Method and system for charging a series battery

• US 8,134,336 B2
• Filed: 06/05/2009
• Issued: 03/13/2012
• Est. Priority Date: 06/05/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Michalske, Steven C., Greening, Thomas C., Ungar, P. Jeffrey, Athas, William C.
• Primary Examiner(s): Aurora, Reena
• Application Number:
  US12/479,343
• Publication Number:
  US 20100308770A1
• Time in Patent Office: 1,012 Days
• Field of Search: 320/116, 320/134, 320/136
• US Class Current: 320/116
• CPC Class Codes: H02J 7/0013 acting upon several batteries simultaneously or sequentially H02J7/1423 takes precedence
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]

Abstract

Some embodiments of the present invention provide a system for charging a series battery, wherein the series battery is comprised of a set of banks which are connected in series, so that the same charging current passes through each bank. During the charging process, the system measures a voltage across each bank in the set of banks. The system then compares the measured voltage with a target voltage for each bank, and adjusts the charging process based on results of the comparisons between the measured voltage and the target voltage.

Claims

1. A method for charging a series battery, comprising:

charging the series battery, wherein the series battery includes a set of banks which are connected in series, so that the same charging current passes through each bank in the set of banks;

measuring a voltage across each bank in the set of banks as the series battery is charging;

for each bank in the set of banks, comparing the measured voltage for the bank with a target voltage for the bank, wherein comparing the measured voltage with the target voltage comprises computing a difference between the measured voltage and the target voltage to produce a set of differences for the set of banks; and

adjusting the charging process based on results of the comparisons between the measured voltage and the target voltage for each bank by limiting a voltage output for the charging process based on a result of a comparison of the differences in the set of differences.

2. The method of claim 1,

wherein adjusting the charging process involves adjusting the charging process based on the set of differences.

3. The method of claim 2, wherein adjusting the charging process based on the set of differences involves:

determining a minimum difference in the set of differences; and

adjusting the charging process based on the minimum difference.

4. The method of claim 1, further comprising determining the target voltage for each bank in the set of banks based on one or more of:

a measured temperature of the bank, a state-of-charge of the bank, and the bank'"'"'s open circuit voltage characteristics.

5. The method of claim 1, wherein each bank includes one or more battery cells which are connected in parallel.

6. The method of claim 1, wherein adjusting the charging process involves adjusting the charging process based on joint current and voltage limits.

7. The method of claim 6, wherein if the current limit is I_L and the voltage limit is V_L, the charging process supplies:

a constant current of I_L at a voltage less than V_L;

or

a constant voltage of V_L with a current less than I_L.

8. The method of claim 7, wherein the charging process involves:

first supplying a constant current; and

when a threshold is reached, supplying a constant voltage.

9. The method of claim 1, wherein adjusting the charging process involves using a closed-loop control system, which uses results of the comparisons between the measured voltages and the target voltages to control the charging process.

10. The method of claim 1, wherein the closed-loop control system uses a proportional-integral-derivative (PID) controller.

11. A system for charging a series battery, comprising:

the series battery, wherein the series battery includes a set of banks which are connected in series;

a battery charger which is coupled to the series battery so that the same charging current passes through each bank in the set of banks;

a set of voltage monitors configured to measure a voltage across each bank in the set of banks as the series battery is charging;

a comparison circuit configured to compare the measured voltage for each bank with a target voltage for the bank, wherein, while comparing the measured voltage with the target voltage, the comparison circuit is configured to compute a difference between the measured voltage and the target voltage to produce a set of differences for the set of banks;

a controller within the battery charger configured to adjust the charging process based on results of the comparisons between the measured voltage and the target voltage for each bank in the set of banks by limiting a voltage output for the charging process based on a result of a comparison of the differences in the set of differences.

12. The system of claim 11,

wherein the controller is configured to adjust the charging process based on the set of differences.

13. The system of claim 12, wherein while adjusting the charging process based on the set of differences, the controller is configured to:

determine a minimum difference in the set of differences; and

adjust the charging process based on the minimum difference.

14. The system of claim 11, further comprising:

a set of temperature monitors configured to monitor a temperature for each bank in the set of banks; and

a target-voltage determination mechanism configured to determine the target voltage for each bank in the set of banks based on one or more of;

the measured temperature of the bank, a state-of-charge of the bank, and the bank'"'"'s open circuit voltage characteristics.

15. The system of claim 11, wherein each bank includes one or more battery cells which are connected in parallel.

16. The system of claim 11, wherein the battery charger is configured to charge based on joint current and voltage limits.

17. The system of claim 16, wherein if the current limit is I_L and the voltage limit is V_L, the battery charger supplies:

a constant current of I_L at a voltage less than V_L;

or

a constant voltage of V_L with a current less than I_L.

18. The system of claim 17, wherein the controller is configured to control the battery charger to:

first supply a constant current; and

when a threshold is reached, supply a constant voltage.

19. The system of claim 11, wherein the controller includes a closed-loop control system, which uses results of the comparisons between the measured voltages and the target voltages to control the charging process.

20. The system of claim 19, wherein the closed-loop control system uses a proportional-integral-derivative (PID) controller.

21. A computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method for charging a series battery, the method comprising:

using a battery charger to charge the series battery, wherein the series battery includes a set of banks which are connected in series, so that the same charging current passes through each bank in the set of banks;

receiving measurements of voltages across each bank in the set of banks as the series battery is charging;

for each bank in the set of banks, computing differences between the measured voltage and the target voltage for each bank to produce a set of differences for the set of banks; and

adjusting the charging process based on the set of differences between the measured voltage and the target voltage for each bank by limiting a voltage output for the charging process based on a result of a comparison of the differences in the set of differences.

22. The computer-readable storage medium of claim 21, wherein adjusting the charging process based on the set of differences involves:

determining a minimum difference in the set of differences; and

adjusting the charging process based on the minimum difference.

23. The computer-readable storage medium of claim 21, wherein the method further comprises determining the target voltage for each bank in the set of banks based on one or more of:

a measured temperature of the bank, a state-of-charge of the bank, and the bank'"'"'s open circuit voltage characteristics.

24. The computer-readable storage medium of claim 21, wherein adjusting the charging process involves adjusting the charging process based on joint current and voltage limits.

25. The computer-readable storage medium of claim 24, wherein if the current limit is I_L and the voltage limit is V_L, the charging process supplies:

a constant current of I_L at a voltage less than V_L;

or a constant voltage of V_L with a current less than I_L.

26. The computer-readable storage medium of claim 24, wherein the charging process involves:

first supplying a constant current; and

when a threshold is reached, supplying a constant voltage.

27. The computer-readable storage medium of claim 21, wherein adjusting the charging process involves using a closed-loop control system, which uses results of the comparisons between the measured voltages and the target voltages to control the charging process.

28. The computer-readable storage medium of claim 27, wherein the closed-loop control system uses a proportional-integral-derivative (PID) controller.