Method of estimating state of charge of secondary cell, state-of-charge estimation device, cell pack, electronic apparatus, and electric vehicle
View Patent ↗A method of estimating a state of charge of a secondary cell includes: calculating a value of (∂E emf /∂T) in advance on the assumption that E emf is an electromotive force of the secondary cell and T is a temperature of the secondary cell; and calculating the state of charge based on at least a value of (∂E emf /∂T) for which a value of the state of charge is set as a variable, a temperature measurement value of the secondary cell, and a current measurement value of the secondary cell.
1. A method, comprising:
in a state-of-charge estimation device configured to estimate a state of charge of a secondary cell:
measuring a temperature of the secondary cell using a temperature measurement device;
calculating a value of to be stored in a storage unit, where E emf is an electromotive force of the secondary cell and T is the temperature of the secondary cell; and
calculating the state of charge based on at least the stored value of ∂E emf /∂T for which a value of the state of charge is set as a variable, a value of the measured temperature of the secondary cell, and a current measurement value of the secondary cell.
2. The method according to claim 1 , wherein the state of charge is calculated based on an internal resistance value of the secondary cell.
3. The method according to claim 1 , further comprising:
calculating the state of charge at time t 1 based on a state of charge at time t 0 and the current measurement value of the secondary cell from time t 0 to time t 1 ;
calculating an actual measurement temperature increase amount ΔT real based on the temperature measurement value of the secondary cell from time t 0 to time t 1 ;
calculating a temperature increase amount ΔT calc of the secondary cell from time t 0 to time t 1 based on the value of ∂ emf /∂T for which the value of the state of charge is set as the variable; and
correcting the state of charge at time t 0 such that an absolute value ΔT diff =|ΔT real −ΔT calc |, which is a difference between the actual measurement temperature increase amount ΔT real and the calculated temperature increase amount ΔT calc of the secondary cell from time t 0 to time t 1 becomes a second value in the event the absolute value ΔT diff exceeds a first value,
wherein the second value is less than the first value.
4. The method according to claim 1 , further comprising:
for a temperature change of the secondary cell is equal to or less than a temperature measurement limit of the temperature measurement device and an open voltage change of the secondary cell is equal to or less than a voltage measurement limit of a voltage measurement device:
measuring an open voltage of the secondary cell by the voltage measurement device;
measuring the temperature of the secondary cell by the temperature measurement device; and
calculating the value of ∂E emf /∂T based on the measured open voltage and the measured temperature.
5. The method according to claim 4 , wherein the voltage measurement limit of the voltage measurement device is 1×10 −6 volts and the temperature measurement limit of the temperature measurement device is 1×10 −2 ° C.
6. The method according to claim 1 , further comprising:
measuring, in a state that is lacking a diffusion reaction of lithium ions, an open voltage of the secondary cell by a voltage measurement device, and the temperature of the secondary cell by the temperature measurement device; and
calculating the value of ∂E emf /∂T based on the measured open voltage and the measured temperature,
wherein the secondary cell includes a lithium-ion secondary cell.
7. The method according to claim 6 , wherein the state in which the diffusion reaction of lithium ions does not occur is a state in which a temperature change of the secondary cell is equal to or less than a temperature measurement limit of the temperature measurement device and an open voltage change of the secondary cell is equal to or less than a voltage measurement limit of the voltage measurement device.
8. The method according to claim 1 , further comprising:
calculating the state of charge at time t 1 based on the state of charge at time t 0 and the current measurement value of the secondary cell from time t 0 to time t 1 ;
calculating an actual measurement temperature increase amount based on the temperature measurement value of the secondary cell from time t 0 to time t 1 ;
calculating a temperature increase amount of the secondary cell from time t 0 to time t 1 based on the value of ∂E emf /∂T; and
correcting the state of charge at time t 0 such that an absolute value, which is a difference between the actual measurement temperature increase amount and the calculated temperature increase amount of the secondary cell from time t 0 to time t 1 becomes a second in the event the absolute value exceeds a first value,
wherein the second value is less than the first value.
9. The method according to claim 1 , further comprising:
calculating a state of charge at time t 1 based on a state of charge at time t 0 and a current measurement value of the secondary cell from time t 0 to time t 1 ; and
correcting the state of charge at time t 0 based on an actual measurement temperature increase amount from time t 0 to time t 1 .
10. A state-of-charge estimation device configured to calculate a state of charge of a secondary cell, comprising:
a storage unit configured to store a value of ∂E emf /∂T where E emf is an electromotive force of the secondary cell and T is a temperature of the secondary cell;
a temperature measurement device configured to measure the temperature of the secondary cell;
a current measurement device configured to measure a current of the secondary cell; and
an arithmetic device configured to calculate the state of charge based on at least the value of ∂E emf /∂T for which a value of the state of charge is set as a variable, a temperature measurement value of the secondary cell, and a current measurement value of the secondary cell.
11. A cell pack, comprising:
a secondary cell; and
a state-of-charge estimation device configured to calculate a state of charge of the secondary cell,
wherein the state-of-charge estimation device includes:
a storage unit configured to store a value of ∂E emf /∂T, wherein E emf is an electromotive force of the secondary cell and T is a temperature of the secondary cell;
a temperature measurement device configured to measure the temperature of the secondary cell;
a current measurement device configured to measure a current of the secondary cell; and
an arithmetic device configured to calculate the state of charge based on at least the value of ∂E emf /∂T for which a value of the state of charge is set as a variable, a temperature measurement value of the secondary cell, and a current measurement value of the secondary cell.
12. An electronic apparatus, comprising:
a secondary cell; and
a cell pack that includes a state-of-charge estimation device configured to calculate a state of charge of the secondary cell,
wherein the state-of-charge estimation device includes:
a storage unit configured to store a value of ∂E emf /∂T, where E emf is an electromotive force of the secondary cell and T is a temperature of the secondary cell;
a temperature measurement device configured to measure the temperature of the secondary cell;
a current measurement device configured to measure a current of the secondary cell; and
an arithmetic device configured to calculate the state of charge based on at least the value of ∂E emf /∂T for which a value of the state of charge is set as a variable, a temperature measurement value of the secondary cell, and a current measurement value of the secondary cell.
13. An electric vehicle, comprising:
a secondary cell; and
a cell pack that includes a state-of-charge estimation device configured to calculate a state of charge of the secondary cell,
wherein the state-of-charge estimation device includes:
a storage unit configured to store a value of ∂E emf /∂T, where E emf is an electromotive force of the secondary cell and T is a temperature of the secondary cell;
a temperature measurement device configured to measure the temperature of the secondary cell;
a current measurement device configured to measure a current of the secondary cell; and
an arithmetic device configured to calculate the state of charge based on at least the value of ∂E emf /∂T for which a value of the state of charge is set as a variable, a temperature measurement value of the secondary cell, and a current measurement value of the secondary cell.