Method for field-directed current regulation of motor current of electric motor

Abstract

The invention relates to a method for the field-directed current regulation of a motor current (Id, Iq) of an electric motor, the motor voltage of which is defined by a maximum voltage (Us, max), using a field-weakening regulator (9) which is designed to regulate the motor current (Id, Iq) of the electric motor if it will be necessary to exceed the maximum voltage (Us, max). Max) for adjusting the motor current (Id, Iq) to a target value, correcting the target value of the command variable for the current adjustment. In the method, a calibration value of a rotor position offset angle between a rotor of the electric motor and a position sensor system is trained and stored by a calibration of the position sensor system, which is configured to determine a rotor position of the rotor. Furthermore, during operation of the electric motor at a motor voltage that is at least approximately the maximum voltage (Us, max), the value of the rotor position offset angle for determining the target value is varied with respect to the calibration value by a variation value ([delta] [alpha]) in such a way that a motor voltage that exceeds the maximum voltage (Us, max) will be required for adjusting the command variable to the target value.

Description

Field of the Invention

[0001] The present invention relates to a method for field-oriented current regulation of the motor current of an electric motor. Background Art

[0002] When performing field-oriented current regulation of the motor current of an electric motor, the regulating parameters, such as the motor current and the motor voltage, relate to a rotor-fixed coordinate system, that is, a coordinate system that rotates together with the rotor of the electric motor. Therefore, for regulation, a rotor position with sufficient accuracy of the rotor is required. Usually, a position sensor system is used to determine the rotor position. Summary of the Invention

[0003] In order to determine the rotor position using a position sensor system, it is necessary to know the rotor position offset angle between the rotor of the electric motor and the position sensor system. For example, for a reference motor, the rotor position offset angle is usually trained once by means of a calibration method. However, each calibration method for determining the rotor position offset angle only has limited accuracy. When performing field-oriented current regulation of the motor current of an electric motor, an error in the rotor position offset angle may lead to significant power losses and efficiency losses of the electric motor.

[0004] The object on which the present invention is based is to provide a method for field-oriented current regulation of the motor current of an electric motor, which method in particular reduces power losses and efficiency losses caused by errors in the determination of the rotor position offset angle.

[0005] This object is achieved according to the invention by the features of claim 1.

[0006] Advantageous designs of the present invention are the subject matter of the dependent claims.

[0007] The method according to the invention relates to field-oriented current regulation of the motor current of an electric motor in the use of a field weakening regulator, the motor voltage of which electric motor is limited by a maximum voltage, and this field weakening regulator is set up to correct the target value of the command variable for current regulation if a motor voltage exceeding the maximum voltage would be required to regulate the motor current to a target value. In the method, first, the calibration value of the rotor position offset angle between the rotor of the electric motor and the position sensor system is trained and stored by calibrating the position sensor system, which position sensor system is set up to determine the rotor position of the rotor. During operation of the electric motor with a motor voltage that is at least approximately the maximum voltage, the value for determining the target value of the rotor position offset angle is changed relative to the calibration value by a varying value such that a motor voltage exceeding the maximum voltage would be required to regulate the command variable to the target value.

[0008] The method according to the invention thus utilizes a field weakening regulator which, if the target value cannot be achieved, automatically corrects the target value of the command variable for current regulation because it requires a motor voltage that exceeds the maximum voltage. According to the invention, this property of the field weakening regulator is utilized during operation of the electric motor with a motor voltage that is at least approximately the maximum voltage. Here, the value for determining the target value of the rotor position offset angle is changed in a targeted manner with a variable value relative to the calibration value such that a motor voltage that exceeds the maximum voltage will be required to regulate the command variable to the target value. This activates the field weakening regulator and causes an automatic correction of the target value of the command variable by the field weakening regulator. By tracking the target value, an efficiency-optimal load point for the operation of the electric motor is ultimately achieved. To avoid disadvantages due to the adaptation of the value of the rotor position offset angle in the base speed range of the electric motor, the adaptation is only used when the degree of modulation of the motor voltage, i.e., the ratio of the motor voltage to the maximum voltage, is at least approximately maximum.

[0009] In one design of the invention, the components of the current vector of the motor current in the d / q coordinate system for the motor current are used as the command variable. The d / q coordinate system is understood as a rotor-fixed coordinate system with axes perpendicular to each other, which are commonly referred to as the d-axis and the q-axis as usual. The components of the current vector of the motor current in such a coordinate system are called the d-component and the q-component of the motor current.

[0010] In one design of the invention, the target value of the command variable is determined based on the required torque of the electric motor, the required speed of the electric motor, the rotor temperature of the rotor of the electric motor, and / or the maximum voltage.

[0011] In a further design of the invention, when the target value is corrected by the field weakening regulator, the value used for determining the target value of the maximum voltage utilization rate is replaced by a value corresponding to a reduced maximum voltage utilization rate, and the maximum voltage utilization rate indicates the maximum ratio of the motor voltage to the maximum voltage. In other words, the maximum voltage utilization rate is artificially reduced in order to cause a correction of the target value.

[0012] In a further design of the invention, the variable value for the rotor position offset angle corresponds to the tolerance accuracy of the calibration of the position sensor system. Thereby, the variable value for the rotor position offset angle is adapted to the accuracy of the calibration of the position sensor system.

[0013] In a further design of the invention, the maximum voltage corresponds to the battery voltage provided by the battery for operating the electric motor and the selected modulation method for controlling the electronic switches of the pulse inverter to achieve the motor voltage. The electric motor is, for example, a motor of an electric vehicle, and the battery is a rechargeable battery of the electric vehicle.

[0014] In a further design variant of the invention, the maximum voltage relates to the d / q coordinate system for the motor voltage.

[0015] In a further design variant of the invention, the field weakening regulator is implemented as a software module. In particular, the invention can then be implemented purely by software and thus does not require additional hardware. As a result, the torque quality, power quality and efficiency quality of the electric motor can be increased without cost.

[0016] In a further design variant of the invention, a correction of the calibration value of the rotor position offset angle is determined from the correction of the target value of the command variable. For example, the correction of the calibration value of the rotor position offset angle is determined such that using the corrected calibration value instead of the calibration value when determining the target value of the command variable results in an improvement in the efficiency of the electric motor. The above-mentioned design variant of the invention thus aims to correct the calibration value of the rotor position offset angle itself and thus generally to improve the field-oriented current regulation of the motor current of the electric motor. Description of the Drawings

[0017] In connection with the following description of the embodiments, the above-described properties, features and advantages of the invention and the manner and means of how to implement them become clearer and more understandable. The embodiments are explained in more detail in conjunction with the drawings. Here:

[0018] Figure 1 show the MTPA curves and current vectors in two quadrants of the d / q coordinate system for the motor current of the electric motor,

[0019] Figure 2 show a block diagram of the field weakening regulator,

[0020] Figure 3 show the curves of a fixed voltage utilization in two quadrants of the d / q coordinate system for the motor current of the electric motor. Detailed Description of the Invention

[0021] Figures 1 to 3 Illustrates an embodiment of a method according to the invention for field-oriented current regulation of the motor currents I d 、I q of an electric motor, the motor voltage of the electric motor being defined by a maximum voltage U s,max . The electric motor is, for example, a motor supplied with electrical energy by a battery, wherein the motor voltage of the electric motor is generated from the battery voltage of the battery by means of a pulse inverter. The pulse inverter has electronic switches which are controlled such that the motor voltage (alternating voltage) of the electric motor is generated from the battery voltage (direct voltage) of the battery. The electronic switches are controlled, for example, by pulse width modulation. The maximum voltage U s,maxIt is obtained from the battery voltage of the battery and the modulation method for controlling the electronic switches of the pulse inverter. The electric motor is, for example, the motor of an electric vehicle, and the battery is a rechargeable battery of the electric vehicle.

[0022] The command variables for the current regulation of the motor current are the d-component I of the motor current in the d / q coordinate system that rotates with the rotor of the electric motor d and the q-component I q . These command variables are determined based on the required torque of the electric motor, the required rotational speed of the electric motor, the rotor temperature of the rotor of the electric motor, and the maximum voltage U s,max .

[0023] The adjustment parameters for the current regulation of the motor current are the d-component of the motor voltage corresponding to the d-component I of the motor current and the q-component of the motor voltage corresponding to the q-component I of the motor current in the d / q coordinate system for the motor voltage d of the motor current, and the q-component of the motor voltage corresponding to the q-component I q of the motor current.

[0024] The method according to the invention is carried out in the case of using the field weakening regulator 9 implemented as a software module. The field weakening regulator 9 is set up such that, if a motor voltage exceeding the maximum voltage U s,max is required to adjust the motor current I d , I q to the target value, the target values of the motor current I d , I q for the current regulation are corrected.

[0025] In the method according to the invention, first, the calibration value of the rotor position offset angle between the rotor of the electric motor and the position sensor system is trained and stored once by calibrating the position sensor system, and the position sensor system is set up to determine the rotor position of the rotor.

[0026] The value of the rotor position offset angle is particularly used to determine the target values of the components I d , I q of the motor current. According to the invention, during the operation of the electric motor with a motor voltage of at least approximately the maximum voltage U s,max , the value of the rotor position offset angle for determining I d , I q is changed with a variable value Δα relative to the calibration value such that a motor voltage exceeding the maximum voltage U s,max is required to adjust the components I d , I q of the motor current to the target value.

[0027] Figure 1 (Appendix Figure 1)Exemplarily shown is a d / q coordinate system for the motor current with components I d 、I q for two quadrants and the MTPA curve 1 (MTPA = Maximum Torque Per Ampere), at the points of which the torque of the electric motor is achieved with the minimum motor current respectively. Except for the range of small motor currents, the points of the MTPA curve 1 are also the points at which the maximum voltage utilization VU Lim of the motor voltage is reached, that is, the maximum ratio of the motor voltage to the maximum voltage U s,max is reached. In addition, Figure 1 exemplarily shown for the two illustrated quadrants of the d / q coordinate system are the current vector 3 in which the motor voltage is approximately the maximum voltage U s,max , the ideal current vector 5 that achieves the points on the MTPA curve 1, and the fictitious current vector 7. In the case of a calibration value that varies with a change value Δα of the rotor position offset angle, the components of the fictitious current vector will respectively replace the components of the current vector 3 and be generated as target values for the motor current components I d 、I q . Figure 1 It is shown that the change value Δα, in particular the sign of the change value Δα, depends on the quadrant of the d / q coordinate system for the motor current.

[0028] Changing the rotor position offset angle with the change value Δα to determine the values for the target values of the components I d 、I q will activate the field weakening regulator 9 because the change value Δα is selected such that a motor voltage exceeding the maximum voltage U s,max will be required to adjust the components I d 、I q of the motor current to the target values. Therefore, the field weakening regulator 9 automatically corrects the target values for the components I d 、I q of the motor current.

[0029] Figure 2 (Appendix Figure 2 ) shows a block diagram of the field weakening regulator 9. The input parameters of the field weakening regulator 9 are the maximum voltage U s,max , the required voltage U S and the maximum voltage utilization VU Lim of the motor voltage. The required voltage U S is the motor voltage required to generate the following motor current, which is based on the rotor temperature of the rotor of the electric motor and the maximum voltage U s,maxto cause the required torque of the electric motor and the required rotational speed of the electric motor. The output parameter of the field weakening regulator 9 is the (artificially) reduced maximum voltage utilization VU Lim,Adj . The field weakening regulator 9 first subtracts the required voltage U s,max from the maximum voltage U S . The result of the subtraction is supplied to the I element 11 (integral element). The output value of the I element 11 is subtracted from the maximum voltage utilization VU Lim . The result of this subtraction is the reduced maximum voltage utilization VU Lim,Adj , which causes a correction of the target values for the components I d 、I q of the motor current.

[0030] Figure 3 (Appendix Figure 3 ) shows the curves 13, 15 of the fixed voltage utilization in the two quadrants already shown in Figure 1 for the d / q coordinate system of the motor current. Here, the points on curve 13 achieve the maximum voltage utilization VU Lim , and the points on curve 15 achieve a voltage utilization VU Lim reduced with respect to VU Lim,Adj .

[0031] List of reference numerals:

[0032] 1 MTPA curve

[0033] 3 Current vector

[0034] 5 Ideal current vector

[0035] 7 Fictitious current vector

[0036] 9 Field weakening regulator

[0037] 11 I element

[0038] 13, 15 Curves of fixed voltage utilization

[0039] Δα Change value

[0040] Us Required voltage

[0041] U s,max Maximum voltage

[0042] VU Lim Maximum voltage utilization

[0043] VU Lim,Adj Reduced maximum voltage utilization.

Claims

1. A method for field-oriented current regulation of the motor current (I d , I q ) of an electric motor in the case of using a field weakening regulator (9), the motor voltage of the electric motor being limited by a maximum voltage (U s,max ), the field weakening regulator being designed such that if a motor voltage exceeding the maximum voltage (U s,max ) would be required to adjust the motor current (I d , I q ) to a target value, the target value of the command variable for the current regulation is corrected, wherein, - Training and storing a calibration value of a rotor position offset angle between a rotor of the electric motor and the position sensor system by calibrating the position sensor system, the position sensor system being provided for determining a rotor position of the rotor, and - During operation of the electric motor at a motor voltage that is at least approximately the maximum voltage (U s,max ), the value for determining the target value of the rotor position offset angle is changed by a varying value (Δα) relative to the calibration value such that a motor voltage exceeding the maximum voltage (U s,max ) would be required to adjust the command variable to the target value.

2. The method according to claim 1, wherein, Use the components (I d , I q ) of the current vector of the motor current in the d / q coordinate system for the motor current as command variables.

3. The method according to claim 1 or 2, wherein Based on the required torque of the electric motor, the required speed of the electric motor, the rotor temperature of the rotor of the electric motor and / or the maximum voltage (U s,max ), the target value of the command variable is determined.

4. The method according to any one of the preceding claims, wherein, When correcting the target value by means of the field weakening regulator (9), the value corresponding to the reduced maximum voltage utilization (VU Lim,Adj ) is used to replace the value of the maximum voltage utilization (VU Lim ) used when determining the target value, where the maximum voltage utilization indicates the maximum ratio of the motor voltage to the maximum voltage (U s,max ).

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

6. The method according to any one of the preceding claims, wherein, The maximum voltage (U s,max ) corresponds to the battery voltage provided by the battery for operating the electric motor and to the selected modulation method for controlling the electronic switches of the pulse inverter to achieve the motor voltage.

7. The method according to any one of the preceding claims, wherein The maximum voltage (U s,max ) relates to the d / q coordinate system for the motor voltage.

8. The method according to any one of the preceding claims, wherein The field weakening regulator (9) is implemented as a software module.

9. The method according to any one of the preceding claims, wherein, A correction of the calibration value of the rotor position offset angle is determined from a correction of a target value of the command variable.

10. The method according to claim 9, wherein, The correction of the calibration value of the rotor position offset angle is determined such that using the corrected calibration value instead of the calibration value when determining the target value of the command variable results in an improvement in the efficiency of the electric motor.

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