System and Method For Equalizing a Battery Pack During a Battery Pack Charging Process

• US 20110127960A1
• Filed: 11/30/2010
• Published: 06/02/2011
• Est. Priority Date: 12/02/2009
• Status: Active Grant

• Current Assignee: Nikola, LLC
• Original Assignee: American Electric Vehicles Inc.
• Inventors: Plett, Gregory L.
• Granted Patent: US 8,427,105 B2
• Time in Patent Office: Days
• US Class Current: 320/116
• CPC Class Codes: H01M 10/482 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 10/486 for measuring temperature
• CPC Class Codes: H02J 7/0014 Circuits for equalisation of charge between batteries
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A system and method for equalizing a battery pack during a battery pack charging process in accordance with an exemplary embodiment is provided. The method includes receiving total capacity estimates for all battery cells in the battery pack, and receiving state-of-charge estimates for all battery cells in the battery pack. The method further includes computing an equalization metric for all battery cells in the battery pack. The method further includes determining an equalization action for all battery cells in the battery pack, and initiating that equalization action. The method further includes executing a battery pack charging step.

Claims

1. A method for equalizing a battery pack during a battery pack charging process, comprising:

receiving a battery cell total capacity estimate indicative of a total capacity of a battery cell for all battery cells in the battery pack;

receiving a battery cell state-of-charge estimate indicative of a state-of-charge of a battery cell for all battery cells in the battery pack;

computing the residual charge capacity of the battery pack based on the present state-of-charge of the battery cell having lowest total capacity estimate and on the lowest total capacity estimate;

computing goal end-of-charge state-of-charge values for all battery cells in the battery pack based on an equalization metric, the total capacity estimates, the state-of-charge estimates, and the residual charge capacity of the battery pack;

computing predicted end-of-charge state-of-charge values for all battery cells in the battery pack based on the state-of-charge estimates, the total capacity estimates, and the residual charge capacity of the battery pack;

computing a state-of-charge mismatch value for all battery cells in the battery pack as the goal end-of-charge state-of-charge value minus the predicted end-of-charge state-of-charge value for that battery cell;

initiating an equalization action for zero or more battery cells in the battery pack, based on the state-of-charge mismatch value for the battery cells in the battery pack; and

executing a battery pack charging step.

2. The method of claim 1, where the equalization metric sets all goal end-of-charge state-of-charge values to a fixed design value.

3. The method of claim 1, where the equalization metric computes a goal-end-of-charge state-of-charge value based on an upper state-of-charge operational design limit, a lower state-of-charge operational design limit, and the total capacity estimates.

4. The method of claim 1 where initiating an equalization action for zero or more battery cells in the battery pack comprises initiating a bucking action for one or more battery cells.

5. The method of claim 4 where the battery cells that are bucked are the ones having greatest absolute state-of-charge mismatch values, where the state-of-charge in values are positive.

6. The method of claim 1 where initiating an equalization action for zero or more battery cells in the battery pack comprises initiating a boosting action for one or more battery cells.

7. The method of claim 6 where the battery cells that are boosted are the ones having greatest absolute state-of-charge mismatch values, where the state-of-charge mismatch values are negative.

8. The method of claim 1 wherein executing a battery pack charging step commands a constant current from the battery pack charging circuit.

9. The method of claim 1 wherein executing a battery pack charging step commands a constant voltage from the battery pack charging circuit.

10. The method of claim 1 wherein executing a battery pack charging step commands a constant power from the battery pack charging circuit.

13. The method of claim 1, wherein the step of computing predicted end-of-charge state-of-charge values for all battery cells in the battery pack based on the state-of-charge estimates, the total capacity estimates, and the residual charge capacity of the battery pack uses the relationship z_k(end)=z_k(t) C^charge(t)/C_k.

14. The method of claim 1, wherein the step of the goal end-of-charge state-of-charge value minus the predicted end-of-charge state-of-charge value for that battery cell uses the relationship z_k^mismatch=z_k^goal−

z_k(end).

11. A system for equalizing a battery pack during a battery pack charging process, comprising:

a computer configured to receive a battery cell total capacity estimate indicative of a total capacity of a battery cell for all battery cells in the battery pack;

the computer further configured to receive a battery cell state-of-charge estimate indicative of a state-of-charge of a battery cell for all battery cells in the battery pack;

the computer further configured to compute the residual charge capacity of the battery pack based on the present state-of-charge of the battery cell having lowest total capacity estimate and on the lowest total capacity estimate;

the computer further configured to compute goal end-of-charge state-of-charge values for all battery cells in the battery pack based on an equalization metric, the total capacity estimates, the state-of-charge estimates, and the residual charge capacity of the battery pack;

the computer further configured to compute predicted end-of-charge state-of-charge values for all battery cells in the battery pack based on the state-of-charge estimates, the total capacity estimates, and the residual charge capacity of the battery pack;

the computer further configured to compute a state-of-charge mismatch value for all battery cells in the battery pack as the goal end-of-charge state-of-charge value minus the predicted end-of-charge state-of-charge value for that battery cell;

the computer further configured to initiate an equalization action for zero or more battery cells in the battery pack, based on the state-of-charge mismatch value for the battery cells in the battery pack; and

the computer further configured to execute a battery pack charging step.

12. A computer readable medium having computer-executable instructions for performing a method for equalizing a battery pack during a battery pack charging process, the method comprising:

receiving a battery cell total capacity estimate indicative of a total capacity of a battery cell for all battery cells in the battery pack;

receiving a battery cell state-of-charge estimate indicative of a state-of-charge of a battery cell for all battery cells in the battery pack;

computing the residual charge capacity of the battery pack based on the present state-of-charge of the battery cell having lowest total capacity estimate and on the lowest total capacity estimate;

computing goal end-of-charge state-of-charge values for all battery cells in the battery pack based on an equalization metric, the total capacity estimates, the state-of-charge estimates, and the residual charge capacity of the battery pack;

computing predicted end-of-charge state-of-charge values for all battery cells in the battery pack based on the state-of-charge estimates, the total capacity estimates, and the residual charge capacity of the battery pack;

computing a state-of-charge mismatch value for all battery cells in the battery pack as the goal end-of-charge state-of-charge value minus the predicted end-of-charge state-of-charge value for that battery cell;

initiating an equalization action for zero or more battery cells in the battery pack, based on the state-of-charge mismatch value for the battery cells in the battery pack; and

executing a battery pack charging step.