currents (Id, Iq) to the setpoint values. In the method, a calibration value of a rotor position offset angle between a rotor of the electric motor and a position sensor system set up to determine a rotor position of the rotor is trained by way of calibration of the position sensor system and stored. Furthermore, a value of the rotor position offset angle used to determine the setpoint values during operation of the electric motor with a motor voltage that is at least approximately the maximum voltage (Us,max) is changed with respect to the calibration value by a change value (Δα) such that a motor voltage that exceeds the maximum voltage (Us,max) would be required to control the reference variables to the setpoint values.

Description

[0001] Description

[0002] Method for field-oriented current control of motor currents of an electric motor

[0003] The invention relates to a method for field-oriented current control of motor currents of an electric motor.

[0004] In field-oriented current control of an electric motor's motor currents, the variables used for control, such as motor currents and motor voltages, are referenced to a rotor-fixed coordinate system, i.e., a coordinate system rotating with the electric motor's rotor. Therefore, the rotor position of the motor is required with sufficient accuracy for control. Typically, a position sensor system is used to determine the rotor position.

[0005] To determine the rotor position using a position sensor system, knowledge of the rotor position offset angle between the electric motor rotor and the position sensor system is required. The rotor position offset angle is typically learned once using a calibration method, for example, for a reference motor. However, every calibration method for determining the rotor position offset angle has only a finite accuracy. Inaccuracies in the rotor position offset angle during field-oriented current control of an electric motor's currents can lead to a significant loss of performance and efficiency of the electric motor.

[0006] The invention is based on the object of specifying a method for field-oriented current control of motor currents of an electric motor, which in particular reduces a loss of power and efficiency due to an inaccuracy in the determination of the rotor position offset angle.

[0007] The object is achieved according to the invention by the features of claim 1.

[0008] Advantageous embodiments of the invention are the subject of the dependent claims. The method according to the invention relates to the field-oriented current control of motor currents of an electric motor whose motor voltage is limited by a maximum voltage, using a field-weakening controller configured to correct setpoints of reference variables for the current control if a motor voltage exceeding the maximum voltage would be required to regulate the motor currents to the setpoints. In the method, a calibration value of a rotor position offset angle between a rotor of the electric motor and a position sensor system configured to determine a rotor position of the rotor is first learned and stored by calibrating the position sensor system.When the electric motor is operated with a motor voltage that is at least approximately the maximum voltage, a value of the rotor position offset angle used to determine the setpoints is changed by a change value compared to the calibration value in such a way that a motor voltage that exceeds the maximum voltage would be required to control the reference variables to the setpoints.

[0009] The method according to the invention therefore uses a field weakening controller that automatically corrects setpoints of reference variables for current control if the setpoints cannot be realized because they require a motor voltage that exceeds the maximum voltage. According to the invention, this property of the field weakening controller is utilized when the electric motor is operating with a motor voltage that is at least approximately the maximum voltage. A value of the rotor position offset angle used to determine setpoints is specifically altered by a change value compared to the calibration value in such a way that regulating the reference variables to the setpoints would require a motor voltage that exceeds the maximum voltage. This activates the field weakening controller and leads to an automatic correction of the setpoints of the reference variables by the field weakening controller.By adjusting the setpoints, an efficient load point for the operation of the electric motor is ultimately achieved. To avoid disadvantages caused by adapting the rotor position offset angle value in the base speed range of the electric motor, adaptation is only used when the motor voltage modulation level, i.e., the ratio of the motor voltage to the maximum voltage, is at least approximately maximum.

[0010] In one embodiment of the invention, components of a current vector of the motor current in a d / q coordinate system for the motor current are used as reference variables. A d / q coordinate system is understood to be a rotor-fixed coordinate system with mutually perpendicular axes, which are commonly referred to as the d-axis and q-axis. The components of a current vector of the motor current in such a coordinate system are referred to as the d-component and q-component of the motor current.

[0011] In one embodiment of the invention, the setpoint values ​​of the reference variables are determined as a function of a required torque of the electric motor, a required speed of the electric motor, a rotor temperature of the rotor of the electric motor and / or the maximum voltage.

[0012] In a further embodiment of the invention, when the field weakening controller corrects the setpoints, a value of a maximum voltage utilization used to determine the setpoints, which indicates a maximum ratio of the motor voltage to the maximum voltage, is replaced by a value corresponding to a reduced maximum voltage utilization. In other words, the maximum voltage utilization is artificially reduced to effect a correction of the setpoints.

[0013] In a further embodiment of the invention, the change value for the rotor position offset angle corresponds to a tolerance accuracy of the calibration of the position sensor system. This adapts the change value for the rotor position offset angle to the accuracy of the calibration of the position sensor system.

[0014] In a further embodiment of the invention, the

[0015] Maximum voltage to a battery voltage provided by a battery for operating the electric motor and a selected modulation method for controlling electronic switches of a pulse-controlled inverter to realize the motor voltage. For example, the electric motor is the engine of an electric vehicle, and the battery is a rechargeable battery of the electric vehicle.

[0016] In a further embodiment of the invention, the maximum voltage is related to a d / q coordinate system for the motor voltage.

[0017] In a further embodiment of the invention, the field weakening controller is implemented as a software module. In particular, the invention can then be implemented purely via software and thus requires no additional hardware. The torque, power, and efficiency of the electric motor can thus be increased at no cost.

[0018] In a further embodiment of the invention, a correction of the calibration value of the rotor position offset angle is determined from the correction of the setpoint values ​​of the reference variables. For example, the correction of the calibration value of the rotor position offset angle is determined in such a way that the use of the corrected calibration value in determining the setpoint values ​​of the reference variables leads to an improvement in the efficiency of the electric motor compared to the use of the calibration value. The aforementioned embodiment of the invention thus aims at a correction of the calibration value of the rotor position offset angle itself and thus at an overall improved field-oriented current control of the motor currents of the electric motor.

[0019] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of exemplary embodiments, which are explained in more detail in conjunction with the drawings.

[0020] FIG 1 shows an MTPA curve and current vectors in two quadrants of a d / q coordinate system for the motor current of an electric motor, FIG 2 shows a block diagram of a field weakening controller,

[0021] FIG 3 Curves of fixed voltage utilization in two quadrants of a d / q coordinate system for the motor current of an electric motor.

[0022] Figures 1 to 3 illustrate an embodiment of the method according to the invention for field-oriented current control of motor currents Id, Iq of an electric motor whose motor voltage is limited by a maximum voltage lls.max. For example, the electric motor is a motor that is supplied with electrical energy from a battery, wherein the motor voltage of the electric motor is generated from a battery voltage of the battery by a pulse-controlled inverter. The pulse-controlled inverter has electronic switches that are controlled in such a way that the motor voltage (AC voltage) of the electric motor is generated from the battery voltage (DC voltage) of the battery. For example, the electronic switches are controlled in a pulse-width modulated manner. The maximum voltage lls.max of the motor voltage results from the battery voltage of the battery and the modulation method for controlling the electronic switches of the pulse-controlled inverter.For example, the electric motor is the engine of an electric vehicle and the battery is a rechargeable battery of the electric vehicle.

[0023] The reference variables of the current control of the motor current are a d-component Id and a q-component l q of the motor current in a d / q coordinate system rotating with the rotor of the electric motor. These command variables are determined as a function of the required torque of the electric motor, the required speed of the electric motor, the rotor temperature of the electric motor rotor, and the maximum voltage lls.max.

[0024] The manipulated variables of the current control of the motor current are a d-component of the motor voltage corresponding to the d-component Id of the motor current and a q-component l q the q-component of the motor voltage corresponding to the motor current in a d / q-coordinate system for the motor voltage.

[0025] The method according to the invention is carried out using a field weakening controller 9, which is implemented as a software module. The field weakening controller 9 is configured to correct setpoints for the motor currents Id, Iq of the current control if a motor voltage exceeding the maximum voltage lls.max would be required to control the motor currents Id, Iq to the setpoints.

[0026] In the method according to the invention, a calibration value of a rotor position offset angle between a rotor of the electric motor and a position sensor system, which is configured to determine a rotor position of the rotor, is first learned and stored once by calibrating the position sensor system.

[0027] The value of the rotor position offset angle is used in particular to determine the setpoints of the components Id, lq of the motor current.

[0028] According to the invention, a value of the rotor position offset angle used for determining the setpoint values ​​for Id, lq is changed by a change value Aa compared to the calibration value during operation of the electric motor with a motor voltage that is at least approximately the maximum voltage lls.max in such a way that a motor voltage that exceeds the maximum voltage lls.max would be required to regulate the components Id, lq of the motor current to the setpoint values.

[0029] Figure 1 (FIG 1 ) shows, by way of example, two quadrants of a d / q coordinate system for the motor current with the components Id, lq and an MTPA curve 1 (MTPA = Maximum Torque Per Ampere), at each of whose points a torque of the electric motor is realized with a minimum motor current. Apart from a range of small motor currents, the points of the MTPA curve 1 are also the points for which maximum voltage utilization VUijm of the motor voltage is achieved, i.e. a maximum ratio of the motor voltage to the maximum voltage lls.max. As an example, Figure 1 also shows, for each of the two quadrants of the d / q coordinate system shown, a current vector 3 for which the motor voltage approximately reaches the maximum voltage lls.max, an ideal current vector 5, which realizes a point on the MTPA curve 1, and a fictitious current vector 7, whose components would result as setpoints for the motor current components Id, lq for the calibration value of the rotor position offset angle changed by the change value Aa, instead of the components of the current vector 3. Figure 1 shows that the change value Aa, in particular the sign of this change value Aa, depends on the quadrant of the d / q coordinate system for the motor current.

[0030] Changing the rotor position offset angle value used to determine the setpoints for the Id, lq components by the change value Aa activates the field weakening controller 9, since the change value Aa is selected such that regulating the Id, lq components of the motor current to the setpoints would require a motor voltage that exceeds the maximum voltage lls.max. The field weakening controller 9 therefore automatically corrects the setpoints for the Id, lq components of the motor current.

[0031] Figure 2 (FIG 2) shows a block diagram of the field weakening controller 9. The input variables of the field weakening controller 9 are the maximum voltage lls.max, a required voltage Us and a maximum voltage utilization VUum of the motor voltage. The required voltage Us is a motor voltage that is necessary to generate a motor current that causes the required torque of the electric motor and the required speed of the electric motor as a function of the rotor temperature of the rotor of the electric motor and the maximum voltage Us.max. The output variable of the field weakening controller 9 is an (artificially) reduced maximum voltage utilization VUum,Adj. The field weakening controller 9 first subtracts the required voltage Us from the maximum voltage Us,max. The result of this subtraction is fed to an I-element 11 (integrator). The output value of the I-element 11 is subtracted from the maximum voltage utilization VUijm.The result of this subtraction is the reduced maximum voltage utilization VUum,Adj, which causes the correction of the setpoints for the components Id, lq of the motor current. Figure 3 (FIG 3) shows curves 13, 15 of fixed voltage utilization in the two quadrants of a d / q coordinate system for the motor current already shown in Figure 1. The points on curve 13 realize the maximum voltage utilization VUijm, and the points on curve 15 realize a voltage utilization VUum,Adj that is reduced compared to VllLim.

[0032] List of reference symbols

[0033] I MTPA curve

[0034] 3 current vector 5 ideal current vector

[0035] 7 fictitious current vector

[0036] 9 field weakening controller

[0037] II I-member

[0038] 13, 15 Curves of fixed voltage utilization Aa change value

[0039] Us need voltage

[0040] Us,max maximum voltage

[0041] VllLim maximum voltage utilization

[0042] VllLim.Adj reduced maximum voltage utilization

Claims

Patent claims 1. Method for field-oriented current control of motor currents (Id, lq) of an electric motor, the motor voltage of which is limited by a maximum voltage (lls.max), using a field weakening controller (9) which is designed to correct setpoints of reference variables for the current control if a motor voltage which exceeds the maximum voltage (lls.max) would be required to control the motor currents (Id, lq) to the setpoints, wherein - a calibration value of a rotor position offset angle between a rotor of the electric motor and a position sensor system, which is set up to determine a rotor position of the rotor, is learned and stored by calibrating the position sensor system, and - a value of the rotor position offset angle used to determine the setpoints is changed by a change value (Aa) compared to the calibration value when the electric motor is operating with a motor voltage that is at least approximately the maximum voltage (lls.max) in such a way that a motor voltage that exceeds the maximum voltage (lls.max) would be required to control the reference variables to the setpoints.

2. Method according to claim 1, wherein components (Id, lq) of a current vector of the motor current in a d / q coordinate system for the motor current are used as reference variables.

3. Method according to claim 1 or 2, wherein the setpoint values ​​of the reference variables are determined as a function of a required torque of the electric motor, a required speed of the electric motor, a rotor temperature of the rotor of the electric motor and / or the maximum voltage (lls.max).

4. Method according to one of the preceding claims, wherein, during the correction of the setpoint values ​​by the field weakening controller (9), a value of a maximum voltage utilization (VUijm) used in determining the setpoint values, which represents a maximum ratio of the motor voltage to the maximum voltage (lls.max) is replaced by a value corresponding to a reduced maximum voltage utilization (VUum,Adj).

5. Method according to one of the preceding claims, wherein the change value (Aa) for the rotor position offset angle corresponds to a tolerance accuracy of the calibration of the position sensor system.

6. Method according to one of the preceding claims, wherein the maximum voltage (lls.max) corresponds to a battery voltage provided by a battery for operating the electric motor and a selected modulation method for controlling electronic switches of a pulse-controlled inverter for realizing the motor voltage.

7. Method according to one of the preceding claims, wherein the maximum voltage (lls.max) is related to a d / q coordinate system for the motor voltage.

8. Method according to one of the preceding claims, wherein the field weakening controller (9) is implemented as a software module.

9. Method according to one of the preceding claims, wherein a correction of the calibration value of the rotor position offset angle is determined from the correction of setpoint values ​​of the reference variables.

10. The method according to claim 9, wherein the correction of the calibration value of the rotor position offset angle is determined such that the use of the corrected calibration value in determining setpoints of the reference variables leads to an improvement in the efficiency of the electric motor compared to the use of the calibration value.

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