DE102020216148A1 - Method for calibrating a device for determining the temperature of a rotor of an electrical machine - Google Patents

Abstract

The present invention relates to a method for calibrating a device (4) for determining a temperature of a rotor (3) of an electrical machine (1), the device (4) comprising: a primary circuit (5) which is fixed with respect to the rotor (3) which has a measuring device (6) for detecting an electrical primary current I primary in the primary circuit (5) or for detecting a variable characterizing the primary current I primary, at least one primary coil (8) and in particular a capacitor (13) for generating an oscillating circuit in the primary circuit (5), and a secondary circuit (10) formed on the rotor (3), which has at least one secondary coil (9) arranged for inductive coupling to the at least one primary coil (8), and at least one temperature-dependent electrical load (11), in particular a temperature-dependent electrical load Resistor having, characterized in that the device (4) is calibrated in such a way that ve Different signal voltages, each with a different frequency, are fed into the primary circuit (5), and that component parameters of the primary circuit (5) and secondary circuit (10) are determined based on the respective frequency of the signal voltages fed in and the amounts of the primary currents Iprimary and/or phase shifts determined for the respective signal voltages of the primary currents Iprimary can be determined.

Description

State of the art

The present invention relates to a method for calibrating a device of an electrical machine, the device for determining the temperature of a rotor of the electrical machine being provided. The transmission of a signal representing the temperature between a stator side and a rotor side of the electrical machine takes place without contact.

Electrical machines are known from the prior art. These are used for different applications, for example as a drive for vehicles. The electrical machine heats up during operation due to power losses, so that the temperature of the rotor of the electrical machine in particular increases. If the electrical machine is permanently excited and thus has permanent magnets in particular in the rotor, then it is necessary to record a rotor temperature. If this rotor temperature rises above a limit temperature, there is a risk of the permanent magnets becoming demagnetized, which can lead to irreparable damage to the electrical machine.

Various devices for determining the rotor temperature are known. These devices use a temperature model, for example, in order to be able to estimate a maximum temperature in the rotor. In order to compensate for measurement inaccuracies or tolerances in the temperature model, the maximum permissible rotor temperature is lower than the limit temperature in order to reliably avoid demagnetization. If the rotor reaches the maximum permitted limit temperature, the output power of the electrical machine is reduced and thus the losses are also reduced, as a result of which a further rise in temperature can be avoided.

Disclosure of Invention

The method according to the invention enables a device for determining a temperature of a rotor of an electrical machine to be calibrated reliably and precisely. Accurate calibration of the device makes it possible to increase the measuring accuracy of the device and thus to bring the maximum permissible rotor temperature closer to the limit temperature, so that an early power limitation of the electrical machine can be avoided. During calibration, component parameters of the device that are subject to tolerances are reliably determined.

The method according to the invention serves to calibrate a device for determining a temperature of a rotor of an electrical machine. The device to be calibrated comprises a primary circuit and a secondary circuit. The primary circuit is arranged in a stator-fixed manner with respect to the electrical machine. This means in particular that the primary circuit is attached to the stator of the electrical machine or to a housing that accommodates the stator. The secondary circuit is formed on the rotor, in particular attached to a rotor body.

The primary circuit is formed on the rotor, in particular attached to a rotor body.

The primary circuit has a measuring device for detecting an electrical primary current I _primary in the primary circuit. Alternatively, the measuring device can be designed to detect a variable that _primarily characterizes the primary current I. Such a characterizing variable is, for example, an electrical voltage that drops across a known electrical resistance in the primary circuit. The primary circuit can have a primary input for feeding a signal voltage into the primary circuit. The signal voltage is in particular an electrical alternating voltage, which is preferably sinusoidal, triangular, sawtooth-shaped or square-wave. Furthermore, the primary circuit has at least one primary coil and, in particular, a capacitor. The capacitor serves in particular to generate an oscillating circuit in the primary circuit. A phase can be set particularly advantageously via the capacitor and a phase sensitivity of the device to the temperature of the rotor can be maximized at a fixed operating point.

A secondary coil is provided in the secondary circuit and can be inductively coupled to the primary coil. This enables inductive coupling between the primary circuit and the secondary circuit, said inductive coupling taking place via the primary coil and the secondary coil. The primary coil and/or the secondary coil are, in particular, electrical windings. Furthermore, the secondary circuit has at least one temperature-dependent electrical load, the temperature-dependent electrical load being in particular a temperature-dependent electrical resistance.

The arrangement of the primary circuit fixed to the stator and the arrangement of the secondary circuit fixed to the rotor thus enable a relative movement between the primary circuit and the secondary circuit. Provision is made for an inductive coupling between the primary coil and the secondary coil to take place at least once per revolution of the rotor. This means that the primary coil and the secondary coil advantageously do not extend over the entire circumference of the rotor, but are formed in the circumferential direction only over a partial area of 360°. Thus, in addition to the temperature, a rotational speed of the rotor can also be detected by determining the number of inductive couplings that have taken place per unit of time.

If a signal voltage is fed into the primary circuit in such a device, then an electrical current I _primary is established in the primary circuit, which is dependent on the electrical resistance of the temperature-dependent electrical load. A temperature of the rotor can thus be derived from the primary current I _primary . Both the phase of the primary current I _primary and the amplitude of the primary current I _primary are sensitive to temperature changes and thus changes in the temperature-dependent electrical load. A temperature of the rotor can thus be derived both from the phase of the primary current and from the amplitude of the primary current, with a mutual plausibility check of the measurement results being possible if the temperature is determined independently of one another from the phase and the amplitude of the primary current I _primary .

The signal voltages are fed into the primary circuit, for example, by a control device correspondingly controlling a signal generator.

The device is preferably calibrated in such a way that different signal voltages, each with a different frequency, are fed into the primary circuit. The signal voltages are fed into the primary circuit, for example, via a primary input. In addition, component parameters of the primary circuit and the secondary circuit are determined using the respective frequency of the signal voltages fed in and the absolute values of the primary currents I _primary and/or phase shifts of the primary currents I _primary determined for the respective signal voltages. The different frequencies of the signal voltages fed in result in different system states, which differ due to the component parameters of the components used in the primary circuit and in the secondary circuit. These component parameters are component parameters that are subject to tolerances, in particular electrical component parameters, the values of which are only known with a tolerance by the manufacturer of the components. Examples of the component parameters of the components of the primary circuit and the secondary circuit are the inductance of the primary coil, the inductance of the secondary coil, the electrical line resistance of the secondary coil, the electrical line resistance of the primary coil, the electrical line resistance of the measuring device, the capacitance of the capacitor and the coupling factor between the primary coil and secondary coil. However, since all of these system states must always lead to the same rotor temperature, the corresponding component parameters can be determined from the different determined primary currents I _primary and the associated signal voltages. A calibration of the device is thus made possible reliably and preferably also quickly. The device can thus precisely detect the temperature of the rotor during further operation, as a result of which a safety margin between the maximum permitted rotor temperature and the limit temperature at which demagnetization occurs can be reduced. This means that higher power can be called up from the electric machine over a longer period of time.

The dependent claims relate to preferred developments of the invention.

The determined component parameters are advantageously stored in an electronic memory. The temperature of the rotor is then calculated based on the updated component parameters. Reliable temperature determination is thus possible, with access to the updated component parameters at all times. The component parameters can either be stored in the memory for the first time or component parameters that have already been stored can be updated. The calibration can therefore be carried out at any time. When determining the temperature, it is always ensured that the current component parameters are always available in the memory.

The electronic memory can, for example, be coupled to a control device for controlling the device. A temperature model can be stored in the memory which, based on the component parameters, assigns an amount and/or a phase shift of the primary current I _primarily to a temperature value. This temperature model is in particular at least one formula and/or table and/or matrix and/or at least one characteristic diagram and/or characteristic curve. This temperature model can be calibrated using the method described above. For this purpose, the component values determined for the calibration are stored in the memory for creating or updating the temperature model.

A system of equations is set up particularly advantageously for the calibration, with the number of component parameters to be determined specifying the number of necessary equations. Thus, as many different signal voltages are fed in as equations are required. Due to the large number of different signal voltages and the resulting large number of signal frequencies, the minimum required number of equations can thus be set up. By setting up more equations than the minimum needed, improved calibration is possible.

The device is advantageously set up, when the signal voltage is fed into the primary circuit, to induce a signal voltage in the secondary circuit by means of an inductive coupling between the primary circuit and the secondary circuit. The inductive coupling between the primary circuit and the secondary circuit takes place through the primary coil and the secondary coil. Due to the secondary voltage induced in the secondary circuit, a secondary current I _secondary flows in the secondary circuit, which is dependent on the temperature-dependent load in the secondary circuit. As a result of the secondary current I _secondary , in turn, a primary current I _primary is produced in the primary circuit. This primary current I _primary is therefore dependent on the secondary current I _secondary , as a result of which the primary current I _primary is also dependent on the rotor temperature. The device is further preferably designed to detect the primary current by means of the measuring device described above. The device is thus set up to determine the temperature of the rotor using the temperature model stored in the memory from an amount of the primary current and/or from a phase shift of the primary current, said phase shift between the signal voltage and the primary current being determined. In this way, reliable temperature detection of the rotor is made possible. The calibrated temperature model ensures that the correct component parameters are used. The temperature determination is therefore of a very high quality, as a result of which, as described above, high rotor temperatures can be permitted without the risk of an unintentional demagnetization of the permanent magnets of the rotor.

The temperature model is particularly advantageously an allocation function. Based on the component parameters and as a function of the frequency of the signal voltage fed in, the assignment function assigns a phase shift and/or an amount of the primary current to the temperature of the rotor. The assignment function is thus preferably predefined and derived from the measuring system, i.e. the primary circuit and the secondary circuit.

The assignment function preferably contains the following equation: $$\phi Z_{Ges}\left(j\omega \right)={\text{tan}}^{-1}\frac{-a\omega L_s+\omega L_p-\frac{1}{\omega C}}{a\left(R_s+R_{NTC}\right)+\left(R_v+R_p\right)}$$

This equation contains the phase shift φ, the electrical resistance Z _ges of the primary circuit and the frequency ω of the signal voltage fed in. The following factor α is used in the above equation: $$a=\frac{{\left(\omega k\right)}^2{L}_p{L}_s}{{\left(R_s+R_{NTC}\right)}^2+{\left(\omega L_s\right)}^2}$$

• L_p: Induktivität der Primärspule,
• L_s: Induktivität der Sekundärspule,
• R_s: Leitungswiderstand der Sekundärspule,
• R_p: Leitungswiderstand der Primärspule,
• R_v: Leitungswiderstand der Messeinrichtung,
• C: Kapazität des Kondensators, und
• κ: Kopplungsfaktor zwischen Primärspule (8) und Sekundärspule und dem von der Temperatur des Rotors abhängigen Parameter:
• R_NTC: Widerstand der temperaturabhängigen Last.

With the following fixed component parameters:

• L _p : inductance of the primary coil,
• L _s : inductance of the secondary coil,
• R _s : line resistance of the secondary coil,
• R _p : line resistance of the primary coil,
• R _v : line resistance of the measuring device,
• C: Capacitance of the capacitor, and
• κ: Coupling factor between primary coil (8) and secondary coil and the parameter dependent on the temperature of the rotor:
• R _NTC : Resistance of the temperature dependent load.

The equation mentioned thus enables the measured phase angle φ and the resistance of the temperature-dependent load to be assigned based on the component parameters of the individual components of the device. With a known signal voltage that was fed into the primary circuit and with a known primary current that was measured using the measuring device, the equation thus makes it possible to establish a connection with the temperature-dependent load R _NTC . This temperature-dependent load is thus the only remaining unknown in the equation, which can therefore be determined accordingly. If, on the other hand, the frequency ω is changed, the other component parameters can also be determined, given a corresponding number of existing equations, as shown above. A correspondingly large number of equations therefore makes it possible to reliably determine the component parameters and thus to carry out the calibration of the device.

Provision is also advantageously made for the complex electrical resistance of the primary circuit to be approximated using a polynomial function. For this purpose, coefficients of the polynomial function are determined using the different signal voltages fed in and the associated absolute values and/or phase shifts of the primary current. Thus, in particular, a large number of measuring points are set up, with each measuring point a signal voltage fed in, in particular the frequency of the signal voltage fed in, and the amount determined for the respective signal voltage and/or the phase shift determined for the respective signal voltage of the primary current. All of these measurement points can be described using a polynomial function, for which purpose corresponding coefficients of the polynomial function are identified. Since said coefficients represent the component parameters, the component parameters can be determined from the coefficients of the polynomial function. Such a method avoids in particular the solving of a complex system of equations.

Rather, the multiplicity of measuring points can be approximated, in particular numerically, by the polynomial function, which reduces the amount of computation involved. If the polynomial function is known, the component parameters can be derived directly from it. This enables the component parameters to be determined quickly and reliably, as a result of which the device can be calibrated easily and with little effort.

The coefficients of the polynomial function are particularly advantageously determined using the least squares method. Thus, the coefficients are determined reliably and, in particular, with little computation in comparison to the solving of complex systems of equations. In addition, the coefficient determination can be performed quickly.

In an alternative, only the imaginary part of the complex electrical resistance is used, so that in particular the phase and the absolute value of the electrical primary current I are _primarily used. For this purpose, the polynomial function has the following structure: $$Im\left\{\underset{\_}{Z}\left(\omega \right)\right\}=a{\mathrm{<figure-callout\; id="3"\; label="\omega "\; filenames="DE102020216148A1\_0037.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^3+b\omega +c{\omega }^{-1}$$

$$b=L_p$$

$$c=-\frac{1}{C}$$

Here, Im{Z(ω)} represents the imaginary part of the complex electrical resistance of the primary circuit, where ω is the frequency of the input signal voltage. The measuring system is thus modeled in turn. Due to Ohm's law of AC technology, the signal voltage fed into the primary circuit, the electrical current I _primary flowing in the primary circuit and the complex resistance of the primary circuit are in a fixed ratio to one another. The coefficients a, b and c of the above formula can thus be determined using the previously described measuring points of the signal voltage fed in and the associated phase shift of the primary current I _primary . If these coefficients have been determined, in particular using the least squares method as described above, then the size of the respective component parameters can be derived from said coefficients. The coefficients a, b and c are related to the component parameters as follows: $$a=-\frac{k^2{L}_p{L}_s{}^2}{R_{\mathrm{<figure-callout\; id="2"\; label="N\; T\; C"\; filenames="DE102020216148A1\_0037.png"\; state="\{\{state\}\}">N</figure-callout>}TC}{}^2}$$

$$b=L_p$$

$$c=-\frac{1}{C}$$

• L_p: Induktivität der Primärspule (8),
• L_s: Induktivität der Sekundärspule (9),
• C: Kapazität des Kondensators (13), und
• κ: Kopplungsfaktor zwischen Primärspule (8) und Sekundärspule (9), und dem von der Temperatur des Rotors (2) abhängigen Parameter:
• R_NTC: Widerstand der temperaturabhängigen Last (11).

With the following fixed component parameters:

• L _p : inductance of the primary coil (8),
• L _s : inductance of the secondary coil (9),
• C: capacitance of the capacitor (13), and
• κ: Coupling factor between the primary coil (8) and secondary coil (9), and the parameter dependent on the temperature of the rotor (2):
• R _NTC : Resistance of the temperature dependent load (11).

The component parameters can thus be determined without solving a complex system of equations. This enables the component parameters to be determined reliably and with little effort, which simplifies the calibration.

Wiederum erfolgt vorteilhafterweise die Ermittlung der Koeffizienten der Polynomfunktion, wobei die Koeffizienten d und e anhand der mehreren eingespeisten Signalspannungen, insbesondere der Frequenzen der eingespeisten Signalspannungen, und der jeweils zugehörigen Beträge, sowie insbesondere Phasen, des Primärstroms I_Primär ermittelt werden. Wiederum besteht ein fester Zusammenhang aufgrund des ohmschen Gesetz der Wechselstromtechnik zwischen dem Primärstrom I_primär, der eingespeisten Signalspannung und dem komplexen elektrischen Widerstand des Primärkreises. Ist die Polynomfunktion aufgestellt, so lassen sich die Bauteilparameter aus dem Koeffizienten d und e wie folgt ermitteln: $$d=\frac{{\kappa }^2{L}_p{L}_s}{R_{NTC}}$$

$$e=R_p+R_v$$

In another alternative, which can be combined in particular with the alternative described above, the focus is on the real part of the complex electrical resistance of the primary circuit. The amplitude or amount of the primary current is therefore decisive. In this case, the following equation is used as a polynomial function, where ω is the frequency of the injected signal voltage and Re{Z(ω)} is the real part of the complex electrical resistance of the primary circuit: $$Re\left\{\underset{\_}{Z}\left(\omega \right)\right\}=\mathrm{i.e}{\omega }^2+e$$

Again, the coefficients of the polynomial function are advantageously determined, with the coefficients d and e being determined using the plurality of signal voltages fed in, in particular the frequencies of the signal voltages fed in, and the respectively associated magnitudes, and in particular phases, of the primary current I _primary . Again, there is a fixed relationship based on Ohm's law of AC technology between the primary current I _primary , the signal voltage that is fed in, and the complex electrical resistance of the primary circuit. Once the polynomial function has been set up, the component parameters can be determined from the coefficients d and e as follows: $$\mathrm{i.e}=\frac{k^2{L}_p{L}_s}{R_{NTC}}$$

$$e=R_p+R_v$$

• R_p: Leitungswiderstand der Primärspule (8), und
• R_v: Leitungswiderstand der Messeinrichtung (6).

With the following fixed component parameters:

• R _p : line resistance of the primary coil (8), and
• R _v : line resistance of the measuring device (6).

The imaginary part described above and the real part of the electrical resistance of the primary circuit are used particularly advantageously for the calibration. Particularly preferably, the component parameters are initially determined using the imaginary part of the electrical resistance of the primary circuit, with the real part being used for additional plausibility checking and/or improvement of the component parameters. Thus, a reliable and accurate calibration can be performed.

The various signal voltages with different frequencies are fed in particularly advantageously with the temperature of the rotor remaining the same. Thus, in particular, the temperature-dependent electrical load is to be considered with a constant resistance value. As a result, this size is no longer a variable value, which means that the component parameters can be reliably determined.

The method according to the invention is advantageously controlled by a control device, it being possible for the control device to be implemented in power electronics of the electrical machine or in a separate electronics unit of the electrical machine. In this way, the device is calibrated by the power electronics or by the separate electronics unit.

The calibration is carried out particularly advantageously during the manufacture of the electrical machine. In particular, the calibration takes place at the end of a production line for the electrical machine. Alternatively or additionally, the calibration is carried out while the electric machine is in operation or is ready for operation. Operational readiness is to be understood in particular as a state in which the electric machine does not deliver any power, but is in particular ready for a delivery of power. Thus, in addition to an initial calibration, a continuous calibration of the electrical machine is also made possible. This ensures a continuously high quality of the determined temperature of the rotor of the electrical machine.

Provision is also particularly advantageously made for the calibration to be carried out within a maximum period of one second. In particular, the time required for the calibration is in the range of a few milliseconds. In this way it is also achieved in particular that the temperature of the rotor is constant during the calibration. Within the time used for the calibration, the calibration of a tolerated variation can be considered to be constant, especially when the electric machine is in steady-state operation or not in operation.

character list

• 1 eine schematische Abbildung einer elektrischen Maschine mit einer Einrichtung, die mit einem Verfahren gemäß einem Ausführungsbeispiel der Erfindung kalibriert wird,
• 2 ein schematisches Schaltbild der Einrichtung der elektrischen Maschine aus 1, und
• 3 eine schematische Darstellung einer Polynomfunktion zur Kalibrierung der Einrichtung mit dem Verfahren gemäß dem Ausführungsbeispiel der Erfindung.

Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawings. In the drawing is:

• 1 a schematic illustration of an electrical machine with a device that is calibrated with a method according to an embodiment of the invention,
• 2 a schematic circuit diagram of the device of the electrical machine 1 , and
• 3 a schematic representation of a polynomial function for calibrating the device with the method according to the embodiment of the invention.

Embodiments of the invention

the 1 show a schematic view of an electrical machine 1 with a stator 2 and a rotor 3. The electrical machine also has a device 4 for determining a temperature of the rotor 3 of the electrical machine 1. The device can be calibrated with a method according to an embodiment of the present invention.

The rotor 3 has a rotor shaft 3A and a rotor body 3B arranged on the rotor shaft 3A. The rotor shaft 3A extends along an axis of rotation 100 about which the rotor 3 is rotatable. The rotor body 3B is in particular a laminated core with an inserted permanent magnet (not shown). The stator 2 is preferably arranged in a housing 2A.

The device 4 comprises a primary circuit 5 fixed to the stator and thus mounted on the stator 2 or on the 2A. In addition, the device 4 has a secondary circuit 10 provided on the rotor 3 . The primary circuit 5 is thus fixed, with the secondary circuit 10 being movable relative to the primary circuit 5 . In particular, the primary circuit 5 can be attached to the stator 2 or to the housing 2A with a form fit and/or with a force fit and/or with a material fit. The secondary circuit 10 is formed on the rotor 3 and is connected to the rotor 3 in a fixed manner, in particular in a rotationally fixed manner. For example, the secondary circuit 10 is on one end of the Rotor body 3B of the rotor 3 and / or arranged on the rotor shaft 3A of the rotor 3 or attached. In particular, the secondary circuit 10 can be attached to the rotor 3 with a form fit and/or with a force fit and/or with a material fit.

2 shows an electrical circuit diagram of device 4.

The primary circuit 5 has at least one measuring device 6 for detecting an electrical primary current I _primary in the primary circuit 5 . In addition, a primary input 7 can be provided, via which signal voltages can be fed into the primary circuit 5 . To generate the signal voltage to be fed into the primary circuit 5, a signal generator 14 can be provided, which is part of the primary circuit 5, for example. Alternatively, the primary circuit 5 can include an external interface 15 for feeding a signal voltage into the primary circuit 5 .

The primary circuit 5 also has at least one primary coil 8 and, for example, a capacitor 13 . The primary coil 8 can in particular be a winding. The capacitor 13 is designed to generate an oscillating circuit in the primary circuit 5 . For example, a series resistor 16 is arranged between the primary input 7 and the capacitor 13 .

The measuring device 6 can be a voltmeter, for example, which measures a voltage drop across the series resistor 16 of the primary circuit 5, so that the primary current I can be determined _primarily by means of the known electrical resistance of the series resistor 16 and by means of the voltage drop measured at the series resistor 16. The signal voltage that is fed in can be determined with a further measuring device or can be known.

The secondary circuit 10 has at least one secondary coil 9 and a temperature-dependent electrical load 11 . The secondary coil 134 is arranged to be inductively coupled to the primary coil 130 . The secondary coil 9 can in particular be an electrical winding. The temperature-dependent electrical load 11 serves as a measuring element and can be a temperature-dependent electrical resistance. In the embodiment shown, the temperature-dependent electrical load 11 is a temperature-dependent electrical resistor with a negative temperature coefficient, i.e. a so-called NTC (negative temperature coefficient). However, other embodiments are also fundamentally conceivable, such as a temperature-dependent electrical resistance with a positive temperature coefficient, i.e. a so-called PTC (positive temperature coefficient). The temperature-dependent electrical load 11 is arranged at a specific position of the rotor 3, for example in a magnet pocket (not shown) accommodating permanent magnets of the rotor body 3B, in order to detect the temperature of the rotor 3 there. The temperature-dependent electrical load 11 is in electrical contact with the secondary coil 9.

The stationary primary coil 8 and the secondary coil 9 , which can be rotated about the axis of rotation 100 with the rotor 3 , are arranged in such a way that the secondary coil 9 is moved past the stationary primary coil 8 once per revolution of the rotor 3 . During the movement past, a secondary voltage is induced in the secondary coil 9 by inductive coupling. When moving past, the primary coil 8 and the secondary coil 9 face each other for a short time. The induced secondary voltage causes a secondary current I _secondary to flow through the temperature-dependent load 11. The amplitude of the secondary current I _secondary is thus determined by the temperature of the rotor 3. The secondary current I _secondary of the secondary circuit 10 is correspondingly dependent on the rotor temperature. As a result of the secondary current I _secondary , a rotor temperature-dependent primary current I _primary is brought about in the primary circuit 5 .

The signal voltage in the primary circuit 5 induces a secondary voltage in the secondary circuit 10 via an inductive coupling of the primary coil 8 to the secondary coil 9. The induced secondary voltage, which is in particular an AC voltage, causes a secondary current I _secondary to flow through the temperature-dependent load 11. The amplitude of the secondary current I _secondary is determined by the temperature of the rotor 3 . The secondary current I _secondary of the secondary circuit 10 is correspondingly dependent on the rotor temperature.

As a result of the secondary current I _secondary , a rotor temperature-dependent primary current I _primary is produced in the primary circuit 5, which is of course an alternating current. The primary current I _primary is detected by the device 4 using the measuring device 6 in the primary circuit 5, for example directly or indirectly via a variable characterizing the primary current I _primary , such as an electrical voltage.

In the case of an AC voltage fed into the primary circuit 5 as a signal voltage, this causes an alternating magnetic flux in accordance with the law of induction, which induces the secondary voltage in the secondary coil 9 magnetically coupled to the primary side 5 .

The AC voltage used as the signal voltage can have any waveform and can be, for example, a sinusoidal, triangular, sawtooth or rectangular waveform.

Temperature changes on the rotor 3 produce a resistance change in the temperature-dependent electrical load 11. This temperature-dependent resistance change in the temperature-dependent load 11 leads to a change in the primary current I _primary of the primary circuit 5. Consequently, there is a relationship between the amplitude and the phase of the primary current I _primary in the primary circuit 5 and the temperature of the rotor 3 to be determined. The primary current I is therefore _primarily detected in the primary circuit 5 by means of the measuring device 6 and the temperature of the rotor 3 at the position of the temperature-dependent load 11 is determined or ascertained from this in a control unit 20 . For this purpose, the measuring device 6 is connected to the control device 20 via a measuring signal line.

The temperature is determined, for example, by means of a temperature model stored in an electronic memory 12 in the form of at least one formula, table, matrix, characteristic diagram or characteristic curve, whereby an association between a measured amplitude and/or a measured phase of the primary current I _primary and an associated Temperature of the rotor 3 is present.

In the exemplary embodiment shown, the memory 12 is implemented, for example, in the control unit 20, with the control unit 20 being used to control the device 4 and/or to control the method according to the invention. Control unit 20 can be implemented in power electronics of electrical machine 1 or in a separate electronics unit of electrical machine 1 .

So there is a wireless and contactless signal transmission. The signal that can be transmitted is the temperature of the rotor 3. The temperature information is indirectly part of the secondary current or, via the inductively coupled coils 130, 136, also part of the primary current. Of course, the signal is only transmitted when the signal voltage is fed in. The capacitor 13 changes the transmission system of the device 4 and thus the system behavior, which can be used to adjust the measuring accuracy of the device 4 .

The temperature model stored in memory 12 models in particular the primary circuit 5 and the secondary circuit 10. The following equation can be represented for this purpose, which has a phase shift φ, the electrical resistance Z _ges of the primary circuit 5 and the frequency ω of the signal voltage: $$\phi Z_{Ges}\left(j\omega \right)={\text{tan}}^{-1}\frac{-a\omega L_s+\omega L_p-\frac{1}{\omega C}}{a\left(R_s+R_{NTC}\right)+\left(R_v+R_p\right)}$$

With the following factor α: $$a=\frac{{\left(\omega k\right)}^2{L}_p{L}_s}{{\left(R_s+R_{NTC}\right)}^2+{\left(\omega L_s\right)}^2}$$

• L_p: Induktivität der Primärspule 8,
• L_s: Induktivität der Sekundärspule 9,
• R_s: Leitungswiderstand der Sekundärspule 9,
• R_p: Leitungswiderstand der Primärspule 8,
• R_v: Leitungswiderstand der Messeinrichtung 6,
• C: Kapazität des Kondensators 13, und
• κ: Kopplungsfaktor zwischen Primärspule 8 und Sekundärspule 9.

This equation is dependent on several electrical component parameters of the primary circuit 5 and secondary circuit 10 components. These are as follows:

• L _p : inductance of the primary coil 8,
• L _s : inductance of the secondary coil 9,
• R _s : line resistance of the secondary coil 9,
• R _p : line resistance of the primary coil 8,
• R _v : line resistance of the measuring device 6,
• C: capacitance of the capacitor 13, and
• κ: Coupling factor between primary coil 8 and secondary coil 9.

Also present in this equation is the parameter R _NTC which is dependent on the temperature of the rotor 2 and which corresponds to the electrical resistance of the temperature-dependent load 11 .

If a signal voltage with a known frequency ω is fed into the primary circuit 5 , the primary current I _primary can be determined via the measuring device 6 . As a result, the phase shift φ of the primary current I _primary is known, with known component parameters only the parameter R _NTC being variable and being able to be determined. Thus, a temperature determination is possible.

To calibrate the temperature model, the electrical component parameters of the components of the primary circuit 5 and the secondary circuit 10 are determined or updated. This calibration is carried out, for example, at the end of a production line for manufacturing the electrical machine 1 . Provision can also be made for the calibration to be carried out repeatedly even during operation or when the electric machine 1 installed in a vehicle, for example, is ready for operation. In this way, measurement inaccuracies of the device due to age-related changes in the component parameters can be avoided.

The calibration is carried out in particular when the temperature of the electrical machine 1 remains the same, so that R _NTC remains constant. This can be achieved in particular by performing the calibration within a small time window of a maximum of one second.

According to the invention, different signal voltages are fed into the primary circuit 5 for the calibration. This is achieved, for example, by the control device 20 controlling the signal generator 14 accordingly. The signal voltages differ in their frequency ω. An associated primary current I _primary is determined for each of the signal voltages that are fed in. The component parameters of the primary circuit 5 and the secondary circuit 10 can be determined according to the invention using the respective frequency of the signal voltages fed in and the magnitudes of the primary currents I _primary and/or phase shifts of the primary currents I _primary determined for the respective signal voltages.

A system of equations can be set up that contains the above equation for the impedance Z _ges for several different frequencies ω. If as many equations are set up as there are component parameters to be determined, then this system of equations can be solved, with the above-mentioned component parameters being able to be determined.

The determined component parameters are stored in the electronic memory 12 in order to subsequently calculate the temperature of the rotor 3 on the basis of the component parameters present in the memory 12, in particular updated ones.

This is how the temperature model is either created or updated.

As an alternative to solving the system of equations, a numerical approximation is also possible. For this purpose, in turn, different signal voltages, which differ in their frequencies ω, are fed into the primary circuit 5 and the associated primary current I _primary is determined. A polynomial function can be determined on the basis of these measured values, with the polynomial function approximating the complex electrical resistance Z(ω) of the primary circuit. The complex electrical resistance Z(ω) can be represented as follows: $$\begin{array}{l}\underset{\_}{Z}\left(\omega \right)=\left(\frac{{\left(\omega k\right)}^2{L}_p{L}_s}{{\left(R_s+R_{NTC}\right)}^2+{\left(\omega L_s\right)}^2}\left(R_s+R_{NTC}\right)+\left(R_v+R_p\right)\right)\\ +j\left(-\frac{{\omega }^3{k}^2{L}_p{L}_s{}^2}{{\left(R_s+R_{NTC}\right)}^2+{\left(\omega L_s\right)}^2}+\omega L_p-\frac{1}{\omega C}\right)\end{array}$$

In one embodiment, the imaginary part Im{Z(ω)} of this complex resistance will be represented by the polynomial function. The imaginary part can be represented as follows: $$\begin{array}{l}Im\left\{\underset{\_}{Z}\left(\omega \right)\right\}=-\frac{{\omega }^3{k}^2{L}_p{L}_s{}^2}{{\left(R_s+R_{NTC}\right)}^2+{\left(\omega L_s\right)}^2}+\omega L_p-\frac{1}{\omega C}\\ \approx \frac{-k^2{L}_p{L}_s{}^2}{{\left(R_{NTC}\right)}^2+{\left(\omega L_s\right)}^2}{\mathrm{<figure-callout\; id="3"\; label="\omega "\; filenames="DE102020216148A1\_0037.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^3+L_p\omega -\frac{1}{C}{\omega }^{-1}\end{array}$$

This approximation is possible because R _S « R _NTC , which means that ( _RS + R _NTC ) ² ≈ ( _RNTC ) ² . Furthermore, it can be assumed that R _NTC » (ωL _S ), whereby the imaginary part can finally be approximated as follows: $$Im\left\{\underset{\_}{Z}\left(\omega \right)\right\}\approx \frac{-k^2{L}_p{L}_s{}^2}{{\left(R_{NTC}\right)}^2}{\mathrm{<figure-callout\; id="3"\; label="\omega "\; filenames="DE102020216148A1\_0037.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^3+L_p\omega -\frac{1}{C}{\omega }^{-1}$$

Thus the imaginary part is assumed as a polynomial function as follows: $$Im\left\{\underset{\_}{Z}\left(\omega \right)\right\}=a{\mathrm{<figure-callout\; id="3"\; label="\omega "\; filenames="DE102020216148A1\_0037.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^3+b\omega +c{\omega }^{-1}$$

$$b=L_p$$

$$c=-\frac{1}{C}$$

The coefficients a, b and c have the following relationship to the component parameters: $$a=-\frac{k^2{L}_p{L}_s{}^2}{R_{\mathrm{<figure-callout\; id="2"\; label="N\; T\; C"\; filenames="DE102020216148A1\_0037.png"\; state="\{\{state\}\}">N</figure-callout>}TC}{}^2}$$

$$b=L_p$$

$$c=-\frac{1}{C}$$

• Mit $$\mathrm{\Theta }=\left[\begin{array}{c}a\\ b\\ c\end{array}\right]:=\left[\begin{array}{ccc}{\mathrm{<figure-callout\; id="3"\; label="\omega "\; filenames="DE102020216148A1\_0037.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^3& \omega & {\omega }^{-1}\end{array}\right]\cdot \left[\begin{array}{c}a\\ b\\ c\end{array}\right]=W\cdot \mathrm{\Theta }$$
  
• ergibt sich gemäß Methode der geringsten Quadrate $$\widehat{\mathrm{\Theta }}=\text{arg}\left(\underset{\mathrm{\Theta }}{min}{\Vert W\cdot \mathrm{\Theta }-\text{y}\Vert }^2\right)$$
  
• so dass $$\mathrm{\Theta }=\left[\begin{array}{c}a\\ b\\ c\end{array}\right];\text{W}=\left[\begin{array}{ccc}{\omega }_0^3& {\omega }_0& {\omega }_0^{-1}\\ {\omega }_1^3& {\omega }_1& {\omega }_1^{-1}\\ ⋮& ⋮& ⋮\\ {\omega }_n^3& {\omega }_n& {\omega }_n^{-1}\end{array}\right];\text{y}=\left[\begin{array}{c}{y}_0\\ y_1\\ ⋮\\ y_n\end{array}\right]$$
  
  $$\widehat{\mathrm{\Theta }}={\left(W^{T}W\right)}^{-1}{W}^{T}y=\left[\begin{array}{c}a\\ b\\ c\end{array}\right]\stackrel{\wedge}{=}\left[\begin{array}{c}-\frac{{\kappa }^2{L}_p{L}_s{}^2}{R_{NTC}{}^2}\\ L_p\\ -\frac{1}{C}\end{array}\right]$$
  

The coefficients a, b and c can be determined from the measured values using the least squares method:

• With $$\mathrm{\theta }=\left[\begin{array}{c}a\\ b\\ c\end{array}\right]:=\left[\begin{array}{ccc}{\omega }^3& \omega & {\omega }^{-1}\end{array}\right]\cdot \left[\begin{array}{c}a\\ b\\ c\end{array}\right]=W\cdot \mathrm{\theta }$$
  
• results from the method of least squares $$\widehat{\mathrm{\theta }}=\text{bad}\left(\underset{\mathrm{\theta }}{min}{\Vert W\cdot \mathrm{\theta }-\text{y}\Vert }^2\right)$$
  
• so that $$\mathrm{\theta }=\left[\begin{array}{c}a\\ b\\ c\end{array}\right];\text{W}=\left[\begin{array}{ccc}{\omega }_0^3& {\omega }_0& {\omega }_0^{-1}\\ {\omega }_1^3& {\omega }_1& {\omega }_1^{-1}\\ ⋮& ⋮& ⋮\\ {\omega }_n^3& {\omega }_n& {\omega }_n^{-1}\end{array}\right];\text{y}=\left[\begin{array}{c}{y}_0\\ y_1\\ ⋮\\ y_n\end{array}\right]$$
  
  $$\widehat{\mathrm{\theta }}={\left(W^{T}W\right)}^{-1}{W}^{T}y=\left[\begin{array}{c}a\\ b\\ c\end{array}\right]\stackrel{\wedge}{=}\left[\begin{array}{c}-\frac{k^2{L}_p{L}_s{}^2}{R_{NTC}{}^2}\\ L_p\\ -\frac{1}{C}\end{array}\right]$$
  

If the coefficients a, b and c are known, the corresponding component parameters can also be determined from the relationship shown. The component parameters are stored in the memory 12 and can thus be used for the subsequent determination of the temperature of the rotor 2 as previously described.

3 shows schematically how the measured values are described by the polynomial function. The imaginary part of the complex electrical resistance Im{Z(ω)} is plotted on the ordinate, while the abscissa shows the frequency.

In addition to the imaginary part, the real part of the complex electrical resistance of the primary circuit 5 is also used particularly advantageously. This can be represented as follows: $$\begin{array}{l}Re\left\{\underset{\_}{Z}\left(\omega \right)\right\}=\frac{{\left(\omega k\right)}^2{L}_p{L}_s\left(R_s+R_{NTC}\right)}{{\left(R_s+R_{NTC}\right)}^2+{\left(\omega L_s\right)}^2}+\left(R_v+R_p\right)\\ =\frac{k^2{L}_p{L}_s\left(R_s+R_{NTC}\right)}{{\left(R_s+R_{NTC}\right)}^2+{\left(\omega L_s\right)}^2}{\mathrm{<figure-callout\; id="2"\; label="\omega "\; filenames="DE102020216148A1\_0037.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^2+\left(R_v+R_p\right)\end{array}$$

It can be assumed that R _NTC » (ωL _s ) and R _s « R _NTC on the one hand, whereby the real part can finally be approximated as follows: $$Re\left\{Z\left(\omega \right)\right\}\approx \frac{k^2{L}_p{L}_s}{R_{N\mathrm{<figure-callout\; id="2"\; label="T\; C\; \omega "\; filenames="DE102020216148A1\_0037.png"\; state="\{\{state\}\}">T</figure-callout>}C}}{\omega }^{}{}^2+\left(R_v+R_p\right)$$

Thus the real part is assumed as a polynomial function as follows: $$Re\left\{\underset{\_}{Z}\left(\omega \right)\right\}=\mathrm{i.e}{\omega }^2+e$$

$$e=R_p+R_v$$

The coefficients d and e show the following relationship to the component parameters: $$\mathrm{i.e}=\frac{k^2{L}_p{L}_s}{R_{NTC}}$$

$$e=R_p+R_v$$

The procedure for determining the component parameters is analogous to the procedure previously described for the imaginary part. Particularly advantageously, the combined consideration of the imaginary part and the real part enables a high-quality determination of the component parameters, as a result of which the device 4 is optimally calibrated.

The calibration method thus enables the component parameters of the components to be determined at any time. Direct access to the individual components is not necessary. The method is therefore particularly advantageous when the components cannot be reached or can only be reached with difficulty, as is the case in particular with the components of the secondary circuit 10 . The calibration ensures that the temperature of the rotor 3 can be reliably determined at any time.

Claims (14)

Method for calibrating a device (4) for determining a temperature of a rotor (3) of an electrical machine (1), the device (4) comprising: • a primary circuit (5) which is arranged in a stator-fixed manner with respect to the electrical machine (1) and which - a measuring device (6) for detecting an electrical primary current I _primary in the primary circuit (5) or for detecting a variable characterizing the primary current I _primary , - at least one primary coil (8), - and in particular a capacitor (13) for generating an oscillating circuit in the primary circuit (5) and • a secondary circuit (10) formed on the rotor (3) which has - at least one secondary coil (9) arranged for inductive coupling to the at least one primary coil (8), and - at least one temperature-dependent electrical load (11), in particular a temperature-dependent electrical resistance, characterized in that the device (4) is calibrated in such a way that • there ss different signal voltages, each with a different frequency, are fed into the primary circuit (5), • for each different signal voltage, a primary current I _primary is recorded by means of the measuring device (6) and • that component parameters of the primary circuit (5) and secondary circuit (10) are determined using the respective Fri frequency of the signal voltages fed in and the absolute values of the primary currents I _primary and/or phase shifts of the primary currents I _primary determined for the respective signal voltages. procedure after claim 1 , characterized in that the determined component parameters are stored in an electronic memory (12) in order to subsequently calculate the temperature of the rotor (3) on the basis of the component parameters present, in particular updated, in the memory (12). procedure after claim 1 or 2 , characterized in that the device (4) has an electronic memory (12) in which a temperature model is stored, which _primarily assigns a temperature value to an amount and/or a phase shift of the primary current I based on the component parameters, the determined for calibration Component values for creating or updating the temperature model are stored in the memory (12). procedure after claim 3 , characterized in that the device (4) is set up, • when the signal voltage is fed into the primary circuit (5) through an inductive coupling between the primary circuit (5) and the secondary circuit (10), a secondary voltage in the secondary circuit (10). induce a secondary current I _secondary flowing through the temperature-dependent load (11) in the secondary circuit (10) and as a result of the secondary current I _secondary causing a primary current I _primary dependent on the rotor temperature in the primary circuit (5), and • the primary current I _primary by means of the measuring device (6 ) and to determine the temperature of the rotor (3) from an amount of the primary current I _primary and/or from a phase shift of the primary current I _primary between the signal voltage and the primary current I _primary using the temperature model stored in the memory (12). procedure after claim 3 or 4 , characterized in that the temperature model is an assignment function which, based on the component parameters and depending on the frequency of the signal voltage fed in, assigns a phase shift and/or an amount of the primary current I _primarily to the temperature of the rotor (2). procedure after claim 5 , characterized in that the assignment function contains the following equation, where φ is the phase shift, ω is the frequency of the signal voltage fed in and Z _ges is the electrical resistance of the primary circuit (5): $$\phi Z_{Ges}\left(j\omega \right)={\text{tan}}^{-1}\frac{-a\omega L_s+\omega L_p-\frac{1}{\omega C}}{a\left(R_s+R_{NTC}\right)+\left(R_v+R_p\right)}$$

With the following factor α: $$a=\frac{{\left(\omega k\right)}^2{L}_p{L}_s}{{\left(R_s+R_{NTC}\right)}^2+{\left(\omega L_s\right)}^2}$$

With the following fixed component parameters: L _p : inductance of the primary coil (8), L _s : inductance of the secondary coil (9), R _s : line resistance of the secondary coil (9), R _p : line resistance of the primary coil (8), R _v : line resistance of the Measuring device (6), C: capacitance of the capacitor (13), and κ: coupling factor between the primary coil (8) and secondary coil (9), and the parameter dependent on the temperature of the rotor (2): R _NTC : resistance of the temperature-dependent load ( 11). Method according to one of the preceding claims, characterized in that the complex electrical resistance of the primary circuit (5) is approximated by means of a polynomial function in that coefficients of the polynomial function are calculated using the different signal voltages fed in and the amount determined for the respective signal voltage and/or the value for the respective Signal voltage specific phase shift of the primary current I _primarily determined and the component parameters are determined from the coefficients of the polynomial function. procedure after claim 7 , characterized in that the coefficients are determined by means of the least squares method. procedure after claim 7 or 8th , characterized in that the polynomial function is constructed as follows, where ω represents the frequency of the signal voltage fed in and Im{Z(ω)} represents the imaginary part of the complex electrical resistance of the primary circuit (5): $$Im\left\{\underset{\_}{Z}\left(\omega \right)\right\}=a{\omega }^3+b\omega +c{\omega }^{-1}$$

where the coefficients a, b and c to be determined have the following relationship to the component parameters: $$a=-\frac{k^2{L}_p{L}_s{}^2}{R_{NTC}{}^2}$$

$$b=L_p$$

$$c=-\frac{1}{C}$$

With the following fixed component parameters: L _p : inductance of the primary coil (8), L _S : inductance of the secondary coil (9), C: capacitance of the capacitor (13), and κ: coupling factor between primary coil (8) and secondary coil (9), and the parameter dependent on the temperature of the rotor (2): R _NTC : resistance of the temperature-dependent load (11). Procedure according to one of Claims 7 until 9 , characterized in that the polynomial function is constructed as follows, where ω is the frequency of the signal voltage fed in and Re{Z(ω)} is the real part of the complex electrical resistance of the primary circuit (5): $$Re\left\{\underset{\_}{Z}\left(\omega \right)\right\}=\mathrm{i.e}{\omega }^2+e$$

and where the coefficients d and e to be determined have the following relationship to the component parameters: $$\mathrm{i.e}=\frac{k^2{L}_p{L}_s}{R_{NTC}}$$

$$e=R_p+R_v$$

With the following fixed component parameters: R _p : line resistance of the primary coil (8), and R _v : line resistance of the measuring device (6). Method according to one of the preceding claims, characterized in that the various signal voltages are fed in at different frequencies while the temperature of the rotor remains the same. Method according to one of the preceding claims, characterized in that the method is controlled by a control unit (20), the control unit (20) being implemented in power electronics of the electrical machine (1) or in a separate electronics unit of the electrical machine (1). . Method according to one of the preceding claims, characterized in that the calibration is carried out during manufacture of the electrical machine (1), in particular at the end of a production line, and/or during operation or when the electrical machine (1) is ready for operation. Method according to one of the preceding claims, characterized in that the calibration is carried out within a maximum period of one second.

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