Detection of Imbalance Across Multiple Battery Cells Measured by the Same Voltage Sensor

• US 20140361743A1
• Filed: 06/11/2013
• Published: 12/11/2014
• Est. Priority Date: 06/11/2013
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Stefanopoulou, Anna, Anderson, Richard Dyche, Li, Yonghua, Lin, Xinfan
• Granted Patent: US 9,770,997 B2
• Time in Patent Office: Days
• US Class Current: 320/109
• CPC Class Codes: B60L 2240/545 Temperature
• CPC Class Codes: B60L 2240/547 Voltage
• CPC Class Codes: B60L 2240/549 Current
• CPC Class Codes: B60L 58/15 Preventing overcharging
• CPC Class Codes: B60L 58/22 Balancing the charge of battery modules
• 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: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

A vehicle having a battery pack with cells arranged in at least groups of two cells in series is disclosed. A controller balances the cells based on a change in voltage across the cells being different than an expected change in voltage. The expected value is based on a current and a time associated with charging or discharging the cells. A controller is disclosed that commands charging and discharging of the battery cells based on a difference between a voltage across the group and the expected value for the group. A method for charging and discharging a battery pack is disclosed. The voltage across a group of cells is measured and compared to an expected value. An imbalance in a cell attribute is estimated according to a difference between the measured voltage and the expected voltage. The voltage across each battery cell is not required.

Claims

1. A vehicle comprising:

a plurality of battery cells arranged into groups of at least two; and

at least one controller programmed to balance at least some of the cells in response to a change in voltage, caused by charging and discharging the cells, across one of the groups different than an expected change in voltage, wherein the expected change in voltage is based on a current and time associated with the charging and discharging.

2. The vehicle of claim 1 wherein the expected change in voltage is further based on a measured voltage across the one of the groups.

3. The vehicle of claim 1 wherein the cells are charged and discharged at a generally constant current.

4. The vehicle of claim 1 wherein the battery cells are lithium based.

5. A vehicle comprising:

a plurality of battery cells arranged into groups of at least two; and

at least one controller programmed to command charging and discharging of the battery cells within one of the groups based on a difference between a measured voltage across the one of the groups and an expected voltage for the one of the groups, wherein the expected voltage is based on a current and time associated with the charging and discharging.

6. The vehicle of claim 5 wherein the charging is commanded such that the voltage of each cell in the one of the groups does not exceed a predetermined voltage.

7. The vehicle of claim 5 wherein the discharging is commanded such that the voltage of each cell in the one of the groups remains above a predetermined voltage.

8. The vehicle of claim 5 wherein the expected voltage is further based on a value of the measured voltage across the one of the groups during a predetermined period of time beginning with vehicle activation.

9. The vehicle of claim 5 wherein the cells are charged and discharged at a generally constant current.

10. The vehicle of claim 5 wherein the charging and discharging is further based on an estimate of at least one of a state of charge and a charge capacity for the cells within the one of the groups calculated from the difference between the voltage across the one of the groups and the expected voltage for the one of the groups.

11. The vehicle of claim 10 wherein the one of the state of charge and the charge capacity is estimated when an average state of charge of the cells within the one of the groups is within a predetermined range.

12. The vehicle of claim 5 wherein the battery cells are lithium based.

13. A method for charging and discharging a battery pack comprising:

measuring a voltage across a group of battery cells;

calculating an expected voltage based on a current and time associated with charging and discharging the cells;

estimating an imbalance in at least one cell attribute between the cells of the group based on a difference between the voltage and the expected voltage; and

charging and discharging the battery pack in response to estimating the imbalance to reduce the imbalance in the at least one cell attribute between the cells of the group.

14. The method of claim 13 wherein the expected voltage is further based on a value of the measured voltage during a predetermined period of time beginning with vehicle activation.

15. The method of claim 13 wherein the expected voltage is further based on a value of the measured voltage during a period of time beginning with vehicle activation and ending when the difference between the value of the voltage and the expected voltage becomes less than a predetermined value.

16. The method of claim 13 wherein the at least one cell attribute includes at least one of state of charge and charge capacity.

17. The method of claim 13 wherein the at least one cell attribute is estimated for each of the cells of the group.