Method and apparatus for determining the state of charge of a lithium-ion battery
First Claim
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1. A method for creating a look-up table of open-circuit voltage versus state of charge for a particular type of lithium-ion battery and determining the capacity thereof, said method comprising the steps of:
- a) charging the battery at an initial constant current until a voltage across said battery increases to a predetermined maximum voltage;
b) continuing to charge the battery at said predetermined maximum voltage until an input current to said battery decreases to a predetermined minimum current;
c) measuring an open-circuit voltage for said battery, said open-circuit voltage being defined as the open-circuit voltage at 100% state of charge for said particular type of lithium-ion battery;
d) recording said open-circuit voltage at 100% state of charge;
e) discharging said battery at a predetermined discharge rate to a predetermined lower cutoff voltage and recording a discharge time period;
f) multiplying said discharge time period times said predetermined discharge rate and storing the product, said multiplication product being defined as the battery capacity for said particular type of lithium-ion battery;
g) measuring an open-circuit voltage for said battery, said open-circuit voltage being defined as the open-circuit voltage at 0% state of charge for said particular type of lithium-ion battery;
h) recording said open-circuit voltage at 0% state of charge;
i) charging said battery with a predetermined percentage of the battery capacity so that a present battery state of charge exceeds a previous battery state of charge;
j) measuring an open-circuit voltage for said battery, said open-circuit voltage being defined as the open-circuit voltage at the present state of charge for said particular type of lithium-ion battery; and
k) recording said open-circuit voltage at the present state of charge;
l) repeating said charging said battery with a predetermined percentage of the battery capacity step (i), said measuring an open-circuit voltage for said battery step (j), and said recording said open-circuit voltage at the present state of charge step (k) until the present state of charge of the battery equals the battery capacity for said particular type of lithium-ion battery; and
m) creating the look-up table of open-circuit voltage versus state of charge for state of charge values from 0% to 100%.
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Abstract
Computer-assisted methods for determining the state of charge of a specific lithium ion battery, without the need for charging and discharging the battery, by utilizing look-up tables or algorithms which store the relationships of state of charge to open-circuit voltage or to ramp-peak current, or to both for that type of specific lithium-ion battery to determine the state of charge for that specific lithium-ion battery.
49 Citations
20 Claims
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1. A method for creating a look-up table of open-circuit voltage versus state of charge for a particular type of lithium-ion battery and determining the capacity thereof, said method comprising the steps of:
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a) charging the battery at an initial constant current until a voltage across said battery increases to a predetermined maximum voltage;
b) continuing to charge the battery at said predetermined maximum voltage until an input current to said battery decreases to a predetermined minimum current;
c) measuring an open-circuit voltage for said battery, said open-circuit voltage being defined as the open-circuit voltage at 100% state of charge for said particular type of lithium-ion battery;
d) recording said open-circuit voltage at 100% state of charge;
e) discharging said battery at a predetermined discharge rate to a predetermined lower cutoff voltage and recording a discharge time period;
f) multiplying said discharge time period times said predetermined discharge rate and storing the product, said multiplication product being defined as the battery capacity for said particular type of lithium-ion battery;
g) measuring an open-circuit voltage for said battery, said open-circuit voltage being defined as the open-circuit voltage at 0% state of charge for said particular type of lithium-ion battery;
h) recording said open-circuit voltage at 0% state of charge;
i) charging said battery with a predetermined percentage of the battery capacity so that a present battery state of charge exceeds a previous battery state of charge;
j) measuring an open-circuit voltage for said battery, said open-circuit voltage being defined as the open-circuit voltage at the present state of charge for said particular type of lithium-ion battery; and
k) recording said open-circuit voltage at the present state of charge;
l) repeating said charging said battery with a predetermined percentage of the battery capacity step (i), said measuring an open-circuit voltage for said battery step (j), and said recording said open-circuit voltage at the present state of charge step (k) until the present state of charge of the battery equals the battery capacity for said particular type of lithium-ion battery; and
m) creating the look-up table of open-circuit voltage versus state of charge for state of charge values from 0% to 100%. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for determining the state of charge of a lithium-ion battery of a particular type using a look-up table of open-circuit voltage versus state of charge for that particular type of lithium-ion battery, said method comprising the steps of:
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a) inputting a battery type into a computer;
b) measuring an open-circuit voltage for said battery, said open-circuit voltage being input into said computer;
c) executing an open-circuit voltage correlation algorithm based on inputs comprising, i) the type of said battery inputted into said computer and ii) the measured open-circuit voltage for said battery; and
d) determining the state of charge of the lithium-ion battery based on said open-circuit voltage correlation algorithm. - View Dependent Claims (8, 9)
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10. A method for creating a look-up table of ramp-peak current versus state of charge for a particular type of lithium-ion battery, said method comprising the steps of:
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a) bringing the battery to a known present state of charge;
b) applying a monotonically increasing current to said battery from a power supply, where there is a dependence of current increase with time;
c) recording said dependence of current increase with time;
d) increasing said monotonically increasing current to said battery until the current reaches a value being defined as the ramp-peak current at the present state of charge for said particular type of lithium-ion battery where either, i) a measured voltage for said battery reaches a predetermined maximum voltage, or ii) said monotonically increasing current equals a maximum current rating of the power supply;
e) recording said ramp-peak current at the present state of charge;
f) repeating said bringing the battery to a known present state of charge step (a), said applying a monotonically increasing current step (b), said recording said dependence of current increase with time step (c), said increasing said monotonically increasing current step (d), and said recording said ramp-peak current at the present state of charge step (e) at a set of predetermined present states of charge for said battery; and
g) creating the look-up table of ramp-peak current versus state of charge for the particular type of lithium-ion battery using the set of predetermined present states of charge for said battery. - View Dependent Claims (11, 12, 13, 14, 15)
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16. A method for determining the state of charge of a lithium-ion battery of a particular type using a look-up table of ramp-peak current versus state of charge for that particular type of lithium-ion battery, said method comprising the steps of:
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a) inputting a battery type into a computer;
b) measuring a ramp-peak current for said battery, said ramp-peak current being input into said computer;
c) executing a ramp-peak current correlation algorithm based on inputs comprising, i) the type of said battery inputted into said computer and ii) the measured ramp-peak current for said battery; and
d) determining the state of charge of the lithium-ion battery based on said ramp-peak current correlation algorithm. - View Dependent Claims (17, 18)
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19. A method for determining the state of charge of a lithium-ion battery of a particular type using both a look-up table of open-circuit voltage versus state of charge and a look-up table of ramp-peak current versus state of charge for that particular type of lithium-ion battery, said method comprising the steps of:
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a) inputting a battery type into a computer;
b) measuring an open-circuit voltage for said battery, said open-circuit voltage being input into said computer;
b) measuring a ramp-peak current for said battery, said ramp-peak current being input into said computer;
c) executing a correlation algorithm based on inputs comprising, i) the type of said battery inputted into said computer, ii) the measured open-circuit voltage for said battery, and iii) the measured ramp-peak current for said battery; and
d) determining the state of charge of the lithium-ion battery based on said correlation algorithm. - View Dependent Claims (20)
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Specification