Method and Apparatus for Modeling Diffusion in an Electrochemical System

• US 20080135316A1
• Filed: 12/06/2006
• Published: 06/12/2008
• Est. Priority Date: 12/06/2006
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations Incorporated (Motors Liquidation Co. GUC Trust)
• Inventors: Frisch, Damon R., Koch, Brian J., Conell, Robert S.
• Granted Patent: US 7,646,166 B2
• Time in Patent Office: Days
• US Class Current: 180/65.4
• CPC Class Codes: B60L 2210/20 AC to AC converters
• CPC Class Codes: B60L 58/10 for monitoring or controlling batteries
• CPC Class Codes: H01M 10/441 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 10/482 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y02T 10/72 Electric energy management in electromobility

Abstract

A method for determining a diffusion voltage in an electrochemical cell (e.g., a battery used in connection with an automotive vehicle) includes estimating a previous diffusion voltage, calculating a new diffusion voltage using an equation based on a diffusion circuit model and the previous diffusion voltage, and setting the previous diffusion voltage equal to the new diffusion voltage. The step of calculating the new diffusion voltage may then be repeated.

Claims

1. A method for determining a diffusion voltage in an electrochemical cell, the method comprising:

estimating a previous diffusion voltage;

calculating a new diffusion voltage using an equation based on a diffusion circuit model and the previous diffusion voltage;

setting the previous diffusion voltage equal to the new diffusion voltage; and

repeating the step of calculating the new diffusion voltage.

2. The method of claim 1 wherein the step of calculating a new diffusion voltage includes using an equation derived from a diffusion circuit model comprising a diffusion capacitor coupled to a variable resistance.

3. The method of claim 2 wherein the step of calculating a new diffusion voltage includes using an equation derived from a diffusion circuit model wherein the variable resistance is based on a charge on the diffusion capacitor.

4. The method of claim 3 wherein the step of calculating a new diffusion voltage includes using a time constant that varies based on the charge on the diffusion capacitor.

5. The method of claim 4 wherein the step of calculating a new diffusion voltage includes relating the time constant and the charge on the diffusion capacitor with an exponential relationship.

6. The method of claim 1 wherein the step of estimating a previous diffusion voltage further comprises estimating the previous diffusion voltage using a voltage measured when a vehicle is turned off and a voltage measured when the vehicle is turned on.

7. The method of claim 6 wherein the step of estimating a previous diffusion voltage further comprises:

determining a first voltage as a difference between a key-off voltage measured when the vehicle is turned off and a key-on voltage measured when the vehicle is turned on;

selecting a starting diffusion voltage based on a predetermined curve of diffusion voltage versus time;

determining a determined diffusion voltage based on the starting diffusion voltage and an elapsed time between when the vehicle is turned off and when the vehicle is turned on; and

estimating the previous diffusion voltage as the determined diffusion voltage if the difference between the starting diffusion voltage and the determined diffusion value matches, within a predetermined amount, the first voltage.

8. The method of claim 1 further comprising relating the diffusion voltage to an electrochemical cell voltage.

9. The method of claim 8 further comprising estimating a state of charge based on the electrochemical cell voltage.

10. An energy management controller for a vehicle comprising:

a processor configured to;

determine an initial diffusion voltage;

calculate a diffusion voltage using an equation based on a diffusion circuit model and the estimated diffusion voltage;

determine a battery condition parameter using the diffusion voltage; and

a memory coupled to the processor, the memory configured to store the battery condition parameter.

11. The controller of claim 10 wherein the diffusion circuit model comprises a diffusion capacitor coupled to a variable resistance.

12. The controller of claim 11 wherein the variable resistance varies based on a charge on the diffusion capacitor.

13. The controller of claim 12 wherein the equation based on the diffusion circuit model includes a time constant that varies based on the charge on the diffusion capacitor.

14. The controller of claim 13 wherein the time constant and the charge on the diffusion capacitor are related with a decreasing exponential relationship.

15. The controller of claim 10 wherein the battery condition parameter is a state of charge of a corresponding battery.

16. The controller of claim 10 wherein the processor is further configured to:

determine a first voltage as a difference between a key-off voltage measured when the vehicle is turned off and a key-on voltage measured when the vehicle is turned on;

select a starting diffusion voltage based on a predetermined curve of diffusion voltage versus time;

determine a determined diffusion voltage based on the first diffusion voltage and an elapsed time between when the vehicle is turned off and when the vehicle is turned on; and

estimate the initial diffusion voltage as the determined diffusion voltage if the difference between the starting diffusion voltage and the determined diffusion voltage matches, within a predetermined amount, the first voltage.

17. The controller of claim 10, wherein the processor is further configured to relate the diffusion voltage to an overall voltage of an associated battery.

18. The controller of claim 17, wherein the processor is further configured to estimate a state of charge based on the overall voltage.

19. A hybrid electric vehicle (HEV) comprising:

an internal combustion engine;

an electric motor generator coupled to the internal combustion engine, the electric motor generator configured for use as a generator to produce a charging voltage;

a battery coupled to the electric motor generator; and

an engine control computer coupled to the internal combustion engine, the electric motor generator and the battery, the engine control computer comprising;

a processor configured to;

estimate an initial diffusion voltage;

calculate a diffusion voltage using an equation based on a diffusion circuit model and the initial diffusion voltage; and

determine a state of charge of the battery using the diffusion voltage; and

a memory coupled to the processor for storing a plurality of parameters regarding battery conditions.

20. The HEV of claim 19 wherein the processor is further configured to:

determine a first voltage as a difference between a key-off voltage of the battery measured when the HEV is turned off and the key-on voltage of the battery measured when the HEV is turned on;

determine a starting diffusion voltage based on a predetermined curve of the diffusion voltage versus time;

determine a determined diffusion voltage based on the estimated value for diffusion voltage and an elapsed time equivalent to a time elapsed when the HEV is turned off and the time the HEV is turned on; and

estimate the initial diffusion voltage as the determined diffusion voltage if the difference between the starting diffusion voltage and the determined diffusion voltage matches, within a predetermined amount, the first voltage.