Method and system for cell equalization using state of charge

• US 20060097698A1
• Filed: 11/11/2004
• Published: 05/11/2006
• Est. Priority Date: 11/11/2004
• Status: Active Grant

• Current Assignee: LG Energy Solution Limited (LG Corporation)
• Original Assignee: LG Chem Limited (LG Corporation)
• Inventors: Plett, Gregory L.
• Granted Patent: US 7,525,285 B2
• Time in Patent Office: Days
• US Class Current: 320/118
• CPC Class Codes: H02J 7/0014 Circuits for equalisation of charge between batteries
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

The present invention relates to an implementation of a method for cell equalization. The present invention uses other information such as the individual cell state-of-charge (SOC) estimates, and individual capacities and/or cell Coulombic efficiencies, possibly available from a dual extended Kalman filter. The present invention defines or refers to an operational SOC range between a minimum and a maximum. The minimum and maximum could be constants or could be dynamic based on functions of other variables. SOC can be measured relative to maximum charge or relative to maximum discharge for each cell. When the SOC is not consistent across the cells, a prioritizing scheme is used to determine which cells require equalization.

Claims

1. A method for cell equalization in battery packs, comprising:

determining a state-of-charge for each cell of a plurality of cells;

determining at least one of a charge capacity and a discharge capacity for each cell of said plurality of cells; and

equalizing one or more cells of said plurality of cells, when at least one of;

a charge capacity of at least one cell of said plurality of cells is lower than a charge capacity of an other cell of said plurality of cells by a selected threshold, and

a discharge capacity of at least one cell of said plurality of cells is lower than a discharge capacity of an other cell of said plurality of cells by a selected threshold.

2. The method of claim 1 wherein determining said charge capacity is performed by calculating a difference between a selected maximum state-of-charge for said each cell and a present state-of-charge for said each cell.

3. The method of claim 2 wherein determining said charge capacity is further performed by multiplying said difference by a total capacity for said each cell.

4. The method of claim 3 wherein determining said charge capacity is further performed employing a Coulombic efficiency calculation.

5. The method of claim 2 wherein determining said charge capacity is further performed by multiplying said difference by a nominal capacity for said each cell.

6. The method of claim 5 wherein determining said charge capacity is further performed employing a Coulombic efficiency calculation.

7. The method of claim 2 wherein said equalizing is performed by depleting some charge from one or more cells of said plurality of cells having charge capacity less than a charge capacity of a selected cell from said plurality of cells by a selected threshold.

8. The method of claim 7, wherein said one or more cells having charge capacity less than a charge capacity of a selected cell from said plurality of cells by a selected threshold is determined by sorting said plurality of cells by charge capacity.

9. The method of claim 1, wherein determining said discharge capacity is performed by calculating a difference between a present state-of-charge for said each cell and a selected minimum state-of-charge for said each cell.

10. The method of claim 9 wherein deterimining said discharge capacity is further performed by multiplying said difference by a total capacity for said each cell.

11. The method of claim 9 wherein deterimining said discharge capacity is further performed by multiplying said difference by a nominal capacity for said each cell.

12. The method of claim 9 wherein said equalizing is performed by adding some charge to one or more cells of said plurality of cells having discharge capacity less than a discharge capacity of a selected cell from said plurality of cells by a selected threshold.

13. The method of claim 12 wherein said one or more cells having discharge capacity less than a discharge capacity of a selected cell from said plurality of cells by a selected threshold is determined by sorting said plurality of cells by discharge capacity.

14. The method of claim 1 wherein said equalizing is performed by moving charge from a first one or more cells to another one or more cells of said plurality of cells.

15. The method of claim 1 wherein equalizing is only performed when a difference between a selected maximum state-of-charge and a selected minimum state-of-charge of said plurality of cells meets or exceeds a selected threshold.

16. The method of claim 1 wherein state-of-charge is determined using a form of at least one of a Kalman filter, a dual Kalman filter, an extended Kalman filter, and a dual extended Kalman filter.

17. The method of claim 1 wherein said equalizing is only performed when a selected state-of-charge estimate falls outside an error bound of another selected state-of-charge estimate by a selected threshold.

18. The method of claim 17 wherein said equalizing is performed when a selected state-of-charge estimate falls outside an error bound of another selected state-of-charge estimate by a selected threshold where said error bound are computed using a state of charge estimation error covariance estimate.

19. The method of claim 1 wherein said equalizing is terminated if a difference between a selected maximum discharge capacity and and a selected minimum discharge capacity and a difference between a selected maximum charge capacity and selected minimum charge capacity falls within a selected threshold.

20. The method of claim 1 wherein said equalizing is terminated if a cell is targeted for both adding charge and depleting charge.

21. A method for cell equalization in battery packs, comprising:

determining a state-of-charge for each cell of a plurality of cells;

prioritizing said plurality of cells according to state-of-charge; and

equalizing said plurality of cells according to said prioritizing.

22. The method of claim 21 wherein said state-of-charge is determined using a form of Kalman filtering.

23. The method of claim 21 wherein said state-of-charge is determined using an extended Kalman filter.

24. The method of claim 22 wherein equalizing is only performed when a difference between a selected maximum state-of-charge and a selected minimum state-of-charge of said plurality of cells meets or exceeds a selected threshold.

25. A system for cell equalization in battery packs, comprising:

a battery pack with a plurality of cells;

a sensor in operable communication with at least two cells of said plurality of cells configured to facilitate determination of state of charge for each cell of said at least two cells; and

a controller in operable communication with said sensor and said plurality of cells;

wherein said controller is configured to to equalize charge of a cell of said at least two cells of said plurality of cells based on a state-of-charge for each cell of said plurality of cells.

26. The system of claim 25 further including a device configured to equalize charge of a cell of said at least two cells of said plurality of cells in operable communication with said plurality of cells and said controller.

27. The system of claim 25 further including said controller determining at least one of a charge capacity and a discharge capacity for each cell of said plurality of cells;

and

equalizing one or more cells of said plurality of cells, when at least one of;

a charge capacity of at least one cell of said plurality of cells is lower than a charge capacity of an other cell of said plurality of cells by a selected threshold, and

a discharge capacity of at least one cell of said plurality of cells is lower than a discharge capacity of an other cell of said plurality of cells by a selected threshold.

28. The system of claim 27 wherein determining said charge capacity is performed by calculating a difference between a selected maximum state-of-charge for said each cell and said present state-of-charge for said each cell.

29. The system of of claim 28 wherein determining said charge capacity is further performed by multiplying said difference by a total capacity for said each cell.

30. The system of claim 29 wherein determining said charge capacity is further performed employing a Coulombic efficiency calculation.

31. The system of claim 27 wherein determining said charge capacity is further performed by multiplying said difference by a nominal capacity for said each cell.

32. The system of claim 31 wherein determining said charge capacity is further performed employing a Coulombic efficiency calculation.

33. The system of claim 25 wherein said equalizing is performed by depleting some charge from one or more cells of said plurality of cells having charge capacity less than a charge capacity of a selected cell from said plurality of cells by a selected threshold.

34. The system of claim 33 wherein said one or more cells having charge capacity less than a charge capacity of a selected cell from said plurality of cells by a selected threshold is determined by sorting said plurality of cells by charge capacity.

35. The system of claim 25 wherein determining said discharge capacity is performed by calculating a difference between a present state-of-charge for said at least one cell and a selected minimum state-of-charge for said each cell.

36. The system of claim 35 wherein determining said discharge capacity is further performed by multiplying said difference by a total capacity for said each cell.

37. The system of claim 35 wherein determining said discharge capacity is further performed by multiplying said difference by a nominal capacity for said each cell.

38. The system of claim 35 wherein equalizing charge is performed by adding some charge to one or more cells of said plurality of cells having discharge capacity less than a discharge capacity of a selected cell from said plurality of cells by a selected threshold.

39. The system of claim 38 wherein said one or more cells having discharge capacity less than a discharge capacity of a selected cell from said plurality of cells by a selected threshold is determined by sorting said plurality of cells by discharge capacity.

40. The system of claim 25, wherein equalizing charge is performed by moving charge from a first one or more cells to another one or more cells of said plurality of cells.

41. The system of claim 25 wherein equalizing charge of a cell is only performed when a difference between a selected maximum state-of-charge and a selected minimum state-of-charge of said plurality of cells meets or exceeds a selected threshold.

42. The system of claim 25 wherein state-of-charge is determined using a form of at least one of a Kalman filter, a dual Kalman filter, an extended Kalman filter, and a dual extended Kalman filter.

43. The system of claim 25 wherein equalizing charge is only performed when a selected state-of-charge estimate falls outside an error bound of another selected state-of-charge estimate by a selected threshold.

44. The system of claim 43 wherein said equalizing charge is performed when a selected state-of-charge estimate falls outside an error bound of another selected state-of-charge estimate by a selected threshold where said error bound are computed using a state of charge estimation error covariance estimate.

45. The system of claim 25 wherein equalizing charge is terminated if a difference between a selected maximum discharge capacity and and a selected minimum discharge capacity and a difference between a selected maximum charge capacity and selected minimum charge capacity falls within a selected threshold.

46. The system of claim 25 wherein equalizing charge is terminated if a cell is targeted for both adding charge and depleting charge.

47. A system for cell equalization in battery packs, comprising:

a means for determining a state-of-charge for each cell of a plurality of cells;

a means for determining at least one of a charge capacity and a discharge capacity for each cell of said plurality of cells; and

a means for equalizing one or more cells of said plurality of cells, when at least one of;

a charge capacity of at least one cell of said plurality of cells is lower than a charge capacity of an other cell of said plurality of cells by a selected threshold, and

a discharge capacity of at least one cell of said plurality of cells is lower than a discharge capacity of an other cell of said plurality of cells by a selected threshold.

48. A storage medium encoded with a machine-readable computer program code, wherein said storage medium includes instructions for causing a computer to implement a method for cell equalization in battery packs comprising:

determining a state-of-charge for each cell of a plurality of cells;

determining at least one of a charge capacity and a discharge capacity for each cell of said plurality of cells; and

equalizing one or more cells of said plurality of cells, when at least one of;

a charge capacity of at least one cell of said plurality of cells is lower than a charge capacity of an other cell of said plurality of cells by a selected threshold, and

a discharge capacity of at least one cell of said plurality of cells is lower than a discharge capacity of an other cell of said plurality of cells by a selected threshold.

49. A computer data signal embodied in a computer readable medium said computer data signal comprising code configured to cause a computer to implement a method for cell equalization in battery packs comprising:

determining a state-of-charge for each cell of a plurality of cells;

determining at least one of a charge capacity and a discharge capacity for each cell of said plurality of cells; and

equalizing one or more cells of said plurality of cells, when at least one of;

a charge capacity of at least one cell of said plurality of cells is lower than a charge capacity of an other cell of said plurality of cells by a selected threshold, and

a discharge capacity of at least one cell of said plurality of cells is lower than a discharge capacity of an other cell of said plurality of cells by a selected threshold.