Method and system for charge equalization of lithium-ion batteries

• US 6,377,024 B1
• Filed: 03/23/2001
• Issued: 04/23/2002
• Est. Priority Date: 03/23/2001
• Status: Expired due to Term

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Choy, Winnie W.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): LUK, LAWRENCE W
• Application Number:
  US09/816,980
• Time in Patent Office: 396 Days
• Field of Search: 320/118, 320/116, 320/117, 320/119, 320/162, 320/152
• US Class Current: 320/118
• CPC Class Codes: H02J 7/0018 using separate charge circuits

Abstract

A system (10) and method (100) for charge and discharge equalization of a lithium-ion battery having a plurality of cells (12) in series. A central charge controller (16) and a central discharge controller (22) command a rate of charge to individual charge controllers (14) associated with each cell (12) of the battery for maintaining equalized charge at each cell (12) of the battery. The charging and discharging is initiated upon sensing a predetermined maximum charge threshold voltage (104) and a predetermined minimum discharge threshold voltage (114) at each cell in the series of cells.

Claims

1. A system for charge and discharge equalization of a lithium-ion battery having a plurality of cells arranged in series, said system comprising:

a plurality of cell chargers wherein a cell charger is associated with a respective cell in the series of cells;

a single discharge controller for the series of cells, said single discharge controller being connected to each cell in the series of cells;

a predetermined charge voltage threshold sensed by a respective cell charger for determining when to adjust charging a respective cell independent of the other cells;

a predetermined discharge voltage threshold sensed by said respective cell charger for determining the activation of each of said cell chargers independent of the other cell chargers; and

said cells are charged and discharged without over-charging and over-discharging.

2. The system as claimed in claim 1 further comprising a central charge command controller for controlling said cell chargers.

3. The system as claimed in claim 2 wherein said central charge command controller provides a commanded charge rate to said plurality of cell chargers.

4. A method for charging and discharging a series of cells in a lithium-ion battery having an independent charger for each cell in the series and a discharger for the series of cells, said method comprising the steps of:

charging each cell in the series of cells at a commanded charge rate;

determining when each cell meets a predetermined maximum charge voltage threshold;

altering the charging of each cell independently of other cells in the series;

determining when a cell meets a predetermined minimum discharge voltage threshold; and

resuming charging of said cell independently of other cells in the series.

5. The method as claimed in claim 4 wherein said step of altering the charging of each cell further comprises terminating the charging of each cell independently of the other cells in the series.

6. The method as claimed in claim 4 wherein said step of altering the charging of each cell further comprises maintaining a constant voltage charge of each cell independently of the other cells in the series.