Charge balancing circuit for double-layer capacitors

• US 20040263121A1
• Filed: 05/20/2004
• Published: 12/30/2004
• Est. Priority Date: 04/25/2003
• Status: Abandoned Application

• Current Assignee: UCAP Power, Inc.
• Original Assignee: Maxwell Technologies Incorporated (Tesla Inc.)
• Inventors: Thrap, Guy C.
• Application Number:
  US10/819,262
• Publication Number:
  US 20040263121A1
• Time in Patent Office: Days
• US Class Current: 320/119
• 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 charge balancing circuit is configured to provide charge balancing for a bank of series connected charge storage devices. One embodiment of the charge balancing circuit comprises a voltage divider, an amplifier, and a negative feedback resistor connected between every two capacitors. The circuit is configured to monitor the voltage in each of the capacitors and, if the voltage in one of the capacitors is higher than the other, the circuit transfers energy from the higher charged capacitor to the lower charged capacitor until the capacitors are balanced. A current limiting resistor can be included for limiting the output current of the amplifier to a safe value and for providing feedback information regarding the health of the capacitor. An additional gain stage can also be included for increasing the output current of the amplifier for banks of large charge storage devices. The circuit can be used in bi-polar applications.

Claims

1. A bi-polar charge balancing apparatus for providing charge balancing of at least two double-layer capacitor cells connected in series, the at least two double-layer capacitor cells capable of being charged by a supply voltage, the charge balancing apparatus comprising:

a voltage divider for equally dividing the supply voltage across the at least two double-layer capacitor cells;

a circuit having inputs and an output, the output for connecting between each of the at least two double-layer capacitor cells, the circuit being connected to the voltage divider such that the voltage divider provides a voltage to an input of the circuit;

a feedback connection for providing feedback regarding a stored voltage in each of the at least two double-layer capacitor cells to an input of the circuit;

wherein the circuit is configured to produce an output current when the stored voltage of a first of the at least two double-layer capacitor cells is higher than the stored voltage of a second of the at least two double-layer capacitor cells, the output current for causing energy stored in the first cell to be transferred to the second cell until the at least two cells are balanced.

2. The charge balancing apparatus of claim 1, wherein the supply voltage is less than about 4 volts x the number of cells connected in series.

3. A charge balancing apparatus for providing charge balancing of at least two charge storage devices connected in series, the at least two charge storage devices capable of being charged by a supply voltage, the charge balancing apparatus comprising:

a voltage divider for equally dividing the supply voltage across the at least two charge storage devices;

a circuit having inputs and an output, the output for connecting between each of the at least two charge storage devices, the circuit being connected to the voltage divider such that the voltage divider provides a voltage to an input of the circuit;

a feedback connection for providing feedback regarding a stored voltage in each of the at least two charge storage devices to an input of the circuit;

wherein the circuit is configured to produce an output current when the stored voltage of a first of the at least two charge storage devices is higher than the stored voltage of a second of the at least two charge storage devices, the output current causing energy stored in the first charge storage device to be transferred to the second charge storage device until the at least two charge storage devices are balanced.

4. The charge balancing apparatus of claim 3 further comprising a current limiting device connected between the circuit and the at least two charge storage devices, the current limiting device being configured to limit the output current of the circuit to a safe value.

5. The charge balancing apparatus of claim 3 further comprising a gain stage for increasing the output current of the circuit.

6. The charge balancing apparatus of claim 3 wherein the voltage divider further comprises two divider resistors of approximately the same value connected to the circuit.

7. The charge balancing apparatus of claim 6 wherein the two divider resistors are of a value high enough to minimize the quiescent current draw of the apparatus.

8. The charge balancing apparatus of claim 3 wherein the feedback connection is configured to cancel any input bias current supplied to the circuit by the voltage divider.

9. The charge balancing apparatus of claim 7 wherein the feedback connection provides a value of approximately half the value of each of the two divider resistors such that the feedback connection effectively cancels any input bias current supplied to the circuit.

10. The charge balancing apparatus of claim 4 wherein the current limiting device has a value equal to the supply voltage divided by the maximum output current of the circuit.

11. The charge balancing apparatus of claim 4 wherein a voltage drop across the current limiting device can be used to provide information regarding the health of the at least two charge storage devices.

12. The charge balancing apparatus of claim 5 wherein each gain stage comprises an amplifier circuit connected between the circuit output and the at least two charge storage devices.

13. The charge balancing apparatus of claim 12 wherein the amplifier circuit comprises two transistors that include a base, emitter and collector and wherein the bases and emitters of each of the two transistors are connected together.

14. The charge balancing apparatus of claim 12 wherein the amplifier circuit comprises two transistors, and wherein the two transistors form a complementary symmetry emitter follower transistor pair.

15. The charge balancing apparatus of claim 12 further comprising a current limiting device connected between the gain stage and the at least two charge storage devices, the current limiting device being configured to limit the output current of the gain stage to a safe value.

16. The charge balancing apparatus of claim 15 wherein the current limiting device has a value based on the supply voltage, the saturation current of the amplifier circuit, and the maximum current rating of the amplifier circuit.

17. The charge balancing apparatus of claim 3, wherein the charge storage devices are double-layer capacitors.

18. A charge balancing circuit for providing charge balancing of n charge storage devices connected in series, wherein n is greater than or equal to 2, the n charge storage devices capable of being charged by a supply voltage, the charge balancing circuit comprising:

n−

1 voltage dividers for equally dividing the supply voltage across the n charge storage devices;

n−

1 amplifiers having inputs and an output, each amplifier being connected at its output between two charge storage devices and each amplifier being connected to one of the n−

1 voltage dividers such that each voltage divider provides a voltage to an input of an amplifier;

n−

1 feedback connections, each feedback connection connected to one of the n−

1 amplifiers, the n−

1 feedback connection for providing feedback regarding stored voltage in the n charge storage devices to an input of one of the n−

1 amplifiers;

wherein each amplifier is configured to produce an output current when the stored voltage at a first of the two charge storage devices to which it is connected is higher then the stored voltage at a second of the two charge storage devices to which it is connected, the output current causing energy stored in the first charge storage device to be transferred to the second charge storage device until the two charge storage devices are balanced.

19. The charge balancing circuit of claim 18, wherein the supply voltage does not exceed about four times the number of charge storage devices.

20. A charge balancing circuit for balancing a voltage between two series connected capacitors, comprising:

an amplifier having an output, the output for connecting between the two capacitors, wherein the amplifier is configured to produce an output current when a stored voltage of a first of the two series connected capacitors is higher than a stored voltage of a second of the at least two series connected capacitors, the output current for causing energy stored in the first capacitor to be transferred to the second capacitor until the two capacitors are balanced.

21. The circuit of claim 20, wherein the amplifier comprises inputs and a feedback connection, wherein the circuit is configured to provide feedback regarding the stored voltage in the two series connected capacitors to an input of the amplifier.

22. The circuit of claim 21, wherein the circuit comprises a voltage divider for equally dividing a circuit supply voltage across the two series connected capacitors.

23. The circuit of claim 20, wherein the capacitors are double-layer capacitors.

24. The circuit of claim 20, wherein the amplifier is configured as an operational amplifier.

25. The circuit of claim of claim 20, wherein the circuit comprises a voltage divider for equally dividing an alternating current supply voltage across the two series connected capacitors.

26. The circuit of claim 25, wherein the circuit includes a converter circuit and wherein the circuit is a bipolar circuit.

27. The circuit of claim 25, wherein the circuit can be used interchangeably and without modification between two or more sets of the two series connected capacitors.

28. A charge balancing device, comprising:

balancing means for balancing a voltage between two series connected capacitors, wherein the balancing means is configured to produce an output current when a stored voltage of a first of the two series connected capacitors is higher than a stored voltage of a second of the two series connected capacitors, the output current for causing energy stored in the first capacitor to be transferred to the second capacitor until the two capacitors are balanced.

29. The charge balancing device of claim 28, wherein the capacitors are double-layer capacitors.

30. A method of balancing a voltage, comprising the steps of:

providing a set of series connected capacitors providing a first voltage;

providing a circuit;

providing the first voltage across the series connected capacitors and across the circuit;

providing a feedback of a second voltage at a connection of the set of series connected capacitors; and

balancing the second voltage using the circuit based on the feedback.

31. The method of claim 30, wherein the set of series connected capacitors are double-layer capacitors.

32. The method of claim 31, wherein the first voltage does not exceed about 4 volts times the number of series connected capacitors.

33. The method of claim 30, further comprising the step of providing a circuit that can be used interchangeably without any modification between the two or more sets of series connected capacitors.

34. A capacitor product, comprising:

a housing;

two series connected capacitor cells housed within the housing; and

a charge balancing circuit operatively coupled to the capacitor cells.

35. The capacitor product of claim 34, wherein the housing comprises a sealed housing, and wherein the capacitor cells and the charge balancing circuit are disposed within the sealed housing.

36. The capacitor product of claim 34, wherein the capacitor cells comprise double-layer capacitor cells.

37. The capacitor product of claim 35, further comprising one or more selective enabling and disabling circuit coupled to the charge balancing circuit and the capacitor cells.

38. The capacitor product of claim 36, wherein the product is rated to operate safely between a voltage of about 4.0 volts and 9.0 volts.

39. The capacitor product of claim 34, wherein the charge balancing circuit comprises an amplifier having a high impedance, the output connected between the two capacitor cells, wherein the amplifier is configured to produce an output current when a stored voltage of a first of the two capacitor cells is higher than a stored voltage of a second of the two capacitor cells, the output current for causing energy stored in the first capacitor cell to be transferred to the second capacitor cell until the two capacitors are balanced.