Method and control device for operating a battery system and battery system

1. A method for operating a battery system connected to an electric energy system, having multiple battery strings connected in parallel, which each comprise a battery, an inverter, and a transformer, comprising:

charging each battery in a string based at least in part on an operating state of the battery system, in which a storing of electric energy in the battery system is requested;

discharging each battery in a string based at least in part on the operating state of the battery system, in which a drawing of electric energy from the battery system is requested,

wherein each battery has an installed, maximum charge capacity and a capacity that is available in the current operating state,

wherein during the discharging a respective currently available capacity corresponds to a state of charge of the respective battery, and

wherein during the charging the currently available capacity corresponds to a difference between the maximum charge capacity and the state of charge of the respective battery,

wherein a total charge output requested during the charging of the battery system and/or a total discharge output requested during the discharging of the battery system is dependent on the currently available capacities of the batteries of the multiple battery strings connected in parallel is distributed as part outputs over the multiple battery strings and thus over the batteries, and

minimizing a number of battery strings being simultaneously utilised simultaneously during a charging operation or discharging operation, wherein the minimum number of strings is based on the currently available capacities of the batteries of the multiple battery strings being greater than a defined first limit value.

2. The method according to claim 1 , further comprising:

distributing as part outputs the total charge output requested during charging or the total discharge output requested during discharging of the battery system over the multiple battery strings such that such multiple battery strings, whose batteries have a higher available capacity, compared with such multiple battery strings, whose batteries have a lower available capacity, are utilised with priority and thus primarily for charging and discharging and loaded with a corresponding part output.

3. The method according to claim 2 , wherein such multiple battery strings are utilised with priority and thus primarily for charging and discharging and loaded with a part output, whose batteries additionally have a lower ageing and/or fewer operating hours and/or a low ampere hour throughput.

4. The method according to claim 2 , wherein the battery strings are simultaneously utilised such that a single battery string, which in each case has a greatest available capacity, is fully loaded via its respective part output before in a case that this battery string cannot provide the total charge output requested during the charging or the total discharge output requested during the discharging of the battery system via its part output alone, a further battery string is utilised and loaded with a part output.

5. The method according to claim 2 , wherein the multiple battery strings are simultaneously utilised and loaded with a part output, via part outputs that are in a relation to one another corresponding to respective currently available capacities.

6. The method according to claim 5 , wherein not more than a defined part quantity of part strings, which maximally corresponds to a defined portion of a total number of the battery strings of the battery system are simultaneously utilised and loaded with a part output.

7. The method according to claim 6 , wherein only battery strings of the battery system are utilised and loaded with a part output, whose respective portion of their part output in a total output is greater than a defined first limit value.

8. The method according to claim 7 , wherein a number of the simultaneously utilised battery strings is determined so that a quotient of a requested total charge output or total discharge output and a sum of available part outputs of the simultaneously utilised battery strings is greater than a defined second limit value and smaller or equal to 1.

9. The method according to claim 5 , wherein all battery strings are simultaneously utilised and loaded with a part output.

10. The method according to claim 2 , wherein the number of the battery strings that are simultaneously utilised during a charging operation or discharging operation and loaded with the part outputs changes dynamically.

11. A control device for operating a battery system, wherein the control device is configured to:

charge and discharge each battery based at least in part on an operating state of the battery system, in which either a storing of electric energy in the battery system or a drawing of electric energy from the battery system is requested,

wherein each battery has an installed, maximum charge capacity and a capacity that is available in the current operating state,

wherein during the discharging a currently available capacity corresponds to a state of charge of the respective battery, and

wherein during the charging the currently available capacity corresponds to a difference between the maximum charge capacity and the state of charge of the respective battery,

wherein a total charge output requested during the charging of the battery system and/or a total discharge output requested during the discharging of the battery system is dependent on currently available capacities of the batteries of the multiple battery strings connected in parallel is distributed as part outputs over the multiple battery strings and thus over the batteries on a control side and

wherein a number of battery strings being simultaneously utilised simultaneously is minimized during a charging operation or discharging operation, wherein the minimum number of strings is based on the currently available capacities of the batteries of the multiple battery strings being greater than a defined first limit value.

12. A battery system, comprising:

multiple battery strings connected in parallel, which comprise a battery, an inverter, and a transformer; and

a control device configured to:

charge and discharge each battery based at least in part on an operating state of the battery system, in which either a storing of electric energy in the battery system or a drawing of electric energy from the battery system is requested,

wherein each battery has an installed, maximum charge capacity and a capacity that is available in the current operating state,

wherein during the discharging the currently available capacity corresponds to a state of charge of the respective battery, and

wherein during the charging the currently available capacity corresponds to a difference between the maximum charge capacity and the state of charge of the respective battery,

wherein a total charge output requested during the charging of the battery system and/or a total discharge output requested during the discharging of the battery system is dependent on currently available capacities of the batteries of the battery strings connected in parallel is distributed as part outputs over the multiple battery strings and thus over the batteries, and

wherein a number of battery strings being simultaneously utilised simultaneously is minimized during a charging operation or discharging operation, wherein the minimum number of strings is based on the currently available capacities of the batteries of the multiple battery strings being greater than a defined first limit value.