MAXIMIZING LIFE OF CAPACITORS IN SERIES MODULES

• US 20130093400A1
• Filed: 06/28/2011
• Published: 04/18/2013
• Est. Priority Date: 06/28/2010
• Status: Active Grant

• Current Assignee: UCAP Power, Inc.
• Original Assignee: Maxwell Technologies Incorporated (Tesla Inc.)
• Inventors: Maynard, Xavier, Setterberg, Mikael, Sartorelli, Gianni, Milewski, Andre
• Granted Patent: US 9,209,653 B2
• Time in Patent Office: Days
• US Class Current: 320/166
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: H02J 15/00 Systems for storing electric energy mechanical systems therefor F01-F04; in chemical form H01M
• 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 device (1) monitors and/or balances an ultracapacitor (3) and/or a module (4) comprising a plurality of ultracapacitors (3) connected in series, the module (4) being connectable in series or in parallel with other modules (4). The device comprises an electronic board (2) comprising digital control and/or command means, such as a microcontroller (5), executing a program for monitoring and balancing the ultracapacitor (3) and/or the module (4). The relative capacitances of the capacitors are measured, and this information is employed to determine when to carry out a controlled discharge of particular capacitors. Temperature information is also employed to determine when to carry out a controlled discharge of particular capacitors. In this way the lifetime of any particular capacitor is, desirably, extended to be no shorter than the lifetime of other longer- lived capacitors in the module.

Claims

1. An apparatus comprising:

a module having a plurality of capacitors in series, one of the capacitors defined as a k^th capacitor;

means sampling voltages at the capacitors at between 10 Hz and 100Hz, the amplitude of voltage changes per capacitor exceeding a predetermined threshold;

means evaluating, during a time interval Δ

t_i when the sampling is taking place, a Δ

v_i for a k^th capacitor of the module and a Δ

v_i for the entire module;

a ratio of the Δ

v_i for the k^th capacitor of the module and the Δ

v_i for the entire module defining a measured relative capacity for the k^th capacitor.

2. The apparatus of claim 1 wherein the predetermined threshold is a value in the range of 0.5V to 1V.

3. The apparatus of claim 1 further comprising:

means selectively discharging particular ones of the capacitors of the module as a function of a respective measured relative capacity of each of the capacitors.

4. The apparatus of claim 1 wherein the capacitors are ultracapacitors.

5. A method for use with apparatus comprising a module having a plurality of capacitors in series, one of the capacitors defined as a k^th capacitor, the method comprising the steps of:

carrying out sampling of voltages at the capacitors at between 10 Hz and 100 Hz, the amplitude of voltage changes per capacitor exceeding a predetermined threshold;

evaluating, during a time interval Δ

t_i when the sampling is taking place, a Δ

v_i for a k^th capacitor of the module and a Δ

v_i for the entire module;

calculating a ratio of the Δ

v_i for the k^th capacitor of the module and the Δ

v_i for the entire module, thereby defining a measured relative capacity for the k^th capacitor.

6. The method of claim 5 wherein the predetermined threshold is a value in the range of 0.5V to 1V.

7. The method of claim 5 further comprising the step of:

selectively discharging particular ones of the capacitors of the module as a function of a respective measured relative capacity of each of the capacitors.

8. The method of claim 5 wherein the capacitors are ultracapacitors.

9. A method for use in a series module of capacitors, each capacitor having a respective temperature, the method comprising:

measuring the temperature of each capacitor in the series module;

identifying a first capacitor in the series module having a temperature higher than the temperature of a second capacitor in the series module; and

causing the first capacitor to be charged to a respective voltage lower than the respective voltage of the second capacitor.

10. The method of claim 9 wherein the step of causing the first capacitor to be charged to a respective voltage lower than the respective voltage of the second capacitor comprises connecting a resistor to the first capacitor for some duration, thereby reducing the voltage of the first capacitor.

11. The method of claim 9 wherein the capacitors are ultracapacitors.

12. A method for use with a plurality of series modules of capacitors, each module having a respective temperature, the method comprising:

measuring the temperature of each module;

identifying a first module having a temperature higher than the temperature of a second module; and

causing the first module to be charged to a respective voltage lower than the respective voltage of the second module.

13. The method of claim 12 wherein the step of causing the first module to be charged to a respective voltage lower than the respective voltage of the second module comprises connecting a resistor to the first module for some duration, thereby reducing the voltage of the first module.

14. The method of claim 12 wherein the step of causing the first module to be charged to a respective voltage lower than the respective voltage of the second module comprises applying a smaller charging current to the first module than to the second module.

15. The method of claim 12 wherein the step of causing the first module to be charged to a respective voltage lower than the respective voltage of the second module comprises applying a charging current to the first module for a shorter duration than to the second module.

16. The method of claim 12 wherein the capacitors are ultracapacitors.

17. A method for use in a series module of capacitors, each capacitor having a respective relative capacitance, each capacitor at a particular moment having a respective charge, each capacitor at a particular moment having a respective voltage, the method comprising:

arriving at an estimate of the respective relative capacitance of each capacitor by means of measurements of voltages at each of the capacitors;

identifying a first capacitor in the series module having an estimated relative capacitance smaller than the estimated relative capacitance of a second capacitor in the series module; and

causing the first capacitor to be charged to a respective level of charge lower than the respective level of charge of the second capacitor.

18. The method of claim 17 wherein the step of causing the first capacitor to be charged to a respective level of charge lower than the respective level of charge of the second capacitor comprises connecting a resistor to the first capacitor for some duration, thereby reducing the charge of the first capacitor.

19. The method of claim 17 wherein the capacitors are ultracapacitors.

20. The method of claim 17 wherein the module at a particular moment has a respective current passing therethrough, the respective current at various times defining positive, negative, and zero values, the step of arriving at an estimate of the respective relative capacity of each capacitor by means of measurements of voltages at each of the capacitors comprises carrying out a multiplicity of relative capacity measurements and averaging the relative capacity measurements, each relative capacity measurement carried out by performing the steps of:

at a first time when the current passing through the module is at a value smaller than a first predetermined threshold, measuring the respective voltage at each of the capacitors, thereby defining a sum of the voltages representing a voltage across the series module;

at a second time, after the current passing through the module has exceeded the first predetermined threshold and has later dropped to a value smaller than the first predetermined threshold, again measuring the respective voltage at each of the capacitors, thereby again defining a sum of the voltages representing a voltage across the series module;

for each capacitor, a difference between the respective voltage at the first time and the respective voltage at the second time defining a respective voltage change;

for the series array, a difference between voltage across the series module at the first time and the voltage across the series module at the second time defining a respective voltage change for the series module;

for each capacitor, a ratio of its respective voltage change to the voltage change in the series module defining the each relative capacity measurement.

21. The method of claim 17 wherein the step of causing the first capacitor to be charged to a respective level of charge lower than the respective level of charge of the second capacitor is not performed at any of the times when measurements of voltages take place.

22. The method of claim 17 wherein the measurements of voltages take place only at times when the step of causing the first capacitor to be charged to a respective level of charge lower than the respective level of charge of the second capacitor is not taking place.

23. An apparatus for use with a series module of capacitors, each capacitor having a respective temperature, the apparatus comprising:

mean measuring the temperature of each.capacitor in the series module;

mean identifying a first capacitor in the series module having a temperature higher than the temperature of a second capacitor in the series module; and

mean causing the first capacitor to be charged to a respective voltage lower than the respective voltage of the second capacitor.

24. The apparatus of claim 23 wherein the means causing the first capacitor to be charged to a respective voltage lower than the respective voltage of the second capacitor comprises a resistor connectable to the first capacitor, thereby reducing the voltage of the first capacitor.

25. The apparatus of claim 23 wherein the capacitors are ultracapacitors.

26. An apparatus for use with a plurality of series modules of capacitors, each module having a respective temperature, the apparatus comprising:

means measuring the temperature of each module;

means identifying a first module having a temperature higher than the temperature of a second module; and

means causing the first module to be charged to a respective voltage lower than the respective voltage of the second module.

27. The apparatus of claim 26 wherein the means causing the first module to be charged to a respective voltage lower than the respective voltage of the second module comprises a resistor selectively connectable to the first module, thereby reducing the voltage of the first module.

28. The apparatus of claim 26 wherein means causing the first module to be charged to a respective voltage lower than the respective voltage of the second module comprises means applying a smaller charging current to the first module than to the second module.

29. The apparatus of claim 26 wherein the means causing the first module to be charged to a respective voltage lower than the respective voltage of the second module comprises means applying a charging current to the first module for a shorter duration than to the second module.

30. The apparatus of claim 26 wherein the capacitors are ultracapacitors.

38. The apparatus of claim 26, further comprising a plurality of series modules of capacitors.

31. An apparatus for use with a series module of capacitors, each capacitor having a respective relative capacitance, each capacitor at a particular moment having a respective charge, each capacitor at a particular moment having a respective voltage, the apparatus comprising:

means arriving at an estimate of the respective relative capacitance of each capacitor by means of measurements of voltages at each of the capacitors;

means identifying a first capacitor in the series module having an estimated relative capacitance smaller than the estimated relative capacitance of a second capacitor in the series module; and

means causing the first capacitor to be charged to a respective level of charge lower than the respective level of charge of the second capacitor.

32. The apparatus of claim 31 wherein the means causing the first capacitor to be charged to a respective level of charge lower than the respective level of charge of the second capacitor comprises a resistor selectively connectable to the first capacitor, thereby reducing the charge of the first capacitor.

33. The apparatus of claim 31 wherein the capacitors are ultracapacitors.

34. The apparatus of claim 31 wherein the module at a particular moment has a respective current passing therethrough, the respective current at various times defining positive, negative, and zero values, the means arriving at an estimate of the respective relative capacity of each capacitor by means of measurements of voltages at each of the capacitors comprises means carrying out a multiplicity of relative capacity measurements and averaging the relative capacity measurements, each relative capacity measurement carried out by performing the steps of:

at a first time when the current passing through the module is at a value smaller than a first predetermined threshold, measuring the respective voltage at each of the capacitors, thereby defining a sum of the voltages representing a voltage across the series module;

at a second time, after the current passing through the module has exceeded the first predetermined threshold and has later dropped to a value smaller than the first predetermined threshold, again measuring the respective voltage at each of the capacitors, thereby again defining a sum of the voltages representing a voltage across the series module;

for each capacitor, a difference between the respective voltage at the first time and the respective voltage at the second time defining a respective voltage change;

for the series array, a difference between voltage across the series module at the first time and the voltage across the series module at the second time defining a respective voltage change for the series module;

for each capacitor, a ratio of its respective voltage change to the voltage change in the series module defining the each relative capacity measurement.

35. The method of claim 31 wherein the step of causing the first capacitor to be charged to a respective level of charge lower than the respective level of charge of the second capacitor is not performed at any of the times when measurements of voltages take place.

36. The method of claim 31 wherein the measurements of voltages take place only at times when the step of causing the first capacitor to be charged to a respective level of charge lower than the respective level of charge of the second capacitor is not taking place.

37. The apparatus of further comprising a series module of capacitors.

39. A method for use with a module comprising a series string of capacitors, the method comprising the steps of:

monitoring a current through the series string of capacitors; and

in the event of a predetermined combination of current through the series string of capacitors and voltage across the series string of capacitors, lowering or limiting the voltage across the series string of capacitors.

40. The method of claim 39 wherein the predetermined combination of current through the series string of capacitors and voltage across the series string of capacitors comprises the current exceeding a predetermined threshold.

41. An apparatus for use with a module comprising a series string of capacitors, the apparatus comprising:

means monitoring a current through the series string of capacitors; and

means responsive to the event of a predetermined combination of current through the series string of capacitors and voltage across the series string of capacitors, for lowering or limiting the voltage across the series string of capacitors.

42. The apparatus of claim 41 wherein the predetermined combination of current through the series string of capacitors and voltage across the series string of capacitors comprises the current exceeding a predetermined threshold.

43. The apparatus of claim 41 further comprising a module comprising a series string of capacitors.