Methods and systems for updating state of charge estimates of individual cells in battery packs
Described herein are methods and systems for updating SOC estimates of individual cells in battery packs. Specifically, SOC estimates are updated in-situ, e.g., while the battery packs remain operational. For example, a cell is charged or discharged, independently from other cells, until the cell OCV is at a set value, corresponding to one of target zones. The target zones have more prominent correlations between the OCV and SOC than other parts of the OCV profile. A new SOC value, corresponding to the cell OCV, is used to update the SOC estimate. In some examples, a set of voltages is obtained while the cell is charged or discharged at a constant current/power, e.g., outside of the target zones. One or more differential capacities are determined from this voltage set, and a new SOC value is obtained based on these differential capacities.
1. An in-situ method for determining a state of charge value of a battery pack including a plurality of battery cells, the method comprising:
changing a magnitude of an external cell current flowing through one or more first battery cells of the plurality of battery cells according to a first test profile, using a first node controller electrically coupled to the one or more first battery cells, while one or more second battery cells of the plurality of battery cells charge or discharge via a second node controller;
obtaining a first voltage reading from the one or more first battery cells, in response to changing the magnitude of the external cell current flowing through the one or more first battery cells according to the first test profile; and
determining a state of charge value of the one or more first battery cells at least partially using the first voltage reading.
2. The method of claim 1 , further comprising controlling the second node controller such that the one or more second battery cells operate according to a compensation profile, while changing the magnitude of the external cell current flowing through the one or more first battery cells according to the first test profile, the compensation profile being different from the first test profile.
3. The method of claim 1 , further comprising, balancing charge among at least the one or more first battery cells and the one or more second battery cells, after determining the state of charge value of the one or more first battery cells.
4. The method of claim 1 , further comprising, after determining the state of charge value of the one or more first battery cells, controlling the first node controller such that the one or more first battery cells operate according to a first operating profile that is different from the first test profile.
5. The method of claim 1 , wherein a voltage of the battery pack is at least substantially unchanged while changing the magnitude of the external cell current flowing through the one or more first battery cells according to the first test profile.
6. The method of claim 1 , wherein the magnitude of the external cell current flowing through the one or more first battery cells is different from a magnitude of an external cell current flowing through the one or more second battery cells, while changing the magnitude of the external cell current flowing through the one or more first battery cells according to the first test profile.
7. The method of claim 1 , further comprising, before changing the magnitude of the external cell current flowing through the one or more first battery cells according to the first test profile, selecting the one or more first battery cells for state of charge determination.
8. The method of claim 7 , wherein selecting the one or more first battery cells for state of charge determination is at least partially based one or more of the following:
a time lapse,
a cycle count,
a confidence level in a state of charge value of a Coulomb counter,
a charge depth of the one or more first battery cells in one or more of previous cycles,
a discharge depth of the one or more first battery cells in one or more of previous cycles,
a charge rate of the one or more first battery cells in one or more of previous cycles,
a discharge rate of the one or more first battery cells in one or more of previous cycles,
a temperature of the one or more first battery cells in the one or more of previous cycles, and
a user input.
9. The method of claim 1 , wherein changing the magnitude of the external cell current flowing through the one or more first battery cells according to the first test profile comprises causing the magnitude of the external cell current flowing through the one or more first battery cells to be zero.
10. The method of claim 9 , wherein the one or more first battery cells are in a first test target zone while causing the magnitude of the external cell current flowing through the one or more first battery cells to be zero.
11. The method of claim 1 , wherein changing the magnitude of the external cell current flowing through the one or more first battery cells according to the first test profile comprises charging or discharging the one or more first battery cells at a constant current or at a constant power.
12. An in-situ method for determining a state of charge value of a battery pack including a plurality of battery cells, the method comprising:
operating one or more first battery cells of the plurality of battery cells according to a first operating profile;
changing operation of the one or more first battery cells such that the one or more first battery cells operate according to a first test profile instead of according to the first operating profile;
obtaining a plurality of voltage readings from the one or more first battery cells while the one or more first battery cells operate according to the first test profile;
determining one or more differential capacity values at least partially using the plurality of voltage readings; and
determining a state of charge value of the one or more first battery cells at least partially using the one or more differential capacity values.
13. The method of claim 12 , wherein the one or more differential capacity values comprise a plurality of first-order differential capacity values.
14. The method of claim 13 , wherein the one or more differential capacity values further comprise at least one second-order differential capacity value.
15. The method of claim 12 , further comprising operating at least one additional battery cell of the plurality of battery cells according to a compensation profile, while the one or more first battery cells operate according to the first test profile.
16. The method of claim 12 , wherein obtaining the plurality of voltage readings from the one or more first battery cells comprises obtaining at least one of the plurality of voltage readings while the one or more first battery cells are in a first test target zone.
17. The method of claim 12 , wherein:
state of charge of the one or more first battery cells changes while the one or more first battery cells operate according to the first test profile; and
obtaining the plurality of voltage readings from the one or more first battery cells comprises obtaining at least two of the voltage readings at different respective states of charge of the one or more first battery cells.
18. An in-situ method for determining a state of charge value of a battery pack including a plurality of battery cells, the method comprising:
using a first node controller, changing operation of one or more first battery cells of the plurality of battery cells to cause the one or more first battery cells to be in a first test target zone, while one or more second battery cells of the plurality of battery cells charge or discharge via a second node controller;
obtaining one or more first voltage readings from the one or more first battery cells, while the one or more first battery cells are in the first test target zone; and
determining a state of charge value of the one or more first battery cells at least partially using the one or more first voltage readings.
19. The method of claim 18 , further comprising controlling the second node controller such that the one or more second battery cells operate according to a compensation profile while the one or more first battery cells are in the first test target zone.
20. The method of claim 18 , wherein the first test target zone corresponds to a state of charge range of the one or more first battery cells where state of charge of the one or more first battery cells can be estimated with an error that is less than a predetermined maximum value.
21. The method of claim 18 , wherein the first test target zone corresponds to one of (a) state of charge of the one or more first battery cells being less than ten percent and (b) state of charge of the one or more first battery cells being greater than ninety percent.