Uninterruptible power supplies with dual-sourcing capability and methods of operation thereof

• US 6,160,722 A
• Filed: 09/22/1999
• Issued: 12/12/2000
• Est. Priority Date: 08/13/1999
• Status: Expired due to Term

• Current Assignee: Eaton Intelligent Power Limited (Eaton Corporation PLC.)
• Original Assignee: Powerware Corporation (Eaton Corporation PLC.)
• Inventors: Thommes, James, Johnson, Robert W. Jr., Raddi, William J.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): Vu, Bao Q.
• Application Number:
  US09/401,423
• Time in Patent Office: 447 Days
• Field of Search: 363/37, 363/56, 363/58, 363/17, 363/24, 363/132, 363/134, 307/66, 307/68
• US Class Current: 363/37
• CPC Class Codes: H02J 9/061 for DC powered loads
• 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
• CPC Class Codes: H02M 5/4585 having a rectifier with controlled elements

Abstract

An uninterruptible power supply (UPS) includes an AC source port configured to connect to an AC power source, a DC source port configured to connect to a DC power source and a load port configured to connect to a load. A rectifier circuit is operative to selectively couple the AC source port to first and second voltage busses through a first inductance. An inverter circuit is operative to selectively couple the load port to the first and second voltage busses through a second inductance. A bidirectional DC source coupling circuit is operative to couple the DC source port to the first and second voltage busses to provide bidirectional power transfer therebetween, preferably such that a voltage at the DC source port is maintained in a substantially fixed proportion to first and second DC voltages at respective ones of the first and second voltage busses. In one embodiment, the bidirectional DC source coupling circuit includes a transformer having first and second inductively coupled windings, the first winding having first and second end taps and a center tap coupled to the neutral bus. A switching circuit is operative to selectively couple the first end tap of the first winding to the first and second voltage busses. A rectifying circuit couples the second end tap of the first winding to the first and second voltage busses. A bidirectional DC-AC converter circuit is coupled between the second winding and the DC source port. Related operating methods are also discussed.

Claims

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

an AC source port configured to connect to an AC power source;

a load port configured to connect to a load;

a rectifier circuit that selectively couples the AC source port to first and second voltage busses through a first inductance;

an inverter circuit that selectively couples the load port to the first and second voltage busses through a second inductance; and

a bidirectional DC source coupling circuit operative to couple a DC power source to the first and second voltage busses to provide bidirectional power transfer between the DC power source and the first and second voltage busses.

2. A UPS according to claim 1, further comprising a DC source port configured to connect to a DC power source, and wherein the bidirectional DC source coupling circuit inductively couples the DC source port to the first and second voltage busses to provide bidirectional power transfer between the DC source port and the first and second voltage busses such that a voltage at the DC source port is maintained in a substantially fixed proportion to first and second DC voltages at respective ones of the first and second voltage busses.

3. A UPS according to claim 2, further comprising a control circuit operative to generate a rectifier control signal and an inverter control signal responsive to at least a load voltage at the load port, wherein the rectifier circuit is responsive to the rectifier control signal to control coupling of the AC source port to the first and second voltage busses, and wherein the inverter circuit is responsive to the inverter control signal to control coupling of the load port to the first and second voltage busses.

4. A UPS according to claim 3:

wherein the AC source port comprises a phase bus and a neutral bus;

wherein the bidirectional DC source coupling circuit comprises a balancer circuit coupled between the first and second voltage busses and operative to selectively couple the first and second voltage busses to the neutral bus through a transformer responsive to a balancer control signal; and

wherein the control circuit is operative to generate the balancer control signal such that the first and second DC voltages are constrained to have substantially equal magnitudes.

5. A UPS according to claim 3, wherein the control circuit is responsive to the voltage at the load port to control the rectifier circuit and the inverter circuit such that current at the AC source port varies up to a current limit to maintain the load voltage at the nominal voltage, and such that, when the current at the AC source port reaches the current limit and the voltage, power is transferred to the load port from both the AC source port and the DC source port to maintain the load terminal at the nominal voltage.

6. A UPS according to claim 5, wherein the control circuit is operative to limit the current at the AC source port.

7. A UPS according to claim 3:

wherein the AC source port comprises a phase bus and a neutral bus;

wherein the load port comprises a load bus and the neutral bus; and

wherein the control circuit is operative to control the rectifier circuit and the inverter circuit such that the phase bus is coupled to respective ones of the first and second voltage busses in a substantially complementary manner and such that the load bus is coupled to respective ones of the first and second voltage busses in a substantially complementary manner.

8. A UPS according to claim 3:

wherein the AC source port comprises a phase bus and a neutral bus;

wherein the load port comprises a load bus and the neutral bus; and

wherein the rectifier circuit comprises;

a first inductor having a first terminal coupled to the phase bus;

a first switch responsive to a first switch control signal to couple and decouple a second terminal of the first inductor and the first voltage bus; and

a second switch responsive to a second switch control signal to couple and decouple the second terminal of the first inductor and the second voltage bus;

wherein the inverter circuit comprises;

a second inductor having a first terminal coupled to the load bus;

a third switch responsive to a third switch control signal to couple and decouple a second terminal of the second inductor and the first voltage bus; and

a fourth switch responsive to a fourth switch control signal to couple and decouple the second terminal of the second inductor and the second voltage bus; and

wherein the control circuit is operative to generate the first, second, third and fourth switch control signals responsive to at least the load voltage at the load port.

9. A UPS according to claim 8, wherein the control circuit operates the first and second switches at substantially complementary duty cycles, and wherein the control circuit operates the third and fourth switches at substantially complementary duty cycles.

10. A UPS according to claim 2:

wherein the AC source port comprises a phase bus and a neutral bus;

wherein the load port comprises a load bus and the neutral bus; and

wherein the bidirectional DC source coupling circuit comprises;

a transformer having first and second inductively coupled windings, the first winding having first and second end taps and a center tap coupled to the neutral bus;

a switching circuit operative to selectively couple the first end tap of the first winding to the first and second voltage busses;

a rectifying circuit coupling the second end tap of the first winding to the first and second voltage busses; and

a bidirectional DC-AC converter circuit coupled between the second winding and the DC source port.

11. A UPS according to claim 10, wherein the switching circuit is operative to constrain the first and second DC voltages to be substantially equal.

12. A UPS according to claim 10, further comprising a control circuit operative to generate first and second control signals, and wherein the switching circuit comprises:

a first switch responsive to the first switch control signal to couple and decouple the first end tap of the first winding of the transformer and the first voltage bus; and

a second switch responsive to the second switch control signal to couple and decouple the first end tap of the first winding of the transformer and the second voltage bus.

13. A UPS according to claim 12, wherein the control circuit constrains the first and second switches to operate at substantially complementary duty cycles of approximately 50%.

14. A UPS according to claim 10, wherein the DC-AC converter circuit comprises a full bridge switching circuit that selectively couples first and second terminals of the DC source port to first and second taps of the second winding of the transformer.

15. A UPS according to claim 10, wherein the rectifying circuit comprises one of:

first and second diodes connected between the second end tap of the first winding of the transformer and respective ones of the first and second voltage busses;

or

seventh and eighth switches connected between the second end tap of the first winding of the transformer and respective ones of the first and second voltage busses.

16. An uninterruptible power supply (UPS), comprising:

an AC source port configured to connect to an AC power source, the AC source port including a phase bus and a neutral bus;

a DC source port configured to connect to a DC power source;

a load port configured to connect to a load, the load port including a load bus and the neutral bus;

first and second voltage busses;

a first switching circuit that selectively couples the phase bus to the first and second voltage busses through a first inductance;

a second switching circuit that selectively couples the load bus to the first and second voltage busses through a second inductance;

a transformer including first and second inductively coupled windings, the first winding including a center tap coupled to the neutral bus;

a third switching circuit that selectively couples the first and second voltage busses to a first end tap of the first winding;

a rectifying circuit that rectifyingly couples a second end tap of the first winding to the first and second voltage busses; and

a DC-AC converter circuit that selectively couples the DC source port to the second winding.

17. A UPS according to claim 16, further comprising a control circuit operative to control the first and second switching circuits responsive to at least a load voltage at the load port.

18. A UPS according to claim 17, wherein the control circuit is operative to control the third switching circuit such that first and second DC voltages at respective ones of the first and second voltage busses are constrained to have substantially equal magnitudes.

19. A UPS according to claim 17, wherein the control circuit is responsive to the voltage at the load port to control the first and second switching circuits such that current at the phase bus varies up to a current limit to maintain the load voltage at the nominal voltage, and such that, when the current at the phase bus reaches the current limit, power is transferred to the load port from both the AC source port and the DC source port to maintain the load terminal at the nominal voltage.

20. A UPS according to claim 19, wherein the control circuit is operative to limit the current at the phase bus.

21. A UPS according to claim 17, wherein the control circuit is operative to control the first and second switching circuits such that the phase bus is coupled to respective ones of the first and second voltage busses in a substantially complementary manner and such that the load bus is coupled to respective ones of the first and second voltage busses in a substantially complementary manner.

22. A UPS according to claim 17:

wherein the first switching circuit comprises;

a first inductor having a first terminal coupled to the phase bus;

a first switch responsive to a first switch control signal to couple and decouple a second terminal of the first inductor and the first voltage bus; and

a second switch responsive to a second switch control signal to couple and decouple the second terminal of the first inductor and the second voltage bus;

wherein the second switching circuit comprises;

a second inductor having a first terminal coupled to the load bus;

a third switch responsive to a third switch control signal to couple and decouple a second terminal of the second inductor and the first voltage bus; and

a fourth switch responsive to a fourth switch control signal to couple and decouple the second terminal of the second inductor and the second voltage bus; and

wherein the control circuit is operative to generate the first, second, third and fourth switch control signals responsive to at least the load voltage at the load port.

23. A UPS according to claim 22, wherein the control circuit operates the first and second switches at substantially complementary duty cycles, and wherein the control circuit operates the third and fourth switches at substantially complementary duty cycles.

24. A UPS according to claim 22:

wherein the third switching circuit comprises;

a fifth switch responsive to a fifth switch control signal to couple and decouple the first end tap of the first winding of the transformer and the first voltage bus; and

a sixth switch responsive to a sixth switch control signal to couple and decouple the first end tap of the first winding of the transformer and the second voltage bus; and

wherein the control circuit is operative to generate the fifth and sixth switch control signals.

25. A UPS according to claim 24, wherein the control circuit constrains the fifth and sixth switches to operate at substantially complementary duty cycles of approximately 50%.

26. A UPS according to claim 16, wherein the DC-AC converter circuit comprises a full bridge switching circuit that selectively couples first and second terminals of the DC source port to first and second taps of the second winding of the transformer.

27. A UPS according to claim 16, wherein the rectifying circuit comprises one of:

first and second diodes connected between the second end tap of the first winding of the transformer and respective ones of the first and second voltage busses;

or

first and second switches connected between the second end tap of the first winding of the transformer and respective ones of the first and second voltage busses.

28. A method of selectively transferring power to a load from an AC source and a DC source, the method comprising the steps of:

selectively coupling the AC source to first and second voltage busses through a first inductance;

selectively coupling the load to the first and second voltage busses through a second inductance; and

bidirectionally coupling the DC source to the first and second voltage busses to provide bidirectional power transfer between the DC source and the first and second voltage busses.

29. A method according to claim 28, wherein said step of bidirectionally coupling comprises the step of inductively coupling the DC source to the first and second voltage busses to provide bidirectional power transfer between the DC source and the first and second voltage busses such that a voltage at the DC source is maintained in a substantially fixed proportion to first and second DC voltages at respective ones of the first and second voltage busses.

30. A method according to claim 29, further comprising the step of selectively coupling the first and second voltage busses to a neutral bus through a transformer such that the first and second DC voltages are constrained to have substantially equal magnitudes.

31. A method according to claim 30, further comprising the steps of:

selectively coupling the AC source port to the first and second voltage busses such that current at the AC source varies up to a current limit to maintain the load voltage at the nominal voltage; and

when the current at the AC source port reaches the current limit and the voltage, transferring power to the load port from both the AC source and the DC source to maintain the load voltage at the nominal voltage.

32. A method according to claim 29:

wherein said step of selectively coupling the AC source comprises the step of selectively coupling a phase bus of the AC source to respective ones of the first and second voltage busses in a substantially complementary manner; and

wherein said step of selectively coupling the load comprises the step of selectively coupling the load to respective ones of the first and second voltage busses in a substantially complementary manner.

33. A method according to claim 30 wherein said step of bidirectionally coupling comprises the steps of:

selectively coupling the neutral bus to the first and second voltage busses through a first portion of a first winding of a transformer having first and second inductively coupled windings;

rectifyingly coupling the first and second voltage busses to the neutral bus through a second portion of the first winding of the transformer;

selectively coupling first and second terminals of the DC source to first and second end taps of the second winding of the transformer.