Method for determining an electrical rotor resistance

Abstract

Method for determining the electrical rotor resistance of a rotor of an electric machine, in particular an asynchronous machine of a motor vehicle, wherein an actual current, in particular a D current, is set in the electric machine based on a target voltage, in particular a D voltage, characterized in that a voltage function, in particular at least sectionally periodic, is generated in a standstill state of the electric machine and a phase shift between the actual current and an actual voltage is determined and the electrical rotor resistance is determined based on the phase shift.

Description

[0001] The invention relates to a method for determining an electrical rotor resistance of a rotor of an electric machine, in particular an asynchronous machine of a motor vehicle, wherein an actual current, in particular a D current, is set in the electric machine based on a target voltage, in particular a D voltage.

[0002] Methods for determining the rotor resistance of electric machine rotors are generally known from the prior art. For example, it is known to record various parameters or quantities of the electric machine, such as the temperatures of the rotor and stator, their inductances, and the like, and to calculate the rotor resistance analytically from this data. However, in practice, such a procedure is very time-consuming due to the necessary recording of the individual parameters of the electric machine and the calculation of the rotor resistance based on these parameters.

[0003] The invention is based on the objective of providing an improved method for determining the electrical rotor resistance of a rotor of an electrical machine.

[0004] The problem is solved by a method with the features of claim 1. Advantageous embodiments are the subject of the dependent claims.

[0005] As described at the outset, the invention relates to a method for determining the electrical rotor resistance of a rotor of an electric machine, specifically an asynchronous machine. The electric machine can, in particular, be configured as a drive unit for a motor vehicle. Based on a target voltage, especially a derivative voltage (D-voltage), a target current, specifically a derivative current, is set in the electric machine. In other words, a specific target current is specified and supplied to a controller, and based on this, a specific target voltage, specifically a derivative voltage, is generated for a power electronics unit or an inverter, so that the power electronics unit or the inverter outputs an actual voltage, specifically an actual derivative voltage, to the electric machine, and based on this, an actual current, specifically an actual derivative current, is established in the electric machine.

[0006] The invention is based on the finding that, in a standstill state of the electric machine, a voltage function, particularly one that is at least sectionally periodic, is generated, and a phase shift between the actual current and the actual voltage is determined. Based on this phase shift, the electrical rotor resistance is then determined. In other words, it is proposed that the method be carried out in a standstill state of the electric machine. A standstill state of the electric machine is understood to be a state in which the rotor is stationary, i.e., it is not rotating and is at 0 rpm. Furthermore, in this standstill state, the electric machine should not generate any torque.

[0007] As described, the target voltage is provided according to a defined voltage function and output as the actual voltage by the power electronics. Based on this output actual voltage, the described actual current results in the electrical machine. The voltage function can be periodic in at least one time interval or sequence, for example, generated as a sinusoidal voltage. The voltage function is generated, for example, by the power electronics or a control unit of the electrical machine. As already described, an actual current is established in the electrical machine due to the voltage function.The method determines a phase shift between the actual current, which arises in response to the voltage function in the electric machine, and the actual voltage, which is output by the power electronics based on the voltage function and the set voltage. Based on this phase shift, the electrical rotor resistance of the electric machine's rotor is then determined.

[0008] In other words, the invention is based on the fact that a specific actual current in the electric machine is stimulated by applying the voltage function. A relationship between the phase shift between the actual voltage and the actual current and the electrical rotor resistance is utilized. It can be previously determined, known, or ascertained which phase shift corresponds to which rotor resistance. This relationship is used to determine the electrical rotor resistance. Advantageously, it is therefore not necessary to record all parameters of the electric machine; instead, the voltage function is selectively applied, and the phase shift between the actual current and the actual voltage is determined. This results in a less complex method for determining the electrical rotor resistance. The target voltage can be used as an approximation for the actual voltage.In this case, any existing slight time delay between target voltage and actual voltage can be neglected due to the desired low frequency range.

[0009] The method can be further developed to determine or specify the rotor temperature for determining the rotor resistance. For example, the rotor resistance can be determined on a test bench, such as during an end-of-line (EOL) test. It is also possible to determine the electrical rotor resistance during operation of the electric machine, for example, to verify it or to track it over the machine's lifetime. For this purpose, the rotor temperature can be recorded, for example, during a specific operating state of the electric machine. Alternatively, the rotor temperature may already be known, for instance, if the ambient conditions on the test bench are constant.In particular, operating conditions in which the rotor temperature corresponds to the stator temperature can be used for determining the rotor resistance during the operation of the electric machine. For example, standstill conditions, especially those lasting for a defined period, can be used to ensure that the rotor and stator temperatures equalize. Determining or setting the rotor temperature further simplifies the determination of the rotor resistance.

[0010] As already described, the voltage function can be periodic, at least in sections. The voltage function defines the target voltage and thus also the actual voltage applied to the electrical machine, which is particularly variable over time. In one embodiment of the method, the voltage function can be generated periodically, particularly sinusoidally, at a fixed frequency in at least one time interval, or at different time intervals with different frequencies. In a simple embodiment, the voltage function can be sinusoidal. This means that the voltage function generates the target voltage, and thus also the actual voltage, as a sine function with a fixed frequency over time. Alternatively, the voltage function can be generated at different time intervals with different frequencies.For example, in a first time interval, the voltage function can be a sine function with a first frequency, and in a second time interval, a second sine function with a second frequency. Specific frequency ranges can be selected that result in a phase shift between the actual current and the actual voltage, which can then be appropriately evaluated.

[0011] In a further development of the method, it can be provided that a frequency-varying voltage function is generated whose frequency is changed, in particular increased, over time. Such a voltage function can also be referred to as a "sweep". The frequency-varying voltage function can be sinusoidal, with the frequency of the voltage function changing over time. In particular, different time intervals can be defined in which specific frequencies of the voltage function are set. For example, the frequency of the voltage function changes continuously over time or in steps. For example, a first time interval with a first frequency, a second time interval with a second frequency, and so on, can be defined. For example, the frequency can change from 5 Hz to 30 Hz or any other desired frequency.This allows the phase shift between the actual current and the actual voltage to be changed with changing frequency, in particular increasing it with increasing frequency.

[0012] As described in the introduction, the relationship between a specific phase shift and the electrical rotor resistance is fundamentally used to determine the latter. In one embodiment of the method, various rotor resistance values ​​for specific phase shifts can be stored in a data memory, from which a specific rotor resistance for a given phase shift is read. For example, the relationship between the phase shift and the rotor resistance may have been previously measured, calculated, or otherwise determined. This relationship can be stored in a data memory, such as a lookup table. Once the phase shift is determined, the corresponding electrical rotor resistance can be ascertained by reading the data memory.

[0013] The method can further involve feeding a specific phase shift into a neural network, which then determines the rotor resistance based on this phase shift. Specifically, the neural network is previously trained to determine the electrical rotor resistance based on the phase shift. For example, known training data can be fed into the neural network. This training data includes, in particular, known patterns of electrical machines, their electrical parameters, and rotor resistances. From this, the neural network can be trained on the relationship between the electrical machine parameters and the rotor resistance. Specifically, the neural network can be trained to determine the corresponding rotor resistance based on the provided phase shift, which is generated by stimulating the actual current with the voltage function.In other words, it is exploited that the training data can be used to train the neural network to determine the corresponding rotor resistance based on the relationship between rotor resistance and phase shift at a given phase shift.

[0014] Specifically, a phase shift function can be determined for different frequencies, and the rotor resistance can be calculated based on this function. Using a phase shift function, i.e., a phase shift for different frequencies, allows for the coverage of various frequency ranges. This makes it possible, for example, to identify a specific frequency range that is particularly suitable for determining the rotor resistance. Furthermore, it allows for the identification of error influences that affect the phase shift to varying degrees across different frequency ranges, and these can be eliminated when determining the rotor resistance.

[0015] In particular, when using a neural network to determine rotor resistance based on phase shift, different datasets can be considered using training data. Specifically, deviations in electrical parameters are used as training data, thus determining their influence on the resulting phase shifts. This means that such influences can be taken into account or detected when using the neural network, enabling a more robust determination of rotor resistance.

[0016] To simplify the determination of rotor resistance, several approximations can be introduced, further simplifying the calculation. For example, it may be possible to set the rotor temperature equal to the stator temperature for determining the rotor resistance, and / or to set the rotor inductance and / or stator inductance, or the stator inductance and leakage inductances, to be constant. Particularly when carrying out the method in an operating state of an electrical machine, especially in a state of electrical machine installation in a motor vehicle, specific operating situations can be selected in which such approximations apply. Alternatively, deviations of individual electrical machine models or individual machines from a large number of identical electrical machines can be neglected to simplify the determination.As described, the actual voltage can also be used as an approximation of the target voltage. In this case, any slight time delay between the target voltage and the actual voltage due to the desired low frequency range can be neglected.

[0017] In addition to the method, the invention relates to a measuring device for determining the electrical rotor resistance of a rotor of an electric machine, in particular an asynchronous machine of a motor vehicle, wherein the electric machine is configured to set an actual current, in particular a dielectric current, based on a setpoint voltage, in particular a dielectric current, and wherein the measuring device is configured to generate a voltage function, in particular a periodic voltage, when the electric machine is at standstill, and to determine a phase shift between the actual current and the actual voltage, and to determine the electrical rotor resistance based on the phase shift. The measuring device is fundamentally configured to carry out the aforementioned method in all its details.Specifically, the determining device can be understood as a test bench on which the electrical rotor resistance of the rotor of the electric machine is determined. The term "electric machine" also includes, in particular, suitable power electronics or control equipment by which the target voltage in the electric machine can be controlled or regulated. Likewise, a determining device can also be understood as a component or module of a motor vehicle, an electric drive system, or the electric machine itself.

[0018] The invention further relates to an electric machine comprising a previously described determining device. The invention also relates to a motor vehicle comprising such an electric machine and / or a described determining device. All advantages, details, and features described with respect to the method are fully transferable to the determining device, the electric machine, and the motor vehicle.

[0019] The invention is explained below with reference to exemplary embodiments and the figures. The figures are schematic representations and show: Fig. 1. A schematic block diagram of a method for determining the electrical rotor resistance of an electrical machine; and Fig. 2 a schematic diagram of various phase shift functions between target current and target voltage over time.

[0020] Fig. Figure 1 schematically shows a method for determining the electrical rotor resistance of a rotor of an electric machine, specifically an asynchronous machine. The electric machine is, for example, a drive unit 1 of a motor vehicle (not shown in detail). In this method, as indicated by arrow 2, a target current, specifically a target D-current, is specified or transferred to a block 3, which can be considered a controller. The controller can, for example, regulate the operation of a control unit or power electronics unit, which is shown as block 4. The control unit or power electronics unit controls the operation of the electric machine, which is shown as block 5.

[0021] Thus, as indicated by arrow 2, the set current is supplied to the controller, i.e., block 3. Based on this, the controller generates a set voltage, specifically a set D-voltage, which is supplied to block 4 and thus to the power electronics. The power electronics set an actual D-voltage for the operation of the electric machine, resulting in an actual D-current in the electric machine, as shown by arrow 6.

[0022] The method is based on determining a phase difference or phase shift between the actual current and the actual voltage. For this purpose, a voltage function is generated as the target voltage or actual voltage, which, for example, is piecewise periodic. Specifically, a so-called sweep function is generated as the voltage function, which is piecewise sinusoidal, with the frequency of the voltage function changing over time. Specifically, the frequency of the voltage function is increased over time. This results in, as exemplified in Fig. 2 for different electrical machines, phase shift functions 7-10 result.

[0023] In general, the present method determines the rotor resistance of an electric machine from the phase shift between the actual current and the actual voltage, in particular between the actual voltage and the actual current. The determination of the rotor resistance is based on the relationship between the phase shift and the rotor resistance. This relationship is determined beforehand, for example, experimentally or by calculation. Subsequently, for the specific electric machine under test, the rotor resistance corresponding to the determined phase shift is read from a data storage device or determined using a neural network.

[0024] Such a neural network can be trained, for example, using known machine data. For training, the neural network can be fed known measurement results from electrical machines, allowing it to learn the relationship between a specific phase shift and rotor resistance. Once the neural network is trained, it can determine the rotor resistance of an unknown electrical machine, given the specific phase shift.

[0025] To determine the rotor resistance, the rotor temperature can be determined or specified. For example, the rotor temperature can be determined using a measuring device, specifically a test bench. There, the rotor temperature can be predetermined, for instance, based on the ambient temperature. Alternatively, the rotor temperature can be determined, for example, by appropriate temperature measurement. If the method is carried out during the operation of an electric machine, such as in the driving operation of a motor vehicle, suitable operating conditions can be used. Specifically, driving conditions can be used in which the stator temperature is equal to the rotor temperature or is a close approximation.

[0026] The method allows for further approximations, particularly in addition to matching rotor and stator temperatures. For example, it can be assumed that the rotor inductance and / or the stator inductance, or the stator inductance and leakage inductances, remain constant during the process. Similarly, it can be assumed that different electrical machines do not differ from one another in the aforementioned parameters, for example, when determining the rotor resistances of various electrical machines in production. The target voltage can be used as an approximation for the actual voltage. In this case, any slight time lag between the target voltage and the actual voltage due to the desired low frequency range can be neglected.

[0027] In Fig.Figure 2 further illustrates that different phase shift functions 7-10 can be obtained for different fault conditions. For example, phase shift function 8 shows a phase shift over time when no fault influence is present. Phase shift function 8 shows an example deviation from phase shift function 7 when a fault is present in a rotor resistance. Phase shift function 9 shows an example deviation from phase shift function 7 with an assumed fault in a stator resistance. Finally, phase shift function 10 shows faults in both the stator resistance and the rotor resistance. The described "faults" can generally be defined or understood as deviations from a reference resistance.

[0028] With sufficient training of the neural network, the neural network can determine such error influences and eliminate them in the determination of the rotor resistance.

[0029] The advantages, details and features described in the individual versions can be combined, interchanged and transferred to one another as desired. Reference sign 1 Drive arrangement 2 Arrow 3-5 Block 6 Arrow 7-10 Phase shift function

Claims

[1] Method for determining an electrical rotor resistance of a rotor of an electric machine, in particular an asynchronous machine of a motor vehicle, wherein, based on a target voltage, in particular a D voltage, an actual current, in particular a D current, is set in the electric machine, characterized by , that in a standstill state of the electrical machine a voltage function, in particular at least sectionally periodic, is generated and a phase shift between the actual current and an actual voltage is determined and the electrical rotor resistance is determined based on the phase shift. [2] Method according to claim 1, characterized by , that the rotor temperature is determined or specified for determining the rotor resistance. [3] Method according to claim 1 or 2, characterized bythat the voltage function is generated periodically, in particular sinusoidally, with a fixed frequency in at least one time interval or with different frequencies in different time intervals. [4] Method according to any of the preceding claims, characterized by , that a frequency-varying voltage function is generated, the frequency of which is changed over time, in particular increased. [5] Method according to any of the preceding claims, characterized by , that different values ​​of the rotor resistance for specific phase shifts are stored in a data memory, whereby a specific rotor resistance for the specific phase shift is read from the data memory. [6] Method according to any of the preceding claims, characterized by , that the specified phase shift is fed to a neural network, whereby the neural network determines the rotor resistance based on the phase shift. [7] Method according to any of the preceding claims, characterized by , that a phase shift function (7-10) is determined for different frequencies and the rotor resistance is determined based on the phase shift function (7-10). [8] Method according to any of the preceding claims, characterized by , that for determining the rotor resistance a rotor temperature is set equal to a stator temperature and / or a rotor inductance and / or a stator inductance and / or leakage inductances are set constant. [9] Determining device for determining an electrical rotor resistance of a rotor of an electric machine, in particular an asynchronous machine of a motor vehicle, wherein the electric machine is configured to set an actual current, in particular a D-current, in the electric machine based on a set voltage, in particular a D-voltage, characterized by, that the determining device is designed to generate a voltage function, in particular at least sectionally periodic, in a standstill state of the electrical machine and to determine a phase shift between the actual current and an actual voltage and to determine the electrical rotor resistance based on the phase shift. [10] Electric machine comprising a determining device according to the preceding claim. [11] Motor vehicle comprising a determining device according to claim 9 and / or an electric machine according to the preceding claim.

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