Method for balancing ultracapacitor cells

• US 9,331,500 B2
• Filed: 04/19/2012
• Issued: 05/03/2016
• Est. Priority Date: 04/19/2012
• Status: Active Grant

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Knitt, Andrew A., Kwok, Wellington Ying-Wei
• Primary Examiner(s): Muralidar, Richard V
• Application Number:
  US13/450,890
• Publication Number:
  US 20130278227A1
• Time in Patent Office: 1,475 Days
• Field of Search: 320/167, 320/166
• US Class Current: 1/1
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: H02J 7/345 using capacitors as storage or buffering devices

Abstract

A method (200) of balancing ultracapacitor cells (102) is provided. The method may measure individual ultracapacitor cell voltages, select a balancing setpoint voltage, compare an actual voltage variation within each ultracapacitor cell (102) with a voltage variation threshold, and enable a balancing element (104) associated with the ultracapacitor cell (102) if the actual voltage variation exceeds the voltage variation threshold.

Claims

1. A method of balancing ultracapacitor cells, comprising the steps of:

measuring individual ultracapacitor cell voltages;

selecting a balancing setpoint voltage;

comparing an actual voltage variation within each ultracapacitor cell with a voltage variation threshold, wherein the voltage variation threshold is a sum of an expected voltage variation and a predefined threshold voltage, the expected voltage variation being calculated based on an expected capacitance variation, the balancing setpoint voltage, and an average cell voltage; and

enabling a balancing element associated with the ultracapacitor cell if the actual voltage variation exceeds the voltage variation threshold.

2. The method of claim 1, wherein the individual ultracapacitor cell voltages are synchronously measured at near zero current conditions.

3. The method of claim 1, wherein the balancing setpoint voltage is selected to approximate the maximum rated voltage of the ultracapacitor cell.

4. The method of claim 1, wherein the actual voltage variation corresponds to a difference between the measured cell voltage of one ultracapacitor cell and a minimum cell voltage.

5. The method of claim 1, further comprising the step of disabling the balancing element after a predefined duration of time.

6. The method of claim 1, wherein the balancing element includes at least one resistor.

7. A method of balancing ultracapacitor cells, comprising the steps of:

monitoring individual cell voltages of the ultracapacitor cells;

selecting a balancing setpoint voltage;

calculating an expected voltage variation based on an expected capacitance variation, the balancing setpoint voltage, and an average cell voltage;

comparing an actual voltage variation within each ultracapacitor cell with the expected voltage variation and a predefined threshold voltage; and

enabling a balancing resistor associated with the ultracapacitor cell if the actual voltage variation exceeds the allowed voltage variation.

8. The method of claim 7, wherein during the step of monitoring, the individual ultracapacitor cell voltages are synchronously measured at near zero current conditions.

9. The method of claim 7, wherein the balancing setpoint voltage is selected to approximate the maximum rated voltage of the ultracapacitor cell.

10. The method of claim 7, wherein the actual voltage variation corresponds to a difference between the measured cell voltage of one ultracapacitor cell and a minimum cell voltage.

11. The method of claim 7, further comprising the step of disabling the balancing resistor after a predefined duration of time.