Method and apparatus for estimating SOC of a battery

• US 8,452,556 B2
• Filed: 09/22/2010
• Issued: 05/28/2013
• Est. Priority Date: 09/22/2010
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations LLC (General Motors Company)
• Inventors: Zhang, Yilu, Shin, Kwang-Keun, Tang, Xidong, Salman, Mutasim A.
• Primary Examiner(s): Huynh, Phuong
• Application Number:
  US12/887,644
• Publication Number:
  US 20120072144A1
• Time in Patent Office: 979 Days
• Field of Search: 702 63- 65, 702 81- 84, 702121-123, 702182-189
• US Class Current: 702/63
• CPC Class Codes: B60L 58/12 responding to state of charge [SoC]
• CPC Class Codes: G01R 31/006 on road vehicles, e.g. automobiles or trucks testing of ignition installations peculiar to internal combustion engines F02P17/00
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/3828 using current integration
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• 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 method of determining a state-of-charge for a battery is provided. A startup state-of-charge of the battery is determined as a function of a present open circuit voltage measurement for a present ignition startup, at least one open circuit voltage observation of a previous ignition startup, and a current draw integration over a time period from a previous ignition startup event to a present ignition startup event. A run state-of-charge change of the battery is determined for an ignition key-on operation. The run state-of-charge change comprises a difference between the present open circuit voltage measurement and the at least one previous open circuit voltage observation, and is determined in response to of a current draw integration over a respective period of time. The state-of-charge of the battery is calculated based on a function of the startup state-of-charge and the run state-of-charge change of the battery.

Claims

1. A method of determining a state-of-charge for a battery, the method comprising the steps of:

measuring open circuit voltages of a vehicle battery during ignition startups by a voltmeter;

determining a startup state-of-charge of the battery by a control module as a function of a present open circuit voltage measurement for a present ignition startup, at least one open circuit voltage observation of a previous ignition startup, and a current draw integration over a time period from a previous ignition startup event to a present ignition startup event;

determining a run state-of-charge change of the battery by the control module for an ignition key-on operation, the run state-of-charge change comprising a difference between the present open circuit voltage measurement and the at least one previous open circuit voltage observation, and determined in response to a current draw integration over a respective period of time; and

calculating the state-of-charge of the battery by the control module based on a function of the startup state-of-charge and the run state-of-charge change of the battery.

2. The method of claim 1 wherein the state-of-charge for a battery is represented by the following formula:

S_oc=SOC_startup+SOC_running=f(V_oc(0),T)+θ

∫

Idt

where f(V_oc(0),T) is the startup state-of-charge and is a function of the open circuit voltage and temperature, and θ

∫

Idt is a run state-of-charge change and is a function of a battery parameter and the current draw integration over the respective period of time.

3. The method of claim 2 wherein the startup state-of-charge is derived from an open circuit voltage estimation based on the following formula:

4. The method of claim 3 wherein the adjustment factor is represented by the following formula:

λ

=e<sup>−

toff(tk)/τ</sup>

where t_off is an elapsed time between an ignition key-on operation and an ignition key-off operation, t_k is a time the ignition key is turned on at the k_th ignition interval, and τ

is a time constant.

5. The method of claim 3 wherein the battery parameter θ

is a function of a previous battery parameter observation and a present estimated battery parameter.

6. The method of claim 5 wherein the battery parameter θ

is represented by the following formula;

7. The method of claim 6 wherein the adjustment factor for the battery parameter is a function of a time that an ignition key is off, and wherein the adjustment factor is determined by the following formula:

λ

=e<sup>−

toff(tk)/τ</sup>

_θ

.

8. The method of claim 6 wherein the present open circuit voltage measurement, the previous open circuit voltage observation, and the battery parameter are normalized at a respective temperature.

9. The method of claim 8 wherein the open circuit voltages for the startup state-of-charge and the run state-of-charge change are normalized at a respective temperature.

10. The method of claim 9 wherein a normalized open circuit voltage for the state-of-charge of the battery is determined as a function of the open circuit voltage determined for the startup state-of-charge at the respective temperature, and a function of the battery parameter and current integration for the run state-of-charge change at the respective temperature.

11. The method of claim 10 wherein the normalized open circuit voltage for the state-of-charge of the battery is converted back to an open circuit voltage at a current temperature.

12. The method of claim 11 wherein the state-of-charge of the battery is determined as a function of the open circuit voltage at the current temperature.

13. The method of claim 1 wherein the state of charge of the battery is displayed to user of the vehicle via a display device.

14. The method of claim 1 wherein a representation of the state of charge of the battery is displayed to user of the vehicle via a display device.

15. A system for determining a state-of-charge of a battery comprising:

a battery;

at least one component for drawing power from the battery;

a voltmeter for measuring an open circuit voltage of the battery at ignition start sequences;

a current sensor for sensing current drawn from the battery; and

a control module for determining a state-of-charge of a battery as a function of the startup state-of-charge and the run state-of-charge change of the battery, the startup state-of-charge being determined at a time of an ignition startup event, the startup state-of-charge being a function of a present open circuit voltage measurement for a present ignition startup, at least one previous open circuit voltage observation, and a current integration over time period from a previous ignition event to a present ignition event, the run state-of-charge change comprising at a time during an ignition on operation, the run state-of-charge change being estimated as a difference between the present open circuit voltage measurement and at least one previous open circuit voltage observation determined in response to current integration over a respective period of time.

16. The system of claim 15 wherein the control module determines the startup state-of-charge from an estimated open circuit voltage based on the following formula:

17. The system of claim 16 wherein the control module determines the adjustment factor based on the following formula:

λ

=e<sup>−

toff(tk)/τ</sup>

where t_off is an elapsed time between an ignition key-on operation and an ignition key-off operation, t_k is a time the ignition key is turned on at the k_th ignition interval, and τ

is a time constant.

18. The system of claim 17 wherein the control module determines the battery parameter based on the following formula:

19. The system of claim 15 wherein the control module determines the adjustment factor for the battery parameter based on the following formula:

λ

=e<sup>−

toff(tk)/τ

θ</sup>

.

20. The system of claim 15 further comprising a display for identifying the state of charge of the battery to a user of the vehicle.