Patent ID: 7899631

Claim:
A method for estimating battery residual capacity based on a stable open circuit voltage (OCV), the method comprising: approximating, in a control unit, a time dependent variation of the open circuit voltage of the battery with a function in which a denominator is a time dependent polynomial of n-th degree, defined as a reciprocal function of n-th degree by the relationship V ⁡ ( t ) = 1 + A 1 · t + A 2 · t 2 + … + A n - 1 · t n - 1 B 0 + B 1 · t + B 2 · t 2 + … + B n · t n + F ⁡ ( t ) + C , where (t) is an elapsed time from when obtaining a voltage value of the battery is started after the battery has stopped charging/discharging, (n) is an integer greater than two, F(t) is an arbitrary function of the time (t), A and B are coefficients in the reciprocal function of n-th degree, and (C) is a constant; obtaining, via a voltage sensor, a number of voltage values of the battery in a predetermined time duration from when the obtaining the voltage value is started, the number of voltage values being equal to or greater than a number of coefficients in the reciprocal function of n-th degree; determining, in the control unit, values of the coefficients in the reciprocal function of n-th degree based on the obtained voltage values using a method of least squares, or a Kalman filter operation, or a neural network; calculating, in the control unit, the stable open circuit voltage from the reciprocal function of n-th degree using the determined values of the coefficients; and estimating, in the control unit, the residual capacity based on the calculated stable open circuit voltage.