Battery SOC estimation with automatic correction

• US 9,108,524 B2
• Filed: 10/22/2013
• Issued: 08/18/2015
• Est. Priority Date: 10/22/2013
• 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, Du, Xinyu, Salman, Mutasim A., Huang, Shuo
• Primary Examiner(s): Shaawat, Mussa A
• Application Number:
  US14/059,751
• Publication Number:
  US 20150112527A1
• Time in Patent Office: 665 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: B60L 2240/545 Temperature
• CPC Class Codes: B60L 2240/547 Voltage
• CPC Class Codes: B60L 2240/549 Current
• CPC Class Codes: B60L 2250/16 by display
• CPC Class Codes: B60L 58/12 responding to state of charge [SoC]
• CPC Class Codes: B60W 20/00 Control systems specially adapted for hybrid vehicles hybrid vehicle design, B60K6/00; electric vehicles B60L
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/382 Arrangements for monitoring battery or accumulator variables, e.g. SoC
• CPC Class Codes: G01R 31/3828 using current integration
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

An embodiment contemplates a method of determining a state-of-charge of a battery for a vehicle. (a) An OCV is measured for a current vehicle ignition startup after ignition off for at least eight hours. (b) An SOC_OCV is determined for the current vehicle ignition startup. (c) An SOC_OCV—est is determined for a current vehicle ignition startup. (d) A determination is made whether the difference in the SOC_OCV for the current startup and the SOC_OCVest for the current startup is less than a predefined error bound using. Steps (a)-(d) is performed in response to the difference being greater than the predefined error; otherwise, determining an ignition-off current for the current vehicle ignition startup as a function of the SOC_OCV of the current vehicle ignition startup and previous vehicle ignition startup, and a SOC based on current integration over time. Determining an SOC_est of the current vehicle ignition startup using the processor.

Claims

1. A method of determining a state-of-charge of a battery for a vehicle, the vehicle being in a charging state when the engine is operating and a non-charging state when the engine is not operating, the method comprising the steps of:

(a) measuring an open circuit voltage (OCV) for a current vehicle ignition startup using a voltmeter, wherein the current vehicle ignition start-up is performed after the vehicle is in the non-charging state for at least eight hours;

(b) determining an open circuit voltage-based state of charge (SOC_OCV) for the current vehicle ignition startup using the processor;

(c) determining an estimated open circuit-based state of charge (SOC<sub>OCV—

est</sub>) for a current vehicle ignition startup using the processor;

(d) determining whether the difference in the SOC_OCV for the current vehicle ignition startup and the SOC_OCVest for the current vehicle ignition startup is less than a predefined error bound using the processor;

(e) performing steps (a)-(d) in response to the difference being greater than the predefined error;

otherwise, proceeding to step (f);

(f) determining an ignition-off current for the current vehicle ignition startup as a function of the SOC_OCV of the current vehicle ignition startup, an SOC_OCV of a previous vehicle ignition startup, and a state-of-charge based on current integration over time using the processor technique;

(g) determining an estimated state of charge (SOC_est) of the current vehicle ignition startup using the processor; and

(h) providing the SOC_est to a vehicle subsystem for use in a vehicle operation where the battery state-of-charge is utilized.

2. The method of claim 1 wherein estimating a SOC_est of the current vehicle ignition startup is determined as a function of the SOC_est of a previous vehicle ignition startup, a state-of-charge based on an ignition-on current integration over time, and a state-of-charge based on the ignition-off current integration over time.

3. The method of claim 2 wherein estimating a SOC_est of the current vehicle ignition startup is represented by the following formula:

4. The method of claim 1 wherein the SOC_OCV—

_est for a current vehicle ignition startup is determined by the following formula;

SOC<sub>OCV—

est</sub>(k)=SOC_OCV(k−

i)+Δ

SOC

where SOC_OCV(k−

i) is and open circuit voltage based SOC at ignition k−

i, and Δ

SOC is the integration of ignition-on current from ignition k−

i to ignition k, and i is a count of the vehicle ignition startup.

5. The method of claim 1 wherein if no error is present in the measurement data, then the formula for determining the vehicle ignition-off current is determined as follows:

6. The method of claim 1 wherein if measurement data error is present and an error distribution is non-uniform, then a particle filter is used for determining the ignition-off current.

7. The method of claim 6 wherein a state space model is defined and a measurement model is defined for determining the ignition-off current.

8. The method of claim 7 wherein the state space model of the SOC for current vehicle ignition startup is defined by the following formula:

9. The method of claim 8 wherein the state space model of the ignition-off current for the vehicle ignition startup is defined by the following formula:

I_off(k)=I_off(k−

1)+ε

₁

where I_off(k) is the ignition-off current for the current vehicle startup, and I_off (k−

1) is the ignition-off current for the previous vehicle startup, and ε

¹ is the measurement error of a current sensor.

10. The method of claim 7 wherein the measurement model is defined by the following formula:

SOC_off(k)=SOC_OCV(k)−

ε

_OCV

where SOC_off(k) is the ignition-off current for the current vehicle startup, and SOC_OCV(k−

1) is the ignition-off current for the previous vehicle startup, and ε

_OCV is the measurement error of the current sensor for the OCV.

11. The method of claim 7 wherein determining the ignition-off current using the particle filter comprises the following steps of:

initializing a particle set;

updating a respective particle in the particle set based on the state space model for determining a estimate of the SOC_est at a k^th ignition start using the state space model;

calculate a weighting factor that is a function of the SOC at a k^th ignition start and the estimate SOC_est at a k^th ignition start;

resampling a particle set as a function of the weighting factor; and

estimating the weighted average of the ignition-off current at current ignition startup.

12. The method of claim 11 wherein the particle set of I_offⁱ(0) for i=1, 2, . . . , N.

13. The method of claim 12 wherein the weighting factor is represented by the following formula:

14. The method of claim 13 wherein the estimated weighted average of the ignition-off current is represented by the following formula:

I_off(k)=Σ

_iwⁱ(k)I_offⁱ(k)

where wⁱ(k) is a respective weight for a particle at each respective ignition start, and I_offⁱ(k) is the measured ignition off current for each particle at each respective ignition start.

15. The method of claim 1 wherein if current sensor error is determined and an error distribution is uniform, then a Kalman filter is used for determining the ignition-off current.

16. The method of claim 1 wherein the step of providing the SOC_est to a vehicle subsystem for use in a vehicle operation includes outputting the SOC_est to a display device for identifying the state-of-charge to the operator of the vehicle.

17. The method of claim 1 further comprising the step of determining whether the estimated SOC is utilized for a duration of time greater than a predetermined period of time, and wherein a return is made to step (a) if the estimated SOC being utilized for a duration of time that is greater than the predetermined period of time.

18. The method of claim 17 wherein if the estimated SOC is utilized for a duration of time that is less than a predetermined period of time, the method comprises the following steps:

determining whether the current ignition-off time is greater than eight hours and the SOC_OCV is within an error bound; and

proceeding to step (f) in response to determining that the current ignition-off time is greater than eight hours and the SOC_OCV is within the error bound, otherwise proceeding to step (a).