Plug-in charge capacity estimation method for lithium iron-phosphate batteries
First Claim
1. A method for estimating a charge capacity of a lithium iron-phosphate battery pack using data from a plug-in charge event, said method comprising:
- initiating the plug-in charge event of the battery pack, recording terminal voltage data during the charge event using a voltmeter, and recording charging current data during the charge event using a current sensor;
completing the plug-in charge event and storing the terminal voltage data and the charging current data;
determining open circuit voltage values from the terminal voltage data at two points in time from the plug-in charge event, including, for at least one of the two points in time, calculating the open circuit voltage by taking the terminal voltage at the point in time and subtracting the charging current at the point in time multiplied by a predetermined battery pack resistance;
determining state of charge values from the open circuit voltage values at the two points in time from the plug-in charge event;
calculating, using a controller including a processor, the charge capacity of the battery pack using the state of charge values and the charging current data; and
communicating the charge capacity of the battery pack, by the controller, to a user of the battery pack.
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Abstract
A method for estimating charge capacity of a lithium iron-phosphate battery pack using data from a plug-in charge event. A laboratory-measured battery pack resistance, which is known to remain constant over a battery pack'"'"'s life, can be used to determine open circuit voltage from terminal voltage during charging. Actual open circuit voltage after charging can be measured later, after the battery pack has rested for a sufficient amount of time. The two values of open circuit voltage, if taken at points on the battery pack'"'"'s SOC-OCV curve which have great enough slope, provide two values of battery pack state of charge. By integrating charging current over the time interval between the two open circuit voltage readings, and using the two state of charge values, the battery pack capacity can be determined from the plug-in charge data.
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Citations
19 Claims
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1. A method for estimating a charge capacity of a lithium iron-phosphate battery pack using data from a plug-in charge event, said method comprising:
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initiating the plug-in charge event of the battery pack, recording terminal voltage data during the charge event using a voltmeter, and recording charging current data during the charge event using a current sensor; completing the plug-in charge event and storing the terminal voltage data and the charging current data; determining open circuit voltage values from the terminal voltage data at two points in time from the plug-in charge event, including, for at least one of the two points in time, calculating the open circuit voltage by taking the terminal voltage at the point in time and subtracting the charging current at the point in time multiplied by a predetermined battery pack resistance; determining state of charge values from the open circuit voltage values at the two points in time from the plug-in charge event; calculating, using a controller including a processor, the charge capacity of the battery pack using the state of charge values and the charging current data; and communicating the charge capacity of the battery pack, by the controller, to a user of the battery pack. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for estimating driving range of an electric vehicle with a lithium iron-phosphate battery pack using data from a plug-in charge event, said method comprising:
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initiating the plug-in charge event of the battery pack, recording terminal voltage data during the charge event using a voltmeter, and recording charging current data during the charge event using a current sensor; completing the plug-in charge event and storing the terminal voltage data and the charging current data; determining open circuit voltage values from the terminal voltage data at two points in time from the plug-in charge event, where the two points in time correspond to locations on a state of charge vs. open circuit voltage curve for the lithium iron-phosphate battery pack where the curve has a slope greater than a predetermined threshold value; determining state of charge values from the open circuit voltage values at the two points in time from the plug-in charge event using the state of charge vs. open circuit voltage curve; calculating, using a controller including a processor, battery pack capacity using the state of charge values and the charging current data; and using the battery pack capacity and the state of charge values, by the controller, to provide estimated driving range values to a driver. - View Dependent Claims (10, 11, 12)
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13. A system for estimating a charge capacity of a lithium iron-phosphate battery pack using data from a plug-in charge event, said system comprising:
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a voltmeter for recording battery pack terminal voltage data before, during and after the charge event; an ammeter for recording battery pack charging current data during the charge event; and a controller in communication with the voltmeter and the ammeter, said controller being configured to control the charging current to the battery pack, said controller also being configured to estimate the charge capacity of the battery pack based on state of charge values for the battery pack at two points in time of the charge event and cumulative charging current between the two points in time. - View Dependent Claims (14, 15, 16, 17, 18, 19)
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Specification