SECONDARY BATTERY STATE-OF-CHARGE ESTIMATOR AND STATE-OF-CHARGE ESTIMATING METHOD

摘要

PROBLEM TO BE SOLVED: To enhance estimation accuracy by using an appropriate SOC (State of Charge) estimation method adapted to the use conditions of a secondary battery.SOLUTION: When a battery current Ib is not more than a limit current |Ijd| set according to battery temperature Tb and is continuously flowing for a period not less than a certain period set according to the battery temperature Tb, the secondary battery 10 is determined to be in a stable state (S100). When the secondary battery 10 is in a stable state, SOC estimation is performed based on an open-circuit voltage-SOC characteristic, assuming that a battery voltage Vb equals the open-circuit voltage OCV (S110). By setting the limit current |Ijd| so that it is parallelized to the temperature dependency of the internal resistance of the secondary battery, the product of the internal resistance and the limit current |Ijd| is kept substantially at a constant value (a constant voltage). This makes it possible to reduce estimation error to within a definite range in a stable state even if SOC estimation is performed on the assumption that the battery voltage Vb equals the open-circuit voltage OCV.