BATTERY PACK CAPACITY LEARN ALGORITHM

• US 20120081075A1
• Filed: 10/05/2010
• Published: 04/05/2012
• Est. Priority Date: 10/05/2010
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations Incorporated (Motors Liquidation Co. GUC Trust)
• Inventors: Skelton, Scott M.
• Granted Patent: US 8,749,201 B2
• Time in Patent Office: Days
• US Class Current: 320/116
• CPC Class Codes: B60L 58/15 Preventing overcharging
• CPC Class Codes: B60L 58/22 Balancing the charge of battery modules
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/382 Arrangements for monitoring battery or accumulator variables, e.g. SoC
• CPC Class Codes: G01R 31/387 Determining ampere-hour charge capacity or SoC
• CPC Class Codes: G01R 31/392 Determining battery ageing or deterioration, e.g. state of health
• CPC Class Codes: H01M 10/4207 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 2220/20 Batteries in motive systems, e.g. vehicle, ship, plane
• CPC Class Codes: H02J 7/0014 Circuits for equalisation of charge between batteries
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: H02J 7/005 Detection of state of health [SOH]
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

A method that considers battery capacity for providing cell balancing for battery cells in a battery pack. The method includes providing a current state-of-charge for each battery cell in the battery pack for a current time frame and a previous state-of-charge for each battery cell in the battery pack from a previous time frame. The method also includes subtracting the current state-of-charge from the previous state-of-charge for each battery cell to generate a cell delta state-of-charge for each cell and providing an average cell delta state-of-charge of the cell delta state-of-charges for all of the cells. The method also includes dividing each cell delta state-of-charge by the average cell delta state-of-charge to provide a relative cell delta state-of-charge for each cell and dividing the current state-of-charge by the relative cell delta state-of-charge for that cell to generate a capacity adjustment state-of-charge that identifies the capacity of the cell.

Claims

1. A method for determining a capacity of battery cells in a battery pack, said method comprising:

providing a current state-of-charge for each battery cell in the battery pack for a current time frame and a previous state-of-charge for each battery cell in the battery pack for a previous time frame;

subtracting the current state-of-charge from the previous state-of-charge for each battery cell to generate a cell delta state-of-charge for each cell;

providing an average cell delta state-of-charge for the cell delta state-of-charges from all of the cells;

dividing each cell delta state-of-charge by the average cell delta state-of-charge to provide a relative cell delta state-of-charge for each cell; and

dividing the current state-of-charge for each cell by the relative cell delta state-of-charge for that cell to generate a capacity adjusted state-of-charge that identifies the capacity of the cell.

2. The method according to claim 1 further comprising filtering the relative delta state-of-charge for each cell so as to reduce the impact of large changes in the relative delta state-of-charge.

3. The method according to claim 2 wherein filtering the relative cell delta state-of-charge includes using an exponentially weighted moving average filter.

4. The method according to claim 1 further comprising using the capacity adjusted state-of-charge for each cell in a cell balancing algorithm that balances the state-of-charge of each cell in the battery pack to be about the same.

5. The method according to claim 1 further comprising generating a capacity fade factor that identifies the age of the battery pack.

6. The method according to claim 5 wherein generating a capacity fade factor includes determining a capacity of the battery pack by determining current flow into and out of the battery pack to determine a battery pack capacity consumed, dividing the battery pack capacity consumed by a theoretical or known capacity of the battery pack to get a change in the state-of-charge of the battery pack, and dividing the change in the state-of-charge of the battery pack by a measured change in state-of-charge of the battery pack to get the capacity fade factor.

7. The method according to claim 1 wherein the battery pack is a high voltage battery pack for an electric vehicle.

8. The method according to claim 7 wherein the high voltage battery pack is a lithium-ion battery pack.

9. A method for determining a capacity of battery cells in a battery pack in an electric vehicle, said method comprising:

providing a current state-of-charge for each battery cell in the battery pack for a current time frame and a previous state-of-charge for each battery cell in the battery pack for a previous time frame;

subtracting the current state-of-charge from the previous state-of-charge for each battery cell to generate a cell delta state-of-charge for each cell;

providing an average cell delta state-of-charge for the cell delta state-of-charges from all of the cells;

dividing each cell delta state-of-charge by the average cell delta state-of-charge to provide a relative cell delta state-of-charge for each cell;

dividing the current state-of-charge for each cell by the relative cell delta state-of-charge for that cell to generate a capacity adjusted state-of-charge that identifies the capacity of the cell;

generating a capacity fade factor that identifies the age of the battery pack; and

using the capacity adjusted state-of-charge for each cell and the capacity fade factor in a cell balancing algorithm that balances the state-of-charge of each cell in the battery pack to be about the same.

10. The method according to claim 9 further comprising filtering the relative delta state-of-charge for each cell so as to reduce the impact of large changes in the relative delta state-of-charge.

11. The method according to claim 10 wherein filtering the relative cell delta state-of-charge includes using an exponentially weighted moving average filter.

12. The method according to claim 9 wherein generating a capacity fade factor includes determining a capacity of the battery pack by determining current flow into and out of the battery pack to determine a battery pack capacity consumed, dividing the battery pack capacity consumed by a theoretical or known capacity of the battery pack to get a change in the state-of-charge of the battery pack, and dividing the change in the state-of-charge of the battery pack by a measured change in state-of-charge of the battery pack to get the capacity fade factor.

13. A system for determining a capacity of battery cells in a battery pack, said system comprising;

means for providing a current state-of-charge for each battery cell in the battery pack for a current time frame and means for providing a previous state-of-charge for each battery cell in the battery pack for a previous time frame;

means for subtracting the current state-of-charge from the previous state-of-charge for each battery cell to generate a cell delta state-of-charge for each cell;

means for providing an average cell delta state-of-charge for the cell delta state-of-charges from all the cells;

means for dividing each cell delta state-of-charge by the average cell delta state-of-charge to provide a relative cell delta state-of-charge for each cell; and

means for dividing the current state-of-charge from each cell by the relative cell delta state-of-charge for that cell to determine a capacity adjusted state-of-charge that identifies the capacity of the cell.

14. The system according to claim 13 further comprising means for filtering the relative delta state-of-charge for each cell to reduce the impact of large changes in the relative delta state-of-charge.

15. The system according to claim 14 wherein the means for filtering the relative cell delta state-of-charge includes uses an exponentially weighted moving average filter.

16. The system according to claim 13 further comprising means for using the capacity adjusted state-of-charge for each cell in a cell balancing algorithm that balances the state-of-charge of each cell in the battery pack to be about the same.

17. The system according to claim 13 further comprising means for generating a capacity fade factor that identifies the age of the battery pack.

18. The system according to claim 17 wherein the means for generating a capacity fade factor determines a capacity of the battery pack by determining current flow into and out of the battery pack to determine a battery pack capacity consumed, divides the battery pack capacity consumed by a theoretical or known capacity of the battery pack to get a change in the state-of-charge of the battery pack, and divides the change in the state-of-charge of the battery pack by a measured change in state-of-charge of the battery pack to get the capacity fade factor.

19. The system according to claim 13 wherein the battery pack is a high voltage battery pack for an electric vehicle.

20. The system according to claim 19 wherein the high voltage battery pack is a lithium-ion battery pack.