Battery system having an intermediate circuit voltage which can be set in a variable fashion

1. A battery system comprising:

a battery;

a DC voltage intermediate circuit connected to the battery;

an AC converter connected to the DC voltage intermediate circuit; and

an electric motor connected to the AC converter,

wherein the DC voltage intermediate circuit includes a capacitor,

wherein the battery includes a battery module string having a plurality of battery modules that are connected in series, and a control unit,

wherein each battery module of the plurality of battery modules includes a coupling unit and at least one battery cell connected between a first input and a second input of the coupling unit,

wherein the coupling unit is configured (i) to switch the at least one battery cell between a first terminal of a respective battery module of the plurality of battery modules and a second terminal of the respective battery module in response to a first control signal, and (ii) in response to a second control signal, to connect the first terminal to the second terminal, and

wherein the control unit is configured to transmit the first control signal to a variable number of battery modules of the battery module string and to transmit the second control signal to a remaining number of battery modules of the battery module string and thus to set a voltage of the DC voltage intermediate circuit in a variable manner.

2. The battery system as claimed in claim 1 , wherein the battery is connected directly to the DC voltage intermediate circuit.

3. The battery system as claimed in claim 1 , wherein at least one of the coupling units of the battery module string is configured to disconnect the first terminal of the respective battery module from the second terminal in response to a third control signal from each other and from the at least one battery cell.

4. The battery system as claimed in claim 1 , wherein:

the coupling unit includes a first output, and

the coupling unit is configured to connect either the first input or the second input to the first output in response to the first control signal.

5. The battery system as claimed in claim 1 , wherein:

the coupling unit includes a first output and a second output, and

the coupling unit is configured (i) to connect the first input to the first output and the second input to the second output in response to the first control signal, and (ii) in response to the second control signal, to disconnect the first input from the first output and the second input from the second output and to connect the first output to the second output.

6. The battery system as claimed in claim 1 , wherein:

the control unit includes a battery cell diagnostic unit connected to the at least one battery cell of the plurality of battery modules,

the control unit is configured to determine a state of aging of the at least one battery cell, and

the control unit is further configured to transmit the second control signal to the battery modules of the plurality of battery modules for whose at least one battery cell the battery cell diagnostic unit has determined the state of aging to be greater than a predetermined maximum state of aging.

7. The battery system as claimed in claim 1 , wherein the at least one battery cell is a lithium-ion battery cell.

8. A motor vehicle comprising:

a battery system including (i) a battery, (ii) a DC voltage intermediate circuit connected to the battery, (iii) an AC converter connected to the DC voltage intermediate circuit, and (iv) an electric motor connected to the AC converter,

wherein the electric motor is configured to drive the motor vehicle,

wherein the DC voltage intermediate circuit includes a capacitor,

wherein the battery includes a battery module string having a plurality of battery modules that are connected in series, and a control unit,

wherein each battery module of the plurality of battery modules includes a coupling unit and at least one battery cell connected between a first input and a second input of the coupling unit,

wherein the coupling unit is configured (i) to switch the at least one battery cell between a first terminal of a respective battery module of the plurality of battery modules and a second terminal of the respective battery module in response to a first control signal, and (ii) in response to a second control signal, to connect the first terminal to the second terminal, and

wherein the control unit is configured to transmit the first control signal to a variable number of battery modules of the battery module string and to transmit the second control signal to a remaining number of battery modules of the battery module string and thus to set a voltage of the DC voltage intermediate circuit in a variable manner.

9. A method for operating a battery system having a battery, a DC voltage intermediate circuit connected to the battery, an AC converter connected to the DC voltage intermediate circuit, and an electric motor connected to the AC converter, wherein the battery includes a plurality of battery cells, the method comprising:

determining a state of aging of the plurality of battery cells;

comparing the state of aging of the plurality of battery cells with a predetermined maximum state of aging;

disconnecting a number of battery cells of the plurality of battery cells, wherein the number of battery cells includes precisely those battery cells of the plurality of battery cells whose state of aging is greater than the maximum state of aging;

bridging the number of battery cells;

connecting in series a remaining number of battery cells of the plurality of battery cells; and

setting a voltage of the DC voltage intermediate circuit in a variable manner.