Method and apparatus for determining a capacity of a battery

• US 9,081,068 B2
• Filed: 09/18/2012
• Issued: 07/14/2015
• Est. Priority Date: 09/18/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Mattisson, Nils E., Greening, Thomas C., Koller, Jeffrey G.
• Primary Examiner(s): DIAO, M BAYE
• Application Number:
  US13/622,242
• Publication Number:
  US 20140077815A1
• Time in Patent Office: 1,029 Days
• Field of Search: 324/427, 324/432, 324/434, 320/132, 702/63
• US Class Current: 1/1
• CPC Class Codes: G01R 19/0069 measuring voltage or current standards
• CPC Class Codes: G01R 19/165 Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
• CPC Class Codes: G01R 21/06 by measuring current and voltage G01R21/08 - G01R21/133 take precedence
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• 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: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: G01R 31/392 Determining battery ageing or deterioration, e.g. state of health
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

Some embodiments of the present invention provide a system that accurately and reliably updates a full charge capacity of a battery. During operation, the system charges the battery from an initial state to a rest point prior to reaching a fully charged state. The system then interrupts the charging process to allow the battery to relax to a resting voltage. Next, the system measures the resting voltage. The system then resumes the charging process toward the fully charged state. The system subsequently estimates the capacity of the battery based on the measured resting voltage and one or more other parameters.

Claims

1. A method for accurately estimating a capacity of a battery, comprising:

determining if a state of charge of the battery corresponding to an initial state is above a state of charge of the battery corresponding to a rest point; and

if so, charging the battery from the initial state to a fully charged state without interrupting the charging process;

if the state of charge of the battery corresponding to the initial state is below the state of charge of the battery corresponding to the rest point, charging the battery from the initial state to the rest point prior to reaching the fully charged state;

interrupting the charging process to allow the battery to relax to a resting voltage;

measuring the resting voltage;

resuming the charging process toward the fully charged state; and

estimating the capacity of the battery based at least on the resting voltage.

2. The method of claim 1, wherein the capacity is a full charge capacity.

3. The method of claim 1, wherein charging the battery from the initial state to the rest point involves charging the battery with a constant current during a time period immediately preceding the rest point.

4. The method of claim 3, wherein interrupting the charging process involves immediately dropping the charging current to zero.

5. The method of claim 3, wherein interrupting the charging process involves reducing the charging current to a low level above zero.

6. The method of claim 1, wherein after reaching the fully charged state, the method further comprises:

allowing the battery to relax to a second resting voltage; and

measuring the second resting voltage corresponding to the fully charged state.

7. The method of claim 6, wherein estimating the capacity of the battery based at least on the resting voltage involves:

computing a first state of charge of the battery corresponding to the resting voltage;

computing a second state of charge of the battery corresponding to the second resting voltage;

determining a coulomb count between the rest point and the fully charged state; and

determining the capacity of the battery based on the first state of charge, the second state of charge, and the coulomb count.

8. The method of claim 7, wherein determining the coulomb count between the rest point and the fully charged state involves:

initiating a coulomb counting from the rest point after resuming the charging process;

concluding the coulomb counting when the fully charged state is reached; and

determining the coulomb count based on the coulomb counting between the rest point and the fully charged state.

9. The method of claim 7, wherein each of the resting voltage and the second resting voltage is an open circuit voltage (OCV).

10. The method of claim 1, wherein prior to charging the battery, the method further comprises selecting the rest point based at least on one or more of the following parameters:

a time required for the battery to relax at the rest point;

an error associated with a coulomb counting between the rest point and the fully charged state;

a likelihood of a user discharging the battery below the rest point; and

an open-circuit-voltage measurement accuracy required to compute a state of charge associated with the rest point.

11. The method of claim 10, wherein selecting the rest point involves ensuring that the time required for the battery to relax at the rest point is significantly shorter than a time to charge the battery from the initial state to the fully charged state without interruption.

12. The method of claim 10, wherein the rest point is in the vicinity of or above a 60% state of charge of the battery.

13. The method of claim 10, wherein the rest point is in the vicinity of or below an 80% state of charge of the battery.

14. A non-transitory computer-readable storage medium storing instructions that when executed by a controller for a battery cause the controller to perform a method for accurately estimating a capacity of the battery, the method comprising:

determining if a state of charge of the battery corresponding to an initial state is above a state of charge of the battery corresponding to a rest point; and

if so, charging the battery from the initial state to a fully charged state without interrupting the charging process;

if the state of charge of the battery corresponding to the initial state is below the state of charge of the battery corresponding to the rest point, charging the battery from the initial state to the rest point prior to reaching the fully charged state;

interrupting the charging process to allow the battery to relax to a resting voltage;

measuring the resting voltage;

resuming the charging process toward the fully charged state; and

estimating the capacity of the battery based at least on the resting voltage.

15. The non-transitory computer-readable storage medium of claim 14, wherein the capacity is a full charge capacity.

16. The non-transitory computer-readable storage medium of claim 14, wherein charging the battery from the initial state to the rest point involves charging the battery with a constant current during a time period immediately preceding the rest point.

17. The non-transitory computer-readable storage medium of claim 16, wherein interrupting the charging process involves immediately dropping the charging current to zero.

18. The non-transitory computer-readable storage medium of claim 14, wherein after reaching the fully charged state, the method further comprises:

allowing the battery to relax to a second resting voltage; and

measuring the second resting voltage corresponding to the fully charged state.

19. The non-transitory computer-readable storage medium of claim 18, wherein determining the capacity of the battery based at least on the resting voltage involves:

computing a first state of charge of the battery corresponding to the resting voltage;

computing a second state of charge of the battery corresponding to the second resting voltage;

determining a coulomb count between the rest point and the fully charged state; and

determining the capacity of the battery based on the first state of charge, the second state of charge, and the coulomb count.

20. The non-transitory computer-readable storage medium of claim 19, wherein determining the coulomb count between the rest point and the fully charged state involves:

initiating a coulomb counting from the rest point after resuming the charging process;

concluding the coulomb counting when the fully charged state is reached; and

determining the coulomb count based on the coulomb counting between the rest point and the fully charged state.

21. The non-transitory computer-readable storage medium of claim 14, wherein prior to charging the battery, the method further comprises selecting the rest point based at least on one or more of the following parameters:

a time required for the battery to relax at the rest point;

an error associated with a coulomb counting between the rest point and the fully charged state;

a likelihood of a user discharging the battery below the rest point; and

an open-circuit-voltage measurement accuracy required to compute a state of charge associated with the rest point.

22. The non-transitory computer-readable storage medium of claim 21, wherein selecting the rest point involves ensuring that the time required for the battery to relax at the rest point is significantly shorter than a time to charge the battery from the initial state to the fully charged state without interruption.

23. A battery with a capacity estimation mechanism, comprising:

a cell;

a voltage sensor configured to measure a voltage for the battery;

a current sensor configured to measure a current for the battery; and

a controller configured to receive inputs from the voltage sensor and the current sensor, and to generate a capacity estimate;

wherein the controller is configured to;

determine if a state of charge of the battery corresponding to an initial state is above a state of charge of the battery corresponding to a rest point; and

if so, charge the battery from the initial state to a fully charged state without interrupting the charging process;

if the state of charge of the battery corresponding to the initial state is below the state of charge of the battery corresponding to the rest point, charge the battery from the initial state to the rest point prior to reaching the fully charged state;

interrupt the charging process to allow the battery to relax to a resting voltage;

measure the resting voltage;

resume the charging process toward the fully charged state; and

estimate the capacity of the battery based at least on the resting voltage.

24. The battery of claim 23, wherein the controller is configured to charge the battery from the initial state to the rest point by charging the battery with a constant current during a time period immediately preceding the rest point.

25. The battery of claim 24, wherein the controller is configured to interrupt the charging process by immediately dropping the charging current to zero.

26. The battery of claim 23, wherein after reaching the fully charged state, the controller is configured to:

allow the battery to relax to a second resting voltage; and

measure the second resting voltage corresponding to the fully charged state.

27. The battery of claim 26, wherein the controller is configured to determine the capacity of the battery by:

computing a first state of charge of the battery corresponding to the resting voltage;

computing a second state of charge of the battery corresponding to the second resting voltage;

determining a coulomb count between the rest point and the fully charged state; and

determining the capacity of the battery based on the first state of charge, the second state of charge, and the coulomb count.

28. The battery of claim 27, wherein the controller is configured to determine the coulomb count between the rest point and the fully charged state by:

initiating a coulomb counting from the rest point after resuming the charging process;

concluding the coulomb counting when the fully charged state is reached; and

determining the coulomb count based on the coulomb counting between the rest point and the fully charged state.

29. A method for evaluating a state of charge of a battery during a charging process, the method comprising:

determining if a state of charge of the battery corresponding to an initial state is above a state of charge of the battery corresponding to a rest point; and

if so, charging the battery from the initial state to a fully charged state without interrupting the charging process;

if the state of charge of the battery corresponding to the initial state is below the state of charge of the battery corresponding to the rest point, charging the battery from the initial state to the rest point prior to reaching the fully charged state;

interrupting the charging process to allow the battery to relax to a resting voltage;

measuring the resting voltage; and

determining a state of charge of the battery at the rest point based at least on the resting voltage.

30. A method for accurately estimating a capacity of a battery, comprising:

charging the battery from an initial state to a rest point prior to reaching a fully charged state;

interrupting the charging process to allow the battery to relax to a resting voltage;

measuring the resting voltage;

resuming the charging process toward the fully charged state; and

estimating the capacity of the battery based at least on the resting voltage;

wherein prior to charging the battery, the method further comprises selecting the rest point based at least on one or more of the following parameters;

a time required for the battery to relax at the rest point;

an error associated with a coulomb counting between the rest point and the fully charged state;

a likelihood of a user discharging the battery below the rest point; and

an open-circuit-voltage measurement accuracy required to compute a state of charge associated with the rest point.

31. The method of claim 30, wherein selecting the rest point involves ensuring that the time required for the battery to relax at the rest point is significantly shorter than a time to charge the battery from the initial state to the fully charged state without interruption.

32. The method of claim 30, wherein the rest point is in the vicinity of or above a 60% state of charge of the battery.

33. The method of claim 30, wherein the rest point is in the vicinity of or below an 80% state of charge of the battery.

34. A battery with a capacity estimation mechanism, comprising:

a cell;

a voltage sensor configured to measure a voltage for the battery;

a current sensor configured to measure a current for the battery; and

a controller configured to receive inputs from the voltage sensor and the current sensor, and to generate a capacity estimate;

wherein the controller is configured to;

charge the battery from an initial state to a rest point prior to reaching a fully charged state;

interrupt the charging process to allow the battery to relax to a resting voltage;

measure the resting voltage;

resume the charging process toward the fully charged state; and

estimate the capacity of the battery based at least on the resting voltage;

wherein prior to charging the battery, the controller is configured to select the rest point based at least on one or more of the following parameters;

a time required for the battery to relax at the rest point;

an error associated with a coulomb counting between the rest point and the fully charged state;

a likelihood of a user discharging the battery below the rest point; and

an open-circuit-voltage measurement accuracy required to compute a state of charge associated with the rest point.

35. The battery of claim 34, wherein while selecting the rest point, the controller is configured to ensure that the time required for the battery to relax at the rest point is significantly shorter than a time to charge the battery from the initial state to the fully charged state without interruption.

36. The battery of claim 34, wherein the rest point is in the vicinity of or above a 60% state of charge of the battery.

37. The method of claim 34, wherein the rest point is in the vicinity of or below an 80% state of charge of the battery.

38. A method for accurately estimating a capacity of a battery, comprising:

charging the battery from an initial state to a rest point prior to reaching a fully charged state;

interrupting the charging process to allow the battery to relax to a resting voltage;

measuring the resting voltage;

resuming the charging process toward the fully charged state; and

estimating the capacity of the battery based at least on the resting voltage;

wherein estimating the capacity of the battery based at least on the resting voltage involves;

computing a first state of charge of the battery corresponding to the resting voltage;

computing a second state of charge of the battery corresponding to the second resting voltage;

determining a coulomb count between the rest point and the fully charged state; and

determining the capacity of the battery based on the first state of charge, the second state of charge, and the coulomb count.

39. The method of claim 38, wherein determining the coulomb count between the rest point and the fully charged state involves:

initiating a coulomb counting from the rest point after resuming the charging process;

concluding the coulomb counting when the fully charged state is reached; and

determining the coulomb count based on the coulomb counting between the rest point and the fully charged state.

40. The method of claim 38, wherein each of the resting voltage and the second resting voltage is an open circuit voltage (OCV).

41. A battery with a capacity estimation mechanism, comprising:

a cell;

a voltage sensor configured to measure a voltage for the battery;

a current sensor configured to measure a current for the battery; and

a controller configured to receive inputs from the voltage sensor and the current sensor, and to generate a capacity estimate;

wherein the controller is configured to;

charge the battery from an initial state to a rest point prior to reaching a fully charged state;

interrupt the charging process to allow the battery to relax to a resting voltage;

measure the resting voltage;

resume the charging process toward the fully charged state; and

estimate the capacity of the battery based at least on the resting voltage;

wherein while estimating the capacity of the battery based at least on the resting voltage, the controller is configured to;

compute a first state of charge of the battery corresponding to the resting voltage;

compute a second state of charge of the battery corresponding to the second resting voltage;

determine a coulomb count between the rest point and the fully charged state; and

determine the capacity of the battery based on the first state of charge, the second state of charge, and the coulomb count.

42. The battery of claim 41, wherein while determining the coulomb count between the rest point and the fully charged state, the controller is configured to:

initiate a coulomb counting from the rest point after resuming the charging process;

conclude the coulomb counting when the fully charged state is reached; and

determine the coulomb count based on the coulomb counting between the rest point and the fully charged state.

43. The battery of claim 41, wherein each of the resting voltage and the second resting voltage is an open circuit voltage (OCV).