Electrical drive arrangement and methods for its operation

Abstract

The invention relates to an electric drive arrangement (1) for a vehicle, comprising a first high-voltage battery (2) and a second high-voltage battery (3) each with two terminals, at least one inverter (5) with two terminals connected to the first high-voltage battery (2), and an electric machine (6), wherein the first high-voltage battery (2) has a higher DC voltage than the second high-voltage battery (3), wherein a voltage converter (10) is arranged which is connected to the first high-voltage battery (2) and to which one of two terminals of the second high-voltage battery (3) is connected via a choke (L4), wherein the same terminal of the second high-voltage battery (3) is further connected via a switching element (12) to a star point (11) of the electric machine (6), wherein a second terminal of the second high-voltage battery (3) is connected to one of the terminals of the first high-voltage battery (2).

Description

[0001] The invention relates to an electric drive arrangement according to the preamble of claim 1 and a method for its operation according to the preamble of claim 6.

[0002] WO 2024 / 109887 A1 describes an energy conversion device and a vehicle. The energy conversion device comprises: a first battery set; a first inductor, wherein a first end of the first inductor is connected to a positive electrode of the first battery set; a first bridge arm, wherein the midpoint of the first bridge arm is connected to a second end of the first inductor and a first end of the first bridge arm is connected to a negative electrode of the first battery set; a second battery set, wherein a positive electrode of the second battery set is connected to a second end of the first bridge arm and a negative electrode of the second battery set is connected to a first end of the first bridge arm;and a controller, wherein the controller is connected to the first bridge arm and the controller is configured to control the first bridge arm in a first state so that the first battery set and the second battery set can be alternately charged and discharged, thereby enabling the heating of the first battery set and the second battery set. In the energy conversion device, the first battery set and the second battery set work together, which enables high system stability. At low temperatures, oscillating heating of the first battery set and the second battery set is carried out, thereby ensuring the charging and discharging performance of the batteries.

[0003] The invention is based on the objective of providing a novel electrical drive arrangement and a novel method for its operation.

[0004] The problem is solved according to the invention by an electric drive arrangement having the features of claim 1 and a method for its operation having the features of claim 6.

[0005] Advantageous embodiments of the invention are the subject of the dependent claims.

[0006] An electric drive arrangement for a vehicle is proposed, comprising a first high-voltage battery and a second high-voltage battery, each with two terminals, at least one inverter with two terminals connected to the first high-voltage battery, and an electric machine, which is controllable, in particular, by the inverter, wherein the first high-voltage battery has a higher DC voltage than the second high-voltage battery. According to the invention, a voltage converter, in particular a low-power DC / DC converter, is arranged, which is connected to the first high-voltage battery and to which one of the two terminals of the second high-voltage battery is connected via an inductor, wherein the same terminal of the second high-voltage battery is further connected via a switching element to a star point of the electric machine, and wherein a second terminal of the second high-voltage battery is connected to one of the terminals of the first high-voltage battery.

[0007] In one embodiment, the inverter is designed as a B6 bridge consisting of six semiconductor switches, two of which form a half-bridge with an upper semiconductor switch and a lower semiconductor switch.

[0008] In one embodiment, the voltage converter is designed as a half-bridge with an upper semiconductor switch and a lower semiconductor switch. The choke is connected, for example, to a center tap of the half-bridge.

[0009] In one embodiment, the electric drive arrangement is configured to use the voltage converter for charging and / or discharging the second high-voltage battery during vehicle operation and / or to use the inverter and at least one inductor of the electric machine as a DC / DC converter for transferring power between the two high-voltage batteries when charging at a fast charging station and for impedance heating of at least one of the high-voltage batteries.

[0010] In one embodiment, the positive terminal of the second high-voltage battery is connected to the voltage converter and can be connected to the neutral point of the electric machine via the switching element, and the negative terminal of the second high-voltage battery is connected to the negative terminal of the first high-voltage battery. Alternatively, the negative terminal of the second high-voltage battery is connected to the voltage converter and can be connected to the neutral point of the electric machine via the switching element, and the positive terminal of the second high-voltage battery is connected to the positive terminal of the first high-voltage battery.

[0011] According to one aspect of the present invention, a method for operating the above-described electric drive arrangement is proposed. According to the invention, the voltage converter is used for charging and / or discharging the second high-voltage battery during vehicle operation, and / or the inverter and at least one inductor of the electric machine are used as a DC / DC converter for transferring power between the two high-voltage batteries when charging at a fast-charging station and for impedance heating of at least one of the high-voltage batteries, particularly at low ambient temperatures.

[0012] In one embodiment, a positive terminal of the second high-voltage battery is connected to the voltage converter and can be connected to the star point of the electric machine via the switching element, and a negative terminal of the second high-voltage battery is connected to a negative terminal of the first high-voltage battery, wherein the switching element is opened during vehicle operation and the lower semiconductor switch of the voltage converter is operated in a pulsed manner to supply a recharging current from the second high-voltage battery to the first high-voltage battery.Alternatively, the negative terminal of the second high-voltage battery is connected to the voltage converter and can be connected to the star point of the electric machine via the switching element, and the positive terminal of the second high-voltage battery is connected to the positive terminal of the first high-voltage battery, whereby the switching element is opened during vehicle operation and the upper semiconductor switch of the voltage converter is operated in a pulsed manner to supply a charging current from the second high-voltage battery to the first high-voltage battery.

[0013] In one embodiment, a positive terminal of the second high-voltage battery is connected to the voltage converter and can be connected to the star point of the electric machine via the switching element, and a negative terminal of the second high-voltage battery is connected to a negative terminal of the first high-voltage battery, wherein, when charging at a low-power charging station, the switching element is open and the voltage converter induces a current from the first high-voltage battery to the second high-voltage battery by operating the upper semiconductor switch of the voltage converter in a pulsed manner.Alternatively, the negative terminal of the second high-voltage battery is connected to the voltage converter and can be connected to the star point of the electric machine via the switching element, and the positive terminal of the second high-voltage battery is connected to the positive terminal of the first high-voltage battery, whereby when charging at a low-power charging station the switching element is open and the voltage converter induces a current from the first high-voltage battery to the second high-voltage battery by operating the lower semiconductor switch of the voltage converter in a pulsed manner.

[0014] In one embodiment, a positive terminal of the second high-voltage battery is connected to the voltage converter and can be connected to the neutral point of the electric machine via the switching element, and a negative terminal of the second high-voltage battery is connected to a negative terminal of the first high-voltage battery. For fast charging at a DC charging station, the switching element is closed, and one, several, or all of the inverter's upper semiconductor switches are operated in a switching manner. Alternatively, the negative terminal of the second high-voltage battery is connected to the voltage converter and can be connected to the neutral point of the electric machine via the switching element, and the positive terminal of the second high-voltage battery is connected to the positive terminal of the first high-voltage battery. For fast charging at a DC charging station, the switching element is closed, and one, several, or all of the inverter's lower semiconductor switches are operated in a switching manner.

[0015] In one embodiment, a positive terminal of the second high-voltage battery is connected to the voltage converter and can be connected to the star point of the electric machine via the switching element, and a negative terminal of the second high-voltage battery is connected to a negative terminal of the first high-voltage battery, wherein, for impedance heating by injecting an AC current from the first high-voltage battery into the second high-voltage battery, the switching element is closed and one, several or all upper semiconductor switches of the inverter are operated in a switching manner.Alternatively, the negative terminal of the second high-voltage battery is connected to the voltage converter and can be connected to the star point of the electric machine via the switching element, and the positive terminal of the second high-voltage battery is connected to the positive terminal of the first high-voltage battery, whereby, for impedance heating by injecting an AC current from the second high-voltage battery into the first high-voltage battery, the switching element is closed and one, several or all lower semiconductor switches of the inverter are operated in a switching manner.

[0016] According to the present invention, the electric drive arrangement comprises two independent high-voltage batteries. During driving, the charge balance of the two high-voltage batteries is achieved via a particularly small voltage converter (DC / DC converter) with a low current. During DC fast charging and also when heating the batteries via an impedance heating method, charging or discharging takes place via the inverter and the electric motor with a high current.

[0017] In this way, cost-effective battery heating via impedance heating and a DC fast charging function can be implemented in a drive arrangement with two high-voltage batteries.

[0018] In this way, the voltage converter can be designed for the low continuous driving power, which helps to keep material costs, installation space and weight low.

[0019] Exemplary embodiments of the invention are explained in more detail below with reference to drawings.

[0020] This shows: Fig. 1 A schematic view of an electric drive arrangement of a vehicle with a first and a second high-voltage battery, Fig. 2 a schematic view of the electrical drive arrangement during DC fast charging, Fig. 3 a schematic view of the electric drive arrangement during battery heating by transferring power from the second high-voltage battery to the first high-voltage battery, and Fig. 4 a schematic view of another embodiment of the electric drive arrangement.

[0021] Corresponding parts are marked with the same reference symbols in all figures.

[0022] Fig. Figure 1 is a schematic view of an electric drive arrangement 1 of a vehicle, for example a passenger car, a commercial vehicle or a bus.

[0023] The electric drive arrangement 1 comprises a first high-voltage battery 2 and a second high-voltage battery 3, at least one electric drive 4 comprising an inverter 5 and an electric machine 6 (symbolized here by three inductors L1, L2, L3, for example, stray inductances of a stator), and further high-voltage components 7, for example, an on-board power supply converter, an on-board charger, and air conditioning components. The first high-voltage battery 2 is directly coupled to a high-voltage system of the vehicle. During DC fast charging, the first high-voltage battery 2 is directly coupled to a DC charging station EVSE, for example, via respective charging contactors 8, 9.

[0024] Each of the high-voltage batteries 2 and 3 has its own specific design, for example, regarding a high-voltage voltage range, possible currents, safety components such as main contactors S_Main_P1, S_Main_N1, S_Main_P2, and S_Main_N2, and fuse functions. The second high-voltage battery 3 also has a voltage converter 10 that can raise its voltage to the level of the first high-voltage battery 2. The condition for this is that the voltage of the second high-voltage battery 3 is always equal to or lower than the voltage of the first high-voltage battery 2. If this is not the case, at least one of the two main contactors S_Main_P2 and S_Main_N2 of the second high-voltage battery 3 must open to interrupt the connection. To save on material costs, the voltage converter 10 is dimensioned so (small) that it can supply the necessary current to recharge the first high-voltage battery 2 from the second high-voltage battery 3 during driving (for example, 25 A to 50 A).However, this is not suitable for charging the second high-voltage battery 3 in the same time as the first high-voltage battery 2 during a fast charging process at a DC charging station EVSE.

[0025] Inverter 5 can be configured as a B6 bridge consisting of six semiconductor switches HS1 to HS6, two of which form a half-bridge with an upper semiconductor switch HS1, HS3, HS5 (high-side switch) and a lower semiconductor switch HS2, HS4, HS6 (low-side switch).

[0026] The voltage converter 10 can be configured as a half-bridge with an upper semiconductor switch HS7 and a lower semiconductor switch HS8.

[0027] The second high-voltage battery 3 is connected via one of its terminals, through a choke L4, to a center tap between the two semiconductor switches HS7 and HS8 of the voltage converter 10. Furthermore, this terminal of the second high-voltage battery 3 can be connected via a switching element 12 to a star point 11 of the electric machine 6. The inverter 5 belonging to the electric machine 6 is connected to the first high-voltage battery 2 via its two terminals. The second terminal of the second high-voltage battery 3 is directly connected to the second terminal of the first high-voltage battery 2.In the example shown, the positive terminal of the second high-voltage battery 3 is connected via the choke L4 to the center tap between the two semiconductor switches HS7, HS8 of the voltage converter 10 and can be connected via the switching element 12 to the star point 11 of the electric machine 6, and the negative terminal of the second high-voltage battery 3 is directly coupled to the negative terminal of the first high-voltage battery 2.

[0028] During vehicle operation, the switching element 12 at star point 11 is open. The inverter 5 and the other high-voltage components 7 are active and are supplied by the first high-voltage battery 2. The second high-voltage battery 3 supplies a charging current to the first high-voltage battery 2 via the voltage converter 10 and thus also contributes to the supply of the other high-voltage components 7. The lower semiconductor switch HS8 is operated in a pulsed manner. When the lower semiconductor switch HS8 is closed, a building-up inductor current I1 flows from the second high-voltage battery 3 via the inductor L4 and the lower semiconductor switch HS8 back to the second battery 3. When the lower semiconductor switch HS8 is open, a freewheeling inductor current I2 flows from the second high-voltage battery 3 via the inductor L4 and the body diode of the upper semiconductor switch HS7 into the first high-voltage battery 2 and from there back to the second high-voltage battery 3.

[0029] During low-power charging, the first high-voltage battery 2 is supplied via an AC charger (not shown) or via the charging contactors 8, 9 to a DC charging station EVSE. To simultaneously charge the second high-voltage battery 3, the voltage converter 10 applies a current from the first high-voltage battery 2 to the second high-voltage battery 3. The upper semiconductor switch HS7 of the voltage converter 10 is operated in a pulsed manner for so-called buck operation. The current path to the second high-voltage battery 3 with the upper semiconductor switch HS7 closed therefore corresponds to that shown in Fig. Figure 1 shows the freewheeling choke current I2 with reversed current direction. When the upper semiconductor switch HS7 is open, a current flows from the choke L4 to the second high-voltage battery 3 and back to the choke L4 via the body diode of the lower semiconductor switch HS8. The current path to the second high-voltage battery 3 when the upper semiconductor switch HS7 is open therefore corresponds to that shown in Figure 1. Fig. 1 shown building up choke current 11 with reverse current direction.

[0030] Fig. Figure 2 is a schematic view of the electrical drive arrangement 1 during DC fast charging.

[0031] During DC fast charging, the charging contactors 8 and 9 are closed, and the first high-voltage battery 2 is directly connected to the DC charging station EVSE. Because the voltage converter 10 is designed for a low current (designed for medium power during driving), the second high-voltage battery 3 cannot be charged as quickly as the first high-voltage battery 2. To enable a higher charging current (for example, 400 A) for the second high-voltage battery 3, the inverter 5 is used. A voltage converter function is also implemented by closing the switching element 12 between the star point 11 of the electric machine 6 and one of the two terminals of the second high-voltage battery 3 (in the example shown, the positive terminal).Inverter 5 and the (stray) inductors L1, L2, L3 of the electric machine 6 also constitute a DC / DC converter, which can be used in standby mode to transfer power from the first high-voltage battery 2 to the second high-voltage battery 3 (or vice versa). The transferable current is significantly higher (for example, the inverter current is designed for 400 A).

[0032] The charging current 13 of the DC charging station EVSE is thus used partly to charge the first high-voltage battery 2 and partly, via the inverter 5 and the electric motor 6, to charge the second high-voltage battery 3. The charging currents for the first high-voltage battery 2 and the second high-voltage battery 3 can be set independently of each other, for example, by setting a current at the inverter 5 (charging current of the second high-voltage battery 3) and the preset charging current 13 at the DC charging station EVSE. The charging current of the first high-voltage battery 2 is then equal to the charging current 13 of the DC charging station EVSE minus the inverter current (charging current of the second high-voltage battery 3).

[0033] The upper semiconductor switches HS1, HS3, HS5 of inverter 5 are operated in a switching manner for so-called buck operation. When the upper semiconductor switches HS1, HS3, HS5 are closed, a building-up inductor current I1 flows from the first high-voltage battery 2 via the upper semiconductor switches HS1, HS3, HS5 and the inductors L1, L2, L3 into the second high-voltage battery 3 and back to the first high-voltage battery 2. When the upper semiconductor switches HS1, HS3, HS5 are open, a freewheeling inductor current 12 flows from the inductors L1, L2, L3 to the second high-voltage battery 3 and via the body diodes of the lower semiconductor switches HS2, HS4, HS6 of inverter 5 back to the inductors L1, L2, L3.

[0034] Fig. Figure 3 is a schematic view of the electric drive arrangement 1 during battery heating by recharging from the second high-voltage battery 3 to the first high-voltage battery 2 (impedance heating).

[0035] If a DC fast charge is to be performed spontaneously with a cold battery (i.e., without the possibility of prior battery temperature pre-charging), this charging process would take quite a long time. (For example, the charging time at a temperature of -7°C would be approximately 100 minutes instead of 20 minutes at 25°C). Pre-heating the battery by warming the coolant and thus transferring heat via a cooling plate of the respective high-voltage battery 2, 3 could reduce this time to approximately 60 minutes. The heating process still takes a relatively long time, however, because with this method the coolant must first be heated, and then the battery cells themselves must be heated via a one-sided connection to the cooler. Therefore, many thermal transitions and capacities must be taken into account with this method.

[0036] The high-voltage batteries 2, 3 can be heated more quickly by applying an AC current. The current waveform is freely selectable (for example, sine or square wave). Heating occurs at the internal resistance of the battery cells. The frequency of the AC current should be greater than 1 Hz to prevent aging of the battery cells.

[0037] In the system shown with two high-voltage batteries 2, 3, the following can be achieved by transferring power from the first high-voltage battery 2 to the second high-voltage battery 3: Fig. 2 as shown and / or from the second high-voltage battery 3 to the first high-voltage battery 2 (as shown in Fig. (3 shown) a heating of the battery cells of the two high-voltage batteries 2, 3 occurs. This process can take place during the DC charging process or also while driving.

[0038] The switching element 12 at star point 11 is closed. The second high-voltage battery 3 supplies a charging current to the first high-voltage battery 2 via the inverter 5. The lower semiconductor switches HS2, HS4, HS6 of the inverter 5 are operated in a switching manner. When the lower semiconductor switches HS2, HS4, HS6 are closed, a building-up inductor current I1 flows from the second high-voltage battery 3 through the inductors L1, L2, L3 and the lower semiconductor switches HS2, HS4, HS6 back to the second high-voltage battery 3. When the lower semiconductor switches HS2, HS4, HS6 are open, a freewheeling inductor current 12 flows from the second high-voltage battery 3 through the inductors L1, L2, L3 and the body diodes of the upper semiconductor switches HS1, HS3, HS5 into the first high-voltage battery 2 and from there back to the second high-voltage battery 3.

[0039] Fig. Figure 4 is a schematic view of another embodiment of the electric drive arrangement 1, wherein the negative high-voltage potential of the second high-voltage battery 3 is adjusted.

[0040] In the example shown, the negative terminal of the second high-voltage battery 3 is connected via the choke L4 to the center tap of the voltage converter 10 and via the switching element 12 to the star point 11 of the electric machine 6, and the positive terminal of the second high-voltage battery 3 is directly coupled to the positive terminal of the first high-voltage battery 2. Therefore, in the Fig. In the example shown in Figure 4, the negative high-voltage potential of the second high-voltage battery 3 is adjusted by the voltage converter 10, the inverter 5, and the electric machine 6 instead of the one shown in the Fig. 1 to 3 subsequent adjustment of the positive high-voltage potential of the second high-voltage battery 3. Reference symbol list 1 electric drive arrangement 2 high-voltage batteries 3 high-voltage batteries 4 electric drive 5 Inverter 6 electric machine 7 additional high-voltage components 8 charging contactor 9 Loading contactor 10 voltage converters 11 Star point 12 switching elements C capacitor EVSE DC charging station HS1, HS3, HS5, HS7 semiconductor switches, upper semiconductor switches HS2, HS4, HS6, HS8 semiconductor switches, lower semiconductor switches 11 building up choke current 12 Freewheel throttle current 13 Charging current L1, L2, L3 Inductance L4 throttle S_Main_P1, Main Contactor S_Main_N1, Main gate S_Main_P2, Main Contactor S_Main_N2 Main Contactor 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 2024 / 109887 A1

[0002]

Claims

[1] Electric drive arrangement (1) for a vehicle, comprising a first high-voltage battery (2) and a second high-voltage battery (3) each having two terminals, at least one inverter (5) having two terminals connected to the first high-voltage battery (2), and an electric machine (6), wherein the first high-voltage battery (2) has a higher DC voltage than the second high-voltage battery (3), characterized by a voltage converter (10) which is connected to the first high-voltage battery (2) and to which one of two terminals of the second high-voltage battery (3) is connected via a choke (L4), wherein the same terminal of the second high-voltage battery (3) is further connected via a switching element (12) to a star point (11) of the electric machine (6), wherein a second terminal of the second high-voltage battery (3) is connected to one of the terminals of the first high-voltage battery (2). [2] Electric drive arrangement (1) according to claim 1, characterized by , that the inverter (5) is configured as a B6 bridge consisting of six semiconductor switches (HS1 to HS6), two of which form a half-bridge with an upper semiconductor switch (HS1, HS3, HS5) and a lower semiconductor switch (HS2, HS4, HS6). [3] Electric drive arrangement (1) according to claim 1 or 2, characterized by , that the voltage converter (10) is designed as a half-bridge with an upper semiconductor switch (HS7) and a lower semiconductor switch (HS8). [4] Electric drive arrangement (1) according to one of the preceding claims, characterized by, that the electric drive arrangement (1) is configured to use the voltage converter (10) for charging and / or discharging the second high-voltage battery (3) during vehicle operation and / or to use the inverter (5) and at least one inductor (L1, L2, L3) of the electric machine (6) as a DC / DC converter for transferring power between the two high-voltage batteries (2, 3) when charging at a fast charging station and for impedance heating of at least one of the high-voltage batteries (2, 3). [5] Electric drive arrangement (1) according to one of the preceding claims, characterized by, that a positive terminal of the second high-voltage battery (3) is connected to the voltage converter (10) and can be connected to the star point (11) of the electric machine (6) via the switching element (12) and a negative terminal of the second high-voltage battery (3) is connected to a negative terminal of the first high-voltage battery (2), or that the negative terminal of the second high-voltage battery (3) is connected to the voltage converter (10) and can be connected to the star point (11) of the electric machine (6) via the switching element (12) and the positive terminal of the second high-voltage battery (3) is connected to the positive terminal of the first high-voltage battery (2). [6] Method for operating an electric drive arrangement (1) according to any one of the preceding claims, characterized by, that the voltage converter (10) is used for charging and / or discharging the second high-voltage battery (3) during vehicle operation and / or the inverter (5) and at least one inductor (L1, L2, L3) of the electric machine (6) are used as a DC / DC converter for transferring between the two high-voltage batteries (2, 3) when charging at a fast charging station and for impedance heating of at least one of the high-voltage batteries (2, 3), especially at low outside temperatures. [7] Method according to claim 6, characterized by, that a positive terminal of the second high-voltage battery (3) is connected to the voltage converter (10) and can be connected to the star point (11) of the electric machine (6) via the switching element (12), and a negative terminal of the second high-voltage battery (3) is connected to a negative terminal of the first high-voltage battery (2), wherein the switching element (12) is open during vehicle operation and the lower semiconductor switch (HS8) of the voltage converter (10) is operated in a pulsed manner to supply a charging current from the second high-voltage battery (3) to the first high-voltage battery (2), or that the negative terminal of the second high-voltage battery (3) is connected to the voltage converter (10) and can be connected to the star point (11) of the electric machine (6) via the switching element (12), and the positive terminal of the second high-voltage battery (3) is connected to the positive terminal of the first high-voltage battery (2).wherein the switching element (12) is opened during vehicle operation and the upper semiconductor switch (HS7) of the voltage converter (10) is operated in a pulsed manner to supply a recharging current from the second high-voltage battery (3) to the first high-voltage battery (2). [8] Method according to claim 6 or 7, characterized by, that a positive terminal of the second high-voltage battery (3) is connected to the voltage converter (10) and can be connected to the star point (11) of the electric machine (6) via the switching element (12), and a negative terminal of the second high-voltage battery (3) is connected to a negative terminal of the first high-voltage battery (2), wherein, when charging at a low-power DC charging station (EVSE), the switching element (12) is open and the voltage converter (10) induces a current from the first high-voltage battery (2) to the second high-voltage battery (3) by operating the upper semiconductor switch (HS7) of the voltage converter (10) in a switching manner, or that the negative terminal of the second high-voltage battery (3) is connected to the voltage converter (10) and can be connected to the star point (11) of the electric machine (6) via the switching element (12), and the positive terminal of the second high-voltage battery (3) is connected to the positive terminal of the first high-voltage battery (2).where, during charging at a low-power DC charging station (EVSE), the switching element (12) is open and the voltage converter (10) induces a current from the first high-voltage battery (2) to the second high-voltage battery (3) by operating the lower semiconductor switch (HS8) of the voltage converter (10) in a pulsed manner. [9] Method according to any one of claims 6 to 8, characterized by, that a positive terminal of the second high-voltage battery (3) is connected to the voltage converter (10) and can be connected to the star point (11) of the electric machine (6) via the switching element (12), and a negative terminal of the second high-voltage battery (3) is connected to a negative terminal of the first high-voltage battery (2), wherein, for fast charging at a DC charging station (EVSE), the switching element (12) is closed and one, several, or all of the upper semiconductor switches (HS1, HS3, HS5) of the inverter (5) are operated in a switching manner, or that the negative terminal of the second high-voltage battery (3) is connected to the voltage converter (10) and can be connected to the star point (11) of the electric machine (6) via the switching element (12), and the positive terminal of the second high-voltage battery (3) is connected to the positive terminal of the first high-voltage battery (2), wherein, for fast charging at a DC charging station (EVSE), the switching element (12) is closed and a,several or all of the lower semiconductor switches (HS2, HS4, HS6) of the inverter (5) are operated in a switching manner. [10] Method according to any one of claims 6 to 9, characterized by, that a positive terminal of the second high-voltage battery (3) is connected to the voltage converter (10) and can be connected to the star point (11) of the electric machine (6) via the switching element (12), and a negative terminal of the second high-voltage battery (3) is connected to a negative terminal of the first high-voltage battery (2), wherein, for impedance heating by inducing an AC current from the first high-voltage battery (2) into the second high-voltage battery (3), the switching element (12) is closed and one, several, or all of the upper semiconductor switches (HS1, HS3, HS5) of the inverter (5) are operated in a switching manner, or that the negative terminal of the second high-voltage battery (3) is connected to the voltage converter (10) and can be connected to the star point (11) of the electric machine (6) via the switching element (12), and the positive terminal of the second high-voltage battery (3) is connected to the positive terminal of the first high-voltage battery (2).wherein, for impedance heating, the switching element (12) is closed by injecting an AC current from the second high-voltage battery (3) into the first high-voltage battery (2), and one, several, or all of the lower semiconductor switches (HS2, HS4, HS6) of the inverter (5) are operated in a switching manner.

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