System and method for monitoring battery state
A method of monitoring a battery includes measuring an open circuit voltage (V oc ) on the battery to determine a measured state of charge (SOC m ) after at least one use, obtaining a calculated state of charge (SOC c ) based on a state of charge prior to the at least one use and a discharge of the battery during the at least one use, and determining a state of the battery based at least in part on a difference between the calculated state of charge and the measured state of charge.
1. A method of monitoring a battery comprising:
measuring an open circuit voltage (V oc ) on the battery to determine a measured state of charge (SOC m ) after at least one use;
obtaining a calculated state of charge (SOC c ) based on a state of charge prior to said at least one use and a discharge of the battery during said at least one use; and
determining a state of said battery based at least in part on a difference between said calculated state of charge and said measured state of charge, and a weighted average of said previously determined differences between said calculated state of charge and said measured state of charge for said battery.
2. The method according to claim 1 , wherein said state of said battery is determined based on a previous state of said battery and said difference between said calculated state of charge and said measured state of charge.
3. The method according to claim 2 , wherein said state of said battery is a percentage of capacity said battery is determined to provide with respect to a rated value of said battery.
4. The method according to claim 1 , wherein said discharge of the battery during said at least one use is calculated using coulomb counting and taking into account an expected capacity.
5. The method according to claim 4 , wherein said expected capacity is calculated based on a rated capacity and a rated current value for said battery as well as an actual current during said at least one discharge.
6. The method according to claim 1 , wherein said discharge of the battery is calculated by determining
IdT
C
′
,
where C′ is determined as follows:
C
′
=
C
∘
(
I
I
∘
)
-
γ
,
where C o is a rated capacity (amp·hours), I is an actual current discharged (amps), I o is a rated current (amps) and γ is based on supplier battery discharge curves.
7. The method according to claim 1 wherein said calculated state of charge is calculated according to the formula:
SOCc
n
=
β
[
SOCc
n
-
1
+
IdT
C
′
]
,
where C′ is an expected capacity of the battery, IdT is an integrated coulomb counting, and β is a value related to a difference between SOCc n-l and SOCm n-l .
8. The method according to claim 7 , wherein the expected capacity of the battery is determined according to the formula:
C
′
=
C
o
(
I
I
o
)
-
γ
,
where C o is the rated capacity (amp·hours), I is the actual current discharged (amps), I o is the rated current (amps) and γ is based on supplier battery discharge curves.
9. The method according to claim 7 , wherein a change in β is determined based on a weighted average of previously determined differences between SOCc and SOCm.
10. The method according to claim 9 , wherein a new value of β is calculated based on a previous value of β and the change in β.
11. The method according to claim 10 , wherein the state of said battery is related to the value of β.
12. A system for monitoring a battery comprising:
a meter for measuring an open circuit voltage on the battery to determine a measured state of charge after at least one use;
a calculation device for determining a calculated state of charge based on a state of charge prior to said at least one use and a calculated discharge of the battery during said at least one use, and for determining a state said battery based at least in part on said difference between said calculated state of charge and said measured state of charge, and a weighted average of said previously determined differences between said calculated state of charge and said measured state of charge for said battery.
13. The system according to claim 12 , wherein said calculation device determines said state of said battery based on a previous state of said battery and said difference between said calculated state of charge and said measured state of charge.
14. The system according to claim 12 , wherein said calculation device determines said state of said battery as a percentage of capacity said battery is determined to provide with respect to a rated value of said battery.
15. The system according to claim 12 , wherein said calculation device determines the calculated discharge of the battery based on coulomb counting and taking into account an expected capacity.
16. The system according to claim 12 , wherein said calculation device determines said expected capacity based on a rated capacity, and a rated current value for said battery as well as an actual current during said at least one discharge.
17. The system according to claim 12 , wherein said calculation device determines said discharge of the battery by determining
IdT
C
′
,
where
C
′
=
C
o
(
I
I
o
)
-
γ
,
where C o is a rated capacity (amp·hours), I is an actual current discharged (amps), I o is a rated current (amps) and γ is based on supplier battery discharge curves.
18. The system according to claim 12 , wherein said calculation device determines said calculated state of charge according to the formula:
SOCc
n
=
β
[
SOCc
n
-
1
+
Idt
C
′
]
,
where C′ is an expected capacity of the battery, IdT is an integrated coulomb counting, and β is a value related to a difference between SOCc n-l and SOCm n-l .
19. The system according to claim 18 , wherein said calculation device determines the expected capacity of the battery according to the formula
C
′
=
C
o
(
I
I
o
)
-
γ
,
where C o is the rated capacity (amp·hours), I is the actual current discharged (amps), I o is the rated current (amps) and γ is based on supplier battery discharge curves.
20. The system according to claim 18 , wherein said calculation device determines a change in β based on a weighted average of previously determined differences between SOCc and SOCm.
21. The system according to claim 20 , wherein said calculation device calculates a new value of β based on a previous value of β and the change in β.
22. The system according to claim 21 , wherein said state of said battery is directly related to the value of β.
23. A method of monitoring a battery comprising:
measuring an electrical characteristic after at least one use to provide a measured electrical characteristic;
obtaining a calculated electrical characteristic based on the electrical characteristic prior to said at least one use and a discharge of the battery during said at least one use; and
determining a state of said battery based at least in part on a difference between said measured electrical characteristic and said calculated electrical characteristic, and a weighted average of said difference and previously determined differences between said calculated electrical characteristic and said measured electrical characteristic.