Unintteruptible power supply systems and methods employing on-demand energy storage

• US 9,106,103 B2
• Filed: 09/23/2011
• Issued: 08/11/2015
• Est. Priority Date: 09/23/2011
• Status: Active Grant

• Current Assignee: Eaton Intelligent Power Limited (Eaton Corporation PLC.)
• Original Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Inventors: Paulakonis, Joseph Charles, Nandam, Pradeep Kumar
• Primary Examiner(s): Fureman, Jared
• Assistant Examiner(s): Perez Borroto, Alfonso
• Application Number:
  US13/243,207
• Publication Number:
  US 20130076141A1
• Time in Patent Office: 1,418 Days
• Field of Search: 307/66
• US Class Current: 1/1
• CPC Class Codes: H02J 7/345 using capacitors as storage or buffering devices
• CPC Class Codes: H02J 9/062 for AC powered loads
• CPC Class Codes: H02J 9/063 Common neutral, e.g. AC input neutral line connected to AC output neutral line and DC middle point

Abstract

An uninterruptible power supply (UPS) system includes first and second busses, a first switching circuit configured to selectively couple an AC source to the first and second busses and a second switching circuit configured to selectively couple the first and second busses to a load. The system also includes a storage capacitor and a third switching circuit configured to couple the storage capacitor between the first and second busses. The system further includes a control circuit configured to control the first, second and third switching circuits to generate an AC voltage at the load.

Claims

1. An uninterruptible power supply (UPS) system comprising:

first and second busses;

a first switching circuit configured to selectively couple an AC source to the first and second busses;

a second switching circuit configured to selectively couple the first and second busses to a load;

a storage capacitor;

a third switching circuit configured to couple the storage capacitor between the first and second busses;

a fourth switching circuit configured to couple an auxiliary power source to the first and second busses; and

a control circuit configured to control the first, second, third, and fourth switching circuits to generate an AC voltage at the load, wherein the control circuit is further configured to cause the third switching circuit to couple the storage capacitor between the first and second busses to maintain the AC voltage at the load while transitioning from supplying power to the load from the AC source to supplying power to the load from the auxiliary power source and to decouple the storage capacitor from at least one of the first and second busses after transitioning to supplying power to the load from the auxiliary power source.

2. The system of claim 1, wherein the fourth switching circuit comprises a mechanical relay configured to selectively couple the auxiliary power source to at least one of the first and second busses and wherein the third switching circuit comprises at least one semiconductor switch configured to couple the storage capacitor to at least one of the first and second busses.

3. The system of claim 1, wherein the storage capacitor comprises a first capacitor and wherein the system further comprises a second capacitor coupled between the first and second busses and having a capacitance substantially less than a capacitance of the storage capacitor.

4. The system of claim 1, wherein the control circuit is configured to cause the second switching circuit to alternately connect the first and second busses to a neutral node for successive half cycles of an AC waveform of the AC source.

5. The system of claim 4, wherein the second switching circuit comprises:

an inverter circuit configured to selectively couple the first and second busses to the neutral node; and

a buck converter circuit configured to selectively couple the first and second busses to the load.

6. The system of claim 1, wherein the control circuit is configured to operate the third switching circuit responsive to a state of the AC source.

7. The system of claim 1, wherein the control circuit is configured to cause the third switching circuit to couple the storage capacitor between the first and second busses in response to a failure of the AC source and/or in response to a voltage transient condition of the AC source.

8. The system of claim 1, wherein the control circuit is configured to cause the third switching circuit to momentarily couple the storage capacitor between the first and second busses to charge the storage capacitor from the AC source.

9. A UPS system comprising:

a boost rectifier circuit having an input port configured to be coupled to an AC source;

first and second busses coupled to an output port of the boost rectifier circuit;

a first capacitor having a first terminal coupled to the first bus and a second terminal coupled to the second bus;

a buck converter circuit having an input port coupled to the first and second busses and an output port configured to be coupled to a load;

an inverter circuit configured to selectively couple the first and second busses to a neutral to generate an AC output at the output of the buck converter circuit;

a second capacitor having a substantially greater capacitance than the first capacitor;

a first switching circuit configured to couple and decouple the second capacitor to and from at least one of the first and second busses responsive to a state of the AC source; and

a second switching circuit configured to couple an auxiliary power source to at least one of the first and second busses,

wherein the first switching circuit is configured to couple the second capacitor between the first and second busses to maintain the AC output while transitioning from supplying power to the load from the AC source to supplying power to the load from auxiliary power source and to decouple the second capacitor from at least one of the first and second busses after transitioning to supplying power to the load from the auxiliary power source.

10. The system of claim 9, wherein the first switching circuit is configured to couple the second capacitor between the first and second busses substantially more quickly than the second switching circuit couples the auxiliary power source to the at least one of the first and second busses.

11. The system of claim 9, wherein the second switching circuit comprises a mechanical relay configured to couple the auxiliary power source to at least one of the first and second busses and wherein the first switching circuit comprises a semiconductor switch configured to couple the second capacitor to at least one of the first and second busses.

12. The system of claim 9, further comprising a current limiting circuit configured to be coupled in series with the second capacitor.

13. The system of claim 9, wherein the first switching circuit is configured to momentarily couple the storage capacitor between the first and second busses to charge the storage capacitor from the AC source.

14. A method of operating a UPS system comprising a first switching circuit configured to selectively couple an AC source to first and second busses and a second switching circuit configured to selectively couple the first and second busses to a load, the method comprising:

detecting a state of the AC source;

coupling a storage capacitor between the first and second busses responsive to the detected state of the AC source to maintain an AC output to the load;

coupling a battery to at least one of the first and second busses to provide power to the load from the battery; and

then

decoupling the storage capacitor from at least one of the first and second busses.

15. The method of claim 14, wherein the storage capacitor comprises a first capacitor, wherein the UPS system further comprises a second capacitor coupled between the first and second busses and having substantially less capacitance than the first capacitor and wherein coupling a storage capacitor between the first and second busses responsive to the detected state of the AC source comprises coupling the first capacitor in parallel with the second capacitor.

16. The method of Claim 14, wherein coupling a battery to at least one of the first and second busses comprises actuating a mechanical relay to couple the battery to at least one of the first and second busses and wherein coupling a storage capacitor between the first and second busses responsive to the detected state of the AC source comprises activating a semiconductor switch to couple the storage capacitor to at least one of the first and second busses.