Patent ID: 7352156

Claim:
A state-of-charge estimating device for estimating a state-of-charge of a secondary battery connected to a load, comprising: a current detecting device for detecting a current I of the secondary battery; a terminal voltage detecting device for detecting a terminal voltage V of the secondary battery; and a controller receiving input from the current detecting device and the terminal voltage detecting device, the controller including: an open-circuit voltage estimating part operable to perform an adaptive digital filter computing treatment to estimate at least one battery parameter in a battery model V = B ⁡ ( s ) A ⁡ ( s ) · I + 1 A ⁡ ( s ) · V O en bloc based on the current I and terminal voltage V of the secondary battery and the battery model V = B ⁡ ( s ) A ⁡ ( s ) · I + 1 A ⁡ ( s ) · V O and to estimate an estimated open-circuit voltage V O of the secondary battery, wherein A(s) and B(s) are polynomials of Laplace operator s; a first state-of-charge estimating part operable to estimate a first state-of-charge value based on the estimated open-circuit voltage V O of the secondary battery and a previously derived relationship between an open-circuit voltage and a state-of-charge of the secondary battery; a second state-of-charge estimating part operable to estimate a second state-of-charge value using a method capable of estimating the state-of-charge even if the current I is constant while one or more of the at least one battery parameter varies; and a state-of-charge estimated value-selecting part operable to switch from the first state-of-charge value to the second state-of-charge value as the state-of-charge when the current I is constant and otherwise to select the first state-of-charge value as the state-of-charge.