Patent ID: 7888912

Claim:
A computer readable storage medium containing thereon a battery state of charge (SOC) estimation program execution by a computer to calculate an SOC of a battery mounted on a vehicle in a wireless transit system, wherein an equivalent circuit of the battery is set in the program, the equivalent circuit being composed of three circuit elements connected in series, including: (i) a first component resistance which is influenced by instantaneous current variation, (ii) a component circuit which comprises a capacitance and a second component resistance connected in parallel, and which is influenced by slow and excessive response, and (iii) an open circuit voltage of the battery, and wherein the program, when executed by the computer, causes the computer to calculate (a) a value of the first component resistance from measurements of current and voltage of the battery, (b) a value of the second component resistance from the calculated value of the first component resistance and a predetermined value of k, where k=the second component resistance/the first component resistance, (c) a value of the capacitance from the calculated value of the second component resistance and a predetermined value of τ, where τ=the capacitance×the second component resistance, (d) a potential of the component circuit from the calculated values of the second component resistance and the capacitance, (e) a value of the open circuit voltage from the calculated potential of the component circuit, and (f) the SOC from the calculated value of the open circuit voltage.