Calculation of state of charge offset using a closed integral method
First Claim
1. A method of calculating an accurate state of charge of a battery installed in an electric vehicle comprising the step of:
- using an estimated average battery state of charge for the battery based on a long-term average open circuit battery voltage to check for accuracy of a measured state of charge based on current flowing into and out of the battery, wherein the long-term average open circuit battery voltage and a long-term average observed battery voltage are equal after a predefined minimum amount of time, Tmin has been exceeded wherein when Tmin has been exceeded, an average hysteresis and an average internal resistance each associated with the battery are negligible.
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Abstract
A state of charge control system and method uses a region of voltage linearity and a long-term average voltage to estimate an average battery state of charge for storage batteries and to eliminate errors due to hysteresis, drift and sensor noncompliance. An average state of charge Sn is calculated using a current integral method and an average state of charge Sv based on an average observed voltage Vn for a time period exceeding a predefined minimum time but before a predefined maximum time has elapsed is also calculated. If the absolute value of the difference between the Sv and Sn are not are within an acceptable error band, then an offset value is calculated to correct the Sn by subtracting the Sv from the Sn, and thus, to maintain a more accurate Sn. Additionally, a closed current integral method is used to reduce errors due to hysteresis.
121 Citations
22 Claims
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1. A method of calculating an accurate state of charge of a battery installed in an electric vehicle comprising the step of:
using an estimated average battery state of charge for the battery based on a long-term average open circuit battery voltage to check for accuracy of a measured state of charge based on current flowing into and out of the battery, wherein the long-term average open circuit battery voltage and a long-term average observed battery voltage are equal after a predefined minimum amount of time, Tmin has been exceeded wherein when Tmin has been exceeded, an average hysteresis and an average internal resistance each associated with the battery are negligible. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of calculating an accurate state of charge of a battery installed in a hybrid vehicle comprising the step of:
calculating an offset value between a voltage-based average battery state of charge Svavg based on a long-term average open circuit battery voltage and a current-based average state of charge Snavg based on a summation of current flowing into and out of the battery when the two average battery state of charges Svavg and Snavg differ by an amount exceeding an acceptable error band, wherein a long-term average open circuit battery voltage and a long-term average observed battery voltage are equal after a predefined minimum amount of time Tmin has been exceeded, wherein when Tmin has been exceeded, an average hysteresis and an average internal resistance each associated with the battery are negligible are equal after a predefined minimum time, Tmin has elapsed. - View Dependent Claims (9, 10, 11, 12)
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13. A method of calculating an accurate state of charge of a battery installed in a hybrid vehicle comprising the steps of:
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calculating an average open circuit voltage to eliminate effects of hysteresis voltages and polarization of the battery that occur during a hybrid cycle; using the average open circuit voltage to calculate an average, voltage-based state of charge of the battery, wherein the long-term average open circuit battery voltage and a long-term average observed battery voltage are equal after a predefined minimum amount of time Tmin has been exceeded, wherein when Tmin has been exceeded, an average hysteresis and an average internal resistance each associated with the battery are negligible are equal after a predefined minimum time, Tmin has elapsed; comparing the calculated average voltage-based state of charge with a current-based average state of charge measured from current flowing into and out of the battery; and correcting the current-based average state of charge when the average voltage-based state of charge differs from the average state of charge measured from current flowing into and out of the battery by a predefined amount. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
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21. A method of calculating an accurate state of charge of a battery installed in a hybrid vehicle comprising the steps of:
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calculating a current-based average state of charge, wherein the current-based average state of charge is calculated using a current integral method; calculating a voltage-based average state of charge, wherein the voltage-based average state of charge is based on an average observed voltage for a time period exceeding a predefined minimum time but before a predefined maximum time, wherein a long-term average open circuit battery voltage and a long-term average observed battery voltage are equal after a predefined minimum amount of time Tmin has been exceeded, wherein when Tmin has been exceeded, an average hysteresis and an average internal resistance each associated with the battery are negligible are equal after a predefined minimum time, Tmin has elapsed; comparing each of the calculated current-based and voltage-based average state of charges to determine if an absolute value of difference between the two respective average state of charges is within an acceptable error band; and offsetting the calculated average current-based state of charge by the difference between the two respective average state of charges when the acceptable error band is exceeded to provide a more accurate average current-based state of charge. - View Dependent Claims (22)
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Specification