Distributed converter and method for equalizing lithium-ion batteries

• US 6,369,546 B1
• Filed: 03/23/2001
• Issued: 04/09/2002
• Est. Priority Date: 03/23/2001
• Status: Expired due to Term

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Canter, Stanley
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): LUK, LAWRENCE W
• Application Number:
  US09/816,981
• Time in Patent Office: 382 Days
• Field of Search: 320/118, 320/116, 320/117, 320/132, 307/66
• US Class Current: 320/118
• CPC Class Codes: H02J 7/0014 Circuits for equalisation of charge between batteries

Abstract

A system and method for charging a lithium-ion battery in which the battery is charged by a bulk charger at a high rate until one or more of the cells reaches a predetermined series threshold voltage. When a predetermined cell threshold voltage is reached, the controller provides instructions as to whether to reduce or terminate the cell charging by the bulk charger. At this point in time, the redundant power supplies begin charging each cell individually through balancing switches. The balancing switches will turn off as their respective cells reach a predetermined cell threshold voltage. Ultimately, each cell will be fully charged to an identical high charge state.

Claims

1. A distributed converter for balancing charge in a lithium-ion battery comprising:

an array of cells having a predetermined number of cell units in parallel forming a cell, each of said cells has a predetermined number of cell units arranged in parallel, thereby forming said array of cells;

a bulk charger for charging at least one cell in said array of cell units to a first predetermined threshold voltage;

a multiplexer for measuring a voltage of each of said cells in said array of cell units;

a plurality of transformer/rectifier circuits, each transformer/rectifier circuit in said plurality of transformer/rectifier circuits being associated with a respective cell in said array of cell units;

a plurality of balancing switches, each equalizing switch in said plurality of balancing switches being associated with a respective transformer/rectifier circuit in said plurality of transformer/rectifier circuits;

a redundant AC power supply supplying power to said plurality of transformer/rectifier circuits; and

a controller for receiving measured voltages from said multiplexer and for controlling an on/off state for each of said plurality of balancing switches, whereby charging and balancing of a cell in said array of cell units occurs when a respective balancing switch is in an “

on”

state until said respective cell reaches a second predetermined threshold voltage.

2. The system as claimed in claim 1 wherein said redundant AC power supply is operated a low frequency.

3. The system as claimed in claim 2 wherein said low frequency is on the order of 10 kHz.

4. The system as claimed in claim 1 wherein each of said series of cells further comprises a bypass switch.

5. The system as claimed in claim 1 wherein said first and second predetermined threshold voltages are fixed voltages.

6. The system as claimed in claim 1 wherein said first and second predetermined threshold voltages are variable voltages.

7. The system as claimed in claim 1 wherein said second predetermined threshold voltage further comprises a plurality of second predetermined threshold voltages wherein each second predetermined threshold voltage is associated with each cell in said array of cell units.

8. The systems as claimed in claim 7 wherein each of said respective second predetermined threshold voltages are variable.

9. A distributed converter for equalizing a lithium-ion battery on board a satellite in a earth orbit comprising:

an array of cell units having a predetermined number of cell units in parallel forming a cell and a predetermined number of cells arranged in series, thereby forming said array of cell units;

a bulk charger for charging said array of cell units to a first predetermined threshold voltage;

a plurality of transformer/rectifier circuits, each transformer/rectifier circuit in said plurality of transformer/rectifier circuits being associated with a respective cell in said array of cell units; and

a controller for controlling said bulk charger to charge each of said series of cells to a first predetermined threshold voltage, for controlling each of said plurality of transformer/rectifier circuits until each of said respective cells reaches a second predetermined threshold voltage, at which time said controller deactivates said transformer/rectifier circuit until all of said respective cells in said array of cell units reaches said second predetermined threshold voltage.

10. The system as claimed in claim 9 further comprising a plurality of balancing switches wherein each of said plurality of transformer/rectifier circuits has a respective balancing switch.

11. The system as claimed in claim 9 further comprising a multiplexer for measuring a voltage of said cell and communicating said measured voltage to said controller.

12. The system as claimed in claim 9 wherein each of said cells further comprises a bypass switch.

13. The system as claimed in claim 9 wherein said first predetermined threshold voltage is a fixed voltage.

14. The system as claimed in claim 9 wherein said first predetermined threshold voltage is a variable voltage.

15. The system as claimed in claim 14 wherein said variable voltage is a function of an age of the satellite and a relative location of the satellite with respect to the sun.

16. The system as claimed in claim 9 wherein said second predetermined threshold voltage is a fixed voltage.

17. The system as claimed in claim 9 wherein said second predetermined threshold voltage is a variable voltage.

18. The system as claimed in claim 9 wherein said second predetermined voltage further comprises a plurality of second predetermined threshold voltages wherein each of said cells in said array of cell units has a respective second predetermined threshold voltage.

19. The system as claimed in claim 18 wherein said plurality of second predetermined threshold voltages for each of said cells in said array of cell units is variable.

20. The system as claimed in claim 19 wherein said variable voltage is a function of an age of the satellite and a relative location of the satellite with respect to the sun.

21. A method for charging and equalizing a lithium-ion battery system having an array of cell units having a predetermined number of cell units in parallel forming a cell and a predetermined number of cells arranged in series, thereby forming the array of cells, a bulk charger, a plurality of transformer/rectifier circuits, each transformer/rectifier circuit in the plurality of transformer/rectifier circuits being associated with a respective cell in the array of cell units, and a controller, said method comprising the steps of:

charging the array of cell units at a high rate using the bulk charger;

measuring the voltage of each cell in the array of cell units;

determining when at least one cell has reached a first predetermined threshold voltage;

modifying a rate of charge of the bulk charger;

applying AC power to each of the transformer/rectifier circuits simultaneously;

measuring the voltage of each cell in the array of cell units;

determining when a cell has reached a second predetermined threshold voltage;

discontinuing AC power to a respective transformer/rectifier circuit for said cell having a voltage meeting said second predetermined threshold voltage.

22. The method as claimed in claim 21 wherein the battery system has a plurality of balancing switches and each transformer/rectifier circuit has a respective balancing switch and wherein after AC power has been discontinued to all of the transformer/rectifier circuits, said method further comprises the steps of:

activating AC power to all of the transformer/rectifier circuits; and

closing all of the balancing switches in the plurality of balancing switches for trickle charging the cells.