System and method for performing ultracapacitor cell balancing

• US 8,198,870 B2
• Filed: 06/29/2009
• Issued: 06/12/2012
• Est. Priority Date: 06/30/2008
• Status: Expired due to Fees

• Current Assignee: Eaton Intelligent Power Limited (Eaton Corporation PLC.)
• Original Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Inventors: Zuercher, Joseph Charles
• Primary Examiner(s): Fantu, Yalkew
• Application Number:
  US12/493,287
• Publication Number:
  US 20090322289A1
• Time in Patent Office: 1,079 Days
• Field of Search: 320/167
• US Class Current: 320/167
• CPC Class Codes: G01R 19/0084 measuring voltage only all subgroups of G01R19/00 take precedence
• 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 circuit for balancing a sub-stack voltage in a stack of ultracapacitors includes a pair of electrical leads that are connectable across a first sub-stack of one or more ultracapacitors, wherein a stack includes N sub-stacks of ultracapacitors coupled to an electrical bus, a discharge device switchably connectable with the pair of electrical leads, the discharge device configured to discharge the sub-stack of ultracapacitors, a voltage sensing circuit coupled to the electrical bus and configured to sense and output a voltage of the stack of ultracapacitors after the first sub-stack of one or more ultracapacitors has been discharged to a given threshold, and a voltage amplifier coupled to the output of the voltage sensing circuit and coupled to the pair of electrical leads, the voltage amplifier configured to provide a re-charge voltage to the first sub-stack of one or more ultracapacitors.

Claims

1. A circuit for balancing a sub-stack voltage in a stack of ultracapacitors, the circuit comprising:

a pair of electrical leads that are connectable across different sub-stacks of one or more ultracapacitors, wherein a stack includes N sub-stacks of ultracapacitors coupled to an electrical bus;

a discharge device switchably connectable with the pair of electrical leads, the discharge device configured to discharge each sub-stack of ultracapacitors;

a voltage sensing circuit coupled to the electrical bus and configured to sense and output a voltage of the stack of ultracapacitors after the first sub-stack of one or more ultracapacitors has been discharged to a given threshold; and

a voltage amplifier coupled to the output of the voltage sensing circuit and coupled to the pair of electrical leads, the voltage amplifier configured to provide a re-charge voltage to the first sub-stack of one or more ultracapacitors.

2. The circuit of claim 1 wherein the voltage amplifier is configured to have a gain of 1/(N−

1).

3. The circuit of claim 1 wherein the voltage amplifier is an operational amplifier connected to the voltage sensing circuit and the pair of electrical leads, and wherein the discharge device is a resistor switchably connectable in series with the pair of electrical leads.

4. The circuit of claim 1 comprising a differential unity gain operational amplifier buffer coupled to an output of the voltage amplifier and configured to pass the voltage from the voltage amplifier to the first sub-stack of one or more ultracapacitors.

5. The circuit of claim 1 wherein the device is an energy storage device configured to store energy and configured to use the stored energy to re-charge the first sub-stack of one or more ultracapacitors.

6. The circuit of claim 5 wherein the device is one of a battery and an ultracapacitor.

7. A method comprising:

A) discharging a sub-set of ultracapacitor cells;

B) measuring a voltage across a stack of N ultracapacitor cells after the sub-set of ultracapacitor cells has been discharged, the stack of N ultracapacitor cells comprising the sub-set of ultracapacitor cells; and

C) re-charging the discharged sub-set of ultracapacitor cells with a voltage amplifier configured to output a voltage proportional to the measured voltage across the stack of N ultracapacitor cells and proportional to a gain of 1/(N−

1).

8. The method of claim 7 wherein the sub-set of ultracapacitors includes only one ultracapacitor cell.

9. The method of claim 7 wherein re-charging the discharged sub-set of ultracapacitor cells comprises outputting an energy via the voltage amplifier that is a product of both the measured voltage across the stack of N ultracapacitor cells and the gain of 1/(N−

1).

10. The method of claim 7 further comprising repeating steps A-C for each sub-set of ultracapacitor cells of the stack of N ultracapacitor cells.

11. The method of claim 7 wherein discharging the sub-set of ultracapacitor cells comprises discharging an energy of the sub-set of ultracapacitor cells through an electrically resistive device.

12. The method of claim 7 wherein discharging energy from the sub-set of ultracapacitor cells comprises storing an energy of the sub-set of ultracapacitor cells into an energy storage unit.

13. The method of claim 12 wherein re-charging the discharged sub-set of ultracapacitor cells comprises re-charging the discharged sub-set of ultracapacitor cells using the energy stored in the energy storage unit.

14. A method comprising:

discharging a sub-set of ultracapacitors of a bank of N ultracapacitors;

sensing a voltage across the bank of N ultracapacitors after the sub-set of ultracapacitors has been discharged;

determining a gain for a voltage amplifier; and

re-charging the sub-set of ultracapacitors with a voltage approximately equal to the product of the sensed voltage and the gain.

15. The method of claim 14 wherein the gain is 1/(N−

1).

16. The method of claim 14 wherein discharging the sub-set of ultracapacitors comprises discharging an energy of the sub-set of ultracapacitors via an electrically resistive device.

17. The method of claim 14 wherein discharging the sub-set of ultracapacitors comprises discharging an energy the sub-set of ultracapacitors into an energy storage device.

18. The method of claim 17 wherein the energy storage device is one of a battery and an ultracapacitor.

19. The method of claim 17 wherein re-charging the sub-set of ultracapacitors comprises re-charging the sub-set of ultracapacitors using the energy stored in the energy storage device.

20. The method of claim 14 wherein the voltage amplifier is an operational amplifier.