Method for opportunistically balancing charge between battery cells

• US 10,084,324 B2
• Filed: 08/30/2016
• Issued: 09/25/2018
• Est. Priority Date: 03/07/2011
• Status: Active Grant

• Current Assignee: A123 Systems Incorporated
• Original Assignee: A123 Systems Incorporated
• Inventors: Moorhead, Brian C., Rutkowski, Brian D.
• Primary Examiner(s): Rossoshek, Helen
• Application Number:
  US15/252,007
• Publication Number:
  US 20160372941A1
• Time in Patent Office: 756 Days
• CPC Class Codes: H01M 10/441 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: H02J 7/0013 acting upon several batteries simultaneously or sequentially H02J7/1423 takes precedence
• 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: Y02E 60/10 Energy storage using batteries

Abstract

Systems and methods for balancing battery cells of a battery pack are disclosed. In one example, a charge imbalance is determined while battery cells operate in a high charge resolution voltage range. The charge imbalance determined during operation in the high charge resolution voltage range may be removed when the battery cells are operated in a low charge resolution voltage range. The system and method may be particularly useful for balancing battery cells that operate in the low charge resolution voltage range for a large portion of their operating time.

Claims

1. A method for balancing charge between battery cells, comprising:

operating a first battery cell with a first voltage and a second battery cell with a second voltage, the first and second battery cells both operating in a first charge region;

measuring a voltage difference between the first voltage and the second voltage in the first charge region without charge balancing between the first battery cell and the second battery cell in the first charge region;

operating the first battery cell and the second battery cell in a second charge region; and

charge balancing between the first battery cell and the second battery cell in the second charge region which is different from the first charge region, the charge balancing based on the voltage difference between the first voltage and the second voltage as measured in the first charge region,

where the first charge region and the second charge region are defined based upon boundaries of a battery voltage versus battery cell charge plot, the first charge region having a higher slope than the second charge region.

2. The method of claim 1, where the first charge region is a lower charge region than the second charge region, and where charge balancing is iteratively performed in response to a lowest capacity battery cell of a battery cell stack.

3. The method of claim 1, where the charge balancing includes adding or draining charge from the first battery cell or the second battery cell.

4. The method of claim 1, where the second charge region is related to a battery cell voltage of a battery cell where a measurement error in the battery cell voltage results in a change in a state of charge estimate of the first battery cell greater than a threshold amount.

5. The method of claim 1, where the first charge region has a higher voltage versus capacity slope than the second charge region.

6. The method of claim 1, where an amount of charge added to or drained from the first or second battery cell is based on an amount of charge inferred from the voltage difference.

7. A method for balancing charge between battery cells, comprising:

operating a first battery cell and a second battery cell in a first region of battery charge, the first and second battery cells operating with a charge imbalance indicated by a voltage difference measured between a voltage of the first battery cell and a voltage of the second battery cell, the voltage difference measured during the first region without performing charge balancing in the first region of battery charge;

charging both the first and second battery cells to transition both the first and second battery cells to a second region of battery charge, where the first region of battery charge and the second region of battery charge are defined by predetermined boundaries of a battery voltage versus battery cell charge plot, and where the first region of battery charge has a greater slope than the second region of battery charge; and

operating the first and second battery cells in the second region of battery charge to reduce the charge imbalance, including charge balancing the first battery cell and the second battery cell by adding or subtracting an amount of charge to the first or second battery cell in the second region of battery charge, the amount of charge based on the voltage difference measured in the first region of battery charge.

8. The method of claim 7, where subtracting charge of the first or second battery cell balances charge between the first and second battery cells, and where the first region of battery charge is a lower battery charge than the second region of battery charge.

9. The method of claim 7, where the first region of battery charge is a higher charge than the second region of battery charge.

10. The method of claim 7, where a slope of battery voltage versus battery cell charge of the first region of battery charge is higher than the slope of battery voltage versus battery cell charge of the second region of battery charge.

11. The method of claim 7, where charge is added to the first or second battery cell via a transformer.

12. The method of claim 7, where charge is subtracted from the first or second battery cell via a resistor.

13. The method of claim 7, further comprising basing a timing of adding or subtracting charge from the first or second battery cell on an amount of charge stored in the first or second battery cell estimated from an amount of current the first or second battery cell sinks or sources and an open circuit voltage of the first or second battery cell in the second region of battery charge.

14. The method of claim 7, further comprising integrating the amount of charge added or subtracted from the first battery cell after estimating an amount of charge stored in the first battery cell.