Electrified vehicle battery state-of-charge monitoring with aging compensation

Patent metadata

Field	Value
Publication number	US-2016103185-A1
Application number	US-201414513400-A
Country	US
Kind code	A1
Filing date	Oct 14, 2014
Priority date	Oct 14, 2014
Publication date	Apr 14, 2016
Grant date	—

Abstract

Determination of an electric vehicle battery state-of-charge (SOC) based on measuring open circuit voltage is subject to error as the relationship changes over time. A method is provided for updating the relationship during aging. A charging current is applied to the battery cell. A favorable charging condition is detected in response to a predetermined charging current. A charging slope vector is compiled during the charging condition comprising a plurality of slope values over respective state-of-charge increments. A plurality of SOC-OCV slope vectors are determined corresponding to a plurality of stored SOC-OCV aging curves, each SOC-OCV slope vector comprising a plurality of slope values over equivalent state-of-charge increments. One of the stored SOC-OCV aging curves is selected having an SOC-OCV slope vector best fitting the charging slope vector for use in converting measured OCV values to battery cell SOC values.

First claim

What is claimed is:

1 . A method of monitoring a battery cell using open circuit voltage (OCV), comprising:
charging the battery cell; detecting a charging condition in response to a predetermined charging current; measuring OCV during battery cell usage following charging; and converting measured OCV values to battery cell SOC values using a selected stored SOC-OCV aging curves having an SOC-OCV slope vector best fitting a charging slope vector, wherein the selected SOC-OCV aging curve is selected based on a) a charging slope vector compiled during the charging condition comprising a plurality of slope values over respective state-of-charge (SOC) increments, and b) a plurality of SOC-OCV slope vectors corresponding to a plurality of stored SOC-OCV aging curves, each SOC-OCV slope vector comprising a plurality of slope values over equivalent state-of-charge increments.

2 . The method of claim 1 wherein the respective state-of-charge increments are detected in response to a predetermined ampere-hour charge increase.

3 . The method of claim 1 further comprising:
measuring an open circuit voltage of the battery cell prior to applying the charging current;
wherein each of the SOC-OCV slope vectors has a starting value determined in response to the measured open circuit voltage.

4 . The method of claim 1 wherein the best fitting SOC-OCV slope vector is determined according to a best fit by least sum of squares of the slope values.

5 . The method of claim 1 wherein the predetermined charging current is detected as a quasi-steady state current maintained within a predetermined range for a predetermined time.

6 . The method of claim 5 wherein the predetermined range corresponds to a peak accuracy for sensing the charging current.

7 . The method of claim 1 wherein the charging condition is further detected in response to a predetermined temperature range.

8 . An electric vehicle, comprising:
a multi-cell battery; a battery charger; a controller compiling a charging slope vector comprising slope values over respective state-of-charge increments, compiling a plurality of SOC-OCV slope vectors for stored SOC-OCV aging curves over equivalent state-of-charge increments, and selecting one of the stored SOC-OCV aging curves having an SOC-OCV slope vector best fitting the charging slope vector for use in converting measured OCV values to battery cell SOC values.

9 . The electric vehicle of claim 8 further comprising a current sensor for measuring a charging current, wherein the respective state-of-charge increments are detected in response to a predetermined ampere-hour charge increase based on the measured charging current.

10 . The electric vehicle of claim 8 further comprising a voltage sensor for measuring an open circuit voltage of a battery cell prior to charging, wherein each of the SOC-OCV slope vectors has a starting value obtained in response to the measured open circuit voltage.

11 . The electric vehicle of claim 8 wherein the best fitting SOC-OCV slope vector is identified according to a best fit by minimal squared Euclidian distance of the slope values.

12 . The electric vehicle of claim 8 wherein the best fitting SOC-OCV slope vector is identified according to a best fit by minimal weighted squared Euclidian distance of the slope values using significance of each slope.

13 . The electric vehicle of claim 8 further comprising a current sensor for measuring a charging current, wherein the charging slope vector is compiled when a predetermined charging current is detected as a quasi-steady state current maintained within a predetermined range for a predetermined time.

14 . The electric vehicle of claim 13 wherein the predetermined range corresponds to a peak accuracy of the current sensor.

15 . The electric vehicle of claim 8 further comprising a temperature sensor measuring a temperature of the battery, wherein the charging slope vector is compiled when the measured temperature is within a predetermined temperature range.

16 . A method of monitoring battery state-of-charge (SOC) comprising:
charging the battery; compiling a charging slope vector comprising slope values over respective state-of-charge increments; compiling a plurality of SOC-OCV slope vectors for stored SOC-OCV aging curves over equivalent state-of-charge increments; and selecting one of the stored SOC-OCV aging curves having an SOC-OCV slope vector best fitting the charging slope vector for use in converting measured OCV values to battery SOC values.

Assignees

• Ford Global Tech Llc

Inventors

• Chang Xiaoguang
• He Chuan
• Wang Xu
• Lee Josephine S

Classifications

• G01R31/3835 Primary

  involving only voltage measurements · CPC title

• G01R31/367

  Software therefor, e.g. for battery testing using modelling or look-up tables · CPC title

• G01R31/374

  with means for correcting the measurement for temperature or ageing · CPC title

• G01R31/392

  Determining battery ageing or deterioration, e.g. state of health · CPC title

• G01R31/3606

  Physics · mapped topic