DEVICE ESTIMATING A STATE OF A SECONDARY BATTERY

A diffusion estimation unit follows a diffusion equation in an active material that is represented by a polar coordinate to estimate a distribution in concentration of lithium in the active material. An open circuit voltage estimation unit obtains an open circuit voltage in accordance with a local SOC(θ) based on a concentration of lithium obtained at an interface of the active material as estimated by the diffusion estimation unit. A current estimation unit uses a battery's voltage measured by a voltage sensor, the estimated open circuit voltage, and a parameter value that is set for the battery by a battery parameter value setting unit, and follows a voltage-current relationship model expression simplified from an electrochemical reaction expression to estimate the battery's current density. A boundary condition setting unit sequentially sets a boundary condition for the diffusion equation of the diffusion estimation unit for the active material's interface, as based on the battery's estimated current density. Thus a battery model that allows an internal state to be estimated based on an electrochemical reaction dynamically and can also achieve an alleviated operating load can be used to estimate a state of a secondary battery.