BATTERY PACK AND BALANCING METHOD OF BATTERY CELLS

• US 20100194339A1
• Filed: 05/15/2009
• Published: 08/05/2010
• Est. Priority Date: 02/04/2009
• Status: Active Grant

• Current Assignee: Samsung SDI Company Limited
• Original Assignee: Samsung SDI Company Limited
• Inventors: Park, Inkyu, Yang, Jongwoon, Kim, Yonguk, Susumu, Segawa
• Granted Patent: US 8,350,528 B2
• Time in Patent Office: Days
• US Class Current: 320/116
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits

Abstract

A balancing method for a battery pack includes balancing battery cells near an end of discharge. A deep discharge of the battery cells can be prevented without using an overdischarge control unit. One battery cell balancing method includes: a balancing check condition determination step for determining whether or not a maximum voltage out of voltages of the battery cells is smaller than a reference voltage; a balancing start condition determination step for determining whether or not a residual capacity difference or voltage difference between the individual battery cells exceeds a reference value; a balancing time calculation step for calculating a balancing time for discharging the battery cell that exceeds the reference value; and a balancing operation step for discharging the selected battery cell when the battery cells are under charge or are at rest or when a discharge current of the battery cells is smaller than a reference current.

Claims

1. A balancing method for a battery pack comprising a plurality of battery cells, the method comprising balancing the battery cells near an end of discharge.

2. The balancing method of claim 1, wherein a deep discharge of the battery cells is prevented without using an overdischarge control unit.

3. A balancing method for a battery pack comprising a plurality of battery cells, the method comprising:

determining whether or not a first condition for performing balancing of the discharge cells exists;

determining whether or not a second condition for performing balancing of the discharge cells exists;

if the first and second conditions exist, calculating a balancing time; and

performing balancing operation in accordance with the balancing time.

4. The balancing method of claim 3, wherein the determining whether or not the first condition exists comprises determining whether or not a maximum voltage among voltages of the plurality of battery cells is smaller than a reference voltage.

5. The balancing method of claim 4, wherein the reference voltage is between about 2.0V and about 3.7V.

6. The balancing method of claim 3, wherein the determining whether or not the second condition exists comprises determining whether or not a residual capacity difference or a voltage difference between two of the plurality of battery cells exceeds a reference value.

7. The balancing method of claim 3, wherein the calculating the balancing time comprises:

selecting a battery cell to be discharged from among the plurality of battery cells; and

calculating the balancing time for the selected battery cell.

8. The balancing method of claim 7, wherein the selecting the battery cell to be discharged comprises selecting at least one battery cell other than a battery cell having a lowest residual capacity from among the plurality of battery cells.

9. The balancing method of claim 8, wherein the calculating the balancing time comprises calculating a balancing time for a residual capacity of the selected at least one battery cell to become substantially equal to the lowest residual capacity.

10. The balancing method of claim 7, wherein the selecting the battery cell to be discharged comprises selecting at least one battery cell other than a battery cell having a lowest voltage from among the plurality of battery cells.

11. The balancing method of claim 10, wherein the calculating the balancing time comprises calculating a balancing time for a voltage of the selected at least one battery cell to become substantially equal to the lowest voltage.

12. The balancing method of claim 3, wherein the performing balancing operation comprises discharging a selected battery cell from among the plurality of battery cells for the calculated balancing time.

13. The balancing method of claim 12, wherein the discharging of the selected battery cell is performed intermittently.

14. The balancing method of claim 3, wherein the determining whether or not the first condition exists comprises determining during a time period that exceeds a reference time:

whether or not a maximum voltage among voltages of the plurality of battery cells is smaller than a reference voltage; and

whether or not a current of the battery pack is smaller than a reference current.

15. The balancing method of claim 14, wherein the first condition exists if, during the time period greater than or equal to the reference time, the maximum voltage remains less than the reference voltage and the current remains less than the reference current.

16. The balancing method of claim 14, wherein either a charge current or a discharge current can be used as the current compared to the reference current.

17. The balancing method of claim 14, wherein if the maximum voltage is equal to or greater than the reference voltage, the method further comprises determining whether or not the balancing time was previously set.

18. The balancing method of claim 17, further comprising determining whether or not a cumulative time for the balancing operation is less than the balancing time, wherein the balancing operation is performed if the cumulative time is less than the balancing time.

19. The balancing method of claim 3, wherein the determining whether or not the second condition exists comprises:

calculating full charge capacities (FCCs) of the plurality of battery cells;

calculating residual capacities of the plurality of battery cells and residual capacity differences between the battery cells, using the calculated FCCs; and

determining whether or not the residual capacity difference between two of the plurality of battery cells exceeds a reference value.

20. The balancing method of claim 19, wherein if the residual capacity difference exceeds the reference value, the second condition exists and the calculating balancing time further comprises selecting a battery cell to be balanced from among the plurality of battery cells, wherein the selected battery cell is not a battery cell having a lowest residual capacity of the plurality of battery cells.

21. The balancing method of claim 3, wherein the balancing operation is performed if the first and second conditions exist or if a cumulative time for the balancing operation did not yet exceed the calculated balancing time.

22. The balancing method of claim 3, wherein the performing balancing operation comprises:

determining balancing operation conditions comprising determining whether or not the battery pack is under charge or is at rest until discharge following the charge, or if the battery pack is under discharge, determining whether or not the discharge current of the battery pack is smaller than the reference current; and

if the balancing operation conditions are met, discharging a selected battery cell from among the plurality of battery cells.

23. The balancing method of claim 22, wherein if the battery pack is not under charge, is not at rest and the discharge current of the battery pack is larger than the reference current, balancing of the plurality of battery cells is terminated.

24. The balancing method of claim 22, wherein the balancing operation is temporarily stopped while the battery pack is discharged at a level above a reference current.

25. A battery cell balancing system for a battery pack comprising a plurality of battery cells, the battery cell balancing system comprising:

a plurality of balancing switches, each of the balancing switches coupled between positive and negative terminals of a corresponding one of the battery cells;

a plurality of balancing resistors, each of the balancing resistors coupled in series with a corresponding one of the balancing switches between the positive and negative terminals of the corresponding one of the battery cells; and

a logic circuit for controlling the balancing switches to selectively discharge the battery cells through the respective balancing resistors near an end of discharge, such that the battery cells have same or similar voltages as each other.

26. The battery cell balancing system of claim 25, wherein an overdischarge control unit is not used while preventing deep discharge of the battery cells.

27. The battery cell balancing system of claim 25, further comprising a control unit for controlling the logic circuit to control the balancing resistors, the control unit comprising:

means for determining whether or not a first condition for performing balancing of the discharge cells exists;

means for determining whether or not a second condition for performing balancing of the discharge cells exists;

means for calculating, if the first and second conditions exist, a balancing time; and

means for performing balancing operation in accordance with the balancing time.

28. A battery pack comprising:

a plurality of battery cells coupled together; and

a battery cell balancing system comprising;

a plurality of balancing switches, each of the balancing switches coupled between positive and negative terminals of a corresponding one of the battery cells;

a plurality of balancing resistors, each of the balancing resistors coupled in series with a corresponding one of the balancing switches between the positive and negative terminals of the corresponding one of the battery cells; and

a logic circuit for controlling the balancing switches to selectively discharge the battery cells through the respective balancing resistors near an end of discharge, such that the battery cells have same or similar voltages as each other.

29. The battery pack of claim 28, further comprising a discharge terminal and a charge terminal, each of the discharge and charge terminals coupled to a battery terminal of at least one of the battery cells, wherein an overcharge control unit is interposed between the battery terminal and the charge terminal, and wherein an overdischarge control unit is not interposed between the battery terminal and the discharge terminal.

30. The battery pack of claim 28, further comprising an analog switch coupled in parallel with one of the plurality of battery cells to sense a voltage of the one of the plurality of battery cells.

31. The battery pack of claim 30, wherein the analog switch comprises a flying capacitor for storing the voltage of the one of the plurality of battery cells to provide the stored voltage to a control unit for controlling the logic circuit to control the balancing switches.

32. The battery pack of claim 31, further comprising a voltage sensing circuit for sensing voltages of the battery cells, and providing the sensed voltages to the control unit.