Method, computing unit and computer program for determining a volumetric flow of a temperature-control fluid, temperature-control system, device for controlling a stator of an electric machine, and electric drive system

Abstract

The invention relates to a method for determining a volumetric flow of a temperature-control fluid (142) in a temperature-control system (140) which is designed to control the temperature of at least one power switch (110, 120, 130), wherein a first of the at least one power switches (110, 120, 130) is arranged upstream of at least one temperature sensor (122, 132) in relation to the temperature-control fluid (142), and wherein the method comprises determining a temporal temperature curve (144, 146) of the temperature-control fluid (142) by means of the at least one temperature sensor, changing a thermal power of the first power switch (110), and determining the volumetric flow of the temperature-control fluid (142) on the basis of a change in the temporal temperature curve (144, 146) that can be associated with the change in the thermal power.

Description

[0001] Description

[0002] title

[0003] Method, computing unit and computer program for determining a volume flow of a temperature control fluid, temperature control system, device for controlling a stator of an electrical machine and electrical drive system

[0004] The present invention relates to a method for determining a volume flow of a temperature control fluid, a computing unit and a computer program for carrying out the method, as well as a temperature control system, a device for controlling a stator of an electrical machine and an electrical drive system.

[0005] Background of the invention

[0006] In a fluid-controlled system, the temperature control efficiency depends, among other things, on the existing volume flow of the temperature control fluid and can, for example, be used as input information in temperature modeling for thermal self-protection. The volume flow is often required in automotive applications as ASIL-A information (automotive safety integrity level; safety classification within the framework of, for example, type approval procedures) and can, for example, be determined with the help of one or more sensors (cooling water inlet and / or cooling water outlet sensor) or checked for plausibility if it is made available from the outside as input information to the system to be temperature-controlled (e.g. inverter for an electrical machine). The volume flow can also, for example, be determined using a dedicated volume flow sensor.

[0007] Disclosure of the Invention: According to the invention, a method for determining a volume flow of a temperature control fluid, a computing unit and a computer program for implementing the method, as well as a temperature control system, a device for controlling a stator of an electric machine, and an electric drive system with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0008] The invention utilizes the measure of determining a temperature profile of a temperature control fluid using a sensor and, in the case of a temporal change in the thermal power of a component upstream of the sensor used for this purpose (i.e., the fluid flows from the component to the sensor), using the thermal response from the temperature profile to determine the volume flow of the temperature control fluid. Simply put: the shorter the time between the change in thermal power and the corresponding change in the temperature profile, the higher the volume flow.

[0009] The terms "upstream" and "downstream" are to be understood literally within the scope of this invention and accordingly mean that the temperature control fluid flows from a component arranged upstream of the sensor to the sensor arranged downstream of the component. In particular, there is no other component with significant thermal power between the component and the sensor arranged downstream of the component.

[0010] A temperature control system usable within the scope of the invention is configured to temperature control at least one circuit breaker, wherein a first of the at least one circuit breaker is arranged upstream of at least one temperature sensor with respect to the temperature control fluid. The circuit breaker can be designed as a transistor, in particular as a MOSFET, IGBT, or bipolar transistor (or can also contain a power diode). The method according to the invention specifically comprises determining a temporal temperature profile of the temperature control fluid by means of the at least one temperature sensor, changing a thermal power of the first circuit breaker, and determining the volume flow of the temperature control fluid based on a change in the temporal temperature profile that can be assigned to the change in the thermal power.As already explained, the volume flow of the temperature control fluid can be determined from the time between the change in thermal power and the arrival of the temperature signal resulting from this change in power. To do this, only the geometry of the line between the "sender" (i.e., the power switch whose thermal power is changed) and the "receiver" (here, the temperature sensor) of the temperature signal must be known, which is typically the case with temperature control systems, since the lines are usually permanently installed.

[0011] In at least one embodiment, the at least one temperature sensor is integrated into a second circuit breaker of the at least one circuit breaker. Circuit breakers, for example in inverters of (partially) electrically powered vehicles, are often equipped with temperature sensors anyway (e.g., for component protection), so this does not incur any additional costs. Furthermore, especially in multi-phase drive machines, several circuit breakers are typically arranged in a defined geometric arrangement relative to one another, which makes determining the volume flow easier and more reliable.

[0012] The at least one temperature sensor can be designed as a sensor for a temperature-dependent property of the second circuit breaker. For example, in semiconductor switches, an electrical resistance can be determined, and from this, the temperature of the switch can be determined, since the resistance depends on the temperature of the semiconductor. Likewise, it can be a temperature sensor for measuring a junction temperature of the circuit breaker.

[0013] In at least one embodiment, the thermal power is changed by changing the duty cycle and / or switching speed of the first circuit breaker. These are relatively easy-to-implement control-related measures for changing the thermal power (also referred to as power loss) of the circuit breaker. A change in the thermal power can consist of either an increase or a decrease in the thermal power.

[0014] In at least one embodiment, the method comprises determining the amount of change in thermal power. In such embodiments, this determined amount is taken into account when determining the volume flow. For example, it can be used to establish a correlation between a change in the temperature profile and the change in thermal power, or to verify the plausibility of the correlation.

[0015] For example, the power loss or its change can be determined from the thermal behavior of the first circuit breaker (e.g., using a temperature sensor of this first circuit breaker). A (periodically) variable power loss in the first circuit breaker leads to a (periodic) temperature fluctuation at the (first) temperature sensor, which is proportional to the amplitude of the power loss change (but is independent of, or very weakly dependent on, the volume flow—especially if the time constant of the periodicity is not chosen too long).

[0016] The change in thermal power can occur abruptly and / or periodically. Such a differential measurement principle can achieve greater robustness compared to stationary methods. This allows a usable result to be achieved to a certain extent even at transient operating points, especially with periodic changes in thermal power.

[0017] A computing unit according to the invention, e.g. a control unit of a motor vehicle, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0018] A device according to the invention for controlling a stator of an electrical machine comprises an inverter designed to be coupled to an electrical machine comprising the stator and a rotor and to provide an electrical voltage for controlling the stator of the electrical machine by means of at least one power switch. The device comprises a temperature control system according to the invention.

[0019] An electric drive system according to the invention comprises a device according to the invention for controlling a stator of an electric machine and an electric machine with the stator and a rotor, which is electrically connected to the inverter of the device for controlling the stator of the electric machine.

[0020] The invention can be advantageously applied to a permanent magnet synchronous machine (PSM) or electrically excited synchronous machine (ESM) as an electrical machine, but also to other types of machines that require commutation of the stator current, such as asynchronous machines (ASM), etc.

[0021] 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.).

[0022] 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.

[0023] Short description of the drawings

[0024] Figure 1 shows schematically a vehicle with a temperature control system as can be used in embodiments of the invention.

[0025] Figure 2 shows schematically an embodiment of a method according to the invention in the form of a simplified flow chart.

[0026] Figure 3 shows a schematic representation of a block diagram of an electric drive system according to an embodiment.

[0027] Embodiment(s) of the invention

[0028] Figure 1 shows a roughly schematic and partial view of a vehicle with a temperature control system, as can be used in embodiments of the invention. The vehicle is designated overall by 100. Furthermore, Figure 1 shows temperature distributions within the temperature control system, as can be observed during operation of the vehicle 100, in a diagram 180.

[0029] The vehicle 100 comprises an electric machine 150, here, for example, a three-phase electric machine, which is configured to drive wheels 160 of the vehicle. In the example shown, each of the three phases is energized by means of a half-bridge to provide the electrical drive energy. The half-bridges typically have two power switches connected in series, with three power switches 110, 120, 130 being shown. The power switches 110, 120, 130 are temperature-controlled by means of a temperature control system 140, in which a temperature control fluid is passed past the power switches 110, 120, 130 in order to dissipate heat from the power switches 110, 120, 130. In the example shown here, with respect to a flow direction of the tempering fluid 142, a first circuit breaker 110 is arranged upstream of a second circuit breaker 120, and this second circuit breaker 120 is in turn arranged upstream of a third circuit breaker 130.

[0030] In the example shown here, a respective temperature sensor 112, 122, 132 is integrated into each of the power switches 110, 120, 130. The temperature sensors are connected in a signal-conducting manner to a computing unit 170 of the vehicle 100, for example, a drive control unit. The computing unit 170 controls the power switches 110, 120, 130 according to a current power requirement in order to drive the vehicle 100. Furthermore, the computing unit 170 is configured to execute an embodiment of a method according to the invention, as shown, for example, in Figure 2.

[0031] Diagram 180 shows a temperature distribution for two different example scenarios. A temperature T is plotted over a distance s (which corresponds to the position within the temperature control system 140).

[0032] As can be seen from a first temperature distribution 144, the temperature (spatially viewed) continuously increases as the temperature control fluid 142 flows through the temperature control system 140. In the operating mode underlying this example, all three power switches are controlled such that their respective thermal outputs are equal to one another, resulting in a uniform temperature increase. The temperature increase is determined, among other things, by the volume flow of the temperature control fluid.

[0033] A second temperature distribution 146 results in an operating mode in which the first circuit breaker 110 is operated with a higher thermal power than the second 120 and third 130 circuit breakers. The temperature of the temperature control fluid 142 rises more sharply as it flows past the first circuit breaker 110 than in the downstream section of the temperature control system 140, resulting in a temperature difference 148 in the downstream section compared to the temperature distribution 144. This temperature difference is used within the scope of the embodiments of the invention to determine a volume flow of the temperature control fluid 142 through the temperature control system 140, as explained in more detail below with reference to Figure 2. References to device components are to be understood in particular as references to the vehicle 100 in Figure 1.However, it should be emphasized in this context that the invention can also be used with other temperature control systems and is not limited to the specific design of the vehicle 100 or its temperature control system 140.

[0034] In Figure 2, an embodiment of a method according to the invention is shown schematically using a simplified flow chart and is designated overall by 200.

[0035] In a step 210, a temporal temperature profile of a temperature control fluid is determined using a sensor arranged downstream of a circuit breaker. In particular, the sensor used here can be one or both of the sensors 122, 132, and the circuit breaker can be the first circuit breaker 110 (or possibly also the second circuit breaker 120).

[0036] In a step 220 of method 200, a thermal power of the first circuit breaker is changed, for example, increased. To achieve this, for example, a duty cycle of the respective first circuit breaker 110 can be changed, or a switching speed of the circuit breaker 110 can be adjusted accordingly. This can influence a power loss of the respective circuit breaker 110. A high percentage of electrical losses are typically released in the form of thermal energy, which leads to a corresponding heating of the temperature control fluid 142.

[0037] This takes advantage of the fact that it is possible to use the system even during regular operation (e.g.

[0038] Driving mode of a battery-electric vehicle 100) to vary the power loss generated in the power switches 110, 120, 130 in individual switches. This power loss variation can be generated, for example, in particular with the help of suitable switching strategies in pulse width modulation (PWM). Such switching strategies include, for example, the methodology of a variable flat top width or a single zero pointer (SZP) process. In this case, one of the two zero pointers can be omitted in only one phase of the B6 bridge by adjusting the switching times of the phases so that the shortest switch-on process is omitted. The SZP is, for example, only applied if it leads to an omission of switching processes in a specific phase (e.g. II). The power loss in this phase would then be reduced compared to the other phases due to the reduced switching processes.Alternatively, the SZP is not applied to a specific phase, but is applied to the others. Other switching strategies that result in unevenly distributed losses in the power switches 110, 120, 130 are equally suitable (e.g., different switching frequencies within an electrical period). The amount of the resulting power loss change (and / or the resulting heat input) can also be calculated and / or otherwise determined within the scope of step 220. For example, the power loss or its change can also be determined from the thermal behavior of the respective power switch 110, 120, 130 (e.g., using the respectively assigned sensor 112, 122, 132).

[0039] In the following, it is assumed that the power loss in the circuit breaker 110 (also referred to as the first circuit breaker 110) changes over time, e.g., deliberately through periodic changes. This (e.g., periodically) variable power loss in the first circuit breaker 110 leads to a (periodic) temperature fluctuation at the temperature sensor 112 that is proportional to the amplitude of the power loss change (but is independent of, or very weakly dependent on, the volume flow—especially if the time constant of the periodicity is not chosen to be too long). The temperature fluctuation measured by the sensors 122, 132 (in the second circuit breakers 120, 130), on the other hand, depends proportionally on the power loss fluctuation amplitude (in the first circuit breaker 110) and on the volume flow of the temperature control fluid 142.By using a quotient of the amplitude of the identified temperature fluctuation at the first circuit breaker 110 (with inherent power loss changes) and the amplitude at the downstream second circuit breaker 120, 130 (without power loss fluctuations), the power loss amplitude is canceled out. This makes it possible to isolate the influence of the volume flow on the measured temperature change.

[0040] In step 230, an expected temperature change downstream of the power switch 110 is determined based on the change in thermal power. This can be done, for example, using appropriate physical models. If the change in power loss is explicitly determined in step 220, as just described, the magnitude of the expected thermal response can be determined more precisely.

[0041] In a step 240, this expected temperature change is compared with an actual temperature change resulting from the temporal temperature profile 210 (this actual temperature change corresponds, for example, to the temperature change 148 shown in the diagram 180 in Figure 1).

[0042] If the expected temperature change and the actual temperature change agree with each other (or agree within permissible tolerances) (e.g., if a deviation between the two values ​​falls below a predeterminable threshold), the method 200 continues with a step 250.

[0043] In step 250, the volume flow of the temperature control fluid 142 in the temperature control system 140 is determined based on a change in the thermal power 220 and the determined correspondence between the expected and actual temperature changes (step 240). In particular, a geometry of the temperature control system 140 can be taken into account, e.g., the line cross-section, the distance between the first power switch and the respective temperature sensor 122, 132 used, etc.

[0044] The volume flow determined in this way can then be used to control the vehicle 100, in particular the temperature control system 140. After step 250, the method can return to step 210 in order to continue monitoring the volume flow or to carry it out essentially continuously. In particular, during continuous operation of the method 200, a periodic variation of the thermal power of the first power switch can be implemented in step 220. This has a particularly advantageous effect on the robustness of the method 200, in particular with respect to non-stationary operating conditions, since the periodicity makes it easy to identify the influence of this variation in the thermal power on the temperature profile, for example, in a Fourier analysis of the temperature profile with the variation frequency of the thermal power as the input parameter.

[0045] The periodicity of the change in thermal power should be selected to be slow enough so that the transfer behavior of the temperature of the temperature control fluid 142 can reach the temperature sensors 122, 132 of the downstream power switches 120, 130 with a certain effect. The resulting amplitude (and phase position) of the temperature oscillation of the known impression periodicity or frequency in the measuring temperature sensors 122, 132 can be evaluated, for example, using a suitable control filter (e.g., an adaptive feedforward cancellation AFC). Thus, the precise amplitude of the Fourier component at this frequency can be determined and analyzed. This analysis is very robust, for example, against noisy measurement signals.It is thus even possible to carry out the analysis of the volume flow in slightly changing operating points if the periodic change in the thermal power (step 220) is kept constant, because a temperature change due to the operating point shift is not modulated with the same periodicity and is filtered out due to the described frequency analysis.

[0046] It should be emphasized here that the described step-by-step procedure within the scope of method 200 serves merely as an example to explain some aspects of the invention, and the invention is by no means limited to the specifically described embodiment. For example, individual or all steps can be performed in a different, for example, reverse, order and / or partially or completely concurrently or in parallel and / or simultaneously with one another.

[0047] Figure 3 shows a schematic representation of a block diagram of an electric drive system 1 with a device 10 for controlling an electric machine 30. The electric drive system 1 comprises an electric machine 30 with a stator, which can be fed by a power converter 11 (so-called inverter), and a rotor. For this purpose, the power converter 11 can be fed, for example, by a DC voltage source such as a battery 20 or the like. The example of a three-phase electric machine 30 shown here serves only to improve understanding and does not represent a limitation of the present invention. Furthermore, any electric machines 30 with a number of electrical phases other than three are of course also possible. For example, it can also be a five- or six-phase electric machine 30 or an electric machine 30 with any other number of phases.

[0048] To control the stator of the electric machine 30, the power converter 11 can convert the DC voltage provided by the battery 20 into a suitable AC voltage. In the case of a three-phase electric machine 30, the power converter 11 can, for example, convert the DC voltage into a three-phase AC voltage. In particular, the amplitude of the AC voltage and / or the value of the output current from the power converter 11 to the stator windings (phases) of the electric machine 30 can be adjusted based on a predetermined setpoint 5.

[0049] For example, the power converter 11 can be a power converter with multiple half-bridges. In particular, the power converter 11 can have at least one half-bridge with two power switches for each phase of the electric machine 30. For example, the power converter 11 for a three-phase electric machine 30 can have a B6 topology with six power switches that are cooled by means of a temperature control system according to embodiments of the invention. The power switches of the power converter 11 can be controlled by the control device 12 using suitable control signals using the setpoint specification 5. In this case, the control device 12 can, for example, provide a control signal for each power switch 110, 120, 130 of the power converter 11 in order to open or close the corresponding power switch.The control of an upper power switch of a half-bridge is complementary to the control of the corresponding lower power switch.

Claims

Claims 1. A method for determining a volume flow of a temperature control fluid (142) in a temperature control system (140) which is configured to temperature control at least one circuit breaker (110, 120, 130), wherein a first of the at least one circuit breaker (110, 120, 130) is arranged upstream of at least one temperature sensor (122, 132) with respect to the temperature control fluid (142), and wherein the method comprises determining a temporal temperature profile (144, 146) of the temperature control fluid (142) by means of the at least one temperature sensor, changing a thermal power of the first circuit breaker (110), and determining the volume flow of the temperature control fluid (142) based on a change in the temporal temperature profile (144, 146) that can be assigned to the change in the thermal power.

2. The method according to claim 1, wherein the at least one temperature sensor (122, 132) is integrated into a second circuit breaker (120, 130) of the at least one circuit breaker.

3. The method according to claim 2, wherein the at least one temperature sensor (122, 132) is designed as a sensor of a temperature-dependent property of the second circuit breaker (120, 130).

4. Method according to one of the preceding claims, wherein the change in the thermal power is carried out by changing a duty cycle and / or a switching speed of the first power switch (110).

5. Method according to one of the preceding claims, wherein the change in thermal power occurs abruptly and / or periodically.

6. Method according to one of the preceding claims, comprising determining an amount of change in the thermal power and taking the determined amount into account when determining the volume flow.

7. The method according to claim 6, wherein the determination of the amount of change in the thermal power is carried out as a function of the thermal behavior of the first power switch (110).

8. A computing unit (170) configured to carry out all method steps of a method according to any one of the preceding claims.

9. A temperature control system which is configured to temperature control at least one circuit breaker (110, 120, 130) by means of a temperature control fluid (142) and comprises at least one temperature sensor (122, 132) downstream of the at least one circuit breaker and a computing unit according to claim 8.

10. A computer program which causes a computing unit to carry out all method steps of a method according to one of claims 1 to 7 when executed on the computing unit.

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

12. Device (10) for controlling a stator of an electrical machine (30), comprising a power converter (11) which is designed to be coupled to an electrical machine (30) comprising the stator and a rotor and to provide an electrical voltage for controlling the stator of the electrical machine (30) by means of at least one power switch (110, 120, 130), and a temperature control system according to claim 9.

13. An electric drive system (1), comprising: a device (10) for controlling a stator of an electric machine (30) according to claim 12, and an electric machine (30) having the stator and a rotor, which is electrically coupled to the power converter (11) of the device (10) for controlling the stator of the electric machine (30).

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