Method for estimating battery state of charge and battery management system applying the same

1. A method for estimating a state of charge (SOC) of a battery module assembly including a plurality of battery modules respectively including a plurality of battery cells, the method comprising:

receiving a battery current from a current sensor, the battery current being an amount of current flowing to or from the battery module assembly;

comparing the battery current and a threshold current;

selecting one of a first method for estimating a state of charge and a second method for estimating a state of charge, according to a result of the comparing, the second method being different from the first method;

estimating a current SOC of the battery cells according to the selected one of the first method and the second method for estimating a state of charge; and

estimating the SOC of the battery module assembly by combining the estimated current SOC of the battery cells,

wherein the estimating of the current SOC of the battery cells includes:

if the battery current is less than or equal to the threshold current, estimating the current SOC for the battery cells based on current cell voltages or a previous SOC of a plurality of battery cells respectively in each battery module, among the plurality of battery modules, according to the first method for estimating a state of charge; and

if the battery current is greater than the threshold current, estimating the current SOC of the battery cells based on a SOC deviation from a representative previous SOC value respectively of each battery module, among the plurality of battery modules, according to the second method for estimating a state of charge.

2. The method of claim 1 , wherein the estimating of the SOC of the battery cells according to the first method for estimating a state of charge includes:

estimating a current SOC of a plurality of battery cells configuring a selected battery module, among the plurality of battery modules, based on respective current cell voltages of the battery cells configuring the selected battery module; and

estimating a current SOC of a plurality of battery cells configuring a non-selected battery module, among the plurality of battery modules, to be equal to a previous SOC of the battery cells configuring the non-selected battery module.

3. The method of claim 1 , wherein the estimating of the SOC of the battery cells according to the second method for estimating a state of charge includes:

estimating the current SOC of a plurality of battery cells configuring a battery module, among the plurality of battery modules, by adding the respective SOC deviation to a previous SOC of the battery cells configuring the battery module.

4. The method of claim 1 , wherein the respective SOC deviation is a deviation between a representative current SOC value and the representative previous SOC value of the battery module.

5. The method of claim 4 , wherein the estimating of the SOC of the battery cells according to the second method for estimating a state of charge includes:

determining the representative current SOC value based on a median cell voltage among the current cell voltages or a mean cell voltage of the current cell voltages for the battery cells configuring the battery module; and

determining the representative previous SOC value based on a median cell voltage among corresponding previous cell voltages or a mean cell voltage of the corresponding previous cell voltages for the battery cells configuring the battery module.

6. A battery management system for estimating a state of charge (SOC) of a battery module assembly including a plurality of battery modules respectively including a plurality of battery cells, comprising:

a cell monitoring IC connected to respective ends of the respective battery cells, the cell monitoring IC being configured to measure cell voltages of the battery cells; and

a main control circuit configured to:

receive a battery current from a current sensor, the battery current being an amount of current flowing to or from the battery module assembly;

compare the battery current and a threshold current;

select one of a first method for estimating a state of charge and a second method for estimating a state of charge, according to a comparison result, the second method being different from the first method; and

estimate a current SOC of the battery cells according to the selected one of the first method and the second method; and

estimate the SOC of the battery module assembly by combining the estimated current SOC of the battery cells,

wherein the main control circuit is further configured to:

if the battery current is less than or equal to the threshold current, select the first method for estimating a state of charge and estimate the current SOC for the battery cells based on current cell voltages or a previous SOC of a plurality of battery cells respectively in each battery module, among the plurality of battery modules; and

if the battery current is greater than the threshold current, select the second method for estimating a state of charge and estimate the current SOC of the battery cells based on a SOC deviation from a representative previous SOC value respectively for each battery module, among the plurality of battery modules.

7. The battery management system of claim 6 , wherein the main control circuit is further configured, with the first method selected, to:

estimate a current SOC of a plurality of battery cells configuring a selected battery module, among the plurality of battery modules, based on the respective current cell voltages of the battery cells configuring the selected battery module; and

estimate a current SOC of a plurality of battery cells configuring a non-selected battery module, among the plurality of battery modules, to be equal to a previous SOC of the battery cells configuring the non-selected battery module.

8. The battery management system of claim 6 , wherein the main control circuit is further configured, with the second method selected, to estimate the current SOC of a plurality of battery cells configuring a battery module, among the plurality of battery modules, by adding the respective SOC deviation to a previous SOC of the battery cells configuring the battery module.

9. The battery management system of claim 8 , wherein the respective SOC deviation is a deviation between a representative current SOC value and the representative previous SOC value of the battery module.

10. The battery management system of claim 9 , wherein:

the representative current SOC value is determined based on a median cell voltage among the current cell voltages or a mean cell voltage of the current cell voltages for the battery cells configuring the battery module; and

the representative previous SOC value is determined based on a median cell voltage among corresponding previous cell voltages or a mean cell voltage of the corresponding previous cell voltages for the battery cells configuring the battery module.