Method, computing unit and computer program for determining the temperature of at least one electrical conductor, and electrical drive system

Abstract

The invention relates to a method for determining the temperature of at least one electrical conductor (120) between a power converter (110) and an electrical machine (130) in an electrical drive system (100), wherein the electrical machine (130) has a liquid cooling system (170) which is also designed to cool the at least one electrical conductor (120). The method (200) has the steps of: energizing the electrical machine (130) using the power converter (110), operating the liquid cooling system (170), measuring, by means of a temperature sensor (150), the temperature of a coolant used in the liquid cooling system, and determining the temperature of the at least one electrical conductor on the basis of the measured temperature of the coolant. The invention also relates to a computing unit (160), to a computer program for carrying out such a method, and to an electrical drive system (100).

Description

[0001] Description

[0002] title

[0003] Method, computing unit and computer program for determining a temperature of at least one electrical conductor and electrical drive system

[0004] The present invention relates to a method for determining a temperature of at least one electrical conductor between a power converter and an electrical machine, a computing unit and a computer program for carrying out the method and an electrical drive system.

[0005] Background of the invention

[0006] In an electric drive system, e.g. in electric vehicles, an electric machine is supplied with electrical energy from a battery by a power converter, or electrical energy generated by the electric machine (e.g. recuperation) is stored in the battery by the power converter.

[0007] To protect power electronics, it is typically necessary to monitor components that can become very hot due to high currents. In modern DC-AC converter electronics for electric drives, busbars (so-called "AC rails" or "busbars", e.g., copper rails) can be used to conduct the current from the power converter's output stage to the electric machine (e.g., three-phase machine). Copper itself has a high maximum limit temperature, but the surrounding components (such as seals, PCBs, or current sensor chips) have a lower limit temperature of, for example, approximately 160°C. Taking manufacturing, aging, and software model tolerances into account, a maximum permissible temperature, the so-called derating temperature threshold, can be calculated, above which the torque of the electric machine must be reduced to prevent the temperature from exceeding the critical temperature.

[0008] For sensorless thermal busbar models (i.e., without a dedicated temperature sensor on the busbar), the converter coolant temperature can be used as a temperature reference.

[0009] Disclosure of the invention

[0010] According to the invention, a method for determining the temperature of at least one electrical conductor between a power converter and an electrical machine, a computing unit and a computer program for implementing the method, and an electric drive system having the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0011] The invention makes use of the measure of detecting a temperature of a coolant, which is used directly for cooling the at least one electrical conductor and for cooling the electrical machine, in particular within the electrical machine, by means of sensors and of determining the temperature of the at least one electrical conductor therefrom.

[0012] Compared to solutions that use the converter's coolant temperature as a temperature reference, this offers the advantage of allowing a more precise estimation of the temperature of the electrical conductor in liquid-cooled electrical machines. This is because the cooling circuit of the electrical machine is typically fluidically separated from the cooling circuit of the converter, so the effects of liquid cooling of the electrical machine (and the electrical conductor whose temperature is to be determined) cannot be accurately captured based on the temperature of the cooling medium cooling the converter.

[0013] In detail, the invention proposes a method for determining a temperature of at least one electrical conductor between a power converter and an electrical machine in an electrical drive system, e.g. of an at least partially electrically driven vehicle, wherein the electrical machine has a liquid cooling system which is also used to cool the at least one electrical conductor, wherein the method comprises energizing the electrical machine using the power converter, operating the liquid cooling system, measuring, by means of a temperature sensor, a temperature of a coolant used in the liquid cooling system and determining the temperature of the at least one electrical conductor on the basis of the measured temperature of the coolant.

[0014] In at least one embodiment, the temperature sensor is arranged inside and / or downstream of the electrical machine and / or downstream of the at least one electrical conductor. Typically, such a sensor is already present, so no additional components are required for the invention. This reduces the costs required for implementation.

[0015] In at least one embodiment, the coolant comprises a thermal oil. Thermal oils are particularly suitable for cooling electrical machines, particularly due to their electrically insulating properties and high temperature stability.

[0016] In at least one embodiment, the method comprises cooling the power converter using a cooling system separate from the liquid cooling system, which in particular uses a cooling medium different from the coolant used in the liquid cooling system. Typically, power converters can be cooled with water-based or air-based cooling or directly using a refrigerant circuit, which has the advantage of a larger coverable temperature range and also enables heating, which can be particularly advantageous during a start-up operating phase.

[0017] In at least one embodiment, the method comprises controlling the electrical machine and / or the power converter as a function of the determined temperature of the at least one electrical conductor. The method can further comprise, in particular, limiting the electrical power delivered by the power converter to the electrical machine if the determined temperature of the at least one electrical conductor exceeds a predeterminable threshold. This allows component protection to be achieved, since, for example, if the threshold is exceeded, the electrical power is reduced, thus preventing further heating of the electrical conductor.

[0018] A computing unit according to the invention, e.g. a control unit of an (electrically driven) motor vehicle, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0019] An electric drive system according to the invention comprises a power converter, an electric machine, at least one electrical conductor between the power converter and the electric machine, a liquid cooling system for cooling the at least one electrical conductor and the electric machine (130), a temperature sensor for measuring a temperature of a coolant used in the liquid cooling system, and a computing unit according to the invention.

[0020] The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, since this entails particularly low costs, in particular if an executing control unit is also used for other tasks and is therefore already present. Finally, a machine-readable storage medium is provided with a computer program stored thereon, as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical, and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible. Such a download can be wired or cable-based or wireless (e.g., via a WLAN network, a 3G, 4G, 5G, or 6G connection, etc.).

[0021] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings. The invention is schematically illustrated in the drawings using an exemplary embodiment and will be described below with reference to the drawings.

[0022] Short description of the drawings

[0023] Figure 1 shows an embodiment of an electric drive system with an electric machine, as can be used in embodiments of the invention, using a schematic block diagram.

[0024] Figure 2 shows schematically an embodiment of the invention using a simplified functional flow diagram.

[0025] Embodiment(s) of the invention

[0026] In Figure 1, an embodiment of an electric drive system with an electric machine, as can be used in embodiments of the invention, is shown schematically using a block diagram and is designated overall by 100.

[0027] The drive system 100 comprises a power converter 110 (also known in technical terms as an inverter or traction inverter), as well as at least one electrical conductor 120 (here in the form of three busbars for three phase windings of an electrical machine 130), which is / are connected between the power converter 110 and phase connections of the electrical machine, designated here by 130. The electrical conductors 120, for example busbars made of copper or another electrically conductive material, are monitored by one or more further (in particular semiconductor) components, e.g. current sensors 180, and are arranged in a housing 140 that is arranged between the power converter 110 and an end plate 132 of the electrical machine 130 and is attached in a fluid-tight manner at least to the end plate 132.On the side of the power converter 110, the housing 140 can also be attached to the power converter 110 in a fluid-tight manner or can have fluid-tight feedthroughs for the electrical conductors 120.

[0028] The housing 140 is configured to allow a liquid coolant, e.g., a thermal oil, to flow through it. For example, an inlet connection 142 for introducing the coolant can be provided for this purpose. In the example shown, openings 134 are provided in the end plate 132 of the electrical machine 130, through which, on the one hand, the electrical conductors 120 or the phase connections of the electrical machine 130 are routed, and, on the other hand, the coolant can flow from the housing into the electrical machine 130, in particular into its stator winding.

[0029] A temperature sensor 150 is provided in the electric machine 130, which detects the temperature of the coolant flowing through the stator and transmits it to a computing unit 160. In the example shown, the coolant is circulated by a coolant pump 170. A heat exchanger can also be provided in the coolant circuit to better dissipate heat. However, such a heat exchanger is not shown in the figure for reasons of clarity.

[0030] The computing unit 160 is connected in a data-conducting manner to the temperature sensor 150, the current sensor 180, the coolant pump 170 and the power converter 110.

[0031] Figure 2 schematically shows an embodiment of the invention using a simplified flowchart and is designated overall by 200. For example, the flowchart can be understood as a visualization of an embodiment of a method 200 according to the invention.

[0032] The method 200 uses a temperature model 280, by means of which a temperature 260 of the at least one electrical conductor 120 and / or a temperature 270 of one or more further components, e.g. of the current sensor(s) 180 on the electrical conductors 120, can be determined. In the example shown here, the input variables of the temperature model 280 are a direct current 211 supplied to the power converter, an alternating current 212 provided by the power converter (e.g. total current of all phases or average current per phase), a (e.g. empirically determined thermal offset 213, which typically occurs, for example, between the electrical conductor and the coolant), and a coolant temperature 214, which can be provided in particular by the temperature sensor 150.

[0033] These input variables form the input vector 210 for the state-space model 280. The state-space model 280 comprises an input matrix 220, an integrator 230, a system matrix 240, and an output matrix 250.

[0034] Matrices 220, 230, 240, and 250 can be determined, for example, through thermal characterization measurements followed by parameter identification. It is advantageous for the test bench setup to best match the target system.

[0035] The temperatures 260, 270 of the at least one electrical conductor 120 or of the one or more further components 180 are determined from the output matrix 250.

[0036] In particular, the method 200 can be carried out essentially by the computing unit 160.

[0037] Based on the determined temperatures 260, 270, the computing unit 160 can control the power converter 110 and / or the coolant pump 170 such that a predeterminable temperature threshold for the temperature 260 of the at least one electrical conductor 120 or for the temperature 270 of the one or more additional components is not exceeded. For this purpose, in particular, the electrical power provided by the power converter 110 can be limited (e.g., by limiting a maximum available current) and / or a delivery rate of the coolant pump 170 can be adjusted (e.g., by adjusting the speed accordingly) according to the determined temperatures 260, 270.As already mentioned at the beginning, the accuracy of the temperature model 280 is significantly improved by using the coolant temperature 214, which refers to the coolant flowing directly around the electrical conductors, compared to conventional solutions that instead use an inverter temperature as an input variable. Thus, the drive system 100, in particular the current sensor(s) 180, can be effectively protected from overheating without unnecessarily severely or prematurely limiting the performance of the drive system 100.

Claims

Claims 1 . Method (200) for determining a temperature (260) of at least one electrical conductor (120) between a power converter (110) and an electrical machine (130) in an electrical drive system (100), wherein the electrical machine (130) has a liquid cooling system (170) which is also configured to cool the at least one electrical conductor (120), the method (200) comprising: Energizing the electrical machine (130) using the power converter (110), Operating the liquid cooling system (170), Measuring (214), by means of a temperature sensor (150), a temperature of a coolant used in the liquid cooling and Determining (250, 280) the temperature (260) of the at least one electrical conductor based on the measured temperature (214) of the coolant.

2. The method (200) according to claim 1, wherein the temperature sensor (150) is arranged inside and / or downstream of the electrical machine (130) and / or downstream of the at least one electrical conductor (120).

3. The method (200) of claim 1 or 2, wherein the coolant comprises a thermal oil.

4. Method (200) according to one of the preceding claims, comprising cooling the power converter (110) using a cooling system separate from the liquid cooling system (170), which in particular uses a cooling medium different from the coolant used in the liquid cooling system.

5. Method (200) according to one of the preceding claims, comprising controlling the electrical machine (130) and / or the power converter (110) in Dependence on the determined temperature (260) of the at least one electrical conductor (120).

6. The method (200) according to claim 5, comprising limiting an electrical power delivered by the power converter (110) to the electrical machine (130) when the determined temperature (260) of the at least one electrical conductor (120) exceeds a predeterminable threshold value.

7. A computing unit (160) configured to carry out all method steps of a method (200) according to any one of the preceding claims.

8. An electric drive system (100), comprising: a power converter (110), an electric machine (130), at least one electrical conductor (120) between the power converter (110) and the electric machine (130), a liquid cooling system (170) for cooling the at least one electrical conductor (120) and the electric machine (130), a temperature sensor (150) for measuring a temperature of a coolant used in the liquid cooling system, and a computing unit (160) according to claim 7.

9. A computer program which causes a computing unit to carry out all method steps of a method according to one of claims 1 to 6 when executed on the computing unit.

10. A machine-readable storage medium having a computer program according to claim 9 stored thereon.

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