Systems and methods for determining cell capacity values in a multi-cell battery

• US 9,037,426 B2
• Filed: 05/13/2011
• Issued: 05/19/2015
• Est. Priority Date: 05/13/2011
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations LLC (General Motors Company)
• Inventors: Schaefer, Sascha
• Primary Examiner(s): Kundu, Sujoy
• Assistant Examiner(s): Malone, Steven J
• Application Number:
  US13/107,171
• Publication Number:
  US 20120290234A1
• Time in Patent Office: 1,467 Days
• Field of Search: 702/63
• US Class Current: 702/63
• CPC Class Codes: B60L 58/12 responding to state of charge [SoC]
• CPC Class Codes: B60L 58/22 Balancing the charge of battery modules
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: H02J 7/00716 in response to integrated charge or discharge current
• CPC Class Codes: H02J 7/04 Regulation of charging current or voltage
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

Systems and methods to determine cell capacities of a vehicle battery pack. Cell capacities may be determined using state of charge (SOC) estimates for the cells and a charge count for the battery pack. The SOC estimates may be determined when the SOC of the battery pack is below a lower threshold and above an upper threshold. Error values may also be generated for the cell capacity values.

Claims

1. A method for reducing sensor based error when determining cell capacity values for a vehicle battery pack comprising:

receiving, at a processor, sensor data indicative of the voltage of the pack, one or more currents of the pack, and voltages for a plurality of cells in the pack;

determining if a state of charge of the pack is below a lower voltage threshold;

determining if a first rest time that the state of charge of the pack below the lower voltage threshold is greater than a first rest time threshold;

determining a first set of state of charge values for the plurality of cells using a voltage-based strategy on the sensor data when the state of charge of the pack is below the lower voltage threshold value and the first rest time threshold is exceeded;

starting a charge count when the first set of state of charge values are determined;

determining if the state of charge of the pack is above an upper voltage threshold once the charge count is started;

determining if a second rest time that the state of charge of the pack above the upper voltage threshold is greater than a second rest time threshold;

determining a second set of state of charge values for the plurality of cells using a voltage-based strategy on the sensor data when the state of charge of the pack is above the upper voltage threshold value and the second rest time threshold is exceeded;

stopping a charge count when the second set of state of charge values are determined;

generating difference values using the differences between the state of charge values in the first and the second sets;

calculating cell capacity values by dividing the charge count value by the difference values; and

regulating the flow of current to the plurality of cells, wherein the amount of current that flows to each cell is determined using the cell capacity values.

2. The method of claim 1 further comprising:

determining cell capacity error values using;

3. The method of claim 1, further comprising:

determining, by the processor, a cell capacity distribution over the entire pack using the cell capacity values.

4. The method of claim 1, further comprising:

discharging the pack until the state of charge is below the lower threshold value; and

storing the discharged energy in a low voltage battery.

5. The method of claim 1, further comprising:

using the cell capacity values to determine which cell has the lowest cell capacity value; and

using the lowest cell capacity value to estimate the capacity of the pack.

6. The method of claim 1, wherein the lower voltage threshold and the upper voltage threshold define a range of voltages that correspond to a relatively flat portion of a voltage-state of charge characteristic of the pack.

7. The method of claim 6, wherein the lower voltage threshold is a state of charge of about 30% and the upper voltage threshold is a state of charge of about 80%.

8. A vehicle controller comprising:

an interface configured to receive sensor data from a plurality of voltage and current sensors, wherein the sensor data is indicative of the voltage of a pack, the currents of the pack, and the voltages for a plurality of cells in the pack;

a voltage-based state of charge generator configured to generate;

a first set of state of charge values for the plurality of cells, when the state of charge of the pack is below a lower voltage threshold value, and

a second set of state of charge values for the plurality of cells, when the state of charge of the pack is above an upper voltage threshold value;

a charge counter configured to determine a charge count value for the battery pack using the sensor data, wherein the charge count is started when the first set of state of charge values are generated, and wherein the charge count is stopped when the second set of state of charge values are generated;

a rest timer configured to determine a rest time for the battery pack wherein the voltage-based state of charge generator receives the rest time from the rest timer and generates the first state of charge values and the second state of charge values only if the rest time is above a rest time threshold, and wherein the rest time threshold is determined using a diffusion time constant of the pack;

a difference evaluator configured to generate difference values using the differences between the state of charge values in the first and the second sets;

a cell capacity calculator configured to calculate cell capacity values by dividing the charge count value by the difference values; and

a cell balancer configured to regulate the flow of current to the plurality of cells, wherein the amount of current that flows to each cell is determined using the cell capacity values.

9. The controller of claim 8, wherein the processing circuit further comprises a capacity error evaluator configured to determining cell capacity error values using:

10. The controller of claim 8, wherein the cell capacity calculator is further configured to determine a cell capacity distribution over the entire pack using the cell capacity values.

11. The controller of claim 8, wherein the processing circuit is further configured to use the cell capacity values to identify the cell having the lowest cell capacity value.

12. The controller of claim 11, wherein the processing circuit is further configured to use the lowest cell capacity value to estimate the capacity of the pack.

13. The method of claim 8, wherein the lower voltage threshold and the upper voltage threshold define a range of voltages that correspond to a relatively flat portion of a voltage-state of charge characteristic of the pack.

14. A system for determining cell capacity values for a vehicle battery pack comprising:

a plurality of cells within the pack;

voltage sensors configured to measure the voltage of the pack and the cells;

current sensors configured to measure the currents into and out of the pack; and

a processing circuit comprising

an interface that receives voltage data from the voltage sensors and current data from the current sensors,

a processor, and

a memory coupled to the processor, wherein the memory stores executable instructions that, when executed by the processor, cause the processor to;

determine if a state of charge of the pack is below a lower voltage threshold,

determine if a first rest time that the state of charge of the pack is below the lower voltage threshold exceeds a first rest time threshold,

determine a first set of state of charge values for the plurality of cells using a voltage-based strategy on the voltage data measured when the state of charge of the pack is below the lower voltage threshold value and the first rest time threshold is exceeded,

start a charge count when the first set of state of charge values are determined,

determine if a state of charge of the pack is above an upper voltage threshold once the charge count is started,

determine if a second rest time that the state of charge of the pack is above the upper voltage threshold exceeds a second rest time threshold,

determine a second set of state of charge values for the plurality of cells using a voltage-based strategy on the sensor data on the voltage data measured when the state of charge of the pack is above the upper voltage threshold value and the second rest time threshold is exceeded,

stop a charge count when the second set of state of charge values are determined,

calculate cell capacity values using the charge count and the first and second sets of state of charge values, and

regulate the flow of current to the plurality of cells, wherein the amount of current that flows to each cell is determined using the cell capacity values.

15. The system of claim 14, wherein the instructions further cause the processor to determine cell capacity error values using:

16. The system of claim 14, wherein the instructions further cause the processor to determine a cell capacity distribution over the entire pack using the cell capacity values.

17. The system of claim 14, wherein the instructions further cause the processor to determine which cell has the lowest cell capacity value.