Method of estimating state of charge of battery

A method of estimating a state of charge of a battery, comprising the steps of:

• measuring electric current in order to integrate the electric current during an estimation of the state of charge;
• calculating a decrement in capacity of the battery according to charging and discharging cycles;
• and
• estimating the state of charge by dividing a value, which is obtained by integrating electric current, by the decrement in the capacity of the battery according to the cycles,
• wherein the decrement in the capacity of the battery according to the cycles is calculated by a following equation (6):
• Fc(cycle)=D5×d5+D4×d4+D3×d3+D2×d2+D1×d+D0 (6)
• wherein DO, D1, D2, D3, D4, and D5 are constants, and d is an integrated discharge capacity.

A method of estimating a state of charge of a battery, comprising the steps of:

• measuring electric current in order to integrate the electric current during an estimation of the state of charge;
• calculating a decrement in capacity of the battery according to charging and discharging cycles;
• and
• estimating the state of charge by dividing a value, which is obtained by integrating electric current, by the decrement in the capacity of the battery according to the cycles,
• wherein the state of charge (SOC) is calculated by a following equation (7):
• SOC
• k
• =
• SOC
• k
• -
• 1
• +
• E
• cha
• ×
• I
• cha
• ×
• t
• -
• E
• dch
• ×
• I
• dch
• ×
• t
• C
• init
• ×
• F
• c
• ⁡
• (
• cycle
• )
• ×
• 100
• (
• 7
• )
• wherein SOCk-1 is a previous SOC, Echa is a charging efficiency, Ldch is a discharging efficiency, Icha is a charging current, Idch is a discharging current, t is time, Cinit is an initial capacity of the battery, and Fc(cycle) is a decrement in a capacity of the battery according to cycles.

An apparatus for estimating a state of charge of a battery, comprising:

• a temperature sensor for measuring temperature;
• a memory for storing parameters indicating a change of an open circuit voltage according to a change of temperature;
• a voltage meter for measuring the open circuit voltage;
• and
• a controller which measures the temperature and the open circuit voltage through the temperature sensor and the open circuit voltage meter during an initial estimation of the state of charge of the battery and obtains the parameters, which indicate the change of the open circuit voltage according to the change of temperature, from the memory, so as to calculate the state of charge of the battery using the parameters and the open circuit voltage measured according to the obtained parameters,
• wherein the state of charge is calculated by the following equation (5):
• y
• =
• a
• ⁡
• [
• 1
• +
• (
• b
• -
• 1
• )
• (
• -
• c
• ⁡
• (
• x
• -
• d
• )
• )
• ]
• 1
• 1
• -
• b
• (
• 5
• )
• in which y is the state of charge, x is the open circuit voltage, and a, b, c, and d are the parameters corresponding to the respective temperatures, in which a indicates an upper asymptote, b is a parameter which indirectly settles a deflection point, c is a scaling factor, and d indicates a position of a deflection point with respect to an X axis.