Method for operating power electronics to convert electrical energy from a vehicle electrical system into heat

Abstract

The present invention relates to a method for operating power electronics (1) for converting electrical energy from a vehicle electrical system (201) into heat by means of a consumer arrangement (50) consisting of two consumers (51). The power electronics (1) has two switches (2, 3) connected in parallel, wherein the switches (2, 3) are switched in such a way that they connect the consumers (51) individually to the vehicle electrical system (201). The invention also relates to a power electronics arrangement (100) with such power electronics (1) and a computer program product for carrying out the method.

Description

[0001] The present invention relates to a method for operating power electronics for converting electrical energy from the electrical system of a powertrain into heat. The invention also relates to a computer program for carrying out the method and to a power electronics arrangement with such operated power electronics.

[0002] The powertrain of a partially or fully electric vehicle typically includes an electric motor connected to the vehicle's electrical system. This system usually operates on direct current (DC). An inverter is generally located between the electrical system and the electric motor.

[0003] There may be excess electrical energy in the drivetrain that needs to be dissipated. This excess electrical energy can, for example, originate from the electric machine when it is operating in generator mode.

[0004] To dissipate excess electrical energy, power electronics can be used to supply consumers with electricity to convert the electrical energy into heat.

[0005] Such power electronics are known from WO 2023 / 036510 A1. The power electronics comprise an inverter that connects three loads to the vehicle's electrical system for converting electrical energy.

[0006] The object of the present invention is to provide an improved method, among at least some other methods, for operating power electronics for converting electrical energy from the electrical system of a powertrain into heat. Furthermore, the invention aims to provide improved or at least other embodiments of a computer program for operating such power electronics, as well as of a power electronics arrangement comprising such power electronics.

[0007] The problem is solved using the features of the independent claims. Advantageous variants are the subject of the dependent claims.

[0008] The core idea of ​​the invention is therefore to equip a power electronics unit for converting electrical energy from the vehicle electrical system of a drive train into heat with two switches. During operation, these switches are connected to a corresponding load within a load arrangement consisting of two loads connected in parallel. Furthermore, the switches are connected to the vehicle electrical system via a common terminal, and the switches can selectively connect the loads to the electrical system individually or in parallel. Thus, depending on the connection of the loads to the electrical system, different amounts of energy are converted from the electrical system. This allows for flexible use of the loads for converting electrical energy into heat and therefore enables demand-based dissipation / reduction of electrical energy from the vehicle electrical system.Consequently, the core idea leads to an adaptable conversion of electrical energy from the vehicle's electrical system into heat, while also being easy to implement.

[0009] The core idea is advantageously implemented in a method for operating such power electronics. The power electronics serve to convert electrical energy from the vehicle's electrical system into heat by means of a consumer arrangement consisting of two loads connected in parallel. Each load generates heat when energized. During operation, the loads are connected to the vehicle's electrical system via a common connection, which is hereinafter also referred to as the first power supply connection. The power electronics include the two switches, which are connected in parallel. These switches are hereinafter also referred to as the first switch and the second switch. Each switch has a corresponding connection through which it is connected to a corresponding load during operation. These connections are hereinafter also referred to as switch terminals.This means that the first switch is connected to one of the loads via its corresponding switch terminal, and the second switch is connected to a second load via its corresponding switch terminal. Furthermore, the switches are connected to the vehicle's electrical system via a common terminal, which is subsequently referred to as the second power supply terminal. In one operating mode, the switches are configured so that only one load is electrically connected to the vehicle's electrical system, thus supplying power only to that load. This operating mode is subsequently referred to as the first operating mode. In another operating mode, the switches are configured so that both loads are connected to the vehicle's electrical system, thus supplying power in parallel. This operating mode is subsequently referred to as the second operating mode.

[0010] When closed, each switch establishes an electrical connection between the associated consumer and the second mains connection, and when open, it disconnects this connection.

[0011] In preferred embodiments, at least one of the switches, preferably the respective switch itself, has a half-bridge with a series connection of a first switching element and a second switching element. This results in advantageous redundancy when disconnecting the electrical connection of the associated consumer from the second mains connection and thus from the vehicle electrical system, and therefore redundancy when interrupting the conversion of electrical energy from the vehicle electrical system by means of the consumer.

[0012] When the switch is open, at least one of the associated switching elements is opened. When the switch is closed, both associated switching elements are closed.

[0013] The switches and the connected devices are conveniently connected to the vehicle's electrical system via the mains connections during operation / use. The switches selectively establish the electrical connection of the respective device to the electrical system in order to direct current flowing through the electrical system, as described, through at least one connected device, thus energizing the device so that it converts the electrical energy into heat. Consequently, electrical energy, and therefore power, is consumed, which is subsequently referred to as power consumption. In a lossless system, the power consumption P is thus equal to the square of the voltage U of the electrical system divided by the total resistance R_total of the device connected to the electrical system, subsequently referred to as total resistance. Therefore, P = U 2 / R_total. The power consumption is therefore inversely proportional to the total resistance.

[0014] If both consumers are disconnected from the vehicle's electrical system, no conversion of electrical energy takes place via the power resistors. Therefore, no power is consumed.

[0015] In the second operating mode, the total resistance R_total is minimized, and thus the power consumption is maximized. The second operating mode can therefore also be referred to as the high-power operating mode.

[0016] In the first operating mode, the total resistance R_total is higher compared to the second operating mode. This results in reduced power consumption in the first operating mode compared to the second. The first operating mode can therefore also be described as the low-power operating mode.

[0017] The respective consumer can be of any design, provided that it generates heat when an electric current from the vehicle's electrical system flows through it, and thus consumes electrical energy. The respective consumer is therefore, in particular, an electrical load.

[0018] For example, at least one of the consumers can be a coil or at least have a coil which, when energized, inductively converts electrical energy from the vehicle electrical system into heat through eddy currents.

[0019] Likewise, at least one of the consumers could be a heating element or similar device.

[0020] In advantageous versions, at least one of the consumers, and in particular the respective consumer, is a power resistor. This leads to simple implementation and scalable heat generation in a compact design. In particular, the generated heat can thus be easily dissipated, for example, to supply another application, such as an air conditioner.

[0021] The power electronics, especially the switches, can in principle be implemented in any way.

[0022] In advantageous embodiments, the power electronics are arranged within an inverter. This allows the switching elements to be switched at higher frequencies. Furthermore, the power electronics are simplified and compact in this way.

[0023] The respective consumer preferably has two connections that allow the consumer to be powered and are hereinafter also referred to as consumer connections.

[0024] The first consumer connection of the first consumer is hereinafter also referred to as the first primary consumer connection, and a second consumer connection of the first consumer is also referred to as the second primary consumer connection. Similarly, the first consumer connection of the second consumer is hereinafter also referred to as the first secondary consumer connection, and a second consumer connection of the second consumer is also referred to as the second secondary consumer connection.

[0025] In preferred variants, the second primary consumer connection and the second secondary consumer connection are connected to the first network connection, so that the consumers are connected in parallel.

[0026] Preferably, in operation, the switch terminal of the first switch is connected to the first primary consumer terminal of the first consumer, and the first secondary consumer terminal of the second switch is connected to the second consumer.

[0027] In preferred embodiments, in the first operating mode, the first switch is closed and the second switch is opened. Thus, only the first load is energized. Alternatively, in the first operating mode, the first switch is opened and the second switch is closed. Thus, only the second load is energized.

[0028] In preferred embodiments, in the second operating mode, both the first and second switches are closed. Thus, both loads are energized, being energized in parallel due to their parallel connection.

[0029] The switches, especially the switching elements of the half-bridges, are advantageously controlled by pulse-width modulation. Pulse-width modulation, hereinafter also referred to as "PWM", is performed at a specific frequency and thus with a specific period. This period is hereinafter also referred to as the PWM cycle.

[0030] Preferably, the respective operating mode is repeated periodically for twice the length of the PWM cycle. The states within the respective operating mode are thus repeated periodically with a period duration equal to twice the PWM cycle duration. By selecting the appropriate operating mode based on the vehicle electrical system voltage and the required power consumption, the so-called ripple currents and voltage ripple on the electrical system are reduced. Advantageously, the control frequency is also varied to achieve an optimum for the respective operating point. The power consumption is modulated by the duty cycle, which is advantageously selected as large as possible by choosing the appropriate operating modes to achieve the desired effects of minimizing voltage ripple with all its associated advantages, e.g.,The goal is to reduce shielding currents, EMC, eddy current losses, unwanted heating of critical components, and the like. This leads to improved operation of the drive train and also makes it possible to design smaller power electronics components, especially power electronics capacitors, while further reducing ripple currents.

[0031] In preferred embodiments, the loads are supplied with a uniform current periodically. This leads to uniform aging and / or stress on the loads and thus to an overall increased service life of the load assembly. Furthermore, this method generates heat uniformly within the load assembly. The latter simplifies the use and / or dissipation of the generated heat. Additionally, this results in a comparatively homogeneous heat distribution within the load assembly.

[0032] The power electronics can be part of an arrangement for converting electrical energy from a powertrain's electrical system into heat. This arrangement, hereinafter also referred to as the power electronics arrangement, advantageously includes a control unit for operating the power electronics, in particular for switching the switches, which is designed accordingly.

[0033] The power electronics arrangement can include the consumer arrangement.

[0034] It is understood that, in addition to methods for operating the power electronics, the power electronics arrangement is also included in the scope of this invention.

[0035] The procedure is preferably carried out using a computer program product.

[0036] The computer program product includes instructions that, when executed by a computer, cause the computer to perform the procedure.

[0037] The computer can be part of the control unit or be equivalent to the control unit.

[0038] It goes without saying that the computer program product itself is also part of the scope of this invention.

[0039] Further important features and advantages of the invention will become apparent from the dependent claims, the drawings and the associated description of the figures based on the drawings.

[0040] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0041] Preferred embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein identical reference numerals refer to identical or similar or functionally identical components. They show, schematically, each one Fig. 1. A highly simplified, circuit diagram-like representation of a powertrain with an on-board electrical system and power electronics for converting electrical energy from the on-board electrical system. Fig. 2 a circuit diagram-like representation of the power electronics and a consumer arrangement in a first operating mode, Fig. 3 the representation from Fig. 2 in a second operating mode, Fig. 4 a diagram to illustrate the operation of the power electronics using the first operating mode, Fig. 5 a diagram to illustrate the operation of the power electronics using the first operating mode, Fig. 6 a diagram to illustrate the operation of the power electronics using the second operating mode, Fig. 7 A diagram to illustrate the operation of the power electronics using the second operating mode.

[0042] One in the Fig. 1 to 3 The power electronics shown as examples 1 serve to convert, in particular to reduce, electrical energy from a Fig. 1 exemplary electric powertrain 200 shown, for example one in Fig. 1 motor vehicle 300, which is indicated but not shown otherwise.

[0043] The electric powertrain 200, hereinafter also referred to simply as powertrain 200, features, as described in the Fig. Figure 1 shows an on-board electrical system 201, which serves to supply an electric machine 202 of the drive train 200. The power electronics 1 convert electrical energy from the on-board electrical system 201 into heat by means of a consumer arrangement 50, which consists of two consumers 51, namely a first consumer 51, 51a and a second consumer 51, 51b, in parallel. The on-board electrical system 201 makes it possible to supply the electric machine 202 with electricity when the electric machine 202 is operating as a motor to drive the vehicle 300. Furthermore, the on-board electrical system 201 makes it possible to tap into electrical energy generated in the electric machine 202 when it is operating as a generator. In the illustrated embodiments, the on-board electrical system 201 is a high-voltage on-board electrical system 201 operated with direct current / direct voltage. An inverter 203 is connected upstream of the electric machine 202.In the illustrated embodiments, the drive train 200 also includes a traction battery 204, which is connected to the electric machine 202 via the on-board network 201 and the inverter 203.

[0044] The conversion, in particular the reduction, of electrical energy by means of the power electronics 1 is effected by connecting the loads 51 to the vehicle electrical system 201, so that a current flowing through the vehicle electrical system 201 flows through the load 51 connected to the vehicle electrical system 201, thus energizing the load 51 through which the current flows. The respective load 51 generates heat, resulting in the aforementioned conversion of electrical energy into heat. The heat generated by the loads 51 can be dissipated and supplied to another application (not shown), for example, an air conditioning system (not shown), in particular of the motor vehicle 300.

[0045] In the illustrated embodiments, the loads 51 are each configured as a power resistor 52, purely by way of example. In these illustrated embodiments, the loads 51 are identical components, meaning they have, in particular, the same resistance R.

[0046] The connection of the respective consumer 51 to the vehicle electrical system 201 is made by means of two in the Fig. The exemplary switches 2, 3 of the power electronics 1 are shown in Figures 1 to 3, namely a first switch 2 and a second switch 3, which are connected in parallel. In the illustrated embodiments, the respective switch 2, 3 is designed and implemented as a half-bridge 4, purely by way of example.

[0047] How in particular Fig. As can be seen from Figure 1, the consumers 51 of the consumer arrangement 50, on the one hand, and the switches 2, 3 of the power electronics 1, on the other hand, can each be connected to the vehicle electrical system 201 via a corresponding connection 5, and are thus connected to the vehicle electrical system 201 during operation. These connections 5 are subsequently also referred to as vehicle electrical system connections 5 or, in short, network connections 5. The consumers 50 are connected to the vehicle electrical system 201 via a first of the network connections 5, 5a. The switches 2, 3 are connected to the vehicle electrical system 201 via a second of the network connections 5, 5b.

[0048] The power electronics 1 can be arranged within an inverter 6. The power electronics 1, in particular the inverter 6, can be located only in the Fig. 2 and Fig. 3 Capacitance 7 shown, in the illustrated embodiments in the form of a capacitor 8, have.

[0049] As shown below, based on the Fig. 2 and Fig. As explained in Figure 3, the power electronics 1 can individually connect and thus power the loads 51 to the vehicle electrical system 201 by means of switches 2 and 3. In the illustrated embodiments and as described in more detail below, each switch 2 and 3 is assigned to one of the loads 51, so that each switch 2 and 3 can connect the corresponding load 51 to the vehicle electrical system 201, thus powering the corresponding load 51. Each switch 2 and 3 has a terminal 9 for connecting to the corresponding load 51, which is also referred to below as switch terminal 9. In the illustrated embodiments, the first load 51, 51a is assigned to the first switch 2, and the second load 51, 51b is assigned to the second switch 3. In a closed state, each switch 2 and 3 connects the corresponding load 51 to the vehicle electrical system 201, and in an open state, it disconnects this connection.

[0050] In the illustrated embodiment, the respective switch 2, 3, configured as a half-bridge 4, has two switching elements 10, 11 connected in series for this purpose, namely a first switching element 10 and a second switching element 11. When the respective switch 2, 3 is closed, both associated switching elements 10, 11 are closed. When the respective switch 2, 3 is open, at least one of the associated switching elements 10, 11 is opened.

[0051] The power electronics 1 can be part of an arrangement 100, which also includes a control unit 101 for controlling the power electronics 1, in particular the switches 2, 3. The control unit 101 is designed accordingly. The arrangement 100 is hereinafter also referred to as the power electronics arrangement 100. The power electronics arrangement 100 can include the load arrangement 50.

[0052] Each consumer 51 has two connections 53, 54 for supplying power to the consumer 51. The first connection 53, 53a of the first consumer 51, 51a is hereinafter also referred to as the first primary consumer connection 53, 53a, and the first connection 53, 53b of the second consumer 51, 51b as the first secondary consumer connection 53, 53b. Similarly, the second connection 54, 54a of the first consumer 51, 51a is hereinafter also referred to as the second primary consumer connection 54, 54a, and the second connection 54, 54b of the second consumer 51, 51b as the second secondary consumer connection 54, 54b. The second primary consumer connection 54, 54a and the second secondary consumer connection 54, 54b are connected to the first network connection 5, 5a, so that the consumers 51 are connected in parallel.

[0053] In the illustrated embodiments, the switch terminal 9 of the first switch 2 is connected to the first primary consumer connection 53, 53a, and the switch terminal 9 of the second switch 3 is connected to the first secondary consumer connection 53, 53b. Furthermore, switches 2 and 3 are both connected to the second mains connection 5, 5b, as described.

[0054] The power electronics 1, in particular the inverter 8, can be controlled by pulse-width modulation. Pulse-width modulation, hereinafter also referred to as "PWM", is performed at a frequency and thus a period C (compare Fig. 4 to 7). This period C is subsequently also referred to as the PWM cycle C.

[0055] Switches 2 and 3 can be switched differently to operate the power electronics 1, and thus also the power electronics assembly 100, in different operating modes 12 and 13. In the different operating modes 12 and 13, the loads 51 are connected to the vehicle electrical system 201 in different ways, so that they receive different currents and thus convert more or less electrical energy from the vehicle electrical system 201 into heat. The load assembly 50 consumes electrical energy and thus a power P, which is subsequently also referred to as power consumption P. In a lossless system, the power consumption P corresponds to the square of the voltage U of the vehicle electrical system 201 divided by the total resistance R_total of the load assembly 50 connected to the vehicle electrical system 201.

[0056] In an exemplary case Fig. In the first operating mode 12 shown in Figure 2, switches 2 and 3 are switched such that only one of the consumers 51 is connected to the vehicle electrical system 201, so that only this consumer 51 is energized. In the first operating mode 12, the power consumption P is therefore P = U 2 / R.

[0057] How Fig. In the illustrated embodiment of the first operating mode 12, the first switch 2 is closed and the second switch 3 is opened, so that only the first consumer 51, 51 a is energized.

[0058] To implement the first operating mode 12, in a variant not shown, the first switch 2 is opened and the second switch 3 is closed. Thus, only the second consumer 51, 51b is energized.

[0059] In the illustrated embodiments, the open state of the respective switch 2 is achieved purely by way of example by opening the two associated switching elements 10, 11.

[0060] In an exemplary case Fig. In the second operating mode 13 shown in Figure 3, switches 2 and 3 are switched such that the loads 51 are connected to the vehicle electrical system 201, so that the loads 51 are energized in parallel. Thus, the power consumption P in the second operating mode 13 is P = 2U 2 / R.

[0061] How Fig. In the second operating mode 13 shown, both switches 2, 3 are closed when the 3 can be removed.

[0062] Switches 2 and 3, and in particular switching elements 10 and 11, can also be switched in various positions in which no power is consumed. For example, it is possible to open both switches 2 and 3 and thus disconnect the consumers 51 from the vehicle electrical system 201, as shown in Fig. 1 shown.

[0063] How the Fig. As can be seen from 4 to 7 and is explained in more detail below, the consumers 51 in the illustrated embodiments are periodically and uniformly supplied with current.

[0064] The operation of the power electronics 1 is described below based on the information provided in the Fig. The exemplary control of switches 2 and 3 shown in sections 4 to 7 is explained by way of example. Fig. Figures 4 to 7 each show a diagram in which time t is plotted along the abscissa and power consumed P along the ordinate. In the Fig. Figures 4 to 7 also show the power consumption P of the first consumer 51, 51a with a solid line L1 and the power consumption of the second consumer 51, 51b with a dashed line L2. More precisely, the Fig. 4 to 7 the maintenance duration of the corresponding operating modes 12, 13 over a period T. In the Fig. From 4 to 7, the PWM cycle C is indicated by vertically running, dashed lines.

[0065] How the Fig. As can be seen from figures 4 to 7, in the illustrated embodiments, the respective operating modes 12 and 13 are periodically repeated for twice the PWM cycle C. The states in the respective operating modes 12 and 13 are thus repeated periodically with a period T, which, for example, corresponds to twice the PWM cycle C for a duty cycle of 100%. The result is reduced amplitudes of the discharge currents during switching, as well as the distribution of the discharge currents across two PWM cycles C and thus two phases of the control of the power electronics 1. The result is a reduction of the so-called ripple currents in the drive train 200 and, in particular, in the vehicle electrical system 201. In addition to improved operation of the drive train 200, components of the power electronics 1, especially the capacitor 6, can therefore be made smaller while further reducing ripple currents.This results in improved operation and a more compact and cost-effective design of power electronics 1.

[0066] The Fig. 4 and Fig. Figure 5 shows the control of switches 2 and 3 using the first operating mode 12. More precisely, the figures show Fig. 4 and Fig. 5 the maintenance duration of the first operating mode 12 over a period T. In these embodiments, no overlapping connection of the consumers 51 to the vehicle electrical system 201 is provided. This means that only one of the consumers 51 is connected to and energized by the vehicle electrical system 101 at any given time. In the embodiments shown, as for example Fig. 4 can be removed, the consumers 51 are connected alternately and at equal time intervals to the vehicle electrical system 201. During the Fig. In the exemplary embodiment shown in Figure 4, the consumers 51 are connected to the vehicle electrical system 201 one after the other for a connection duration that corresponds to a maximum of one-eighth of the period T, with the connection duration being evenly distributed over the period T. This results in a periodically uniform current being supplied to the consumers 51. The alternating connection of the consumers 51 to the vehicle electrical system 101 means that the electrical energy converted into heat is distributed between both consumers 51. This leads, for example, to reduced wear of the power electronics 1.

[0067] At the in Fig. In the embodiment shown in Figure 4, the consumers 51 are alternately connected to the vehicle electrical system 201 for one-eighth of the period T and disconnected from the vehicle electrical system 101 for the following seven-eighths of the period T. In the illustrated embodiment, the first consumer 51, 51a is connected to the vehicle electrical system 201 for the first eighth of the period T and disconnected from the vehicle electrical system 201 for the following seven-eighths of the period T. Furthermore, the second consumer 51, 51b is connected to the vehicle electrical system 201 for the fifth-eighth of the period T and disconnected from the vehicle electrical system 201 for the remaining eighths of the period T.

[0068] At the in Fig. In the embodiment shown in Figure 5, the consumers 51 are alternately connected to the vehicle electrical system 201 for one-sixteenth of the period T, disconnected from the system 201 for the following twelve-sixteenths of the period T, connected to the system 201 for the next sixteenth of the period C, and disconnected from the system 201 for the remaining sixteenths of the period T. In the illustrated embodiment, the first consumer 51, 51a is connected to the system 201 for the first sixteenth and the thirteenth sixteenth of the period T and disconnected from the system 201 for the remaining sixteenths of the period T. Furthermore, the second consumer 51, 51b is connected to the system 201 for the fifth and the ninth sixteenth of the period T and disconnected from the system 201 for the remaining sixteenths of the period T.

[0069] In these embodiments, the converted energy E during a period T can thus be (1 / 5)TxP, where P corresponds to the power consumption of a consumer 51, i.e., the power consumption P in the first operating mode 12.

[0070] The Fig. 6 and Fig. Figure 7 shows an exemplary control of switches 2 and 3 using the second operating mode 13. In the illustrated embodiments, the loads 51 are operated in the second operating mode 13, i.e., energized in parallel, for at least six-eighths, or three-quarters, of the period T. In the illustrated embodiments, each load 51 is connected to the vehicle electrical system 201 for a maximum of seven-eighths of the period T. Furthermore, the loads 51 are alternately disconnected from the vehicle electrical system 501, whereby only one of the loads 51 can be energized at a time, and thus the first operating mode 12 can be present.

[0071] At the in Fig. In the embodiment shown in Figure 6, the respective consumer 51 is connected to the vehicle electrical system 201 for a total of seven eighths of the period T and disconnected from the vehicle electrical system 201 for the other eighth of the period T, wherein the disconnections of the consumers 51 from the vehicle electrical system 201 are equally spaced in time.

[0072] At the in Fig. In the embodiment shown in 7, the respective consumer 51 is connected to the vehicle electrical system 201 for a total of six eighths of the period T and disconnected from the vehicle electrical system 201 for the other two eighths of the period T, wherein in each eighth of the period T one of the consumers 51 is disconnected from the vehicle electrical system 101.

[0073] In the control systems of the exemplary embodiments of the Fig. 6 and Fig.7. The converted energy E during a period T can thus be (17 / 10)TxP, where P corresponds to the power consumption of a consumer 51 in the first operating mode.

[0074] The operation of the power electronics 1, and in particular the switching of switches 2 and 3, is preferably implemented by means of a computer program containing corresponding instructions. Preferably, when the computer program is executed by a computer (not shown) and / or by the control unit 101, these instructions cause the computer and / or the control unit 101 to operate the power electronics 1 as described. QUOTES INCLUDED IN THE DESCRIPTION

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

[0000] WO 2023 / 036510 A1

[0005]

Claims

[1] Method for operating power electronics (1) for converting electrical energy from a vehicle electrical system (201) of a power train (200) into heat by means of a consumer arrangement (50) consisting of two consumers (51) in parallel connection which generate heat when energized, wherein the consumers (51) are connected to the vehicle electrical system via a first mains connection (5, 5a) during operation. - with two switches connected in parallel (2, 3), namely a first switch (2) and a second switch (3), - wherein each switch (2, 3) has an associated switch terminal (9) via which the switch (2, 3) is connected in operation to an associated consumer (51), - wherein the switches (2, 3) are connected to the on-board power supply (201) via a second mains connection (5, 5b) during operation, - wherein the switches (2, 3) are switched in a first operating mode (12) such that only one of the consumers (51) is electrically connected to the vehicle electrical system (201), so that only this consumer (51) is energized, - wherein the switches (2, 3) are switched in a second operating mode (13) such that the consumers (51) are connected in parallel to the vehicle electrical system (201), so that the consumers (51) are powered in parallel. [2] Method according to claim 1, characterized by , - that in operation the switch terminal (9) of the first switch (2) is connected to a first first consumer terminal (53, 53a) of a first of the consumers (51, 51a), - that in operation the switch terminal (9) of the second switch (3) is connected to a first second consumer terminal (53, 53b) of a second consumer (51, 51b), - that in the operation a second primary consumer connection (54, 54a) of the first consumer (51, 51a) and a second secondary consumer connection (54, 54b) of the second consumer (51, 51b) are connected to the first network connection, - that in the first operating mode (12): • the first switch (2) is closed and the second switch (3) is opened, • or • the first switch (2) is opened and the second switch (3) is closed, - that in the second operating mode (13) the first switch (2) and the second switch (3) are closed. [3] Method according to claim 1 or 2, characterized by, that at least one of the switches (2, 3) is configured as a half-bridge (4) with a series connection of a first switching element (10) and a second switching element (11), wherein both switching elements (10, 11) of the switch (2, 3) are closed to close the switch (2, 3), and wherein at least one of the switching elements (10, 11) of the switch (2, 3) is opened to open the switch (2, 3). [4] Method according to any one of claims 1 to 3, characterized by , - that the switches (2, 3) are controlled with a PWM signal, - that the respective operating mode (12, 13) is periodically repeated for twice the duration of a PWM cycle (C). [5] Method according to any one of claims 1 to 4, characterized by , that the consumers (51) are periodically and uniformly supplied with current in at least one of the operating modes (12, 13), in particular in the respective operating mode (12, 13). [6] Computer program product comprising instructions which, when executed by a computer, cause the computer to operate the power electronics (1) according to any one of claims 1 to 5. [7] Power electronics arrangement (1) for converting electrical energy from an on-board network (201) of a power train (200) into heat by means of a consumer arrangement (50) consisting of two consumers (51) in parallel connection which generate heat when energized, wherein the consumers (51) are connected to the on-board network (201) via a first network connection (5, 5a) during operation. - with two switches connected in parallel (2, 3), - wherein each switch (2, 3) has an associated switch terminal (9) via which the switch (2, 3) is connected in operation to an associated consumer (51), - wherein the switches (2, 3) are connected to the on-board power supply (201) via a second mains connection (5, 5b) during operation, - with a control device (101) connected to the power electronics (1), which is designed to operate the power electronics (1) according to the method according to one of claims 1 to 5. [8] Power electronics arrangement according to claim 7, characterized by , - that the power electronics arrangement (100) includes the consumer arrangement (50), - that the switch terminal (9) of the first switch (2) is connected to a first first consumer terminal (53, 53a) of a first of the consumers (51, 51a), - that the switch terminal (9) of the second switch (3) is connected to a first secondary consumer terminal (53, 53b) of a second consumer (51, 51b), - that in operation a second primary consumer connection (54, 54a) of the first consumer (51, 51a) and a second secondary consumer connection (54, 54b) of the second consumer (51, 51b) are connected to the on-board network (201) via the first network connection (5, 5a). [9] Power electronics arrangement according to claim 7 or 8, characterized by , that the power electronics (1) is arranged inside an inverter (6). [10] Power electronics arrangement according to any one of claims 7 to 9, characterized by , that at least one of the consumers (51) is a power resistor (52).

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