Harmonic calculation in an electric drive using space vector representation of the harmonic system

Abstract

Method for determining a harmonic component (OA) in a multi-phase control signal (S) of a multi-phase electrical machine (EM), comprising the steps of:operating the electrical machine (EM) with the control signal (S) in that the control signal (S) generates a rotating field with a fundamental angular frequency (ωGin) of the electrical machine;Calculating a space vector representation (R) of the control signal for a harmonic angular frequency (ωO) which is different from the fundamental angular frequency (ωG) by partially or completely mapping (Trot) the multi-phase control signal (S) to a space vector representation (R) with the harmonic angular frequency (ωO), wherein the electrical machine (EM) is operated with a load angle (θLW) and with a power factor angle (φel) and wherein the space vector representation (R) is calculated based on the load angle (θLW) and the power factor angle (φel), and determining the level of the harmonic component (OA) based on the amplitude (A) of the complex representation (R).

Description

[0001] Electric drives, especially in vehicles, feature an electric motor that is set in motion by magnetic fields. In many drive types, a rotating magnetic field (stator magnetic field) is generated in the stator of the electric motor using a three-phase current. The magnetic rotor follows this stator magnetic field and thus rotates relative to the stator.

[0002] In the publication “Identification of time-variant high frequency parameters for sensorless control of PMSM using an internal model principle based high frequency current control”, SEILMEIER, Markus [ua], IEEE: 20th International Conference on Electrical Machines - 2-5 September 2012 - Marseille, France, 2012, pages 987-993, stator properties are measured by injecting a test RF signal into the stator and extracting the response using d,q transformation.

[0003] In the publication “Model based closed loop control scheme for compensation of harmonic currents in PM-synchronous machines”, SEILMEIER, Markus [ua], SPEEDAM 2010: International Symposium on Power Electronics, Electrical Drives, Automation and Motion, 14-16 June 2010, Pisa, Italy, 2010, pp. 1-6, a 5th and 7th harmonic of the driving fundamental wave are each represented with a d,q coordinate system that rotates at the speed corresponding to the harmonic in order to intervene in a vector control in such a way that a compensation of the harmonics results.

[0004] In addition to a stator magnetic field generated at a fundamental frequency or angular frequency, harmonics at this fundamental frequency can arise, for example, due to bearing damage or non-ideal control. These harmonics generate losses and also noise. Therefore, it is advantageous in the development and operation of electric drives to detect and quantify these harmonic components. To extract harmonic signals or generally for spectral analysis, a Fourier transformation is usually used in order to be able to detect the individual spectral components. However, calculating the spectral components in this way is computationally complex, particularly in real-time applications. It is therefore an object of the invention to demonstrate a possibility by which harmonic components in the control signal of an electrical machine can be easily calculated.

[0005] This problem is solved by the subject matter of the independent claims. Further properties, features, embodiments, and advantages are revealed by the dependent claims, the description, and the figure.

[0006] It is proposed not to calculate all spectral components simultaneously using spectral analysis, but rather to calculate a space vector representation of a harmonic angular frequency under investigation. This determines the magnitude (i.e., amplitude or signal strength) of the harmonic component. Since such a space vector representation only concerns one harmonic angular frequency (in contrast to the multitude of frequencies in spectral analysis) and, furthermore, the necessary matrix transformations can be calculated in advance, this results in a significantly reduced computational effort. Even with variable speeds, the harmonic angular frequency can be tracked without requiring a high computational effort.

[0007] The underlying idea is that a rotating field also exists for the harmonic or harmonic component under investigation, which rotates according to the angular frequency of the harmonic component (harmonic angular frequency). This allows the signal strength of the harmonic system to be recorded, which in turn allows the magnitude of the harmonic component to be determined. Since the space vector representation is calculated for the harmonic angular frequency, which is different from the fundamental angular frequency of the control signal of the electrical machine, only the magnitude of the harmonic component of the space vector representation relative to the harmonic angular frequency is recorded.In particular, the existing rotation system of the fundamental angular frequency can be easily separated from the space vector representation, which refers to the harmonic angular frequency, since when considering the space vector representation for the harmonic angular frequency, influences from the system of the fundamental angular frequency are only alternating current or alternating voltage influences, which eliminate themselves over a corresponding period of time, or which can be easily separated from the fundamental frequency components in another way.

[0008] For example, when considering the space vector representation for the harmonic angular frequency over an entire cycle, instantaneous influences from the system of the fundamental angular frequency do arise, but these disappear when considering the entire cycle (through averaging). In other words, when considering the space vector representation for the harmonic angular frequency, a component that does not correspond to this angular frequency is masked out because it does not correspond to the space vector representation for the harmonic angular frequency. If a space vector representation is used for the harmonic angular frequency, then influences from systems of other angular frequencies do not contribute to the phasor or vector length of the space vector representation for the harmonic angular frequency.Furthermore, corresponding components that do not match the space vector representation of the harmonic angular frequency can be easily separated by simple averaging, high-pass filtering or separating alternating signal components from the space vector representation of the harmonic angular frequency.

[0009] A method is described for determining a corresponding harmonic component in a multi-phase control signal of a multi-phase electrical machine. The electrical machine is preferably a synchronous machine, which can be permanently excited or separately excited. Furthermore, the electrical machine can be an asynchronous machine. The electrical machine is preferably a traction machine of a vehicle. The electrical machine can, for example, be three-phase or six-phase, although other numbers of phases are also possible. The electrical machine preferably has at least three phases. The electrical machine is preferably an internal rotor, but can also be configured as an external rotor. The control signal is, in particular, a power signal, for example, a signal with an effective voltage of more than 60 V or an effective current of more than 10 A.The control signal can be a current signal, a voltage signal, or a (multi-dimensional) signal that represents both the current and voltage of the electrical machine. The control signal can also have three or six phases, or a different number of phases (at least three). Preferably, the phase numbers of the electrical machine and the control signal correspond.

[0010] The electric machine is operated by the control signal. The control signal generates a (magnetic) rotating field with a fundamental angular frequency in the electric machine. The control signal is thus an alternating signal whose frequency corresponds to the fundamental angular frequency. The conversion between frequency and angular frequency is known to those skilled in the art. The fundamental and angular frequencies can, in particular, be determined from a given rotational speed.

[0011] A space vector representation of the control signal for a harmonic angular frequency is calculated. This results in a space vector representation of the control signal that relates to the harmonic angular frequency. The harmonic angular frequency is different from the fundamental angular frequency. In particular, the harmonic angular frequency is an integer multiple of the fundamental angular frequency. The magnitude of the multiple is preferably at least two. The harmonic angular frequency can generally be k times the angular frequency, with the magnitude of k being greater than one. In particular, non-integer (rational) multiples are also conceivable, for example, 1.5 times or similar.

[0012] The space vector representation, which refers to the harmonic angular frequency, can fully or partially represent the respective frequency component of the control signal. In particular, the space vector representation can partially represent the control signal, although the space vector representation provides a measure of the strength of the harmonic component. In this case, the space vector representation (which also refers to the harmonic angular frequency) can only represent a co-rotating system or only a counter-rotating system (relative to the rotor rotation direction) that refers to the respective angular frequency. Alternatively, or in combination with this, the space vector representation (which also refers to the harmonic angular frequency) can only represent a real part or only an imaginary part of the respective frequency component of the control signal.In particular, the space vector representation of the control signal for the harmonic angular frequency can be calculated by partially mapping the multiphase control signal onto a space vector representation of the harmonic component. One embodiment provides that the space vector representation of the control signal for the harmonic angular frequency is calculated by mapping the multiphase control signal onto a space vector representation with real and imaginary parts of the harmonic component for two opposite directions of rotation. In other words, the space vector representation can be complex and include both a co-rotating and counter-rotating rotation system (with the harmonic angular frequency), or only the real or imaginary part thereof, or only one of the two (oppositely rotating) rotation systems of the harmonic component.

[0013] The space vector representation of the control signal for the harmonic angular frequency can be calculated by partially or completely mapping the multi-phase control signal to a space vector representation based on the harmonic angular frequency. The space vector representation is preferably rotor-related, although stator-related space vector representations are also possible. The extraction of the magnitude of the harmonic component differs slightly in this case. The control signal is preferably mapped to a space vector representation based on rotation at the harmonic angular frequency. In particular, the space vector representation can be realized using a phasor whose angular frequency corresponds to the harmonic angular frequency. This means that only the relevant harmonic component (corresponding to the harmonic angular frequency) is represented in the space vector representation.This results in a space vector representation of the harmonic rotating field. From this, the magnitude of the harmonic component can be extracted.

[0014] Finally, it is intended that the level or signal strength of the harmonic component is determined based on the amplitude of the complex representation. Since the space vector representation is already provided with a certain amplitude (e.g. of the phasor), the level or strength of the harmonic component can be easily determined from this. In particular, the real and / or imaginary components can be used to determine the level of the harmonic component. In other words, components can be used for the determination that only concern the active power or the reactive power, or that concern the apparent power. In addition, the space vector representations or their amplitudes can be used whose direction of rotation corresponds to the direction of rotation of the fundamental rotating field (i.e.of the fundamental angular frequency-related rotating field) and / or of the system running in opposite direction to this (which represents part of the space vector representation of the control signal for the harmonic angular frequency).

[0015] In particular, when determining the harmonic content, it can be averaged, for example, over one or more revolutions. Furthermore, low-pass filtering can be performed when determining the level of the harmonic content. In particular, real and imaginary components can be calculated individually and, if necessary, summed together to determine the level of the harmonic content.

[0016] A co-rotating space vector representation and a counter-rotating space vector representation can be calculated as the space vector representation of the control signal for the harmonic angular frequency. Both space vector representations relate to the rotating field of the harmonic component. The co-rotating space vector representation has a direction of rotation that corresponds to the direction of rotation of the rotating field (i.e., the fundamental angular frequency). The counter-rotating space vector representation has a direction of rotation that is opposite to this. The magnitude of the harmonic component can be determined based on the sum of the respective magnitudes of the harmonic components of the two space vector representations. This allows the strength or magnitude of the harmonic component to be determined regardless of the direction of rotation of the rotating field that makes up the harmonic component. It is not necessary to know the direction of rotation of the rotating field that makes up the harmonic component (i.e.,Rotating field of the harmonic angular frequency). Alternatively, only the co-rotating or counter-rotating space vector representation can be calculated, with the harmonic component or its intensity being determined based on this space vector representation. This can be used in particular if, for example, it is already known from the type of fault that the harmonic component is linked to a harmonic rotating field that co-rotates (or counter-rotates).

[0017] Preferably, the space vector representation is calculated as a rotor-related space vector representation. The space vector representation can provide a coordinate system that rotates relative to the stator. Furthermore, the space vector representation can provide at least one phasor that rotates relative to the stator. The rotation of the coordinate system or of the phasor occurs at the harmonic angular frequency. With such a rotor-related space vector representation, a quasi-static representation results. In particular, this representation does not vary with the changing angular position of the system in question. The magnitude of the harmonic component is specified by at least one variable of at least one axis of the coordinate system or by at least one amplitude of the phasor. The coordinate system is in particular a coordinate system that lies in the complex plane.At least one value of an axis of the coordinate system can be a value of the real part or the imaginary part. Values from the real and imaginary axes can also be used. These can be combined, for example by adding the respective squares, whereby the resulting sum itself or the square root of this sum is used as the height or strength of the harmonic component. The axes of the coordinate system can represent the d-component or the q-component of the rotating field, which rotates at the harmonic angular frequency. The space vector representation is obtained in particular through a d / q transformation, which can also be referred to as a Park transformation. This transformation is performed for the harmonic angular frequency.

[0018] For space vector representations that are stator-related, the coordinate system can also be obtained using a Clarke transformation, which assumes rotation at the harmonic angular frequency. In the case of rotor-related coordinate systems, the strength of the harmonic component results from the quasi-stationary amplitude (or the rms value) of at least one of the coordinate axes (e.g., the d or q coordinate axis). Quasi-stationary in this context means that the quantity in question varies with the speed but does not vary with the rotor rotation. In the case of a stator-related coordinate system (e.g., a representation in α, β components), the amplitude (i.e., a quantity on at least one axis of the coordinate system) varies with the rotational movement according to the harmonic angular frequency.Here, the strength of the harmonic component can be determined as the strength of the corresponding alternating signal; alternatively, in a stator-related coordinate system, the strength of the harmonic component can be determined as the magnitude of the space vector representation (i.e. in particular the length of the phasor or vector) as the height of the harmonic component.

[0019] The space vector representation can further correspond to a positive and / or negative sequence system, a representation of the rotating system as symmetrical components, which rotates at the harmonic angular frequency. Thus, the magnitude of the harmonic component can be determined based on the amplitude of the positive and / or negative sequence system. The space vector representation is calculated by transforming the harmonic system to a representation using symmetrical components. As mentioned, the amplitude of the positive sequence system, the negative sequence system, or a combination of the amplitudes (especially the sum) can be used to determine the magnitude.

[0020] Both the representation in a d, q coordinate system (Park transformation) and the representation using symmetric components are rotor-related representations. The Clarke transformation, or the representation in the corresponding α, β components, on the other hand, is a stator-related transformation or representation. Determining the magnitude of the harmonic component in rotor-related representations corresponds to determining the DC component. When determining the magnitude of the harmonic component from stator-related space vector representations, for example, the rms value of a quantity that is part of the space vector representation is used. In other words, in stator-related space vector representations, the rms value of this space vector representation can be determined as the magnitude of the harmonic component.

[0021] As mentioned, the space vector representation can be calculated as a rotor-related space vector representation by calculating a co-rotating space vector representation and a counter-rotating space vector representation (with opposite rotation direction). Both space vector representations are calculated based on the harmonic angular frequency. It is also possible to calculate only the co-rotating or only the counter-rotating space vector representation. When using rotor-related space vector representations, however, it should be noted that they are already based on rotation at the fundamental angular frequency. In this context, "rotor-related" means that the corresponding space vector representation assumes a rotor rotating at the fundamental angular frequency.

[0022] However, the rotating system that forms the harmonic components rotates at the harmonic angular frequency relative to the (simple fundamental angular frequency) and thus relative to the rotor. To take into account that the space vector representation of the harmonic components is based on rotation relative to the rotor (and not the stator), and that a rotor-related representation is not static but already rotates at the fundamental angular frequency, the fundamental angular frequency should be subtracted when forming the co-rotating space vector representation (which rotates at the harmonic angular frequency relative to the fundamental angular frequency in the same direction as the fundamental system) in order to obtain a harmonic-related space vector representation that rotates at the harmonic angular frequency relative to the rotor or relative to the rotational movement at the fundamental angular frequency. The fundamental angular frequency is the basis for the space vector representation of the fundamental system.In a similar way, in a counter-rotating space vector representation, the fundamental angular frequency is preferably added to the harmonic angular frequency in order to take account of the space vector representation, which already rotates at the fundamental angular frequency. The corresponding counter-rotating space vector representation is thus obtained by a space vector transformation with an angular frequency that corresponds to the sum of the harmonic angular frequency and the fundamental angular frequency. In other words, the counter-rotating space vector representation corresponds to a rotor-related space vector representation (and thus rotates at the fundamental angular frequency), which also rotates at the harmonic angular frequency. In a rotor-related space vector representation, the fundamental angular frequency must therefore be added or subtracted in order to account for the harmonics orto obtain a representation for their rotating system that corresponds to the rotation of the rotating system relative to the fundamental system (whose representation rotates with the harmonic angular frequency) with the harmonic angular frequency.

[0023] The multi-phase control signal is thus mapped onto the co-rotating space vector representation with an angular frequency that corresponds to the harmonic angular frequency minus the fundamental angular frequency (since the rotor already rotates at the fundamental angular frequency and the space vector representation of the harmonic signal rotates relative to this fundamental system).

[0024] Alternatively, or in combination with this, the multiphase control signal can be mapped to the counter-rotating space vector representation with an angular frequency that corresponds to the sum of the harmonic angular frequency and the fundamental angular frequency. Thus, the space vector representations refer to a harmonic rotating field that rotates at the harmonic angular frequency relative to the fundamental system.

[0025] The magnitude of the harmonic component can be determined based on the amplitude of one of the space vector representations or based on the amplitudes of the space vector representations. In particular, the magnitude of the harmonic component can be determined based on a combination of the amplitudes of the space vector representations. Such a combination is, for example, the addition of the amplitudes, the addition of the absolute values of the amplitudes, or the square root of the sum of the squares of the amplitudes of the space vector representations. The space vector representations can be complex representations, whereby the magnitude of the harmonic component can correspond to the (apparent) power of the complex representation, or can correspond only to the real or imaginary part of the space vector representation. In particular, the magnitude can correspond to the root of the sum of the squares of the real part and the imaginary part of the complex representation or to this sum itself.

[0026] Preferably, the electrical machine is operated with a load angle and a power factor angle. The space vector representation is calculated based on the load angle and the power factor angle. The load angle and / or the power factor angle can be specified. Furthermore, it can be provided that the load angle is measured or calculated based on operating parameters of the electrical machine. For example, the load angle can be calculated based on the current torque and / or the output power. The power factor angle can also be specified or measured or calculated. In particular, the angular offset between the current and voltage of the control signal can be calculated. The load angle and the power factor angle relate to the fundamental angular frequency.

[0027] It can be provided that a current component (or a voltage component) of the control signal is converted by means of a Clark transformation into a space vector representation (related to the fundamental angular frequency), which corresponds to an α, β representation. In other words, the control signal can be transformed into a stator-related space vector representation (based on the fundamental angular frequency). This results in a space vector representation with two mutually perpendicular axes (α, β axis). From this space vector representation, the power factor angle can be calculated or read out, in particular as an angle relative to an axis of the coordinate system of the space vector representation. The resulting power factor angle can be filtered. In particular, the space vector representation (based on the harmonic angular frequency) is determined taking into account the power factor angle, the load angle, or the sum thereof.The space vector representation therefore also includes the power factor angle, the load angle and, in particular, the sum of these.

[0028] The space vector representation can correspond to a Park transformation, in particular the result of a Park transformation. The space vector representation can thus provide a d / q coordinate system. This rotates at the angular frequency of the harmonic frequency, i.e., at the harmonic angular frequency. The d value of the coordinate system, the q value of the coordinate system, or the square root of the sum of the squares of these values indicates the magnitude of the harmonic component. This can be determined in this way for a co-rotating or counter-rotating space vector representation. In particular, the space vector representation can be determined for the current control signal (as it occurs in the electrical machine or results from the voltage control of the inverter in the electrical machine), for the voltage control signal (as it is output from the inverter to the electrical machine), or for both.Thus, a space vector representation can be provided for the current control signal and the voltage control signal, respectively, for the co-rotating and counter-rotating system, which rotates at the harmonic angular frequency (relative to the stator). From this, the power can be determined from the current or voltage representations.

[0029] The individual space vector representations (for the co-rotating system, for the counter-rotating system and / or for the current control signal and the voltage control signal) can each be filtered using a low-pass filter. In other words, the (moving) average can be calculated. This corresponds to an extraction of the DC signal components, i.e. an extraction of the DC component of the co-rotating system and the counter-rotating system for the current control signal and the voltage control signal, respectively. This particularly affects only the q-component of the coordinate system. Conversion to a space vector representation or filtering can be followed by a calculation of the d-component and the q-component, respectively, for the current control signal and the voltage control signal. The power can be obtained, in particular, by complex multiplication of the d- and q-components thus obtained, respectively, for the current control signal and the voltage control signal.The resulting power can be considered as the magnitude of the harmonic component. Simplified methods involve considering only the current or only the voltage drive signal to determine the magnitude of the harmonic component. Furthermore, only the co-rotating or only the counter-rotating system can be considered, i.e., a co-rotating or only counter-rotating space vector representation.

[0030] As mentioned, a Fortescue transformation or a space vector representation can also be used as symmetrical components (positive and negative sequence systems). The space vector representation can thus correspond to a Fortescue transformation. This provides at least one phasor, which corresponds to a positive and / or negative sequence system that rotates at the angular frequency of the harmonic frequency (relative to the stator). The amplitude of the phasor or a combination of the phasors indicates the magnitude of the harmonic component. In particular, when using the positive and negative sequence systems, the amplitude of the phasor can be calculated for each system, with the magnitude of the harmonic component resulting from the sum of the magnitudes of the two amplitudes. The combination of the phasors can thus be provided by adding the magnitudes of the two systems.

[0031] As mentioned, the control signal can comprise a current signal. This is referred to as a current control signal. The corresponding current signal represents the phase current in the electrical machine (for the multiple phases). The control signal can also comprise a voltage signal that represents the phase voltage of the electrical machine. This can also be referred to as a voltage control signal. The voltage control signal represents the phase voltages of the electrical machine for the phases of the machine.

[0032] The space vector representation of the current signal and the space vector representation of the voltage signal can be calculated. The magnitude of the harmonic component is determined, in particular, by the active power of the current amplitude and the voltage amplitude of the two space vector representations. Alternatively, the apparent power of the current amplitude and the voltage amplitude of the two space vector representations is calculated as the magnitude or strength of the harmonic component.

[0033] Some designs also provide for an active power factor to be calculated from the phase shift between the space vector representations of the current control signal and the voltage control signal. The magnitude of the harmonic component can then be determined from the complex power resulting from the two space vector representations, as well as from the active power factor, which corresponds to the phase shift between the two space vector representations. In this case, the magnitude of the harmonic component results from an active power calculated from the space vector representations of the voltage and current control signals. The phase shift or the calculated active power factor is thus used in the calculation of the harmonic component.

[0034] Further embodiments provide that the magnitude of the harmonic component is calculated based on a low-pass filtered amplitude of the complex representation. This can be the amplitude of the real part, the imaginary part, or a combination thereof. In particular, the real and imaginary parts of the complex representation can be combined before or after the respective amplitudes are low-pass filtered, in particular by determining the magnitude of the complex representation (i.e., by determining the square root of the squares of the real and imaginary parts). The complex representation results from a complex space vector representation, which is a representation in a complex plane and thus has only one real part axis and one imaginary part axis.

[0035] Furthermore, it can be provided that the space vector representation of the control signal for the harmonic frequency is calculated by partially or completely mapping the multi-phase control signal onto an intermediate space vector representation with a stator-fixed coordinate system. This is combined, in particular, by partially or completely mapping this intermediate space vector representation onto a complex representation whose angular frequency corresponds to the harmonic frequency (and which relates to the rotor). The intermediate space vector representation can therefore be obtained by partially or completely mapping the multi-phase control signal using a Clark transformation. This stator-fixed intermediate space vector representation is then converted in a known manner into a rotor-related or rotor-fixed space vector representation, the latter corresponding to a Park transformation.

[0036] The method can be used in particular to detect the harmonic component at variable speeds, i.e., at variable fundamental angular frequencies. The space vector representation, which refers to the harmonic frequency, is changed with the fundamental angular frequency or in accordance with the change in speed. In other words, the harmonic frequency, which forms the basis for the space vector representation, is adapted to changes in speed or speed of the electric machine. In particular, when detecting a change in the fundamental angular frequency, the harmonic angular frequency is changed proportionally to the fundamental angular frequency. If the fundamental angular frequency changes by a factor of x, a harmonic angular frequency increased by a factor of x is also used in the space vector representation.

[0037] In addition to adapting to speed changes, the method presented here can also be used to evaluate several different harmonic angular frequencies. Within the same time period, the levels of harmonic components of several different harmonic angular frequencies can be determined. In particular, several space vector representations are calculated for different harmonic angular frequencies. The harmonic angular frequencies differ and are also different from the fundamental angular frequency.For example, the harmonic component of the third and fifth harmonics for the same control signal can be determined by transformation into space vector representations that rely on rotations of different speeds, such as a space vector representation based on a rotation with the third harmonic angular frequency and another space vector representation based on a rotation with the fifth harmonic angular frequency.

[0038] Furthermore, the detected harmonic content can be used to determine the fault. In particular, the ratios of the magnitudes of harmonic components of different harmonic angular frequencies can be used to determine the corresponding fault types. Different ratios of the magnitudes to one another are preferably mapped to different fault types. The mapped fault types can then be output. For example, if the fifth harmonic is expected to be significantly stronger than the third harmonic in the case of a bearing fault, while the third harmonic would dominate the fifth harmonic in the case of an inverter fault, these different fault types can be differentiated from one another using the ratios of the magnitudes of the various harmonic components and output.

[0039] Finally, an electric vehicle drive train with a multi-phase electric machine and an inverter is described. The inverter is connected to the electric machine via a phase connection (with multiple phases) in a controlling manner. A detection module is connected to the phase connection. The detection module is designed to carry out the method according to one of the variants described here. The detection module is configured to detect the multi-phase current flowing through the phase connection. Alternatively or in combination therewith, the detection module is configured to detect the voltage applied to the phase connection (i.e., the voltage between the various phases of the phase connection). The detection module further comprises a data interface configured to output the level of the harmonic component determined by the detection module.The data interface is particularly configured to output multiple harmonic components if multiple harmonic components are calculated for different harmonic angular frequencies in the acquisition module. Alternatively, or in combination with this, the data interface can be configured to output the aforementioned error types.

[0040] A computer program product can be provided that is configured to carry out the method described here. In particular, the computer program product can be configured both to operate the electrical machine and to calculate the space vector representation and to determine the level of the harmonic component. Furthermore, a computer program product can be provided that is not configured to operate the electrical machine, but is configured to calculate the space vector representation and to determine the level of the harmonic component. The computer program product can have an input section in which parameters representing the control signal are transferred. An output section can be provided in which the level of the harmonic component is output as one or more parameters.The computer program product is configured to execute the method described here (or simply the steps of calculating and determining the level of the harmonic component) when executed in a processor. The processor can have an input interface to which the control signal or variables representing it are input. These are, in particular, measured variables that characterize the control signal, in particular its voltage and / or current waveform.

[0041] The calculation of the space vector representation and the determination of the level of the harmonic component can be provided in different ways. The calculation of the space vector representation can be performed in a preparation step. In this step, parameters are stored that represent the space vector representation or a matrix corresponding to the space vector representation. In particular, the space vector representation can be calculated by generating a transformation matrix to generate the space vector representation. The transformation matrix can represent a Clarke transformation or a Park transformation, or it can represent a decomposition into symmetric components, for example in the form of a Fortescue matrix (at least for the positive and / or negative sequence system). This matrix can be generated in a preparation step.This transformation can be called up in a real-time calculation step, particularly if corresponding data representing the transformation was stored in the preparation step. The space vector representation is then obtained by applying the transformation matrix (pre-stored) to the current control signal, i.e. to data that represents the control signal. This means that part of the calculation can be carried out outside of real time, particularly in a preparation phase before the start of operation, i.e. before the control signal is generated, while in real time, i.e. with an existing, current control signal or during operation of the electrical machine, the relevant, already calculated transformation matrix is simply called up in order to generate the space vector representation (for the current control signal).

[0042] An exemplary embodiment provides that first (in a preparatory phase before operation of the electrical machine) a transformation matrix is generated, by means of which later (during operation of the electrical machine) the space vector representation can be calculated, in particular in real time. For this purpose, the harmonic angular frequency is selected, and the corresponding transformation matrices for a co-rotating system and a counter-rotating system (both with harmonic angular frequency relative to the stator) are generated. The transformation matrix, which represents the co-rotating system, takes into account that the fundamental system (which rotates at the fundamental angular frequency) refers to the stator (i.e. rotates relative to it) and is rotor-fixed, i.e. does not rotate above the rotor.This results in a co-rotating transformation matrix based on the harmonic angular frequency minus the fundamental angular frequency, and a counter-rotating transformation matrix based on the sum of the harmonic and fundamental angular frequencies. This takes into account that the harmonic system rotates relative to the fundamental system at the harmonic angular frequency, and the fundamental system rotates relative to the stator at the fundamental angular frequency (abbreviated to: fundamental angular frequency).

[0043] The transformation matrices map the multiphase rotation system to a rotor-related system and further map the multiphase signals to a single (complex) quantity, such as a phasor or a complex representation thereof. The transformation matrices can correspond to a Park transformation or a d / q transformation. Alternatively, they correspond to a Fortescue transformation for mapping to co- and counter-rotating symmetric components.

[0044] In the example mentioned, the transformation matrices for the co-rotating system are generated for both the voltage control signal and the current control signal. The same applies to the transformation matrices of the counter-rotating system. The matrices are part of the space vector representation or serve to generate the space vector representation. Both the transformation matrices and the space vector representation refer to the harmonic system of the control signal, i.e., the rotating system of the control signal, which rotates at the harmonic angular frequency.

[0045] The current control signal is applied to the corresponding transformation matrix. The same applies to the voltage control signal. Until the control signal is applied to the transformation matrices, the method can be executed offline or in a preparatory phase, thus eliminating some of the required computing power during operation, i.e., during the determination of the level of the harmonic component using the control signal.

[0046] Applying the Park transformation as a transformation matrix for the current control signal results in a co-rotating d-component, a co-rotating q-component, a counter-rotating d-component, and a counter-rotating q-component. The voltage control signal also has the corresponding four components: co-rotating d- and q-components and counter-rotating d- and q-components.

[0047] In a subsequent step, the resulting components are averaged or low-pass filtered. In particular, only the DC component is filtered out. A DC component is defined as a component whose frequency is not greater than a frequency corresponding to the rate of change of the rotational speed. This allows even slowly changing rotational speeds to be taken into account. As already described, the relevant harmonic angular frequency is adjusted proportionally to changing rotational speeds of the electrical machine (i.e., changing drive speeds).

[0048] The power of the rotating system (or system for short), which rotates at the harmonic angular frequency (in both directions), is calculated from the resulting components. The resulting power is preferably calculated by calculating the reactive and active components, i.e., calculating the d and q components for both the co-rotating and counter-rotating systems. In particular, the real part or the d-component of the current is multiplied by the d-component or the real part of the voltage. This is also calculated for the imaginary parts of the respective voltages and currents. The calculation is carried out for the positive and negative sequence systems. The components resulting from the multiplication of the real parts and the components resulting from the imaginary part are calculated and added for the negative and positive sequence systems.

[0049] The real and reactive components, or the d and q components, are calculated and summed (generally: combined) for both the negative-sequence system and the positive-sequence system. As mentioned, the space vector representation can be calculated for the current and for the voltage of the control signal (related to the harmonic angular frequency). The magnitude of the harmonic component is then preferably determined from the product of the resulting current and voltage amplitudes and the angle between current and voltage or the angle between the d and q components (i.e., the angle of the phasor or vector in the d / q coordinate system). The magnitude of the harmonic component is determined in particular from the apparent power of the rotating system (related to the harmonic angular frequency) for both the co-rotating system and the counter-rotating system. The phase angle between current and voltage can be taken into account here.

[0050] Alternative embodiments calculate the total active power of the co-rotating and counter-rotating systems (which rotate at the harmonic angular velocity). Other embodiments provide for the corresponding calculation of the reactive component (for both the co-rotating and counter-rotating systems). The active and reactive power can also be calculated individually and summed in a subsequent step. The magnitude of the harmonic component thus corresponds to the apparent power, the sum of the reactive and active components, or only the reactive component, or only the active component. All of these quantities are suitable for calculating the magnitude of the harmonic component with sufficient accuracy, thus obtaining a measure of the harmonic strength using a low-computational-intensive procedure.

[0051] The calculation of the transformation matrices can, in particular, take into account the angle between current and voltage as well as the load angle. In particular, the current angle between current and voltage (power factor) and / or the current load angle can be taken into account when calculating the transformation matrices, in particular by considering the sum of both angles. A given transformation matrix can be adapted to these angles by simply adjusting it. This adjustment can be performed in real time (during operation of the electrical machine). For this purpose, for example, pre-stored transformation matrices for specific, corresponding pre-stored angles can be retrieved.

[0052] A similar approach can be used when using a Fortescue transformation, whereby a Fortescue transformation also operates in a complex plane, thus resulting in the obvious equivalents to the d- and q-transformations or d- and q-components. With a Fortescue transformation, the fixed system (relative to the harmonic angular velocity) can also be calculated and used for error analysis.

[0053] The Fig. 1 serves to explain in more detail embodiments of the procedure described here.

[0054] Shown is an electric drive, in particular a vehicle drive (traction drive), with a battery BAT as a DC voltage source, an inverter INV connected to it, and an electric machine EM that is connected to the battery BAT via the inverter INV. The electric machine has an electrical angle φel and a load angle θLW. The electric machine EM is connected to the inverter INV via three phase connections 1, 2, 3. The electric machine EM is connected to the AC side of the inverter INV. The battery BAT is connected to the DC side of the inverter INV. The inverter is suitable for generating a control signal S from the DC voltage of the battery BAT. The control signal S has two components, namely a current component I and a voltage component U, as symbolically shown.The motor angle φel (or the angle φel + θLW) exists between the current control signal I and the voltage control signal U (which together form the control signal S).

[0055] It is symbolically shown that the current control signal I contains two three-phase rotating systems, namely a system which rotates at the fundamental angular frequency ω G rotates relative to the stator (ie rotor-fixed), and a system that rotates at the harmonic angular frequency ω O rotates relative to the stator (and thus also relative to the system with the fundamental angular frequency with [ω O - ω G ] rotates). The current control signal I is the sum of these two three-phase systems. To illustrate that the harmonic angular frequency ω O is greater than the fundamental angular frequency ω G, the system rotating at the harmonic angular frequency is represented by a double-headed arrow as the rotation arrow, while the arrow representing the rotation at the fundamental angular frequency is represented by a single arrow. The double-headed arrow rotates (by ω O / ω G ) faster than the simple arrow. For a better overview, only the rotating components are shown in the Fig. 1 symbolically shown, where the current control signal I can also include counter-rotating systems for the fundamental angular frequency and for the harmonic angular frequency, as shown in the dashed rectangle shown top right with the co-rotating and counter-rotating system MS, GS.

[0056] The dashed rectangle in the upper right corner of the drawing shows symbolically and exemplarily (using symmetrical components) the background of the transformation described here. The transformation Trot SKshows the transformation of the harmonic rotation system (of the current control signal I) by subdividing it into a positive-sequence system MS and a negative-sequence system GS. The arrow of the harmonic rotation system pointing in both directions of rotation indicates that it contains two opposing individual rotation systems. This can be divided, as shown, into a positive-sequence system MS, which contains the following harmonic rotation system (with harmonic angular frequency ω O ) rotates, and into a component of the counter-system GS with opposite direction of rotation, represented by -ω O These two systems are contained in the harmonic rotation system shown on the left and can be separated by appropriate transformation. Also shown is the zero-order system NS, which represents a DC component offset.

[0057] The positive sequence system MS and the negative sequence system GS are shown in three-phase form for clarity. It is important that the phase phasors of the positive sequence system MS are of equal length (and offset by 120 degrees).

[0058] The same applies to the negative sequence system GS. Therefore, the positive sequence system can be represented by a single phasor. The same applies to the negative sequence system GS. This results in a space vector representation RSK for the current component (current component - reference symbol SK), which can be represented by a single phasor due to the symmetry of the phase vectors. The division principle shown corresponds in particular to a Fortescue transformation, i.e. a representation as symmetric components. However, this representation can also be used to understand a Park transformation. The Park transformation is carried out on the co-rotating and the counter-rotating harmonic rotation system, both of which are contained as harmonic components in the control signal. A first Park transformation result (i.e. resulting representation), which concerns the co-rotating system, and a second Park transformation result (i.e.resulting representation), which concerns the counter-rotating rotating system, corresponds to the two summands MS, GS. In the Park transformation, a multi-phase system is also replaced by a single-phase, complex (rotating) system, i.e. by d and q components. The two Park transformations (for the co-rotating and counter-rotating system) result in two simplified d / q representations, corresponding to the reference symbols MS and GS. What both transformations have in common is that the absolute value of the two systems MS, GS can be calculated from them. This represents the strength or level of the harmonic component OA. In simplified terms, the absolute value of the amplitude A can be calculated from this, starting from the co-rotating system MS and the counter-rotating system GS. In a dq transformation, this applies primarily to the real part and the imaginary part.Simplified embodiments consider only the real part, i.e. the d-component of the following system and the counter-rotating system.

[0059] The Fig. Figure 1 shows that a mapping Trot to a rotor-related space vector representation R can be achieved for both the current control signal and the voltage control signal (I, U). Alternatively, a static mapping Tstat is performed before the mapping using Trot in order to obtain an intermediate space vector representation ZR. The static mapping Tstat forms the harmonic angular frequency ω OThe multiphase system is mapped to a single-phase system. A Clark transformation is shown, which, as an intermediate space vector representation ZR, is a single-phase, stator-related, complex representation. This includes, as the real part α, the corresponding real current component, which results from transforming the multiphase system to this single-phase, stator-related space vector representation ZR. Furthermore, the intermediate space vector representation ZR includes a complex component jβ, which, as a single-phase imaginary part, represents the relevant multiphase components of the control signal.

[0060] It is shown that the optional intermediate space vector representation ZR is implemented for the current control signal I as well as for the voltage control signal U. For the voltage control signal U, a stator-related space vector representation ZR' results, which can also be referred to as an intermediate space vector representation. The stator-related intermediate space vector representation ZR', which concerns the voltage control signal, also has a real component α and an imaginary component jβ and, in contrast to the control signal, is single-phase (albeit complex). In summary, the two optional intermediate space vector representations are the result of a Clark transformation (see Tstat) for the harmonic angular frequency ω O and represent the current and voltage control signal in the complex plane as a single-phase vector with the harmonic angular frequency ω O turns.

[0061] The figure Trot refers to the harmonic angular frequency ω O and maps either the control signal (or the current and voltage control signal) or the intermediate space vector representation ZR to a rotor-related space vector representation R. The load angle φel and the load angle θLW are combined to form an angle θ. The mapping Trot is performed taking this angle θ into account. This angle is thus considered as the total angular offset in the space vector representation R.

[0062] In the Fig. 1, the mapping Trot corresponds to a Park transformation or d / q transformation, which corresponds to a rotor-related space vector representation R with a (real) d-axis and (imaginary) q-axis. For the rotating system of the harmonics, a space vector representation R results, which is expressed as ω Orotates, whereby in preferred embodiments, a counter-rotating space vector representation RG is also generated. R represents the traveling harmonics as a rotor-related space vector representation, while RG is the counter-rotating space vector representation of the harmonics. Both representations are complex rotor-related and single-phase. The following result from the control of the control signal, related to the harmonic angular frequency ω O , the complex quantities A and A', which can also be referred to as phasors. In the example shown, the magnitude of these quantities corresponds to the level of the harmonic component. Preferably, the sum of the magnitudes of A and A' is used to represent the level (i.e., strength) of the harmonic component.

[0063] Alternative, simplified embodiments provide that the level of the harmonic component OA is formed only by A or only by A'. The following space vector representations R and RG are shown for the current control signal. For the voltage control signal, Fig. 1 shows the concurrent space vector representation R' and the counter-concurrent space vector representation RG'. It can be seen that the space vector representation R of the current control signal is realized with the two real and imaginary instantaneous quantities Id and Iq, while the systems R' and RG', which represent the voltage control signal for the harmonic angular frequency ω O which use the real and imaginary instantaneous voltage quantities Ud and Uq, respectively. The representations RG and RG' correspond to the space vector representations that represent the counter-rotating rotation systems of the control signals for the harmonic angular frequency ω OThe space vector representations RG and RG' represent the current and voltage control signals for the harmonic, rotor-related and single-phase.

[0064] The imaginary and real parts are extracted from the rotor-related space vector representations R, R' shown. This is represented by the extraction block Extr. This results in the harmonic component OA as the harmonic component of the current control signal I, and the extraction of the space vector representation R' results in the magnitude of the harmonic component OA' for the voltage control signal U. Optionally, after the extraction and before the output of the two harmonic components for current and voltage, a low-pass filter TP takes place. This is represented by the low-pass filter block TP, which can also correspond to a (moving) averaging. The harmonic components OA, OA' calculated in this way can be used individually or in combination. The harmonic component OA corresponds to the magnitude of the space vector representation R. The harmonic component OA' corresponds to the magnitude of the space vector representation R' of the control signal.

[0065] To calculate the magnitude of the harmonic component as power, both harmonic components for the current or voltage can be multiplied together. In particular, the phase angle φ (as the power factor cos φ) between the two complex representations of the current or voltage of the respective harmonic components can be taken into account, in particular the angle of the complex current vector and the complex voltage vector of the quantities A, A'. The multiplication of the harmonic components, represented by the mult block, can be provided separately for the real parts and for the imaginary parts of the complex representations of the current-related and voltage-related harmonic components. Here, the real amplitudes of current and voltage of the harmonic component are multiplied together and added to the product of the imaginary components of the harmonics within the current and voltage control signals.Where appropriate, the power factor, i.e., the angle between the complex representations A' and A as cos φ, is taken into account. This can be done by using the lengths or magnitudes of the two representations R, RG as A and A' to calculate the apparent power of the harmonics, and then multiplying this by the power factor φ (i.e., by cos φ). This yields the active power component of the harmonic component.

[0066] One embodiment provides that the space vector representation is calculated for the current I and for the voltage U of the control signal S. The magnitude of the harmonic component can be calculated from the product of the resulting current and voltage amplitudes |A|, |A'| and the angle φ between current and voltage.

[0067] The following relationships can be used to calculate the level of the harmonic as signal power: P=Id*Ud+Iq*Uq.

[0068] If both the co-rotating harmonic system (positive system) and the counter-rotating harmonic system (counter system) are to be calculated, the result is:

[0069] P = Re{U M} * Re{I M} + Im{U M} * In{I M}, where the index M represents the current I and the index M represents the voltage U for the positive-sequence system (co-rotating system). The power can be calculated for the negative-sequence system in the same way. The two powers are combined to form a quantity that represents the magnitude of the harmonics.

[0070] Furthermore, especially with an α, β space vector representation, the magnitude can be calculated as power P = Îα*Ûα + Îβ * Ûβ, i.e., based on the peak values Û, Î of the voltage and current. Here, too, only the positive or negative sequence system can be considered, or preferably a combination (sum) of the calculated powers of the positive and negative sequence systems.

[0071] The mappings or transformations Tstat and Trot can be calculated in advance and can in particular be parameterized in advance with the harmonic angular frequency ω O In particular, this angular frequency ω O can also be adjusted when the speed of the electric machine changes. In this case, the angular frequency ω Oproportional to the fundamental angular frequency or proportional to the speed of the electrical machine EM. The calculation sequence shown can therefore be split into two parts, with the generation of the maps Trot and, if applicable, Tstat being carried out once or before the generation of the control signal and being stored in a memory. During operation of the electrical machine or to determine the level of the harmonic component, the map can then be called up instead of calculating it during operation of the electrical machine. During operation of the electrical machine, the control signal is then used to map the maps to a rotor-related space vector representation R in order to calculate the level of the harmonic component during operation of the electrical machine.

[0072] Mapping occurs during operation and to determine the level of the harmonic component, while the generation of the Trot and Tstat maps can be performed in a preparatory step before the electrical machine is operated. This step can be performed, for example, during the programming of a corresponding computing device or at the end of the line during assembly of the electrical machine. In particular, the map can be generated before the electrical machine begins operating, either before each start-up of the electrical machine or before the first start-up of the electrical machine.

Claims

[1] Method for determining a harmonic component (OA) in a multi-phase control signal (S) of a multi-phase electrical machine (EM) with the steps: Operating the electrical machine (EM) with the control signal (S) in that the control signal (S) generates a rotating field with a fundamental angular frequency (ω G generated in the electrical machine; Calculating a space vector representation (R) of the control signal for a harmonic angular frequency (ω O , which are different from the fundamental angular frequency (ω G is, by partially or completely mapping (Trot) the multi-phase control signal (S) to a space vector representation (R) with the harmonic angular frequency (ω O , wherein the electrical machine (EM) is operated with a load angle (θLW) and with a power factor angle (φel) and wherein the space vector representation (R) is calculated based on the load angle (θLW) and the power factor angle (φel), and Determine the level of the harmonic component (OA) based on the amplitude (A) of the complex representation (R). [2] Method according to claim 1, wherein the space vector representation (R) of the control signal for the harmonic angular frequency (ω O ) a co-rotating space vector representation (R) is calculated, the direction of rotation of which corresponds to the direction of rotation of the rotating field, and a counter-rotating space vector representation (RG) is calculated, the direction of rotation of which is opposite to the direction of rotation of the rotating field, and the level of the harmonic component (OA) is determined on the basis of the two space vector representations. [3] Method according to claim 1 or 2, wherein the space vector representation (R, R SK) a coordinate system (MS) or at least one phasor (A) which is connected to the harmonic angular frequency (ω O ) rotates relative to the stator, wherein at least one size of an axis of the coordinate system (i d ) or at least one amplitude of the phasor (A) indicates the level of the harmonic component (OA). [4] Method according to claim 1, 2 or 3, wherein the space vector representation (R) is calculated as a rotor-related space vector representation by calculating a co-rotating space vector representation (R) which is oscillating relative to the rotating field with harmonic angular frequency (ω O ) in the same direction as the rotating field, and calculating a counter-rotating space vector representation (RG) that is opposite to the rotating field with harmonic angular frequency (ω O) rotates in the opposite direction of rotation to the rotating field, wherein the multi-phase control signal (S) is mapped to the co-rotating space vector representation (R) and the counter-rotating space vector representation (RG); and determining the level of the harmonic component (OA) based on the amplitudes (A) of the space vector representations (R, RG). [5] Method according to one of the preceding claims, wherein the space vector representation (R) corresponds to a Park transformation and provides a d / q coordinate system (d, q) which is proportional to the angular frequency (ω O ) of the harmonic frequency, where the d-value of the coordinate system, the q-value of the coordinate system or the square root of the sum of the squares of these values indicates the level of the harmonic component (OA). [6] Method according to one of the preceding claims, wherein the space vector representation (R) corresponds to a Park transformation and provides two oppositely rotating d / q coordinate systems, each rotating at the angular frequency of the harmonic frequency, wherein a combination of the d and q values of the two coordinate systems indicates the level of the harmonic component (OA). [7] Method according to one of claims 1-4, wherein the space vector representation (R) corresponds to a Fortescue transformation and provides at least one phasor corresponding to a positive and / or negative sequence system (MS, GS) which is oscillated at the angular frequency (ω O ) of the harmonic frequency, whereby the amplitude of the phasor or a combination of the phasors indicates the level of the harmonic component (OA). [8] Method according to one of the preceding claims, wherein the control signal comprises a current signal (I) which represents the phase current in the electrical machine (EM), and a voltage signal (U) which represents the phase voltage of the electrical machine (EM), wherein the space vector representation (R) of the current signal (I) and the space vector representation (R') of the voltage signal (U) are calculated and the level of the harmonic component (OA) is calculated as the active power of the current amplitude (A) and the voltage amplitude (A') of the two space vector representations (R, R'). [9] Method according to one of the preceding claims, wherein the control signal comprises a current signal (I) which represents the phase current in the electrical machine (EM) and a voltage signal (U) which represents the phase voltage, wherein the space vector representation (R) of the current signal (I) and the space vector representation (R') of the voltage signal (U) are calculated and an active power factor is calculated from the phase offset (φ) between the two space vector representations (R, R'). [10] Method according to one of the preceding claims, wherein the level of the harmonic component (OA, OA') is calculated from the low-pass filtered (TP) amplitude of the complex representation (R, R'). [11] Method according to one of the preceding claims, wherein the space vector representation (R, R') of the control signal (S) for the harmonic frequency is calculated by partially or completely mapping (Tstat) the multi-phase control signal (S) onto an intermediate space vector representation (ZR) with a stator-fixed coordinate system (α, jβ) and by partially or completely mapping (Trot) this intermediate space vector representation (ZR) onto a complex representation whose angular frequency (ω O ) corresponds to the harmonic frequency. [12] Method according to one of the preceding claims, wherein upon detecting a change in the fundamental angular frequency (ω G the harmonic angular frequency (ω O ) proportional to the fundamental angular frequency (ω G is changed. [13] Method according to one of the preceding claims, wherein within the same time period the levels of the harmonic components for several different harmonic angular frequencies (ω O ) can be determined. [14] Method according to claim 13, wherein different ratios of the heights to each other are mapped to different types of defects and the types of defects are output. [15] Electric vehicle drive train with a multi-phase electric machine (EM) and an inverter (I) which is connected to the electric machine (EM) via a phase connection (1, 2, 3) in a control manner, wherein a detection module is connected to the phase connection (1, 2, 3), the detection module is designed to carry out the method according to one of the preceding claims and the detection module is set up to detect the multi-phase current (I) flowing through the phase connection (1, 2, 3) and / or the voltage (U) applied to the phase connection (1, 2, 3) as the control signal (S), and wherein the detection module further has a data interface which is set up to output the level of the harmonic component (OA) determined by the detection module.

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