Method and control unit for operating a motor vehicle as well as motor vehicle

Abstract

Method for operating a motor vehicle, wherein the motor vehicle has at least one electric machine (11) and at least one traction battery (10), wherein in motor operation of the respective electric machine (11) the respective traction battery (10) is discharged more and in generator operation of the respective electric machine (11) the respective traction battery (10) is charged more depending on its state of charge, wherein a respective converter (13) is connected between the respective electric machine (11) and the respective traction battery (10).Then, if, in the generator operation of the respective electric machine (11), the electrical energy generated by it cannot be used, or can only be partially used, for further charging of the respective traction battery (10), depending on the state of charge of the respective traction battery (10), it is determined, depending on at least one operating parameter of the respective electric machine (11) and depending on at least one operating parameter of the respective converter (13), whether and / or to what extent or proportion an electrical power loss dependent on a switching frequency of the respective converter (13) is to be generated by the respective electric machine (11) and / or by the respective converter (13), whereby, depending on this, the switching frequency for the respective converter (13) is determined and the converter is operated at this switching frequency.

Description

[0001] The invention relates to a method and control device for operating a motor vehicle and to a motor vehicle.

[0002] The drivetrain of an electric vehicle or a hybrid vehicle has at least one electric motor acting as a drive unit, which can provide drive power to an output. Furthermore, such a motor vehicle has at least one traction battery. When the respective electric motor is operated as a motor, the respective traction battery is discharged more rapidly. When the respective electric motor is operated as a generator, the respective traction battery can be charged more rapidly, depending on its state of charge.

[0003] A respective converter is connected between the respective traction battery and the respective electric machine of an electric vehicle or a hybrid vehicle, which converts alternating voltages into direct voltages or direct voltages into alternating voltages, depending on whether the respective electric machine is operated as a motor or generator.

[0004] To brake a motor vehicle, a motor vehicle also has a mechanical braking device that interacts with the vehicle's wheels and is designed as a friction brake. In a motor vehicle whose drivetrain has at least one electric motor, braking can also be carried out by the respective electric motor when the respective electric motor is in generator mode. This can generate electrical energy, which can be used in a so-called recuperation mode to charge the respective traction battery more effectively. Whether electrical energy generated during braking with the electric motor in generator mode can be used to charge the traction battery depends on the charge state of the traction battery.

[0005] If, due to the charge level of the traction battery, the electrical energy generated by a generator-driven electric motor during braking of the vehicle cannot be used, or can only be used partially, to charge the traction battery more effectively, for example, because the traction battery is already fully or almost fully charged, the electric motor in motor vehicles known from practice is not braked further or only to a limited extent by a generator-driven electric motor. Instead, the vehicle is then braked via the mechanical braking system assigned to the wheels. The mechanical braking system must be designed and dimensioned for this load case.

[0006] There is a need to relieve the load on a mechanical braking device even if, due to the charge state of the motor vehicle's traction battery, the electrical energy generated during braking by a generator-driven electrical machine cannot be used or can only be used partially to charge the traction battery.

[0007] AT 12 010 U2 describes an electric vehicle with an electric motor, a traction battery, and friction brakes assigned to the wheels. If, during braking, the electrical energy generated by a generator-driven electric motor cannot be used to charge the traction battery, an additional energy sink is provided that can absorb the energy that cannot be stored in the traction battery. AT 12 010 U2 proposes deliberately selecting suboptimal operation for the generator-driven electric motor and the converter in order to convert electrical energy generated by a generator-driven electric motor that cannot be used to charge the traction battery into power loss. This can reduce the load on the friction brake.

[0008] DE 11 2013 004 242 T5, DE 10 2015 006 454 A1 and DE 10 2005 058 829 A1 disclose further prior art.

[0009] There is a need to generate power losses in a motor vehicle with at least one electric machine serving as a drive unit, which can be operated both as a motor and as a generator, in order to relieve the load on a mechanical braking device of the output, particularly during a braking operation, even if the electrical energy generated in the generator operation of the respective electric machine cannot be used or can only be used partially to charge the traction battery more strongly.

[0010] The object of the invention is to provide a corresponding method and control device for operating a motor vehicle and a motor vehicle with such a control device.

[0011] This object is achieved by a method according to patent claim 1, by a control device according to patent claim 7 and by a motor vehicle according to patent claim 10.

[0012] According to the invention, if during generator operation of the respective electrical machine the electrical energy generated by the same can not be used or can only be used partially to charge the respective traction battery more strongly depending on the charge state of the same, it is determined depending on at least one operating parameter of the respective electrical machine and depending on at least one operating parameter of the respective converter whether and / or to what extent or proportion an electrical power loss dependent on a switching frequency of the respective converter should be generated by the respective electrical machine and / or by the respective converter or should occur in the area of ​​the respective electrical machine and / or in the area of ​​the respective converter.

[0013] Depending on this, the switching frequency for the respective inverter is determined and the respective inverter is operated with the specified switching frequency.

[0014] According to the invention, the electrical power loss arising in the interaction between the respective electrical machine and the respective inverter is considered as a function of the switching frequency of the respective inverter. Depending on at least one operating parameter of the respective electrical machine and depending on at least one operating parameter of the respective inverter, it is determined whether and / or to what extent or proportion the electrical power loss dependent on the switching frequency of the respective inverter should arise or be generated in the area of ​​the respective electrical machine and / or in the area of ​​the respective inverter. Depending on this, the switching frequency for the subsequent operation of the respective inverter is determined and the inverter is operated at this switching frequency.

[0015] During generator operation of the respective electrical machine, depending on the selected switching frequency of the respective converter, the electrical power loss is generated either to a greater extent or proportion in the area of ​​the respective electrical machine, or to a greater extent or proportion in the area of ​​the respective converter, or even equally by the converter and the electrical machine, in order to relieve the load on the mechanical braking device. This ultimately makes it possible to reduce the load on a mechanical braking device and reduce its size.

[0016] Preferably, if the electrical power loss dependent on the switching frequency of the respective converter is to be generated to a greater extent or proportion in the area of ​​the respective electrical machine, the switching frequency of the respective converter is reduced or a relatively low switching frequency is determined for it. Preferably, if the electrical power loss dependent on the switching frequency of the respective converter is to be generated to a greater extent or proportion in the area of ​​the respective converter, the switching frequency of the respective converter is increased or a relatively high switching frequency is determined for it, optionally additionally increasing the switching time of the converter or using a relatively long switching time for the operation of the converter.

[0017] At relatively low switching frequencies of an inverter, the respective inverter has a high efficiency, but the respective electrical machine has a low efficiency, whereas at relatively high switching frequencies of an inverter, the respective inverter has a relatively low efficiency and the respective electrical machine has a relatively high efficiency. Accordingly, at a relatively low switching frequency of the respective inverter, a relatively low electrical power loss occurs in the area of ​​the respective inverter, but a relatively high additional electrical power loss occurs in the area of ​​the respective electrical machine. If, on the other hand, the switching frequency of the respective inverter is relatively high, a relatively high electrical power loss occurs in the area of ​​the respective inverter and a relatively low additional electrical power loss occurs in the area of ​​the respective electrical machine.

[0018] The operating parameters of the respective electrical machine and / or the respective converter are considered to be, in particular, the temperature of the respective component and / or the aging state of the respective component. The aging state is a thermal aging state, with the thermal aging state becoming more severe the longer the respective component has been exposed to high temperatures. Electrical power loss is preferably generated more strongly in the area of ​​the component with a lower temperature and / or whose thermal aging state is lower.

[0019] Preferred developments of the invention will become apparent from the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail, without being limited thereto, with reference to the drawings. Herein: Fig. 1 a block diagram of a powertrain of an electric vehicle; Fig. 2a a diagram illustrating the switching frequency-dependent power loss of an electrical machine; Fig. 2b a diagram illustrating the switching frequency-dependent power loss of a converter; Fig. 2c a diagram illustrating the switching frequency-dependent power loss of the system consisting of an electrical machine and a converter; Fig. 3 a diagram to illustrate the switching time-dependent power loss of an inverter.

[0020] Fig. 1 shows, in a highly schematic manner, components of an electrically powered motor vehicle, namely a traction battery 10 and an electric machine 11. The electric machine 11 serves to provide drive power to an output 12 of the motor vehicle.

[0021] The electric machine 11 can be operated as a motor or as a generator. When the electric machine 11 is operated as a motor, the traction battery 10 is discharged more rapidly. When the electric machine 11 is operated as a generator, the traction battery 10 is charged more rapidly, depending on its charge level. If the motor vehicle is to be accelerated, the electric machine 11 is operated as a motor. If the motor vehicle is to be decelerated, the electric machine 11 can be used for braking when operating as a generator.

[0022] A converter 13 is connected between the electric machine 11 and the traction battery 10. The converter 13 converts DC voltage into AC voltage or AC voltage into DC voltage, depending on whether the electric machine 11 is operating as a motor or generator. When the electric machine 11 is operating as a motor, the converter 13 converts DC voltage into AC voltage in order to discharge the traction battery 10 more effectively. When the electric machine 11 is operating as a generator, the converter 12 converts AC voltage into DC voltage in order to charge the traction battery 10 more effectively, depending on the charge level of the traction battery 10.

[0023] As already explained, when the electric machine 11 is operated as a generator, a braking torque can be generated by the electric machine 11 at the output 12 of the motor vehicle. Fig. 1 further shows a transmission 14. The motor vehicle can be braked at the output 12 via a mechanical braking device designed as a friction brake (not shown).

[0024] Although in Fig. While only a single electric machine 11 is shown in FIG. 1, the motor vehicle may also have multiple electric machines 11. Thus, each driven wheel of the motor vehicle may be assigned an electric machine 11. If multiple electric machines 11 are present, they may be coupled to the traction battery 10 via corresponding converters 13. Multiple traction batteries may also be present.

[0025] If, in generator operation of the electric machine 11, electrical energy generated by the electric machine 11 cannot be used or can only be used partially to charge the traction battery 10 more strongly, because, for example, the traction battery 10 is already charged too far or too strongly, in particular completely or almost completely, it is determined according to the invention depending on at least one operating parameter of the electric machine 10 and depending on at least one operating parameter of the converter 13 whether and / or to what extent or proportion an electrical power loss dependent on the switching frequency of the converter 13, which occurs in the area of ​​the converter 13 and the electric machine 11, is to be generated by the electric machine 11 or by the converter 13 and is therefore to occur in the area of ​​the electric machine 11 or in the area of ​​the converter 13.Depending on this, the switching frequency for the converter 13 is determined in order to subsequently operate the converter 13 with this switching frequency.

[0026] Fig. 2a, Fig. 2b and Fig. 2c shows the curves 15, 16 and 17, respectively, the power losses PV at an operating point depending on the switching frequency f of the converter 13.

[0027] The curve 15 of the Fig. 2a the switching frequency dependent power loss PV of the electrical machine 11, the curve 16 of the Fig. 2b the switching frequency-dependent power loss of the converter 13 and Fig. 2c with the curve 17 the switching frequency-dependent power loss PV of the entire system consisting of electrical machine 11 and converter 13.

[0028] The curve 15 of the Fig. Figure 2a shows that the power loss PV of the electric machine 11 decreases with increasing switching frequency f of the converter 13.

[0029] According to curve 16 of the Fig. 2b, the power loss PV of the converter 13 increases with the switching frequency f thereof.

[0030] By superimposing the curves 15 and 16, the curve 17 results for an operating point as an example according to Fig. 2 for the total electrical power loss PV of electrical machine 11 and converter 13 as a function of the switching frequency f of converter 13 c. At frequency f', the switching frequency-dependent power loss PV of the entire system comprising electrical machine 11 and converter 13 is minimal.

[0031] The operating parameters of the electrical machine 11 and the converter 13, depending on which it is determined whether and to what extent or proportion the power loss, which depends on the switching frequency f of the converter 13, should occur or be generated in the area of ​​the electrical machine 11 or in the area of ​​the converter 13, can preferably be the current thermal aging of the respective module. Thermal aging correlates with a temperature reserve of the respective module. If a module has aged less thermally, it has a higher temperature reserve and can therefore be exposed to higher temperatures for longer without its functionality being impaired or even damaging the module.

[0032] Alternatively or additionally, the current temperature or a time interval for which the respective component is operated in a current temperature range can also be used as an operating parameter of the electrical machine 11 and the operating parameter of the converter 13. For example, if the electrical machine 11 is currently operating for a relatively long period of time in a relatively high temperature range, but the converter 13 is not, it can be determined from this that electrical power loss should be generated to a greater extent or proportion in the area of ​​the converter 13 in the future.

[0033] If the electrical power loss dependent on the switching frequency f of the converter 13 is to be incurred or generated to a greater extent or proportion in the area of ​​the electrical machine 11, the switching frequency f of the converter 13 is reduced or a relatively low or small switching frequency of the converter 13 is determined for its operation. The switching frequency of the converter 13 is preferably reduced or determined such that the switching frequency selected for the operation of the converter 13 corresponds to at least 1 to 5 times, in particular 2 to 5 times, a fundamental oscillation frequency of the electrical machine 11, wherein the fundamental oscillation frequency of the electrical machine 11 depends on a number of pole pairs of the electrical machine 11 and a rotational speed thereof.

[0034] If, on the other hand, it is determined that the electrical power loss dependent on the switching frequency f of the converter 13 is to be generated or generated to a greater extent or proportion in the area of ​​the converter 13, the switching frequency of the converter 13 is increased or a relatively high switching frequency is determined for the operation of the converter 13. Then, if the electrical power loss dependent on the switching frequency of the converter 13 is to be generated to a greater extent or proportion in the area of ​​the converter 13 and a relatively high switching frequency f is selected for the operation of the converter 13 for this purpose, a switching time of the converter 13 can optionally be increased or a relatively long switching time can be selected for the operation of the converter 13.

[0035] Fig. Figure 3 shows curves 18, 19 and 20 for a shutdown process of the inverter 13 over time t. The shutdown process begins at time t1 and is completed at time t2. The time period Δt between times t1 and t2 corresponds to the switching time of the inverter 13 for the Fig. 3 shown shutdown process. During the shutdown process, the electrical current is reduced according to curve 18, and the electrical voltage across the respective switching element of the converter 13 is increased according to curve 19. The hatched area under curve 20 of the Fig. 3 corresponds to the power loss incurred during the switching process. The shorter the switching time, the lower the power loss in the area of ​​converter 13. The power loss in the area of ​​converter 13 can therefore be influenced by the selection of the switching time. For a constant switching frequency f of converter 13, the longer the switching time, the greater the power loss, both during a switch-off process and during a switch-on process.

[0036] It is therefore within the meaning of the present invention, if during generator operation of the electrical machine 11 the electrical energy generated by the latter cannot be used or can only be used partially to charge the traction battery 10 more strongly, in particular because the traction battery 10 is already too strongly or far charged, the interaction of converter 13 and electrical machine 11 must be considered with regard to the electrical power loss that arises in the area of ​​the converter 13 and the electrical machine 11, which power loss depends on the switching frequency of the converter 13. The respective switching frequency for the converter 13, at which the converter is operated, is determined depending on at least one operating parameter of the electrical machine 11 and depending on at least one operating parameter of the converter 13, in order to dissipate power loss either to a greater extent or proportion in the area of ​​the electrical machine 11 or to a greater extent orShare in the area of ​​the converter 13 or evenly distributed or equally proportionally by the electrical machine 11 and the converter 13, namely depending on the at least one operating parameter of the electrical machine 11 and the at least one operating parameter of the converter 13.

[0037] The switching frequency-dependent power losses PV of the converter 13 and the electric machine 11 are known on the control side and stored in a control unit, whereby these switching frequency-dependent losses of the electric machine 11 and the converter 13 can be determined empirically either by simulations or by measurements on a test bench.

[0038] If, during generator operation of the electric machine 11, the electrical energy generated by the electric machine 11 cannot be used, or can only be used partially, to charge the traction battery 10 more strongly, the amount of electrical energy generated by the electric machine 11 that cannot be used to charge the traction battery 10 more strongly can be determined. If this amount can be fully converted into electrical power loss, braking can be carried out exclusively via the generator-operated electric machine 11. If this amount cannot be fully converted into electrical power loss, at least assistance from a mechanical braking device is required for braking.

[0039] The amount of electrical energy generated by the generator-operated electrical machine 11 that cannot be used to charge the traction battery 10 more strongly and converted into electrical power loss is converted into electrical power loss by the converter 13 and / or the electrical machine 11 depending on the switching frequency of the converter 13. The switching frequency for the operation of the converter 13 is determined depending on the at least one operating parameter of the electrical machine 11 and depending on the at least one operating parameter of the converter 13, in particular depending on its thermal aging and / or its temperature. Depending on this, the electrical power loss is generated partly by the converter 13 and partly by the electrical machine 11.

[0040] During motor operation of the electrical machine 11, the switching frequency of the converter 13 is always selected to ensure minimal electrical power loss. During motor operation of the electrical machine 11, the switching frequency f' of the Fig. 2c is selected for the operation of the converter 13.

[0041] During generator operation of the electric machine 11, electrical power losses can be generated in the area of ​​the electric machine 11 and the converter 13, namely when the electrical energy generated during generator operation of the electric machine 11 cannot be used or can only be used partially to charge the traction battery 10. In this case, the switching frequency f of the converter 13 can be adjusted, for example, based on the switching frequency f' of the Fig. 2c can either be increased or decreased or a relatively large or a relatively small switching frequency f is determined for the converter 13.

[0042] If electrical power losses are to occur to a greater extent or proportion in the area of ​​the converter 13, because, for example, the converter has a higher temperature reserve until a load limit is reached, the switching frequency f of the converter 13 is determined, for example, based on the switching frequency f' of the Fig. 2c is increased or a relatively high switching frequency is determined

[0043] If, however, electrical power loss, which depends on the switching frequency of the converter 13, is to occur to a greater extent or proportion in the area of ​​the electrical machine 11, because, for example, the electrical machine 11 has a higher temperature reserve compared to the converter 13 until the respective limit value is reached, a relatively small switching frequency f is selected for the operation of the converter 13 or the switching frequency f of the converter 13 .B. starting from the switching frequency f' of the Fig.2c is shifted toward a relatively low switching frequency. However, the switching frequency of the converter 13 should preferably be at least 1 to 5 times, in particular 2 to 5 times, higher than the fundamental oscillation frequency of the electrical machine 11.

[0044] As already explained, if a larger portion of the power loss is to be generated in the area of ​​the converter 13, the switching time of the converter 13 can also be increased or extended, especially if the converter has controllable gate drivers. The switching time can be changed by varying the voltage rise rates of the gate drivers.

[0045] The respective converter 13 is preferably a pulse-controlled inverter.

[0046] The invention further relates to a control unit configured to automatically execute the method according to the invention on the control side. The control unit is preferably an electronic control unit, such as the electronic engine control unit for the electric machine 11.

[0047] If, during generator operation of the respective electrical machine, the electrical energy generated by the respective electrical machine cannot be used or can only be used partially to charge the respective traction battery, depending on the charge state of the latter, the control unit determines, depending on at least one operating parameter of the respective electrical machine and at least one operating parameter of the respective converter, whether and / or to what extent or proportion an electrical power loss dependent on a switching frequency of the respective converter should be generated by the respective electrical machine or by the respective converter. Depending on this, the control unit determines the switching frequency for the respective converter for subsequent operation of the same at this switching frequency.

[0048] The invention further relates to a motor vehicle which, in addition to the electric machine 11, the traction battery 10 and the converter 13, has the control unit which is configured to automatically execute the method according to the invention on the control side.

[0049] The motor vehicle is an electric vehicle or hybrid vehicle.

[0050] With the invention, it is possible to relieve the load on a mechanical braking device even when electrical power is generated during generator operation of the electrical machine 10 which, depending on the charge state of the traction battery 12, cannot be used or can only be used partially by the traction battery 10 to charge the same, namely by generating electrical power losses depending on the switching frequency of the converter 13 in the area of ​​the converter 13 and / or more in the area of ​​the electrical machine 11. As a result, the mechanical braking device, such as a friction brake of the output 12, can ultimately be relieved and, if necessary, made smaller. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] AT 12 010 U2

[0007] DE 11 2013 004 242 T5

[0008] DE 10 2015 006 454 A1

[0008] DE 10 2005 058 829 A1

[0008]

Claims

[1] Method for operating a motor vehicle, wherein the motor vehicle has at least one electric machine (11) and at least one traction battery (10), wherein in a motor operation of the respective electric machine (11) the respective traction battery (10) is discharged more intensively and in a generator operation of the respective electric machine (11) the respective traction battery (10) is charged more intensively depending on its state of charge, wherein a respective converter (13) is connected between the respective electric machine (11) and the respective traction battery (10), characterized by , that when, in generator operation of the respective electrical machine (11), electrical energy generated by the respective electrical machine (11) cannot be used or can only be used partially to charge the respective traction battery (10) more strongly, depending on the charge state of the same, it is determined depending on at least one operating parameter of the respective electrical machine (11) and depending on at least one operating parameter of the respective converter (13) whether and / or to what extent or proportion an electrical power loss dependent on a switching frequency of the respective converter (13) is to be generated by the respective electrical machine (11) and / or by the respective converter (13), and Depending on this, the switching frequency for the respective converter (13) is determined and the converter is operated with this switching frequency. [2] Method according to claim 1, characterized bythat when the electrical power loss dependent on the switching frequency of the respective converter (13) is to be generated to a greater extent or proportion by the respective electrical machine (11) than by the respective converter (13), the switching frequency of the respective converter (13) is reduced or a relatively small or low switching frequency is determined for the respective converter (13). [3] Method according to claim 2, characterized by that the switching frequency for the respective converter (13) is determined such that the switching frequency of the respective converter (13) corresponds to at least 1 to 5 times, in particular 2 to 5 times, a fundamental oscillation frequency of the respective electrical machine (11), wherein the fundamental oscillation frequency of the respective electrical machine (11) is dependent on a number of pole pairs of the respective electrical machine (11) and a speed of the respective electrical machine (11). [4] Method according to claim 1 or 2, characterized by that when the electrical power loss dependent on the switching frequency of the respective converter (13) is to be generated to a greater extent or proportion by the respective converter (13) than by the respective electrical machine (11), the switching frequency of the respective converter (13) is increased or a relatively large or high switching frequency is determined for the respective converter (13). [5] Method according to claim 4, characterized by that in addition a switching time of the respective converter (13) is increased or a relatively large or long switching time is used for the respective converter (13). [6] Method according to one of claims 1 to 5, characterized by that the respective converter (13) is designed as a pulse inverter. [7] Control unit for operating a motor vehicle, wherein the motor vehicle has at least one electric machine (11) and at least one traction battery (10), wherein a respective converter (13) is connected between the respective electric machine (11) and the respective traction battery (10), characterized by , that the control unit then, when, in generator operation of the respective electrical machine (11), electrical energy generated by the same, depending on the charge state of the respective traction battery (10), cannot be used or can only be used partially to charge the same more strongly, depending on at least one operating parameter of the respective electrical machine (11) and depending on at least one operating parameter of the respective converter (13), determines whether and / or to what extent or proportion an electrical power loss dependent on a switching frequency of the respective converter (13) should be generated by the respective electrical machine (11) and / or by the respective converter (13), the control unit determines the switching frequency for the respective converter (13) depending on this for subsequent operation of the same with this switching frequency. [8] Control device according to claim 7, characterized bythat the same is arranged to carry out the method according to one of claims 1 to 6 automatically on the control side. [9] Control device according to claim 7 or 8, characterized by that it is an engine control unit of the electric machine (11). [10] Motor vehicle, wherein the motor vehicle has at least one electric machine (11) and at least one traction battery (10), wherein a respective converter (13) is connected between the respective electric machine (11) and the respective traction battery (10), characterized by a control device according to claim 7, 8 or 9.

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