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Method and system for iteratively determining with improved accuracy a state of charge of a battery having a number of cells

  • US 10,422,834 B2
  • Filed: 01/14/2016
  • Issued: 09/24/2019
  • Est. Priority Date: 01/14/2015
  • Status: Active Grant
First Claim
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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:

  • 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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