System and method for calculating a state of charge of a battery

• US 7,446,505 B2
• Filed: 08/24/2006
• Issued: 11/04/2008
• Est. Priority Date: 08/24/2006
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Bekritsky, Benjamin, Paul, Christopher R., Cabana, Joseph
• Primary Examiner(s): TSO, EDWARD H
• Application Number:
  US11/509,466
• Publication Number:
  US 20080048616A1
• Time in Patent Office: 803 Days
• Field of Search: 320/107, 320/132, 320/149
• US Class Current: 320/132
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements

Abstract

Described is a system and method for determining determining a present state of charge of a battery and determining a rate of change of the state of charge of the battery, the rate of change being determined based on a charge current being supplied to the battery. Then, an updated state of charge is determined based on the rate of change.

Claims

1. A method, comprising:

determining a first state of charge of a battery;

determining a rate of change of the state of charge of the battery, the rate of change being determined based on a charge current being supplied to the battery; and

determining an updated state of charge as a function of only the first state of charge, the rate of change, and a time period from the determining the first state of charge and the updated state of charge.

2. The method of claim 1, further comprising:

displaying the updated state of charge.

3. The method of claim 1, wherein the first state of charge is determined based on an open circuit battery voltage.

4. The method of claim 1, wherein the first state of charge is determined based on information received from a calculation of the state of charge during the discharging of the battery.

5. The method of claim 1, wherein at least two measurements of charge current are used to determine the rate of change.

6. The method of claim 5, wherein, when a first of the at least two measurements of charge current is substantially equal to a fast charge current, the rate of change is determined based on the following formula,

ROC=100×

(I_old+I_new)/(2×

C×

60),

where ROC is the rate of change, I_old is the first of the at least two measurements of charge current, I_new is a second of the at least two measurements of charge current and C a capacity of the battery.

7. The method of claim 5, wherein, when a first of the at least two measurements of charge current is less than a fast charge current, a ratio of a second of the at least two measurements of charge current to the first of the at least two measurements of charge current is determined.

8. The method of claim 7, wherein, when the ratio is less than 1, the rate of change is determined based on the following formula,

ROC=(100−

SOC_old)/TTT

where ROC is the rate of change, SOC_old is the present state of charge and TTT is a time to terminate charging.

9. The method of claim 8, wherein the TTT is incremented by a predetermined value when the second of the at least two measurements multiplied by the ratio is greater than a charge termination current.

10. The method of claim 1, wherein measuring the charge current is performed one of periodically and non-periodically.

11. The method of claim 2, wherein the updated state of charge is displayed as a percentage of a capacity of the battery.

12. A system, comprising:

a current sensor measuring a charge current being supplied to a rechargeable battery;

a processor calculating a first state of charge of the rechargeable battery and calculating a rate of change of a state of charge of the rechargeable battery based on the charge current, the processor calculating an updated state of charge of the rechargeable battery as a function of only the first state of charge, the rate of change, and a time period from the determining the first state of charge and the undated state of charge.

13. The system of claim 12, further comprising:

a voltage sensor measuring a voltage of the battery prior to a start of a charging operation, wherein the voltage is used by the processor to calculate the state of charge prior to the start of the charging operation.

14. The system of claim 12, further comprising:

a display displaying the updated state of charge.

15. The system of claim 12, further comprising:

a memory storing the charge current.

16. The system of claim 12, wherein the rechargeable battery is a lithium ion battery.

17. The system of claim 12, wherein at least two measurements of charge current are used to determine the rate of change.

18. The system of claim 17, wherein, when a first of the at least two measurements of charge current is substantially equal to a fast charge current, the rate of change is determined based on the following formula,

ROC=100×

(I_old+I_new)/(2×

C×

60),

where ROC is the rate of change, I_old is the first of the at least two measurements of charge current, I_new is a second of the at least two measurements of charge current and C a capacity of the battery.

19. The system of claim 17, wherein, when a first of the at least two measurements of charge current is less than a fast charge current, a ratio of a second of the at least two measurements of charge current to the first of the at least two measurements of charge current is determined.

20. The system of claim 19, wherein, when the ratio is less than 1, the rate of change is determined based on the following formula,

ROC=(100−

SOC_old)/TTT

where ROC is the rate of change, SOC_old is the present state of charge and TTT is a time to terminate charging.

21. The system of claim 20, wherein the TTT is incremented by a predetermined value when the second of the at least two measurements multiplied by the ratio is greater than a charge termination current.

22. A device, comprising:

current measuring means for measuring a charge current being supplied to a rechargeable battery;

calculating means for calculating a first state of charge of the rechargeable battery;

calculating means for calculating a rate of change of a state of charge of the rechargeable battery based on the charge current, the calculating means calculating an updated state of charge of the rechargeable battery as a function of only the first state of charge, the rate of change, and a time period from the determining the first state of charge and the updated state of charge.

23. A computer readable storage medium including a set of instructions executable by a processor, the set of instructions operable to:

determine a first state of charge of a battery;

receive an indication of a charge current being supplied to the battery;

determine a rate of change of the state of charge of the battery, the rate of change being determined based on the indication of the charge current; and

determine an updated state of charge as a function of only the first state of charge, the rate of change, and a time period from the determining the first state of charge and the updated state of charge.