Method of estimating residual capacity of battery

• US 5,635,842 A
• Filed: 02/05/1996
• Issued: 06/03/1997
• Est. Priority Date: 06/30/1993
• Status: Expired due to Fees

• Current Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Original Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Inventors: Nagano, Masao, Takemoto, Hideharu, Yokoo, Masahide
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): Solis, Jose M.
• Application Number:
  US08/595,448
• Time in Patent Office: 484 Days
• Field of Search: 320/48, 320/43, 340/636, 324/429, 324/430, 324/427
• US Class Current: 324/427
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: Y10S 320/21 State of charge of battery

Abstract

In estimating the residual capacity of a battery according to the maximum output estimating process, a reference point is established in advance at the intersection of a plurality of current/voltage characteristic linear curves corresponding to various residual capacities of the battery or in an area in the vicinity of the intersections of the curves. A current/voltage characteristic linear curve is determined so as to pass through the reference point and a measured operating point of the battery which corresponds to the present discharging current and output voltage values measured when the battery is discharged. Then, a maximum transfer power value of the battery is determined from the current/voltage characteristic linear curve thus determined, and the present residual capacity of the battery is estimated from the maximum transfer power value.

Claims

1. A method of estimating the residual capacity in a battery under use, comprising the steps of:

a) measuring a singe first point of current/voltage characteristic of said battery;

b) retrieving a stored value of a second current/voltage characteristic point, said stored value obtained from a calibrating procedure, said procedure having obtained said second point as the intersection between current/voltage plots corresponding to various different residual capacities;

c) extracting the maximum transfer power value from said both first and second current/voltage characteristic points and estimating said residual capacity of said battery from said maximum transfer power value.

2. A method according to claim 1, wherein said calibrating procedure includes the steps of:

obtaining several current/voltage plots, each plot obtained at a different value of residual capacity, of at least one battery of the same type as said battery under use;

obtaining, from said points, a common intersection point and storing its value as said second current/voltage characteristic point.

3. A method according to claim 1, wherein said step of extracting the maximum transfer power includes determining a current/voltage characteristic linear curve by a line through said first and second current/voltage characteristic points.

4. A method according to claim 3, further comprising steps of:

measuring a plurality of current/voltage characteristic points of said battery during a present discharge of the battery; and

determining a present current/voltage characteristic linear curve so as to pass through said second current/voltage characteristic plurality of current/voltage characteristic points.

5. A method according to claim 4, further comprising the steps

determining the average of the plurality of measured current/voltage characteristic points during said present discharge;

and

determining said present current/voltage characteristic linear curve so as to pass through said second current/voltage characteristic point and an average measured operating point of said battery which corresponds to said determined avenge of the plurality of measured current/voltage characteristic points during discharging of said battery.

6. A method according to claim 3, further comprising the step of:

determining said current/voltage characteristic linear curve with said first current/voltage characteristic point being determined from a plurality of measured current/voltage voltage characteristic points by a method of least squares.

7. A method according to claim 1, further comprising a step of establishing said second current/voltage characteristic point by making a plurality of sets of measurements of discharging current and output voltage for the battery under varying temperature conditions for developing a plurality of current/voltage characteristic linear curves.

8. A method according to claim 1, further comprising a step of establishing said second current/voltage characteristic point by measuring an open voltage and an internal resistance of the battery in both a fully charged state and a rally discharged state for locating said second current/voltage characteristic point on a predetermined current/voltage characteristic linear curve of the battery.

9. A method according to claim 8, wherein said predetermined current/voltage characteristic linear curve is based on a discharging state of the battery expressed by V=V_O -R_O 1 where V is output voltage of the battery, 1 is output current, V_O is the open voltage and R_O is the internal resistance of the battery.

10. A method according to claim 1, wherein said calibrating procedure includes developing a plurality of current/voltage characteristic linear curves by measuring the discharging current and output voltage of a test battery of the same type as said battery under use under varying values of discharging current and varying values of battery capacity.

11. A method according to claim 10, wherein said plurality of current/voltage characteristic linear curves are projected beyond the actual measured values of discharge current and output voltage.

12. A method according to claim 11, wherein said second current/voltage characteristic point is at substantially an intersection of said curves in an area of projected curves.

13. A method according to claim 1, wherein said second current/voltage characteristic points is in a range of negative discharge current.

14. A method of calibrating batteries of a given type for later extracting residual capacity values in batteries of the same given type comprising the steps of:

a) obtaining several current/voltage plots, each plot obtained at a different value of residual capacity;

b) obtaining, from said plots, a common intersection point and storing its value as a reference point, said reference point adapted to be used later in extracting maximum transfer power values for batteries of said given type.

15. A method according to claim 14, wherein the step of obtaining a reference point includes measuring an open voltage and an internal resistance of a test battery of the given type in both a fully charged state and a fully discharged state for locating the reference point on a predetermined current/voltage characteristic linear curve of said test battery.

16. A method according to claim 14, wherein said several current/voltage plots are developed by measuring the discharging current and output voltage of a test battery of the given type under varying values of discharging current.

17. A method according to claim 14, wherein said several current/voltage plots are projected beyond the actual measured values of discharge current and output voltage.

18. A method according to claim 17, wherein said common intersection of said plots is in an area of projected curves.

19. A method according to claim 14, wherein the reference point is in a range of negative discharge current.