METHOD AND DEVICE FOR NON-CONTACT SENSING OF THE TEMPERATURE OF A ROTARY PART OF AN ELECTRIC MACHINE

Description

[0001] The invention relates to a method and a device for non-contact detection of the temperature of a rotating part of an electric machine.

[0002] In electrical machines, there is often a desire to determine the temperature of a rotor or other rotating parts precisely during operation, i.e., to within a few degrees Celsius (1-5 °C). Accurate temperature knowledge is important for monitoring purposes, among other things. It is known from the theory of electrical machines that the rotor temperature can exceed the maximum upper temperature limit at certain operating points. If the temperature is not monitored or not determined precisely, damage to the electrical machine can occur.

[0003] Document DE 10 2011 108 382 A1 describes an electrical machine comprising a rotor and a stator, wherein at least one element is arranged on the rotor and thermally connected to it, the absorptivity of which changes as a function of temperature for incident photons from a light source, and wherein a measurement signal is determined which depends on the instantaneous absorptivity of the element and represents a measure of the element or rotor temperature.

[0004] DE 69 905 907 T2 describes a thermal insulation layer with an embedded thermoluminescent indicator material. It is intended that a heat-resistant coating comprising an indicator material is applied to a machine component, in particular to a blade of a gas turbine. Due to the integration of the indicator material into the coating, it exhibits increased resistance to erosion or thermal shock.

[0005] The object of the invention is to provide a measure by which the temperature and rotational position of a rotating part of an electric machine can be precisely determined with moderate effort.

[0006] The present invention is solved by a method having the features of claim 1. The problem is further solved by a device having the features of claim 7. Preferred embodiments of the invention are described in the dependent claims, the description and the figures, wherein further features described or shown in the dependent claims and / or in the description and / or the figures, individually or in any combination, may constitute an object of the invention unless the context clearly indicates otherwise.

[0007] The present invention relates to a method for non-contact temperature detection of a rotating part of an electric machine mounted to rotate with respect to an axis of rotation by means of a marking with fluorescent marking structures, which are arranged in at least one ring-shaped arrangement around the axis of rotation distributed on the rotating part and thermally connected to it, wherein the at least one arrangement of the fluorescent marking structures forms a coding in the manner of a barcode, a light source for exciting the fluorescent marking structures and at least one light sensor for detecting fluorescent light emitted as a result of the excitation of the fluorescent marking structures, wherein a quantity correlating with a temperature-dependent decay time constant τ of the material of the fluorescent marking structures is determined and the temperature of the rotating part is determined via this.

[0008] The core of the invention is that the temperature of the rotating part can be detected over a wide rotational speed range – almost to standstill – by utilizing the physical effect that the decay time constant of a fluorescent body is temperature-dependent. A further feature of the invention is that the temperature can be detected without contact, thus enabling the thermal detection of very hot objects with temperatures up to 1000 °C.

[0009] The rotating part is a rotating component of the electric machine. Typically, the electric machine has a rotor and a stator, with the rotating part being specifically the rotor.

[0010] By using a suitable device for non-contact temperature measurement of a rotating part of an electric machine, the temperature can be determined with very high steady-state accuracy. The accuracy is on the order of approximately 1-5 degrees Celsius.

[0011] This results in the following advantages for the application of electrical machines, and especially for the permanent magnet synchronous machine (PSM): A) Reduction of overall costs: The temperature class of magnets used in the electric machine can be lowered because the precise (sufficient) determination of the rotor temperature eliminates the need for a safety margin. This assumption is valid if an electrical power output in the range of 150-250 kW can be assumed for electric machines. B) Power compensation: The power drop in the PSM (Power Shift Mechanism) can be compensated for in the field-weakened range by increasing the current. The power drop results from the torque reduction, which in turn results from the rotor tipping. The rotor tipping, in turn, results from the heating of the magnets in the rotor. The rotor tipping, and thus the torque and power reduction, increases with increasing rotational speed if it is not compensated.Current compensation is achieved, for example, by field-oriented control of the permanent magnet synchronous machine through increasing the stator current via the power electronics. C) Component protection: Precise knowledge of the rotor temperature allows for the development and implementation of improved monitoring and derating strategies in the functional software. With prior art methods for rotor temperature measurement, derating is initiated too early due to insufficient or no accurate knowledge of the rotor temperature. D) Improvement of the functional safety concept: Torque monitoring for torque errors can be improved by precise knowledge of the rotor temperature. This improvement results in a narrower tolerance band (comparison between target and actual torque). The narrower tolerance band leads to shorter detection and shutdown times.E) Reduction of overall software application time: Prior art methods for determining rotor temperature using a rotor temperature model (estimation model) require numerous vehicle measurements and tests in hot and cold environments. By accurately determining the rotor temperature using the method presented here, the software application effort is significantly reduced. The result: time and cost savings.

[0012] In the method, it is preferably provided that the fluorescent marking structures are guided past the light source and then past the light sensor or past the light sensors one after the other by rotating the rotating part.

[0013] Another feature is that, through a clever arrangement and number of light sensors, the temperature accuracy is increased, and the rotational speed and direction of rotation can also be detected.

[0014] According to the invention, the arrangement of the fluorescent marking structures forms a coding system similar to a barcode. In this way, it is also possible to determine the rotational position of the rotating part.

[0015] According to a further preferred embodiment of the invention, the marking comprises two parallel arrangements with different fluorescent marking structures, which are jointly excited by means of the light source.

[0016] According to a further preferred embodiment of the invention, the rotational position and / or rotational speed and / or direction of rotation of the rotating part is additionally determined from the signal of the detected fluorescence light.

[0017] Furthermore, it is advantageously provided that the fluorescent marking structures have ruby ​​as the fluorescent material, in particular in the form of a ruby ​​powder coating.

[0018] According to a further preferred embodiment of the invention, the light source is designed as a light-emitting diode or laser diode (LED) and / or the at least one light sensor is designed as a photoreceiver, in particular a photodiode (PD).

[0019] According to a further preferred embodiment of the invention, the quantity correlating with the temperature-dependent decay time constant τ of the material of the fluorescent marking structures is determined in advance by a reference measurement using the marking, the light source and the at least one light sensor.

[0020] The present invention further relates to a device for non-contact temperature detection of a rotating part of an electric machine which is mounted to rotate about an axis of rotation, with a marking with fluorescent marking structures which are arranged in at least one ring-shaped arrangement around the axis of rotation distributed on the rotating part and are thermally connected to it, wherein the at least one arrangement of the fluorescent marking structures forms a coding in the form of a barcode, a light source for exciting the fluorescent labeling structures, at least one light sensor for detecting fluorescent light emitted as a result of the exciting fluorescent labeling structures, and an evaluation unit that is set up to determine from the detected fluorescence light a quantity that correlates with a temperature-dependent decay time constant τ of the material of the fluorescent marking structures and to determine the temperature of the rotating part via this quantity.

[0021] The advantageous embodiments mentioned in connection with the aforementioned method for non-contact temperature detection of a rotating part rotating with respect to a rotational axis also apply analogously to the device described above. This device is specifically designed to carry out the aforementioned method.

[0022] According to a preferred embodiment of the device according to the invention, a fixed spatial arrangement of the light source, the at least one light sensor and the axis of rotation is provided, in which the fluorescent marking structures of the at least one arrangement can be moved past the light source and then past the light sensor or past the light sensors one after the other by rotating the rotating part.

[0023] According to a further preferred embodiment of the device according to the invention, the evaluation unit is set up to determine in advance the quantity correlating with the decay time constant τ of the material of the fluorescent marking structures by means of a reference measurement using the marking, the light source and the at least one light sensor.

[0024] According to the invention, the at least one arrangement of the fluorescent marking structures is a coding that forms a kind of barcode.

[0025] According to a further preferred embodiment of the device according to the invention, the rotating part is a rotor or at least a rotor component of the electric machine. The electric machine itself is in particular a permanent magnet synchronous machine (PSM).

[0026] The invention also relates to an electric machine with a rotating part mounted to rotate about an axis of rotation and a device described above for non-contact temperature detection of the rotating part. The rotating part is, in particular, a rotor of the electric machine. The electric machine itself is, in particular, a permanent magnet synchronous machine (PMS).

[0027] The invention is illustrated below with reference to preferred embodiments in the drawings and described in more detail below. Fig. 1 a device for temperature detection of a rotating part of an electric machine according to a first embodiment of the invention, Fig. 2 Graphs of the corresponding optical signals related to a single fluorescent labeling structure, Fig. 3 Graphs of relevant quantities in determining a quantity correlating with the temperature-dependent decay time constant τ of the material of the fluorescent element and Fig. 4 a device for temperature detection according to a second embodiment of the invention.

[0028] The Fig. 1 Figure 1 shows a rotating part 10 of an electric machine, which is mounted to rotate with respect to a rotational axis 12, and a device 14 for non-contact detection of the temperature T of the rotating part 10. The rotating part 10 is in particular a rotor 16 of the electric machine.

[0029] The device 14 for non-contact temperature detection of the rotating part 10 comprises a marker 18 with fluorescent marker structures, which are arranged in at least one ring-shaped arrangement 20 around the axis of rotation 12 distributed on the rotating part 10 and thermally connected to it, a light source 22 for exciting the fluorescent marker structures, at least one light sensor 24 for detecting fluorescent light emitted as a result of the excitation of the fluorescent marker structures, and an evaluation unit 26, which is configured to determine from the detected fluorescent light a quantity that correlates with a temperature-dependent decay time constant τ of the material of the fluorescent marker structures and to determine the temperature of the rotating part 10 via this quantity.

[0030] The link between the quantity correlating with a temperature-dependent decay time constant τ of the material of the fluorescent marking structures and the temperature is stored, for example, in a (not shown) database of the evaluation unit 26.

[0031] The spatial arrangement of the light source 22, the light sensors 24, and the rotation axis 12 of the rotating part 10 within the electric machine is defined such that the fluorescent structures are guided past the light source 22 and subsequently past the light sensors 24 by rotating the rotating part 12 (arrow 28). For this purpose, the light source 22 and the light sensors 24 are arranged / attached to a machine-fixed part of the electric machine, such as a housing or a stator corresponding to the rotor 16 (not explicitly shown).

[0032] In this example, the light source 22 is designed as a light-emitting diode or laser diode (LED), and the light sensors 24 are designed as photoreceptors, more precisely photodiodes (PD). The fluorescent structures feature ruby ​​as the fluorescent material, particularly in the form of a powder coating.

[0033] The Fig. 2 The graphs of the corresponding optical signals are shown, each representing a signal intensity, here expressed as power P per unit area, over time t. The upper graph shows the constant signal from the light source 22. The middle graph shows the fluorescence signal of one of the fluorescent structures, and the three lower graphs show the discrete signals from the light sensors 24. These discrete signals are triggered by the respective position of the fluorescent structure relative to the light source 22 and the light sensors 24.

[0034] The Fig. 3 shows two graphs of relevant quantities in determining the quantity correlating with the temperature-dependent decay time constant τ of the material of the fluorescent element and the temperature.

[0035] The intensity of the fluorescent light detected by the light sensors 24 and the time difference between the signals detected by the different sensors 24 are used to determine the quantity corresponding to the decay time constant τ of the material of the fluorescent element (left graph), and the temperature of the fluorescent structure and the thermally connected rotating part 10 is determined via this quantity and the temperature dependence of the decay time constant τ.

[0036] In the present case of the Fig. 3 This applies, for example, to the first and a third light sensor 24: τ = − Δ t ln P 1 P 3

[0037] In the specific example shown, therefore: τ = 6 ms / ln 0,58 / 0,115 = 3,7 ms

[0038] With the graph in the second graph of Fig. 3 Given the relationship, a temperature of 7°C results.

[0039] The Fig. 4 Figure 1 shows an alternative embodiment of the device 14 for temperature detection. The light source 22 is pulsed and illuminates the entire marking 18. In this embodiment, the marking 18 has two parallel arrangements 20 of different fluorescent marking structures, each forming a barcode. More precisely, in this specific case, there are two parallel arrangements 20 of fluorescent marking structures that are identical in structure but oriented antiparallel to each other.

[0040] The light sensors 24 are implemented in the form of a CCD sensor 30 or a CCD line and are optically coupled to the fluorescent marking structures of the marking 18 at corresponding "readout positions" via light guide elements 32.

[0041] At standstill and with each rotation, the position is determined by reading the code position using the 24 light sensors. The rotational speed is calculated mathematically by deriving it from the position. The resolution is variable and depends on the barcode used – for example, a resolution of 9 bits (0.70°) can be achieved either with a 512 code or with interpolation.

[0042] The sum signal of the light sensors / photodetectors is used to measure the temperature, whereby the two ring-shaped arrangements 20 are always sampled by means of the CCD line 30.

[0043] In addition to the core of the invention, its advantages and "best-mode" will be described again in other words below: The core of the invention disclosure is that the temperature, rotational speed, direction of rotation, and even the position of a rotating part can be detected contactlessly by utilizing the physical effect that the decay time constant of a fluorescent body is temperature-dependent. Temperature measurement with this method / device is possible across the entire rotational speed range, i.e., even when the part is stationary.

[0044] By using the device 14 for non-contact temperature detection of a rotating part 10 of an electric machine, the temperature can be determined with very high steady-state accuracy. The order of magnitude here is approximately 1-5 degrees Celsius.

[0045] The measurement principle described here allows for the construction of a so-called combined sensor (smart sensor), capable of determining up to four physical quantities. This combined sensor is particularly advantageous for use in electric machines, and especially in permanent magnet synchronous machines (PSMs). The specific advantages include: reduced overall costs, increased performance, improved functional safety, and enhanced component protection. Reference symbol

[0046] 10 Rotating part 12 Rotation axis 14 Device 16 Rotor 18 Marking 20 Ring-shaped marking Structure arrangement 22 Light source 24 Light sensor 26 Evaluation unit 28 Arrow 30 CCD sensor 32 Light guide elements T Temperature of the rotating part τ Decay time constant

Claims

1. Method for non-contact sensing of the temperature of a rotating part (10) of an electric machine, which rotating part is mounted rotatably with respect to an axis (12) of rotation, by means of - a marking (18) with fluorescent marking structures which are arranged on the rotating part (10) in a manner distributed in at least one ring-shaped arrangement (20) around the axis (12) of rotation and are thermally connected to said rotating part, wherein the at least one arrangement (20) of the fluorescent marking structures forms a barcode-type coding, - a light source (22) for exciting the fluorescent marking structures and - at least one light sensor (24) for detecting fluorescent light emitted on account of the excitation of the fluorescent marking structures, from which a variable correlating with a temperature-dependent decay time constant τ of the material of the fluorescent marking structures is ascertained and the temperature of the rotating part (10) is determined by way of this variable.

2. Method according to Claim 1, characterized in that the fluorescent marking structures of the arrangement (20) are guided past the light source (22) and subsequently past the light sensor (24) or successively past the light sensors (24) by the rotation of the rotating part (10).

3. Method according to either of Claims 1 and 2, characterized in that the marking (18) has two parallel extending arrangements (20) of different fluorescent marking structures, which are excited jointly by means of the light source (18).

4. Method according to any of Claims 1 to 3, characterized in that furthermore a rotational position and / or rotational speed and / or rotational direction of the rotating part (10) are / is determined from the signal of the detected fluorescent light.

5. Method according to any of Claims 1 to 4, characterized in that the fluorescent marking structures comprise ruby, in particular in the form of a ruby powder coating, as fluorescent material.

6. Method according to any of Claims 1 to 5, characterized in that the variable correlating with the temperature-dependent decay time constant τ of the material of the fluorescent marking structures is ascertained beforehand by a reference measurement by means of the marking (18), the light source (22) and the at least one light sensor (24).

7. Device (14) for non-contact sensing of the temperature of a rotating part (10) of an electric machine, which rotating part is mounted rotatably with respect to an axis (12) of rotation, with - a marking (18) with fluorescent marking structures which are arranged on the rotating part (10) in a manner distributed in at least one ring-shaped arrangement (20) around the axis (12) of rotation and are thermally connected to said rotating part, wherein the at least one arrangement (20) of the fluorescent marking structures forms a barcode-type coding, - a light source (22) for exciting the fluorescent marking structures, - at least one light sensor (24) for detecting fluorescent light emitted on account of the excitation of the fluorescent marking structures, and an evaluation unit (26) configured to ascertain from the detected fluorescent light a variable correlating with a temperature-dependent decay time constant τ of the material of the fluorescent marking structures and to determine the temperature of the rotating part (10) by way of this variable.

8. Device according to Claim 7, characterized by a fixed spatial arrangement of the light source (22), the at least one light sensor (24) and the axis (12) of rotation in which the fluorescent marking structures of the arrangement (20) are guidable past the light source (22) and subsequently past the light sensor (24) or successively past the light sensors (24) by rotation of the rotating part (10).