Method and system for monitoring state of lead acid battery

• US 20040085072A1
• Filed: 11/05/2002
• Published: 05/06/2004
• Est. Priority Date: 11/05/2002
• Status: Active Grant

• Current Assignee: Furukawa Battery Company Limited (Furukawa Electric Company Limited)
• Original Assignee: Furukawa Battery Company Limited (Furukawa Electric Company Limited)
• Inventors: Miyata, Koji, Takahashi, Kiyoshi, Kanou, Tetsuya, Watakabe, Yuichi, Narita, Masanobu
• Granted Patent: US 6,838,883 B2
• Time in Patent Office: Days
• US Class Current: 324/426
• CPC Class Codes: G01N 27/02 by investigating impedance
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/379 for lead-acid batteries
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables

Abstract

In order to monitor a state of a battery, a threshold value of an internal impedance of the battery is first determined. It is prepared an approximate expression indicating a correlation between a residual capacity of the battery and an internal impedance of the battery which is greater than the threshold value. The internal impedance of the battery is then measured. When the measured internal impedance is the threshold value or less, the residual capacity is determined as an initial value. When the measured internal impedance is greater than the threshold value, the residual capacity is monitored with the approximate expression.

Claims

1. A method of monitoring a state of a battery, comprising the steps of:

determining threshold value of an internal impedance of the battery;

preparing an approximate expression indicating a correlation between a residual capacity of the battery and an internal impedance of the battery which is greater than the threshold value;

measuring the internal impedance of the battery;

determining the residual capacity as an initial value when the measured internal impedance is the threshold value or less; and

monitoring the residual capacity with the approximate expression when the measured internal impedance is greater than the threshold value.

2. A system of monitoring a state of a battery, comprising;

a storage, in which an approximate expression indicating a correlation of a residual capacity of the battery and an internal impedance of the battery which is greater than a threshold value is previously stored;

an instrument, which measures the internal impedance of the battery; and

a monitor, which monitors the residual capacity with the approximate expression when the measured internal impedance is greater than the threshold value, and determines the residual capacity as an initial value when the measured internal impedance is the threshold value or less.

3. A method of monitoring a state of a battery, comprising the steps of measuring an internal impedance of the battery every time when a first time period is elapsed;

storing the measured internal impedance as time-serial impedance data;

monitoring a residual capacity of the battery;

gathering the time-serial impedance data during a second time period prior to a time point at which the monitored residual capacity becomes a threshold value or less;

obtaining an approximate expression indicating a correlation between the internal impedance and the residual capacity based on the gathered time-serial impedance data; and

predicting a residual lifetime of a battery based on the obtained approximate expression.

4. The monitoring method as set forth in claim 3, wherein the threshold value is 85% of an initial capacity.

5. A method of monitoring a state of a battery, comprising the steps of:

measuring an internal impedance of the battery every time when a first time period is elapsed;

storing the measured internal impedance as time-serial impedance data;

obtaining an average value of the time-serial impedance data every time when a second time period is elapsed;

comparing an average value of a certain second time period and a preceding second time period to obtain a changing rate of the average value; and

generating an alarm when the obtained changing rate is not less than a predetermined value.

6. A method of monitoring a state of a battery, comprising the steps of:

measuring an internal impedance of the battery every time when a first time period is elapsed;

storing the measured internal impedance as time-serial impedance data;

obtaining an average value of the time-serial impedance data every time when a second time period is elapsed;

obtaining an approximate expression based on the time-serial impedance data every time when the second time period is elapsed;

predicting a time point at which a changing rate of the average value becomes a predetermined value or more, based on the approximate expression; and

displaying the predicted time point as a residual lifetime of the battery.

7. A system of monitoring a state of a battery, comprising:

a instrument, which measures an internal impedance of the battery every time when a first time period is elapsed;

a storage, which stores the measured internal impedance as time-serial impedance data;

a monitor, which monitors a residual capacity of the battery; and

a calculator, which gathers the time-serial impedance data during a second time period prior to a time point at which the monitored residual capacity becomes a threshold value or less;

obtains an approximate expression indicating a correlation between the internal impedance and the residual capacity based on the gathered time-serial impedance data; and

predicts a residual lifetime of a battery based on the obtained approximate expression.

8. The monitoring system as set forth in claim 7, wherein the threshold value is 85% of an initial capacity.

9. A system of monitoring a state of a battery, comprising:

an instrument, which measures an internal impedance of the battery every time when a first time period is elapsed;

a storage, which stores the measured internal impedance as time-serial impedance data;

a calculator, which obtains an average value of the time-serial impedance data every time when a second time period is elapsed;

a comparator, which compares an average value of a certain second time period and a preceding second time period to obtain a changing rate of the average value; and

an alarm, which generates an alarm when the obtained changing rate is not less than a predetermined value.

10. A system of monitoring a state of a battery, comprising:

an instrument, which measures an internal impedance of the battery every time when a first time period is elapsed;

a storage, which stores the measured internal impedance as time-serial impedance data;

a calculator, which obtains an average value of the time-serial impedance data every time when a second time period is elapsed;

obtains an approximate expression based on the time-serial impedance data every time when the second time period is elapsed; and

predicts a time point at which a changing rate of the average value becomes a predetermined value or more, based on the approximate expression; and

a display, which displays the predicted time point as a residual lifetime of the battery.

11. A method of measuring an internal impedance of a battery, comprising the steps of:

measuring an internal impedance and a temperature of the battery at the same time;

storing the measured internal impedance and the measured temperature as time-serial impedance data and time-serial temperature data;

obtaining a correction coefficient based on a correlation between the time-serial impedance data and the time-serial temperature data during a predetermined time period; and

correcting the measured internal impedance with the correction coefficient as a value at a reference temperature.

12. A system for measuring an internal impedance of a battery, comprising:

an instrument, which measures an internal impedance and a temperature of the battery at the same time;

a storage, which stores the measured internal impedance and the measured temperature as time-serial impedance data and time-serial temperature data;

a calculator, which obtains a correction coefficient based on a correlation between the time-serial impedance data and the time-serial temperature data during a predetermined time period; and

a corrector, which corrects the measured internal impedance with the correction coefficient as a value at a reference temperature.