Lithium-Ion Battery Diagnostic and Prognostic Techniques

• US 20080094029A1
• Filed: 10/24/2006
• Published: 04/24/2008
• Est. Priority Date: 10/24/2006
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Singh, Harmohan N.
• Granted Patent: US 7,612,540 B2
• Time in Patent Office: Days
• US Class Current: 320/118
• CPC Class Codes: G01R 31/388 involving voltage measurements
• CPC Class Codes: G01R 31/396 Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery
• CPC Class Codes: H01M 10/052 Li-accumulators
• CPC Class Codes: H01M 10/441 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 10/482 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

Embodiments provide a method and a system for determining cell imbalance condition of a multi-cell battery including a plurality of cell strings. To determine a cell imbalance condition, a charge current is applied to the battery and is monitored during charging. The charging time for each cell string is determined based on the monitor of the charge current. A charge time difference of any two cell strings in the battery is used to determine the cell imbalance condition by comparing with a predetermined acceptable charge time difference for the cell strings.

Claims

1. A method for determining cell imbalance of a battery comprising:

applying a charge current to a battery comprising a plurality of cell strings, wherein each of the plurality of cell strings comprises a plurality of cells;

comparing a voltage per cell of each cell in a first cell string of the plurality of cell strings with a safe voltage limit; and

disenabling charging of the first cell string of the plurality of cell strings if any voltage per cell in the first cell string is higher than or equal to the safe voltage limit.

2. The method of claim 1 further comprising,

comparing a voltage per cell of each cell in a second cell string of the plurality of cell strings with a safe voltage limit, wherein the second cell string is configured parallel to the first cell string, and

disenabling charging of the second cell string of the plurality of cell strings if any voltage per cell in the second cell string is higher than or equal to the safe voltage limit.

3. The method of claim 2 further comprising,

monitoring a charge time of the first and the second cell string, and

determining a charge time difference between the first and the second cell strings.

4. The method of claim 3 further comprising comparing the charge time difference between the first and the second cell strings with a predetermined acceptable charge time difference for the plurality of cell strings.

5. The method of claim 4, wherein a condition in which the charge time difference between the first and the second cell strings is greater than the predetermined acceptable charge time difference indicates a cell imbalance condition of the battery.

6. The method of claim 3 further comprising determining an impending cell imbalance condition of the first cell string by comparing the charge time of the first cell string with an acceptable charge time for the plurality of cell strings.

7. The method of claim 6, wherein the charge time of the first cell string is shorter than the acceptable charge time indicates an impending cell imbalance condition.

8. The method of claim 1 further comprising monitoring the charge current to at least one of the battery and the first cell string.

9. The method of claim 1, wherein the charge current to the battery is sensed with a sudden current reduction, when the first cell string is disenabled.

10. The method of claim 1 further comprising determining a cell imbalance condition at individual cell levels.

11. The method of claim 1, wherein the battery further comprises at least one substring, wherein each substring comprises one or more cells.

12. The method of claim 1, wherein the safe voltage limit is about 4.1 volts per cell.

13. A method for determining cell imbalance of a battery comprising:

applying a charge current to a battery, wherein the battery comprises a plurality of cell strings;

monitoring the battery charge current;

counting a charge time for every cell string of the plurality of cell strings based on the monitoring of the battery charge current;

determining a charge time difference between any two cell strings of the plurality of cell strings; and

comparing the charge time difference between any two cell strings of the plurality of cell strings with a predetermined acceptable charge time difference for the plurality of cell strings of the battery,

wherein a condition in which the charge time difference is greater than the predetermined acceptable charge time difference indicates a cell imbalance condition of the battery.

14. The method of claim 13, wherein the charge time difference is equal to or less than the predetermined acceptable charge time difference indicates a good battery.

15. The method of claim 13, wherein the charge time is counted from a start of a constant voltage charge mode.

16. The method of claim 13, wherein counting the charge time based on the monitoring of the battery charge current comprises,

counting the charge time when the battery charge current is sensed with a sudden current reduction, wherein the sudden current reduction indicates a charge completion of one of the plurality of cell strings.

17. The method of claim 13 further comprising counting the charge time for every cell string by monitoring a charge current to every individual cell string.

18. The method of claim 13, wherein the charge time difference is calculated from an absolute value for a difference of the charge time between any two cell strings of the plurality of cell strings.

19. The method of claim 13, wherein the charge time is affected by battery conditions, wherein the battery conditions comprise at least a state-of-charge level.

20. The method of claim 13 further comprising determining an impending cell imbalance condition by comparing the charge time of one of the plurality of cell strings with an acceptable charge time for the plurality of cell strings.

21. The method of claim 20, wherein a condition in which the charge time is shorter than the acceptable charge time indicates an impending cell imbalance condition.

22. The method of claim 13 further comprising determining a cell imbalance condition at individual cell levels, wherein each of the plurality of cell strings of the battery comprises a plurality of individual cells.

23. A system for determining cell imbalance of a battery comprising:

a charger for providing a charge current to a battery comprising a plurality of cell strings, wherein each of the plurality of cell strings comprises a plurality of cells;

a first series of voltage sensors connected to a first cell string of the plurality of cell strings, wherein each voltage sensor of the first series of voltage sensors connects to monitor a voltage of each cell of the plurality of cells in the first cell string; and

an OR gate configured to receive a logical or of output from the first series of voltage sensors to control a charging process of the first cell string via a first switch.

24. The system of claim 23 further comprising a current sensor disposed in series with the battery.

25. The system of claim 23 further comprising,

a second series of voltage sensors connected to a second cell string of the plurality of cell strings, wherein each voltage sensor of the second series of voltage sensors connects to monitor each cell voltage of the plurality of cells in the second cell string;

and

the OR gate configured to receive a logical or of output from the second series of voltage sensors to control a charging process of the second cell string via a second switch.

26. The system of claim 25, wherein the second cell string of the plurality of cell strings is configured parallel to the first cell string.

27. The system of claim 23 further comprising a time counter configured to count a charge time of each of the plurality of the cell strings.

28. The system of claim 23, wherein one or more of the first series of voltage sensors, the OR gate, and the switch is located within at least one of the charger and the battery.

29. The system of claim 23, wherein the first switch is disenabled when any cell voltage of the plurality of cells of the first cell string indicates a less safe cell voltage sensed by the first series of voltage sensor.

30. The system of claim 23, wherein the first switch is enabled when every cell voltage of the plurality of cells of the first cell string indicates a safe cell voltage sensed by the first series of voltage sensor.

31. The system of claim 23, further comprising an AND gate logic scheme configured to receive a logical level output from the first series of voltage sensors.