Battery system with one or more strings, each comprising several battery modules that can be connected in series, wherein at least one battery module of each string is intended to supply a low-voltage network with electrical energy.

Abstract

Battery system (10) with one or more strings (15, 16, 17), each comprising several battery modules that can be connected in series and that can be connected to the corresponding string (15, 16, 17) in at least one orientation, and a control unit (30) configured to connect the battery modules of each string (15, 16, 17) to the respective string (15, 16, 17) to connect the respective switching units to generate a single-phase or multi-phase output voltage (AW) of the battery system (10) corresponding to the number of strings (15, 16, 17), wherein a group of coupling elements (70) located in each strand (15, 16, 17) comprises a coupling element (71, 72, 73) which can be connected to at least one predefined battery module of the battery modules of the corresponding string (15, 16, 17) via the switching units assigned to it and which couples out a voltage applied by the corresponding at least one predefined battery module to the corresponding string (15, 16, 17) via the switching units assigned to it and couples it into a low-voltage network (60) if this voltage corresponds to a supply voltage for supplying the low-voltage network (60), or can couple this voltage out and into the low-voltage network (60) if this voltage corresponds to the supply voltage for supplying the low-voltage network (60), characterized in that The control unit (30) switches a counter-voltage corresponding to the voltage coupled into the low-voltage network (60) into the respective string (15, 16, 17) by means of battery modules of the respective string (15, 16, 17), of which the voltage coupled into the low-voltage network (60) is not provided.

Description

[0001] The present invention relates to a battery system with multiple strings, each comprising several battery modules that can be connected in series. The invention also relates to a method for supplying a low-voltage network by means of at least one battery module of a battery system with multiple strings, each comprising several battery modules that can be connected in series. State of the art

[0002] By connecting battery cells in series, electrochemical cells can be used to create high-capacity, high-voltage energy storage systems suitable, for example, for powering electric vehicles. Due to their high energy density, lithium-ion battery cells are currently the preferred solution.

[0003] As an example, a battery system with an integrated inverter is described here, comprising several strings, each containing multiple battery modules. Each battery module contains either a single battery cell or a network of several battery cells. In such a battery system with an integrated inverter, varying the voltage generated by each string requires a rapid change in the current flow, resulting in a corresponding current flowing through or past the respective battery module. Here, battery cells or modules are operated with currents whose current flows change at frequencies within a broad frequency range, extending into the kilohertz range. Such a battery system is also called a direct inverter battery system. A three-phase AC output voltage can be generated using a direct inverter battery system.Unlike a conventional battery system, which comprises a high-voltage energy storage unit and a central inverter that converts the DC voltage supplied by the high-voltage energy storage unit into an AC output voltage for the conventional battery system, a battery system with a direct inverter cannot use a simple DC-DC converter to generate a supply voltage for a low-voltage network. Such a low-voltage network could be, for example, a vehicle's 12 V or 48 V electrical system. The question therefore arises as to how to efficiently and cost-effectively supply electrical energy to the vehicle's electrical consumers.

[0004] Document DE 10 2013 212 716 A1 describes a system with an energy storage device and a DC power supply circuit, wherein the energy storage device has at least two power supply branches, which are each coupled at a first output to at least one output terminal of the energy storage device for generating an AC voltage at the output terminals and at a second output to a common busbar, wherein each of the power supply branches has a plurality of energy storage modules connected in series.

[0005] Document DE 10 2005 015 658 A1 describes a switching device for linking different electrical voltage levels in a motor vehicle, in which a drive voltage level has an electric drive machine controllable via a power converter and a drive energy storage device associated with an intermediate circuit, and in which the drive voltage level is connected to a vehicle electrical system voltage level via an electrical converter, wherein the electrical converter is designed as a coupling circuit which is connected on the drive side to at least one node of a winding circuit of the electric drive machine and to a voltage potential referenced to the intermediate circuit, and which is connected on the vehicle electrical system side via a switching unit which has at least one non-zero finite impedance. Disclosure of the invention

[0006] According to the invention, a battery system with one or more strings is provided, each string comprising several battery modules that can be connected in series and which can be connected to the respective string in at least one orientation. The battery system further comprises a control unit configured to connect the battery modules of each string to the respective string via switching units assigned to that string, such that a single-phase or multi-phase output voltage of the battery system is generated, corresponding to the number of strings. The battery system further comprises a group of coupling elements, comprising one coupling element in each string that can be connected to at least one predefined battery module of the battery modules of the respective string via the switching units assigned to that module or modules.Preferably, each decoupling element couples a voltage applied to the corresponding string by the corresponding at least one predefined battery module via the switching units assigned to it or these modules, and feeds it into a low-voltage network, provided this voltage corresponds to a supply voltage for the low-voltage network. Alternatively, preferably, each decoupling element can couple a voltage applied to the corresponding string by the corresponding at least one predefined battery module via the switching units assigned to it or these modules, and feed it into a low-voltage network, provided this voltage corresponds to the supply voltage for the low-voltage network. The control unit is configured to switch a counter-voltage corresponding to the voltage coupled into the respective string by means of battery modules of the respective string that do not provide the voltage coupled into the low-voltage network.

[0007] According to the invention, a method for supplying a low-voltage network by means of a battery system with one or more strings is further provided, each string comprising several battery modules that can be connected in series and which can be connected to the corresponding string in at least one orientation. The battery system further comprises a control unit configured to connect the battery modules of each string to the respective string via switching units assigned to that string, such that a single-phase or multi-phase output voltage of the battery system corresponding to the number of strings is generated.Preferably, the method involves enabling the extraction of a voltage applied to the corresponding string by at least one predefined battery module of each string via the switching units assigned to that module(s), and enabling the coupling of this voltage into the low-voltage network, provided that the voltage applied to the corresponding string by each predefined battery module corresponds to a supply voltage for the low-voltage network. The method includes the step of switching a counter-voltage corresponding to the voltage coupled into the low-voltage network into the respective string by means of battery modules of the respective string that do not supply the voltage coupled into the low-voltage network.In the method, a further preferred step involves extracting a voltage applied to the corresponding string from at least one predefined battery module of each string via the switching units assigned to it or these, and coupling this voltage into the low-voltage network, if the voltage applied to the corresponding string by each at least one predefined battery module corresponds to a supply voltage for supplying the low-voltage network.

[0008] The output voltage can be generated in the form of an alternating current (AC) or a direct current (DC) output voltage.

[0009] The dependent claims describe preferred embodiments of the invention.

[0010] Preferably, each battery module comprises at least one battery cell.

[0011] Preferably, the battery system comprises at least one further group of additional decoupling elements, each group comprising one further decoupling element in each string. Each further group of additional decoupling elements is assigned to a further low-voltage network. Furthermore, each decoupling element of a further group of additional decoupling elements is assigned at least one further predefined battery module from the battery modules of the corresponding string. The functionality of each further group of additional decoupling elements with respect to the further predefined battery modules assigned to it and the low-voltage network assigned to it is identical to the functionality previously described for the group of decoupling elements with respect to the predefined battery modules and the low-voltage network.

[0012] Preferably, all battery modules of the battery system are designed identically to each other.

[0013] A significant advantage of the invention is that the supply voltage for the low-voltage network can be generated directly by each string. This is achieved by using the coupling element of each string to tap into a voltage generated by a suitable number of predefined battery modules, thus providing the supply voltage directly via the predefined battery modules of each string. This avoids losses caused by voltage matching. Because the predefined battery modules of each string can be used to supply the low-voltage network with electrical energy via the corresponding coupling element, multiple redundant options for supplying the low-voltage network with electrical energy are available, thereby increasing the availability of the electrical energy required to supply the low-voltage network.

[0014] In a preferred embodiment of the invention, the control unit applies a voltage present at each of at least one predefined battery module to the corresponding string via the switching units assigned to these modules as a DC voltage corresponding to the supply voltage, which is coupled out via the corresponding coupling element and is or can be coupled directly into the low-voltage network.

[0015] In a further preferred embodiment of the invention, the battery system according to the invention comprises an isolation transformer via which the group of coupling elements couples the voltage applied to the corresponding string by the at least one predefined battery module and coupled out by means of the corresponding coupling element into the low-voltage network. The control unit converts a voltage applied to each of the at least one predefined battery modules, via the switching units assigned to them, into an alternating voltage applied to the corresponding string, which is coupled out via the corresponding coupling element and applied to the isolation transformer for coupling into the low-voltage network.

[0016] A very advantageous aspect of the invention is that the alternating voltage for the isolation transformer can be generated using the usual switching units of the battery system, without the need for additional switches.

[0017] Preferably, the control unit switches a counter-voltage corresponding to the voltage coupled into the low-voltage network into the respective string by means of battery modules of the respective string, which do not provide the voltage coupled into the low-voltage network.

[0018] Preferably, the control unit shifts charge from the non-predefined battery modules to the predefined battery modules by controlling the switching units of the battery modules of the corresponding string, based on a predetermined orientation of the output voltage of a string. This always occurs when the predefined battery modules are connected to the corresponding string in an orientation opposite to the predetermined orientation.

[0019] Preferably, an electric motor is operated by means of the multi-phase output voltage of the battery system according to the invention, which is generated in the form of a single or multi-phase AC output voltage. A very advantageous aspect of the invention is that, by suitable control of the switching units assigned to the battery modules of the battery system, simultaneous supply of the electric motor and the low-voltage network can be ensured, and preferably, charge state balancing between the charge states of differently loaded battery modules of the battery system can also be achieved. This allows different load situations, such as those occurring in winter and summer, to be handled optimally.By selectively charging battery modules and by shifting the charge between battery modules of each string, the total charge of the battery system according to the invention can be distributed in a desired ratio between the undefined battery modules and the predefined battery modules. No explicit recharging times are required for this.

[0020] Another aspect of the invention relates to a vehicle with a battery system according to the invention. Brief description of the drawings

[0021] Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawings. Except for exceptions that are explicitly introduced and explained, the same reference numerals are used for identical components and parameters. Each component and parameter is introduced once and, upon repetition, is treated as already known, regardless of which drawing or embodiment a corresponding descriptive section in which the respective component or parameter appears repeatedly refers to. The drawings show: Fig. 1 an arrangement comprising a battery system according to a first embodiment of the invention and a low-voltage network to be supplied with electrical energy by means of the battery system, Fig. 2 several waveforms of output alternating voltages, each shown as a function of time, each generated by a different string of the battery system in the Fig. The arrangement shown in 1 is generated in connection with a first concrete realization of this arrangement, and Fig. 3 several waveforms of output alternating voltages, each shown as a function of time, each generated by a different string of the battery system in the Fig. The arrangement shown in 1 is generated in connection with a second concrete realization of this arrangement. embodiment of the invention

[0022] Fig. Figure 1 shows an arrangement with a battery system 10 designed according to a first embodiment of the invention, including an integrated inverter. The battery system 10 comprises a first string 15, a second string 16, and a third string 17. Each string 15, 16, 17 comprises several battery module assemblies 20, each of which has a battery module (not shown separately) and a switching unit (not shown separately) associated with this battery module and controllable by means of a control unit 30 of the battery system 10. Each battery module comprises at least one battery cell (not shown). The battery modules of the battery system 10 are identical. Each switching unit is configured to bridge the battery module associated with it via two terminals 21, 22 and connect it to the corresponding string 15, 16, 17 in a negative or positive orientation.Furthermore, the control unit 30 is configured to control the switching units of each string 15, 16, 17 such that the battery modules of each string 15, 16, 17 each generate an associated AC output voltage of a three-phase AC output voltage of the battery system 10. The AC output voltage generated by the first string 15 corresponds to the first phase of the AC output voltage of the battery system 10. The AC output voltage generated by the second string 16 corresponds to the second phase of the AC output voltage of the battery system 10. The AC output voltage generated by the third string 17 also corresponds to the third phase of the AC output voltage of the battery system 10.To generate the output AC voltage assigned to each string 15, 16, 17, a time-varying number of battery modules of the corresponding string 15, 16, 17 are connected to the respective string 15, 16, 17 in at least one orientation, and the remaining battery modules of the corresponding string 15, 16, 17 are bypassed. The three strings 15, 16, 17 are each connected at one end to ground 40 and at the other end to an electric motor 50 such that the electric motor 50 can be operated by means of the three-phase output AC voltage of the battery system 10. Each switching unit is preferably designed as an H-bridge consisting of several power semiconductor switches controllable by means of the control unit 30. For the sake of simplicity, only the battery module assembly 20 for each string 15, 16, 17 that is directly connected to the electric motor 50 has been designated with the corresponding reference numeral.For the same reason, only those two terminals 21, 22 of each string 15, 16, 17 were provided with the corresponding reference numerals that are assigned to the battery module located in the battery module assembly 20 of the corresponding string 15, 16, 17, which is directly connected to the electric motor 50. Furthermore, each string 15, 16, 17 comprises a battery module usable as a power supply unit, which is a predefined battery module of the battery modules of the corresponding string 15, 16, 17 and by means of which a supply voltage for supplying a low-voltage network 60 can be provided. The battery module usable as a power supply unit of each string 15, 16, 17 is directly connected to ground 40 and, together with the switching unit assigned to it, forms a power supply unit 23 of the corresponding string 15, 16, 17, which is consequently also directly connected to ground 40.The two terminals assigned to the battery module of each string 15, 16, 17, which can be used as a power supply unit, are each designated as power supply terminals 24, 25.

[0023] The low-voltage network 60 is preferably an on-board electrical system used in a vehicle with a chassis ground. The low-voltage network 60 forms part of the system in the Fig. 1. Arrangement shown.

[0024] If no galvanic isolation of the battery system 10 and the low-voltage network 60 is required, the low-voltage network 60 is supplied with the supply voltage present at the low-voltage network 60 and generated in the form of a DC voltage.

[0025] If galvanic isolation of the battery system 10 and the low-voltage network 60 is required, the low-voltage network 60 is connected to an isolation transformer 65. The isolation transformer 65 must be supplied with an alternating voltage. The low-voltage network 60 is then supplied by means of the supply voltage applied to the isolation transformer 65, which is generated in the form of an alternating voltage. For the sake of completeness, in the Fig. 1 also the isolation transformer 65 as part of the in the Fig. The arrangement shown in 1 is illustrated.

[0026] Furthermore, the control unit 30 is configured to control the switching unit assigned to the supply unit of each string 15, 16, 17 such that the supply unit of each string 15, 16, 17 provides the supply voltage in the form of DC voltage for the low-voltage network 60 or in the form of AC voltage for the isolation transformer 65 between its two assigned supply terminals 24, 25. Preferably, the DC voltage for the low-voltage network 60 is provided by the supply unit of each string 15, 16, 17 between its assigned supply terminals 24, 25 by connecting the predefined battery module of the supply unit of the corresponding string 15, 16, 17 in a positive orientation to the corresponding string 15, 16, 17.Preferably, the supply voltage in the form of alternating voltage for the isolation transformer 65 is generated directly via the switching unit assigned to the supply unit of each string 15, 16, 17 and not via additional switches implemented in the battery system 10.

[0027] The battery system 10 further comprises a group of coupling elements 70, with a first coupling element 71 arranged in the first strand, a second coupling element 72 arranged in the second strand 16, and a third coupling element 73 arranged in the third strand 17. Each coupling element 71, 72, 73 can be configured as a diode or as a power semiconductor switch controllable by means of the control unit 30.

[0028] Preferably, the coupling element 71, 72, 73 of each strand 15, 16, 17 is designed to connect the supply terminals 24, 25 assigned to the supply unit of the corresponding strand 15, 16, 17 directly to the low-voltage network 60 when the DC voltage for the low-voltage network 60 is present and otherwise to disconnect directly from the low-voltage network 60.

[0029] Furthermore, the coupling element 71, 72, 73 of each strand 15, 16, 17 is preferably designed to connect the supply terminals 24, 25 assigned to the supply unit of the corresponding strand 15, 16, 17 to the isolating transformer 65 and thus also to the low-voltage network 60 when the alternating voltage for the isolating transformer 65 is present, and otherwise to disconnect them from the isolating transformer 65 and thus also from the low-voltage network.

[0030] Any battery module 20 of each string 15, 16, 17, which differs from the predefined battery module of the supply unit of the corresponding string 15, 16, 17 and does not have to be used to generate the instantaneous output AC voltage of the corresponding string 15, 16, 17, can also be used as a compensation unit, by means of which a compensation voltage opposite to the supply voltage can be provided. The compensation unit of each string 15, 16, 17 together with the switching unit associated with it form a compensation device 26. In the Fig. For explanatory purposes, the battery module assembly of each string 15, 16, 17 that is directly connected to the supply unit 23 of the corresponding string 15, 16, 17 is shown as the compensation unit 26 of the corresponding string 15, 16, 17 and is provided with the corresponding reference numeral. The two terminals assigned to the battery module of the compensation unit of each string 15, 16, 17 are each referred to as compensation terminals 27, 28.

[0031] If the predefined battery module of each supply unit for generating the previously defined DC voltage for the low-voltage network 60 is connected in a positive orientation to the corresponding string 15, 16, 17, then each supply unit can supply the low-voltage network 60 whenever the AC output voltage assigned to the corresponding string 15, 16, 17 for operating the electric motor 50 has a negative instantaneous voltage value whose magnitude is not too large. If the AC output voltage assigned to each string 15, 16, 17 for operating the electric motor 50 has a negative instantaneous voltage value whose magnitude is relatively large, then all battery modules of the corresponding string 15, 16, 17, that is, also the predefined battery module of the supply unit of the corresponding string 15, 16, 17, must be connected in a negative orientation to the corresponding string 15, 16, 17.This situation is only to be expected with one of the three strands 15, 16, 17 at a time, so that the low-voltage network 60 can be supplied with electrical energy simultaneously by means of one strand or even by means of two strands of the three strands 15, 16, 17, depending on the size of the supply voltage.

[0032] If galvanic isolation between the battery system 10 and the low-voltage network 60 is required, each string 15, 16, 17 can generate the AC voltage for the isolation transformer 65 whenever the output AC voltage assigned to the corresponding string 15, 16, 17 for operating the electric motor 50 assumes an instantaneous voltage value whose magnitude is not too high. Due to the generation of the AC voltage for the isolation transformer 65 by the power supply unit of each string 15, 16, 17, the output AC voltage assigned to the corresponding string 15, 16, 17 for operating the electric motor 50 would deviate from a desired curve. This effect is compensated for by connecting an arbitrary battery module of the string 15, 16, 17 whose power supply unit is instantaneously generating the supply voltage in the form of the AC voltage for the isolation transformer 65 in a reversed configuration.The counter-current battery module of the corresponding string 15, 16, 17 differs from the predefined battery module of the supply unit of the corresponding string 15, 16, 17. Furthermore, the counter-current battery module of the corresponding string 15, 16, 17 forms the currently selected compensation unit of the corresponding string 15, 16, 17 and provides a counter-voltage between the compensation terminals 27, 28 assigned to it, corresponding to the AC voltage generated by the supply unit of the corresponding string 15, 16, 17 for the isolation transformer 65. Consequently, the remaining battery modules of each string 15, 16, 17, which each differ from the supply unit and from the currently selected compensation unit of the corresponding string 15, 16, 17, provide the output AC voltage to be generated by the corresponding string 15, 16, 17 for operating the electric motor 50.Each strand 15, 16, 17, by means of which an output AC voltage for operating the electric motor 50 is to be generated, the instantaneous voltage value of which is relatively large, is not used to supply the low-voltage network 60 with electrical energy. The selection of the compensation unit of each strand 15, 16, 17 would advantageously be such that an above-average discharged battery module of the corresponding strand 15, 16, 17 is recharged by the other battery modules of the corresponding strand 15, 16, 17.

[0033] The increased load on individual battery modules of the battery system 10 with integrated inverter is taken into account in every operating strategy of this battery system 10. The predefined battery module of the power supply unit of each string 15, 16, 17 of the battery system 10 is used as infrequently as possible solely for operating the electric motor 50 and not for simultaneously supplying the low-voltage network 60, since each such battery module is already under a heavier load due to supplying the low-voltage network 60. By intelligently controlling the switching units of the battery modules of the battery system 10, a charge shift from the non-predefined battery modules of the corresponding string 15, 16, 17 to the predefined battery module of the corresponding power supply unit can occur in each string 15, 16, 17 when the associated output AC voltage is negative. Fig. 1 The fact that all switching units of the battery system 10 and preferably also the coupling elements 71, 72, 73 can be controlled by means of the control unit 30 is indicated by arrows.

[0034] The representation from the Fig. 2 refers to a first concrete implementation of the [unclear] in the Fig. 1. Arrangement shown. The representation from the Fig. 3 refers to a second concrete realization of the [unclear] in the Fig. 1 arrangement shown. In each realization, each string 15, 16, 17 of the battery system 10 generates an associated output AC voltage for operating the electric motor 50, which assumes voltage values ​​that are each greater than or equal to a negative minimum voltage value SN0 of -180 V and less than or equal to a positive maximum voltage value SP0 of +180 V. Fig. 2 and Fig. Figure 3 each shows a first waveform W1 of the output AC voltage generated by the first string 15 as a function of time t, a second waveform W2 of the output AC voltage generated by the second string 16 as a function of time t, and a third waveform W3 of the output AC voltage generated by the third string 17. In each realization, the three waveforms W1, W2, W3 of the output AC voltages of the three strings 15, 16, 17 together represent a waveform AW of the three-phase output AC voltage of the battery system 10. Here, W denotes the axis that represents possible voltage values.

[0035] In the first implementation, the isolation transformer 65, which supplies the low-voltage network 60 with electrical energy, requires an initial AC voltage that can be generated from an initial DC voltage of 14 V. This means that in the first implementation, the initial DC voltage of 14 V is present at the predefined battery module of the supply unit of each string 15, 16, 17 and can be converted into the initial AC voltage for the isolation transformer 65 via the switching unit assigned to the supply unit of each string 15, 16, 17.

[0036] In the second implementation, the isolation transformer 65, which supplies the low-voltage network 60 with electrical energy, requires a second AC voltage, which can be generated from a second DC voltage of 45 V. This means that in the second implementation, the second DC voltage of 45 V is present at the predefined battery module of the supply unit of each string 15, 16, 17 and can be converted into the second AC voltage for the isolation transformer 65 via the switching unit assigned to the supply unit of each string 15, 16, 17.

[0037] In each implementation, a single string 15, 16, 17 is selected to generate the AC voltage for the isolation transformer 65. The instantaneous AC output voltage W1, W2, W3 of this string is sufficient to operate the electric motor 50 without using the predefined battery module of its power supply unit, and also without using at least one non-predefined battery module of its battery modules, which can be selected as a compensation unit. This means that in each implementation, a single string 15, 16, 17 is selected to generate the AC voltage for the isolation transformer 65. The instantaneous AC output voltage W1, W2, W3 of this string is sufficient to operate the electric motor 50 without using at least two battery modules of its battery modules.This also means that in each implementation for generating the alternating voltage for the isolation transformer 65, a strand 15, 16, 17 is selected in which a counter-voltage corresponding to the alternating voltage for the isolation transformer 65 can also be switched.

[0038] This means that in the first implementation, each strand 15, 16, 17 selectable for generating the first AC voltage for the isolation transformer 65 generates an instantaneous output AC voltage W1, W2, W3 for operating the electric motor 50, the voltage value of which does not fall below a negative first voltage value SN1 of -152 V and does not exceed a positive second voltage value SP1 of +152 V. From the Fig. 2 shows that at any given time two strands of the three strands 15, 16, 17 can be selected to generate the first alternating voltage for the isolation transformer 65.

[0039] This further means that in the second realization, each strand 15, 16, 17 selectable for generating the second AC voltage for the isolation transformer 65 generates an instantaneous output AC voltage W1, W2, W3 for operating the electric motor 50, the voltage value of which does not fall below a negative first voltage value SN1 of -90 V and does not exceed a positive second voltage value SP1 of +90 V. From the Fig. As can be seen in Figure 3, at any given time, a single strand of the three strands 15, 16, 17 can be selected to generate the second alternating voltage for the isolation transformer 65.

[0040] In addition to the preceding written disclosure, reference is hereby made to the further disclosure of the invention in the following: Fig. 1, Fig. 2 to Fig. 3. Referenced.

Claims

[1] Battery system (10) with one or more strings (15, 16, 17) each comprising several battery modules that can be connected in series and that can be connected to the corresponding string (15, 16, 17) in at least one orientation, and a control unit (30) configured to connect the battery modules of each string (15, 16, 17) to the respective string (15, 16, 17) to connect the respective switching units to generate a single-phase or multi-phase output voltage (AW) of the battery system (10) corresponding to the number of strings (15, 16, 17), wherein a group of coupling elements (70) located in each strand (15, 16, 17) comprises a coupling element (71, 72, 73) which can be connected to at least one predefined battery module of the battery modules of the corresponding string (15, 16, 17) via the switching units assigned to it and which couples out a voltage applied by the corresponding at least one predefined battery module to the corresponding string (15, 16, 17) via the switching units assigned to it and couples it into a low-voltage network (60) if this voltage corresponds to a supply voltage for supplying the low-voltage network (60), or can couple this voltage out and into the low-voltage network (60) if this voltage corresponds to the supply voltage for supplying the low-voltage network (60), characterized by , that The control unit (30) switches a counter-voltage corresponding to the voltage coupled into the low-voltage network (60) into the respective string (15, 16, 17) by means of battery modules of the respective string (15, 16, 17), of which the voltage coupled into the low-voltage network (60) is not provided. [2] Battery system (10) according to claim 1, characterized by , that the control unit (30) applies a voltage present at each of at least one predefined battery module to the corresponding string (15, 16, 17) via the switching units assigned to these as a DC voltage corresponding to the supply voltage, which is coupled out via the corresponding coupling element (71, 72, 73) and is or can be coupled directly into the low-voltage network (60). [3] Battery system (10) according to claim 1, characterized byan isolation transformer (65) via which the group of coupling elements (70) couples the voltage applied to the corresponding string (15, 16, 17) by the at least one predefined battery module and coupled out by means of the corresponding coupling element (71, 72, 73) into the low-voltage network (60), wherein the control unit (30) converts a voltage applied to each at least one predefined battery module via the switching units assigned to them into an alternating voltage applied to the corresponding string (15, 16, 17), which is coupled out via the corresponding coupling element (71, 72, 73) and applied to the isolation transformer (65) for coupling into the low-voltage network (60). [4] Battery system (10) according to any one of the preceding claims, characterized by, that the control unit (30) shifts charge from the non-predefined battery modules to the predefined battery modules by controlling the switching units of the battery modules of the corresponding string (15, 16, 17) when the output voltage (W1, W2, W3) of a string (15, 16, 17) is in a predetermined orientation, if the predefined battery modules are connected to the corresponding string (15, 16, 17) in an orientation opposite to the predetermined orientation. [5] Method for supplying a low-voltage network (60) by means of a battery system (10) with one or more strings (15, 16, 17), each comprising several battery modules that can be connected in series and that can be connected to the corresponding string (15, 16, 17) in at least one orientation, and a control unit (30) configured to connect the battery modules of each string (15, 16, 17) to the respective string (15, 16, 17) via switching units assigned to that string (15, 16, 17) in such a way that a single-phase or multi-phase output voltage (AW) of the battery system (10) corresponding to the number of strings (15, 16, 17) is generated, comprising the steps: Enabling the extraction of a voltage applied to the corresponding string (15, 16, 17) by at least one predefined battery module of the battery modules of each string (15, 16, 17) via the switching units assigned to this or these, and enabling the coupling of this voltage into the low-voltage network (60), or Extraction of a voltage applied to the corresponding string (15, 16, 17) by at least one predefined battery module of the battery modules of each string (15, 16, 17) via the switching units assigned to it or these, and coupling of this voltage into the low-voltage network (60), in each case if the voltage applied to the corresponding string (15, 16, 17) by each of the at least one predefined battery module corresponds to a supply voltage for supplying the low-voltage network (60). characterized by , Switching a counter-voltage corresponding to the voltage coupled into the low-voltage network (60) into the respective string (15, 16, 17) by battery modules of the respective string (15, 16, 17), which do not provide the voltage coupled into the low-voltage network (60). [6] Method according to claim 5, characterized by Applying a voltage to each of at least one predefined battery module via the switching units assigned to these to the corresponding string (15, 16, 17) as a DC voltage corresponding to the supply voltage, which is decoupled and directly coupled into the low-voltage network (60) or can be coupled into it. [7] Method according to claim 5, characterized byConverting a voltage applied to each at least one predefined battery module via the switching units assigned to them into an alternating voltage, which is coupled out and applied to an isolation transformer (65) for coupling into the low-voltage network (60), via which the voltage applied and coupled out by each at least one predefined battery module to the corresponding string (15, 16, 17) is coupled into the low-voltage network (60). [8] Method according to any one of claims 6 to 7, characterized byControl of the switching units of the battery modules of a string (15, 16, 17) at a predetermined orientation of the output voltage (W1, W2, W3) of the corresponding string (15, 16, 17) such that charge is shifted from the non-predefined battery modules to the predefined battery modules when the predefined battery modules are connected to the corresponding string (15, 16, 17) in an orientation opposite to the predetermined orientation.

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