Methods and apparatuses for determining battery capacity

• US 7,405,571 B1
• Filed: 09/13/2005
• Issued: 07/29/2008
• Est. Priority Date: 09/15/2004
• Status: Expired due to Fees

• Current Assignee: HDM Systems Corporation
• Original Assignee: HDM Systems Corporation
• Inventors: Liu, David S. C.
• Primary Examiner(s): Nguyen; Matthew V
• Assistant Examiner(s): Tran; Nguyen
• Application Number:
  US11/226,651
• Time in Patent Office: 1,050 Days
• Field of Search: 324/430, 324/425, 324/426, 324/427, 320/132, 702/65
• US Class Current: 324/430
• 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: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: G01R 35/005 Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence

Abstract

Methods and apparatuses for determining a battery capacity are described. According to one embodiment, an exemplary method includes generating virtual calibration data of the battery based on one or more characteristics of the battery, determining a virtual open circuit voltage (Voc) of the battery while the battery is being used, and estimating the capacity of the battery based on the determined virtual open circuit voltage of the battery and the virtual calibration data of the battery, while the battery is being used.

Claims

1. A method for measuring a capacity of a battery, the method comprising:

generating virtual calibration data of the battery based on one or more characteristics of the battery;

determining an internal impedance (R_i) of the battery, including

applying a first load (I₁) across the battery,

measuring a first voltage (V₁) across the battery while the battery is being applied with the first load (I₁),

applying a second load (I₂) to the battery for a predetermined time duration in addition to the first load (I₁), and

measuring, during the predetermined time duration, a second voltage (V₂) across the battery in view of the first load (I₁) and the second load (I₂), wherein the internal impedance is determined based on at least a portion of V₁, V₂, I₁, and I₂;

determining a virtual open circuit voltage (V_oc) of the battery based on the internal impedance of the battery while the battery is being used; and

estimating the capacity of the battery based on the determined virtual open circuit voltage of the battery and the virtual calibration data of the battery, while the battery is being used.

2. The method of claim 1, wherein the battery is being discharged by the first load when the capacity of the battery is estimated.

3. The method of claim 2, wherein the internal impedance (R₁) of the battery is determined as follows, while the battery is being discharged:

R_i=|V₂−

V₁|/|I₂−

I₁|.

4. The method of claim 3, wherein the virtual open circuit voltage (V_oc) of the battery is determined as follows, while the battery is being discharged:

V_oc=V₁+I₁*R_i.

5. The method of claim 1, wherein the battery is being charged by a charging current (I_ch) when the first load (I₁) is being applied, and wherein the virtual open circuit voltage (V_oc) of the battery is determined further based on the charging current (I_ch).

6. The method of claim 5, wherein the internal impedance (R_i) of the battery is determined as follows, while the battery is being charged:

R_i=|V₂−

V₁|/|I₂−

I₁|.

7. The method of claim 6, wherein the virtual open circuit voltage (V_oc) of the battery is determined as follows, while the battery is being charged:

V_oc=V₁+|I₁−

I_ch|*R_i.

12. The method of claim 1, wherein the virtual calibration data of the battery is generated based on a type of the battery and stored as a lookup table for looking up the capacity of the battery in real time based on the determined virtual open circuit voltage (V_oc).

13. The method of claim 12, further comprising:

dividing a battery capacity represented by the lookup table into a plurality of segments maintained within the lookup table, each segment corresponding to a range of virtual reference voltages; and

in response to the determined virtual open circuit voltage (V_oc), determining the battery capacity by looking up within the lookup table a battery capacity corresponding to a range of virtual reference voltage that contains the determined Voc.

8. A method for measuring a capacity of a battery, the method comprising:

generating virtual calibration data of the battery based on one or more characteristics of the battery;

determining a virtual open circuit voltage (V_oc) of the battery while the battery is being used;

determining an internal impedance (R_i) of the battery, wherein the virtual open circuit voltage of the battery is determined based on the internal impedance of the battery; and

estimating the capacity of the battery based on the determined virtual open circuit voltage of the battery and the virtual calibration data of the battery while the battery is being used, wherein the battery is being discharged and charged substantially concurrently when the capacity of the battery is estimated, including

obtaining a difference (Δ

I) between a charge current (I₁) and a discharge current (I₂) while the battery is being discharged and charged substantially concurrently,

applying a second load (I₃) that is grater than Δ

I₄,

measuring a second voltage (V₃) across the battery while the second load (I₃) is being applied,

applying a third load (I₄) that is grater than the second load (I₃), and

measuring a third voltage (V₄) across the battery in view of the second load (I₃) and the third load (I₄), wherein at least one of the internal impedance and virtual open circuit voltage (V_oc) of the battery is determined based on at least a portion of V₃, V₄, I₁, I₂, I₃, and I₄.

9. The method of claim 8, wherein the internal impedance (R_i) of the battery is determined as follows:

R_i=|V₄−

V₃|/|I₄−

I₃|.

10. The method of claim 9, wherein the virtual open circuit voltage (V_oc) of the battery is determined as follows:

V_oc=V₃+R_i|I₃−

Δ

I|.

11. The method of claim 9, wherein the virtual open circuit voltage (V_oc) of the battery is determined as follows:

V_oc=V₄+R_i|I₄−

Δ

I|.

14. An apparatus for measuring a capacity of a battery, comprising:

a database to maintain virtual calibration data of the battery based on one or more characteristics of the battery; and

a controller to determine an internal impedance (R_i) of the battery, including

applying a first load (I_i) across the battery,

measuring a first voltage (V₁) across the battery while the battery is being applied with the first load (I₁),

applying a second load (I₂) to the battery for a predetermined time duration in addition to the first load (I₁), and

measuring, during the predetermined time duration, a second voltage (V₂) across the battery in view of the first load (I₁) and the second load (I₂), wherein the internal impedance is determined based on at least a portion of V₁, V₂, I₁, and I₂,

wherein the controller is configured to determine a virtual open circuit voltage (V_oc) of the battery based on the internal impedance of the battery while the battery is being used, wherein the controller is configured to estimate the capacity of the battery based on the determined virtual open circuit voltage of the battery and the virtual calibration data of the battery stored on the database while the battery is being used.

15. The apparatus of claim 14, wherein the battery is being discharged when the capacity of the battery is estimated, and wherein the controller is configured further to

measure a first voltage (V₁) across the battery while the battery is being discharged by a first load (I₁),

apply a second load (I₂) to the battery in addition to the first load (I₁), and

measure a second voltage (V₂) across the battery in view of the first load (I₁) and the second load (I₂), wherein at least one of the internal impedance and virtual open circuit voltage (V_oc) of the battery is determined based on at least a portion of V₁, V₂, I₁, and I₂.

16. The apparatus of claim 14, wherein the battery is being charged when the capacity of the battery is estimated, and wherein the controller is configured further to

apply a first load (I₁) to the battery while the battery is being charged with a charging current (I_ch),

measure a first voltage (V₁) across the battery while the first load (I₁) is being applied to the battery,

apply a second load (I₂) to the battery in addition to the first load (I₁) while the battery is being charged, and

measured a second voltage (V₂) across the battery in view of the first load (I₁) and the second load (I₂) while the battery is being charged, wherein at least one of the internal impedance and virtual open circuit voltage (V_oc) of the battery is determined based on at least a portion of V₁, V₂, I_ch, I₁, and I₂.

17. An apparatus for measuring a capacity of a battery, comprising:

a database to maintain virtual calibration data of the battery based on one or more characteristics of the battery; and

a controller to determine a virtual open circuit voltage (V_oc) of the battery while the battery is being used, wherein the controller is configured to estimate the capacity of the battery based on the determined virtual open circuit voltage of the battery and the virtual calibration data of the battery stored on the database while the battery is being used,

wherein the controller is configured further to determine an internal impedance (R_i) of the battery, wherein the virtual open circuit voltage of the battery is determined based on the internal impedance of the battery,

wherein the battery is being discharged and charged substantially concurrently when the capacity of the battery is estimated, and wherein the controller is configured further to

obtain a difference (Δ

I) between a charge current (I₁) and a discharge current (I₂) while the battery is being discharged and charged substantially concurrently,

apply a second load (I₃) that is grater than Δ

I,

measure a second voltage (V₃) across the battery while the second load (I₃) is being applied,

apply a third load (I₄) that is grater than the second load (I₃), and

measure a third voltage (V₄) across the battery in view of the second load (I₃) and the third load (I₄), wherein at least one of the internal impedance and virtual open circuit voltage (V_oc) of the battery is determined based on at least a portion of V₃, V₄, I₁, I₂, I₃, and I₄.

18. An apparatus for measuring a capacity of a battery, comprising:

means for generating virtual calibration data of the battery based on one or more characteristics of the battery;

means for determining an internal impedance (R_i) of the battery, including

means for applying a first load (I₁) across the battery,

means for measuring a first voltage (V₁) across the battery while the battery is being applied with the first load (I₁),

means for applying a second load (I₂) to the battery for a predetermined time duration in addition to the first load (I₁), and

means for measuring, during the predetermined time duration, a second voltage (V₂) across the battery in view of the first load (I₁) and the second load (I₂), wherein the internal impedance is determined based on at least a portion of V₁, V₂, I₁, and I₂;

means for determining a virtual open circuit voltage (Voc) of the battery based on the internal impedance of the battery while the battery is being used; and

means for estimating the capacity of the battery based on the determined virtual open circuit voltage of the battery and the virtual calibration data of the battery, while the battery is being used.