Circuit and method for measurement of battery capacity fade
First Claim
1. A method of determining a present zero-current capacity of a battery independent of the condition of the battery, comprising:
- (a) determining that the battery is in a zero-current relaxed state;
(b) measuring a starting open circuit voltage of the battery;
(c) integrating a measurable current flowing for the battery to determine an amount of charge transferred, and then determining that the battery is in a zero-current relaxed state;
(d) measuring an ending open circuit voltage of the battery;
(e) obtaining a starting depth of discharge corresponding to the starting open circuit voltage and an ending depth of discharge corresponding to the ending open circuit voltage; and
(f) determining the present zero-current capacity by dividing the amount of charge transferred during step (c) by a difference between the ending depth of discharge and the starting depth of discharge.
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Accused Products
Abstract
The remaining run-time (t_rem) of a battery is determined independently of the condition of the battery and the amount of load on the battery by obtaining the value of a present total zero-current capacity (Qmax) of the battery based on relaxed-battery OCV values measured just before and just after a charging or discharging cycle. A current through the battery is integrated to determine a transfer of charge (Q) from the battery, and a value of total run-time (t_total) that would be required to reduce the open circuit voltage of the battery to a predetermined lower limit (Vmin) is determined. The remaining run-time (t_rem) is determined by subtracting the duration of the integrating from the total run-time (t_total).
77 Citations
24 Claims
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1. A method of determining a present zero-current capacity of a battery independent of the condition of the battery, comprising:
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(a) determining that the battery is in a zero-current relaxed state;
(b) measuring a starting open circuit voltage of the battery;
(c) integrating a measurable current flowing for the battery to determine an amount of charge transferred, and then determining that the battery is in a zero-current relaxed state;
(d) measuring an ending open circuit voltage of the battery;
(e) obtaining a starting depth of discharge corresponding to the starting open circuit voltage and an ending depth of discharge corresponding to the ending open circuit voltage; and
(f) determining the present zero-current capacity by dividing the amount of charge transferred during step (c) by a difference between the ending depth of discharge and the starting depth of discharge.
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2. A method of determining a present capacity of a battery delivering a load current, comprising:
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(a) obtaining a value of a present total zero-current capacity of the battery by performing the steps of i. determining that the battery is an a zero-current relaxed state, ii. measuring a starting open circuit voltage of the battery, iii. partially discharging the battery and integrating the discharging current to determine an amount of charge transferred, and then allowing the battery to relax, iv. measuring an ending open circuit voltage of the battery, v. obtaining a starting depth of discharge corresponding to the starting open circuit voltage and an ending depth of discharge corresponding to the ending open circuit voltage, and vi. determining the present total zero-current capacity by dividing the amount of charge transferred during step (a)(iii) by a difference between the ending depth of discharge and the starting depth of discharge;
(b) using a last measured value of open circuit voltage to determine a starting depth of discharge of a present discharging or charging cycle;
(c) causing a battery current to flow through the battery in the course of the present discharging or charging cycle;
(d) integrating the battery current to determine a total transfer of charge to or from the battery;
(e) determining a change in depth of discharge which occurred during the total transfer of charge by dividing the total transfer of charge by the present zero-current capacity; and
(f) algebraically adding the change in depth of discharge to the starting depth of discharge to obtain a present depth of discharge of the battery. - View Dependent Claims (3, 4, 5, 6)
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7. A method of determining a remaining run-time of a battery independently of the age of the battery, comprising:
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(a) obtaining the value of a present total zero-current capacity of the battery;
(b) determining a net transfer of charge from the battery caused by flow of a current through the battery;
(c) determining a value of total run-time that would be required to reduce the terminal voltage of the battery from a predetermined starting value to a predetermined lower limit and also determining the duration of the flow of the current; and
(d) determining the remaining run-time by subtracting the duration of the flow of the current from the total run-time. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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14. A method of determining a present usable energy of a battery delivering a load current at a constant power level, comprising:
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(a) obtaining a value of a present total zero-current capacity of the battery by performing the steps of i. determining that the battery is an a zero-current relaxed state, ii. measuring a starting open circuit voltage of the battery, iii. partially discharging the battery and integrating the discharging current to determine an amount of charge transferred, and then allowing the battery to relax, iv. measuring an ending open circuit voltage of the battery, v. obtaining a starting depth of discharge corresponding to the starting open circuit voltage and an ending depth of discharge corresponding to the ending open circuit voltage, and vi. determining the present total zero-current capacity by dividing the amount of charge transferred during step (a)(iii) by a difference between the ending depth of discharge and the starting depth of discharge;
(b) using a last measured value of open circuit voltage to determine a starting depth of discharge for the delivering of the load current at the constant power level;
(c) causing the battery to deliver the load current at the constant power level;
(d) iteratively, recursively performing the functions of i. computing values of the load current according to the equation ii. integrating the computing values of the load current to obtain a passed charge value Q and using it to determine a depth of discharge value DOD=DOD0+Q/Qmax, iii. computing a value v according to the expression v=OCV(DOD, T)−
I(v,R,Pow)*R(DOD,T);
(e) determining a termination time t=t_term at which the expression OCV(DOD0+t*I(v,R,Pow)/Qmax)−
I(v,R,Pow)*R(DOD0+t*I(v,R,Pow)/Qmax) is equal to a predetermined minimum battery voltage; and
(f) computing the present usable energy according to the expression E_usable=Pow*T_term.
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15. A system for determining a remaining run-time of a battery independently of the age of the battery, comprising:
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(a) a processor coupled to a digital bus, and a memory for storing data representing the relationship between the OCV (open circuit voltage) and DOD (depth of discharge) of the battery, a first ADC, and a second ADC all coupled to the digital bus;
(b) a first algorithm stored in the memory for execution by the processor to obtain the value of a present total zero-current capacity of the battery in response to both a first open circuit voltage measured while the battery was relaxed and before a first current began flowing through the battery and a second open circuit voltage measured after the first current stopped flowing through the battery and the battery relaxed;
(c) circuitry including the second ADC and a current sensor for sensing a second current flowing through the battery and integrating the second current with respect to time to determine a transfer of charge to or from the battery; and
(d) a second algorithm stored in the memory for execution by the processor to determine a value of total run-time that would be required to reduce the open circuit voltage of the battery to a predetermined lower limit and the duration of the integrating and also to determine the remaining run-time by subtracting the duration of the integrating from the total run-time. - View Dependent Claims (16, 17, 18, 19, 20)
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21. A system for determining a present zero-current capacity of a battery independent of the condition of the battery, comprising:
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(a) means for determining that the battery is in a zero-current relaxed state;
(b) means for measuring a starting open circuit voltage of the battery;
(c) means for partially discharging the battery and integrating a discharging current to determine an amount of charge transferred, and then allowing the battery to relax;
(d) means for measuring an ending open circuit voltage of the battery;
(e) means for obtaining a starting depth of discharge corresponding to the starting open circuit voltage and an ending depth of discharge corresponding to the ending open circuit voltage; and
(f) means for determining the present zero-current capacity by dividing the amount of charge transferred during step (c) by a difference between the ending depth of discharge and the starting depth of discharge.
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22. A system for determining a present capacity of a battery delivering a load current, comprising:
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(a) means for obtaining a value of a present total zero-current capacity of the battery, including i. means for determining that the battery is an a zero-current relaxed state, ii. means for measuring a starting open circuit voltage of the battery, iii. means for partially discharging the battery and integrating the discharging current to determine an amount of charge transferred, and then allowing the battery to relax, iv. means for measuring an ending open circuit voltage of the battery, v. means for obtaining a starting depth of discharge corresponding to the starting open circuit voltage and an ending depth of discharge corresponding to the ending open circuit voltage, and vi. means for determining the present total zero-current capacity by dividing the amount of charge transferred during step (a)(iii) by a difference between the ending depth of discharge and the starting depth of discharge;
(b) means for using a last measured value of open circuit voltage to determine the starting depth of discharge of a present discharging or charging cycle;
(c) means for causing a battery current to flow through the battery in the course of the present discharging or charging cycle;
(d) means for integrating the battery current to determine a total transfer of charge to or from the battery;
(e) means for determining a change in depth of discharge which occurred during the total transfer of charge by dividing the total transfer of charge by the present zero-current capacity; and
(f) means for algebraically adding the change in depth of discharge to the starting depth of discharge to obtain a present depth of discharge of the battery. - View Dependent Claims (23)
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24. A system for determining a remaining run-time of a battery independently of the age of the battery, comprising:
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(a) means for obtaining the value of a present total zero-current capacity of the battery;
(b) means for causing a current to flow through the battery;
(c) means for integrating the current to determine a transfer of charge from the battery;
(d) means for determining a value of total run-time that would be required to reduce the open circuit voltage of the battery to a predetermined lower limit and also determining the duration of the integrating; and
(e) means for determining the remaining run-time by subtracting the duration of the integrating from the total run-time.
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Specification