Model-based battery fuel gauges and methods

• US 8,198,863 B1
• Filed: 10/22/2007
• Issued: 06/12/2012
• Est. Priority Date: 12/13/2006
• Status: Active Grant

• Current Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Original Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Inventors: Wortham, Jason Allen
• Primary Examiner(s): Tso, Edward
• Assistant Examiner(s): PIGGUSH, AARON C
• Application Number:
  US11/876,531
• Time in Patent Office: 1,695 Days
• Field of Search: 320/132, 320/136, 320/162, 324/427
• US Class Current: 320/132
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: H01M 10/488 Cells or batteries combined with indicating means for external visualization of the condition, e.g. by change of colour or of light density
• CPC Class Codes: H02J 7/0014 Circuits for equalisation of charge between batteries
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

Model-based battery fuel gauges that connect across a rechargeable battery and track the per-cent state of charge of the battery. The model based fuel gauges provide a measure of the open terminal voltage of a battery, even when the battery is powering a load, to provide the state of charge information. Analog and digital implementations of the battery model fuel gauges may be used, and incorporated into a battery powered device in various ways, including constantly powered implementations and implementations that are turned on and off with the battery powered device. Various exemplary embodiments are disclosed.

Claims

1. A method of monitoring the state of charge of a battery, including when delivering current to a load on the battery, comprising:

modeling at least one time constant of the battery over a range of state of charge of the battery to establish a battery model;

monitoring the battery terminal voltage;

without using a measured value of current, estimating an open circuit voltage of the battery using the battery model and the battery terminal voltage, including when delivering current to a load on the battery; and

,

without using a measured value of current, estimating the state of charge of the battery based on the estimated open circuit voltage of the battery and the battery model.

2. The method of claim 1 wherein the battery is a rechargeable battery.

3. The method of claim 1 wherein the battery is modeled as a resistor and capacitor (RC) network.

4. The method of claim 3 wherein the RC network comprises a single resistor and single capacitor.

5. The method of claim 4 wherein the resistor in the battery model is of a constant value.

6. The method of claim 4 wherein the capacitor in the battery model is varied with the estimate of the open circuit voltage.

7. The method of claim 6 wherein a range of the open circuit voltage of the battery is divided into a plurality of segments, and wherein the value of the capacitor in the battery model is assumed constant for each individual segment, and varies from at least one segment to an adjacent segment.

8. The method of claim 7 wherein the value of the capacitor in the battery model for each segment is proportional to the inverse of the average rate of change of the open circuit voltage of the battery per amp-hour of current withdrawn from the battery for the open circuit voltage range of the respective segment.

9. The method of claim 1 wherein the method is practiced by use of digital circuitry.

10. The method of claim 9 wherein the digital circuitry is disposed within a device to be powered by a battery, and the digital circuitry is connected to terminals to be connected to a battery so that the digital circuitry will be connected to the battery whenever the battery is in the device, whether the device is turned on or not.

11. The method of claim 1 further comprised of setting the voltage on a capacitor in the battery model to the initial terminal voltage of the battery when the monitoring of the state of charge of a battery begins.

12. The method of claim 1 wherein the monitoring the state of charge of a battery is practiced during both charging of the battery and when delivering current to a load.

13. The method of claim 3 wherein the values of the resistor and capacitor in the battery model have the same time constant as the battery being modeled, independent of whether the values of the resistor and capacitor in the battery model correspond to the corresponding values for the battery.

14. The method of claim 3 wherein the capacitor in the battery model is varied with the estimate of the open circuit voltage.

15. The method of claim 14 wherein a range of the open circuit voltage of the battery is divided into a plurality of segments, and wherein the value of the capacitor in the battery model is assumed constant for each individual segment, and varies from at least one segment to an adjacent segment.

16. The method of claim 15 wherein the value of the capacitor in the battery model for each segment is proportional to the inverse of the average rate of change of the open circuit voltage of the battery per amp-hour of current withdrawn from the battery for the open circuit voltage range of the respective segment.

17. The method of claim 1 wherein the battery is modeled as a filter.

18. The method of claim 17 wherein the battery model is implemented in at least one of a DSP, a logic filter, a microprocessor operating under software control, firmware and analog circuitry.

19. The method of claim 1 used in addition to a coulomb counter to provide optimal short term and long term accuracy in the estimated state of charge of the battery.

20. The method of claim 3 wherein the battery model is modeled as a multiple resistor and multiple capacitor (RC) network.

21. The method of claim 5 wherein the capacitor in the battery model is a constant value.

22. The method of claim 21 wherein the values of the resistor and the capacitor do not correspond to the corresponding values for the battery, but have values selected to have the same time constant as the battery.

23. The method of claim 1 wherein the method is practiced under software control, the software being stored on a non-transitory medium.

24. The method of claim 1 wherein the method is practiced in a digital signal processor.

25. The method of claim 1 wherein the method is practiced in a logic filter.

26. A non-transitory medium storing software, which when executed, performs the method of claim 1.

27. A method of monitoring the state of charge of a rechargeable battery, including when delivering current to a load on the battery, comprising:

modeling the battery as a resistor-capacitor (RC) circuit having at least one time constant, the modeling being over a range of state of charge of the battery to establish a battery model, the value of the resistor modeling the change in battery terminal voltage with short term delivery of current to the load on the battery, and the value of the capacitor modeling the inverse of the rate of change of open circuit voltage of the battery per amp-hour of current withdrawn from the battery;

monitoring the battery terminal voltage;

without using a measured value of current, estimating the open circuit voltage of the battery using the battery model and a battery terminal voltage, including when delivering current to a load on the battery; and

,

without using a measured value of current, estimating the state of charge of the battery based on the estimated open circuit voltage of the battery and the battery model.

28. The method of claim 27 wherein the resistor in the battery model is of a constant value.

29. The method of claim 27 wherein the capacitor in the battery model is varied with the estimate of the open circuit voltage.

30. The method of claim 29 wherein a range of the open circuit voltage of the battery is divided into a plurality of segments, and wherein the value of the capacitor in the battery model is assumed constant for each individual segment, and varies from at least one segment to an adjacent segment.

31. The method of claim 30 wherein the value of the capacitor in the battery model for each segment is proportional to the inverse of the average rate of change of the open circuit voltage of the battery per amp-hour of current withdrawn from the battery for the open circuit voltage range of the respective segment.

32. The method of claim 27 wherein the method is practiced by use of digital circuitry.

33. The method of claim 32 wherein the digital circuitry is disposed within a device to be powered by a battery, and the digital circuitry is connected to terminals to be connected to a battery so that the digital circuitry will be connected to the battery whenever the battery is in the device, whether the device is turned on or not.

34. The method of claim 27 further comprising setting the voltage on the capacitor in the model to the terminal voltage of the battery when the monitoring of the state of charge of a battery begins.

35. The method of claim 27 wherein the monitoring the state of charge of a battery is practiced during both charging of the battery and when delivering current to a load.

36. The method of claim 27 wherein the method is practiced under software control, the software being stored on a non-transitory medium.

37. The method of claim 27 wherein the method is practiced in a digital signal processor.

38. The method of claim 27 wherein the method is practiced in a logic filter.

39. A non-transitory medium storing software, which when executed, performs the method of claim 27.

40. A method of estimating the state of charge of a battery, including when delivering current to a load on the battery, comprising:

modeling the battery as a resistor and capacitor (RC) network having at least one time constant, the modeling being over a range of state of charge of the battery to establish a battery model;

monitoring the battery terminal voltage;

without using a measured value of current, estimating an open circuit voltage of the battery using the battery model and the battery terminal voltage, including when delivering current to of a load on the battery; and

,

without using a measured value of current, estimating the state of charge of the battery based on the estimated open circuit voltage of the battery and the battery model.

41. The method of claim 40 wherein the battery is a rechargeable battery.

42. The method of claim 40 wherein the values of the resistors and capacitors in the battery model have the same time constants as the battery being modeled, independent of whether the values of the resistors and capacitors in the battery model correspond to the corresponding values for the battery.

43. The method of claim 42 wherein the RC network comprises a single resistor and single capacitor.

44. The method of claim 43 wherein the resistor in the battery model is of a constant value.

45. The method of claim 44 wherein the capacitor in the battery model is varied with the estimate of the open circuit voltage.

46. The method of claim 45 wherein a range of the open circuit voltage of the battery is divided into a plurality of segments, and wherein the value of the capacitor in the battery model is assumed constant for each individual segment, and varies from at least one segment to an adjacent segment.

47. The method of claim 46 wherein the value of the capacitor in the battery model for each segment is proportional to the inverse of the average rate of change of the open circuit voltage of the battery per amp-hour of current withdrawn from the battery for the open circuit voltage range of the respective segment.

48. The method of claim 40 wherein the method is practiced by use of digital circuitry.

49. The method of claim 48 wherein the digital circuitry is disposed within a device to be powered by a battery, and the digital circuitry is connected to terminals to be connected to a battery so that the digital circuitry will be connected to the battery whenever the battery is in the device, whether the device is turned on or not.

50. The method of claim 40 further comprised of setting the voltage on a capacitor in the model to the initial terminal voltage of the battery when the monitoring of the state of charge of a battery begins.

51. The method of claim 40 wherein the monitoring of the state of charge of a battery is practiced during both charging of the battery and when delivering current to a load.

52. The method of claim 40 wherein the method is practiced under software control, the software being stored on a non-transitory medium.

53. The method of claim 40 wherein the method is practiced in a digital signal processor.

54. The method of claim 40 wherein the method is practiced in a logic filter.

55. A non-transitory medium storing software, which when executed, performs the method of claim 40.

56. A method of monitoring the state of charge of a rechargeable battery, including when delivering current to a load on the battery, comprising:

modeling the battery as a resistor-capacitor (RC) circuit, the value of the resistor modeling the change in battery terminal voltage with short term load on the battery, and the value of the capacitor modeling the inverse of the rate of change of the open circuit voltage of the battery per amp-hour of current withdrawn from the battery;

monitoring the battery terminal voltage;

without using a measured value of current, estimating an open circuit voltage of the battery using the battery model and a battery terminal voltage, including when delivering current to a load on the battery; and

,

without using a measured value of current, estimating the state of charge of the battery based on the estimated open circuit voltage of the battery and the battery model, including when delivering current to a load on the battery.

57. The method of claim 56 wherein the resistor in the battery model is of a constant value.

58. The method of claim 57 wherein the capacitor in the battery model is varied with the estimate of the open circuit voltage.

59. The method of claim 58 wherein a range of the open circuit voltage of the battery is divided into a plurality of segments, and wherein the value of the capacitor in the battery model is assumed constant for each individual segment, and varies from at least one segment to an adjacent segment.

60. The method of claim 59 wherein the value of the capacitor in the battery model for each segment is approximately proportional to the inverse of the average rate of change of the open circuit voltage of the battery per amp-hour of current withdrawn from the battery for the open circuit voltage range of the respective segment.

61. The method of claim 56 wherein the method is practiced by use of digital circuitry.

62. The method of claim 61 wherein the digital circuitry is disposed within a device to be powered by a battery, and the digital circuitry is connected to terminals to be connected to a battery so that the digital circuitry will be connected to the battery whenever the battery is in the device, whether the device is turned on or not.

63. The method of claim 56 further comprising setting the voltage on the capacitor in the battery model to the terminal voltage of the battery when the monitoring of the state of charge of a battery begins.

64. The method of claim 56 wherein the monitoring the state of charge of a battery is practiced during both charging of the battery and when delivering current to a load on the battery.

65. The method of claim 56 wherein the method is practiced under software control, the software being stored on a non-transitory medium.

66. The method of claim 56 wherein the method is practiced in a digital signal processor.

67. The method of claim 56 wherein the method is practiced in a logic filter.

68. A non-transitory medium storing software, which when executed, performs the method of claim 56.