Fast search algorithm for finding initial diffusion voltage in electro-chemical systems

• US 8,054,046 B2
• Filed: 01/23/2008
• Issued: 11/08/2011
• 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 LLC (General Motors Company)
• Inventors: Gielniak, Michael J., Frisch, Damon R., Koch, Brian J., Lin, Jian
• Primary Examiner(s): Tso; Edward
• Assistant Examiner(s): PIGGUSH, AARON C
• Application Number:
  US12/018,653
• Publication Number:
  US 20080135315A1
• Time in Patent Office: 1,385 Days
• Field of Search: 320/104, 320/134, 320/136, 320/148, 320/156, 320/157, 320/161, 320/162, 324/427
• US Class Current: 320/156
• CPC Class Codes: B60L 2210/20 AC to AC converters
• CPC Class Codes: B60L 58/10 for monitoring or controlling batteries
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• 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
• CPC Class Codes: Y10S 903/903 having energy storing means, e.g. battery, capacitor

Abstract

A method for rapidly determining an initial diffusion voltage (V_diff)_initial as a starting point in calculating a diffusion voltage in an electro-chemical cell (e.g., a battery used in an automotive vehicle) includes obtaining a time difference t_off between a time when the cell was last turned-OFF and a time when the cell was next turned-ON, selecting a starting diffusion voltage (V_diff)_start based on t_off, determining a trial diffusion voltage V_diff based on a diffusion circuit model and (V_diff)_start, calculating an error voltage V_error=(V_diff)−|V_OFF−V_ON| where V_OFF and V_ON are cell voltages at turn-OFF and turn-ON respectively, repeating the foregoing determining and calculating steps using for each iteration (V_diff)_start=(V_diff)_previous+V_error until V_error is less than or equal to a first predetermined tolerance amount ε, storing in a memory a value of V_diff corresponding to the condition V_error≦ε, and setting (V_diff)_initial equal to the just stored value of V_diff. A further diffusion voltage V_diff is then determined using the same diffusion circuit model and the just obtained (V_diff)_initial and is advantageously used by a controller in an electric propulsion vehicle to determine a state of charge of the propulsion battery.

Claims

1. A method for determining an initial diffusion voltage (V_diff)_initial as a starting point when calculating a diffusion voltage V_diff in an electrochemical cell, comprising:

obtaining a time difference t_off between a time when the cell was last turned-OFF and a time when the cell was next turned-ON;

selecting a starting diffusion voltage (V_diff)stat based on t_off;

determining a trial diffusion voltage V_diff based on a diffusion circuit model and (V_diff)_start;

calculating an error voltage V_error=(V_diff)−

|V_OFF−

V_ON| where V_OFF and V_ON are cell voltages at cell turn-OFF and cell turn-ON respectively;

repeating the foregoing determining and calculating steps using for each iteration (V_diff)_start=(V_diff)_previous+V_error until V_error is less than or equal to a first predetermined tolerance amount ε

;

storing in a memory a value of V_diff corresponding to the condition V_error≦

ε

; and

setting (V_diff)_initial equal to the just stored value of V_diff.

2. The method of claim 1, wherein the selecting step comprises:

if t_off≦

t1, where t1 is a first predetermined constant, setting Δ

t used in determining V_diff equal to (t_off)/b, where b is first predetermined amount, and setting (V_diff)_start=|V_OFF−

V_ON|.

3. The method of claim 2, wherein the selecting step further comprises:

if t_off is not ≦

t1, determining whether t_off≧

t2 where t2 is a second predetermined constant greater than t1;

if t_off is not ≧

t2, setting Δ

t=Δ

t_a where Δ

t_a is second predetermined amount smaller than t1 and setting (V_diff)_start=|V_OFF−

V_ON|; and

if t_off≧

t2, setting (V_diff)_start=0.

4. The method of claim 2, wherein b has a value between about 5 and 25.

5. The method of claim 4, wherein b has a value between about 7 and 15.

6. The method of claim 3, wherein Δ

t_a has a value between about t 1/20 and t⅕

.

7. The method of claim 3, wherein t2 is in a range of about 20 to 60 times t1.

8. The method of claim 7, wherein t2 is in a range of about 30 to 50 times t1.

9. The method of claim 8, wherein t2 is about 35 to 37 times t1.

10. The method of claim 2, wherein t1 is in the range of about 400 to 800 seconds.

11. The method of claim 6, wherein t1 is about 600 seconds.

12. An energy management controller for a vehicle containing a battery, comprising:

a memory configured to store a battery condition parameter;

a processor coupled to the memory and configured to;

determine an initial diffusion voltage (V_diff)_initial of the battery by;

obtaining a time difference t_off between a time when the battery was last turned-OFF and a time when the battery was next turned-ON;

selecting a starting diffusion voltage (V_diff)_start based on t_off;

determining a trial diffusion voltage V_diff based on a diffusion circuit model of the battery and (V_diff)_start;

calculating an error voltage V_error=(V_diff)−

|V_OFF−

V_ON| where V_OFF and V_ON are battery voltages at battery turn-OFF and battery turn-ON respectively;

repeating the foregoing determining and calculating steps using for each iteration (V_diff)_start=(V_diff)_previous+V_error until V_error is less than or equal to a first predetermined tolerance amount ε

;

storing in the memory a value of V_diff corresponding to the condition V_error≦

ε

; and

then

setting (V_diff)_initial equal to the just stored value of V_diff; and

then

obtain a further diffusion voltage V_diff based on the diffusion circuit model of the battery and the initial diffusion voltage (V_diff)_initial obtained in the setting step; and

determine the battery condition parameter using the just obtained further diffusion voltage V_diff.

13. The controller of claim 12, wherein the processor is further adapted to select (V_diff)_start by operations comprising:

if t_off≦

t1, where t1 is a first predetermined constant, setting Δ

t used in determining V_diff equal to (t_off)/b, where b is first predetermined amount, and setting (V_diff)_start=|V_OFF−

V_ON|.

14. The controller of claim 13, wherein the processor is still further adapted to select (V_diff)_start by operations comprising:

if t_off is not ≦

t1, determining whether t_off≧

t2 where t2 is a second predetermined constant greater than t1;

if t_off is not ≧

t2, setting Δ

t=Δ

t_a where Δ

t_a is second predetermined amount smaller than t1 and setting (V_diff)_start=|V_OFF−

V_ON|; and

if t_off≧

t2, setting (V_diff)_start=0.

15. The controller of claim 13, wherein b has a value between about 7 and 15.

16. The controller of claim 12, wherein the processor is further configured to relate the just obtained further diffusion voltage V_diff to an overall voltage of the battery.

17. The controller of claim 12, wherein the processor is further configured to estimate a state of charge of the battery based on the just obtained further diffusion voltage V_diff.

18. 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 memory for storing a plurality of parameters regarding battery conditions; and

a processor coupled to the memory and configured to;

determine an initial diffusion voltage (V_diff)_initial by;

obtaining a time difference t_off between a time when the battery was last turned-OFF and a time when the battery was next turned-ON;

selecting a starting diffusion voltage (V_diff)_start based on t_off;

determining a trial diffusion voltage V_diff based on a diffusion circuit model of the battery and (V_diff)_start;

calculating an error voltage V_error=(V_diff)−

|V_OFF−

V_ON| where V_OFF and V_ON are battery voltages at battery turn-OFF and battery turn-ON respectively;

repeating the foregoing determining and calculating steps using for each iteration (V_diff)_start=(V_diff)_previous+V_error until V_error is less than or equal to a first predetermined tolerance amount ε

;

storing in the memory a value of V_diff corresponding to the condition V_error≦

ε

; and

then

setting (V_diff)_initial equal to the just stored value of V_diff; and

then

obtain a further value of diffusion voltage V_diff based on the diffusion circuit model of the battery and (V_diff)_initial obtained in the setting step; and

determine a state of charge of the battery using the just obtained further value of diffusion voltage V_diff.

19. The HEV according to claim 18, wherein the step of selecting the starting diffusion voltage (V_diff)_start comprises:

if t_off≦

t1, where t1 is a first predetermined constant, setting Δ

t used in determining V_diff equal to (t_off)/b where b is first predetermined amount and setting (V_diff)_start=|V_OFF−

V_ON|;

if t_off is not ≦

t1, determining whether t_off≧

t2 where t2 is a second predetermined constant greater than t1;

if t_off is not ≧

t2, setting Δ

t=Δ

t_a where Δ

t_a is second predetermined amount smaller than t1 and setting (V_diff)_start=|V_OFF−

V_ON|; and

if t_off≧

t2, setting (V_diff)_start=0.

20. The HEV according to claim 19, wherein t1 is in the range of about 400 to 800 seconds.