Apparatus for estimating charge state of secondary battery and method therefor

1. An apparatus for estimating a state of charge of a secondary battery with an Extended Kalman Filter, comprising:

a sensor unit configured to measure, at time intervals, a voltage and a current of the secondary battery; and

a control unit electrically connected to the sensor unit and configured to:

estimate the state of charge of the secondary battery by repeatedly performing an algorithm of the Extended Kalman Filter by using a state equation that time-updates a state parameter including the state of charge of the secondary battery and a polarization voltage of the secondary battery, and an output equation that predicts the voltage of the secondary battery using an open circuit voltage according to the state of charge, the polarization voltage, and an internal resistance voltage generated by an internal resistance of the secondary battery;

initiate charging and discharging of the battery based on the estimated state of the state of the secondary battery; and

increase a time index of said Extended Kalman Filter algorithm in response to a continued charging or discharging of the secondary battery,

wherein, the control unit determines the secondary battery is in key-off state using the measured current, and when implementing an algorithm of the Extended Kalman Filter, increases a difference between a state of charge noise regarding the state of charge, and a polarization voltage noise regarding the polarization voltage.

2. The apparatus of claim 1 , wherein the control unit is configured to increase the state of charge noise and fix the polarization voltage noise; fix the state of charge noise and decrease the polarization voltage noise; or increase the state of charge noise and decrease the polarization voltage noise.

3. The apparatus of claim 2 , wherein, when implementing an algorithm of the Extended Kalman Filter, the control unit is configured to decrease a sensor noise regarding the current and/or the voltage.

4. The apparatus of claim 1 , wherein the state equation includes a state of charge update equation that time-updates the state of charge with ampere-counting.

5. The apparatus of claim 1 , the state equation includes a polarization voltage update equation that time-updates the polarization voltage with a RC circuit.

6. The apparatus of claim 1 , the output equation represents the voltage of the secondary battery as an output parameter according to a sum of the open circuit voltage, the polarization voltage, and the internal resistance voltage.

7. The apparatus of claim 1 , further comprising a storage unit connected to the control unit, wherein the control unit is configured to store a convergence value of the state of charge estimated after key-off time of the secondary battery into the storage unit as a current state of charge of the secondary battery.

8. The apparatus of claim 1 , further comprising a display unit connected to the control unit, wherein the control unit is configured to display a convergence value of the state of charge estimated after key-off time of the secondary battery as a current state of charge of the secondary battery in a form of graphic user interface (GUI) on the display unit.

9. The apparatus of claim 1 , further comprising a communication interface connected to the control unit, wherein the control unit is configured to output a convergence value of the state of charge estimated after key-off time of the secondary battery as a current state of charge of the secondary battery to outside through the communication interface.

10. The apparatus of claim 1 , wherein the control unit estimates a convergence value of the state of charge estimated after the key-off time of the secondary battery as a current state of charge of the secondary battery, and estimates a state of health of the secondary battery using changes in the estimated current state of charge.

11. A method for estimating a state of charge of a secondary battery with an Extended Kalman Filter, comprising:

(a) measuring, at time intervals, a voltage and a current of the secondary battery;

(b) repeatedly implementing a following algorithm of the Extended Kalman Filter including,

time-updating a state parameter including the state of charge of the secondary battery and a polarization voltage of the secondary battery,

time-updating an error covariance of the state parameter,

predicting the voltage of the secondary battery corresponding to an output parameter using an open circuit voltage according to the state of charge, the polarization voltage, and an internal resistance voltage according to an internal resistance of the secondary battery,

estimating a gain of the Extended Kalman Filter,

estimating the state parameter using an error between the predicted voltage and the measured voltage and the estimated gain, and

correcting the error covariance of the state parameter using the gain;

(c) determining whether or not the secondary battery is in key-off state using the measured current;

(d) when determining that the secondary battery is in key-off state, when implementing an algorithm of the Extended Kalman Filter, increasing a difference between a state of charge noise regarding the state of charge, and a polarization voltage noise regarding the polarization voltage;

(e) initiating, the charging and discharging of the secondary battery based on the estimated state of the secondary battery; and

(f) increasing a time index of said Extended Kalman Filter algorithm in response to a continued charging or discharging of the secondary battery.

12. The method of claim 11 , wherein the step (d) comprises:

increasing the state of charge noise and fixing the polarization voltage noise;

fixing the state of charge noise and decreasing the polarization voltage noise; or

increasing the state of charge noise and decreasing the polarization voltage noise.

13. The method of claim 12 , further comprising:

when implementing an algorithm of the Extended Kalman Filter, decreasing a sensor noise regarding the current and/or the voltage.

14. The method of claim 11 , further comprising estimating a convergence value of the state of charge estimated after key-off time of the secondary battery as a current state of charge of the secondary battery.

15. The method of claim 14 , further comprising storing, displaying or outputting the current state of charge.

16. The method of claim 14 , further comprising estimating a state of health of the secondary battery using the changes in the current state of charge that is estimated with the convergence value of the state of charge estimated when the secondary battery becomes key-off state.