Battery status detecting method, battery status detecting apparatus, and expression deriving method

• US 20090037124A1
• Filed: 04/16/2008
• Published: 02/05/2009
• Est. Priority Date: 07/30/2007
• Status: Active Grant

• Current Assignee: Mitsumi Electric Co., Ltd. (MinebeaMitsumi Inc.)
• Original Assignee: Mitsumi Electric Co., Ltd. (MinebeaMitsumi Inc.)
• Inventors: Majima, Yoshihide
• Granted Patent: US 8,234,087 B2
• Time in Patent Office: Days
• US Class Current: 702/63
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements

Abstract

A battery status detecting method for detecting a battery status of a secondary battery that supplies power to an electrical load is disclosed. This method includes measuring a discharge current value of the secondary battery, and estimating the dischargeable capacity or the dischargeable time of the secondary battery with the measured discharge current value based on discharge characteristics of the secondary battery indicating the discharge status of the secondary battery when the voltage of the secondary battery drops to a predetermined voltage specified by the electrical load.

Claims

1. A battery status detecting method for detecting a battery status of a secondary battery that supplies power to an electrical load, the method comprising:

a current measuring step of measuring a discharge current value of the secondary battery; and

an estimating step of estimating a dischargeable capacity or a dischargeable time of the secondary battery with the measured discharge current value based on discharge characteristics of the secondary battery indicating a discharge status of the secondary battery when a voltage of the secondary battery drops to a predetermined voltage specified by the electrical load.

2. The battery status detecting method as claimed in claim 1, wherein

the discharge characteristics indicate a relationship between a discharge capacity and the discharge current value of the secondary battery.

3. The battery status detecting method as claimed in claim 2, wherein

the discharge characteristics are represented by an expression described as:

Q=A·

I+B ln (I)+C−

(FCC−

remaining capacity)

where Q represents the dischargeable capacity of the secondary battery, I represents the discharge current value of the secondary battery, FCC represents a full charge capacity of the secondary battery, and A, B, and C represent coefficients of the expression.

4. The battery status detecting method as claimed in claim 3, wherein

values of the coefficients A, B, and C of the expression vary according to a temperature of the secondary battery.

5. The battery status detecting method as claimed in claim 2, wherein

the discharge characteristics are represented by an expression described as:

Q=A·

I+B·

(1/I)+C−

(FCC−

remaining capacity)

where Q represents the dischargeable capacity of the secondary battery, I represents the discharge current value of the secondary battery, FCC represents a full charge capacity of the secondary battery, and A, B, and C represent coefficients of the expression.

6. The battery status detecting method as claimed in claim 5, wherein

values of the coefficients A, B, and C of the expression vary according to a temperature of the secondary battery.

7. The battery status detecting method as claimed in claim 1, wherein

the discharge characteristics reflect variations according to a temperature of the secondary battery.

8. A battery status detecting apparatus that detects a battery status of a secondary battery that supplies power to an electrical load, the apparatus comprising:

a storage unit that stores characteristics data used for determining secondary battery discharge characteristics indicating a discharge status of the secondary battery when a voltage of the secondary battery drops to a predetermined voltage specified by the electrical load; and

an estimating unit that estimates a dischargeable capacity or a dischargeable time of the secondary battery using the characteristics data stored in the storage unit.

9. The battery status detecting apparatus as claimed in claim 8, wherein

the discharge characteristics indicate a relationship between a discharge capacity and a discharge current value of the secondary battery.

10. The battery status detecting apparatus as claimed in claim 9, wherein

the discharge characteristics are represented by an expression described as:

Q=A·

I+B·

ln(I)+C−

(FCC−

remaining capacity)

where Q represents the dischargeable capacity of the secondary battery, I represents the discharge current value of the secondary battery, FCC represents a full charge capacity of the secondary battery, and A, B, and C represent coefficients of the expression; and

the characteristics data include data for determining values of the coefficients A, B, and C.

11. The battery status detecting apparatus as claimed in claim 10, wherein

the values of the coefficients A, B, and C of the expression vary according to a temperature of the secondary battery.

12. The battery status detecting apparatus as claimed in claim 9, wherein

the discharge characteristics are represented by an expression described as:

Q=A·

I+B·

(1/I)+C−

(FCC−

remaining capacity)

where Q represents the dischargeable capacity of the secondary battery, I represents the discharge current value of the secondary battery, FCC represents a full charge capacity of the secondary battery, and A, B, and C represent coefficients of the expression; and

the characteristics data include data for determining values of the coefficients A, B, and C.

13. The battery status detecting apparatus as claimed in claim 12, wherein

the values of the coefficients A, B, and C of the expression vary according to a temperature of the secondary battery.

14. An expression deriving method for deriving a dischargeable capacity computing expression for computing a dischargeable capacity of a secondary battery that supplies power to an electrical load, the method comprising:

a measuring step of measuring first discharge characteristics indicating a relationship between a voltage and a discharge capacity of the secondary battery, the first discharge characteristics being measured with respect to a plurality of discharge current values of the secondary battery;

a converting step of converting the first discharge characteristics into second discharge characteristics indicating a relationship between the discharge capacity and the discharge current value of the secondary battery when the voltage of the secondary battery drops to a predetermined voltage specified by the electrical load; and

an expression deriving step of deriving the dischargeable capacity computing expression based on the second discharge characteristics of the secondary battery.

15. The expression deriving method as claimed in claim 14, wherein

the expression deriving step includes approximating the second discharge characteristics of the secondary battery as a discharge model function corresponding to the dischargeable capacity computing expression and determining a value of a coefficient of the discharge model function.

16. The expression deriving method as claimed in claim 15, wherein

the measuring step includes measuring the first discharge characteristics of the secondary battery with respect to a plurality of temperatures of the secondary battery;

the converting step includes converting the first discharge characteristics into the second discharge characteristics with respect to each of the temperatures; and

the expression deriving step includes determining the value of the coefficient of the discharge model function with respect to each of the temperatures, determining a correlation between the temperatures and the value of the coefficient determined with respect to each of the temperatures, and deriving a coefficient computing expression for computing a corresponding value of the coefficient of the discharge model function for a given temperature based on the determined correlation.

17. The expression deriving method as claimed in claim 15, wherein

the discharge model function is expressed as:

Q=A·

I+B·

ln(I)+C−

(FCC−

remaining capacity)

where Q represents the dischargeable capacity of the secondary battery, I represents the discharge current value of the secondary battery, FCC represents a full charge capacity of the secondary battery, and A, B, and C each represent the coefficient of the discharge model function.

18. The expression deriving method as claimed in claim 15, wherein

the discharge model function is expressed as:

Q=A·

I+B·

(1/I)+C−

(FCC−

remaining capacity)

where Q represents the dischargeable capacity of the secondary battery, I represents the discharge current value of the secondary battery, FCC represents a full charge capacity of the secondary battery, and A, B, and C each represent the coefficient of the discharge model function.

19. The expression deriving method as claimed in claim 14, wherein

the measuring step includes measuring the first discharge characteristics of the secondary battery with respect to a plurality of temperatures of the secondary battery;

and

the converting step includes converting the first discharge characteristics into the second discharge characteristics with respect to each of the temperatures.