State of charge estimation device and method of estimating state of charge

1. A state of charge estimation device for estimating a state of charge of an electric storage device, the state of charge estimation device comprising:

a voltage measurement component configured to measure a voltage across the electric storage device;

a current measurement component configured to measure a current flowing through the electric storage device; and

a controller component configured to, when an estimation of the state of charge of the electric storage device based on an accumulated amount of currents measured by the current measurement component is defined as a current accumulation method and an estimation of the state of charge of the electric storage device based on an open circuit voltage (OCV) of the electric storage device measured by the voltage measurement component is defined as an OCV method, permit the estimation of the state of charge by the OCV method when a condition that an error in the estimation of the state of charge of the electric storage device by the current accumulation method exceeds an error in estimation of the state of charge of the electric storage device by the OCV method is satisfied,

wherein the condition that the error in the estimation of the state of charge of the electric storage device by the current accumulation method exceeds the error in the estimation of the state of charge of the electric storage device by the OCV method includes a condition that an increase/decrease in a remaining capacity of the electric storage device since a previous estimation by the OCV method exceeds an increase/decrease in the remaining capacity corresponding to the error in the previous estimation by the OCV method.

2. The state of charge estimation device according to claim 1 , wherein the condition that the error in estimation of the state of charge of the electric storage device by the current accumulation method exceeds the error in estimation of state of charge of the electric storage device by the OCV method further includes a condition that the accumulated amount of currents since the previous estimation by the OCV method exceeds an accumulated current amount corresponding to the error in the previous estimation by the OCV method.

3. The state of charge estimation device according to claim 1 , wherein the condition that the error in estimation of the state of charge of the electric storage device by the current accumulation method exceeds the error in the estimation of the state of charge of the electric storage device by the OCV method further includes a condition that an operation time of the state of charge estimation device since the previous estimation by the OCV method exceeds an operation time corresponding to the error in the previous estimation by the OCV method.

4. The state of charge estimation device according to claim 1 , wherein the controller component is further configured to:

define an estimated state of charge based on estimation based on results of the estimation by the current accumulation method and the OCV method with a heavier weight assigned to the OCV method when the state of charge estimated by the OCV method is within a specified range in which a variation in the open circuit voltage relative to a variation in the state of charge is larger than a reference value; and

define an estimated state of charge based on estimation results of the estimation by the current accumulation method and the OCV method with a heavier weight assigned to the current accumulation method when the state of charge estimated by the OCV method is not within the specified range.

5. A method of estimating a state of charge of an electric storage device, the method comprising:

when an estimation of the state of charge of the electric storage device based on an accumulated amount of currents measured by a current measurement component is defined as a current accumulation method and an estimation of the state of charge of the electric storage device based on an open circuit voltage (OCV) of the electric storage device measured by the voltage measurement component is defined as an OCV method, permitting the estimation of the state of charge by the OCV method when a condition that an error in estimation of the state of charge of the electric storage device by the current accumulation method exceeds an error in the estimation of the state of charge of the electric storage device by the OCV method is satisfied,

wherein the condition that the error in the estimation of the state of charge of the electric storage device by the current accumulation method exceeds the error in the estimation of the state of charge of the electric storage device by the OCV method includes a condition that an increase/decrease in a remaining capacity of the electric storage device since a previous estimation by the OCV method exceeds an increase/decrease in the remaining capacity corresponding to the error in the previous estimation by the OCV method.

6. The state of charge estimation device according to claim 1 , wherein the electric storage device is configured to be used in a vehicle.

7. The state of charge estimation device according to claim 1 , wherein the electric storage device includes an iron phosphate lithium ion battery.

8. The state of charge estimation device according to claim 1 , wherein the controller component is further configured to:

define an estimated state of charge based on estimation based on results of the estimation by the current accumulation method and the OCV method with a heavier weight assigned to the OCV method when the state of charge estimated by the OCV method is within a specified range in which a variation in the open circuit voltage relative to a variation in the state of charge is larger than a reference value.

9. The state of charge estimation device according to claim 1 , wherein the controller component is further configured to:

define an estimated state of charge based on an estimation based on results of the estimation by the current accumulation method and the OCV method with a different weight assigned to the OCV method when the state of charge estimated by the OCV method is within a specified range in which a variation in the open circuit voltage relative to a variation in the state of charge is larger than a reference value.

10. The state of charge estimation device according to claim 9 , wherein the controller component is further configured to:

define an estimated state of charge based on estimation results of the estimation by the current accumulation method and the OCV method with a different weight assigned to the current accumulation method when the state of charge estimated by the OCV method is not within the specified range.

11. The state of charge estimation device according to claim 1 , wherein the controller component is further configured to:

define an estimated state of charge based on estimation results of the estimation by the current accumulation method and the OCV method with a heavier weight assigned to the current accumulation method when the state of charge estimated by the OCV method is not within a specified range in which a variation in the open circuit voltage relative to a variation in the state of charge is larger than a reference value.

12. The state of charge estimation device according to claim 11 , wherein the controller component is further configured to:

define the estimated state of charge based on an estimation based on results of the estimation by the current accumulation method and the OCV method with a different weight assigned to the OCV method when the state of charge estimated by the OCV method is within the specified range.

13. The state of charge estimation device according to claim 1 , wherein the controller component is further configured to:

define an estimated state of charge based on estimation results of the estimation by the current accumulation method and the OCV method with a different weight assigned to the current accumulation method when the state of charge estimated by the OCV method is not within a specified range in which a variation in the open circuit voltage relative to a variation in the state of charge is larger than a reference value.

14. The state of charge estimation device according to claim 1 , wherein the controller component is further configured to:

define an estimated state of charge based on estimation based on results of the estimation by the current accumulation method and the OCV method.

15. The state of charge estimation device according to claim 1 , further comprising:

a memory device storing a value for a fully-charged capacity of the electric storage device smaller than an actual value of the fully-charged capacity to provide a margin of the remaining capacity.

16. A state of charge estimation device for estimating a state of charge of an electric storage device, the state of charge estimation device comprising:

a voltage measurement component configured to measure a voltage across the electric storage device;

a current measurement component configured to measure a current flowing through the electric storage device; and

a controller component configured to:

when an estimation of the state of charge of the electric storage device based on an accumulated amount of currents measured by the current measurement component is defined as a current accumulation method and an estimation of the state of charge of the electric storage device based on an open circuit voltage (OCV) of the electric storage device measured by the voltage measurement component is defined as an OCV method, permit the estimation of the state of charge by the OCV method when a condition that an error in the estimation of the state of charge of the electric storage device by the current accumulation method exceeds an error in estimation of the state of charge of the electric storage device by the OCV method is satisfied;

define an estimated state of charge based on an estimation based on results of the estimation by the current accumulation method and the OCV method with a heavier weight assigned to the OCV method when the state of charge estimated by the OCV method is within a specified range in which a variation in the open circuit voltage relative to a variation in the state of charge is larger than a reference value; and

define an estimated state of charge based on estimation results of the estimation by the current accumulation method and the OCV method with a heavier weight assigned to the current accumulation method when the state of charge estimated by the OCV method is not within the specified range.

17. The state of charge estimation device according to claim 16 , wherein the electric storage device is configured to be used in a vehicle.

18. The state of charge estimation device according to claim 16 , wherein the electric storage device includes an iron phosphate lithium ion battery.

19. The state of charge estimation device according to claim 16 , wherein the condition that the error in the estimation of the state of charge of the electric storage device by the current accumulation method exceeds the error in the estimation of the state of charge of the electric storage device by the OCV method includes a condition that an increase/decrease in a remaining capacity of the electric storage device since a previous estimation by the OCV method is different from an increase/decrease in the remaining capacity corresponding to the error in the previous estimation by the OCV method.

20. The state of charge estimation device according to claim 19 , further comprising:

a memory device storing a value for a fully-charged capacity of the electric storage device smaller than an actual value of the fully-charged capacity to provide a margin of the remaining capacity.