Dual feed power supply systems with enhanced power quality

• US 20040070278A1
• Filed: 10/15/2002
• Published: 04/15/2004
• Est. Priority Date: 10/15/2002
• Status: Active Grant

• Current Assignee: Rockwell Automation, Inc.
• Original Assignee: Soft Switching Technologies Corp. (Rockwell Automation, Inc.)
• Inventors: Kranz, William R., Schneider, Robert, Divan, Deepakraj M.
• Granted Patent: US 7,129,599 B2
• Time in Patent Office: Days
• US Class Current: 307/64
• CPC Class Codes: H02J 3/0073 for providing alternative feeding paths between load and source when the main path fails, e.g. transformers, busbars
• CPC Class Codes: Y04S 10/52 Outage or fault management, e.g. fault detection or location

Abstract

A dual feed power supply system provides the high reliability of a dual utility feed, with minimization of interruptions in the power supplied to critical loads during switching, and compensation for voltage sags occurring on the primary power feed. First and second AC input buses are connected through a transfer switching apparatus to each of the phase lines of a distribution bus. The transfer switching apparatus has a first input terminal connected to one of the phase lines of the first input bus and a second input terminal connected to one of the phase lines of the second input bus, and an output terminal connected to one of the phase lines of the distribution bus. Input switches allow switching from one or the other of the AC input buses to the distribution bus, with a fast transfer switch used to interrupt the supply of power from the input buses to the distribution bus during switching of the input switches. Power is drawn from a DC energy storage device through an inverter to supply AC power to the distribution bus during switching events to minimize interruption of the power supplied to the distribution bus and to critical loads connected thereto. Power may also be drawn from the input buses during voltage sags on one or both of the buses and delivered through the inverter to the distribution bus at the desired nominal output voltage levels.

Claims

1. A transfer switching apparatus comprising:

(a) a first input terminal and a second input terminal each of which may be provided with AC power from one of the lines of two separate AC input buses, and an output terminal that is available for connection to one of the lines of a distribution bus;

(b) a first input switch connected between the first input terminal and a junction node and a second input switch connected between the second input terminal and the junction node, the input switches responsive to control signals to open and close, the first input switch being normally closed and the second input switch being normally open, and a bi-directional transfer switch connected between the junction node and the output terminal, the transfer switch responsive to control signals to open and close the transfer switch;

(c) a first rectifier connected to the first input terminal to receive AC power therefrom and provide DC output voltage to DC bus lines and a second rectifier connected to the second input terminal to receive AC power therefrom and provide DC voltage to the DC bus lines in parallel with the DC voltage provided by the first rectifier, the first and second rectifiers connected to the first and second input terminals independently of the first and second input switches;

(d) a DC electrical energy storage device connected to the DC bus lines to receive DC power therefrom and deliver DC power thereto; and

(e) an inverter connected to the DC bus lines and having an AC output connected to the output terminal, the inverter responsive to control signals to provide AC output voltage to the output terminal.

2. The apparatus of claim 1 including a controller means connected to provide control signals to the first and second input switches, to the transfer switch and to the inverter, and connected to receive signals indicating the voltage at the first and second input terminals and at the output terminal, the controller means normally controlling the first and second input switches to maintain the first input switch closed and the second input switch open and controlling the transfer switch to maintain it closed during normal availability of power at the first input terminal, and upon a fault condition of the power provided to the first input terminal controlling the transfer switch to open and controlling the inverter to provide AC output power to the output terminal, then controlling the first input switch to open, then controlling the second input switch to close, then controlling the transfer switch to close to provide AC power from the second input terminal to the output terminal while controlling the inverter to turn off and cease supplying output power to the output terminal.

3. The apparatus of claim 1 including a controller means connected to provide control signals to the inverter for controlling the inverter to turn on to provide AC power at the phase and frequency of the power provided from the first input terminal through the first input switch and to turn off the transfer switch when a selected level of sag occurs in the AC voltage at the first input terminal to maintain the voltage level at the output terminal at a selected nominal voltage level greater than the level of voltage available at the first input terminal.

4. The apparatus of claim 3 further including a voltage boosting auto-transformer connected between the output of the inverter and the output terminal.

5. The apparatus of claim 1 wherein the DC electrical energy storage device comprises a capacitor.

6. The apparatus of claim 1 wherein the DC electrical energy storage device comprises two capacitors connected together at a node and connected in series across the DC bus lines, wherein the first and second rectifiers are formed as pairs of diodes, each connected together at a node and connected in series across the DC bus lines, the nodes between the pairs of diodes in the first and second rectifiers connected respectively to the first and second input terminals, and further including a neutral return line connected to the node between the capacitors to provide a current return path for power supplied to the first and second input terminals.

7. The apparatus of claim 6 wherein the inverter comprises two gate controlled static switches each with anti-parallel diodes, the static switches connected together at a node and connected in series across the DC bus lines.

8. The apparatus of claim 7 wherein the static switches of the inverter are insulated gate bipolar transistors.

9. The apparatus of claim 6 including a transformer for each input bus, wherein the first and second output terminals are each connected to a single phase secondary of one of the transformers having a primary connectable to AC input bus lines, wherein the single phase secondaries are connected together at a node that is connected to the neutral return line.

10. The apparatus of claim 9 wherein the transformer having a secondary connected to the first input terminal has a selected high duty rating and the transformer having a secondary connected to the second input terminal has a low duty rating which is less than the rating of the transformer connected to the first output terminal.

11. The apparatus of claim 1 further including a boost transformer connected between the AC output of the inverter and the output terminal to provide a boost in the AC voltage from the inverter as applied to the output terminal.

12. The apparatus of claim 1 further including an inductor connected between the output of the inverter and the output terminal.

13. The apparatus of claim 1 wherein the transfer switch is a static switch comprised of anti-parallel connected thyristor

14. The apparatus of claim 1 wherein the input switches are electromechanical switches.

60. The apparatus of claim 1 wherein the first and second input switches are static switches comprised of anti-parallel connected thyristors.

15. A dual feed power supply system comprising:

(a) a first AC input bus and a second AC input bus each having three phase lines;

(b) an AC distribution bus having three phase lines;

(c) for each of the three phases of the input buses and the distribution bus, a transfer switching apparatus connected to receive power from phase lines of the AC input buses and connected to supply power to a phase line of the distribution bus, each transfer switching apparatus comprising;

(1) a first input terminal and a second input terminal each of which is connected to be provided with AC power from one of the phase lines of the AC input buses, and an output terminal that is connected to one of the phase lines of the distribution bus;

(2) a first input switch connected between the first input terminal and a junction node and a second input switch connected between the second input terminal and the junction node, the input switches responsive to control signals to open and close, the first input switch being normally closed and the second input switch being normally open, and a bi-directional transfer switch connected between the junction node and the output terminal, the transfer switch responsive to control signals to open and close the transfer switch;

(3) a first rectifier connected to the first input terminal to receive AC power therefrom and provide DC output voltage to DC bus lines and a second rectifier connected to the second input terminal to receive AC power therefrom and provide DC voltage to the DC bus lines in parallel with the DC voltage provided by the first rectifier, the first and second rectifiers connected to the first and second input terminals independently of the first and second input switches;

(4) a DC electrical energy storage device connected to the DC bus lines to receive DC power therefrom and deliver DC power thereto;

(5) an inverter connected to the DC bus lines and having an AC output connected to the output terminal, the inverter responsive to control signals to provide AC output voltage to the output terminal; and

(6) controller means connected to provide control signals to the first and second input switches, to the transfer switch and to the inverter, and connected to receive signals indicating the voltage at the first and second input terminals and at the output terminal, the controller means normally controlling the first and second input switches to maintain the first input switch closed and the second input switch open and controlling the transfer switch to maintain it closed during normal availability of power at the first input terminal, and upon a fault condition of the power provided to the first input terminal controlling the transfer switch to open and controlling the inverter to provide AC output power to the output terminal, then controlling the first input switch to open, then controlling the second input switch to close, then controlling the transfer switch to close to provide AC power from the second input terminal to the output terminal while controlling the inverter to turn off and cease supplying output power to the output terminal.

16. The power supply system of claim 15 including a controller means connected to provide control signals to the inverter for controlling the inverter to turn on to provide AC power at the phase and frequency of the power provided from the first input terminal through the first electromechanical switch and to turn off the transfer switch when a selected level of sag occurs in the AC voltage at the first input terminal to maintain the voltage level at the output terminal at a selected nominal voltage level greater than the level of voltage available at the first input terminal.

17. The power supply system of claim 16 further including a voltage boosting auto-transformer connected between the output of the inverter and the output terminal.

18. The power supply system of claim 15 wherein the DC electrical energy storage device comprises a capacitor.

19. The power supply system of claim 15 wherein the DC electrical energy storage device comprises two capacitors connected together at a node and connected in series across the DC bus lines, wherein the first and second rectifiers are formed as pairs of diodes, each connected together at a node and connected in series across the DC bus lines, the nodes between the pairs of diodes in the first and second rectifiers connected respectively to the first and second input terminals, and further including a neutral return line connected to the node between the capacitors to provide a current return path for power supplied to the first and second input terminals.

20. The power supply system of claim 19 wherein the inverter comprises two gate controlled static switches each with anti-parallel diodes, the static switches connected together at a node and connected in series across the DC bus lines.

21. The power supply system of claim 20 wherein the static switches of the inverter are insulated gate bipolar transistors.

22. The power supply system of claim 19 including a transformer having a primary coupled to each input bus, wherein the first and second input terminals are each connected to a single phase secondary of one of the transformers, wherein the single phase secondaries are connected together at a node that is connected to a neutral return line.

23. The power supply system of claim 22 wherein the transformer having a secondary connected to the first input terminal has a selected high duty rating and the transformer having a secondary connected to the second input terminal has a low duty rating which is less than the rating of the transformer connected to the first output terminal.

24. The power supply system of claim 15 further including a boost transformer connected between the AC output of the inverter and the output terminal to provide a boost in the AC voltage from the inverter as applied to the output terminal.

25. The power supply system of claim 15 further including an inductor connected between the output of the inverter and the output terminal.

26. The power supply system of claim 15 wherein the transfer switch is a static switch comprised of anti-parallel connected thyristors.

27. The power supply system of claim 15 wherein the distribution bus is a first distribution bus, and further including a second three phase AC distribution bus, and including for each of the three phases of the second distribution bus, a transfer switching apparatus connected to receive power from the AC input buses and connected to supply power to a phase line of the second AC distribution bus, each transfer switching apparatus comprising:

(a) a first input terminal and a second input terminal each of which is provided with AC power from one of the phase lines of AC input buses, and an output terminal that is for connection to one of the phase lines of the second distribution bus;

(b) a first input switch connected between the first input terminal and a junction node and a second input switch connected between the second input terminal and the junction node, the input switches responsive to control signals to open and close, the first input switch being normally open and the second input switch being normally closed, and a bi-directional transfer switch connected between the junction node and the output terminal, the transfer switch responsive to control signals to open and close the transfer switch;

(c) a first rectifier connected to the first input terminal to receive AC power therefrom and provide DC output voltage to DC bus lines and a second rectifier connected to the second input terminal to receive AC power therefrom and provide DC voltage to the DC bus lines in parallel with the DC voltage provided by the first rectifier, the first and second rectifiers connected to the first and second input terminals independently of the first and second input switches;

(d) a DC electrical energy storage device connected to the DC bus lines to receive DC power therefrom and deliver DC power thereto;

(e) an inverter connected to the DC bus lines and having an AC output connected to the output terminal, the inverter responsive to control signals to provide AC output voltage to the output terminal;

(f) controller means connected to provide control signals to the first and second input switches, to the transfer switch and to the inverter, and connected to receive signals indicating the voltage at the first and second input terminals and at the output terminal, the controller means normally controlling the first and second input switches to maintain the second input switch closed and the first input switch open and controlling the transfer switch to maintain it closed during normal availability of power at the second input terminal, and upon a fault condition of the power provided to the second input terminal controlling the transfer switch to open and controlling the inverter to provide AC output power to the output terminal, then controlling the second input switch to open, then controlling the first input switch to close, then controlling the transfer switch to close to provide AC power from the first input terminal to the output terminal while controlling the inverter to turn off and cease supplying output power to the output terminal.

28. The power supply system of claim 27 including a controller means for each of the transfer switching apparatus connected to supply power to the second distribution bus that is connected to provide control signals to the inverter for controlling the inverter to turn on to provide AC power at the phase and frequency of the power provided from the first input terminal through the first switch and to turn off the transfer switch when a selected level of sag occurs in the AC voltage at the second input terminal to maintain the voltage level at the output terminal at a selected nominal voltage level greater than the level of voltage available at the second input terminal.

29. The power supply system of claim 28 further including for each of the transfer switching apparatus connected to the second distribution bus a voltage boosting auto-transformer connected between the output of the inverter and the output terminal.

30. The power supply system of claim 27 wherein the DC electrical energy storage device of the transfer switching apparatus comprises a capacitor.

31. The power supply system of claim 27 wherein the DC electrical energy storage device in the transfer switching apparatus comprises two capacitors connected together at a node and connected in series across DC bus lines, wherein the first and second rectifiers are formed as pairs of diodes, each connected together at a node and connected in series across the DC bus lines, the nodes between the pairs of diodes in the first and second rectifiers connected respectively to the first and second input terminals, and further including a neutral return line connected to the node between the capacitors to provide a current return path for power supplied to the first and second input terminals.

32. The power supply system of claim 15 wherein the input switches are electro-mechanical switches.

33. A transfer switching apparatus comprising:

(a) a first input terminal and a second input terminal each of which may be provided with AC power from one of the lines of two separate AC input buses, and an output terminal that is available for connection to one of the lines of a distribution bus;

(b) a first input switch connected between the first input terminal and a junction node and a second input switch connected between the second input terminal and the junction node, the input switches responsive to control signals to open and close, the first input switch being normally closed and the second input switch being normally open, and a bi-directional transfer switch connected between the junction node and the output terminal, the transfer switch responsive to control signals to open and close the transfer switch;

(c) a first rectifier connected to the first input terminal to receive AC power therefrom and provide DC output voltage to DC bus lines and a second rectifier connected to the second input terminal to receive AC power therefrom and provide DC voltage to the DC bus lines in parallel with the DC voltage provided by the first rectifier, the first and second rectifiers connected to the first and second input terminals independently of the first and second input switches;

(d) a DC electrical energy storage device connected to the DC bus lines to receive DC power therefrom and deliver DC power thereto;

(e) an inverter connected to the DC bus lines and having an AC output connected to the output terminal, the inverter responsive to control signals to provide AC output voltage to the output terminal; and

(f) a controller means connected to provide control signals to the inverter for controlling the inverter to turn on to provide AC power at the phase and frequency of the power provided from the first input terminal through the first input switch and to turn off the transfer switch when a selected level of sag occurs in the AC voltage at the first input terminal to maintain the voltage level at the output terminal at a selected nominal voltage level greater than the level of voltage available at the first input terminal.

34. The apparatus of claim 33 including a controller means connected to provide control signals to the first and second input switches, to the transfer switch and to the inverter, and connected to receive signals indicating the voltage at the first and second input terminals and at the output terminal, the controller means normally controlling the first and second input switches to maintain the first input switch closed and the second input switch open and controlling the transfer switch to maintain it closed during normal availability of power at the first input terminal, and upon a fault condition of the power provided to the first input terminal controlling the transfer switch to open and controlling the inverter to provide AC output power to the output terminal, then controlling the first input switch to open, then controlling the second input switch to close, then controlling the transfer switch to close to provide AC power from the second input terminal to the output terminal while controlling the inverter to turn off and cease supplying output power to the output terminal.

35. The apparatus of claim 33 further including a voltage boosting auto-transformer connected between the output of the inverter and the output terminal.

36. The apparatus of claim 33 wherein the DC electrical energy storage device comprises a capacitor.

37. The apparatus of claim 33 wherein the DC electrical energy storage device comprises two capacitors connected together at a node and connected in series across the DC bus lines, wherein the first and second rectifiers are formed as pairs of diodes, each connected together at a node and connected in series across the DC bus lines, the nodes between the pairs of diodes in the first and second rectifiers connected respectively to the first and second input terminals, and further including a neutral return line connected to the node between the capacitors to provide a current return path for power supplied to the first and second input terminals.

38. The apparatus of claim 37 wherein the inverter comprises two gate controlled static switches each with anti-parallel diodes, the static switches connected together at a node and connected in series across the DC bus lines.

39. The apparatus of claim 38 wherein the static switches of the inverter are insulated gate bipolar transistors.

40. The apparatus of claim 37 including a transformer for each input bus, wherein the first and second output terminals are each connected to a single phase secondary of one of the transformers having a primary connectable to AC input bus lines, wherein the single phase secondaries are connected together at a node that is connected to the neutral return line.

41. The apparatus of claim 40 wherein the transformer having a secondary connected to the first input terminal has a selected high duty rating and the transformer having a secondary connected to the second input terminal has a low duty rating which is less than the rating of the transformer connected to the first output terminal.

42. The apparatus of claim 33 further including an inductor connected between the output of the inverter and the output terminal.

43. The apparatus of claim 33 wherein the transfer switch is a static switch comprised of anti-parallel connected thyristors.

44. The apparatus of claim 33 wherein the first and second input switches are electro-mechanical switches.

45. A method of providing power to critical loads on a distribution bus from dual power feeds providing power to two AC input buses, comprising:

(a) when acceptable power is provided on a first of the AC input buses transmitting the power from each phase line of the first AC input bus through a first input switch and a fast transfer switch to each of the phase lines of the distribution bus;

(b) when a power failure occurs on the first AC input bus, opening the transfer switch to shut off power from the first input bus to the distribution bus and providing power from an inverter to each phase line of the distribution bus to maintain the output voltage at the distribution bus at a desired voltage level, wherein power is provided to the inverter from a DC storage device, then opening the first input switch which is connected to the first of the AC input buses, then closing a second input switch that is connected to each of the phase lines of the second of the AC input buses to provide a power path to the transfer switch, then closing the transfer switch to provide AC power from the second AC input bus to the distribution bus while turning the inverter off to cease supplying power from the inverter to the distribution bus.

46. The method of claim 45 further including charging the DC storage device with power from either the first input bus or the second input bus, or both, when power is available on the input buses.

47. The method of claim 46 wherein the DC storage device is a capacitor and power is drawn from one or both of the AC input buses and is rectified to provide a DC voltage to charge the capacitor.

48. A method of supplying power to a distribution bus from first and second AC input buses comprising:

(a) drawing power from one or both of the AC input buses when power is available thereon and rectifying the AC power to a DC voltage, and charging a DC storage device with the rectified power from the first or second AC input buses;

(b) normally providing power from the first AC input bus through a transfer switch to the distribution bus when normal power is available on the first AC input bus, and when a selected voltage sag occurs on the first AC input bus, opening the transfer switch to cut off the supply of power from the first input bus through the transfer switch to the distribution bus and turning on an inverter connected to the DC storage device to draw power therefrom, and providing an AC output voltage from the inverter to the distribution bus to maintain the voltage on the distribution bus at a selected level while simultaneously continuing to draw power from either the first AC input bus or the second AC input bus or both to charge the DC storage device.

49. The method of claim 48 wherein the DC storage device comprises a capacitor and wherein the power from one or both of the AC input buses is rectified to a DC voltage to continuously charge the capacitor.

50. A transfer switching apparatus comprising:

(a) a first input terminal and a second input terminal each of which may be provided with AC power from one of the lines of two separate AC input buses, and an output terminal that is available for connection to one of the lines of a distribution bus;

(b) a first input switch connected between the first input terminal and a junction node and a second input switch connected between the second input terminal and the junction node, the input switches responsive to control signals to open and close, the first input switch being normally closed and the second input switch being normally open, the junction node connected to the output terminal;

(c) a first rectifier connected to the first input terminal to receive AC power therefrom and provide DC output voltage to DC bus lines and a second rectifier connected to the second input terminal to receive AC power therefrom and provide DC voltage to the DC bus lines in parallel with the DC voltage provided by the first rectifier, the first and second rectifiers connected to the first and second input terminals independently of the first and second input switches, wherein the first and second rectifiers are formed as pairs of diodes, each connected together at a node and connected in series across the DC bus lines, the nodes between the pairs of diodes in the first and second rectifiers connected respectively to the first and second input terminals;

(d) a DC electrical energy storage device connected to the DC bus lines to receive DC power therefrom and deliver DC power thereto, wherein the DC electrical energy storage device comprises two capacitors connected together at a node and connected in series across the DC bus lines, and further including a neutral return line connected to the node between the capacitors to provide a current return path for power supplied to the first and second input terminals;

(e) an inverter connected to the DC bus lines and having an AC output connected to the output terminal, the inverter responsive to control signals to provide AC output voltage to the output terminal.

51. The apparatus of claim 50 including a bi-directional transfer switch connected between the junction node and the output terminal, and a controller means connected to provide control signals to the first and second input switches, to the transfer switch and to the inverter, and connected to receive signals indicating the voltage at the first and second input terminals and at the output terminal, the controller means normally controlling the first and second input switches to maintain the first input switch closed and the second input switch open and controlling the transfer switch to maintain it closed during normal availability of power at the first input terminal, and upon a fault condition of the power provided to the first input terminal controlling the transfer switch to open and controlling the inverter to provide AC output power to the output terminal, then controlling the first input switch to open, then controlling the second input switch to close, then controlling the transfer switch to close to provide AC power from the second input terminal to the output terminal while controlling the inverter to turn off and cease supplying output power to the output terminal.

52. The apparatus of claim 50 including a bi-directional transfer switch connected between the junction node and the output terminal, and a controller means connected to provide control signals to the inverter for controlling the inverter to turn on to provide AC power at the phase and frequency of the power provided from the first input terminal through the first input switch and to turn off the transfer switch when a selected level of sag occurs in the AC voltage at the first input terminal to maintain the voltage level at the output terminal at a selected nominal voltage level greater than the level of voltage available at the first input terminal.

53. The apparatus of claim 52 further including a voltage boosting auto-transformer connected between the output of the inverter and the output terminal.

54. The apparatus of claim 50 wherein the inverter comprises two gate controlled static switches each with anti-parallel diodes, the static switches connected together at a node and connected in series across the DC bus lines.

55. The apparatus of claim 54 wherein the static switches of the inverter are insulated gate bipolar transistors.

56. The apparatus of claim 50 including a transformer for each input bus, wherein the first and second output terminals are each connected to a single phase secondary of one of the transformers having a primary connectable to AC input bus lines, wherein the single phase secondaries are connected together at a node that is connected to the neutral return line.

57. The apparatus of claim 56 wherein the transformer having a secondary connected to the first input terminal has a selected high duty rating and the transformer having a secondary connected to the second input terminal has a low duty rating which is less than the rating of the transformer connected to the first output terminal.

58. The apparatus of claim 50 further including a boost transformer connected between the AC output of the inverter and the output terminal to provide a boost in the AC voltage from the inverter as applied to the output terminal.

59. The apparatus of claim 50 further including an inductor connected between the output of the inverter and the output terminal.