Method of estimating state of charge and open circuit voltage of battery, and method and device for computing degradation degree of battery

• US 6,850,038 B2
• Filed: 05/14/2003
• Issued: 02/01/2005
• Est. Priority Date: 05/14/2002
• Status: Expired due to Fees

• Current Assignee: Yazaki Corporation
• Original Assignee: Yazaki Corporation
• Inventors: Arai, Youichi, Miyazaki, Yoshiya, Satake, Shuji
• Primary Examiner(s): Tibbits, Pia
• Application Number:
  US10/437,454
• Publication Number:
  US 20040008031A1
• Time in Patent Office: 629 Days
• Field of Search: 320/132, 324/129, 324/130
• US Class Current: 320/132
• CPC Class Codes: H01M 10/48 Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals, H01M50/569
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A method of estimating a state of charge of a battery, a method of estimating an open circuit voltage of a battery, and a method and device for computing a degradation degree of a battery are provided. As a degradation degree, a ratio of a total electrical quantity chargeable or dischargeable of a battery at any time point to an initial electrical quantity that is a total electrical quantity chargeable or dischargeable of the battery upon non-degradation is computed, and by using the degradation degree, a state of charge or an open circuit voltage of the battery is accurately estimated.

Claims

1. A method of estimating a state of charge of a battery, in which an electrical quantity corresponding to any open circuit voltage of the battery is estimated on the basis of an initial electrical quantity that is a total electrical quantity chargeable or dischargeable of the battery upon non-degradation, the method comprising the steps of:

computing, as a degradation degree, a ratio of a total electrical quantity chargeable or dischargeable of the battery at any time point to the initial electrical quantity; and

multiplying an electrical quantity estimated corresponding to said any open circuit voltage by the degradation degree, thereby estimating a state of charge of the battery at said any time point.

2. A method of estimating a state of charge of a battery, in which an electrical quantity corresponding to any open circuit voltage of the battery is estimated on the basis of an initial electrical quantity that is a total electrical quantity chargeable or dischargeable between an open circuit voltage upon fully charged state and an open circuit voltage upon completion of a discharge which are predetermined for the battery upon non-degradation, the method comprising the steps of:

computing, as a degradation degree, a ratio of a total electrical quantity chargeable or dischargeable between an open circuit voltage upon fully charged state and an open circuit voltage upon completion of a discharge of the battery at any time point to the initial electrical quantity; and

multiplying an electrical quantity estimated corresponding to said any open circuit voltage by the degradation degree, thereby estimating a state of charge of the battery at said any time point.

3. The method of estimating a state of charge of a battery according to claim 2, wherein the open circuit voltage upon fully charged state and the open circuit voltage upon completion of a discharge for the battery upon non-degradation are determined on the basis of a relation between an open circuit voltage and a state of charge, which relation is predetermined as an approximate expression computed by using data of state of charge in a range in which the state of charge exceeds a predetermined state of charge and data of open circuit voltage corresponding to the state of charge in the range, and

if said any open circuit voltage exceeds an open circuit voltage corresponding to the predetermined state of charge on the approximate expression, the electrical quantity corresponding to said any open circuit voltage is estimated to be a state of charge corresponding to an open circuit voltage which is obtained by substituting said any open circuit voltage into an expression of the approximate expression, and

if said any open circuit voltage does not exceed an open circuit voltage corresponding to the predetermined state of charge on the approximate expression, the electrical quantity corresponding to said any open circuit voltage is estimated to be a state of charge which is computed by adding or subtracting an integrated value of a charge or discharge current to or from a state of charge before a start of a charge or discharge.

4. The method of estimating a state of charge of a battery according to claim 3, wherein the predetermined relation between an open circuit voltage and a state of charge of the battery is expressed by an approximate expression expressing an approximate straight line which is computed with least squares method by using data of state of charge in a range in which the state of charge exceeds a predetermined state of charge and data of open circuit voltage corresponding to the state of charge in the range.

5. A method of estimating a state of charge of a battery, in which an electrical quantity corresponding to any open circuit voltage of the battery is estimated on the basis of an initial electrical quantity that is a total electrical quantity chargeable or dischargeable of the battery upon non-degradation, the method comprising the steps of:

computing, as a degradation degree, a ratio of a change in an open circuit voltage corresponding to any change in the electrical quantity of the battery upon non-degradation to a change in an open circuit voltage actually arising in the battery at any time point in response to said any change in the electrical quantity; and

multiplying an electrical quantity estimated corresponding to said any open circuit voltage by the degradation degree, thereby estimating a state of charge of the battery at said any time point.

6. A method of estimating a state of charge of a battery, in which an electrical quantity corresponding to any open circuit voltage of the battery is estimated on the basis of an initial electrical quantity that is a total electrical quantity chargeable or dischargeable of the battery upon non-degradation, the method comprising the steps of:

computing, as a degradation degree, a ratio of a change in an electrical quantity actually arising in the battery at any time point in response to a change in said any open circuit voltage to a change in an electrical quantity in response to a change in said any open circuit voltage of the battery upon non-degradation; and

multiplying an electrical quantity estimated corresponding to said any open circuit voltage by the degradation degree, thereby estimating a state of charge of the battery at said any time point.

7. A method of estimating a state of charge of a battery, in which an electrical quantity corresponding to any open circuit voltage of the battery is estimated on the basis of an initial electrical quantity that is a total electrical quantity chargeable or dischargeable of the battery upon non-degradation, the method comprising the steps of:

computing, as a degradation degree, a value obtained by multiplying a first ratio and a second ratio, wherein the first ratio is a ratio of a difference between an open circuit voltage upon fully charged state and an open circuit voltage upon completion of a discharge of the battery at any time point to a difference between those of the battery upon non-degradation, and the second ratio is a ratio of a change in an open circuit voltage in response to any change in an electrical quantity for the battery upon non-degradation to a change in an open circuit voltage actually arising in the battery at any time point in response to said any change in an electrical quantity; and

multiplying an electrical quantity estimated corresponding to said any open circuit voltage by the degradation degree, thereby estimating a state of charge of the battery at said any time point.

8. A method of estimating an open circuit voltage of a battery, in which an open circuit voltage corresponding to any electrical quantity of the battery is estimated on the basis of an initial electrical quantity that is a total electrical quantity chargeable or dischargeable of the battery upon non-degradation, the method comprising the steps of:

computing, as a degradation degree, a ratio of a total electrical quantity chargeable or dischargeable of the battery at any time point to the initial electrical quantity; and

revising an open circuit voltage estimated corresponding to said any electrical quantity by the degradation degree, thereby estimating an open circuit voltage of the battery at said any time point.

9. A method of estimating an open circuit voltage of a battery, in which an open circuit voltage corresponding to any electrical quantity of the battery is estimated on the basis of an initial electrical quantity that is a total electrical quantity chargeable or dischargeable between an open circuit voltage upon fully charged state and an open circuit voltage upon completion of a discharge which are predetermined for the battery upon non-degradation, the method comprising the steps of:

computing, as a degradation degree, a ratio of a total electrical quantity chargeable or dischargeable between an open circuit voltage upon fully charged state and an open circuit voltage upon completion of a discharge of the battery at any time point to the initial electrical quantity; and

revising an open circuit voltage estimated corresponding to said any electrical quantity by the degradation degree, thereby estimating an open circuit voltage of the battery at said any time point.

10. The method of estimating an open circuit voltage of a battery according to claim 9, wherein the open circuit voltage upon fully charged state and the open circuit voltage upon completion of a discharge for the battery upon non-degradation are determined on the basis of a relation between an open circuit voltage and a state of charge, which relation is predetermined as an approximate expression computed by using data of state of charge in a range in which the state of charge exceeds a predetermined state of charge and data of open circuit voltage corresponding to the state of charge in the range, and

if the open circuit voltage corresponding to said any electrical quantity exceeds an open circuit voltage corresponding to the predetermined state of charge in the approximate expression, the open circuit voltage corresponding to said any electrical quantity is estimated to be an open circuit voltage which is measured after a charge or discharge, and

if the open circuit voltage corresponding to said any electrical quantity does not exceed an open circuit voltage corresponding to the predetermined state of charge in the approximate expression, the open circuit voltage corresponding to said any electrical quantity is estimated to be an open circuit voltage corresponding to a state of charge which is obtained by substituting a state of charge, which is computed by adding or subtracting an integrated value of a charge or discharge current to or from a state of charge before a start of a charge or discharge, into the approximate expression.

11. The method of estimating an open circuit voltage of a battery according to claim 10, wherein the predetermined relation between an open circuit voltage and a state of charge of the battery is expressed by an approximate expression expressing an approximate straight line which is computed with least squares method by using data of state of charge in a range in which the state of charge exceeds a predetermined state of charge and data of open circuit voltage corresponding to the state of charge in the range.

12. A method of estimating an open circuit voltage of a battery, in which an open circuit voltage corresponding to any electrical quantity of the battery is estimated on the basis of an initial electrical quantity that is a total electrical quantity chargeable or dischargeable of the battery upon non-degradation, the method comprising the steps of:

computing, as a degradation degree, a ratio of a change in an open circuit voltage corresponding to any change in the electrical quantity of the battery upon non-degradation to a change in an open circuit voltage actually arising in the battery at any time point in response to said any change in the electrical quantity; and

revising an open circuit voltage estimated corresponding to said any electrical quantity by the degradation degree, thereby estimating an open circuit voltage of the battery at said any time point.

13. A method of estimating an open circuit voltage of a battery, in which an open circuit voltage corresponding to any electrical quantity of the battery is estimated on the basis of an initial electrical quantity that is a total electrical quantity chargeable or dischargeable of the battery upon non-degradation, the method comprising the steps of:

computing, as a degradation degree, a ratio of a change in an electrical quantity actually arising in the battery at any time point in response to a change in said any open circuit voltage to a change in an electrical quantity in response to a change in said any open circuit voltage of the battery upon non-degradation; and

revising an open circuit voltage estimated corresponding to said any electrical quantity by the degradation degree, thereby estimating an open circuit voltage of the battery at said any time point.

14. A method of estimating an open circuit voltage of a battery, in which an open circuit voltage corresponding to any electrical quantity of the battery is estimated on the basis of an initial electrical quantity that is a total electrical quantity chargeable or dischargeable of the battery upon non-degradation, the method comprising the steps of:

computing, as a degradation degree, a value obtained by multiplying a first ratio and a second ratio, wherein the first ratio is a ratio of a difference between an open circuit voltage upon fully charged state and an open circuit voltage upon completion of a discharge of the battery at any time point to a difference between those of the battery upon non-degradation, and the second ratio is a ratio of a change in an open circuit voltage in response to any change in an electrical quantity for the battery upon non-degradation to a change in an open circuit voltage actually arising in the battery at any time point in response to said any change in an electrical quantity; and

revising an open circuit voltage estimated corresponding to said any electrical quantity by the degradation degree, thereby estimating an open circuit voltage of the battery at said any time point.

15. A method of computing a degradation degree of a battery comprising a step of computing, as the degradation degree, a ratio of a total electrical quantity chargeable or dischargeable of the battery at any time point to an initial electrical quantity that is a total electrical quantity chargeable or dischargeable of the battery upon non-degradation.

16. A method of computing a degradation degree of a battery comprising a step of computing, as the degradation degree, a ratio of a total electrical quantity chargeable or dischargeable between an open circuit voltage upon fully charged state and an open circuit voltage upon completion of a discharge of the battery at any time point to an initial electrical quantity, which is a total electrical quantity chargeable or dischargeable between an open circuit voltage upon fully charged state and an open circuit voltage upon completion of a discharge that are predetermined for the battery upon non-degradation.

17. A method of computing a degradation degree of a battery comprising a step of computing, as the degradation degree, a ratio of a change in an open circuit voltage corresponding to any change in an electrical quantity of the battery upon non-degradation to a change in an open circuit voltage actually arising in the battery at any time point in response to said any change in the electrical quantity.

18. The method of computing a degradation degree of a battery according to claim 17, wherein a discharge current flowing during a discharge is intermittently measured and the measured discharge current is integrated with time, thereby computing said any decrease in the electrical quantity.

19. The method of computing a degradation degree of a battery according to claim 17, wherein a charge current flowing during a charge is intermittently measured and the measured discharge current is integrated with time by multiplying a real-time charging efficiency, thereby computing said any increase in the electrical quantity.

20. The method of computing a degradation degree of a battery according to claim 17, wherein a change in an open circuit voltage in response to said any change in the electrical quantity is computed as a difference between an open circuit voltage before a start of charge or discharge, which is estimated or measured from a terminal voltage of the battery, and an open circuit voltage after a halt of charge or discharge, which is computed on the basis of an initial electrical quantity that is a total electrical quantity chargeable or dischargeable of the battery upon non-degradation, and

the change in an open circuit voltage actually arising in the battery at any time point in response to said any change in the electrical quantity is computed as a difference between an open circuit voltage before a start of charge or discharge, which is estimated or measured from a terminal voltage of the battery, and an open circuit voltage after a halt of charge or discharge, which is estimated or measured from a terminal voltage of the battery.

21. The method of computing a degradation degree of a battery according to claim 18, wherein a change in an open circuit voltage in response to said any change in the electrical quantity is computed as a difference between an open circuit voltage before a start of charge or discharge, which is estimated or measured from a terminal voltage of the battery, and an open circuit voltage after a halt of charge or discharge, which is computed on the basis of an initial electrical quantity that is a total electrical quantity chargeable or dischargeable of the battery upon non-degradation, and

the change in an open circuit voltage actually arising in the battery at any time point in response to said any change in the electrical quantity is computed as a difference between an open circuit voltage before a start of charge or discharge, which is estimated or measured from a terminal voltage of the battery, and an open circuit voltage after a halt of charge or discharge, which is estimated or measured from a terminal voltage of the battery.

22. The method of computing a degradation degree of a battery according to claim 19, wherein a change in an open circuit voltage in response to said any change in the electrical quantity is computed as a difference between an open circuit voltage before a start of charge or discharge, which is estimated or measured from a terminal voltage of the battery, and an open circuit voltage after a halt of charge or discharge, which is computed on the basis of an initial electrical quantity that is a total electrical quantity chargeable or dischargeable of the battery upon non-degradation, and

the change in an open circuit voltage actually arising in the battery at any time point in response to said any change in the electrical quantity is computed as a difference between an open circuit voltage before a start of charge or discharge, which is estimated or measured from a terminal voltage of the battery, and an open circuit voltage after a halt of charge or discharge, which is estimated or measured from a terminal voltage of the battery.

23. A method of computing a degradation degree of a battery comprising a step of computing, as the degradation degree, a ratio of a change in an electrical quantity actually arising in the battery at any time point in response to said any change in an open circuit voltage to a change in an electrical quantity in response to any change in an open circuit voltage of the battery upon non-degradation.

24. A method of computing a degradation degree of a battery comprising a step of computing, as the degradation degree, a value obtained by multiplying a first ratio and a second ratio, wherein the first ratio is a ratio of a difference between an open circuit voltage upon fully charged state and an open circuit voltage upon completion of a discharge of the battery at any time point to a difference between those of the battery upon non-degradation, and the second ratio is a ratio of a change in an open circuit voltage in response to any change in an electrical quantity for the battery upon non-degradation to a change in an open circuit voltage actually arising in the battery at any time point in response to said any change in an electrical quantity.

25. A device for computing a degradation degree of a battery comprising:

first means for computing a change in an electrical quantity during a charge or discharge of a battery;

second means for computing a change in an open circuit voltage in response to any change in an electrical quantity computed by the first means on the basis of an initial electrical quantity that is a total electrical quantity chargeable or dischargeable of the battery upon non-degradation;

third means for estimating or measuring a change in an open circuit voltage actually arising in the battery at any time point in response to said any change in an electrical quantity; and

fourth means for computing, as the degradation degree, a rate of the change in an open circuit voltage computed by the second means to the change in an open circuit voltage estimated or measured by the third means.