Method and apparatus for providing uninterruptible power

• US 20060044846A1
• Filed: 08/31/2004
• Published: 03/02/2006
• Est. Priority Date: 08/31/2004
• Status: Active Grant

• Current Assignee: American Power Conversion Corporation (Schneider Electric SE)
• Original Assignee: American Power Conversion Corporation (Schneider Electric SE)
• Inventors: Nielsen, Henning Roar, Hjort, Thomas Enne
• Granted Patent: US 7,274,112 B2
• Time in Patent Office: Days
• US Class Current: 363/34
• CPC Class Codes: H02J 9/062 for AC powered loads
• CPC Class Codes: H03K 17/687 the devices being field-effect transistors

Abstract

Methods and apparatus for providing uninterruptible power are provided by aspects of the invention. One aspect is more particularly directed to an uninterruptible power supply for providing power to a load. The uninterruptible power supply includes an input to receive input power, an output to provide output power, an input power circuit coupled to the input and having a DC output that provides DC power having a first DC voltage level, a capacitor having a first end coupled to the DC output of the input power circuit and having a second end, a back-up power source coupled to the input power circuit, an output power circuit coupled to the DC output of the input power circuit and to the output of the uninterruptible power supply to provide the output power, and a capacitor discharge circuit coupled to the first end of the capacitor and the second end of the capacitor and configured in a first mode of operation to discharge a voltage across the capacitor, such that an average discharge current through the discharge circuit is inversely proportional to a voltage across the capacitor for a first range of voltages across the capacitor.

Claims

1. An uninterruptible power supply for providing power to a load, the uninterruptible power supply comprising:

an input to receive input power;

an output to provide output power;

an input power circuit coupled to the input and having a DC output that provides DC power having a first DC voltage level;

a capacitor having a first end coupled to the DC output of the input power circuit and having a second end;

a back-up power source coupled to the input power circuit;

an output power circuit coupled to the DC output of the input power circuit and to the output of the uninterruptible power supply to provide the output power; and

a capacitor discharge circuit coupled to the first end of the capacitor and the second end of the capacitor and configured in a first mode of operation to discharge a voltage across the capacitor, such that an average discharge current through the discharge circuit is inversely proportional to a voltage across the capacitor for a first range of voltages across the capacitor.

2. The uninterruptible power supply of claim 1, wherein the capacitor discharge circuit is configured in a second mode of operation such that the discharge current through the discharge circuit is proportional to the voltage across the capacitor for a second range of voltages that is less than the first range of voltages.

3. The uninterruptible power supply of claim 2, wherein the capacitor discharge circuit is configured in the first mode of operation to control the discharge current, such that the discharge current has a waveform containing a series of pulses with a duty cycle of the pulses being inversely proportional to the voltage across the capacitor over at least the first range of voltages.

4. The uninterruptible power supply of claim 3, wherein the first range of voltages is equal to a range of voltages from a lower threshold level to the first DC voltage level, and the second range of voltages is equal to a range of voltages from zero to the lower threshold level.

5. The uninterruptible power supply of claim 4, wherein the capacitor discharge circuit includes:

a passive discharge circuit having an input coupled to the first end of the capacitor and an output;

a switch having an input coupled to the output of the passive discharge circuit and an output coupled to the second end of the capacitor; and

a control circuit coupled to the switch to control an operational state of the switch based on the voltage across the capacitor.

6. The uninterruptible power supply of claim 1, wherein the capacitor discharge circuit is configured in the first mode of operation to control the discharge current, such that the discharge current has a waveform containing a series of pulses with a duty cycle of the pulses being inversely proportional to the voltage across the capacitor over at least the first range of voltages.

7. The uninterruptible power supply of claim 1, wherein the capacitor discharge circuit includes:

a passive discharge circuit having an input coupled to the first end of the capacitor and an output;

a switch having an input coupled to the output of the passive discharge circuit and an output coupled to the second end of the capacitor; and

a control circuit coupled to the switch to control an operational state of the switch based on the voltage across the capacitor.

8. An uninterruptible power supply for providing power to a load, the uninterruptible power supply comprising:

an input to receive input power;

an output to provide output power;

an input power circuit coupled to the input and having a DC output that provides DC power having a first DC voltage level;

a capacitor having a first end coupled to the DC output of the input power circuit and having a second end;

a back-up power source coupled to the input power circuit;

an output power circuit coupled to the DC output of the input power circuit and to the output of the uninterruptible power supply to provide the output power; and

means for discharging a voltage across the capacitor, such that an average discharge current of the capacitor is inversely proportional to a voltage across the capacitor for a first range of voltages across the capacitor.

9. The uninterruptible power supply of claim 8, further comprising means for discharging the voltage across the capacitor such that the discharge current is proportional to the voltage across the capacitor for a second range of voltages that is less than the first range of voltages.

10. The uninterruptible power supply of claim 9, further comprising means for discharging the voltage across the capacitor such that the discharge current has a waveform containing a series of pulses with a duty cycle of the pulses being inversely proportional to the voltage across the capacitor over at least the first range of voltages.

11. The uninterruptible power supply of claim 10, wherein the first range of voltages is equal to a range of voltages from a lower threshold level to the first DC voltage level, and the second range of voltages is equal to a range of voltages from zero to the lower threshold level.

12. The uninterruptible power supply of claim 8, further comprising means for discharging the voltage across the capacitor such that the discharge current has a waveform containing a series of pulses with a duty cycle of the pulses being inversely proportional to the voltage across the capacitor over at least the first range of voltages.

13. The uninterruptible power supply of claim 9, wherein the first range of voltages is equal to a range of voltages from a lower threshold level to the first DC voltage level, and the second range of voltages is equal to a range of voltages from zero to the lower threshold level.

14. A method of discharging a voltage across a capacitor in a uninterruptible power supply, the method comprising:

charging the capacitor to a first voltage value;

detecting the voltage across the capacitor; and

discharging the capacitor using a discharge current having an average value that is inversely proportional to the voltage across the capacitor, such that over at least a first range of voltages across the capacitor, the average value of the discharge current increases as the voltage across the capacitor decreases.

15. The method of claim 14, further comprising:

during discharge of the capacitor, detecting that the voltage across the capacitor has decreased to a second voltage value, less than the first voltage value;

discharging the capacitor using a discharge current having an average value that is proportional to the voltage across the capacitor, such that for a second range of voltages the average value of the discharge current decreases as the voltage across the capacitor decreases.

16. The method of claim 15, further comprising controlling the discharge current, while the voltage across the capacitor is within the first voltage range, such that the discharge current has a waveform containing a series of pulses with a duty cycle of the pulses being inversely proportional to the voltage across the capacitor over the first range of voltages.

17. The method of claim 16, further comprising controlling the discharge current to be continuous over the second range of voltages.

18. The method of claim 17, wherein the first range of voltages is equal to a range of voltages from the first voltage value to the second voltage value, and the second range of voltages is equal to a range of voltages from the second voltage value to a voltage level of zero.

19. The method of claim 14, further comprising controlling the discharge current, while the voltage across the capacitor is within the first voltage range such that the discharge current has a waveform containing a series of pulses with a duty cycle of the pulses being inversely proportional to the voltage across the capacitor over the first range of voltages.

20. The method of claim 15, further comprising controlling the discharge current to be continuous over the second range of voltages.

21. The method of claim 15, wherein the first range of voltages is equal to a range of voltages from the first voltage value to the second voltage value, and the second range of voltages is equal to a range of voltages from the second voltage value to a voltage level of zero.