Method for operating an electric motor

Abstract

The present invention relates to a method for operating an electric motor (12), wherein the electric motor (12) is in a rotor-stator-rotor configuration and has a first gap (22) with a first thickness d1 between a first rotor (18) and a stator (20) and a second gap (26) with a second thickness d2 between the stator (20) and a second rotor (24), and wherein the first rotor (18) and the second rotor (24) can be electrically excited separately, the method comprising the following process steps: a) Detecting a first open-circuit voltage of the first rotor (18) and detecting a second open-circuit voltage of the second rotor (24); b) Classifying the first open-circuit voltage and the second open-circuit voltage; and c) Setting the electrical excitation of at least one of the first rotor (18) and the second rotor (24) based on at least one of the classified open-circuit voltages.

Description

[0001] The present invention relates to a method for operating an electric motor. The present invention further relates to an electric drive system and a computer program product, which are designed to carry out the method for operating the electric motor.

[0002] Electric motors, especially as powertrains for vehicles, are becoming increasingly widespread. Electric motors often comprise a plurality of stators and / or rotors arranged adjacent to one another on an axis.

[0003] Due to design and manufacturing constraints, the assembly is subject to tolerances. These tolerances require, on the one hand, large air gaps between the rotor and stator. On the other hand, one-sided deviations from the nominally identical air gaps can lead to different forces acting on the assembly components. This, in turn, can lead to undesirable effects, such as one-sided bearing loading, which is detrimental to service life and thus costs, or even negatively impact NVH behavior.

[0004] DE 10 2020 126 068 A1 relates to an axial flux machine with a rotor and two stators axially spaced from the rotor. A first stator comprises a first stator winding. A second stator comprises a second stator winding. To reduce axial vibrations, a device is provided for generating an axially directed force on the rotor by applying different currents to opposing phase coils of the first and second stator windings.

[0005] The state-of-the-art solutions can be further improved, in particular with regard to compensating for tolerances of the assembly and reducing the associated disadvantages.

[0006] The object of the present invention is to at least partially overcome at least one disadvantage of the prior art. In particular, the object of the present invention is to provide a solution that can advantageously compensate for component tolerances and / or reduce their disadvantages.

[0007] The object is achieved by a method having the features of claim 1. The object is further achieved by a computer program product having the features of claim 8 and by an electric drive system having the features of claim 9. Preferred embodiments of the invention are described in the subclaims, in the description or the figures, wherein further features described or shown in the subclaims or in the description or the figures can represent an object of the invention individually or in any combination, unless the context clearly indicates the opposite.

[0008] A method is described for operating an electric motor, wherein the electric motor is in a rotor-stator-rotor configuration and has a first gap with a first thickness d1 between a first rotor and a stator and a second gap with a second thickness d2 between the stator and a second rotor, and wherein the first rotor and the second rotor are electrically excitable separately from one another, the method comprising the following method steps: a) detecting a first open circuit voltage of the first rotor and detecting a second open circuit voltage of the second rotor; b) classifying the first open-circuit voltage and the second open-circuit voltage; and c) adjusting the electrical excitation of at least one of the first rotor and the second rotor based on at least one of the classified open circuit voltages.

[0009] By means of such a process, design-related tolerances, in particular of the rotor-stator-rotor assembly, can be compensated or their disadvantages can be reduced or completely prevented.

[0010] The method described here is therefore used to operate an electric motor. In principle, the electric motor is not restricted; however, it is essential that the electric motor is in a rotor-stator-rotor configuration. Such a configuration is to be understood in particular as meaning that the electric motor in this configuration has a first gap with a first thickness d1 between a first rotor and a stator, and a second gap with a thickness d2 between the stator and a second rotor. The stator and the rotors are expediently arranged on an axis, with the first rotor and the second rotor being arranged axially opposite one another adjacent to the stator. The first rotor and the second rotor can be electrically excited separately from one another. This can be achieved in particular by supplying current to the first and / or the second rotor, whereby current supply is possible independently of one another.For this purpose, the rotors have a coil, which can run continuously through the rotors, particularly in corresponding windings. The stator can also be actively excited. However, it is not fundamentally impossible for the stator to have one or more passive magnets.

[0011] For example, the electric motor can be an axial flux machine (AFM) with two rotors, also known as a double rotor, which is in a rotor-stator-rotor configuration. Due to the technology, axial flux machines have two rotor disks, each outside the stator, which are considered two rotors for the purposes of the invention.

[0012] In principle, however, radial flux machines (RFM) with electrical excitation in the rotor are also conceivable and covered by the scope of the invention.

[0013] For example, due to design constraints, the thickness d1 of the first gap may differ from the thickness d2 of the second gap. To compensate for the resulting disadvantages, the method for operating the aforementioned electric motor comprises the following steps.

[0014] According to process step a), a first open-circuit voltage of the first rotor is detected, and a second open-circuit voltage of the second rotor is detected. Thus, the open-circuit voltage of both rotors is determined from the rotor-stator-rotor configuration. This is easily achieved using the included measuring systems and electronics used to control the current supply.

[0015] According to method step b), the first open-circuit voltage and the second open-circuit voltage are then classified. Classification can be performed in various ways, as explained in detail below. It is essential that the open-circuit voltage is indicative of the distance between the respective rotor and the stator. In other words, the first open-circuit voltage is indicative of the distance d1, and the second open-circuit voltage is indicative of the distance d2.

[0016] According to method step c), the electrical excitation of at least one rotor is adjusted based on at least one of the classified open-circuit voltages. This means that the excitation is not simply based on a predetermined value, but rather that the classification of the first and / or second open-circuit voltage is taken into account when adjusting the excitation of the first and / or second rotor. This step can be performed, for example, via appropriate control in the inverter, such as by reducing or increasing the voltage. Alternatively, it is also possible to enable hardware implementation via an adapted series resistor in the excitation circuit.

[0017] The method described here thus takes advantage of the fact that the open-circuit voltage of the respective rotors can provide an indication of the respective distance between the rotors and the stator. It may be sufficient to infer a difference in the open-circuit voltages, for example, from a difference in the thicknesses d1 and d2, also referred to as gap thicknesses.

[0018] It has been shown that an asymmetric structure, which manifests itself in different gap thicknesses d1 and d2, can result in particular disadvantages. Such asymmetries can occur in electric motors due to design and manufacturing reasons, as the stator and rotor assembly is subject to certain tolerances. These tolerances require, on the one hand, large air gaps between the rotor and stator. On the other hand, one-sided deviations from the nominally identical air gaps can lead to different forces on the components of the assembly. This, in turn, can lead to undesirable effects, such as one-sided bearing loading, which is detrimental to service life and thus costs, or to negatively influenced NVH behavior.

[0019] If, according to the invention, at least one rotor is energized and thus excited based on at least one of the classified open-circuit voltages, these effects can be effectively counteracted. It has been shown that exciting at least one rotor, preferably both rotors, based on the classification makes it possible to effectively counteract the disadvantages that arise, in particular, from asymmetry.

[0020] In particular, the present invention works as follows. With uniform excitation of the first rotor and the second rotor and an asymmetric gap thickness, a different force acts from the rotors on the stator. Since this respective force depends on the magnetic flux of the first rotor and the second rotor, respectively, in addition to the gap thickness d1 and d2, the magnetic flux and thus ultimately the acting force can be adjusted by asymmetrically energizing the rotors. This can improve the forces acting on the bearings and also the NVH behavior.

[0021] This makes it possible to reduce the bearing load on the rotors, which can significantly increase the service life of the corresponding assembly.

[0022] This also results in improved NVH (noise, vibration, harshness) performance. Accordingly, the operation of a vehicle with a correspondingly powered electric motor can be significantly improved and made particularly comfortable for passengers.

[0023] Furthermore, there are advantages in the manufacturing of such systems. Counteracting different gap thicknesses can potentially allow for coarser tolerances of gap thicknesses, as this effectively counteracts any resulting disadvantages. Likewise, the components can be designed with a smaller size.

[0024] In principle, a possible reduction in the air gap thickness could also improve performance. Furthermore, the forces acting on the rotors could be reduced.

[0025] Another advantage is that the method is particularly simple. This is especially true when compared to a stator-rotor-stator configuration. In this configuration, controlling the excitation would be significantly more complex, so the method according to the present invention is characterized by its simplicity and thus also by a greatly reduced susceptibility to errors.

[0026] It may be preferred that a classification according to method step b) is carried out based on a difference between the open-circuit voltages, i.e., the first open-circuit voltage and the second open-circuit voltage. This embodiment thus takes advantage of the fact that it is not absolutely necessary to determine the absolute gap thicknesses d1 and d2, but rather that it is preferably sufficient to determine a difference between the thicknesses d1 and d2 to achieve the advantages of the invention. Accordingly, this embodiment may be preferred and can be particularly simple to implement.

[0027] In principle, it may be preferable for classification according to method step b) to be based on predeterminable limit values. This embodiment can also make the method particularly simple, since no complex computational operations are required; instead, a comparatively simple and error-free comparison can be made using predeterminable data. This can also be particularly simple in the previously described embodiment, according to which classification according to method step b) is based on a difference in the open-circuit voltages, since it is easy to verify whether the difference lies within a predeterminable value range or not.

[0028] Accordingly, it can be advantageous for the predeterminable limit values ​​to relate to an asymmetry and thus a difference between the first thickness d1 and the second thickness d2. As described above, the limit values ​​in this case can define a range in which the thicknesses are equal or have a tolerable difference. In particular, by counteracting an asymmetry, the aforementioned disadvantages can be effectively counteracted. Accordingly, a difference in the open-circuit voltages can be attributed to an asymmetry, i.e., a different gap thickness. This can be achieved by determining the limit values ​​based on appropriate tests or by providing simulations.

[0029] Particularly when asymmetry exists, it can be advantageous for the first rotor and the second rotor to be excited asymmetrically, i.e., with different strengths, in process step c). This is because different or asymmetrical excitation can effectively and precisely counteract the disadvantages caused by different gap thicknesses d1 and d2. For example, the excitation can be reduced in one rotor and / or increased in the second rotor, based on a fundamentally planned or implemented excitation.

[0030] Basically, the level of excitation setting depends on the respective open-circuit voltage or its classification, and thus depends on the strength of the asymmetry.

[0031] It may further be preferred that the method is a calibration method which is carried out at predeterminable operating points during the operation of an electric motor. In this embodiment, the method can be carried out at given operating points, for example when starting or commissioning the electric motor, during servicing, or even periodically during operation, i.e., for example, through specialized control in real time during operation or when errors occur. This generally makes it possible to detect and counteract a varying gap thickness. However, it is also possible for the excitation of the rotors to be carried out for a certain period of time based on the classified data without further monitoring, i.e., without carrying out the method according to the invention, since the risk of a changing gap thickness can be neglected after short operating periods.

[0032] For further technical features or advantages of the method, reference is made to the description of the computer program product, the drive system, the figures and the description of the figures.

[0033] Also described is a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method as described above.

[0034] Such a computer program product can, for example, be loaded onto a control unit of the electric motor or a control unit for the electric motor and include control commands that initialize the steps of the method described here. Accordingly, the control unit can, for example, initialize corresponding measurements and control the excitation of the rotors, as described above with reference to the method.

[0035] The advantage of such a computer program product can be seen in the fact that, as is also relevant for the method, by detecting in particular different gap thicknesses between the stator and the rotors, the resulting disadvantages, such as increased bearing load and negatively influenced NVH behavior, can be counteracted.

[0036] For further technical features or advantages of the computer program product, reference is made to the description of the method, the drive system, the figures and the description of the figures.

[0037] Also described is an electric drive system comprising an electric motor, wherein the electric motor is in a rotor-stator-rotor configuration and has a first gap with a first thickness d1 between a first rotor and a stator and a second gap with a second thickness d2 between the stator and a second rotor, and wherein the first rotor and the second rotor are electrically excitable separately from one another, wherein the drive system has a control unit which is designed to carry out a method as described.

[0038] With regard to the intended electric motor, reference is made to the above description. The electric motor can preferably be an axial flux machine, but is not intended to be limited to this. The drive system now has a control unit, which can be part of the electric motor or connected to it, which is designed to carry out the described method. For this purpose, a computer program product described above can be loaded onto the control unit or a data processing device comprised thereby.

[0039] The advantage of such a drive system can be seen in the fact that, as is also relevant in the method, the resulting disadvantages, such as increased bearing load and negatively influenced NVH behavior, can be counteracted by detecting, in particular, different gap thicknesses between the stator and the rotors.

[0040] For further technical features or advantages of the drive system, reference is made to the description of the method, the computer program product, the figures and the description of the figures.

[0041] The invention is further explained below with reference to the figures, where individual or multiple features of the figures may constitute a feature of the invention, either individually or in combination. Furthermore, the figures are to be viewed only as examples and in no way limiting. Fig. 1 shows an electric drive system according to an embodiment of the present invention, and Fig. 2 shows a detailed view of an electric motor for a drive system from the Fig. 1.

[0042] In the Fig. 1 shows a schematic representation of an electric drive system 10 which can be used, for example, in an electrically powered vehicle.

[0043] Essentially, the drive system 10 comprises an electric motor 12 and a control unit 14, which is connected to the electric motor 12 via a data connection 16. Through the data connection 16, the control unit 14 can influence the operation of the electric motor 12 and retrieve data relating to the function of the electric motor 12.

[0044] The electric motor 12 is shown in a detailed view in the Fig. 2 shown.

[0045] The electric motor 12 is in a rotor-stator-rotor configuration and is designed in particular as an axial flux machine. Accordingly, the electric motor 12, or the rotor-stator-rotor configuration, has a first gap 22 with a first thickness d1 between a first rotor 18 and a stator 20, and a second gap 26 with a thickness d2 between the stator 20 and a second rotor 24. The first rotor 18 and the second rotor 24 each comprise a correspondingly wound coil 28, 30 for forming different poles 32, 34. Accordingly, the first rotor 18 and the second rotor 24 can be electrically excited separately from one another by a corresponding current supply.

[0046] It is further shown that the stator 20 also has a coil 36 for electrically exciting it to form various poles 38, 40. In principle, however, the stator 20 can also comprise a permanent magnet.

[0047] Often, the thicknesses d1 and d2 are different due to the design, which means that with uniform excitation or current supply to the first rotor 18 and the second rotor 24, a different force, shown by the arrows 42, 44, acts from the rotors 18, 24 on the stator 20. Since this respective force depends on the magnetic flux of the first rotor 18 or the second rotor 24 in addition to the gap thickness d1 and d2, the magnetic flux and thus ultimately the acting force can be adjusted by asymmetrically supplying current to the rotors 18, 24. This can improve the forces acting on the bearings and also the NVH behavior. For this purpose, it is possible to infer any asymmetry between the gap thicknesses d1 and d2 based on the open-circuit voltages.

[0048] A correspondingly applicable procedure, which may preferably be a calibration procedure, comprises the following process steps: a) detecting a first open circuit voltage of the first rotor 18 and detecting a second open circuit voltage of the second rotor 24; b) classifying the first open-circuit voltage and the second open-circuit voltage, in particular based on a difference between the open-circuit voltages and based on predeterminable limit values; and c) adjusting the electrical excitation of at least one of the first rotor 18 and the second rotor 24 based on at least one of the classified

[0049] Open-circuit voltages, wherein in process step c) the first rotor 18 and the second rotor 24 are excited asymmetrically.

[0050] The limit values ​​preferably concern an asymmetry of the first distance d1 and the second distance d2. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2020 126 068 A1

[0004]

Claims

[1] Method for operating an electric motor (12), wherein the electric motor (12) is in a rotor-stator-rotor configuration and has a first gap (22) with a first thickness d1 between a first rotor (18) and a stator (20) and a second gap (26) with a second thickness d2 between the stator (20) and a second rotor (24), and wherein the first rotor (18) and the second rotor (24) are electrically excitable separately from one another, characterized by that the procedure comprises the following steps: a) detecting a first open circuit voltage of the first rotor (18) and detecting a second open circuit voltage of the second rotor (24); b) classifying the first open-circuit voltage and the second open-circuit voltage; and c) adjusting the electrical excitation of at least one of the first rotor (18) and the second rotor (24) based on at least one of the classified open circuit voltages. [2] Method according to claim 1, characterized by that a classification according to process step b) is carried out based on a difference in the open circuit voltages. [3] Method according to one of claims 1 or 2, characterized by that a classification according to process step b) is carried out based on predeterminable limit values. [4] Method according to claim 3, characterized by that the predeterminable limit values ​​relate to an asymmetry of the first thickness d1 and the second thickness d2. [5] Method according to one of claims 1 to 4, characterized by that in method step c) the first rotor (18) and the second rotor (24) are excited asymmetrically. [6] Method according to one of claims 1 to 5, characterized by that the method is a calibration method which is carried out at predeterminable operating points during the operation of an electric motor (12). [7] Method according to one of claims 1 to 6, characterized bythat the electric motor (12) is an axial flux machine. [8] A computer program product comprising instructions which, when executed by a computer, cause the computer to carry out a method according to any one of claims 1 to 7. [9] An electric drive system (10) comprising an electric motor (12), wherein the electric motor is in a rotor-stator-rotor configuration and has a first gap (22) with a first thickness d1 between a first rotor (18) and a stator (20) and a second gap (26) with a second thickness d2 between the stator (20) and a second rotor (24), and wherein the first rotor (18) and the second rotor (24) are electrically excitable separately from one another, characterized by that the drive system (10) has a control unit (14) which is designed to carry out a method according to one of claims 1 to 7. [10] Electric drive system (10) according to claim 9, characterized by that the electric motor (12) is an axial flux machine.

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