Battery pack capacity learn algorithm
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.
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, using a microprocessor, 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.