Method for operating a high-voltage system

Abstract

The invention relates to a method for operating a high-voltage system (1) for an electrically operated vehicle, wherein the high-voltage system (1) comprises at least one high-voltage battery (2) formed by two battery elements (2.1, 2.2) connected electrically in series, at least one electric machine (4) having three stator windings (L1, L2, L3), and at least one inverter (3) for converting a DC voltage from the high-voltage battery (2) into a three-phase AC voltage for supplying the electric machine (4), wherein the inverter (3) has three half-bridges each having an upper semiconductor switch (S1, S3, S5) and a lower semiconductor switch (S2, S4, S6), wherein the high-voltage battery (2) has a battery centre tap (6) between the battery elements (2.1, 2.2), wherein the stator windings (L1, L2, L3) are interconnected to form a neutral point (5), wherein the battery centre tap (6) is couplable to the neutral point (5) by a first switching element (S_MA), wherein either a second switching element (S_DC_400_P) is arranged between the neutral point (5) and the positive charging connection (DC_P) or a second switching element (S_DC_400_N) is arranged between the neutral point (5) and the negative charging connection (DC_N), wherein additionally a third switching element (S_DC_800_P) is arranged between a positive charging connection (DC_P) and a positive pole of the high-voltage battery (2), wherein a fourth switching element (S_DC_N) at a negative high-voltage potential (HV-) is arranged between a negative charging connection (DC_N) and a negative pole of the high-voltage battery (2), wherein the high-voltage system (1) is operated in an operating state with simultaneous DC boost charging of the high-voltage battery (2) at a charging station (10) with a voltage that is lower than a voltage of the high-voltage battery (2) and charge transfer between the battery elements (2.1, 2.2), wherein the first switching element (S_MA), the second switching element (S_DC_400_P) and t

Description

[0001] Mercedes-Benz Group AG

[0002] Method for operating a high-voltage system

[0003] The invention relates to a method for operating a high-voltage system according to the preamble of claim 1.

[0004] One requirement for a battery electric vehicle with a voltage level of more than 500V (for example 800V) is the ability to raise the output voltage of a charging station to the voltage level of the high-voltage battery.

[0005] Another objective is to warm a cold high-voltage battery as quickly as possible before DC charging, so that it can accept the desired charging currents. For this purpose, a provided battery center tap between two electrically series-connected sub-batteries of the high-voltage battery allows one sub-battery to be charged into the other, and vice versa.

[0006] CN 118269716 A describes a charging system, a charging control method, electronic equipment, and a vehicle, wherein the charging system comprises a motor coil, an electrical motor control module, a boost-buck circuit module, and a control module, the first end of which is connected to the positive electrode end of a battery pack, the second end to which is connected to the negative electrode end, and the third end to the motor coil. The boost-buck circuit module is used to control the connection state of the battery pack and the motor coil, wherein the first and second ends of the boost-buck circuit module are suitable for being connected accordingly to the first and second ends of a power supply device, the second end of which is also connected to the negative electrode end of the battery pack, and the third end to the neutral point of the motor coil.The control module is used to control the charging voltage of the power supply unit for the battery pack. Additionally, the control module is connected to both the engine control module and the boost-buck circuit module and is used to control these two modules for charging the battery pack.

[0007] From DE 10 2022 211479 A1, a device for charging a battery is known, comprising an inverter which has: DC connection terminals having a positive terminal and a negative terminal, several motor connection terminals configured for connection to an electric motor, wherein the electric motor has several windings, each having a first end and a second end, wherein the first end of each winding is electrically connectable to a respective motor connection terminal, and the second ends of the windings are electrically connected to each other in such a way as to form a star point, and several switching elements configured to establish an electrical connection between the DC connection terminals and the several motor connection terminals, and a capacitor electrically connected to the DC connection terminals.wherein the capacitor has two capacitor elements connected in series which are electrically connected to each other at a center tap point, wherein a first capacitor element of the two capacitor elements is connected between the positive terminal and the center tap point, a second capacitor element of the two capacitor elements is connected between the center tap point and the negative terminal, the positive terminal and the negative terminal are electrically connectable to the battery, and the center tap point is electrically connected to a branch point, wherein the branch point is electrically connectable only to the star point and to a charging source positive terminal of a charging source.

[0008] From DE 10 2022 127 780 A1, a method for electrical energy transfer between a pair of series-connected batteries coupled between the positive and negative DC busbars of an inverter, which is operationally coupled to a plurality of stator phase windings of a stator winding of a motor, is known, comprising: coupling a midpoint of the pair of series-connected batteries to the stator winding of the motor; and controlling the inverter to operate the inverter and the stator winding as a switched-mode power converter to charge at least one of the stator phase windings from one of the two series-connected batteries and to discharge the at least one of the stator phase windings to the other of the two series-connected batteries.

[0009] From US Patent 2023 / 0327596, a power conversion device is known, comprising a rotating electric machine having star-connected windings, an inverter having series-connected units with upper branch switches and lower branch switches, a connecting path electrically connecting a negative terminal of a first electrical storage device, a positive terminal of a second electrical storage device connected in series with the first electrical storage device, and a star point of the windings, a connecting switch arranged in the connecting path and serving to establish an electrical connection of the negative terminal of the first electrical storage device, the positive terminal of the second electrical storage device, and the star point when the connecting switch is open, and likewise the electrical connection of the negative terminal of the first electrical storage device.to interrupt the positive connection of the second electrical storage and the star point when the connecting switch is off, a determining unit that serves to determine whether it is necessary to switch on the connecting switch, and a control that switches on the connecting switch when the determining unit determines that switching on the connecting switch is necessary to perform a switching control operation on the upper branch switches and the lower branch switches.

[0010] The invention is based on the objective of providing a novel method for operating a high-voltage system.

[0011] The problem is solved according to the invention by a method for operating the high-voltage system with the features of claim 1.

[0012] Advantageous embodiments of the invention are the subject of the dependent claims.

[0013] A method for operating a high-voltage system for an electrically powered vehicle is proposed, wherein the high-voltage system comprises at least one high-voltage battery formed from two electrically connected partial batteries, at least one electric machine with three stator windings, and at least one inverter for converting a DC voltage from the high-voltage battery into a three-phase AC voltage for supplying the electric machine, wherein the high-voltage battery has a battery center tap between the partial batteries, wherein the stator windings are connected to form a star point, and wherein the battery center tap can be coupled to the star point by a first switching element.In this case, either a second switching element is arranged between the star point and the positive charging terminal or a second switching element is arranged between the star point and the negative charging terminal, wherein a third switching element is further arranged between a positive charging terminal and a positive pole of the high-voltage battery, wherein a fourth switching element is arranged in a negative high-voltage potential between a negative charging terminal and a negative pole of the high-voltage battery.

[0014] The high-voltage system can be configured for operation in a DC boost charging mode, where the high-voltage battery is charged at a charging station with a voltage lower than the high-voltage battery's voltage, with or without recharging between the sub-batteries (e.g., for temperature control). In this operating mode, the first, second, and fourth switching elements are closed, and the third switching element is open.

[0015] Furthermore, the high-voltage system can be configured for operation in an operating state for DC charging of the high-voltage battery at a charging station with a voltage that is at least as high as the voltage of the high-voltage battery, in which the first switching element and the second switching element are open, and the third switching element and the fourth switching element are closed.

[0016] Furthermore, the high-voltage system can be configured for operation in a DC boost charging state of the high-voltage battery at a charging station with a voltage lower than the voltage of the high-voltage battery, in which the first switching element and the third switching element are open, and the second switching element and the fourth switching element are closed.

[0017] Furthermore, the high-voltage system can be configured for operation in a DC charging state for the high-voltage battery at a charging station with a voltage at least as high as the voltage of the high-voltage battery, with transferring between the sub-batteries, in which the first and third switching elements are closed and the second and fourth switching elements are open. Furthermore, the high-voltage system can be configured for operation in a driving state in which the first, second, third, and fourth switching elements are open.

[0018] Furthermore, the high-voltage system can be configured for operation in an operating state for driving the vehicle with recharging between the partial batteries, in which the first switching element is closed, the second switching element, the third switching element and the fourth switching element are open.

[0019] In one embodiment, the first switching element is located inside the high-voltage battery.

[0020] The inverter has three half-bridges, each with an upper semiconductor switch and a lower semiconductor switch. Each stator winding is connected to one of the center taps of the half-bridges.

[0021] According to the invention, the method for operating the high-voltage system described above is provided for in an operating state with simultaneous DC boost charging of the high-voltage battery at a charging station with a voltage lower than the voltage of the high-voltage battery and transferring power between the sub-batteries. According to the invention, for this purpose, the first switching element, the second switching element, and the fourth switching element are closed, and the third switching element is opened. The second sub-battery is charged by directly connecting the charging station via the first and second switching elements. One, several, or all of the lower semiconductor switches are operated in a pulsed manner for transferring power from the second sub-battery to the first sub-battery. Furthermore, one, several, or all of the upper semiconductor switches are operated in a pulsed manner for transferring power from the first sub-battery to the second sub-battery.

[0022] In one embodiment, the lower semiconductor switches and the upper semiconductor switches are operated alternately or simultaneously in opposite phase.

[0023] In one embodiment, a current integral of a current for the transfer from the second sub-battery to the first sub-battery and / or for the transfer from the first sub-battery to the second sub-battery is set by adjusting a duty cycle of a pulse-width modulated signal for the clocking control of the semiconductor switches.

[0024] In one embodiment, for simultaneous charging of the first partial battery, the current integral set by clocking the lower semiconductor switches is chosen to be larger than the current integral set by clocking the upper semiconductor switches.

[0025] In the high-voltage system, the neutral point of the electric motor can be connected via two switching elements to either the battery's center tap, one pole of the DC charging port, or both simultaneously. This allows one battery half to be directly connected to the charging station and charged. The (bidirectional) boost function allows the inverter to superimpose an additional current on this charging current, which flows through both battery halves. This freely selectable current can be either DC or AC. Together with the controllable current of the DC charging station and the adjustable inverter current, the DC charging current and the AC transfer current for both battery halves can be set.

[0026] The present invention makes it possible to heat the battery using an inverter in the vehicle via the impedance heating method and simultaneously perform the boost function.

[0027] A high-voltage system is presented in which both impedance heating and boosting of the charging voltage via the inverter and the electric machine are possible (even simultaneously).

[0028] Both the inverter and the connection to the neutral point of the electric motor can be used synergistically for impedance heating and boosting functions. Apart from the switching element at the battery center tap and the connection from the neutral point to a DC charging terminal, no additional switching elements are required.

[0029] Exemplary embodiments of the invention are explained in more detail below with reference to drawings.

[0030] This shows:

[0031] Fig. 1 shows a schematic circuit diagram of a high-voltage system of an electrically operated device.

[0032] Vehicle with a battery, an electric motor and an inverter that can be used as a boost DC / DC converter to charge the battery, Fig. 2 a schematic circuit diagram of another embodiment of a

[0033] High-voltage system of an electrically powered vehicle with a battery consisting of two electrically connected partial batteries, an electric machine and an inverter that can be used for charging between the partial batteries,

[0034] Fig. 3 shows a schematic circuit diagram of another embodiment of a

[0035] High-voltage system of an electric vehicle with a battery consisting of two electrically connected partial batteries, an electric machine and an inverter that can be used both as a boost DC / DC converter for charging the battery and for charging between the partial batteries,

[0036] Fig. 4 shows a schematic circuit diagram of the high-voltage system from Figure 3 in a

[0037] Operating state DC charging at 400 V and impedance heating, showing a current from one charging station to the second partial battery,

[0038] Fig. 5 shows a schematic circuit diagram of the high-voltage system from Figure 3 in a

[0039] Operating state DC charging at 400 V and impedance heating, where a current is shown during the transfer of the first partial battery from the second partial battery,

[0040] Fig. 6 shows a schematic circuit diagram of the high-voltage system from Figure 3 in a

[0041] Operating state DC charging at 400 V and impedance heating, where a current is shown during the transfer of the second partial battery from the first partial battery, and

[0042] Fig. 7 shows a schematic circuit diagram of another embodiment of the

[0043] High-voltage system.

[0044] Corresponding parts are marked with the same reference symbols in all figures.

[0045] Figure 1 is a schematic circuit diagram of a high-voltage system 1 of an electrically powered vehicle, for example, a passenger car, a commercial vehicle, or a bus. The high-voltage system 1 comprises at least one high-voltage battery 2, at least one inverter 3, and at least one electric machine 4, which is symbolized here by three stator windings LI, L2, L3. The inverter 3 comprises, for example, semiconductor switches S1 to S6, in particular three half-bridges, each with a high-side switch S1, S3, S5 and a low-side switch.

[0046] Switches S2, S4, S6. The semiconductor switches S1 to S6 can be designed, for example, as MOSFETs or IGBTs. One requirement for a battery electric vehicle with a voltage level above 500V (e.g., 800V) is the ability to boost the output voltage of a charging station 10 to the voltage level of the high-voltage battery 2. One way to achieve this is by boosting via the electric machine 4 and the inverter 3. In this process, a neutral point 5 of the electric machine 4 is made accessible. The stray inductance of the electric machine 4, together with the inverter 3, acts as a boost DC / DC converter.Since the charging power via inverter 3 is limited by the maximum current of the stator windings LI, L2, L3 of the electric machine 4 and the maximum heat dissipation of the semiconductor switches S1 to S6 of inverter 3, it is advantageous to use a bypass contactor S_DC_800_P between a positive charging terminal DC_P and a positive terminal of the high-voltage battery 2 for charging at 800 V. This bypass contactor allows inverter 3 to be bypassed at a positive high-voltage potential HV+. Thus, when charging at 800 V, the charging station is directly coupled to the high-voltage battery 2 via this bypass contactor S_DC_800_P. Furthermore, a contactor S_DC_N can be arranged at a negative high-voltage potential HV- between a negative charging terminal DC_N and a negative terminal of the high-voltage battery 2. The maximum charging current is then limited only by the design of the connections, the contactors S_DC_800_P and S_DC_N, or the charging capacity of the high-voltage battery 2.This maximum charging current is usually higher than when the current is routed through the electric machine 4 and the inverter 3 when charging at 800 V.

[0047] Another contactor S_DC_400_P can be arranged between the star point 5 and the positive charging terminal DC_P. Furthermore, the high-voltage battery can have two main battery contactors, S_Main_P and S_Main_N.

[0048] Figure 2 is a schematic circuit diagram of another embodiment of a high-voltage system 1 of an electrically powered vehicle, which is similar to the high-voltage system 1 from Figure 1.

[0049] Another objective is to heat a cold high-voltage battery 2 as quickly as possible before DC charging so that it can accept the desired charging currents. For this purpose, a battery center tap 6 is provided between two electrically series-connected sub-batteries 2.1, 2.2 of the high-voltage battery 2. This allows one sub-battery 2.1 to be transferred to the other sub-battery 2.2 and vice versa. The frequency of the alternating current flowing during this process must be less than 1 kHz to avoid reducing the lifespan of the high-voltage battery 2 (typically 10 Hz to 100 Hz). This generates waste heat at the resistive components of the battery cells, which directly warms the battery cells. The inverter 3, including the tap at the star point 5, serves as the means for transferring the charge between the halves 2.1, 2.2.

[0050] The aim of the invention is to provide a high-voltage system 1 that enables the two vehicle functions according to Figures 1 and 2 simultaneously (DC boosting and impedance heating) and requires as few additional components as possible.

[0051] Figure 3 is a schematic circuit diagram of another embodiment of a high-voltage system 1 of an electrically powered vehicle, for example, a passenger car, a commercial vehicle, or a bus. The high-voltage system 1 comprises at least one high-voltage battery 2 formed from two electrically series-connected partial batteries 2.1, 2.2, at least one inverter 3, and at least one electric machine 4, which is symbolized here by three stator windings LI, L2, L3. The inverter 3 comprises, for example, semiconductor switches S1 to S6, in particular three half-bridges, each with a high-side switch S1, S3, S5 and a low-side switch S2, S4, S6. The semiconductor switches S1 to S6 can, for example, be designed as MOSFETs or IGBTs. The high-voltage battery 2 has a battery center tap 6 between the two electrically series-connected partial batteries 2.1, 2.2.

[0052] The electric machine 4 has an accessible tap at a star point 5 of the stator windings LI, L2, L3. The battery center tap 6 can be connected to the star point 5 via a switching element S_MA. This switching element S_MA is located inside the high-voltage battery 2 to meet HV safety requirements. Furthermore, the high-voltage battery 2 has a main battery contactor S_Main_P at the positive terminal and a main battery contactor S_Main_N at the negative terminal. The high-voltage battery 2 may also include other elements such as fuses, voltage and current measuring devices, and / or a pre-charging circuit, which are not relevant to the description of the invention.

[0053] Other possible components of the high-voltage system 1, such as an on-board charger, at least one on-board power supply converter, or air conditioning components, are not shown. They are usually supplied via the main battery contactors S_Main_P and S_Main_N.

[0054] A bypass contactor S_DC_800_P is arranged between a positive charging terminal DC_P and a positive terminal of the high-voltage battery 2 to bypass inverter 3 at a positive high-voltage potential HV+. Furthermore, a contactor S_DC_N is arranged at a negative high-voltage potential HV- between a negative charging terminal DC_N and a negative terminal of the high-voltage battery 2. Another contactor S_DC_400_P is arranged between the neutral point 5 and the positive charging terminal DC_P.

[0055] The switch positions of contactors S_DC_400_P, S_DC_800_P, and S_DC_N allow switching between the vehicle states of DC charging, DC charging with voltage boost, battery heating (impedance heating), and driving. It is also possible to perform some functions simultaneously, for example, impedance heating and DC charging with boost. This is shown in the following overview table:

[0056] During DC charging at 400 V with boost function, both sub-batteries 2.1 and 2.2 are charged evenly via inverter 3 and electric motor 4. During DC charging at 400 V without boost function, the second sub-battery 2.2 is charged directly from charging station 10. Both sub-batteries 2.1 and 2.2 are also charged via inverter 3 and electric motor 4. In all operating states listed in the table above, the main contactors S_Main_P and S_Main_N are closed. Therefore, they are not listed separately in the table. In another operating state, "Vehicle deactivated / parked," all switching elements S_DC_400_P, S_DC_800_P, S_DC_N, and S_MA, and optionally also the main contactors S_Main_P and S_Main_N, are open. This operating state is also not listed in the table above.

[0057] Considering the switch positions for operating states 1, 2, 3, 4, 6, and 7, the resulting systems are identical to those shown in Figures 1 and 2. Operating state 5 is a special case and will be described in more detail below.

[0058] Figure 4 is a schematic circuit diagram of the high-voltage system 1 from Figure 3 in operating state 5 – DC charging at 400 V and impedance heating. At a junction 7 of the connection between the neutral point 5 of the electric machine 4, the battery center tap 6, and the connection to the charging station 10, the sum of all partial currents is always zero. During a charging process, the current from the charging station 10 is directed towards this junction 7 (during a discharging process from the high-voltage battery 2 to the charging station 10, the current from this junction 7 is directed towards the charging station 10). From junction 7 onwards, this current divides into partial currents via the battery center tap 6 and via the inverter 3 and the electric machine 4. The current via the inverter 3 and the electric machine 4 can be adjusted by the switching and / or control of the inverter 3. The current can also change its polarity depending on the setting.The electricity coming from charging station 10 can be commanded to a predetermined limit value by communication between the vehicle and charging station 10.

[0059] Figure 4 shows a current II which is used to charge the second partial battery 2.2 by directly coupling the charging station 10.

[0060] Figure 5 is a schematic circuit diagram of the high-voltage system 1 from Figure 3 in operating state 5 - DC charging at 400 V and impedance heating during charging of the first partial battery 2.1 from the second partial battery 2.2.

[0061] By switching the lower semiconductor switches S2, S4, S6 of inverter 3, the second sub-battery 2.2 is recharged into the first sub-battery 2.1. When the lower semiconductor switches S2, S4, S6 are closed, a positive current 12 flows from the battery center tap 6 to the neutral point 5 of the electric machine 4 via the stator windings LI, L2, L3 and the lower semiconductor switches S2, S4, S6 back to the second sub-battery 2.2. The current 12 increases during this process. When the lower semiconductor switches S2, S4, S6 are open, a positive current 13, driven by the energy in the stator windings LI, L2, L3, flows from the battery center tap 6 to the neutral point 5 of the electric machine 4 via the stator windings LI, L2, L3 and the freewheeling paths of the upper semiconductor switches S1, S3, S5 back to the first sub-battery 2.1. Current 13 weakens in the process.

[0062] Figure 6 is a schematic circuit diagram of the high-voltage system 1 from Figure 3 in operating state 5 - DC charging at 400 V and impedance heating when charging the second partial battery 2.2 from the first partial battery 2.1.

[0063] By switching the upper semiconductor switches Sl, S3, S5 of inverter 3, the first sub-battery 2.1 is recharged into the second sub-battery 2.2. When the upper semiconductor switches Sl, S3, S5 are closed, a negative current 12 flows from the battery center tap 6 to the neutral point 5 of the electric machine 4 via the stator windings LI, L2, L3 and the upper semiconductor switches Sl, S3, S5 back to the first sub-battery 2.1. The current 12 increases during this process. When the upper semiconductor switches Sl, S3, S5 are open, a negative current 13, driven by the energy in the stator windings LI, L2, L3, flows from the battery center tap 6 to the neutral point 5 of the electric machine 4 via the stator windings LI, L2, L3 and the freewheeling paths of the lower semiconductor switches S2, S4, S6 to the second sub-battery 2.2. The current 13 decreases during this process.

[0064] Simultaneous boosting and impedance heating corresponds to the superposition of the charging current of charging station 10 with the transfer current.

[0065] Charging the vehicle with simultaneous boost function and impedance heating can thus be understood as a superposition of the DC charging current from charging station 10 to the second sub-battery 2.2 and a simultaneous switching between charging from the first sub-battery 2.1 to the second sub-battery 2.2 and vice versa. If the two current integrals of the AC component are equal, then on average only the second sub-battery 2.2 is charged. For simultaneous charging of the first sub-battery 2.1, the current integral in the state shown in Figure 5 (charging the first sub-battery 2.1 from the second sub-battery 2.2) must be larger than the current integral of the state shown in Figure 6.

[0066] Figure 7 is a schematic circuit diagram of an alternative embodiment of the high-voltage system 1. In contrast to the embodiment shown in Figures 3 to 6, in which the inverter 3 and the electric machine 4 are used to increase the positive high-voltage potential HV+ between the charging station 10 and the high-voltage battery 2, in the alternative embodiment according to Figure 7 the adjustment of the negative high-voltage potential HV- can be carried out by the inverter 3 and the electric machine 4. Instead of the contactor S_DC_400_P, the embodiment according to Figure 7 has a contactor S_DC_400_N, which is arranged between the neutral point 5 and the negative charging terminal DC_N.

[0067] Reference symbol list

[0068] 1 High-voltage system

[0069] 2 high-voltage batteries

[0070] 2.1, 2.2 Partial battery

[0071] 3 Inverter

[0072] 4 Machine

[0073] 5 Star Point

[0074] 6 Battery center tap

[0075] 7 Junction

[0076] 10 charging stations

[0077] DC_P, DC_N charging port

[0078] HV+, HV- High-voltage potential

[0079] II, 12, 13 Current

[0080] LI, L2, L3 Stator winding

[0081] S1 to S6 semiconductor switches

[0082] S_DC_400_P Contactor, switching element

[0083] S_DC_400_N Contactor, switching element

[0084] S_DC_800_P Contactor, Bypass Contactor, Switching Element

[0085] S_DC_N contactor, switching element

[0086] S_MA switching element

[0087] S_Main_P, S_Main_N Battery main contactor

Claims

Mercedes-Benz Group AG Patent claims 1. Method for operating a high-voltage system (1) for an electrically powered vehicle, wherein the high-voltage system (1) comprises at least one high-voltage battery (2) formed from two electrically connected partial batteries (2.1, 2.2), at least one electric machine (4) with three stator windings (LI, L2, L3), and at least one inverter (3) for converting a DC voltage from the high-voltage battery (2) into a three-phase AC voltage for supplying the electric machine (4), wherein the inverter (3) comprises three half-bridges, each with an upper semiconductor switch (S1, S3, S5) and each with a lower semiconductor switch (S2, S4, S6), wherein the high-voltage battery (2) has a battery center tap (6) between the partial batteries (2.1, 2.2), wherein the stator windings (LI, L2, L3) are connected to form a star point (5), and wherein the battery center tap (6) is connected by a first switching element (S_MA) to star point (5) can be coupled,wherein either a second switching element (S_DC_400_P) is arranged between the star point (5) and the positive charging terminal (DC_P) or a second switching element (S_DC_400_N) is arranged between the star point (5) and the negative charging terminal (DC_N), wherein furthermore a third switching element (S_DC_800_P) is arranged between a positive charging terminal (DC_P) and a positive terminal of the high-voltage battery (2), wherein a fourth switching element (S_DC_N) is arranged in a negative high-voltage potential (HV-) between a negative charging terminal (DC_N) and a negative terminal of the high-voltage battery (2), characterized in that the high-voltage system (1) is operated in an operating state with simultaneous DC boost charging of the high-voltage battery (2) at a charging station (10) with a voltage lower than the voltage of the high-voltage battery (2), and recharging between the partial batteries (2.1, 2.2), wherein the first switching element (S_MA),the second switching element (S_DC_400_P) and the fourth switching element (S_DC_N) are closed and the third switching element (S_DC_800_P) is or will be open, with the second, The sub-battery (2.2) is charged by direct coupling of the charging station (10) via the first switching element (S_MA) and the second switching element (S_DC_400_P), wherein the lower semiconductor switches (S2, S4, S6) are operated in a switching manner for a transfer from the second sub-battery (2.2) to the first sub-battery (2.1) and / or wherein the upper semiconductor switches (S1, S3, S5) are operated in a switching manner for a transfer from the first sub-battery (2.1) to the second sub-battery (2.2).

2. Method according to claim 1, characterized in that the lower semiconductor switches (S2, S4, S6) and the upper semiconductor switches (S1, S3, S5) are operated alternately or simultaneously in opposite phase.

3. Method according to claim 1 or 2, characterized in that a current integral of a current (12, 13) for the transfer from the second partial battery (2.2) to the first partial battery (2.1) and / or for the transfer from the first partial battery (2.1) to the second partial battery (2.2) is set by adjusting a duty cycle of a pulse width modulated signal for the clocking control of the semiconductor switches (S1 to S6).

4. Method according to claim 3, characterized in that for simultaneous charging of the first partial battery (2.1) the current integral set by clocking the lower semiconductor switches (S2, S4, S6) is selected to be larger than the current integral set by clocking the upper semiconductor switches (S1, S3, S5).

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