METHOD AND APPARATUS FOR DETERMINING STATE OF CHARGE OF A BATTERY

• US 20100090651A1
• Filed: 10/09/2009
• Published: 04/15/2010
• Est. Priority Date: 10/10/2008
• Status: Active Grant

• Current Assignee: Imergy Power Systems, Inc.
• Original Assignee: Deeya Energy Incorporated
• Inventors: Firouzi, Ali, Sahu, Saroj Kumar
• Granted Patent: US 8,264,202 B2
• Time in Patent Office: Days
• US Class Current: 320/132
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: H01M 10/48 Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals, H01M50/569
• CPC Class Codes: H01M 8/188 by recharging of redox couples containing fluids; Redox flow type batteries
• CPC Class Codes: H01M 8/20 Indirect fuel cells, e.g. fuel cells with redox couple being irreversible H01M8/18 takes precedence
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

A method and apparatus for determining the state of charge (SOC) of a battery is discussed. The method involves measuring the terminal voltage across the battery and the current flowing through the battery at a plurality of different times and fitting a line equation with a slope and an intercept to the terminal voltage and current data. The open-circuit voltage (OCV) is calculated from the intercept of the linear equation and the SOC is determined from the OCV by reference to a lookup table.

Claims

1. A method of determining a state of a battery, comprising:

measuring a terminal voltage across the battery and a current flowing through the battery at a plurality of different times to obtain terminal voltage and current data;

fitting a line equation with a slope and an intercept to the terminal voltage and current data; and

calculating from the intercept of the linear equation the open-circuit voltage (OCV) of the battery.

2. The method of claim 1, further including:

determining the state-of-charge (SOC) of the battery from the OCV.

3. The method of claim 2, wherein determining the SOC includes:

referencing a look-up table based on the OCV.

4. The method of claim 1, wherein the battery is a flow battery.

5. The method of claim 1, wherein measuring the terminal voltage and the current includes:

altering a charging current while charging the battery; and

measuring the terminal voltage at the charging current.

6. The method of claim 1, wherein measuring the terminal voltage and the current includes:

measuring the terminal voltage as a load current varies during discharge.

7. The method of claim 5, further including:

determining an equivalent series resistance (ESR) from the slope; and

utilizing the ESR during discharge to determine the OCV from a single measurement of the terminal voltage at a discharge current.

11. The method of claim 1, wherein measuring the terminal voltage and the current includes:

varying a charging current during charging; and

determining the terminal voltage for each of the current at the charging current.

12. The method of claim 11, further including:

calculating an equivalent series resistance (ESR) from the slope.

13. The method of claim 12, further including:

determining the OCV based on a single measurement of terminal voltage and discharge current.

8. A method for calculating the state of charge (SOC) of a battery, comprising the steps of:

measuring a terminal voltage across the battery and a current flowing through the battery system at a plurality of different times;

determining a linear equation that describes a relationship between the terminal voltage and the current;

calculating the open-circuit voltage (OCV) from the linear equation; and

determining the SOC of the battery using the calculated OCV.

9. The method of claim 8 wherein the state-of-charge of the battery is determined from the OCV by reference to a look-up table.

10. The method of claim 9, further including:

calculating an equivalent series resistance for the battery from the slope of the linear equation.

14. An apparatus for determining a state of charge (SOC) of a battery, comprising:

a current sensor electrically coupled to determine a current value related to a current through the battery at a plurality of times;

a voltage sensor electrically coupled to determine a terminal voltage value related to a terminal voltage across the battery at the plurality of times;

a first analog to digital converter (ADC) electrically coupled to the voltage sensor to receive the terminal voltage value and to provide a digitized voltage value;

a second analog to digital converter (ADC) electrically coupled to the current sensor to receive the current value and provide a digitized current value; and

an interpolator equation calculator (IEC) electrically coupled to the first ADC and to the second ADC to receive the digitized voltage value and the digitized current value for each of the plurality of times, the IEC determining a line equation that best fits the digitized voltage value and digitized current value at the plurality of times.

15. The apparatus of claim 14, further including:

a memory where the IEC stores the digitized voltage value and the digitized current value for each of the plurality of times.

16. The apparatus of claim 15, wherein the IEC determines an open-circuit voltage for the battery based on an intercept of the line equation.

17. The apparatus of claim 16, further including:

a stored look-up table and wherein the IEC determines the open-circuit voltage by interpolating from the stored look-up table.

18. The apparatus of claim 14, wherein the IEC determines the equivalent resistance of the battery from a slope of the line equation.

19. The apparatus of claim 14, wherein a single ADC may be used to digitize both, voltage and current measurements.

20. The apparatus of claim 14 wherein the battery may be a flow battery.