Method and apparatus for estimating state of charge of secondary battery

• US 20050073315A1
• Filed: 09/29/2004
• Published: 04/07/2005
• Est. Priority Date: 10/01/2003
• Status: Active Grant

• Current Assignee: Panasonic EV Energy Company, Limited (Toyota Motor Corporation)
• Original Assignee: Panasonic EV Energy Company, Limited (Toyota Motor Corporation)
• Inventors: Kimura, Tadao, Yamabe, Norito, Minamiura, Keiichi, Murakami, Yusai
• Granted Patent: US 7,355,411 B2
• Time in Patent Office: Days
• US Class Current: 324/433
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

When a power switch portion 10 is in an open state and a charge/discharge path of the secondary battery 100 is in a disconnected state, an electromotive force calculation portion 109 calculates a battery electromotive force Veq by subtracting a polarized voltage Vpol stored in a polarized voltage storage portion 113 from an open-circuit voltage OCV measured by a voltage measurement portion 102. Based on the electromotive force, a state-of-charge estimation portion 110 estimates a state of charge SOC. Thus, a polarized voltage to be considered for the estimation of SOC can be limited. The state of charge (SOC) of a secondary battery can be estimated with high accuracy and quickly.

Claims

1. A method for estimating a state of charge of a secondary battery, comprising the steps of:

measuring an open-circuit voltage of the secondary battery when a charge/discharge path of the secondary battery is in a disconnected state;

storing a polarized voltage of the secondary battery;

calculating an electromotive force of the secondary battery by subtracting the stored polarized voltage from the measured open-circuit voltage; and

estimating the state of charge of the secondary battery based on the calculated electromotive force.

3. The method according to claim 1, further comprising:

determining whether or not the charge/discharge path is in the disconnected state; and

measuring a terminal voltage of the secondary battery as the open-circuit voltage when it is determined in the determining step that the charge/discharge path is in the disconnected state.

4. The method according to claim 3, further comprising:

measuring a current flowing through the secondary battery,

wherein in the determining step, it is determined based on a value of the measured current whether or not the charge/discharge path is in the disconnected state.

5. The method according to claim 1, further comprising:

measuring a current flowing through the secondary battery;

calculating a charge/discharge amount of the secondary battery based on the measured current; and

calculating the polarized voltage based on the calculated charge/discharge amount.

6. The method according to claim 5, wherein in the polarized voltage calculating step, the polarized voltage is calculated based on a look-up table or an expression that stores characteristics of the polarized voltage versus the charge/discharge amount where a temperature is a parameter, the characteristics being previously obtained.

7. The method according to claim 1, wherein in the state-of-charge estimating step, the state of charge is estimated based on a look-up table or an expression that stores characteristics of the state of charge versus the electromotive force where a temperature is a parameter, the characteristics being previously obtained.

2. A method for estimating a state of charge of a secondary battery, wherein the secondary battery is used in an intermediately charged state as a power source for a motor and a drive source for a load, the method comprising the steps of:

measuring an open-circuit voltage of the secondary battery when a charge/discharge path of the secondary battery is in a disconnected state;

storing a polarized voltage of the secondary battery;

calculating an electromotive force of the secondary battery by subtracting the stored polarized voltage from the measured open-circuit voltage; and

calculating the state of charge of the secondary battery based on the calculated electromotive force.

15. The method according to claim 2, further comprising:

determining whether or not the charge/discharge path is in the disconnected state; and

measuring a terminal voltage of the secondary battery as the open-circuit voltage when it is determined in the determining step that the charge/discharge path is in the disconnected state.

16. The method according to claim 2, further comprising:

measuring a current flowing through the secondary battery;

calculating a charge/discharge amount of the secondary battery based on the measured current; and

calculating the polarized voltage based on the calculated charge/discharge amount.

17. The method according to claim 2, wherein in the state-of-charge estimating step, the state of charge is estimated based on a look-up table or an expression that stores characteristics of the state of charge versus the electromotive force where a temperature is a parameter, the characteristics being previously obtained.

8. An apparatus for estimating a state of charge of a secondary battery, comprising:

a voltage measurement portion for measuring an open-circuit voltage of the secondary battery when a charge/discharge path of the secondary battery is in a disconnected state;

a polarized voltage storage portion for storing a polarized voltage of the secondary battery;

an electromotive force calculation portion for calculating an electromotive force of the secondary battery by subtracting the polarized voltage stored in the polarized voltage storage portion from the open-circuit voltage measured by the voltage measurement portion; and

a state-of-charge estimation portion for estimating the state of charge of the secondary battery based on the electromotive force from the electromotive force calculation portion.

10. The apparatus according to claim 8, further comprising:

a disconnected state determination portion for determining whether or not the charge/discharge path is in the disconnected state,

wherein a terminal voltage of the secondary battery measured by the voltage measurement portion is used as the open-circuit voltage when it is determined by the disconnected state determination portion that the charge/discharge path is in the disconnected state.

11. The apparatus according to claim 10, further comprising:

a current measurement portion for measuring a current flowing through the secondary battery,

wherein the disconnected state determination portion determines based on a value of the current measured by the current measurement portion whether or not the charge/discharge path is in the disconnected state.

12. The apparatus according to claim 8, further comprising:

a current measurement portion for measuring a current flowing through the secondary battery;

a charge/discharge amount calculation portion for calculating a charge/discharge amount of the secondary battery based on the current measured by the current measurement portion; and

a polarized voltage calculation portion for calculating the polarized voltage based on the charge/discharge amount calculated by the charge/discharge amount calculation portion.

13. The apparatus according to claim 12, further comprising:

a temperature measurement portion for measuring a temperature of the secondary battery,

wherein the polarized voltage calculation portion calculates the polarized voltage based on the temperature measured by the temperature measurement portion and a look-up table or an expression that stores characteristics of the polarized voltage versus the charge/discharge amount where the temperature is a parameter, the characteristics being previously obtained.

14. The apparatus according to claim 8, further comprising:

a temperature measurement portion for measuring a temperature of the secondary battery,

wherein the state-of-charge estimation portion estimates the state of charge based on the temperature measured by the temperature measurement portion and a look-up table or an expression that stores characteristics of the state of charge versus the electromotive force where the temperature is a parameter, the characteristics being previously obtained.

9. An apparatus for estimating a state of charge of a secondary battery, wherein the secondary battery is used in an intermediately charged state as a power source for a motor and a drive source for a load, the apparatus comprising:

a voltage measurement portion for measuring an open-circuit voltage of the secondary battery when a charge/discharge path of the secondary battery is in a disconnected state;

a polarized voltage storage portion for storing a polarized voltage of the secondary battery;

an electromotive force calculation portion for calculating an electromotive force of the secondary battery by subtracting the polarized voltage stored in the polarized voltage storage portion from the open-circuit voltage measured by the voltage measurement portion; and

a state-of-charge estimation portion for estimating the state of charge of the secondary battery based on the electromotive force from the electromotive force calculation portion.

18. The apparatus according to claim 9, further comprising:

a disconnected state determination portion for determining whether or not the charge/discharge path is in the disconnected state,

wherein a terminal voltage of the secondary battery measured by the voltage measurement portion is used as the open-circuit voltage when it is determined by the disconnected state determination portion that the charge/discharge path is in the disconnected state.

19. The apparatus according to claim 9, further comprising:

a current measurement portion for measuring a current flowing through the secondary battery;

a charge/discharge amount calculation portion for calculating a charge/discharge amount of the secondary battery based on the current measured by the current measurement portion; and

a polarized voltage calculation portion for calculating the polarized voltage based on the charge/discharge amount calculated by the charge/discharge amount calculation portion.

20. The apparatus according to claim 9, further comprising:

a temperature measurement portion for measuring a temperature of the secondary battery, wherein the state-of-charge estimation portion estimates the state of charge based on the temperature measured by the temperature measurement portion and a look-up table or an expression that stores characteristics of the state of charge versus the electromotive force where the temperature is a parameter, the characteristics being previously obtained.