DYNAMICALLY ADAPTIVE METHOD FOR DETERMINING THE STATE OF CHARGE OF A BATTERY

• US 20090091299A1
• Filed: 10/04/2007
• Published: 04/09/2009
• Est. Priority Date: 10/04/2007
• 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: GIELNIAK, MICHAEL J., TANG, XIDONG, KOCH, BRIAN J., LIN, JIAN, FRISCH, DAMON R.
• Granted Patent: US 7,768,233 B2
• Time in Patent Office: Days
• US Class Current: 320/137
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: H01M 10/0525 Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• CPC Class Codes: H01M 10/441 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 10/443 in response to temperature
• CPC Class Codes: H01M 10/446 Initial charging measures
• CPC Class Codes: H01M 10/448 End of discharge regulating measures
• CPC Class Codes: H01M 10/482 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A method for determining the state of charge (SOC) of a lithium ion battery is provided. The method leverages a circuit model of the lithium ion battery, and generates four battery parameters from which the SOC is derived.

Claims

1. A method for determining state of charge (SOC) of a battery, the method comprising:

obtaining sampled terminal voltage data for a lithium ion battery, the lithium ion battery being characterized by its ohmic resistance (R), its open circuit voltage (V_oc), a double layer time constant (τ

=C_dlR_ct), where C_dl is a double layer capacitance of the lithium ion battery and R_ct is charge transfer resistance;

obtaining sampled terminal current data for the lithium ion battery;

calculating a present V_oc value from the sampled terminal voltage data and the sampled terminal current data, the present V_oc value being dependent upon V_dl values of the lithium ion battery; and

generating a present SOC value from the present V_oc value.

2. The method of claim 1, further comprising obtaining sampled battery temperature data for the lithium ion battery, wherein generating a present SOC value comprises generating the present SOC value from the present V_oc value and the sampled battery temperature data.

3. The method of claim 1, further comprising adaptively updating the present SOC value by repeating over time the steps of obtaining sampled terminal voltage data, obtaining sampled terminal current data, calculating a present V_oc value, and generating a present SOC value.

4. The method of claim 1, further comprising:

providing an arbitrary initial terminal voltage value;

providing an arbitrary initial terminal current value; and

setting an initial condition for generation of the present SOC value, the initial condition being based upon the arbitrary initial terminal voltage value and the arbitrary initial terminal current value.

5. The method of claim 1, further comprising calculating a present R value from the sampled terminal voltage data and the sampled terminal current data.

6. The method of claim 1, further comprising calculating a present V_dl value from the sampled terminal voltage data and the sampled terminal current data.

7. The method of claim 1, further comprising calculating a present A value from the sampled terminal voltage data and the sampled terminal current data.

8. The method of claim 1, further comprising:

comparing the present SOC value to a threshold value; and

if the present SOC value is less than the threshold value, initiating charging of the lithium ion battery.

9. A method for determining state of charge (SOC) of a battery having an ohmic resistance (R), a double layer voltage (V_dl), an open circuit voltage (V_oc), and a characterizing constant

10. The method of claim 9, further comprising obtaining sampled battery temperature data for the battery, wherein generating a present SOC value comprises generating the present SOC value from the battery parameters θ

₁ and θ

₄ and from the sampled battery temperature data.

11. The method of claim 9, further comprising:

providing an arbitrary initial terminal voltage value;

providing an arbitrary initial terminal current value; and

setting an initial condition for generation of the present SOC value, the initial condition being based upon the arbitrary initial terminal voltage value and the arbitrary initial terminal current value.

12. The method of claim 9, further comprising:

comparing the present SOC value to a threshold value; and

if the present SOC value is less than the threshold value, initiating charging of the battery.

13. The method of claim 9, further comprising calculating a present V_oc value for the battery in accordance with the relationship

14. The method of claim 9, wherein calculating battery parameters θ

₁, θ

₂, θ

₃, and θ

₄ comprises;

computing a gain vector (G) in accordance with the relationship

15. The method of claim 14, further comprising updating P in accordance with the relationship

16. A diagnostic and control system for a vehicle battery, the diagnostic and control system comprising:

a lithium ion battery pack having an ohmic resistance (R), a double layer voltage (V_dl), an open circuit voltage (V_oc), and a characterizing constant

17. The diagnostic and control system of claim 16, the computer-executable instructions being written to:

obtain sampled battery temperature data for the lithium ion battery pack; and

generate the present SOC value from the present V_oc value and the sampled battery temperature data.

18. The diagnostic and control system of claim 16, the computer-executable instructions being written to adaptively update the present SOC value by repeating over time the steps of obtaining sampled terminal voltage data, obtaining sampled terminal current data, calculating a present V_oc value, and generating a present SOC value.

19. The diagnostic and control system of claim 16, the computer-executable instructions being written to:

provide an arbitrary initial terminal voltage value;

provide an arbitrary initial terminal current value; and

set an initial condition for generation of the present SOC value, the initial condition being based upon the arbitrary initial terminal voltage value and the arbitrary initial terminal current value.

20. The diagnostic and control system of claim 16, the computer-executable instructions being written to:

compare the present SOC value to a threshold value; and

if the present SOC value is less than the threshold value, initiate charging of the lithium ion battery pack.