Method and system for iteratively determining with improved accuracy a state of charge of a battery having a number of cells
First Claim
1. A method for iteratively determining state of charge (SOC) of a battery cell in a multi-cell battery comprising multiple battery cells, the method comprising:
- selecting a cell (“
selected cell”
) from the multiple battery cells of the multi-cell battery by;
using a voltmeter to measure, multiple times during an election period, a cell voltage (SEV) of each of the battery cells; and
using a controller to determine the selected cell to be the battery cell found most often to have the lowest measured SEV during the election period; and
using the controller to perform a number of iterations, wherein each of the iterations comprises;
determining a predicted SOC of the selected cell from an initial SOC value or an SOC of the selected cell determined from performing a previous one of the iterations;
determining a predicted error covariance of the predicted SOC from an initial error covariance value or an error covariance determined from performing the previous one of the iterations;
using an ammeter to measure current flowing through the selected cell (“
current measurement”
);
updating the predicted SOC to determine an updated SOC of the selected cell, wherein updating the predicted SOC comprises adding a weighted correction factor that is determined using the predicted error covariance to the predicted SOC and using a difference between the measured SEV of the selected cell and a predicted SEV of the selected cell, and wherein the weighted correction factor decreases as the magnitude of the current measurement increases and increases as the magnitude of the current measurement decreases; and
updating the predicted error covariance to determine an updated error covariance.
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Abstract
A method and system for iteratively determining state of charge (SOC) of a battery cell (“selected cell”) using a controller. For each of the iterations, the controller determines determine a predicted SOC of the selected cell; determines a predicted error covariance of the predicted SOC; and updates the predicted SOC and the predicted error covariance for use in subsequent iterations of the method. The updated SOC is treated as the SOC of the selected cell for that iteration of the method. Cell voltage used to determine the updated SOC may be low-pass filtered prior to its use. When the selected cell is one of multiple cells in a battery pack, the selected cell may be selected to have the lowest SEV of the cells in the pack. The error covariance may also vary directly with pack current magnitude to model inaccuracies that generally directly vary with current flow.
23 Citations
16 Claims
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1. A method for iteratively determining state of charge (SOC) of a battery cell in a multi-cell battery comprising multiple battery cells, the method comprising:
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selecting a cell (“
selected cell”
) from the multiple battery cells of the multi-cell battery by;using a voltmeter to measure, multiple times during an election period, a cell voltage (SEV) of each of the battery cells; and using a controller to determine the selected cell to be the battery cell found most often to have the lowest measured SEV during the election period; and using the controller to perform a number of iterations, wherein each of the iterations comprises; determining a predicted SOC of the selected cell from an initial SOC value or an SOC of the selected cell determined from performing a previous one of the iterations; determining a predicted error covariance of the predicted SOC from an initial error covariance value or an error covariance determined from performing the previous one of the iterations; using an ammeter to measure current flowing through the selected cell (“
current measurement”
);updating the predicted SOC to determine an updated SOC of the selected cell, wherein updating the predicted SOC comprises adding a weighted correction factor that is determined using the predicted error covariance to the predicted SOC and using a difference between the measured SEV of the selected cell and a predicted SEV of the selected cell, and wherein the weighted correction factor decreases as the magnitude of the current measurement increases and increases as the magnitude of the current measurement decreases; and updating the predicted error covariance to determine an updated error covariance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A system for iteratively determining state of charge (SOC) of a battery cell in a multi-cell battery comprising multiple battery cells, the system comprising:
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a multi-cell battery comprising multiple battery cells; voltmeters for measuring a voltage across each of the battery cells; an ammeter for measuring a current flowing through each of the battery cells; and a controller communicatively coupled to the voltmeters and the ammeter, the controller configured to perform a method comprising; selecting a cell (“
selected cell”
) from the multiple battery cells of the multi-cell battery by;using the voltmeters to measure, multiple times during an election period, a cell voltage (SEV) of each of the battery cells; and determining the selected cell to be the battery cell found most often to have the lowest measured SEV during the election period; and determining a predicted SOC of the selected cell from an initial SOC value or an SOC of the selected cell determined from performing a previous one of the iterations; determining a predicted error covariance of the predicted SOC from an initial error covariance value or an error covariance determined from performing the previous one of the iterations; using the ammeter to measure current flowing through the selected cell (“
current measurement”
);updating the predicted SOC to determine an updated SOC of the selected cell, wherein updating the predicted SOC comprises adding a weighted correction factor that is determined using the predicted error covariance to the predicted SOC and using a difference between the measured SEV of the selected cell and a predicted SEV of the selected cell, and wherein the weighted correction factor decreases as the magnitude of the current measurement increases and increases as the magnitude of the current measurement decreases; and updating the predicted error covariance to determine an updated error covariance. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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Specification