System comprising an electric motor and a structure-borne sound sensor

Abstract

System comprising an electric motor and a structure-borne sound sensor, wherein the sensor is electrically connected to an evaluation unit, in particular which is integrated into an inverter supplying the electric motor, wherein the evaluation unit is designed to subject the sensor signal to a Fourier transformation and to determine the frequency of a slip-dependent vibration mode and from this to determine the rotational speed of the rotor shaft of the electric motor.

Description

[0001] The invention relates to a system comprising an electric motor and a structure-borne sound sensor.

[0002] DE 10 2011 101 599 B4 discloses a system for determining structure-borne sound in a test specimen.

[0003] A method for determining a synchronous speed is known from DE 10 2020 005 050 A1.

[0004] The invention is therefore based on the object of further developing the speed detection in an electric motor in a cost-effective manner.

[0005] According to the invention, the object is achieved in the system according to the features specified in claim 1.

[0006] Important features of the invention in the system comprising an electric motor and a structure-borne sound sensor are that

[0007] in particular wherein the structure-borne sound sensor is arranged on the electric motor, in particular for detecting structure-borne sound generated by the electric motor, wherein the sensor is electrically connected to an evaluation unit, in particular which is arranged integrated in a converter feeding the electric motor, wherein the evaluation unit is designed to subject the sensor signal to a Fourier transformation and to determine the frequency of a slip-dependent oscillation mode and therefrom to determine the speed of the rotor shaft of the electric motor, in particular wherein the evaluation unit has a memory in which the number of stator slots and the number of rotor slots of the electric motor are stored.

[0008] The advantage here is that the speed of the rotor shaft can be easily determined from the recorded vibrations using a simple, cost-effective vibration sensor using Fourier transformation.

[0009] In an advantageous embodiment, the electric motor is fed by a converter, in particular in which the evaluation unit is integrated, wherein an angle sensor is arranged on the electric motor to detect the rotational position of the rotor shaft of the electric motor, in particular - wherein the converter is designed to determine a speed of the rotor shaft from the values ​​detected by the angle sensor and to compare this with the speed determined from the frequency of the slip-dependent vibration mode and, in the event of an inadmissibly large deviation between the two speeds, to display and / or forward a warning and / or to put the electric motor into a safe state.

[0010] A major advantage is that the evaluation of the signals recorded by the structure-borne sound sensor can be carried out using the signal electronics integrated in the converter. This is because the signal electronics incorporates a microcontroller that, in addition to the control calculations for controlling the electric motor, also performs the Fourier transformation of the value curves recorded by the structure-borne sound sensor. This eliminates the need for additional hardware, particularly with the exception of structure-borne sound.

[0011] In an advantageous embodiment, a pulse wire sensor is arranged on the electric motor, which determines the absolute number of revolutions, in particular the number of revolutions completed, of the rotor shaft by detecting a permanent magnet that is rotationally fixedly connected to the rotor shaft. The evaluation unit, or at least a region of the evaluation unit comprising a counting unit, is or can be electrically supplied from the pulse wire sensor. It is advantageous that the counting unit of the evaluation unit can be supplied from the voltage pulses emitted by the pulse wire sensor.

[0012] Important features of the procedure are that In a first step, the temporal progression of the structure-borne noise at the electric motor is recorded, wherein in a second method step following the first method step, a frequency spectrum is determined, in particular by means of Fourier transformation of the temporal course of the structure-borne sound, wherein in a third method step following the second method step, the frequency f_1 of a slip-dependent vibration mode is determined from the frequency spectrum and the speed of the rotor shaft is determined therefrom, where parameters of the electric motor, such as the number of stator slots, the number of rotor slots and the number of pole pairs, the supply frequency of the motor voltage applied to the electric motor and the synchronous speed, in particular the rotating field speed, are taken into account to determine the slip-free frequency f_0 of the vibration mode, in particular using f_0−f_1=ω s(μ / p−1) and n=nsyn(1−s), where ω is the supply frequency of the electric motor, s is the slip value, p is the number of pole pairs, n syn the synchronous speed of the electric motor and n is the speed of the rotor shaft, where μ=p⋅(1+N2p⋅g) or µ = µ 3p = 3p + gN2, where g is an integer, where N2 is the number of slots of the rotor of the electric motor.

[0013] The advantage here is that the speed can be determined from the structure-borne sound measurement. This eliminates the need for any special hardware. The method is particularly simple to implement with an asynchronous electric motor. The type of vibration mode is known, and thus the parameters that lead to its formation are also known.

[0014] In an advantageous embodiment, the slip of the electric motor is determined from the difference between frequency f_1 and frequency f_0, taking the parameters into account, and from this, the speed of the electric motor's rotor shaft is determined, whereby the synchronous speed, in particular the rotating field speed, is taken into account and / or used. The advantage here is that the determination is easy to implement and only a vibration sensor or structure-borne sound sensor is required as a sensor.

[0015] In an advantageous embodiment, the electric motor is fed by a converter in which a model value for the torque generated by the electric motor is determined and from this a model value for the slip is determined and from this a model value for the frequency f_1 is determined,

[0016] In the third method step, the frequency assigned to a local maximum is determined as the first frequency f_1 in the frequency spectrum within a frequency range containing the model value for the frequency f_1 and having a predetermined bandwidth and / or having a predetermined bandwidth around the model value for the frequency f_1. The advantage of this is that the risk of confusing the oscillation mode with another oscillation mode whose frequency is very close is reduced.

[0017] In an advantageous embodiment, the electric motor is fed by a converter in which a model value for the torque generated by the electric motor is determined at regular intervals and from this a respective model value for the slip is determined and the first to the third method step is carried out in each case, so that for different values, in particular for a substantially slip-free and a slip-affected value, of the slip in the respective third method step, the frequency f_1 of the slip-dependent oscillation mode is determined from the frequency spectrum and the speed of the rotor shaft is determined from the different values ​​of the frequency f_1 assigned to different values ​​of the slip, in particular using the context Δf_1=ω Δs(μ / p−1) and n−nsyn≈Δn=−nsyn Δs, where Δf_1 is the difference between two frequencies f_1 determined at different slip values, ω is the supply frequency of the electric motor, Δs is the difference between the two slip values, p is the number of pole pairs, Δn is the difference between the speeds of the electric motor at the two different slip values, n syn the synchronous speed of the electric motor and n is the speed of the rotor shaft, where μ=p⋅(1+N2p⋅g) or µ = µ 3p = 3p + gN2, where g is an integer, where N2 is the number of slots on the electric motor's rotor. The advantage of this is that the speed can be determined as accurately as possible during operation and the associated temperatures. However, it is important that the torque does not always remain constant during operation, but rather becomes very small at certain intervals. This improves the consideration of thermal influences. For example, the first frequency f_1 is determined during slip-free operation and then at rated load or rated torque. This allows for a simple yet sufficiently accurate determination of the rotor shaft speed.

[0018] In an advantageous embodiment, the speed determined in this way is fed to a converter, which also receives the angle values ​​of the electric motor's rotor shaft, measured by an angle sensor. This is advantageous because the control quality can be improved. In particular, the speed calculated from the structure-borne sound sensor or vibration sensor can be used as a pilot control value. This is fed to the control device via a pilot control path. This enables very rapid adjustment of the control device.

[0019] In an advantageous embodiment, the speed thus determined is compared with a speed determined from the angle values ​​of the electric motor's rotor shaft detected by an angle sensor. If the two speeds deviate from each other by an unacceptably large amount, a warning message is displayed or forwarded, particularly via a data exchange connection. This is advantageous in that safety is increased. In particular, safety-oriented operation of the system is enabled.

[0020] In an advantageous embodiment, the signals of the pulse wire sensor triggered by a permanent magnet connected to the rotor shaft in a rotationally fixed manner when the magnet rotates past a pulse wire sensor are fed to a counting unit, from which the absolute number of revolutions of the rotor shaft is determined, In particular, the absolute rotational position and / or angular position is determined from the pulse wire signals and the speed determined from the frequency of the slip-dependent oscillation mode. The advantage here is that the rotations of the rotor shaft can be detected even in the event of a power failure.

[0021] In an advantageous embodiment, the motor is fed by the converter in such a way that when the motor is started and / or when the motor is operated, different values ​​of the frequency f1 occur, The structure-borne sound amplitude corresponding to the respective frequency f1 is determined and monitored for exceeding a threshold value. The advantage of this method is that a distinction can be made between the structure-borne sound amplitude caused by fault-free engine operation and the additional structure-borne sound amplitude that occurs when engine damage is detected. A threshold value is therefore used that is not exceeded when the engine is fault-free. However, if engine damage occurs, a high amplitude is generated. Structure-borne sound detection is therefore used both for speed determination and for damage detection. In particular, damage detection also functions in the speed determination operating range.

[0022] In an advantageous embodiment, in addition to determining the speed from the slip-dependent vibration mode, it is checked whether one or more, in particular other, harmonics caused by the use can be detected, in particular with a signal-to-noise ratio above a threshold value, in particular to improve the reliability of speed determination and / or to exclude resonance oscillations occurring in the slip-dependent frequency band.

[0023] The advantage here is the increased reliability in determining the speed. While the slip-dependent vibration mode generates a structure-borne sound amplitude sufficiently large for detection, a resonance vibration, particularly due to manufacturing or damage, could occur in the measuring range and thus cause confusion. However, since the harmonic is searched for and whether the harmonic associated with the fundamental is present, interference with the speed determination can be detected and / or avoided.

[0024] Further advantages emerge from the dependent claims. The invention is not limited to the combination of features in the claims. Further possible combinations of claims and / or individual claim features and / or features of the description and / or the figures will become apparent to those skilled in the art, particularly from the problem and / or the problem posed by comparison with the prior art.

[0025] The invention will now be explained in more detail using schematic illustrations: In the Fig. 1 is the drive according to the invention, comprising an electric motor 1, a sensor 2 and a Fig. 1 not shown, which feeds the electric motor 1.

[0026] As shown in the figure, a first sensor is arranged on the electric motor 1, which detects structure-borne sound, in particular vibrations. The first sensor is preferably arranged on a bearing flange or bearing plate of the electric motor, in particular magnetically held or attached with a screw part, such as a screw or threaded bolt.

[0027] The first sensor is connected to an evaluation unit, which is optionally integrated in the converter, in particular in the signal electronics of the converter.

[0028] The evaluation unit determines the exact frequency value of a first type of vibration. For example, the sensor signal is Fourier transformed and a characteristic frequency is then identified in the spectrum, particularly the frequency with the largest amplitude.

[0029] The frequency of the first vibration type, in particular the vibration mode, is determined as accurately as possible. Preferably, the frequency of the first vibration type depends on the slip of the electric motor, which is designed as an asynchronous motor. Thus, the speed of the rotor shaft of the asynchronous motor can be determined by recording and evaluating the temporal progression of the structure-borne sound using the first sensor.

[0030] In addition, the electric motor has a second sensor for detecting the angular position, in particular for detecting the rotational position, of the rotor shaft.

[0031] The values ​​of the angular position, in particular the rotational position, detected by the second sensor are fed to the converter, in particular its signal electronics.

[0032] Thus, the values ​​detected by the first sensor 2 and the second sensor are available to a control device of the signal electronics in order to control the electric motor, and a higher level of accuracy and control quality can be achieved than when using only a single sensor.

[0033] Alternatively or additionally, the speed is determined from the values ​​of the angular position of the electric motor's rotor shaft detected by the second sensor and fed to the signal electronics, in particular the control device. Thus, two speed values ​​determined by different physical means are available to the signal electronics, thus enabling safety-related monitoring of the speed values.

[0034] In this way, the safe operation of the drive can be guaranteed.

[0035] Alternatively or additionally, a pulse wire sensor, in particular a Wiegand sensor, can also be provided, which generates an electrical voltage pulse when a permanent magnet connected to the rotor shaft in a rotationally fixed manner rotates past and is thus used to determine the absolute number of revolutions of the rotor shaft. The electronic counting unit, designed to determine the number, is powered only by the respective voltage pulse. In this way, the counting unit can be operated without an external electrical supply. Likewise, the first sensor, including the evaluation unit, can be designed using a piezo element and can thus be electrically powered by the vibrations to be detected. Together with the counting unit, a speed value and the absolute number of revolutions completed by the rotor shaft can be displayed or made available at any time, in particular for the signal electronics of the converter.

[0036] The evaluation unit and the counting unit can also be arranged together, separately from the signal electronics, directly on the electric motor.

[0037] In further embodiments of the invention, another vibration sensor, such as a microphone, is used instead of the structure-borne sound sensor.

[0038] In further embodiments of the invention, parameters of the electric motor are stored in a memory of the evaluation unit and / or the signal electronics, so that parameters characterizing the electric motor, such as the number of stator slots, the number of rotor slots, the number of phases, or other winding-related parameters, the number of pole pairs, and the grid frequency, can be taken into account by determining the frequency of slot-related, slip-dependent harmonics. Thus, the slip-dependent frequency band corresponding to one of the harmonics can be determined, and then, in the structure-borne sound spectrum determined by transformation from the recorded values, the maximum within this frequency band can be assigned as the amplitude of the first frequency.

[0039] In alternative further embodiments according to the invention, a model value for the torque supplied by the electric motor is determined by the signal electronics of the converter, in particular according to a machine model of the electric motor, and for two different torque values, the respective structure-borne sound spectrum is determined from currently recorded values ​​by transformation and then the first frequency of the slip-dependent harmonic is determined by determining the largest local maximum, which shifts depending on the torque, in particular is arranged in a predetermined tolerance band.

[0040] A specific embodiment is described below. The electric motor 1 is designed as a three-phase three-phase asynchronous machine and generates induction rotating waves B through the slotting of the stator winding. v (φ,t) = B̂ vcos(v· φ- ω · t) with the ordinal numbers v) = p · (1+3g), where p is the number of pole pairs and g = 0,±1,±2,... Each of the induction rotating waves excites a vibration mode of the electric motor.

[0041] With a particular amplitude, those slot harmonics occur which can excite a vibration mode of the electric motor with a particular amplitude and have the ordinal numbers v N = p + g · N1, where N1 is the number of stator slots.

[0042] In addition to the harmonics caused by the use, harmonics caused by the magnetic saturation also occur and generate saturation residual fields, especially with the third harmonic Bμ3p(φ,t)=B^μ3p⋅cos(μ3p⋅φ−(3s+μ3pp⋅(1−s)⋅ω⋅t)) with atomic numbers µ 3p =3p+gN2. This excites further vibration modes of the electric motor.

[0043] The vibration mode excited by the rotor, i.e. the induction wave generated by the rotor, B µ(φ, t) = B̂ µ · cos(µ · φ - s· ω · t) has the ordinal numbers μ=p⋅(1+N2p⋅g), where s is the slip of the motor and N2 is the number of slots of the rotor.

[0044] The two induction rotary waves combine to form radial force waves of ordinal number r in the following form: Rr(φ,t)=1μ0BvBμcos(rφ−ωTont) with r=μ±v and ωTon=ω[(μp−1)⋅(1−s)+2]for rr=μ+υ or ωTon=ω[(μp−1)⋅(1−s)] for rr=μ−v

[0045] Thus, further vibration modes of the electric motor are excited with these frequencies.

[0046] The value curve recorded by the vibration sensor, specifically the structure-borne sound sensor, is used by the evaluation unit to determine a frequency spectrum. This spectrum shows the amplitudes assigned to the individual vibration modes.

[0047] At the audio frequencies, i.e. the vibration modes arranged in the audible range, with the participation of the groove harmonics, correspondingly sharp individual tones can occur.

[0048] For example, at a first frequency, a very high amplitude is formed as a local, particularly sharp maximum. This oscillation mode, which occurs in an asynchronous machine, i.e., an asynchronous motor with N1=36 and N2=28 and which is electrically fed with a supply frequency of ω=50 Hz, is particularly clearly recognizable.

[0049] In this example case, the ordinal numbers v =26 combine with a saturation residual field µ 3p =30 to a radial force wave of 4th order with a tone frequency according to (2) of 900 Hz at no-load, i.e. in slip-free operation of the asynchronous machine.

[0050] Due to the load, the slip of the machine increases and according to the factor (1-s) in (2), the frequency decreases to, for example, 857 Hz, as can then be determined using the method according to the invention.

[0051] Therefore, the difference 900 Hz - 857 Hz = ω s (µ / p - 1) or transformed: s=1−(900 Hz−857 Hz) / ω(μ / p−1).

[0052] From this relationship, the speed can be determined directly according to n = n syn (1 - s), where n syn the synchronous speed, in particular the rotating field speed.

[0053] If, in addition to determining the electric motor's speed, a check is carried out to determine whether one or more other harmonics caused by usage are detectable, especially with a signal-to-noise ratio above a threshold, the reliability of speed determination can be improved. This is because if a disturbing resonance oscillation or one caused by a design defect occurs in the slip-dependent frequency band, confusion with the slip-dependent oscillation mode could occur. However, by detecting a harmonic caused by usage, this confusion can be identified and / or prevented. List of reference symbols 1 electric motor 2 sensors 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 2011 101 599 B4

[0002] DE 10 2020 005 050 A1

[0003]

Claims

[1] System comprising an electric motor and a structure-borne sound sensor, in particular wherein the structure-borne sound sensor is arranged on the electric motor, in particular for detecting structure-borne sound generated by the electric motor, wherein the sensor is electrically connected to an evaluation unit, in particular which is arranged integrated in a converter feeding the electric motor, characterized by , that the evaluation unit is designed to subject the sensor signal to a Fourier transformation and to determine the frequency of a slip-dependent oscillation mode and from this to determine the speed of the rotor shaft of the electric motor, in particular wherein the evaluation unit has a memory in which the number of stator slots and the number of rotor slots of the electric motor are stored. [2] System according to claim 1, characterized by , that the electric motor is powered by a converter, in particular in which the evaluation unit is integrated, wherein an angle sensor is arranged on the electric motor to detect the rotational position of the rotor shaft of the electric motor, in particular - wherein the converter is designed to determine a speed of the rotor shaft from the values ​​detected by the angle sensor and to compare this with the speed determined from the frequency of the slip-dependent vibration mode and, in the event of an inadmissibly large deviation between the two speeds, to display and / or forward a warning and / or to put the electric motor into a safe state. [3] System according to one of the preceding claims, characterized by , that a pulse wire sensor is arranged on the electric motor, which determines the absolute number of revolutions, in particular the revolutions completed, of the rotor shaft by detecting a permanent magnet connected to the rotor shaft in a rotationally fixed manner, in particular, wherein the evaluation unit or at least a region of the evaluation unit comprising a counting unit is or can be electrically supplied from the pulse wire sensor. [4] Method for operating an electric motor, in particular method for operating a system according to one of the preceding claims, in particular wherein the electric motor is an asynchronous motor supplied with a three-phase voltage, characterized by , that In a first step, a temporal progression of the structure-borne sound detected by a sensor on the electric motor is recorded, wherein in a second method step following the first method step, a frequency spectrum is determined, in particular by means of Fourier transformation, in particular FFT, of the curve, wherein in a third method step following the second method step, the frequency f_1 of a slip-dependent vibration mode is determined from the frequency spectrum and the speed of the rotor shaft is determined therefrom, where parameters of the electric motor, such as the number of stator slots, the number of rotor slots and the number of pole pairs, the supply frequency of the motor voltage applied to the electric motor and the synchronous speed, in particular the rotating field speed, are taken into account to determine the slip-free frequency f_0 of the vibration mode, in particular using f_0−f_1=ω s(μ / p−1) and n=nsyn(1−s), where ω is the supply frequency of the electric motor, s is the slip value, p is the number of pole pairs, n syn the synchronous speed of the electric motor and n is the speed of the rotor shaft, where μ=p⋅(1+N2p⋅g) or µ = µ 3p = 3p+gN2, where g is an integer, where N2 is the number of slots of the rotor of the electric motor. [5] Method according to one of the preceding claims, characterized by , that from the difference between the frequency f_1 and the frequency f_0, taking into account the parameters of the slip of the electric motor, and from this the speed of the rotor shaft of the electric motor, whereby the synchronous speed, in particular the rotating field speed, taken into account and / or used. [6] Method according to one of the preceding claims, characterized by , that the electric motor is fed by an inverter in which a model value for the torque generated by the electric motor is determined and from this a model value for the slip is determined and from this a model value for the frequency f_1 is determined, wherein in the third process step in the frequency spectrum within a frequency range, which contains the model value for the frequency f_1 and has a predetermined bandwidth and / or which has a predetermined bandwidth around the model value for the frequency f_1, the frequency assigned to a local maximum is determined as the first frequency f_1. [7] Method according to one of the preceding claims, characterized by , that the electric motor is fed by a converter in which a model value for the torque generated by the electric motor is determined at regular intervals and from this a respective model value for the slip is determined and the first to the third method step is carried out in each case, so that for different values, in particular for a substantially slip-free and a slip-affected value, of the slip in the respective third method step, the frequency f_1 of the slip-dependent oscillation mode is determined from the frequency spectrum and the speed of the rotor shaft is determined from the different values ​​of the frequency f_1 assigned to different values ​​of the slip, in particular using the context Δf_1=ω Δs(μ / p−1) and n≈nsyn+Δn=nsyn(1−Δs), where Δf_1 is the difference between two frequencies f_1 determined for different slip values, ω is the supply frequency of the electric motor, Δs is the difference between the two slip values, p is the number of pole pairs, Δn is the difference between the speeds of the electric motor at the two different slip values, n syn the synchronous speed of the electric motor and n is the speed of the rotor shaft, where μ=p⋅(1+N2p⋅g) or µ = µ 3p =3p+gN2, where g is an integer, where N2 is the number of slots of the rotor of the electric motor. [8] Method according to one of the preceding claims, characterized by that the speed determined in this way is fed to an inverter, to which the angle values ​​of the rotor shaft of the electric motor, recorded by means of an angle sensor, are also fed. [9] Method according to one of the preceding claims, characterized bythat the speed determined in this way is compared with a speed determined from the angle values ​​of the rotor shaft of the electric motor detected by means of an angle sensor and, if the two speeds deviate from each other by an unacceptably high amount, a warning message is displayed or forwarded, in particular via a data exchange connection. [10] Method according to one of the preceding claims, characterized by , that a counting unit which receives signals from the pulse wire sensor triggered by a permanent magnet connected to the rotor shaft in a rotationally fixed manner when the magnet rotates past a pulse wire sensor, from which the absolute number of revolutions of the rotor shaft is determined, in particular, the absolute rotational position and / or angular position is determined from the signals of the pulse wire and from the rotational speed determined from the frequency of the slip-dependent oscillation mode. [11] Method according to one of the preceding claims, characterized by , that the motor is supplied by the inverter in such a way that different values ​​of the frequency f1 occur when the motor is started and / or when the motor is running, wherein the structure-borne sound amplitude corresponding to the respective frequency f1 is determined and monitored for exceeding a threshold value, in particular for detecting engine damage generating a resonance vibration. [12] Method according to one of the preceding claims, characterized by , that In addition to determining the speed from the slip-dependent vibration mode, it is checked whether one or more, in particular other, harmonics caused by the use of the motor can be detected, in particular with a signal-to-noise ratio above a threshold value, in particular to improve the reliability of speed determination and / or to exclude resonance oscillations occurring in the slip-dependent frequency band.

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