Method and apparatus for calibrating an offset angle

Abstract

A method (100) for calibrating the offset angle (PhiO) of a field orientation regulator of a motor (210) between the angle signal (W) of a position sensor (220) and the direction of the rotor flux (RF), comprising the steps of: periodically changing (120) a current vector (Is) along a constant torque line; determining (130) a rotational speed signal (n_t) of the position sensor (220) of the motor (210); and calibrating (140) the offset angle (PhiO) based on the determined rotational speed signal (n_t).

Description

Technical Field

[0001] This invention relates to a method and apparatus for calibrating the offset angle of a field orientation adjuster for an electric motor. Furthermore, this invention relates to a drivetrain with corresponding equipment, a vehicle having a drivetrain, a computer program, and a computer-readable storage medium. Background Technology

[0002] In electric and hybrid vehicles, electric motors, preferably synchronous motors, are typically used as traction or drive mechanisms. To adjust the drive torque with the required precision, the drive adjustment unit must know the precise position of the rotor flux. Since the position of the rotor flux is closely related to the rotor position, the flux direction can, in principle, be determined by the mechanical position angle. This mechanical position angle is typically detected using a position sensor, preferably a rotary transformer, incremental encoder, or others. In addition to the mechanical angle, the drive adjustment unit must also know the so-called offset angle, which represents the deviation between the zero-crossing point of the sensor and the direction of the rotor flux, i.e., the offset. Different methods for determining this offset are known from the prior art. For example, document DE 10 2008 001 408 A1 discloses a method for determining the motor offset angle. This offset angle is determined as a function of the difference between the field angle, the applied stator magnetic field, and the determined sensor angle. Methods and apparatus for calibrating this offset angle are needed. Summary of the Invention

[0003] A method is provided for calibrating the offset angle of a field orientation regulator of a motor between an angle signal from a motor position sensor and the direction of rotor flux. The method includes the steps of: periodically changing a current vector along a constant torque line, preferably in the d / q coordinate system of the field orientation regulator; determining a speed signal of the motor; and calibrating the offset angle based on the determined speed signal.

[0004] Field-oriented regulators for motors are known. Here, it is assumed that the primarily sinusoidal AC parameters (e.g., AC voltage and AC current) are not directly regulated as instantaneous values ​​changing over time, but rather as instantaneous values ​​with phase angles eliminated within a period. For this purpose, the detected AC parameters are transmitted to a coordinate system rotating at the frequency of the AC parameters. Then, within the rotating coordinate system, DC parameters are generated from the AC parameters during the static operation of the motor; all commonly used regulation techniques can be applied to these DC parameters. A position sensor is used to determine the rotor position, and its output angle signal is used to determine the rotor relative to the stator. A rotating magnetic field is generated during motor operation due to the multiphase, phase-shifted AC current applied to the stator. The direction of this rotating magnetic field corresponds to the direction of the resulting total magnetic flux, which is generated by the superposition of the rotor flux generated by the permanent magnets and the stator flux generated by the stator current. Accurately understanding the deviation (i.e., offset angle) between the angle signal and the actual rotor flux direction is crucial for the regulation, as the rotor flux direction is calculated from the angle signal and the offset angle for motor regulation, i.e., the pre-set value of the stator current. In a rotating coordinate system, i.e., the d / q coordinate system—which rotates synchronously with the rotor flux and whose d-axis points in the direction of the rotor flux—the stator current is represented as a stator current vector Is, characterized by its absolute value and its direction. This current vector rotates synchronously with the motor's rotating stator or rotor flux. In the d / q coordinate system, the current vector can be decomposed into two components, Isd and Isq, which are DC parameters in the static state. Machine-specific lines along which the motor outputs constant torque can be displayed in this coordinate system. The motor regulator can access the parameters of these lines using a family of characteristic curves or parameterizable data. Different operating points of these lines can be set by varying the stator current vector with different Isd and Isq components. In one step of this method, operating points are set along this constant torque line by periodically changing the current vector, preferably by changing its absolute value and / or direction. A motor connected to the regulator can then operate at these operating points. If the offset angle assumed by the regulator is consistent, the torque output by the motor remains constant, and therefore the motor speed also remains constant. If the assumed offset angle is incorrect, the actual operating point is located near the constant torque line. This generates periodic torque oscillations, which cause periodic oscillations in the motor speed. In a further step, the resulting speed or speed change process is determined as a speed signal. Preferably, the speed signal is determined from the angle signal of a position sensor. The offset angle is calibrated based on the speed signal. For this purpose, the magnitude of the offset angle is preferably changed until the amplitude of the speed signal is below a threshold during current vector changes. The offset angle obtained in this way is very close to the true value.Therefore, in principle, the offset angle can be calibrated during motor operation, preferably during normal driving of the motor-driven vehicle, provided that the pre-given torque remains constant for a sufficiently long period (e.g., 1...2 seconds). For this purpose, a basic current vector is preferably provided, which generates the torque desired by the controller. This basic current vector is preferably superimposed with an oscillating component, which preferably oscillates at a defined frequency and preferably points in the direction of the constant torque line. Depending on the deviation of the assumed offset angle from the true value, fluctuations of varying intensities occur in the resulting torque. The assumed offset angle is continuously adjusted until, preferably, the oscillation measured at the rotor speed is minimal or the amplitude of the oscillation is below a threshold. The offset angle resulting from these minimal oscillations closely approximates the true offset angle and is used for further operation of the motor regulator.

[0005] Advantageously, a method for calibrating the offset angle of a field-oriented regulator for a motor is provided. This method is a solution of regulation techniques that minimizes the need for components or mechanical measures. The achievable accuracy is very high compared to known solutions, and is preferably independent of the quality of the machine model used in the regulator and its calibration. Furthermore, the offset angle calibration can be performed during driving operation, and under ideal conditions—i.e., when there is no or very little detuning of the offset angle within the regulator—it will not be noticeable to the driver.

[0006] In another design of the present invention, calibrating the offset angle based on the determined rotational speed signal includes the following steps: changing the offset angle in a positive or negative direction; determining the rotational speed signal of the position sensor; comparing the determined rotational speed signal with a previously determined rotational speed signal; changing the offset angle in the same direction when the oscillation amplitude of the determined rotational speed signal is less than that of the previously determined rotational speed signal; changing the offset angle in the opposite direction when the oscillation amplitude of the determined rotational speed signal is greater than that of the previously determined rotational speed signal; and ending the calibration when the oscillation amplitude of the determined rotational speed signal is less than a pre-given first limit value.

[0007] A method is provided for calibrating an offset angle based on a determined speed signal. For this purpose, the offset angle is changed in a positive or negative direction, preferably incrementally, preferably increasing by an absolute value of approximately 0.1 degrees to 1 degree. Based on a comparison of the resulting speed signal with a previously determined speed signal, a further direction for changing the offset angle is determined, thereby iteratively minimizing oscillations in the speed signal. The method terminates when the amplitude of the determined oscillations in the speed signal is less than a pre-given first limit value. This limit value is calibrated in an application-specific manner, thereby preferably preventing incorrectly set torque and the resulting risks to motor operation or unsuitable motor operation. Advantageously, a method for simply calibrating an offset angle based on a determined speed signal is provided.

[0008] In another design of the invention, the method is performed according to a second limit value, i.e., when the pre-given rated torque is lower than the second limit value.

[0009] Preferably, the second limit value is a very low torque value, preferably close to zero, for example, much less than 1 Nm. A line with constant torque is generated in the d / q coordinate system, where the q-component of the stator current vector is equal to 0.

[0010] Advantageously, a method is provided in which a more precise understanding of the motor characteristics is preferably not required, as possible errors due to inaccurate motor models can be eliminated.

[0011] In another design of the invention, the frequency is periodically changed within the natural frequency range of the motor or transmission system having the motor. Preferably, the frequency is within the first natural frequency range of the motor or transmission system having the motor. The small oscillations resulting in the torque then also result in larger oscillations in the determined rotational speed. This advantageously improves the sensitivity of the method.

[0012] In another design of the invention, the periodic changes are performed at different amplitudes based on the oscillation amplitude of the determined rotational speed signal.

[0013] Preferably, when the oscillation amplitude of the determined rotational speed signal is lower than a pre-defined third limit value, the periodic change is performed with an amplitude greater than the previous change. The increased amplitude of the current vector change near the sought optimal value results in an increased excitation for the oscillation of the rotational speed signal to be determined, which itself decreases as the distance from the optimal value decreases.

[0014] Advantageously, the sensitivity of the method is further increased near the optimal value sought.

[0015] In another design of the invention, the offset angle is calibrated by means of a gradient method based on the oscillation evaluation of the rotational speed signal.

[0016] To determine the minimum oscillation of the rotor speed, the oscillation amplitude near the minimum is considered and integrated into the evaluation using a gradient method. Preferably, the gradient method near the minimum considers not only the minimum value but also the oscillation variation or oscillation gradient near the minimum. This advantageously determines the sought minimum value more accurately.

[0017] In another design of the invention, the offset angle is calibrated based on the d-component of the measured phase current.

[0018] The phase current is measured or determined during the method. Preferably, the d-component of the stator current vector is determined by means of a search algorithm. This algorithm calculates a compensation angle, which is added to an offset angle used internally by the regulator. Here, the phase shift between the modulated harmonic component in the d-component of the stator current vector and the resulting harmonic component in the rotor frequency is used to calculate the optimal compensation angle by means of the regulator. An alternative method is advantageously provided.

[0019] In another design of the invention, the motor is configured as the vehicle's drivetrain and the method is performed when the vehicle is stationary.

[0020] This method is performed when the vehicle is stationary, with the motor to be adjusted acting as the drive. For this purpose, the vehicle's drive wheels are preferably braked by mechanical brakes. Due to the nature of the mechanical transmission system, the activation energy in the stationary state has a beneficial effect on the achievable accuracy because the position sensor signal then contains only oscillations generated by the oscillating current vector, rather than additionally superimposed with rotational motion, which contains inherent oscillations, for example, due to alternating load torque. Advantageously, a method for calibrating the offset angle with particularly high accuracy is provided.

[0021] Furthermore, the present invention relates to a computer program comprising instructions which, when executed by a computer, cause the computer to perform the steps of the methods described to date.

[0022] Furthermore, the present invention relates to a computer-readable storage medium including instructions that, when executed by a computer, cause the computer to perform the steps of the methods described to date.

[0023] Furthermore, the present invention relates to an apparatus for calibrating the offset angle of a motor's field orientation regulator between an angle signal from a motor's position sensor and the direction of the motor's rotor flux. The apparatus is configured to periodically change a current vector along a constant torque line, and preferably pre-given this current vector Is for manipulating the motor, determining a speed signal of the motor, and calibrating the offset angle based on the determined speed signal. Preferably, the speed signal is determined based on the angle signal from the position sensor.

[0024] Advantageously, a device is provided for calibrating the offset angle of a field orientation regulator for a motor. The achievable accuracy is very high compared to known solutions, and is preferably independent of the quality of the machine model used in the regulator and its data input.

[0025] Furthermore, the present invention relates to a transmission system and the described device, particularly a device having power electronics and / or an electric drive. Such a transmission system is used, for example, to drive electric vehicles. Safe operation of the transmission system can be achieved by means of the described method and device.

[0026] Furthermore, the present invention relates to a vehicle having the described drivetrain. Therefore, it is advantageous to provide a vehicle comprising a device by which the offset angle of the field orientation adjuster of the motor can be calibrated.

[0027] It is understood that the features, characteristics, and advantages of the method according to the invention are correspondingly applicable to or can be applied to the device or the transmission system and the vehicle, and vice versa.

[0028] Other features and advantages of embodiments of the present invention will become apparent from the following description with reference to the accompanying drawings. Attached Figure Description

[0029] The invention will be explained in more detail below based on some figures, for which:

[0030] Figure 1 A schematic diagram of a device for calibrating the offset angle of a motor's field orientation adjuster is shown.

[0031] Figure 2 The d / q plot of the field-oriented regulator is shown.

[0032] Figure 3 A schematic illustration of a vehicle with a drivetrain is shown.

[0033] Figure 4 A flowchart illustrating a method for calibrating the offset angle of a field orientation adjuster for a motor is shown. Detailed Implementation

[0034] Figure 1 Device 200 is shown, preferably having logic device 205 for calibrating the offset angle PhiO of the motor's field orientation regulator between the angle signal W from the position sensor 220 of the motor 210 and the direction of the motor's rotor flux RF. Device 200 is configured to periodically change the current vector Is along a constant torque line, and preferably pre-given the current vector Is for manipulating and operating the motor. Device 200 is also configured to determine a speed signal n_t of the motor 210, preferably caused by the angle signal W from the position sensor 220, and to calibrate the offset angle PhiO based on the determined speed signal n_t.

[0035] Figure 2A d / q graph of the field-oriented regulator is shown. Two additional graphs, d' / q' and d" / q", are superimposed on this d / q graph. This is used to graphically display the effect of the deviation (+ / -Delta) between the actual and assumed offset angles. In the d / q graph, it is assumed that largely sinusoidal AC parameters (e.g., AC voltage and AC current used to energize the motor) are transmitted to a coordinate system rotating at the frequency of the AC parameters. DC parameters are then generated from these AC parameters during the static operation of the motor within this rotating coordinate system. In the d / q coordinate system, which rotates synchronously with the rotor flux and whose d-axis points in the direction of the rotor flux, the stator current is represented as a stator current vector Is, characterized by its absolute value and its direction. This current vector Is rotates synchronously with the rotating stator or rotor flux of the motor. Motor-specific lines T1, T2, T3, and T4 along which the motor outputs constant torque can be displayed in this coordinate system. The motor regulator can access the parameters of these lines using a family of characteristic curves or parameterizable data. Different operating points on these lines can be set by varying the stator current vector with different Isd and Isq components. In one step of the method, the operating point is set along this constant torque line by periodically changing the current vector Is. If the offset angle assumed by the regulator is consistent, the output torque remains constant, and therefore the motor speed also remains constant. Superimposed d' / q' and d" / q" graphs exemplarily illustrate how the position of the current vector Is changes according to an erroneous offset angle with a + / - Delta deviation to the shown current vector Is'' or Is'. With the current vectors Is'' and Is' changing accordingly, the set value is no longer located on the constant torque lines T1, T2, T3, T4. In the case of an incorrect assumed offset angle, the actual set operating point is located beside the constant torque line. Periodic torque oscillations are generated, which cause periodic oscillations in the motor speed. In a further step, the resulting speed or speed change process is determined as a speed signal. The offset angle is calibrated based on the rotational speed signal. For this purpose, the magnitude of the offset angle is preferably changed until the amplitude of the rotational speed signal falls below a threshold during the change of the current vector Is. The offset angle obtained in this way is very close to the true value. To change the current vector Is, a basic current vector is preferably provided, which produces the torque desired by the controller. This basic current vector is preferably superimposed with an oscillating component, which preferably oscillates at a defined frequency and preferably points in the direction of the constant torque line. Depending on the deviation of the assumed offset angle from the true value, fluctuations of varying intensities appear in the resulting torque. The assumed offset angle is continuously adjusted until, preferably, the oscillation measured at the rotor speed becomes minimal or the amplitude of the oscillation falls below a threshold.The offset angle resulting from these minimal oscillations closely approximates the true offset angle and is used for further operation of the motor regulator.

[0036] Figure 3 A vehicle 400 with a drivetrain 300 is shown schematically. The drivetrain includes a device for calibrating the offset angle (PhiO) of the field orientation adjuster of the motor (210).

[0037] Figure 4 A schematic flow diagram of a method 100 for calibrating the offset angle PhiO of a field orientation regulator of motor 210 between the angle signal W of a position sensor 220 of the motor and the direction of the rotor flux RF of the motor is shown. The method begins with step 110. In step 120, the current vector Is changes periodically along a constant torque line. Motor 210 is manipulated or operated according to this pre-given current vector. In step 130, the rotational speed signal n_t of the position sensor 220 of motor 210 is determined. Then, in step 140, the offset angle PhiO is calibrated according to the determined rotational speed signal n_t. In step 150, the offset angle PhiO is preferably changed in the positive or negative direction. And in step 160, the rotational speed signal n_t0 is determined by means of the position sensor. Then, in step 170, the determined rotational speed signal n_t0 is compared with a previously determined rotational speed signal n_t-1 and / or the determined rotational speed signal n_t0 is compared with a pre-given first limit value G1. In step 180, if the oscillation amplitude of the determined speed signal n_t0 is lower than that of the previously determined speed signal n_t-l, the offset angle PhiO is changed in the same direction; in step 182, if the oscillation amplitude of the determined speed signal n_t0 is greater than that of the previously determined speed signal n_t-l, the offset angle PhiO is changed in the opposite direction. After step 180 or step 182, the method preferably branches to step 160. When the oscillation amplitude of the determined speed signal n_t0 is less than a pre-given first limit value G1, the calibration ends in step 184. The method ends at step 190.

Claims

1. A method (100) for calibrating an offset angle (PhiO) of a field-oriented regulator of an electric machine (210) between an angle signal (W) of a position sensor (220) and a direction of a rotor flux (RF), the method comprising the steps of: periodically varying (120) a current vector (Is) along a constant torque line; determining (130) a rotational speed signal (n_t) of the electric machine (210); calibrating (140) the offset angle (PhiO) depending on the determined rotational speed signal (n_t), wherein the magnitude of the offset angle is varied until the amplitude of oscillations of the rotational speed signal during current vector variation is below a threshold value.

2. The method according to claim 1, wherein calibrating (140) the offset angle (PhiO) depending on the determined rotational speed signal (n_t) comprises the steps of: varying (150) the offset angle (PhiO) towards a positive or negative direction; determining (160) a rotational speed signal (n_t0) of the position sensor; comparing (170) the determined rotational speed signal (n_t0) with a previously determined rotational speed signal (n_t-l); varying (180) the offset angle (PhiO) towards the same direction when the amplitude of oscillations of the determined rotational speed signal (n_t0) is smaller than in the previously determined rotational speed signal (n_t-l); varying (182) the offset angle (PhiO) towards the opposite direction when the amplitude of oscillations of the determined rotational speed signal (n_t0) is greater than in the previously determined rotational speed signal (n_t-l); ending the calibration (184) when the amplitude of oscillations of the determined rotational speed signal (n_t0) is smaller than a predefinable first limit value (G1).

3. The method according to any of the preceding claims 1 to 2, wherein the method (100) is performed depending on a second limit value (G2), wherein the method (100) is performed when a predefinable rated torque (Td) is below the second limit value (G2).

4. The method according to any of the preceding claims 1 to 2, wherein the periodic variation (120) is performed at a frequency (F) in a range of eigenfrequencies (Fe) of the electric machine (210) or a drive train (300) having the electric machine (210), the frequency being in a range of a first eigenfrequency (Fe1) of the electric machine (210) or the drive train (300) having the electric machine.

5. The method according to any of the preceding claims 1 to 2, wherein the offset angle (PhiO) is calibrated (140) depending on an oscillation evaluation of the rotational speed signal (n_t) by means of a gradient method.

6. The method according to any of the preceding claims 1 to 2, wherein the offset angle (PhiO) is calibrated (140) depending on a d-component of a measured phase current (Iph).

7. The method according to any of the preceding claims 1 to 2, wherein the electric machine (210) is arranged as a drive train of a vehicle, wherein the method is performed when the vehicle is stationary.

8. A computer program product comprising a computer program with instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method (100) according to any one of claims 1 to 7.

9. A computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method (100) according to any one of claims 1 to 7.

10. A device (200) for calibrating an offset angle (PhiO) of a field oriented regulator of an electric machine (210) between an angle signal of a position sensor (220) and a direction of a rotor flux (RF), wherein the device (200) is arranged to: periodically change a current vector (Is) along a constant torque line, determine a rotational speed signal (n_t) of the electric machine (210), and calibrate the offset angle (PhiO) depending on the determined rotational speed signal (n_t), wherein a magnitude of the offset angle is changed until an amplitude of oscillations of the rotational speed signal during current vector changes is below a threshold value.

11. A drive train (300) having the device (200) according to claim 10.

12. A vehicle (400) having the drive train (300) according to claim 11.

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