Battery state estimation system, battery control system, battery system, and battery state estimation method

• US 9,537,325 B2
• Filed: 08/19/2013
• Issued: 01/03/2017
• Est. Priority Date: 08/24/2012
• Status: Active Grant

• Current Assignee: Vehicle Energy Japan, Inc.
• Original Assignee: Hitachi Automotive Systems Limited (Hitachi, Ltd.)
• Inventors: Igarashi, Naoyuki, Ohkawa, Keiichiro
• Primary Examiner(s): Garbowski, Leigh
• Application Number:
  US13/970,128
• Publication Number:
  US 20140055100A1
• Time in Patent Office: 1,233 Days
• Field of Search: None
• US Class Current: 1/1
• 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 comprising:

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

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

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

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

an SOC_v computing unit configured to determine an SOC_v value based on a state of charge of a battery using the voltage applied across the battery;

an SOC_i computing unit configured to determine an SOC_i value based on the current flowing through the battery to calculate a state of charge of the battery;

a weight computing unit that is configured to;

compare the temperature of the battery to a temperature threshold value;

compare the current flowing through the battery to a current threshold value;

determine a weighting factor (W), based on the internal resistance of the battery and the current flowing through the battery but not the temperature of the battery, when at least one of the following is determined based on the comparisons;

the temperature of the battery is greater than a temperature threshold value, or the current flowing through the battery is greater than the current threshold value;

determine W, based on the internal resistance of the battery, the current flowing through the battery, and the temperature of the battery, when the temperature of the battery is determined, based on the comparison, to be less than or equal to the temperature threshold value and the current flowing through the battery is determined, based on the comparison, to be less than or equal to the current threshold value, wherein determining W includes;

identifying a value Wgain based on the temperature of the battery and the current flowing through the battery, and

determining W based on the value Wgain; and

a SOC_w computing unit that is configured to;

calculate a state of charge SOC_w value according to Equation 1,

Equation 1;

SOC_w=W*SOC_v+(1−

W)*SOC_i. 

 

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

wherein when the temperature of the battery is less than or equal to the temperature threshold value and the current flowing through the battery is less than or equal to the current threshold value, W is determined to be less than 1.

3. The battery state estimation system according to claim 2, further comprising:

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 value Wgain are defined,

wherein the weight computing unit is further configured to determine W based on the association table.

4. The battery state estimation system according to claim 3, wherein the weight computing unit is further configured to determine W by linearly interpolating a correlation between the temperature and the value Wgain defined in the association table.

5. The battery state estimation system according to claim 3, wherein the weight computing unit is further configured to determine W by linearly interpolating a correlation between the current and the value Wgain defined in the association table.

6. The battery state estimation system according to claim 2, further comprising:

a resistance table including a correlation between the temperature of the battery and the internal resistance of the battery,

wherein the resistance measuring unit measures the internal resistance of the battery based on the resistance table with the temperature of the battery as a key.

7. The battery state estimation system according to claim 1, further comprising:

an SOC table that includes a correlation between an open circuit voltage of the battery and a state of charge of the battery,

wherein the SOC_v computing unit is further configured to calculate the state of charge of the battery based on the SOC table with the open circuit voltage of the battery as a key.

8. The battery state estimation system according to claim 1, wherein when the temperature of the battery is less than or equal to the temperature threshold value and the current flowing through the battery is less than or equal to the current threshold value, the weight computing unit sets a weight factor used by the SOC_i computing unit to determine the state of charge of the battery higher than in instances in which one or more of the temperature threshold value or the current threshold value are exceeded.

9. A method of estimating a state of charge of a chargeable battery, comprising:

measuring a temperature of the battery;

measuring a current flowing through the battery;

determining an SOC_v value based on a voltage applied across the battery;

determining an SOC_i value based on the current flowing through the battery;

comparing the temperature of the battery to a temperature threshold value;

comparing the current flowing through the battery to a current threshold value; and

determining a weighting factor (W), based on an internal resistance of the battery and the current flowing through the battery, but not the temperature of the battery, when at least one of the following is determined based on the comparisons;

the temperature of the battery is greater than a temperature threshold value, or the current flowing through the battery is greater than the current threshold value;

determining W, based on the internal resistance of the battery, the current flowing through the battery and the temperature of the battery, when the temperature of the battery is determined, based on the comparison, to be less than or equal to the temperature threshold value and the current flowing through the battery is determined, based on the comparison, to be less than or equal to the current threshold value, wherein determining W includes;

identifying a value Wgain based on the temperature of the battery and the current flowing through the battery, and

determining W based on the value Wgain; and

calculating an SOC_w value accordingly to Equation 1,

Equation 1;

SOC_w=W*SOC_v+(1−

W)*SOC_i.