Inspection of anisotropy of inductance of electric motor during end line commissioning

Abstract

The invention relates to a method for determining and / or ascertaining the difference in length between the d-axis and the q-axis of an ellipse, in particular for checking the anisotropy of the inductance of an electric motor during end-line commissioning. The invention also relates to a device, in particular a control unit, an electric machine and a computer program product.

Description

Field of the Invention

[0001] The present disclosure relates to a method for determining and / or ascertaining the length difference between the d-axis and the q-axis of an ellipse, in particular for verifying the anisotropy of the inductance of an electric motor during end-line commissioning. The present disclosure also relates to a device, in particular a control unit, an electric machine, and a computer program product. Background Art

[0002] When an electric motor operates without sensors, the rotor position sensor that is usually used to determine the current angle of the rotor is omitted. Current sensor signals and measured or estimated phase voltages are used to determine the rotor position and speed of the motor via a model.

[0003] Below a rotational speed threshold of the absolute rotational speed, a so-called injection signal needs to be fed in, which supports the identification of the rotor position and speed in this rotational speed range. Starting from a stationary rotor, the rotor position must be determined by an initialization routine.

[0004] For a certain number of points on the voltage circuit path, the initial rotor position can be confirmed by specifying an AC voltage excitation - high-frequency oscillations in the d-voltage and the q-voltage, where the excitation voltage amplitude results in a current amplitude. Due to the d-q coordinates, an ellipse must be formed in the d-q plane at a certain current in the case of a circular excitation of the voltage. In this regard, the major axis of the ellipse corresponds to the d-direction. This direction of the major axis describes the initial value of the rotor position.

[0005] In the prior art, it has been proposed to use an iterative controller method to find the longer major axis of the ellipse, which corresponds to the d-axis. By applying an injection signal to the voltage, the current can be measured. However, here it is not transformed into the assumed d-direction, but into the assumed d - 45° direction and the assumed d + 45° direction. Compared with the evaluation of the current in the d-direction and the q-direction, this enables a significantly larger current amplitude to be achieved, where when the true d-axis is found, the current in the q-direction disappears. This makes the detection more robust to interference, especially in dynamic situations. Then, the amplitude of the injection signal in the current is determined using a band-pass filter, and the two values of ±45° are compared. Then, the assumed angle is corrected such that the two amplitudes in the +45° and -45° directions become equal in magnitude. The correction is selected in such a way as to find the longer semi-axis, i.e., the d-axis. If the sign is reversed during the correction, the algorithm finds the shorter semi-axis - i.e., the q-axis.

[0006] Compared with embedded magnets, the inductances Ld and Lq of bonded magnets are usually more similar to each other. Then, the ellipse is less distinct and more circular.

[0007] The methods according to the prior art require different inductances in the d - direction and the q - direction because only in this way is the ellipse obvious. Even if the ellipse is not very obvious, it should be reliably recognized. The aim is to provide the following method: During commissioning, determine the inductance ratio in the system from the control unit that will be connected during operation later, and thus evaluate the inductance. This is intended to take into account the system - specific effects of current measurement and motor parameters.

[0008] Therefore, the objective technical purpose of the present disclosure is to eliminate or at least improve the drawbacks existing in the prior art. In particular, to determine the initial angle faster and more accurately. Summary of the Invention

[0009] The above - mentioned object is achieved by the aspects of claim 1. In other words, this object is achieved by a method for determining and / or ascertaining the length difference between the d - axis and the q - axis of an ellipse, in particular for verifying the anisotropy of the inductance of an electric motor during final - line commissioning, wherein,

[0010] the ellipse is formed in the d - q plane at a certain current under circular excitation of the voltage, and wherein the method comprises the following steps:

[0011] a) Provide a motor with a stationary rotor,

[0012] b) Determine, by means of an iterative method, the q - axis of the ellipse, in particular the minor semi - axis, and set the angle offset Gamma_q1, and

[0013] c) Determine, by means of an iterative method, the d - axis of the ellipse, in particular the major semi - axis, and set the angle offset Gamma_d1, wherein the d - axis and the q - axis are found by sign changes in the iterative method,

[0014] d) Analyze the amplitudes of the current responses of the injected signal in the d - direction and the q - direction,

[0015] e) Ascertain the ratio of the current responses in the d - direction and the q - direction, and

[0016] f) Transform the phase currents to d - 45°, d + 45°, d + 0° and q - 45°, q + 45° and q + 0°.

[0017] In particular, a method for determining the initial rotor position of the rotor of a motor, in particular a synchronous motor, comprises the following steps:

[0018] a) Provide a motor with a stationary rotor,

[0019] b) Provide a starting value d_est, which represents the first angle of the rotor position,

[0020] c) Generate a three - phase AC voltage excitation in the motor by specifying an AC voltage in the direction of d_est.

[0021] d) For the first modified value d_est-45°, convert the three-phase current response of the AC voltage excitation of the motor into a first AC current component i_[d_est-45°].

[0022] e) For the second modified value d_est+45°, convert the three-phase current response of the AC voltage excitation of the motor into a second AC current component i_[d_est+45°].

[0023] f) For the first AC current component i_[d_est-45°], calculate the length of the first AC current vector having d and q components.

[0024] g) For the second AC current component i_[d_est+45°], calculate the length of the second AC current vector having d and q components.

[0025] h) Determine the absolute value of the difference in length between the first AC current vector and the second AC current vector according to delta_i = |i_d_est+45°| – |i_d_est-45°|.

[0026] i) If the condition that the absolute value of the difference in length between the first AC current vector and the second AC current vector according to delta_i = |i_d_est+45°| – |i_d_est-45°| = [0–FTW] is within the defined interval between 0 and the defined error tolerance FTW is satisfied, provide the initial rotor angle to excite the motor and terminate the method.

[0027] j) If the following condition is satisfied: the absolute value of the difference in length between the first AC current vector and the second AC current vector delta_i = |i_d_est+45°| – |i_d_est-45°| > 0.

[0028] k) In the case of |i_d_est+45°| > |i_d_est-45°|, adjust the starting value d_est in a way that rotates clockwise by a predetermined amount by an angle representing the rotor position, and

[0029] l) In the case of |i_d_est+45°| < |i_d_est-45°|, adjust the starting value d_est in a way that rotates counterclockwise by a predetermined amount by an angle representing the rotor position.

[0030] m) Repeat steps c) to l).

[0031] In other words, steps a) and b) of the present disclosure can be carried out by performing the above-described method. In this way, at least the d-axis can be determined. The determination of the q-axis according to step c) of the claimed method can also be carried out with the aid of the above-described method, where the sign is reversed accordingly during the correction in order to find / determine the shorter semi-axis, i.e., the q-axis.

[0032] In other words, the first step is to find the short semi-axis of the ellipse. This gives the angle offset Gamma_q1. For this purpose, the above-described method with steps a) to m) is used together with other signs for angle correction. Then the long semi-axis is found. Here, the angle offset Gamma_d1 is found. This is also the above-described method with steps a) to m).

[0033] It is preferred if Gamma_d1 and Gamma_q1 differ by substantially ±90°. In other words, the difference between gamma_d1 and gamma_q1 should be approximately 90° or -90° because it is assumed that the d-axis and the q-axis intersect at right angles.

[0034] Once the d-axis and the q-axis are found using the algorithm from the method with steps a) to m) and using the sign changes in the algorithm, the amplitudes of the current responses of the injected signal in the d-direction and the q-direction are analyzed. Thereby, the ratio of the current responses in the d-direction and the q-direction can be confirmed; these values represent the inductance data Ld and Lq. If the axes are found, the phase current must be transformed not only to d - 45° and d + 45°, but also to d + 0°. This also applies to the q-axis. If the current amplitudes in d and q are too similar, the motor can be screened out.

[0035] It is advantageous if steps b) to f) can be repeated as many times as necessary. This process can be repeated several times, especially to ensure that the results are accurate.

[0036] It is advantageous if the starting values q_est and / or d_est are randomly selected when repeating the method, especially steps b) to f).

[0037] It is preferred if, after performing steps a) and b), the determined d-axis is provided as the starting value for determining the q-axis.

[0038] It is advantageous if the circular path is traversed at least once to precisely find 4 solutions, especially for the -d-axis and the +d-axis as well as the -q-axis and the +q-axis.

[0039] In other words, since the algorithm or method searches for the next angle as solutions of two +45° and -45° current amplitudes of the same length, it can be meaningful to randomly select the starting value of the assumed axis for repetition. However, it is also a good idea to first find a certain axis and define it as the assumed starting value of the next axis. Ideally, the algorithm should go around the circular path once and only find 4 solutions in this regard - the -q axis and +q axis, as well as the -d axis and +d axis.

[0040] It is advantageous if the demagnetization of the magnet can be inferred from the comparison of the inductances from end-of-line commissioning. Then a normalization method for angle initialization is performed to operate the motor, and the long semi-axis is searched for. Using the initial value of this angle, the 180° ambiguity is resolved according to the method with steps a) to m).

[0041] Alternatively, the verification can also be performed during the startup of the control device each time the vehicle is used. For example, the comparison of the inductances from end-of-line commissioning can be used to draw conclusions about the demagnetization of the magnet. In principle, a weaker magnet is more critical for the accidental coincidence Ld = Lq because of the smaller pre-saturation of iron. For example, such a change may request access to the workshop to replace components.

[0042] Furthermore, the present disclosure relates to a device, in particular a control unit for controlling and exciting an electric motor, for performing the verification method according to any one of the above aspects.

[0043] Furthermore, the present disclosure relates to an electric motor, in particular a synchronous motor, which includes a stator and a rotor rotatable relative to the stator and a device for controlling and exciting the electric motor. In this case, it is preferred if the device is designed according to the above aspects.

[0044] Finally, the present disclosure also relates to a computer program product stored on a machine-readable carrier or a computer data signal implemented by electromagnetic waves, which has program code adapted to execute the method according to any one of the foregoing aspects. Description of the Drawings

[0045] The present disclosure will be described in more detail below with reference to the drawings without limiting the general concept of the invention.

[0046] Figure 1 Different positions of the d-axis in the d / q coordinate system are shown,

[0047] Figure 2 Different positions of the q-axis in the d / q coordinate system are shown,

[0048] Figure 3 The electric motor is shown in a schematic representation,

[0049] Figure 4A motor vehicle having a hybrid powertrain and an all-electrically operable powertrain is schematically shown. Detailed Description

[0050] The following will describe in more detail a method for determining the initial rotor position of the rotor 1 of the electric machine 2, in particular a synchronous electric machine, with reference to Figure 1

[0050]

[0051] First, an electric machine 2 with a stationary rotor 1 is provided, as Figure 3 shown by way of example. By means of a control unit 3 in the electric machine 2, a three-phase AC voltage excitation is then generated in the electric machine 2, which is also indicated in Figure 3

[0050]

[0052] First, a random starting value d_est is provided, which represents a first angle of the rotor position. Based on this starting value d_est, an AC voltage excitation is applied in the d_est direction. The three-phase currents are measured and transformed into the d_est - 45° direction, and a modified value d_est - 45° is calculated. Similarly, a second modified value d_est + 45° is calculated, which corresponds to the starting value d_est plus 45°.

[0053] Subsequently, a conversion of the three-phase current response of the AC voltage excitation of the electric machine 2 to the first AC current component i_[d_est - 45°] for the first modified value d_est - 45° is performed,

[0054] and a conversion of the three-phase current response of the AC voltage excitation of the electric machine to the second AC current component i_[d_est + 45°] for the second modified value d_est + 45° is performed.

[0055] These two AC current components are shown in Figure 1 Figs. a) to c). Now, a calculation of the length of the first AC current vector having d and q components for the first AC current component i_[d_est - 45°] is performed, and a calculation of the length of the second AC current vector having d and q components for the second AC current component i_[d_est + 45°] is performed.

[0056] Figure 1 The corresponding ellipse in the true d-q plane is schematically shown. The "estimated" d-axis d_est is shown here and does not coincide with the d-axis direction of the d-q plane. The AC current components i_(d_est + 45°) and i_(d_est - 45°) are plotted to match the estimated direction of the d-axis.

[0057] Then, determine the absolute value of the difference in length between the first AC current vector and the second AC current vector according to delta_i = |i_d_est + 45°| – |i_d_est - 45°|.

[0058] If the following condition is satisfied: the absolute value of the difference in length between the first AC current vector and the second AC current vector, delta_i = |i_d_est + 45°| – |i_d_est - 45°| > 0, which can be seen in Figure 1 images a) and b), then distinguish between the other two alternative solutions.

[0059] For the first case where |i_d_est + 45°| > |i_d_est - 45°|, adjust the starting value d_est in a manner that rotates clockwise by a predetermined amount by the angle representing the rotor position, as shown in images a) and b).

[0060] From Figure 1 images a) and b) in, it is clearly seen that the lengths of the AC current components are different. Therefore, the "estimated" d-axis (d_est) must rotate clockwise along the short path. This new "estimated" d-direction is then the new starting value for the next iteration. An iteration in the next iteration is shown in Figure 1 image b).

[0061] For the second case where |i_d_est + 45°| < |i_d_est - 45°|, adjust the starting value d_est in a manner that rotates counterclockwise by a predetermined amount by the angle representing the rotor position. However, this is not shown in Figure 1 it.

[0062] Perform these iterations until the following condition is satisfied according to delta_i = |i_d_est + 45°| – |i_d_est - 45°| = [0 – FTW]: the absolute value of the difference in length between the first AC current vector and the second AC current vector is within a defined interval between 0 and the defined error tolerance value FTW.

[0063] In other words, repeat the process until the projections of the AC current components and thus the lengths of the absolute values of the AC current components are equal. Then, the initial angle of the rotor position can be easily confirmed according to the angle of the "estimated" d-axis. This can be seen in Figure 1 image c). Then, based on this, provide the initial rotor angle to energize the motor and terminate the method.

[0064] After this initial angle is determined, the d-axis is known and the electric machine 2 can be rotated in the desired direction of rotation. This prevents the electric machine from rotating in the wrong direction during motor operation, even for a short period of time. As with the methods known in the prior art, suitable standard methods must still be used to confirm and eliminate possible "180° errors".

[0065] Figure 2 Almost completely corresponds to Figure 1 , where the minor axis of the ellipse is sought here - i.e., the axis in the q-direction. Therefore, no further description is provided here, since the above description can be understood with respect to Figure 2 , with the difference that "d" must be replaced by "q".

[0066] As Figure 3 shown, the control unit 3 for controlling and exciting the electric machine 2 includes a processor 4 and a memory 5 containing computer program code, where the memory 5 and the computer program code are configured to cause the control unit 3 to execute the above method using the processor 4.

[0067] Different from that shown in Figure 3 , the control unit 3 preferably does not have a connection to a rotor position sensor 6 for detecting the rotor position of the rotor 1 and can be controlled without a sensor. Figure 3 The electric machine 2 shown has a stator 7 that can be excited and a rotor 1 that can rotate relative to the stator 7, and a control unit 3 for controlling and exciting the electric machine 2 or the stator 7.

[0068] In particular, the electric machine 2 is intended to be used in a hybrid powertrain or a fully electric-operable powertrain 8 of a motor vehicle 9 as also outlined in Figure 4 .

[0069] The present disclosure is not limited to the embodiments shown in the drawings. Therefore, the above description is not to be considered restrictive, but rather illustrative. The appended claims are to be understood as meaning that the stated features exist in at least one embodiment of the present disclosure. This does not exclude the existence of other features. In the case where the claims and the above description define a "first" feature and a "second" feature, such naming is used to distinguish between two features of the same type and does not define a priority order.

[0070] List of reference numerals

[0071] 1 Rotor

[0072] 2 Electric machine

[0073] 3 Control unit

[0074] 4 Processor

[0075] 5 Memory

[0076] 6 Rotor Position Sensor

[0077] 7 Stator

[0078] 8 Powertrain

[0079] 9 Motor Vehicle

Claims

1. A method for determining and / or ascertaining the length difference between the d-axis and the q-axis of an ellipse, in particular for verifying the anisotropy of the inductance of an electric motor during final line commissioning, wherein, the ellipse is formed in the d-q plane at a certain current under a circular excitation of voltage, and wherein the method comprises the following steps: g) providing an electric machine with a stationary rotor, h) determining, by means of an iterative method, the d-axis of the ellipse, in particular the minor semi-axis, and setting an angular offset Gamma_q1, and i) determining, by means of an iterative method, the q-axis of the ellipse, in particular the major semi-axis, and setting an angular offset Gamma_d1, wherein the d-axis and the q-axis are found by a sign change in the iterative method, j) analyzing the amplitudes of the current responses of the injected signal in the d-direction and the q-direction, k) ascertaining the ratio of the current responses in the d-direction and the q-direction, and l) transforming the phase currents to d - 45°, d + 45°, d + 0° and q - 45°, q + 45° and q + 0°.

2. The verification method according to claim 1, characterized in that gamma_d1 and gamma_q1 differ by substantially ±90°.

3. The verification method according to claim 1 or 2, characterized in that Steps b) to f) can be repeated as required.

4. The verification method according to any one of claims 1 to 3, characterized in that, When repeating the method, in particular steps b) to f), the starting values q_est and / or d_est are randomly selected.

5. The verification method according to any one of claims 1 to 3, characterized in that After performing steps a) and b), the determined d-axis is provided as a starting value for determining the q-axis.

6. The verification method according to any one of claims 1 to 5, characterized in that, Going around the circular path at least once to precisely find 4 solutions, in particular for the -d-axis and the +d-axis and the -q-axis and the +q-axis.

7. The verification method according to any one of claims 1 to 6, characterized in that The demagnetization of the magnet can be inferred from the comparison of the inductances from the final line commissioning.

8. A device for performing the verification method according to any one of claims 1 to 8, in particular a control unit for controlling and exciting an electric machine.

9. An electric machine, in particular a synchronous machine, comprising a stator and a rotor rotatable relative to the stator and means for controlling and exciting the electric machine, characterized in that, The device is designed according to claim 8.

10. A computer program product stored on a machine-readable medium or a computer data signal represented by an electromagnetic wave, having program code adapted to perform the method according to claims 1 to 8.

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