BATTERY STATE ESTIMATION SYSTEM, BATTERY CONTROL SYSTEM, BATTERY SYSTEM, AND BATTERY STATE ESTIMATION METHOD

• US 20140055100A1
• Filed: 08/19/2013
• Published: 02/27/2014
• Est. Priority Date: 08/24/2012
• Status: Active Grant

• Current Assignee: Vehicle Energy Japan, Inc. (Nissan Motor Co., Ltd.)
• Original Assignee: Hitachi Vehicle Energy, Ltd. (Hitachi, Ltd.)
• Inventors: OHKAWA, Keiichiro, IGARASHI, Naoyuki
• Granted Patent: US 9,537,325 B2
• Time in Patent Office: Days
• US Class Current: 320/152
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/3828 using current integration
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries

Abstract

A battery state estimation system estimates a state of charge of a chargeable battery. A SOCv computing unit calculates a state of charge of the battery using a voltage applied across the battery. A SOCi computing unit integrates a current flowing through the battery to calculate a state of charge of the battery. A SOCw computing unit which performs weighted addition to the state of charge of the battery calculated by the SOCv computing unit and the state of charge of the battery calculated by the SOCi computing unit, wherein when the temperature of the battery is a threshold value or less and the current flowing through the battery is a threshold value or less, the SOCw computing unit sets the specific gravity at the state of charge of the battery calculated by the SOCi computing unit larger than that in other cases upon the weighted addition.

Claims

1. A battery state estimation system which estimates a state of charge of a chargeable battery, said battery state estimation system comprising:

an SOCv computing unit which calculates a state of charge of the battery using a voltage applied across the battery;

an SOCi computing unit which integrates a current flowing through the battery to calculate a state of charge of the battery; and

an SOCw computing unit which performs weighted addition to the state of charge of the battery calculated by the SOCv computing unit and the state of charge of the battery calculated by the SOCi computing unit,

wherein when the temperature of the battery is a predetermined temperature threshold value or less and the current flowing through the battery is a predetermined current threshold value or less, the SOCw computing unit sets the specific gravity at the state of charge of the battery calculated by the SOCi computing unit larger than that in other cases upon the weighted addition.

2. The battery state estimation system according to claim 1, including:

a temperature measuring unit which measures the temperature of the battery;

a current measuring unit which measures the current flowing through the battery;

a voltage measuring unit which measures the voltage applied across the battery;

a resistance measuring unit which measures an internal resistance of the battery; and

a weight computing unit which calculates a weight used when the SOCw computing unit performs the weighted addition,

wherein the weight computing unit calculates the weight in such a manner that the weight related to the state of charge calculated by the SOCv computing unit becomes large as the current flowing through the battery becomes smaller, and the weight related to the state of charge calculated by the SOCv computing unit becomes large as the internal resistance of the battery becomes smaller, and

wherein when the temperature of the battery is a predetermined temperature threshold value or less and the current flowing through the battery is a predetermined current threshold value or less, the weight is further multiplied by a coefficient less than 1 to thereby decrease the weight related to the stage of charge of the battery calculated by the SOCv computing unit and increase the weight related to the state of charge of the battery calculated by the SOCi computing unit.

3. The battery state estimation system according to claim 2, including a storage unit which stores therein an association table in which a correlation between the temperature of the battery, the current flowing through the battery and the coefficient is defined,

wherein the weight computing unit calculates the weight by referring to the association table with the temperature of the battery and the current flowing through the battery as keys.

4. The battery state estimation system according to claim 3, wherein the weight computing unit calculates the weight by linearly interpolating a correlation between the temperature and the weight defined in the association table with respect to the temperature undefined in the association table.

5. The battery state estimation system according to claim 3, wherein the weight computing unit calculates the weight by linearly interpolating a correlation between the current and the weight defined in the association table with respect to the current undefined in the association table.

6. The battery state estimation system according to claim 2, including a resistance table in which a correlation between the temperature of the battery and the internal resistance of the battery is defined,

wherein the resistance measuring unit measures the internal resistance of the battery by referring to the resistance table with the temperature of the battery as a key.

7. The battery state estimation system according to claim 1, including an SOC table in which a correlation between an open circuit voltage of the battery and a state of charge of the battery is defined,

wherein the SOCv computing unit calculates the state of charge of the battery by referring to the SOC table with the open circuit voltage of the battery as a key.

8. A battery control system comprising:

a battery state estimation system according to claim 1,

wherein the battery control system controls the battery using the state of charge of the battery estimated by the battery state estimation system.

9. A battery system comprising:

a battery control system according to claim 8; and

a battery controlled by the battery control system.

10. A method of estimating a state of charge of a chargeable battery, comprising the steps of:

performing an SOCv operation for calculating a state of charge of the battery using a voltage applied across the battery;

performing an SOCi operation for integrating a current flowing through the battery to calculate a state of charge of the battery; and

performing an SOCw operation for performing weighted addition to the state of charge of the battery calculated in the SOCv operation step and the state of charge of the battery calculated in the SOCi operation step,

wherein in the SOCw operation step, when the temperature of the battery is a predetermined temperature threshold value or less and the current flowing through the battery is a predetermined current threshold value or less, the specific gravity at the state of charge of the battery calculated in the SOCi operation step is set larger than that in other cases upon the weighted addition.