Systems and methods for balancing battery cells

• US 8,952,660 B2
• Filed: 08/29/2011
• Issued: 02/10/2015
• Est. Priority Date: 08/05/2011
• Status: Expired due to Fees

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: Zhang, Wei
• Primary Examiner(s): Williams, Arun
• Application Number:
  US13/220,158
• Publication Number:
  US 20130033231A1
• Time in Patent Office: 1,261 Days
• Field of Search: 320/116
• US Class Current: 320/116
• CPC Class Codes: H01M 10/4207 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 2010/4271 Battery management systems including electronic circuits, e.g. control of current or voltage to keep battery in healthy state, cell balancing
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A cell balancing system includes multiple bypass paths and a battery management circuit. The multiple bypass paths are coupled in parallel to the battery cells. The battery management circuit is coupled to the bypass paths and monitors cell voltages of the battery cells, compares the cell voltages with a first reference voltage for a first stage, enables a bypass path in the first stage if a battery cell in parallel with the bypass path has a cell voltage at the first reference voltage, and compares the cell voltages of the battery cells with a second reference voltage for a second stage if a specified cell voltage in the first stage is at the first reference voltage.

Claims

1. A cell balancing system for balancing a plurality of battery cells, comprising:

a plurality of bypass paths coupled in parallel to said battery cells;

a battery management circuit coupled to said bypass paths and operable for monitoring cell voltages of said battery cells in a charging mode, operable for comparing said cell voltages with a reference voltage to determine which bypass path of said bypass paths to enable, operable for setting said reference voltage to a first reference voltage in a first stage of said charging mode, operable for enabling a first bypass path of said bypass paths in said first stage if a first battery cell in parallel with said first bypass path has a cell voltage at said first reference voltage in said first stage, operable for, if the minimum cell voltage of said cell voltages in said first stage increases to said first reference voltage, then disabling said first bypass path and entering a second stage of said charging mode, and operable for, in said second stage, setting said reference voltage to a second reference voltage that is greater than said first reference voltage.

2. The cell balancing system as claimed in claim 1, wherein said battery management circuit enables a second bypass path of said bypass paths in said second stage if a second battery cell in parallel with said second bypass path has a voltage at said second reference voltage in said second stage.

3. The cell balancing system as claimed in claim 2, wherein if the minimum cell voltage of said cell voltages in said second stage increases to said second reference voltage, then said battery management circuit disables said second bypass path and enters a third stage of said charging mode, and wherein in said third stage, said battery management circuit sets said reference voltage to a third reference voltage that is greater than said second reference voltage.

4. The cell balancing system as claimed in claim 1, further comprising:

a thermal detection circuit coupled to said battery cells and operable for detecting a temperature of said battery cells,

wherein said thermal detection circuit sends a thermal sensing signal representative of said temperature to said battery management circuit.

5. The cell balancing system as claimed in claim 4, wherein said battery management circuit compares said thermal sensing signal with a threshold, selects an enabled bypass path according to a priority of said enabled bypass path, and disables said enabled bypass path if said thermal sensing signal exceeds said threshold.

6. The cell balancing system as claimed in claim 5, wherein said priority is determined based on a difference between a cell voltage of a battery cell coupled in parallel with said enabled bypass path and said first reference voltage.

7. The cell balancing system as claimed in claim 1, wherein if said first bypass path is enabled in said first stage, then said battery management circuit controls said first bypass path to remain enabled in said first stage before entering said second stage.

8. A cell balancing circuit for balancing a plurality of battery cells, comprising:

a comparison circuit operable for receiving cell voltages of said battery cells in a charging mode, and for comparing said cell voltages with a reference voltage to determine which bypass path of a plurality of bypass paths coupled in parallel with said battery cells to enable; and

a balancing controller coupled to said comparison circuit, and operable for setting said reference voltage to a first reference voltage in a first stage of said charging mode, and operable for enabling a first bypass path of said bypass paths in said first stage if a first battery cell in parallel with said first bypass path has a cell voltage at said first reference voltage in said first stage, operable for, if the minimum cell voltage of said cell voltages in said first stage increases to said first reference voltage, disabling said first bypass path and entering a second stage of said charging mode, and operable for, in said second stage, setting said reference voltage to a second reference voltage that is greater than said first reference voltage.

9. The cell balancing circuit as claimed in claim 8, wherein said balancing controller enables a second bypass path of said bypass paths in said second stage if a second battery cell in parallel with said second bypass path has a cell voltage at said second reference voltage in said second stage.

10. The cell balancing circuit as claimed in claim 9, wherein if the minimum cell voltage of said cell voltages in said second stage increases to said second reference voltage, then said balancing controller disables said second bypass path and enters a third stage of said charging mode, and wherein in said third stage, said balancing controller sets said reference voltage to a third reference voltage that is greater than said second reference voltage.

11. The cell balancing circuit as claimed in claim 8, wherein said balancing controller receives a thermal sensing signal representative of a temperature of said battery cells, and compares said thermal sensing signal with a threshold.

12. The cell balancing circuit as claimed in claim 11, wherein said balancing circuit disables an enabled bypass path according to a priority of said enabled bypass path if said thermal sensing signal exceeds said threshold.

13. The cell balancing circuit as claimed in claim 8, wherein if said first bypass path is enabled in said first stage, then said balancing controller controls said first bypass path to remain enabled in said first stage before entering said second stage.

14. A method for balancing a plurality of battery cells, comprising:

monitoring cell voltages of said battery cells in a charging mode;

comparing, using a comparison circuit, said cell voltages with a reference voltage to determine which bypass path of a plurality of bypass paths coupled in parallel with said battery cells is to be enabled;

setting said reference voltage to a first reference voltage in a first stage of said charging mode;

enabling a first bypass path of said bypass paths in said first stage if a first battery cell in parallel with said first bypass path has a cell voltage at said first reference voltage;

disabling said first bypass path and controlling said comparison circuit to enter a second stage of said charging mode, if the minimum cell voltage of said cell voltages in said first stage increases to said first reference voltage; and

setting said reference voltage to a second reference voltage that is greater than said first reference voltage, in said second stage.

15. The method as claimed in claim 14, further comprising:

enabling a second bypass path of said bypass paths in said second stage if a second battery cell in parallel with said second bypass path has a cell voltage at said second reference voltage.

16. The method as claimed in claim 15, further comprising:

disabling said second bypass path and controlling said comparison circuit to enter a third stage of said charging mode, if the minimum cell voltage of said cell voltages in said second stage increases to said second reference voltage; and

setting said reference voltage to a third reference voltage that is greater than said second reference voltage, in said third stage.

17. The method as claimed in claim 14, further comprising:

detecting a temperature of said battery cells by a thermal detection circuit;

comparing a thermal sensing signal representative of said temperature with a threshold; and

disabling an enabled bypass path according to a priority of said enabled bypass path if said thermal sensing signal exceeds said threshold,

wherein said priority of said enabled bypass path is determined based on a difference between a cell voltage of a battery cell coupled in parallel with said enabled bypass path and said first reference voltage.

18. The method as claimed in claim 14, further comprising:

if said first bypass path is enabled in said first stage, then controlling said first bypass path to remain enabled in said first stage before entering said second stage.