Determination and control of battery state

• US 5,672,951 A
• Filed: 09/18/1995
• Issued: 09/30/1997
• Est. Priority Date: 11/04/1994
• Status: Expired due to Fees

• Current Assignee: New Energy and Industrial Technology Development Organizatio
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Shiota, Hisashi
• Primary Examiner(s): TSO, EDWARD H
• Application Number:
  US08/529,396
• Time in Patent Office: 743 Days
• Field of Search: 320/5, 320/30, 320/39, 320/43, 320/48, 324/426, 324/427, 324/428, 324/430, 324/432, 340/635, 340/636, 429/90
• US Class Current: 320/132
• CPC Class Codes: G01R 31/3828 using current integration
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: H02J 7/00714 in response to battery charging or discharging current

Abstract

A technique for measuring battery characteristics comprises measuring a battery terminal voltage, a charge/discharge current and a charge/discharge time. The technique entails arithmetically determining an integrated power, an integrated charge quantity and an integrating time interval over a period extending from a start of a charge/discharge process to an end thereof, determining a mean terminal voltage by dividing the integrated power by the integrated charge quantity, determining a mean charge current by dividing the integrated charge quantity by the integrating time interval, determining a polarization resistance of the battery on the basis of the mean terminal voltage and the mean current by using a battery polarization resistance model, and finally determining an open-circuit voltage of the battery on the basis of the polarization resistance. The information culled from the above technique may be used to control a charge/discharge process and to predict the remaining life of the battery.

Claims

1. A parameter measuring method for measuring parameters of a secondary battery, comprising the steps of:

measuring and storing a terminal voltage, a charge/discharge current and a charge/discharge time of said secondary battery in charge/discharge cycles of said battery;

arithmetically determining an integrated power, an integrated charge quantity and an integrating time interval over a period extending from a start of a charge/discharge process to an end thereof in an immediately preceding cycle;

determining a mean terminal voltage including a mean terminal voltage in a charging process and a mean terminal voltage in a discharging process by dividing said integrated power by said integrated charge quantity;

determining a mean current including a mean charge current and a mean discharge current by dividing said integrated charge quantity by said integrating time interval;

determining a polarization resistance of said secondary battery on the basis of said mean terminal voltage and said mean current by using a battery polarization resistance model; and

determining an open-circuit voltage of said secondary battery on the basis of said polarization resistance.

2. A parameter measuring method for measuring parameters of a secondary battery according to claim 1,

wherein said secondary battery is a lithium secondary battery.

3. A method of controlling charge/discharge of a secondary battery by using a parameter measuring method according to claim 1, comprising the steps of:

controlling a predestinated charge/discharge current which is to flow to and from, respectively, said secondary battery on the basis of said polarization resistance and said open-circuit voltage and a predetermined upper limit open-circuit voltage in the charging process, a predetermined lower limit open-circuit voltage in the discharging process and a polarization limit voltage such that a charge/discharge control voltage given as a product of a predestinated charge/discharge current flowing to and from, respectively, said second battery, and the polarization resistance, does not exceed said polarization limit voltage;

determining a residual capacity of said secondary battery on the basis of said open-circuit voltage;

arithmetically determining a residual charge/discharge time of said secondary battery on the basis of said residual capacity and said predestinated charge/discharge current; and

terminating a charge/discharge process of said secondary battery within said residual charge/discharge time such that, in the discharging process, said open-circuit voltage does not drop below said lower limit open-circuit voltage, while in the charging process, said open-circuit voltage does not exceed said upper limit open-circuit voltage.

4. A method of predicting a life of said secondary battery by using a parameter measuring method according to claim 1, comprising the steps of:

storing changes occurring in said polarization resistance in a plurality of charge/discharge cycles of said secondary battery;

performing a polynomial approximating extrapolation based on a method of least squares, as a function of a charge/discharge cycle repetition number of said secondary battery; and

determining as an effective charge/discharge cycle repeatable number the charge/discharge cycle repetition number at a time point when said polarization resistance attains a polarization resistance limit.

5. A charge/discharge control apparatus for a secondary battery, comprising:

a measuring means for measuring a terminal voltage, a charge/discharge current and a charge/discharge time of the secondary battery;

memory means for storing said terminal voltage, said charge/discharge current and said charge/discharge time;

control means for controlling a predestinated charge/discharge current which is to flow to and from, respectively, said secondary battery; and

arithmetic means for arithmetically determining an open-circuit voltage, a polarization resistance thereof, a life cycle number, a residual charge/discharge time and a charge/discharge control voltage, respectively, of said secondary battery on the basis of said terminal voltage, said charge/discharge current, said predestinated charge/discharge current and said charge/discharge time.

6. A secondary battery control apparatus according to claim 5,

wherein said secondary battery is a lithium secondary battery.

7. An apparatus for storing electric energy, comprising:

measuring means for measuring a terminal voltage, a charge/discharge current and a charge/discharge time of a secondary battery;

memory means for storing said terminal voltage, said charge/discharge current and said charge/discharge time;

control means for controlling a predestinated charge/discharge current which is to flow to and from, respectively, said secondary battery;

arithmetic means for arithmetically determining an open-circuit voltage, a polarization resistance thereof, a life cycle number, a residual charge/discharge time and a charge/discharge control voltage, respectively, of said secondary battery on the basis of said terminal voltage, said charge/discharge current, said predestinated charge/discharge current and said charge/discharge time; and

electric power conversion means for convening an AC electric power into a DC power, and for storing said DC power in said secondary battery.

8. An apparatus for measuring parameters of a secondary battery, comprising:

means for measuring and storing a terminal voltage, a charge/discharge current and a charge/discharge time of said secondary battery in charge/discharge cycles of said battery;

means for arithmetically determining an integrated power, an integrated charge quantity and an integrating time interval over a period extending from a start of a charge/discharge process to an end thereof in an immediately preceding cycle;

means for determining a mean terminal voltage including a mean terminal voltage in a charging process and a mean terminal voltage in a discharging process by dividing said integrated power by said integrated charge quantity;

means for determining a mean current including a mean charge current and a mean discharge current by dividing said integrated charge quantity by said integrating time interval;

means for determining a polarization resistance of said secondary battery on the basis of said mean terminal voltage and said mean current by using a battery polarization resistance model; and

means for determining an open-circuit voltage of said secondary battery on the basis of said polarization resistance.

9. The apparatus for measuring parameters of a secondary battery according to claim 8,

wherein said secondary battery is a lithium secondary battery.

10. The apparatus for measuring parameters of a secondary battery according to claim 8, further including means for controlling charge/discharge of said secondary battery, comprising:

means for controlling a predestinated charge/discharge current which is to flow to and from, respectively, said secondary battery on the basis of said polarization resistance and said open-circuit voltage and a predetermined upper limit open-circuit voltage in the charging process, a predetermined lower limit open-circuit voltage in the discharging process and a polarization limit voltage such that a charge/discharge control voltage given as a product of a predestinated charge/discharge current flowing to and from, respectively, said second battery, and the polarization resistance, does not exceed said polarization limit voltage;

means for determining a residual capacity of said secondary battery on the basis of said open-circuit voltage;

means for arithmetically determining a residual charge/discharge time of said secondary battery on the basis of said residual capacity and said predestinated charge/discharge current; and

means for terminating a charge/discharge process of said secondary battery within said residual charge/discharge time such that, in the discharging process, said open-circuit voltage does not drop below said lower limit open-circuit voltage, while in the charging process, said open-circuit voltage does not exceed said upper limit open-circuit voltage.

11. The apparatus for measuring parameters of a secondary battery according to claim 8, further including means for predicting a life of said secondary battery, comprising:

means for storing changes occurring in said polarization resistance in a plurality of charge/discharge cycles of said secondary battery;

means for performing a polynomial approximating extrapolation based on a method of least squares, as a function of a charge/discharge cycle repetition number of said secondary battery; and

means for determining as an effective charge/discharge cycle repeatable number the charge/discharge cycle repetition number at a time point when said polarization resistance attains a polarization resistance limit.