Methods for reducing noise and / or torque ripple in separately excited electrical machines

Abstract

Method (300) for adapting the sound generation on a separately excited electrical machine (100), wherein - the machine (100) comprises a rotor (103) with a rotor winding (104) for generating a magnetic rotor flux and a stator (101) with a stator winding (102) for generating a rotating magnetic field; - the method (300) comprises varying (301) one of the electrical rotor power supplied to the rotor winding (104) depending on sound information; - the sound information includes information relating to sound of the electric machine (100); - the method (300) comprises modulating, in a first period, a voltage applied to the stator winding (102) with a signal in order to determine a rotor position of the rotor (103); - the signal includes a signal component with a frequency between 100Hz and 20kHz; - the sound information displays information relating to the sound generated by modulating the voltage at the stator winding (102); and - the rotor power is varied during the first period to reduce the amount of noise generated by modulating the voltage at the stator winding (102).

Description

[0001] The invention relates to a method and a corresponding control unit for reducing sound (especially noise) and / or torque irregularities in separately excited electrical machines, e.g., separately excited synchronous machines.

[0002] Electric machines can be used in vehicles to propel them and / or to recuperate energy during braking. During operation, an electric machine typically generates noise (structure-borne and / or acoustic noise) that can be disturbing to a vehicle user.

[0003] The causes of noise can be very diverse and may differ for each electrical machine. For example, nonlinear effects can lead to noise generation. Each electrical machine can therefore produce different types of noise. Noise can be dampened by shielding, but this incurs additional costs and requires additional installation space in a vehicle.

[0004] DE 196 08 992 A1 describes a method for reducing the noise generated by a generator. US 9 106 178 B2 describes a method for reducing the torque ripple of an electric machine. DE 20 2014 010 397 U1 describes a method for reducing the noise of a servo motor. US 9 013 137 B2 describes a method for determining the rotor position of an electric machine.

[0005] This document addresses the technical challenge of efficiently and reliably reducing the noise generated by a separately excited electric machine. Furthermore, this document addresses the technical challenge of efficiently and reliably reducing irregularities in the torque curve produced by a separately excited electric machine.

[0006] The problem is solved by the independent claim. Advantageous embodiments are described, among other things, in the dependent claims.

[0007] According to one aspect, a method for adjusting (especially reducing) the noise generation at and / or by a separately excited electrical machine is described. The machine comprises a rotor with (at least) one rotor winding for generating a magnetic rotor flux (along a so-called d-axis). The machine also comprises a stator with (at least) one stator winding (typically with three stator windings) for generating a rotating magnetic field.

[0008] The method involves varying the electrical rotor power supplied to the rotor winding as a function of sound information, where the sound information comprises or indicates information relating to sound from the electrical machine. The sound information can, for example, include information relating to sound generated by the electrical machine at a current time or generated at a previous time (e.g., during a test phase of the machine). The sound information can be acquired using a sound sensor, in particular a microphone, and / or a structure-borne sound sensor. When varying the rotor power, the time profile of the rotor power can be adjusted as a function of the sound information. The variation of the rotor power can be achieved by varying the rotor current through (at least one) rotor winding.

[0009] By adjusting the rotor power used to generate the rotor flux, the sound produced by the electric machine (structure-borne and / or acoustic sound) can be modified. For example, the sound can be adjusted to a specific target sound level (e.g., to adjust the sound profile of the electric machine). Furthermore, the level of generated sound can be efficiently reduced.

[0010] The sound information can include information relating to sound generated (or that would be generated) by the electric machine when the electric machine is operated with a reference rotor power, in particular with a (time-dependent) reference profile of the rotor power. The reference rotor power can, in particular, correspond to a time-constant rotor power of a specific value.

[0011] The rotor power can then be changed compared to the reference rotor power; in particular, the time course of the rotor power can be changed compared to the reference course in order to reduce the amount of noise generated by the electric machine.

[0012] The sound information can, for example, indicate a fundamental sound that is (or would be) generated by the electric machine when driven with the reference rotor power, particularly when driven with the reference rotor power curve. The rotor power can then be modified relative to the reference rotor power, and in particular, the time curve of the rotor power can be modified relative to the reference curve, such that the rotor generates an anti-sound that at least partially compensates for the fundamental sound. For this purpose, the anti-sound can be out of phase with the fundamental sound.

[0013] As explained above, the rotor power can include a constant component (e.g., the reference waveform) to generate a constant magnetic rotor flux. Varying the rotor power can then involve modulating this constant component (e.g., the reference waveform) with a modulation signal, where the modulation signal depends on the sound information. The modulation signal typically depends on the sound of the electric machine in such a way that the modulation signal itself conveys information about the sound of the electric machine. Thus, the sound information can encompass the modulation signal, or the sound information can correspond to the modulation signal.

[0014] The sound information can be acquired during the operation of the electric machine. Varying the rotor power can then involve adjusting, and in particular regulating, the rotor power based on the acquired sound information and on target sound information, which indicates the desired level of sound to be generated by the electric machine. The target sound information can, for example, indicate that no sound should be generated. By considering the target sound information, the sound generated by the electric machine can be reliably and precisely adjusted, and in particular reduced.

[0015] On the other hand, the sound information can be recorded during a test phase of the electric machine. Different sound information can be recorded for different operating states of the electric machine. These different operating states can include, for example, different rotational speeds and / or different torques.

[0016] Furthermore, based on the varying sound information, data sets for different operating states can be generated, each showing a temporal profile of the rotor power. This allows the noise generated by the electric machine to be adjusted, particularly reduced. Thus, a database with numerous data sets for a corresponding variety of operating states can be provided based on the sound information. These data sets can each display a temporal profile of the rotor power (dependent on the operating state), with the respective profile of the rotor power depending on the specific (operating state-dependent) sound information. These data sets can then be used during operation of the electric machine to adjust its noise level (depending on the machine's operating state).

[0017] The method can include, in particular, determining the current operating state of the electric machine and selecting a data set for that current operating state from the database. The data set for the current operating state depends on sound information from the electric machine for that current operating state (which was, for example, recorded during a test phase). The rotor power can then be varied depending on the time profile displayed in the data set. By providing data sets with predetermined time profiles for the rotor power, the use of a sound sensor during the operation of an electric machine can be eliminated (thereby reducing costs and installation space).

[0018] The method can involve modulating, during a first period, a voltage applied to the stator winding with a signal to determine the rotor position. Specifically, a so-called high-frequency signal injection process can be used to determine the rotor position (without using a rotor position sensor). The signal can include a frequency component between 100 Hz and 20 kHz (i.e., within the audible range for humans). The acoustic information can indicate the sound generated by modulating the voltage on the stator winding (and, in particular, by the signal). The rotor power can then be varied during the first period to reduce the amount of sound generated by modulating the voltage on the stator winding. This allows for convenient measurement of the rotor position without the use of a rotor position sensor.

[0019] According to another aspect, a method for adjusting (especially reducing) the torque ripple of a separately excited electric machine is described. The torque produced by a machine can exhibit irregularities (i.e., ripple) during one revolution of the machine's rotor. The method can be designed to reduce or even eliminate this torque ripple.

[0020] The machine comprises a rotor with a rotor winding for generating a magnetic rotor flux and a stator with a stator winding for generating a rotating magnetic field. The method involves varying the electrical rotor power supplied to the rotor winding as a function of ripple information, wherein the ripple information includes or indicates information relating to a non-uniformity in the torque curve produced by the machine (in particular, the curve during one revolution of the machine's rotor).

[0021] Therefore, modulation of the rotor flux can be used to reduce the torque ripple of a machine. This torque ripple can be caused by asymmetries in the machine's design and / or in the pole configuration.

[0022] Ripple information can be acquired for a machine in advance. Specifically, the (average) torque curve generated by the machine during one rotor revolution can be recorded as ripple information for different operating states. Furthermore, a modulation signal can be determined based on this ripple information, which can then be used to modulate the rotor power and reduce torque ripple. This modulation signal can depend on the machine's operating state or mode. In other words, different modulation signals can be provided for different operating states or modes.

[0023] The aspects described in this document regarding sound-information-dependent rotor power adjustment can be applied analogously to rotor power adjustment based on ripple information. In particular, rotor power adjustment can involve modulating a (constant) reference rotor power curve with a modulation signal. This modulation signal is dependent on the ripple information. Consequently, the modulation signal indicates any unevenness in the torque curve produced by the machine. The ripple information can therefore include or correspond to the modulation signal.

[0024] Furthermore, the rotor power can be adjusted depending on the sound information and / or the ripple information (possibly also in combination). Thus, in different operating states or modes (possibly selectively or in combination), various disturbances (noise emission and / or torque ripple) of the machine can be at least partially eliminated by adjusting the rotor power.

[0025] According to another aspect, a control unit (e.g. with a processor) is described that is set up to execute the procedures described in this document.

[0026] According to another aspect, a vehicle (in particular a road vehicle, e.g. a passenger car, a truck or a motorcycle) is described that includes the control unit described in this document.

[0027] Another aspect described is a software (SW) program. The SW program can be configured to run on a processor and thereby execute the procedure described in this document.

[0028] Another aspect describes a storage medium. This storage medium can include a software program configured to run on a processor and thereby execute the procedure described in this document.

[0029] It should be noted that the methods, devices, and systems described in this document can be used both alone and in combination with other methods, devices, and systems described in this document. Furthermore, any aspect of the methods, devices, and systems described in this document can be combined with one another in a variety of ways. In particular, the features of the claims can be combined with one another in a variety of ways.

[0030] The invention will now be described in more detail using exemplary embodiments. Fig. 1 an exemplary electric machine; Fig. 2 an exemplary time course of an emitted sound signal and an anti-sound signal; and Fig. 3 A flowchart of an exemplary procedure for adjusting the sound emission of an electric machine.

[0031] As stated at the outset, this document deals with the efficient and reliable reduction of noise emitted by an electric machine. In this context, it shows Fig. Figure 1 shows an exemplary separately excited synchronous machine 100. The machine 100 comprises a stator 101 with one or more stator windings 102 for generating a rotating magnetic field. Furthermore, the machine 100 comprises a rotor 103 with at least one rotor winding 104 for generating a stationary magnetic field, which has a north pole on one side of the rotor 103 and a south pole on the opposite side. The rotor 103 is rotatably mounted in an interior space of the machine 100, so that the rotor 103 can rotate with the rotating magnetic field. The rotor winding 104 is supplied with electrical energy (in particular with direct current) via a slip ring 105.

[0032] The machine 100 can be controlled by a control unit 110. In particular, the rotational frequency of the rotating magnetic field can be adjusted by the control unit 110 to adapt the rotational speed of the rotor 103 of the machine 100. Furthermore, the rotor current (typically a direct current) can be set. By adjusting the level of the rotor current, the torque generated by the machine 100 can, for example, be changed.

[0033] When the rotor 103 rotates, sound can be emitted, particularly in the air gap 106 between the rotor 103 and the stator 101, resulting in the generation of noise. Due to the rotation of the rotor 103, the emitted sound is typically periodic, with the periodicity of the emitted sound depending on the rotational speed of the rotating magnetic field. Fig. Figure 2 shows an example sound signal 204 (amplitude 202 as a function of time 201) emitted by an electric machine 100. The sound signal 204 can be detected by a sound sensor 111 (e.g., a microphone or a structure-borne sound sensor). The sound signal 204 can be detected during a test phase (e.g., for different rotational speeds or different operating states of the electric machine). Alternatively or additionally, the sound signal 204 can be detected during operation of the electric machine 100.

[0034] The control unit 110 can be configured to adjust the electrical power supplied to the rotor winding 104 depending on the sound signal 204 or, more generally, depending on sound information related to the sound emitted by the machine 100. For this purpose, the rotor current can be modulated depending on the sound information. The temporal modulation of the electrical power supplied to the rotor winding 104 can be carried out in such a way that the sound emission of the machine 100 is at least partially compensated by the modulation. In particular, the modulation can cause the emission of an anti-sound, whereby the anti-sound at least partially compensates for the (fundamental) sound emitted by the machine 100. This is in Fig. 2 illustrated by the anti-sound signal 203, which has an opposite phase to the (fundamental) sound signal 204.

[0035] The modulation of the electrical power supplied to the rotor winding 104 can be determined during a test phase. In particular, a modulation signal for the rotor current and / or the rotor voltage can be determined (for different operating states of the machine 100) that reduces (especially minimizes) the noise emission of the electric machine 100. Different modulation signals for different operating states can thus be determined in advance and stored in data sets. During operation of the electric machine 100, the current operating state of the machine 100 can then be determined and the corresponding modulation signal selected. The electrical power supplied to the rotor winding 104 (also referred to as rotor power) can then be modulated with the predetermined modulation signal to reduce the noise emission of the electric machine 100 in the current operating state.

[0036] Alternatively or additionally, the current sound emission of the electric machine 100 can be detected during operation using a sound sensor 111. The control unit 110 can then determine a modulation signal for the rotor power during operation, so that the current sound emission of the electric machine 100 is reduced, in particular minimized. For this purpose, a control system can be implemented with the detected current sound emission as the controlled variable and the modulation signal as the controlled variable.

[0037] To adjust the modulation signal, the control unit 110 can, if necessary, access a model of the machine 100 that shows how the sound emission of the electric machine 100 changes when the rotor power modulation is altered. In other words, the model can show the effect of the rotor power modulation on the sound emission. The model can be determined during a test phase for an electric machine 100. For example, the model can include characteristic maps that show the sound emission of the machine 100 as a function of the rotor power modulation (e.g., as a function of the amplitude and / or frequency of the modulation).

[0038] In a separately excited synchronous machine 100, an additional degree of freedom is available via the control of the rotor current. This degree of freedom can be used to generate an anti-noise signal (with opposite polarity to the actual noise generated by the machine 100). By generating an anti-noise signal with a specific frequency, amplitude, and phase, and through destructive interference, the noise generated by the machine 100 can thus be (at least partially) eliminated.

[0039] For this purpose, the sound energy of the noise generated by the machine 100 can be determined. The rotor current of a separately excited synchronous machine 100 is typically a direct current. During operation of the machine 100, a high-frequency component can be modulated onto the direct current to at least partially compensate for interfering acoustic harmonics in the air gap 106 of the electric machine 100 or outside the electric machine 100. In particular, by injecting a suitable rotor current into the rotor 103 of the separately excited synchronous machine 100, an anti-noise wave F1 can be generated, which at least partially compensates for an interfering noise wave F2 of the electric machine 100. This can be achieved, in particular, by generating an anti-noise wave F1 that has a phase difference of 180° to the interfering noise wave F2.

[0040] Noise compensation can be used, for example, to at least partially eliminate disruptive noise that can occur when determining the rotor position by injecting a high-frequency signal into the stator 101. These high-frequency injection signals can have a frequency in the audible range, potentially generating substantial noise. During the rotor position measurement by injecting a high-frequency signal, the rotor power can be modulated to at least partially compensate for the noise caused by the measurement. Specifically, by modulating the rotor power (i.e., by appropriately calibrating amplitude, phase, and frequency), an anti-noise wave can be generated in the rotor 103, which at least partially compensates for the measurement noise. This allows for convenient rotor position measurement without rotor position sensors.

[0041] Fig.Figure 3 shows a flowchart of an exemplary method 300 for adjusting the sound generation of a separately excited electric machine 100. The machine 100 comprises a rotor 103 with (at least) one rotor winding 104 for generating a magnetic rotor flux and a stator 101 with (at least) one stator winding 102 for generating a rotating magnetic field. Typically, the rotor winding 104 is supplied with a constant rotor power to generate a constant magnetic rotor flux. The method 300 comprises varying 301 the electrical rotor power supplied to the rotor winding 104 as a function of sound information, wherein the sound information includes information relating to sound generated by the electric machine 100.In particular, the temporal profile of the rotor power can be adjusted in such a way that the noise generated by the electric machine 100 (especially with constant rotor power) is at least partially eliminated. This makes it possible to reduce the noise generated by an electric machine 100 in a cost-effective and space-saving manner.

[0042] The present invention is not limited to the embodiments shown. In particular, it should be noted that the description and the figures are intended only to illustrate the principle of the proposed methods, devices, and systems.

Claims

[1] Method (300) for adapting the sound generation on a separately excited electrical machine (100), wherein - the machine (100) comprises a rotor (103) with a rotor winding (104) for generating a magnetic rotor flux and a stator (101) with a stator winding (102) for generating a rotating magnetic field; - the method (300) comprises varying (301) one of the electrical rotor power supplied to the rotor winding (104) depending on sound information; - the sound information includes information relating to sound of the electric machine (100); - the method (300) comprises modulating, in a first period, a voltage applied to the stator winding (102) with a signal in order to determine a rotor position of the rotor (103); - the signal includes a signal component with a frequency between 100Hz and 20kHz; - the sound information displays information relating to the sound generated by modulating the voltage at the stator winding (102); and - the rotor power is varied during the first period to reduce the amount of noise generated by modulating the voltage at the stator winding (102). [2] Method (300) according to claim 1, wherein - the sound information includes information relating to sound generated by the electric machine (100) when the electric machine (100) is operated with a reference rotor power, in particular with a reference rotor power curve; and - the rotor power is changed compared to the reference rotor power, in particular a time course of the rotor power is changed compared to the reference course in order to reduce an amount of the sound produced by the electric machine (100). [3] Method (300) according to any one of the preceding claims, wherein - the sound information indicates a fundamental sound that is generated by the electric machine (100) when driven with a reference rotor power, in particular when driven with a time-based reference profile of the rotor power; and - the rotor power is changed in such a way compared to the reference rotor power, in particular a time course of the rotor power is changed in such a way compared to the reference course, that an anti-sound is generated by the rotor (103) which at least partially compensates the fundamental sound. [4] Method (300) according to any one of the preceding claims, wherein - the rotor power includes a constant component to generate a constant magnetic rotor flux; - varying (301) the rotor power includes modulating the constant portion of the rotor power with a modulation signal; and - the modulation signal depends on the sound information. [5] Method (300) according to one of the preceding claims, wherein the method (300) comprises capturing the sound information by means of a sound sensor (111), in particular by means of a microphone and / or by means of a structure-borne sound sensor. [6] Method (300) according to claim 5, wherein varying (301) the rotor power comprises adjusting, in particular controlling, the rotor power depending on the detected sound information and depending on target sound information indicating which sound is to be generated by the electric machine (100). [7] Method (300) according to any one of the preceding claims, wherein - the procedure (300) includes determining a current operating state of the electrical machine (100); - the procedure (300 includes selecting a data record for the current operating state from a database; - the database contains a large number of data records for a corresponding large number of different operating states of the electrical machine (100); - the data set for the current operating state depends on sound information from the electric machine (100) for the current operating state; - the data set shows a time-dependent progression of the rotor power; and - the rotor power varies depending on the time course shown in the data set. [8] Method (300) according to one of the preceding claims, wherein varying (301) the rotor power comprises varying a rotor current through the rotor winding (104). [9] Method (300) according to one of the preceding claims, wherein the varying (301) of the rotor power comprises adjusting a time profile of the rotor power. [10] Control unit for adjusting the sound generation on a separately excited electric machine (100), wherein - the machine (100) comprises a rotor (103) with a rotor winding (104) for generating a magnetic rotor flux and a stator (101) with a stator winding (102) for generating a rotating magnetic field; - the control unit is set up to vary the electrical rotor power supplied to the rotor winding (104) depending on sound information; - the sound information includes information relating to sound of the electric machine (100); - the control unit is set up to modulate a voltage applied to the stator winding (102) with a signal in a first period of time in order to determine a rotor position of the rotor (103); - the signal includes a signal component with a frequency between 100Hz and 20kHz; - the sound information displays information relating to the sound generated by modulating the voltage at the stator winding (102); and - the rotor power is varied during the first period to reduce the amount of noise generated by modulating the voltage at the stator winding (102).

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