WO2024074539A1 - Calculating harmonics in an electric drive using a space vector representation of the harmonic system - Google Patents

Abstract

The invention relates to a method for ascertaining a harmonic component (OA) in a multiphase control signal (S) of a multiphase electric machine (M), having the following steps: operating the electric machine (M) using the control signal (S) in that the control signal (S) generates a rotating magnetic field with a fundamental angular frequency (ꞷG) in the electric machine. Additionally, a space vector representation (R) of the control signal is calculated for a harmonic angular frequency (ꞷO), wherein the harmonic angular frequency (ꞷO) differs from the fundamental angular frequency (ꞷG). The calculation allows for a partial or complete mapping (Trot) of the multiphase control signal (S) to a space vector representation (R) with the harmonic angular frequency (ꞷO). The level of the harmonic component (OA) is ascertained using the amplitude (A) of the complex representation (R). The invention additionally relates to an electric vehicle powertrain for carrying out the method.

Description

Description

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

Electric drives, especially those of vehicles, have an electric machine that is set in motion by means of magnetic fields. In many types of drives, a rotating magnetic field (stator magnetic field) is generated in the stator of the electric machine by means of a three-phase current. The magnetic rotor follows this stator magnetic field and thus rotates relative to the stator.

In addition to this stator magnetic field, which is generated with a fundamental frequency or with a fundamental angular frequency, harmonics to this fundamental frequency arise, for example, due to bearing damage or non-ideal control. These harmonics generate losses and also noise. It is therefore advantageous to identify and quantify these harmonic components during the development and operation of electric drives. A Fourier transformation is usually used to extract harmonic signals or generally for spectral analysis in order to be able to identify the individual spectral components. However, such a calculation of the spectral components is computationally complex, especially in real-time applications. It is therefore an object of the invention to show a possibility with which harmonic components in the control signal of an electrical machine can be calculated in a simple manner.

This object is achieved by the subject matter of the independent claims. Further properties, features, embodiments and advantages emerge from the dependent claims, the description and the figure.

It is proposed not to calculate all spectral components simultaneously using spectral analysis, but to calculate a space vector representation of a harmonic angular frequency to be investigated. The level (ie amplitude or signal strength) of the harmonic component is determined. Since such a space vector representation only affects one harmonic angular frequency (in contrast to the large number of frequencies in spectral analysis) and the required matrix transformations can be calculated in advance, the calculation effort is significantly reduced. Even with variable speeds, the harmonic angular frequency can be tracked without this requiring a high level of calculation effort.

The underlying idea is that there is also a rotating field for the harmonic or harmonic component to be examined, which rotates according to the angular frequency of the harmonic component (harmonic angular frequency). This makes it possible to record the signal strength of the harmonic system, which makes it possible to determine the level of the harmonic component. 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 level of the harmonic component of the space vector representation for the harmonic angular frequency is recorded. In particular, the existing rotating system of the fundamental angular frequency can be easily separated from the space vector representation that relates 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.

For example, when considering the space vector representation for the harmonic angular frequency over an entire cycle, there are indeed instantaneous influences from the system of the fundamental angular frequency, 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 hidden 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.

A method is described for determining a corresponding harmonic component in a multiphase control signal of a multiphase electrical machine. The electrical machine is preferably a synchronous machine, which can be permanently excited or separately excited. The electrical machine can also be an asynchronous machine. The electrical machine is preferably a traction machine of a vehicle. The electrical machine can be three-phase or six-phase, for example, 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 designed 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 (multidimensional) signal that represents both the current and the voltage of the electrical machine. The control signal can also have three or six phases or another number of phases (at least three). The phase numbers of the electrical machine and the control signal preferably correspond.

The electrical machine is operated with the control signal. The control signal generates a (magnetic) rotating field with a basic angular frequency in the electrical machine. The control signal is therefore an alternating signal whose Frequency corresponds to the fundamental angular frequency. The conversion between

Frequency and angular frequency are known to those skilled in the art. The fundamental and angular frequency can be determined in particular from a given speed.

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 amount of the multiple is preferably at least two. The harmonic angular frequency can generally be k times the angular frequency, with the amount of k being greater than one. In particular, non-integer (rational) multiples are also conceivable, for example 1.5 times or similar.

The space vector representation, which relates to the harmonic angular frequency, can fully or partially represent the relevant frequency component of the control signal. In particular, the space vector representation can partially represent the control signal, whereby the space vector representation, however, represents a measure of the strength of the harmonic component. In this case, the space vector representation (which also relates to the harmonic angular frequency) can only represent a co-rotating system or only a counter-rotating system (relative to the direction of rotor rotation) that relates to the relevant angular frequency. Alternatively or in combination with this, the space vector representation (which also relates to the harmonic angular frequency) can only represent a real part or only an imaginary part of the relevant 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 multi-phase 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 The harmonic angular frequency is calculated by mapping a 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.

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 onto a space vector representation based on the harmonic angular frequency. The space vector representation is preferably rotor-related, although stator-related space vector representations can also be considered. The extraction of the level of the harmonic component differs slightly here. The control signal is preferably mapped onto a space vector representation based on a rotation with the harmonic angular frequency. In particular, the space vector representation can be implemented using a phasor whose angular frequency corresponds to the harmonic angular frequency. As a result, only the relevant harmonic component (corresponding to the harmonic angular frequency) is reproduced in the space vector representation. This results in a space vector representation of the harmonic rotating field. The level of the harmonic component can be extracted from this.

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 determined from this in a simple manner. 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 contain the active power or which concern the reactive power, or which concern the apparent power. In addition, the space vector representations or their amplitudes can be used, the direction of rotation of which corresponds to the direction of rotation of the fundamental rotating field (ie the rotating field related to the fundamental angular frequency) and/or the system running in the opposite direction (which represents part of the space vector representation of the control signal for the harmonic angular frequency).

In particular, when determining the harmonic component, it can be averaged, for example over one or more revolutions. Furthermore, low-pass filtering can be carried out when determining the level of the harmonic component. In particular, real and imaginary components can be calculated individually and, if necessary, added together to determine the level of the harmonic component.

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 level of the harmonic component can be determined using the sum of the respective levels of the harmonic components of the two space vector representations. This means that the strength or level of the harmonic component can be determined regardless of the direction of rotation of the rotating field that makes up the harmonic component. It is not necessary to know which direction of rotation the rotating field that makes up the harmonic component has (i.e. the rotating field of the harmonic angular frequency). Alternatively, only the co-rotating or only the counter-rotating space vector representation can be calculated, with the harmonic component or its strength being determined using this space vector representation. This can be applied in particular if, for example, it is already known from the type of error that the Harmonic component is linked to a harmonic rotating field which rotates (or which rotates in the opposite direction).

The space vector representation is preferably calculated as a rotor-related space vector representation. The space vector representation can provide a coordinate system that rotates relative to the stator. The space vector representation can also provide at least one phasor that rotates relative to the stator. The rotation of the coordinate system or the phasor occurs at the harmonic angular frequency. A rotor-related space vector representation of this type results in a quasi-static representation. In particular, this representation does not vary with the changing angular position of the system in question. The level of the harmonic component is specified by at least one size 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. The at least one size of an axis of the coordinate system can be a size of the real part or the imaginary part. Sizes of 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 created in particular by a d/q transformation, which can also be referred to as a Park transformation. This transformation is carried out for the harmonic angular frequency.

In the case of space vector representations that are stator-related, the coordinate system can also be obtained by means of a Clarke transformation, which assumes a rotation with 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 from the effective value) of at least one of the coordinate axes (such as the d or q coordinate axis). In this context, quasi-stationary means that the relevant quantity changes with the speed, but does not vary with the rotation of the rotor. In the case of a stator-related coordinate system (e.g. a representation in a, ß 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. 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 amount of the space vector representation (i.e. in particular the length of the phasor or vector) as the height of the harmonic component.

The space vector representation can also correspond to a positive and/or negative system of a representation of the rotating system as symmetrical components, which rotates at the harmonic angular frequency. The level of the harmonic component can thus be determined based on the amplitude of the positive and/or negative 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 system, the negative system or a combination of the amplitudes (in particular the sum) can be used to determine the level.

Both the representation in a d,q coordinate system (Park transformation) and the representation using symmetrical components is a rotor-related representation. The Clarke transformation or the representation in the corresponding a, ß components, on the other hand, is a stator-related transformation or representation. The determination of the level of the harmonic component in rotor-related representations corresponds to the determination of the DC component. When determining the level of the harmonic component from space vector representations that are stator-related, for example, the effective value of a quantity that is part of the space vector representation is used. In other words, in stator-related Space vector representations of the effective value of this space vector representation can be determined as the level of the harmonic component.

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 direction of rotation). 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 must be taken into account that these are already based on a rotation with the fundamental angular frequency. In this context, "rotor-related" means that the corresponding space vector representation is based on a rotor that rotates with the fundamental angular frequency.

However, the rotating system that forms the harmonic components rotates with the harmonic angular frequency relative to the (simple fundamental angular frequency) and thus relative to the rotor. In order to take into account that the space vector representation of the harmonic components is based on a 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 with 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 with the harmonic angular frequency relative to the rotor or relative to the rotational movement with the fundamental angular frequency. The fundamental angular frequency is the basis for the space vector representation of the fundamental system. In a similar way, the fundamental angular frequency is preferably added to the harmonic angular frequency in a counter-rotating space vector representation in order to take into account 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 rotating at the fundamental angular frequency), which also rotates at the harmonic angular frequency. With a rotor-related space vector representation, the fundamental angular frequency must therefore be added or subtracted in order to obtain a representation for the harmonics or their rotating system that corresponds to the rotation of the rotating system relative to the fundamental system (whose representation rotates at the harmonic angular frequency) at the harmonic angular frequency.

The multiphase control signal is thus mapped onto the 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).

Alternatively or in combination with this, the multiphase control signal can be mapped onto 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. As a result, the space vector representations refer to a harmonic rotating field that rotates with the harmonic angular frequency relative to the fundamental system.

The level of the harmonic component can be determined using an amplitude of one of the space vector representations or using the amplitudes of the space vector representations. In particular, the level of the harmonic component can be determined using 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 amounts 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, where the level of the harmonic component of the (apparent) power can correspond to the complex representation, or can only correspond to the real or imaginary part of the space vector representation. In particular, the level of the root of the sum of the squares of the real part and the imaginary part can correspond to the complex representation or to this sum itself.

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. In addition, 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 or the power factor angle relate to the fundamental angular frequency.

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 (based on the fundamental angular frequency) that corresponds to an a, ß 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 (a, ß - axis). The power factor angle can be calculated or read out from this space vector representation, 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 of these. The space vector representation therefore also includes the power factor angle, the load angle and in particular the sum of these.

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 with the angular frequency of the harmonic frequency, i.e. with 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 level 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 which 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. A space vector representation can therefore be provided for the current control signal and the voltage control signal 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.

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 direct signal components, i.e. an extraction of the direct current component of the co-rotating system and the counter-rotating system for the current control signal and the voltage control signal respectively. This particularly only affects the q component of the coordinate system. The conversion into a space vector representation or filtering can be followed by a calculation of the d component and the q component for the current control signal respectively. and the voltage control signal follow. The power can be obtained in particular by complex multiplication of the d and q components obtained in this way for the current control signal and the voltage control signal. The resulting power can be regarded as the level of the harmonic component. Simplified methods provide that only the current or only the voltage control signal is considered in order to determine the level of the harmonic component. Furthermore, only the co-rotating or only the counter-rotating system can be considered, i.e. only a co-rotating or only a counter-rotating space vector representation.

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 that 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 level 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 level of the harmonic component resulting from the sum of the amounts of the two amplitudes. The combination of the phasors can thus be provided by adding the amounts of the two systems.

As mentioned, the control signal can have 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 have 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. The space vector representation of the current signal and the space vector representation of the voltage signal can be calculated. The level of the harmonic component is determined in particular as 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 level or strength of the harmonic component.

Designs provide that an active power factor is also calculated from the phase shift between the space vector representations of the current control signal and the voltage control signal. The level of the harmonic component can then result from the complex power that results from the two space vector representations, as well as from the active power factor that corresponds to the phase shift between the two space vector representations. In this case, the level of the harmonic component results from an active power that is calculated from space vector representations of the voltage and current control signals. The phase shift or the calculated active power factor is therefore included in the calculation of the harmonic component.

Further embodiments provide that the level 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 low-pass filtering of the respective amplitudes, in particular by determining the magnitude of the complex representation (that is, 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. 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.

The method can be used in particular to detect the harmonic component at variable speeds, i.e. at variable fundamental angular frequencies. In this case, 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 is the basis for the space vector representation, is adapted to changes in speed or speed of the electrical machine. In particular, when the change in the fundamental angular frequency is detected, the harmonic angular frequency is changed proportionally to the fundamental angular frequency. If there is a change in the fundamental angular frequency by a factor of x, a harmonic angular frequency increased by a factor of x is also used in the space vector representation.

In addition to an adaptation 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 at 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.

Furthermore, the error can be deduced from the determined harmonic component. In particular, the corresponding types of error can be deduced from the ratios of the heights of harmonic components of different harmonic angular frequencies. Different ratios of the heights to one another are preferably mapped to different types of error. The mapped types of error can then be output. If, for example, in the case of a bearing error, the fifth harmonic would be expected to be significantly stronger than the third harmonic, while in the case of an inverter error the third harmonic would dominate the fifth harmonic, then these different types of error can be differentiated from one another using the ratios of the heights of the various harmonic components and output.

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 several phases). 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 set up to detect the multi-phase current flowing through the phase connection. Alternatively or in combination with this, the detection module is set up to detect the voltage applied to the phase connection (i.e. the voltage between the different phases of the phase connection). The detection module also has a data interface which is used to Output of the level of the harmonic component determined by the acquisition 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 designed to output the aforementioned types of errors.

A computer program product can be provided that is set up to carry out the method described here. In particular, the computer program product can be set up both to operate the electrical machine and to calculate the space vector representation and to determine the level of the harmonic component. In addition, a computer program product can be provided that is not set up to operate the electrical machine, but 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 are transferred that represent the control signal. 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 set up to carry out the method described here when running in a processor (or just the steps of calculating and determining the level of the harmonic component). The processor can have an input interface to which the control signal is entered or variables that represent it. These are in particular measured variables that characterize the control signal, in particular its voltage and/or current curve.

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 carried out in a preparatory step. In this step, parameters are stored that represent the space vector representation or a matrix that corresponds 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 can represent a decomposition into symmetrical 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, especially 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 representing the control signal. As a result, part of the calculation can be carried out outside of real time, in particular in a preparatory phase before the start of operation, i.e. before the generation of the control signal, while in real time, i.e. when the current control signal exists 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).

An exemplary embodiment provides that first (in a preparatory phase before the operation of the electrical machine) a transformation matrix is generated, by means of which the space vector representation can be calculated later (during the operation of the electrical machine), 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 basic system (which rotates at the basic angular frequency) relates 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 basic angular frequency, and a counter-rotating transformation matrix based on the sum of the harmonic and fundamental angular frequency. 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 (in short: fundamental angular frequency).

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

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 are used 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. to the rotating system of the control signal, which rotates at the harmonic angular frequency.

The current control signal is applied to the associated transformation matrix. The same applies to the voltage control signal. Until the control signal is applied to the transformation matrices, the process can be carried out offline or in preparation, so that part of the required computing power is not required during operation, i.e. during the determination of the level of the harmonic component using the control signal. When the Park transformation is used as a transformation matrix for the current control signal, a co-rotating d-component, a co-rotating q-component, a counter-rotating d-component and a counter-rotating q-component result. The corresponding four components also result for the voltage control signal, i.e. co-rotating d- and q-components and counter-rotating d- and q-components.

In a subsequent step, the resulting components are averaged or low-pass filtered. In particular, only the DC voltage component is filtered out. A DC voltage component is a component whose frequency is not greater than a frequency that corresponds to the rate of change of the speed. This means that slowly changing speeds can also be taken into account. As already described, the relevant harmonic angular frequency is adjusted proportionally to changing speeds of the electrical machine (i.e. to changing drive speeds).

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 the counter-rotating system. 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 system and for the negative system. The components resulting from the multiplication of the real parts and the components resulting for the imaginary part are calculated and added for the counter system and for the positive system.

The real and reactive components or the d and q components are calculated and summed for both the negative and positive systems (generally: combined). 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 level of the harmonic component is then preferably determined from the product of the resulting current and voltage amplitude amounts 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 level of the harmonic component is determined in particular by 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.

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 level of the harmonic component thus corresponds to the apparent power, the sum of the reactive and active components, or just the reactive component, or just the active component. All of these quantities are suitable for calculating the level of the harmonic component with sufficient accuracy in order to arrive at a measure of the strength of the harmonics using a procedure that is not very computationally intensive.

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 taking into account the sum of both angles. A given transformation matrix can be adapted to these angles or this angle by simply adjusting it. This adjustment can in particular be made in real time (during operation of the electrical machine). For this purpose, for example, pre-stored Transformation matrices for specific, associated pre-stored angles can be retrieved.

When using a Fortescue transformation, the same procedure can be followed, whereby a Fortescue transformation also works in a complex plane, and therefore the obvious equivalents to the d and q transformations or d and q components arise. With a Fortescue transformation, the fixed system (related to the harmonic angular velocity) can also be calculated and used for error analysis.

Figure 1 serves to explain in more detail embodiments of the procedure described here.

Shown is an electric drive, in particular a vehicle drive (traction drive), with a battery BAT as a direct voltage source, an inverter INV connected to it and an electric machine EM which is connected to the battery BAT via the inverter INV. The electric machine has an electrical angle (pel and a load angle 9LW. 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 alternating current side of the inverter INV. The battery BAT is connected to the direct current side of the inverter INV. The inverter is suitable for generating a control signal S from the direct voltage of the battery BAT. The control signal S has, as symbolically shown, two components, namely a current component I and a voltage component U. The motor angle (pel) (or the angle (pel + 0LW)) exists between the current control signal I and the voltage control signal U (which together form the control signal S).

It is symbolically shown that the current control signal I contains two three-phase rotating systems, namely a system that rotates with the fundamental angular frequency CÜG relative to the stator (ie rotor-fixed), and a system that rotates with the harmonic angular frequency wo relative to the Stator rotates (and thus also rotates with respect to the system with the fundamental angular frequency at [wo - WG]). The current control signal I is the sum of these two three-phase systems. To show that the harmonic angular frequency wo is greater than the fundamental angular frequency WG, the system that rotates with the harmonic angular frequency is shown with a double arrow as a rotation arrow, while the arrow that represents the rotation with the fundamental angular frequency is shown with just a single arrow. The double arrow rotates (by O/ G) faster than the single arrow. For better clarity, only the co-rotating components are shown symbolically in Figure 1, whereby the current control signal I can also contain 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.

The dashed rectangle at the top right of the drawing shows the background of the transformation described here symbolically and by way of example (using symmetrical components). The transformation TrotsK shows the transformation of the harmonic rotation system (of the current control signal I) by dividing it into a positive system MS and a counter system GS. The arrow of the harmonic rotation system pointing in both directions of rotation is intended to show that these contain two individual counter-rotating systems. As shown, this can be divided into a positive system MS, which rotates the co-rotating harmonic rotation system (with harmonic angular frequency wo), and into a component of the counter system GS with an opposite direction of rotation, shown with -wo. 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 system NS, which represents a DC component offset.

The positive phase system MS and the negative phase system GS shown are shown in three phases for better understanding. It is important that the phase vectors of the positive phase system MS are of the same length (and offset by 120 degrees). The same applies to the counter-system GS. Therefore, the positive system can be represented by a single phasor. The same applies to the counter-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 symmetrical 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 rotary system, both of which are contained as harmonic components in the control signal. A first Park transformation result (ie resulting representation), which relates to the co-rotating system, and a second Park transformation result (ie resulting representation), which relates to the counter-rotating rotary system, correspond 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 amount of the two systems MS, GS can be calculated from them. This reflects the strength or level of the harmonic component OA.

In simplified terms, the amount of amplitude A can be calculated from this, starting from the co-rotating system MS and the counter-rotating system GS. This applies to a dq transformation, preferably for the real part and the imaginary part. Simplified embodiments only take the real part into account, i.e. the d-component of the co-rotating system and the counter-rotating system.

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 carried out before the mapping using Trot in order to achieve a Intermediate space vector representation ZR. The static mapping Tstat maps the multiphase system to a single-phase system for the harmonic angular frequency wo. A Clark transformation is shown, which as an intermediate space vector representation ZR is a single-phase, stator-related, complex representation. This includes as real part a the corresponding real current component that results from transforming the multiphase system to this single-phase, stator-related space vector representation ZR. The intermediate space vector representation ZR also includes a complex component jß, which as a single-phase imaginary part represents the relevant multiphase components of the control signal.

It is shown that the optional intermediate space vector representation ZR is carried out 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 a as well as an imaginary component jß 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 wo and represent the current and voltage control signals in the complex plane as a single-phase vector that rotates at the harmonic angular frequency wo.

The mapping Trot refers to the harmonic angular frequency wo 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 (pel and the load angle 0LW are combined to form an angle 0. The mapping Trot is carried out taking this angle 0 into account. This angle is therefore taken into account as a total angle offset in the space vector representation R. In Figure 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 rotates with wo, whereby in preferred embodiments an opposite space vector representation RG is also generated. R represents the rotating harmonics as a rotor-related space vector representation, while RG is the opposite space vector representation of the harmonics. Both representations are complex rotor-related and single-phase. When the control signal is controlled, the complex quantities A and , which can also be referred to as phasors, result in relation to the harmonic angular frequency wo. The amount of these quantities corresponds in the example shown to the level of the harmonic component. Preferably, the sum of the amounts of A and A' is used to represent the level (i.e. strength) of the harmonic component.

Alternative, simplified embodiments provide that the level of the harmonic component OA is formed only by A or only by A'. The concurrent space vector representation R and the counter-rotating space vector representation RG are shown for the current control signal. The concurrent space vector representation R' and the counter-rotating space vector representation RG' are shown for the voltage control signal in Figure 1. 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 wo, use the real and imaginary instantaneous voltage quantities Lid and llq. 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 wo. The space vector representations RG and RG' represent the current or voltage control signal for the harmonic in a rotor-related and single-phase manner. The imaginary and real parts are extracted from the rotor-related space vector representations R, R' shown. This is shown by the extraction block Extr. The harmonic component OA is the harmonic component of the current control signal I and the extraction of the space vector representation R' gives the level of the harmonic component OA' for the voltage control signal U. Optionally, a low-pass filter TP takes place after the extraction and before the output of the two harmonic components for current and voltage. This is shown by the low-pass filtering 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 amount of the space vector representation R. The harmonic component OA' corresponds to the amount of the space vector representation R' of the control signal.

In order to calculate the level of the harmonic component as power, both harmonic components for the current or for the voltage can be multiplied together. In particular, the phase angle <p (as the power factor cos <p) between the two complex representations of the current or the 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 the voltage-related harmonic components. In this case, the real amplitudes of the 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. If necessary, the power factor, i.e. the angle between the complex representations A' and A, is taken into account as cos <p. This can be done by using the lengths or the 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 <p (ie by cos <p). This gives the active power component of the harmonic component. 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 level of the harmonic component can be calculated from the product of the resulting current and voltage amplitude amounts |A|, |AJ and the angle <p between current and voltage.

The following relationships can be used to calculate the level of the harmonic as signal power:

P = ld*Ud + lq*Uq.

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

P = Re{U _M } * e{livi} + lm{UM} * lm{lM}, where the index M stands for the current I and the index M for the voltage U for the positive sequence system (co-rotating system) and a power can be calculated in the same way for the negative sequence system. The two powers are combined and form a quantity that represents the level of the harmonics.

Furthermore, especially in the case of an a, ß space vector representation, the height can be calculated as power P = la*Üa + Iß * Üß, i.e. based on the peak values Ü, I of the voltage and current. Here too, only the positive or negative sequence system can be considered, or preferably a combination (sum) of the powers of the positive and negative sequence systems calculated in this way.

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 wo. In particular, this angular frequency wo can also be adjusted when the speed of the electrical machine changes. In this case, the angular frequency wo is adjusted proportionally to the fundamental angular frequency or proportionally to the speed of the electrical machine EM. The calculation sequence shown can thus be divided into two parts, whereby the generation of the images Trot or, if applicable, Tstat is carried out once or before the generation of the control signal and is stored in a memory. During operation of the electrical machine or to determine the level of the harmonic component, the image 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 be mapped using the images to a rotor-related space vector representation R in order to calculate the level of the harmonic component from this during operation of the electrical machine.

The mapping takes place during operation and to determine the level of the harmonic component, while the generation of the maps Trot, Tstat can be carried out in a preparatory step before the electrical machine is operated. This step can be carried out, for example, when programming a corresponding computing device or at the end of the production line when assembling the electrical machine. In particular, the mapping can be generated before the electrical machine begins to operate, either before each start of the electrical machine or before the first start of the electrical machine.

Claims

Patent claims 1 . Method for determining a harmonic component (OA) in a multiphase control signal (S) of a multiphase electrical machine (M), comprising the steps: Operating the electrical machine (M) with the control signal (S) in which the control signal (S) generates a rotating field with a fundamental angular frequency (WG) in the electrical machine; Calculating a space vector representation (R) of the control signal for a harmonic angular frequency (wo) which is different from the fundamental angular frequency (WG) by partially or completely mapping (Trot) the multiphase control signal (S) to a space vector representation (R) with the harmonic angular frequency (wo) and Determine the level of the harmonic component (OA) using the amplitude (A) of the complex representation (R). 2. Method according to claim 1, wherein a co-rotating space vector representation (R) is calculated as the space vector representation (R) of the control signal for the harmonic angular frequency (wo), the direction of rotation of which corresponds to the direction of rotation of the rotating field, and a counter-rotating space vector representation 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, RSK) provides a coordinate system (MS) or at least one phasor (A) which rotates with the harmonic angular frequency (wo) relative to the stator, wherein at least one size of an axis of the coordinate system (id) or at least one amplitude of the phasor (A) indicates the level of the harmonic component (OA). Method according to claim 1, 2 or 3, wherein the space vector representation is calculated as a rotor-related space vector representation by calculating a co-rotating space vector representation (R) which rotates in the same direction of rotation as the rotating field relative to the rotating field with harmonic angular frequency (wo), and calculating a counter-rotating space vector representation (RG) which rotates in the opposite direction of rotation as the rotating field relative to the rotating field with harmonic angular frequency (wo), wherein the multi-phase control signal (S) is mapped onto 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). Method according to one of the preceding claims, wherein the electrical machine is operated with a load angle (9LW) and with a power factor angle (cpel) and wherein the space vector representation is calculated based on the load angle (0LW) and the power factor angle (cpel). Method according to one of the preceding claims, wherein the space vector representation corresponds to a Park transformation and provides a d/q coordinate system (d, q) which rotates at the angular frequency (wo) of the harmonic frequency, wherein 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). Method according to one of the preceding claims, wherein the space vector representation 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. Method according to one of claims 1 - 5, wherein the space vector representation corresponds to a Fortescue transformation and provides at least one phasor which corresponds to a positive and/or negative system (MS, GS) which rotates at the angular frequency (wo) of the harmonic frequency, wherein the amplitude of the phasor or a combination of the phasors indicates the level of the harmonic component. Method according to one of the preceding claims, wherein the control signal has 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 is calculated as the active power of the current amplitude (A) and the voltage amplitude (A') of the two space vector representations (R, R'). Method according to one of the preceding claims, wherein the control signal has 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 (cp) between the two space vector representations (R, R'). Method according to one of the preceding claims, wherein the level of the harmonic component (OA, OA') is calculated based on the low-pass filtered (TP) amplitude of the complex representation (R, R'). Method according to one of the preceding claims, wherein the space vector representation (R, R') of the control signal (S) for the 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 (a, jß) and by partially or completely mapping (Trot) this intermediate space vector representation (ZR) onto a complex representation whose angular frequency (wo) corresponds to the harmonic frequency. Method according to one of the preceding claims, wherein when a change in the fundamental angular frequency (WG) is detected, the harmonic angular frequency (wo) is changed proportionally to the fundamental angular frequency (G). Method according to one of the preceding claims, wherein the levels of the harmonic components for several different harmonic angular frequencies (wo) are determined within the same time period. Method according to claim 14, wherein different ratios of the levels to one another are mapped onto different types of error and the types of error are output. 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 controlling 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 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.