Method and apparatus for determining the state of charge of a lithium-ion battery
AssigneeHoneywell International Inc.
InventorsJames V. Guiheen, Harmohan Singh, Thirumalai G. Palanisamy
Life of this patent
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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.
Claims20
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%.
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:
- 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.
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:
- 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.
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:
- 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.
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:
- 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.
Dependencies are inferred from the claim text.