Battery state of charge voltage hysteresis estimator

1. A battery control module for use with a battery, comprising:

a voltage measuring module that measures battery voltage;

a current measuring module that measures battery current; and

a state of charge (SOC) module that communicates with said current and voltage measuring modules and that determines a feature of a SOC transient based on a comparison of a measured battery voltage to a first voltage for said battery at an upper reset limit SOC and a second voltage for said battery at a lower reset limit SOC,

wherein said first and second voltages are calculated based on an open circuit voltage of said battery, an ohmic resistance of said battery and a polarization voltage for said measured battery voltage, and

wherein said SOC module determines an estimated SOC of said battery and a range for said estimated SOC based on a measured battery current and said measured battery voltage, and determines a modified SOC that is based on said estimated SOC, said range and said feature of said SOC transient.

2. The battery control module of claim 1 wherein said SOC module determines said modified SOC based on

SOC=soc Low+( soc High− soc Low)*( v Avg− h LowAvg)/( h HighAvg− h LowAvg),

where socLow is a low SOC value in said range, socHigh is a high SOC value in said range, Vavg is a running average of said measured battery voltage, and HLowAvg and hHighAvg are running averages of said second and first voltages, respectively.

3. A method for determining a state-of-charge (SOC) of a battery, comprising:

measuring a battery voltage;

measuring a battery current;

measuring a battery temperature;

determining a first voltage of said battery at an upper reset limit SOC based on an open circuit voltage of said battery, an ohmic resistance of said battery, a polarization voltage for said measured battery voltage, a measured battery current and a battery temperature;

determining a second voltage of said battery at a lower reset limit SOC based on said open circuit voltage of said battery, said ohmic resistance of said battery, said polarization voltage for said measured battery voltage, said measured battery current and said battery temperature;

determining a feature of a SOC transient based on a comparison of said measured battery voltage to said first and second voltages, and

determining a modified SOC of said battery based on said feature of said SOC transient and estimated SOC of said battery.

4. The method of claim 3 wherein said determining said modified SOC employs equation

SOC=soc Low+( soc High− soc Low)*( v Avg− h LowAvg)/( h HighAvg− h LowAvg),

where socLow is a low SOC value in said range, socHigh is a high SOC value in said range, Vavg is a running average of said measured battery voltage, and HLowAvg and hHighAvg are running averages of said second and first voltages, respectively.

5. A battery control module for use with a battery, comprising:

voltage measuring means for measuring battery voltage;

current measuring means for measuring battery current; and

state of charge (SOC) determining means for communicating with said current and voltage measuring means, determining a feature of a SOC transient based on a comparison of a measured battery voltage to a first voltage of said battery at an upper reset limit SOC and a second voltage for said battery at a lower reset limit SOC,

wherein said first and second voltages are calculated based on an open circuit voltage of said battery, an ohmic resistance of said battery and a polarization voltage for said measured battery voltage, and

wherein said SOC determining means determining an estimated SOC of said battery and a range for said estimated SOC based on a measured battery current and said measured battery voltage, and determining a modified SOC based on said estimated SOC, said range and said feature of said SOC.

6. The battery control module of claim 5 wherein said SOC determining means determines said modified SOC based on equation

SOC=soc Low+( soc High− soc Low)*( v Avg− h LowAvg)/( h HighAvg− h LowAvg),

where socLow is a low SOC value in said range, socHigh is a high SOC value in said range, Vavg is a running average of said measured battery voltage, and HLowAvg and hHighAvg are running averages of said second and first voltages, respectively.

7. The battery control module of claim 1 further comprising a filter that filters said measured battery voltage and outputs a filtered measured battery voltage to said SOC module.

8. The battery control module of claim 1 wherein said feature includes a ratio that corresponds to at least one of a magnitude and a direction of said SOC transient.

9. The battery control module of claim 1 wherein said first and second voltages are calculated based on said measured battery current and a battery temperature.

10. The method of claim 3 further comprising filtering said measured battery voltage prior to determining said feature.

11. The method of claim 3 wherein said feature includes a ratio that corresponds to at least one of a magnitude and a direction of said SOC transient.

12. The battery control module of claim 5 further comprising a filter that filters said measured battery voltage and outputs a filtered measured battery voltage to said SOC determining means.

13. The battery control module of claim 5 wherein said feature includes a ratio that corresponds to at least one of a magnitude and a direction of said SOC transient.

14. The battery control module of claim 5 wherein said first and second voltages are calculated based on said measured battery current and a battery temperature.