Electric drive system with two inverters connected in series and method for its operation, as well as electrically driven vehicle with such an electric drive system

Abstract

The invention relates to an electric drive system (1) for a vehicle, comprising at least two electric machines (3.1, 3.2) each having three stator windings (L1 to L6) for driving the vehicle, at least one high-voltage battery (2) and two inverters (4.1, 4.2) for converting a direct voltage of the high-voltage battery (2) into an alternating voltage for supplying one of the electric machines (3.1, 3.2), wherein the inverters (4.1, 4.2) can be connected in series with one another and can be controlled and / or regulated in such a way that one of the inverters (4.1, 4.2) with the electric machine (3.1, 3.2) connected thereto can be used as a bidirectional DC / DC converter for supplying the other inverter (4.1, 4.2) with a voltage which is lower than the direct voltage of the high-voltage battery (2) or for recuperating energy from the battery connected to the other inverter (4.1, 4.2). electrical machine (3.1, 3.2).

Description

The invention relates to an electric drive system according to the preamble of claim 1, a method for operating the same according to the preamble of claim 3 and an electrically driven vehicle according to the preamble of claim 8.In driving electric powered vehicles at low powers and / or speeds, the efficiency in the inverter is determined by the switching losses that are dependent on the DC operating voltage.The losses in the inverter are divided into switching losses and forward losses. The switching losses thereby exhibit a dependence on the high-voltage DC voltage to be switched, i.e. the higher this voltage, the greater the switching losses. In addition, during each switching operation, a certain switching energy is released as a loss in the form of heat. It can thus also be seen that the switching loss power of the inverter during operation is proportional to the clock frequency of the inverter.The following measures are known in the prior art for reducing the losses:Faster switching on and off of the semiconductors:Specifically, by using new semiconductors such as SiC and GaN transistors, the turn-on and turn-off operation can be made faster, thereby reducing the product of the current and the applied voltage over the time of the switching operation. A disadvantage here is that faster switching processes generate higher-frequency EMC disturbances and more stress the insulation of the stator windings. In addition, SiC semiconductors (mainly used for 800V HV DC voltages) are considerably more expensive than IGBTs.varying the DC operating voltage of the inverter by a DC / DC converter connected upstream: the converter can optimize the operating voltage of the inverter depending on the operating point and thus achieve an efficiency advantage in the inverter. The disadvantage here is that this additional device is large, heavy and expensive.lowering the clock frequency at certain operating points: reducing the clock frequency at some operating points results in a lower number of switching operations per unit time. This automatically leads to a reduction of the switching losses (on-state losses remain unchanged therefrom). A disadvantage here is that, as the clock frequency is lowered, the voltage swing at the intermediate circuit capacitor is increased (AC component increases). This results in a larger voltage ripple generated by the inverter. Either all other components are designed for functionality at an increased voltage ripple or the intermediate circuit capacitor in the inverter must be increased in size in order to still meet the existing ripple requirements at a reduced clock frequency.DE 10 2021 003 882 A1 describes an electric drive system for a vehicle, witha first electric three-phase machine and a second electric three-phase machine for driving at least one drive axle of the vehicle,an electrical energy store for electrically supplying the first and second three-phase electrical machines during a driving operation of the vehicle, wherein a first inverter of the first three-phase electrical machine and a second inverter of the second three-phase electrical machine are each coupled to the electrical energy store, anda vehicle-side charging connection for electrically coupling the electrical energy store to a vehicle-external charging unit, whereina charging voltage of the vehicle-side charging connection can be converted into a supply voltage for charging the electrical energy store as a function of the first and / or second inverter.DE 10 2022 134 499 A1 discloses a vehicle drive system having a battery and having at least one drive motor and an associated inverter circuit. The vehicle drive system has two drive motors, wherein one inverter circuit is designed to actuate one drive motor. A boost circuit is connected between the battery and the inverter circuits. A switch is configured to switch a connection state of the inverter circuits with the step-up circuit between the series circuit and the parallel circuit.DE 10 2017 212 853 A1 discloses a highly integrated converter system for a motor vehicle having a drive train, wherein the drive train has a first electric motor and at least one second electric motor. The highly integrated converter system has a first inverter for the first electric motor and a second inverter for the second electric motor. In the highly integrated converter system, the first inverter is connected with two inputs to the two potentials of a battery and the two inputs of the second inverter can be connected in parallel via switches to the inputs of the first inverter.The object of the invention is to specify a novel electric drive system, a novel method for the operation thereof and a novel electrically driven vehicle.The object is achieved according to the invention by an electric drive system having the features of claim 1, a method for operating the same having the features of claim 3 and an electrically driven vehicle having the features of claim 8.Advantageous embodiments of the invention are the subject matter of the dependent claims.An electric drive system for a vehicle is proposed, having at least two electric machines each having three stator windings for driving the vehicle, at least one high-voltage battery and two inverters for converting a DC voltage of the high-voltage battery into an AC voltage for supplying one of the electric machines each. According to the invention, the inverters can be connected in series with one another and can be controlled and / or regulated in such a way that one of the inverters with the electric machine connected thereto can be operated as a bidirectional DC / DC converter for supplying the other inverter with a voltage which is lower than the DC voltage of the high-voltage battery or for recuperation of energy from the electric machine connected to the other inverter.According to the invention, a first inverter has two inputs, each of which is connected to one of two high-voltage potentials of the high-voltage battery, wherein the second inverter has two inputs, of which one is likewise connected to one of the high-voltage potentials, wherein the other input of the second inverter can be selectively connected to the first high-voltage potential of the high-voltage battery via a first switching element, wherein the first inverter has three half bridges comprising in each case two semiconductor switches connected in series between the inputs, that is to say in each case one high-side switch and in each case one low-side switch, which have in each case a center tap, to which in each case one stator winding of the electric machine is connected, wherein a second switching element is connected to the center tap of one of the half bridges, which second switching element is connected to the same input of the second inverter as the first switching element.The switching elements can be configured, for example, in each case as a contactor, a relay or a semiconductor switch.In one embodiment, the semiconductor switch or switches are embodied as a MOSFET or as an IGBT with a freewheeling diode.Furthermore, in each case an intermediate circuit capacitor can be connected between the inputs of the inverters.The second inverter can likewise have three half bridges each comprising two semiconductor switches connected in series between the inputs, each having a center tap to which a stator winding of the electric machine is connected.According to one aspect of the present invention, a method for operating the above-described electric drive system is proposed. According to the invention, the first shift element is or is closed and the second shift element is opened for operation at higher powers and / or rotational speeds, wherein the first shift element is or is opened and the second shift element is or is closed for operation at lower powers.By opening the first switching element and closing the second switching element, the first inverter together with the electric machine connected thereto can be used as a bidirectional buck DC / DC converter. Its reduced output voltage at the center tap of the half bridge connected to the second switching element is used as an input voltage for the second inverter. Thus, during travel, the DC operating voltage at the second drive formed from the second inverter and the second electric machine is lowered.In one embodiment, the first switching element is connected to the input of the first inverter, to which the high-side switches thereof are connected, wherein, when the second switching element is closed and the first switching element is open, in a buck operation, the high-side switches are operated in a clocking manner at least one of the half bridges to which the second switching element is not connected. Alternatively, the first switching element can be connected to the input of the first inverter, to which input the low-side switch thereof is connected, wherein, when the second switching element is closed and the first switching element is open, in a buck operation, the low-side switch is operated in a clocking manner at least one of the half bridges to which the second switching element is not connected.In one embodiment, the first switching element is connected to the input of the first inverter, to which the high-side switches thereof are connected, wherein, when the second switching element is closed and the first switching element is open, in a boost mode, the low-side switch is operated in a clocking manner at least one of the half bridges to which the second switching element is not connected. Alternatively, the first switching element is connected to the input of the first inverter, to which the low-side switches thereof are connected, wherein, when the second switching element is closed and the first switching element is open, in boost operation, the high-side switch is operated in a clocked manner at least one of the half bridges to which the second switching element is not connected.In one embodiment, in order to reduce losses in half bridges, of which one of the semiconductor switches is operated in a clocked manner, the respective other semiconductor switch can be switched on if the semiconductor switch operated in a clocked manner is switched off and a current flow through a freewheeling diode or body diode of the respective other semiconductor switch is detected.In one embodiment, two high-side switches or two low-side switches of two half-backs not connected to the first switching element can be operated in a clocked manner with a time offset.According to one aspect of the present invention, an electrically driven vehicle is proposed, which has the above-described electric drive system having two drives, each of which comprises one of the inverters and one of the electric machines.In one embodiment, each of the two drives can be separately coupled to a driven wheel and / or a transmission via a clutch and can be separated therefrom.According to the invention, during travel through one of the inverters and the electric machine connected thereto, the DC operating voltage at the other inverter is reduced. This is possible if the vehicle is moved at low powers and / or speeds (e.g. city traffic and cross country travel), since on the one hand driving is then carried out only with one drive and on the other hand the induced voltage in the other drive is still low. The voltage drop reduces the switching losses in the other drive. The solution according to the invention therefore enables more efficient operation of an electrically driven vehicle at lower operating voltages without influencing the behavior of the drive.Exemplary embodiments of the invention are explained in more detail below with reference to drawings.The following are shown: FIG. 1 is a schematic view of an electric drive system for an electrically driven vehicle, FIG. 2 shows a schematic view of the electric drive system in a buck operation, and FIG. 3 shows a schematic view of the electric drive system in a boost mode.Corresponding parts are provided with the same reference numerals in all figures.FIG. 1 is a schematic view of an electric drive system 1 for an electrically driven vehicle. The electric drive system 1 has at least one electric energy store 2, in particular a high-voltage battery 2, and at least two electric machines 3.1, 3.2 each having three stator windings L1, L2, L3, and L4, L5, L6, which can be supplied with energy from the high-voltage battery 2 via a respective inverter 4.1, 4.2 in order to drive the vehicle.The high-voltage battery 2 has a positive high-voltage potential HV+ and a negative high-voltage potential HV-.The vehicle can be an at least partially electrically operated vehicle such as a hybrid vehicle or electric vehicle, in particular a passenger car, a commercial vehicle or a bus.The electric machines 3.1, 3.2 for driving the vehicle can each be designed as electric three-phase machines. In particular, this electric three-phase machine is an electric motor. In particular, the electric three-phase machine can be operated in a motor mode and thus as an electric motor. In order to operate the electric three-phase machine in the motor mode, the electric three-phase machine can be supplied via its phases with an electric alternating voltage, in particular with an electric high-voltage alternating voltage. The phases of the electric three-phase machine can be connected to one another, for example, via a common star point.In order that the electric machines 3.1, 3.2 can be supplied with an alternating voltage, the electric drive system 1 and thus the vehicle has at least one high-voltage battery 2. With the aid of the high-voltage battery 2, the electric machines 3.1, 3.2 and, if appropriate, further vehicle components and / or vehicle systems and / or on-board electrical systems can be supplied with electrical energy.A battery voltage can be provided with the aid of the high-voltage battery 2. In particular, the vehicle can be a battery-operated vehicle with a voltage level of 800 volts. In this case, a voltage of substantially 800 volts can be provided by means of the battery voltage.The electric machines 3.1, 3.2 require an alternating voltage for their operating state. This alternating voltage can be provided by means of the respective inverter 4.1, 4.2. The battery voltage is converted into an alternating voltage. In particular, the AC voltage is provided for the electric machine 3.1, 3.2 by a respective primary function or main function of the inverter 4.1, 4.2.For example, the inverter 4.1, 4.2 can be respectively connected or arranged between the high-voltage battery 2 and the respective electric machine 3.1, 3.2.The inverters 4.1, 4.2 form a drive with the respectively connected electric machine 3.1, 3.2. The two drives can be located in the immediate vicinity, for example by being installed on a front axle and / or a rear axle. It is immaterial what type of inverter 4.1, 4.2 it is (2-level B6, 3-level T-type, NPC, Flying Cap etc.) It can be provided that each of the two drives can be separated from a driven wheel and / or transmission separately via a clutch. The first inverter 4.1 has two inputs E1, E2, which are each connected to one of the high-voltage potentials HV+, HV- of the high-voltage battery 2. The second inverter 4.2 likewise has two inputs E3, E4, of which one, here the input E4, is likewise connected to one of the high-voltage potentials HV+, HV- (here HV-). The other input E 3 is selectively connected to the first high-voltage potential HV+, HV- of the high-voltage battery 2 via a first switching element S 1 (for example a contactor, a relay or a semiconductor switch).The first inverter 4.1 has three half bridges HB1, HB2, HB3 each comprising two semiconductor switches connected in series between the high-voltage potentials HV+, HV-, that is to say in each case one high-side switch HS1 to HS3 and in each case one low-side switch LS1 to LS3, which each have a center tap to which in each case one stator winding L1 to L3 of the electric machine 3.1 is connected. Furthermore, an intermediate circuit capacitor C1 can be connected between the high-voltage potentials HV+, HV-. A second switching element S 2 (for example a contactor, a relay or a semiconductor switch) is connected to the center tap of one of the three half bridges HB 1 to HB 3 (here HB 3). The second switching element S2 is connected to the same input E3 of the second inverter 4.2 as the first switching element S1. The input E3 of the second inverter 4.2 can be coupled via the second switching element S2 to the center tap of the half bridge HB3 of the first inverter 4.1.By opening the switching element S 1 and closing the switching element S 2, the first inverter 4.1 together with the electric machine 4.1 connected thereto can be used as a bidirectional buck DC / DC converter. Its reduced output voltage at the center tap of half bridge HB 3 is used as an input voltage for second inverter 4.2. Thus, during travel, the DC operating voltage at the second drive formed from the second inverter 4.2 and the second electric machine 3.2 is reduced, which substantially reduces the switching losses in its inverter 4.2. As a result, the driving efficiency is increased. This is possible, for example, in situations in which the vehicle is moved at low powers and / or speeds (for example city traffic, cross country travel, slower highway travel).The second inverter 4.2 can likewise have three half bridges HB4, HB5, HB6 each comprising two semiconductor switches connected in series between the inputs E3, E4, each having a center tap to which a stator winding L4 to L6 of the electric machine 3.2 is connected. Furthermore, an intermediate circuit capacitor C 2 can be connected between the high-voltage potentials inputs E 3, E 4.Each of the semiconductor switches can be designed, for example, as a MOSFET or as an IGBT with a freewheeling diode.In a first state, the switching element S 1 is closed and the switching element S 2 is open. Thus, the first inverter 4.1 and the second inverter 4.2 are directly coupled to the high-voltage battery 2. Both inverters 4.1, 4.2 can function as drive inverters. The DC operating voltage of both inverters 4.1, 4.2 corresponds to the battery voltage of the high-voltage battery 2 (minus voltage drop across an internal resistance of the battery or across the lines, etc.). This corresponds to the typical operation of inverters 4.1, 4.2.In a second state, the switching element S 1 is open and the switching element S 2 is closed. The first inverter 4.1 now constitutes a DC / DC converter with the inductance of at least one, in particular two or three, stator windings L 1 to L 3 of the electric machine 3.1. This DC / DC converter controls and / or regulates the operating voltage of the second inverter 4.2 with its output voltage. The input voltage of the first inverter 4.1 corresponds to the battery voltage. The first inverter 4.1 is capable of both transmitting power from the high-voltage battery 2 to the second inverter 4.2 and, conversely, of transmitting power from the second inverter 4.2 to the high-voltage battery 2. It is thus bi-directional. Therefore, these two operation states will be described in more detail below.FIG. 2 is a schematic view of the electric drive system 1 in the second state in a buck operation, in which power is transmitted from the high-voltage battery 2 to the second inverter 4.2 (shown in FIG. 1 ).In this example, the high-side switch HS 1 of one of the half bridges HB 1 to which the switching element S 2 is not connected is operated in a clocked manner and the output voltage is tapped at the center tap of the third half bridge HB 3. When the high-side switch HS 1 is closed, a current 11 flows from the high-voltage battery 2 (positive high-voltage potential HV+) via the stator windings L 1 and L 3 to the second inverter 4.2 and from there via the negative high-voltage potential HV- back to the high-voltage battery 2. If a predefined upper limit value is reached in this case (for example a setpoint voltage upper limit at the second inverter 4.2 or a setpoint current upper limit of a throttle current through one of the stator windings L 1 to L 3), the high-side switch HS 1 is opened. The energy stored in the inductances of the stator windings L 1 and L 3 drives the current flow in the inductances even further. The energy gradually degrades and the current also reduces. This free-wheeling path of the current I 2 does not take place via the high-voltage battery 2 but via the free-wheeling diode or body diode of the low-side switch LS 1 of the same half bridge HB 1 in which the clocking high-side switch HS 1 is arranged. To reduce losses, the low-side switch LS 1 can be switched on as soon as a current flows through its free-wheeling diode or body diode.In this example, the high-side switch HS 2 of the half bridge HB 2 can also be switched to the conductive state in parallel with the high-side switch HS 1. Thus, the transmitted current increases in sum. The choke free-wheeling can then take place in addition to the low-side switch LS 1 in parallel also via the low-side switch LS 2 of the further half bridge HB 2. In addition, an interleaved operation is also conceivable, that is to say a clocked operation of the high-side switches HS 1, HS 2 offset in time. The current ripple in the high-voltage battery 2 and also at the output to the second inverter 4.2 can thus be reduced. In principle, in the design of the first inverter 4.1, it is freely selectable at which half bridge HB 1 to HB 3 the tap for the output voltage for the second inverter 4.2 takes place.FIG. 3 is a schematic view of the electric drive system 1 in the second state in a boost mode, in which power is transmitted from the second inverter 4.2 to the high-voltage battery 2.The power flow takes place from the second inverter 4.2 via the first drive, used as a DC / DC converter, comprising the first inverter 4.1 and the first electric machine 3.1 to the high-voltage battery 2, for example during recuperation of the vehicle. The voltage across the intermediate circuit capacitor C 2 of the second inverter 4.2 is lower than the battery voltage. In the illustrated operating mode, the low-side switch LS 1 is operated in a clocked manner. The voltage from the second inverter 4.2 is present at the center tap of the third half bridge HB 3 of the first inverter 4.1 because of the switched-on second switching element S 2 (switching element S 1 is open). When the low-side switch LS 1 is closed, a current I 1 flows from the second inverter 4.2 (positive potential at the input E 3) via the stator windings L 3 and L 1, the closed low-side switch LS 1 and the negative high-voltage potential HV- back to the second inverter 4.2. In this case, the current through the stator windings L 3, L 1 increases over time and the voltage of the intermediate circuit capacitor C 2 of the inverter 4.2 is reduced. If a limit value is reached (for example a predefined setpoint voltage lower limit at the second inverter 4.2 or a setpoint current upper limit in the case of the throttle current through the stator windings L 1, L 3), the low-side switch LS 1 is opened. The energy stored in the inductances of the stator windings L 1 and L 3 drives the current flow in the inductances even further. The energy gradually degrades and the current I2 is also reduced. This free-wheeling path of the current I 2 runs via the free-wheeling diode or body diode of the high-side switch HS 1 and the high-voltage battery 2. the high-side switch HS 1 can be switched through to reduce the losses as soon as a current is detected via the body diode or free-wheeling diode.In this example, the low-side switch LS 2 of the half bridge HB 2 can also be switched to the conductive state in parallel with the low-side switch LS 1. Thus, the transmitted current increases in sum. The choke free-wheeling can then take place in addition to the high-side switch HS 1 in parallel also via the high-side switch HS 2 of the further half bridge HB 2. In addition, an interleaved operation is also conceivable, that is to say a clocked operation of the low-side switches LS 1, LS 2 offset in time. The current ripple in the high-voltage battery 2 and also at the output to the second inverter 4.2 can thus be reduced. In principle, in the design of the first inverter 4.1, it is freely selectable at which half bridge HB 1 to HB 3 the tap for the output voltage for the second inverter 4.2 takes place.List of reference characters1 Drive system 2 Energy store, high-voltage battery 3.1, 3.2 Electric machine 4.1, 4.2 Inverters C1, C2 Intermediate circuit capacitor E1 to E4 Input HB1 to HB6 Half bridge HS1 to HS6 High-side switch HV+ High-voltage potential, positive high-voltage potential HV-High-voltage potential, negative high-voltage potential I1, I2 Current LS1 to LS6 Low-side switch L1, L2, L3, L4, L5, L6 Stator winding S1, S2 Switching element

Claims

An electric drive system (1) for a vehicle, having at least two electric machines (3.1, 3.2) each having three stator windings (L1 to L6) for driving the vehicle, at least one high-voltage battery (2) and two inverters (4.1, 4.2) for converting a DC voltage of the high-voltage battery (2) into an AC voltage for supplying one of the electric machines (3.1, 3.2) in each case, wherein the inverters (4.1, 4.2) can be connected in series with one another and a first inverter (4.1) has two inputs (E1, E2) which are each connected to one of two high-voltage potentials (HV+, HV-) of the high-voltage battery (2), wherein the second inverter (4.2) has two inputs (E3, E4), of which one, likewise to one of the high-voltage potentials (HV+, Hv-) of the high-voltage battery (2), wherein the other input (E3, E4) of the second inverter (4.2) can be selectively connected to the first high-voltage potential (HV+, HV-) of the high-voltage battery (2) via a first switching element (S1), characterized in that the inverters (4.1, 4.2) can be controlled and / or regulated in such a way that one of the inverters (4.1, 4.2) with the electrical machine (3.1, 3.2) connected thereto can be operated as a bidirectional DC / DC converter for supplying voltage to the other inverter (4.1, 4.2) with a voltage which is lower than the DC voltage of the high-voltage battery (2) or can be operated for recuperation of energy from the electrical machine (3.1, 3.2) connected to the other inverter (4.1, 4.2), wherein the first inverter (4.1) has three half bridges (HB1, HB2, HB3) each comprising two semiconductor switches connected in series between the inputs (E1, E2), that is to say in each case one high-side switch (HS1 to HS3) and in each case one low-side switch (LS1 to LS3), which each have a center tap to which in each case one stator winding (L1 to L3) of the electric machine (3.1) is connected, wherein a second switching element (S2) is connected to the center tap of one of the half bridges (HB1 to HB3), which switching element is connected to the same input (E3) of the second inverter (4.2) as the first switching element (S1).Electric drive system (1) according to Claim 1, characterized in that the semiconductor switch or switches is / are designed as a MOSFET or as an IGBT with a freewheeling diode.Method for operating the electric drive system (1) according to one of the preceding claims, characterized in that, for operation at higher powers, the first switching element (S1) is or is closed and the second switching element (S2) is or is opened, wherein, for operation at lower powers, the first switching element (S1) is or is opened and the second switching element (S2) is or is closed.Method according to Claim 3, characterized in that the first switching element (S1) is connected to the input (E1) of the first inverter (4.1), to which input its high-side switch (HS1 to HS3) is connected, wherein, when the second switching element (S2) is closed and the first switching element (S1) is open, in a buck operation, the high-side switch (HS1, HS2) of at least one of the half bridges (HB1, HB2), to which the second switching element (S2) is not connected, is operated in a clocking manner, or in that the first switching element (S1) is connected to the input (E2) of the first inverter (4.1), to which input its low-side switch (LS1 to LS3) is connected, wherein, when the second switching element (S2) is closed and the first switching element (S1) is open, in a buck operation, the low-side switch (LS1, LS2) of at least one of the half bridges (HB1, HB2) to which the second switching element (S2) is not connected is operated in a clocking manner.Method according to Claim 3 or 4, characterized in that the first switching element (S1) is connected to the input (E1) of the first inverter (4.1), to which input its high-side switch (HS1 to HS3) is connected, wherein, when the second switching element (S2) is closed and the first switching element (S1) is open, in a boost mode, the low-side switch (LS1, LS2) operates in a clocking manner at least one of the half bridges (HB1, HB2) to which the second switching element (S2) is not connected, or in that the first switching element (S1) is connected to the input (E2) of the first inverter (4.1), to which input its low-side switch (LS1 to LS3) is connected, wherein, when the second switching element (S2) is closed and the first switching element (S1) is open, in boost operation the high-side switch (HS1, HS2) of at least one of the half bridges (HB1, HB2) to which the second switching element (S2) is not connected is operated in pulsing fashion.Method according to Claim 4 or 5, characterized in that in half bridges (HB1, HB2), of which one of the semiconductor switches is operated in a clocked manner, the respective other semiconductor switch is switched on when the semiconductor switch operated in a clocked manner is switched off and a current flow through a freewheeling diode or body diode of the respective other semiconductor switch is detected.Method according to one of Claims 4 to 6, characterized in that two high-side switches (HS1, HS2) or two low-side switches (LS1, LS2) of two half-backs (HB1, HB2) which are not connected to the first switching element (S1) are operated in a clocked manner with a time offset.Electrically driven vehicle, characterized byan electric drive system (1) according to either of Claims 1 and 2 having two drives, comprising in each case one of the inverters (4.1, 4.2) and one of the electric machines (3.1, 3.2), wherein one of the inverters (4.1, 4.2) with the electric machine (3.1, 3.2) connected thereto is operable as a bidirectional DC / DC converter of the other inverter (4.1, 4.2).Electrically driven vehicle according to Claim 8, characterized in that each of the two drives can be coupled separately via a clutch to a driven wheel and / or a transmission and can be disconnected therefrom.

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