Remaining capacity calculation method for secondary battery, and battery pack

• US 20050237027A1
• Filed: 04/13/2005
• Published: 10/27/2005
• Est. Priority Date: 04/27/2004
• Status: Active Grant

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Hogari, Masaki, Sasaki, Taichi
• Granted Patent: US 7,459,884 B2
• Time in Patent Office: Days
• US Class Current: 320/132
• CPC Class Codes: G01R 31/382 Arrangements for monitoring battery or accumulator variables, e.g. SoC

Abstract

A remaining capacity calculation method for a secondary battery and a battery pack are provided. Dischargeable electric power is accurately calculated and accuracy of a remaining capacity rate found by an electric power integration method may be improved by providing a remaining capacity calculation method for a secondary battery. The method includes calculating a consumed electric power by way of integration of voltage and current measured at a preset time interval when using the secondary battery; calculating an available dischargeable electric power by subtracting an energy loss and unavailable energy from a discharge electric power of the secondary battery; and calculating a remaining capacity rate from a ratio between the calculated electric power and the dischargeable electric power.

Claims

1. A remaining capacity calculation method for a secondary battery comprising:

calculating a used electric power by integration of voltage and current measured at a preset time interval when using the secondary battery;

calculating an available dischargeable electric power by subtracting an energy loss and unavailable energy from a discharge electric power of the secondary battery; and

calculating a remaining capacity rate from a ratio between the calculated electric power and the dischargeable electric power.

2. The remaining capacity calculation method according to claim 1, wherein

the dischargeable electric power is calculated as an area based on an intersection of a straight line, an abscissa-axis and an ordinate-axis, where the straight line is a line obtained by approximation of discharge voltage associated with full charge to termination of discharge of the secondary battery, and wherein the abscissa-axis represents discharge capacity and the ordinate-axis represents voltage.

3. The remaining capacity calculation method according to claim 2, wherein

the straight line is expressed as y=−

ax+b1, where a comprises a value calculated based on data of a discharge curve of the secondary battery, and b1 comprises a voltage for an unloaded condition under full charge.

4. The remaining capacity calculation method according to claim 3, wherein b1 comprises a load factor, and if there is load it is moved in a minus direction as compared with a value of the unloaded condition, such that as the discharge current increases an amount of movement in the minus direction increases.

5. The remaining capacity calculation method according to claim 2, wherein

unavailable capacity due to conditions of load and temperature and capacity reduction due to degradation of the secondary battery are calculated by moving a discharge termination point to a minus direction over the abscissa-axis.

6. The remaining capacity calculation method according to claim 2, wherein

a table of correspondence relationship between the remaining capacity rate and a DC impedance factor is prepared, and

a discharge termination voltage in a discharge termination section is obtained taking into consideration an increase in the DC impedance.

7. A battery pack of a secondary battery, comprising a measurement unit for measuring voltage and current of the secondary battery, and a remaining capacity calculation unit;

wherein the remaining capacity calculation unit measures the voltage and current when using the secondary battery at preset time interval, and integrates the used electric power by way of integration of the voltage and the current;

calculates an available dischargeable electric power by subtracting an energy loss and unavailable energy from a discharge electric power of the secondary battery; and

calculates a remaining capacity rate from a ratio between the integrated electric power and the dischargeable electric power.