Systems and methods for connecting battery strings to a DC bus

1. A method for connecting a plurality of battery strings to a direct-current (DC) bus, the method comprising:

sorting the plurality of battery strings in an order based on respective output voltage values of the battery strings, the sorted plurality of battery strings including, in the order, at least a first battery string and a second battery string;

connecting the first battery string to a pre-charge circuit;

pre-charging the DC bus using the first battery string and the pre-charge circuit;

connecting the first battery string to the DC bus; and connecting the second battery string to the DC bus;

wherein pre-charging the DC bus further comprises: decreasing a first impedance of the pre-charge circuit; and increasing a second impedance of a discharge circuit connected to the DC bus.

2. The method of claim 1 , wherein the plurality of battery strings are sorted in an ascending order of the respective output voltage values.

3. The method of claim 1 , wherein the plurality of battery strings are sorted in a descending order of the respective output voltage values.

4. The method of claim 1 , further comprising measuring the output voltage values of the plurality of battery strings before the sorting.

5. The method of claim 1 , further comprising: determining a difference in output voltage values of the first battery string and the second battery string; and if the difference exceeds a predetermined threshold, pre-charging the DC bus before connecting the second battery string.

6. The method of claim 1 , further comprising: determining that two battery strings have approximately equal output voltage values; and connecting the two battery strings to the DC bus at substantially the same time.

7. The method of claim 1 , wherein connecting the first battery string to the DC bus further comprises: closing one or more contactors between the first battery string and the DC bus.

8. The method of claim 1 , further comprising: increasing the first impedance after a DC bus voltage reaches a steady state.

9. A system for connecting a plurality of battery strings to a DC bus, the system comprising:

one or more pre-charge circuits; and

a controller configured to:

sort the plurality of battery strings in an order based on respective output voltage values of the battery strings, the sorted plurality of battery strings including, in the order, at least a first battery string and a second battery string;

connect the first battery string to a pre-charge circuit;

pre-charge the DC bus using the first battery string and the pre-charge circuit;

connect the first battery string to the DC bus;

connect the second battery string to the DC bus;

decrease a first impedance of the pre-charge circuit; and

increase a second impedance of a discharge circuit connected to the DC bus.

10. The system of claim 9 , wherein the controller is further configured to sort the plurality of battery strings in an ascending order of the respective output voltage values.

11. The system of claim 9 , wherein the controller is further configured to sort the plurality of battery strings in a descending order of the respective output voltage values.

12. The system of claim 9 , further comprising a voltage meter configured to measure the output voltage values of the plurality of battery strings before the sorting.

13. The system of claim 9 , wherein the controller is further configured to: determining a difference in output voltage values of the first battery string and the second battery string; and if the difference exceeds a predetermined threshold, pre-charging the DC bus before connecting the second battery string.

14. The system of claim 9 , wherein the controller is further configured to: determining that two battery strings have approximately equal output voltage values; and connecting the two battery strings to the DC bus at substantially the same time.

15. The system of claim 9 , wherein the controller is further configured to: increasing the first impedance after a DC bus voltage reaches a steady state; and decreasing the second impedance.

16. The system of claim 9 , wherein: the pre-charge circuit comprises a first transistor; and the discharge circuit comprises a second transistor, wherein the controller is further configured to: operate the first transistor to change the first impedance; and operate the second transistor to change the second impedance.

17. A method for connecting battery strings to a direct-current (DC) bus, the method comprising:

sorting a plurality of battery strings in an order according to a performance parameter of the battery strings, the plurality of battery strings including, in the order, a first battery string and a second battery string;

connecting the first battery string to a pre-charge circuit;

pre-charging the DC bus using the first battery string and the pre-charge circuit;

connecting the first battery string to the DC bus;

connecting the second battery string to the DC bus;

decreasing a first impedance of the pre-charge circuit; and

increasing a second impedance of a discharge circuit connected to the DC bus.

18. The method of claim 17 , wherein the performance parameter is at least one of an output voltage or a maximum power output of the battery strings.