Battery system, remaining capacity estimation device, and remaining capacity estimation method

1. A battery system comprising:

a battery;

a current measurement unit configured to measure a current charged to or discharged from the battery;

a voltage measurement unit configured to measure an output voltage of the battery;

a function creation unit configured to create a function representing a depth-of-discharge characteristic of the battery on the basis of the measured current and output voltage, and further including

a current variation measurement unit configured to calculate a depth of discharge of the battery on the basis of the current charged to or discharged from the battery and the output voltage of the battery;

a data accumulation unit configured to accumulate data created by associating the output voltage of the battery and the depth of discharge corresponding to the output voltage of the battery; and

a formula creation unit configured to create the function representing the depth-of-discharge characteristic of the battery on the basis of the accumulated data, and further including

a function supplementing unit configured to supplement the function representing the depth-of-discharge characteristic in a vicinity of a discharge endpoint where the data is not accumulated, by adding a part of a predetermined depth-of-discharge characteristic function in the vicinity of the discharge end point to the function created from the accumulated data; and

a remaining capacity calculation unit configured to calculate a remaining capacity corresponding to the output voltage of the battery using the created function.

2. The battery system according to claim 1 , wherein the function creation unit updates the function representing the depth-of-discharge characteristic of the battery for each preset period of time or for each preset charging count.

3. The battery system according to claim 1 , wherein the function creation unit causes a display unit to display an alarm for urging replacement of the battery if a full-charge-state dischargeable current capacity of the battery indicated by the created function is equal to or lower than a threshold value.

4. A remaining capacity estimation device for estimating a remaining capacity of a battery, comprising:

a function creation unit configured to create a function representing a depth-of-discharge characteristic of the battery on the basis of a current charged to or discharged from the battery and an output voltage of the battery, and further including

a current variation measurement unit configured to calculate a depth of discharge of the battery on the basis of the current charged to or discharged from the battery and the output voltage of the battery;

a data accumulation unit configured to accumulate data created by associating the output voltage of the battery and the depth of discharge corresponding to the output voltage of the battery, and

a formula creation unit configured to create the function representing the depth-of-discharge characteristic of the battery on the basis of the accumulated data, and further including

a function supplementing unit configured to supplement the function representing the depth-of-discharge characteristic in a vicinity of a discharge endpoint where the data is not accumulated, by adding a part of a predetermined depth-of-discharge characteristic function in the vicinity of the discharge end point to the function created from the accumulated data, and

a remaining capacity calculation unit configured to calculate a remaining capacity corresponding to the output voltage of the battery using the created function.

5. A remaining capacity estimation device for estimating a remaining capacity of a battery, comprising:

a function creation unit configured to create a table regarding a depth of discharge corresponding to an output voltage of the battery on the basis of a current charged to or discharged from the battery and the output voltage of the battery, and further including

a current variation measurement unit configured to calculate a depth of discharge of the battery on the basis of the current charged to or discharged from the battery and the output voltage of the battery;

a data accumulation unit configured to accumulate data created by associating the output voltage of the battery and the depth of discharge corresponding to the output voltage of the battery; and

a formula creation unit configured to create the function representing the depth-of-discharge characteristic of the battery on the basis of the accumulated data, and further including

a function supplementing unit configured to supplement the function representing the depth-of-discharge characteristic in a vicinity of a discharge endpoint where the data is not accumulated, by adding a part of a predetermined depth-of-discharge characteristic function in the vicinity of the discharge end point to the function created from the accumulated data; and

a remaining capacity calculation unit configured to calculate a remaining capacity corresponding to the output voltage of the battery using the created table.

6. A remaining capacity estimation method for estimating a remaining capacity of a battery, comprising:

measuring a current charged to or discharged from the battery;

measuring an output voltage of the battery;

creating an index representing a depth-of-discharge characteristic of the battery on the basis of the measured current and output voltage, and further including

calculating a depth of discharge of the battery on the basis of the current charged to or discharged from the battery and the output voltage of the battery;

accumulating data created by associating the output voltage of the battery and the depth of discharge corresponding to the output voltage of the battery; and

creating the function representing the depth-of-discharge characteristic of the battery on the basis of the accumulated data, and

supplementing the function representing the depth-of-discharge characteristic in a vicinity of a discharge endpoint where the data is not accumulated, by adding a part of a predetermined depth-of-discharge characteristic function in the vicinity of the discharge end point to the function created from the accumulated data; and

calculating a remaining capacity corresponding to the output voltage of the battery using the created function.

7. The remaining capacity estimation method according to claim 6 , wherein a function indicating the depth-of-discharge characteristic of the battery is created as the index in creating the index.

8. The remaining capacity estimation method according to claim 7 , wherein a table of a depth of discharge corresponding to the output voltage of the battery is created as the index in creating the index.

9. The remaining capacity estimation method according to claim 8 , wherein

in measuring the current and measuring the output voltage, the ambient temperature is measured,

in creating the index, the table of the depth of discharge is created for each specified temperature range, and

in calculating the remaining capacity, the remaining capacity corresponding to the output voltage of the battery is calculated using the table created for each specified temperature range.