Generator with DC boost for uninterruptible power supply system or for enhanced load pickup

• US 6,737,762 B2
• Filed: 10/26/2001
• Issued: 05/18/2004
• Est. Priority Date: 10/26/2001
• Status: Active Grant

• Current Assignee: ONAN Corporation (Cummins Incorporated)
• Original Assignee: ONAN Corporation (Cummins Incorporated)
• Inventors: Koenig, David J.
• Primary Examiner(s): Toatley, Jr., Gregory J.
• Assistant Examiner(s): Polk, Sharon A.
• Application Number:
  US09/999,788
• Publication Number:
  US 20030080622A1
• Time in Patent Office: 935 Days
• Field of Search: 307/48, 307/86, 307/64, 307/66
• US Class Current: 307/48
• CPC Class Codes: H02J 9/062 for AC powered loads
• CPC Class Codes: H02J 9/068 Electronic means for switching from one power supply to another power supply, e.g. to avoid parallel connection
• CPC Class Codes: Y02B 90/10 Applications of fuel cells in buildings

Abstract

A local power generation system generates a substantially DC voltage at an inverter input, which is modulated to generate a resulting output AC power signal to a load. The inverter input voltage may be obtained from an engine generator, providing an AC power signal that is rectified, or from a fuel cell generator providing a DC voltage that is converted to the desired voltage value at the inverter input. An energy storage device helps maintain the DC voltage when load power draw increases, until the engine (or fuel cell reaction) accelerates enough to accommodate the increased power demand. The system may also be used in an uninterruptible power supply (UPS) application, in which the load draws power from a utility-provided AC power source until a fault condition appears. When the fault condition appears, the load switches its power draw from the utility-provided AC power source to the inverter output. The energy storage device helps maintain the DC voltage at the inverter input until the generator (engine or fuel cell) starts and accelerates to a level sufficient provide the DC voltage. The system may also include switching devices for providing uninterruptible power to a critical load, while permitting a noncritical load to be subjected to a fault-condition on the utility-provided AC power signal for a short period of time, before switching to receive power from the inverter output.

Claims

1. A system providing AC electrical power to a first load device, the system including:

a generator, including a generator output;

a fault condition detector, including an input that is coupled to a utility to detect a fault condition at the utility, and including an output that is coupled to the generator to initiate a generator startup after the fault condition has been detected;

an inverter circuit, including an inverter input and an inverter output, the inverter input coupled to the generator output, the inverter output adapted to be coupled to the first load device;

an energy storage device that provides power to the first load device during the generator startup;

a first DC-to-DC converter circuit, including a first converter input and a first converter output, the first converter input coupled to the energy storage device, and the first converter output coupled to the inverter input; and

an electrical energy supply circuit, including an energy supply circuit input and an energy supply circuit output, the energy supply circuit output coupled to the energy storage device, the energy supply circuit input coupled to a power source that is selected from at least one of a utility-provided AC power source outside of the system and the generator output.

2. The system of claim 1, in which the generator includes at least one of a fuel cell and an engine generator.

3. The system of claim 2, in which the engine generator is at least one of a variable speed engine generator and a constant speed engine generator.

4. The system of claim 1, further including a first rectifier coupled in series between the generator output and the inverter input, the first rectifier having a first rectifier input and a first rectifier output, the first rectifier input coupled to the generator output.

5. The system of claim 4, further including a second DC-to-DC converter coupled in series between the first rectifier and the first inverter, the second DC-to-DC converter having a second converter input and a second converter output, the second converter input coupled to the first rectifier output, and the second converter output coupled to the inverter input.

6. The system of claim 4, further including an AC-to-AC voltage converter coupled in series between the generator output and the first rectifier input.

7. The system of claim 1, further including a second DC-to-DC converter coupled in series between the generator output and the inverter input, the second DC-to-DC converter including a second converter input and a second converter output, the second converter input coupled to the generator output and the second converter output coupled to the inverter input.

8. The system of claim 1, in which the energy storage device includes at least one of a capacitor and a rechargeable battery.

9. The system of claim 8, in which the capacitor includes an electrochemical capacitor.

10. The system of claim 1, in which the first DC-to-DC converter includes a step-up DC-to-DC converter converting a lower voltage received at the first converter input from the energy storage device to a higher voltage provided by the first converter output to the inverter input.

11. The system of claim 1, in which the energy supply circuit includes a rectifier that includes:

a first diode, having an anode coupled to the generator output; and

a second diode, having an anode coupled to the utility-provided AC power source.

12. The system of claim 1, in which the energy supply circuit includes a second DC-to-DC converter, having a second converter input and a second converter output, the second converter input coupled to the generator output, and the second converter output coupled to the energy storage device.

13. The system of claim 1, in which the energy supply circuit includes:

a rectifier, having a rectifier input coupled to at least one of the generator output and the utility-provided AC power source, the rectifier having a rectifier output;

a switch, coupling the rectifier output to the energy storage device, the switch including a control terminal; and

a regulator circuit, coupled to the energy storage device to sense a voltage, and coupled to the control circuit of the switch to regulate conduction of the switch to maintain a predetermined voltage at the energy storage device.

14. The system of claim 1, in which the energy storage device includes an energy storage capacity that is limited to an approximate energy needed to approximately maintain a steady voltage at the inverter input when a motor within the first load device is started and draws surge power from the inverter output.

15. The system of claim 1, in which the energy storage device includes an energy storage capacity that is limited to an approximate energy needed to approximately maintain a steady voltage at the inverter input during a first time period in which the engine generator is started and until the generator output reaches a steady-state output voltage sufficient to maintain the voltage at the inverter input.

16. The system of claim 15, in which the first time period also includes a waiting period before the engine generator is started.

17. The system of claim 16, in which the waiting period is between about 0.5 second and about 5 seconds.

18. The system of claim 17, in which the waiting period is about 3 seconds.

19. The system of claim 1, in which the energy storage device includes an energy storage capacity that is limited to an approximate energy needed to approximately maintain a steady voltage at the inverter input for an interim time that is between about 0.5 seconds and about 60 seconds.

20. The system of claim 19, in which the interim time is about 10 seconds.

21. The system of claim 1, further including:

a first switch, coupled between the utility-provided AC power source and the inverter output, the first switch including a first switch-control input; and

the fault condition detector circuit is coupled to the utility-provided AC power source to detect a fault condition of the utility-provided AC power source, the detector circuit including a detector output coupled to the first switch-control input to operate the first switch to isolate the inverter output and the first load device from the utility-provided AC power source when the fault condition is detected.

22. The system of claim 21, in which the fault condition includes an at least ½

cycle undervoltage of the utility-provided AC power source.

23. The system of claim 21, in which the inverter circuit includes a synchronization circuit to synchronize a signal at the inverter output to the utility-provided AC power source.

24. The system of claim 23, in which the synchronization circuit operates to synchronize the signal at the inverter output to the utility-provided AC power source at least after the first switch isolates the first load from the utility-provided AC power source.

25. The system of claim 21, in which the fault detector output provides a control signal to the first switch-control input to operate the first switch to recouple the first load to the utility-provided AC power source after the fault detector detects the ceasing of the fault condition at the AC power source.

26. The system of claim 25, in which the inverter momentarily operates synchronously in parallel with the recoupled utility-provided AC power source to avoid a momentary break in power to the first load during the recoupling.

27. The system of claim 21, in which the fault detector output provides a control signal to the first switch-control input to operate the first switch to recouple the first load to the utility-provided AC power source after the fault detector detects the ceasing of the fault condition at the AC power source, and after the energy storage device has been recharged for a predetermined delay period.

28. The system of claim 25, in which the inverter circuit includes a synchronization circuit to synchronize a signal at the inverter output to the utility provided AC power source before the first load is recoupled to the utility-provided AC power source.

29. The system of claim 1, further providing power to a second load device, and further including a switch, having first and second states, the switch conductively coupling the second load to the utility-provided AC power source when the switch is in the first state, the switch conductively coupling the second load to the inverter output when the switch is in the second state.

30. The system of claim 29, in which the generator is coupled to the switch to provide a control signal transitioning the switch from the first state to the second state after the generator has been turned on and is capable of maintaining the inverter input at a predetermined sufficient voltage.

31. The system of claim 29, further including a timer coupled to the generator and the switch, the timer including a timer output coupled to the switch to provide a control signal to transition the switch from the first state to the second state at a predetermined time after the generator has been turned on.

32. The system of claim 29, further including:

a second switch, coupling the inverter output to the first load; and

a third switch, coupling the second load in parallel with the first load.

33. A method of providing an electrical AC output signal to a first load, the method including:

generating a first approximately DC voltage from a fuel;

modulating the first DC voltage into the AC output signal;

providing the AC output signal to the first load; and

transferring energy from an energy storage device onto the first DC voltage to maintain the first DC voltage at a first predetermined DC voltage value while the first load draws a surge power AC output signal, and in which the transferring includes converting a second DC voltage value provided by the energy storage device to the first predetermined DC voltage value, and in which the transferring includes using the energy storage device having an energy storage capacity that is limited to approximately the energy storage needed to maintain the first DC voltage long enough for a generator to accelerate, to accommodate the surge power AC output signal.

34. The method of claim 33, further including transferring energy to the energy storage device from at least one of:

an generator-provided power source; and

a utility-provided AC power source.

35. A method of providing AC electrical power to a first load, the method including:

decoupling the first load from a utility-provided AC power source that, during normal operation, is provided to the first load without AC-to-DC-to AC conversion, upon detecting a fault condition at the utility-provided AC power source;

modulating a DC voltage to provide backup AC power;

coupling the backup AC power to the first load when the first load is decoupled from the utility-provided AC power source;

turning on an generator to provide energy to the DC voltage; and

transferring energy from an energy storage device to the DC voltage during a time from the turning on of the generator to a time at which the generator is supplying sufficient power to maintain the DC voltage at a first predetermined voltage value, and in which the transferring energy from the energy storage device includes DC-to-DC converting a second voltage value provided by the energy storage device to the first predetermined voltage value of the DC voltage.

36. The method of claim 35, in which the decoupling the first load includes triggering the decoupling by detecting a zero-cross of the utility-provided AC power source.

37. The method of claim 35, in which the detecting the fault condition includes detecting an at least ½

cycle undervoltage of the utility-provided AC power source.

38. The method of claim 35, in which the transferring energy from the energy storage device includes using the energy storage device having an energy storage capacity that is limited to approximately the energy storage needed to maintain the first DC voltage for a time from the turning on of the generator to the time at which the generator is supplying sufficient power to maintain the DC voltage at a first predetermined voltage value.

39. The method of claim 35, further including transferring energy to the energy storage device from at least one of:

the generated power from the generator; and

the utility-provided AC power source.

40. The method of claim 35, further including transferring a second load from the utility provided-AC power source to the backup AC power from the modulated DC voltage after a time at which the generator is supplying sufficient power to maintain the DC voltage at a first predetermined voltage value.

41. The method of claim 35, in which the modulating the DC voltage to provide backup AC power to the first load includes synchronizing the backup AC power to the utility-provided AC power source at least upon the decoupling of the first load from the utility-provided AC power source.

42. The method of claim 35, further including:

detecting a ceasing of the fault condition at the utility-provided AC power source; and

recoupling the first load to the utility-provided AC power source.

43. The method of claim 42, in which the recoupling follows the detecting the ceasing of the fault condition and a recharging of the energy storage device.

44. The method of claim 42, further including synchronizing the backup AC power to the utility-provided AC power source before the recoupling the first load to the utility-provided AC power source.

45. The method of claim 42, further including decoupling the first load from the backup AC power.

46. The method of claim 44, in which the decoupling follows an operating the backup AC power synchronously in parallel with the utility-provided AC power source momentarily to avoid a break in power to the first load.

47. A system providing AC electrical power to a first load device, the system including:

a generator, including a generator output;

an inverter circuit, including an inverter input and an inverter output, the inverter input coupled to the generator output, the inverter output adapted to be coupled to the first load device;

an energy storage device;

a first DC-to-DC converter circuit, including a first converter input and a first converter output, the first converter input coupled to the energy storage device, and the first converter output coupled to the inverter input;

an electrical energy supply circuit, including an energy supply circuit input and an energy supply circuit output, the energy supply circuit output coupled to the energy storage device, the energy supply circuit input coupled to a power source that is selected from at least one of a utility-provided AC power source outside of the system and the generator output;

a first rectifier coupled in series between the generator output and the inverter input, the first rectifier having a first rectifier input and a first rectifier output, the first rectifier input coupled to the generator output; and

a second DC-to-DC converter coupled in series between the first rectifier and the first inverter, the second DC-to-DC converter having a second converter input and a second converter output, the second converter input coupled to the first rectifier output, and the second converter output coupled to the inverter input.

48. The system of claim 47, further including an AC-to-AC voltage converter coupled in series between the generator output and the first rectifier input.

49. A system providing AC electrical power to a first load device, the system including:

a generator, including a generator output;

an inverter circuit, including an inverter input and an inverter output, the inverter input coupled to the generator output, the inverter output adapted to be coupled to the first load device;

an energy storage device;

a first DC-to-DC converter circuit, including a first converter input and a first converter output, the first converter input coupled to the energy storage device, and the first converter output coupled to the inverter input; and

an electrical energy supply circuit, including an energy supply circuit input and an energy supply circuit output, the energy supply circuit output coupled to the energy storage device, the energy supply circuit input coupled to a power source that is selected from at least one of a utility-provided AC power source outside of the system and the generator output, wherein the energy supply circuit includes a rectifier that includes;

a first diode, having an anode coupled to the generator output; and

a second diode, having an anode coupled to the utility-provided AC power source.

50. A system providing AC electrical power to a first load device, the system including:

a generator, including a generator output;

an inverter circuit, including an inverter input and an inverter output, the inverter input coupled to the generator output, the inverter output adapted to be coupled to the first load device;

an energy storage device;

a first DC-to-DC converter circuit, including a first converter input and a first converter output, the first converter input coupled to the energy storage device, and the first converter output coupled to the inverter input; and

an electrical energy supply circuit, including an energy supply circuit input and an energy supply circuit output, the energy supply circuit output coupled to the energy storage device, the energy supply circuit input coupled to a power source that is selected from at least one of a utility-provided AC power source outside of the system and the generator output, wherein the energy supply circuit includes;

a rectifier, having a rectifier input coupled to at least one of the generator output and the utility-provided AC power source, the rectifier having a rectifier output;

a switch, coupling the rectifier output to the energy storage device, the switch including a control terminal; and

a regulator circuit, coupled to the energy storage device to sense a voltage, and coupled to the control circuit of the switch to regulate conduction of the switch to maintain a predetermined voltage at the energy storage device.

51. A system providing AC electrical power to a first load device and a second load device, the system including:

a generator, including a generator output;

an inverter circuit, including an inverter input and an inverter output, the inverter input coupled to the generator output, the inverter output adapted to be coupled to the first load device;

an energy storage device;

a first DC-to-DC converter circuit, including a first converter input and a first converter output, the first converter input coupled to the energy storage device, and the first converter output coupled to the inverter input; and

an electrical energy supply circuit, including an energy supply circuit input and an energy supply circuit output, the energy supply circuit output coupled to the energy storage device, the energy supply circuit input coupled to a power source that is selected from at least one of a utility-provided AC power source outside of the system and the generator output;

a switch, having first and second states, the switch conductively coupling the second load to the utility-provided AC power source when the switch is in the first state, the switch conductively coupling the second load to the inverter output when the switch is in the second state; and

a timer coupled to the generator and the switch, the timer including a timer output coupled to the switch to provide a control signal to transition the switch from the first state to the second state at a predetermined time after the generator has been turned on.

52. A method of providing AC electrical power to a first load, the method including:

decoupling the first load from a utility-provided AC power upon detecting a fault condition at the utility-provided AC power source;

modulating a DC voltage to provide backup AC power;

coupling the backup AC power to the first load when the first load is decoupled from the utility-provided AC power source;

turning on an generator to provide energy to the DC voltage; and

transferring energy from an energy storage device to the DC voltage during a time from the turning on of the generator to a time at which the generator is supplying sufficient power to maintain the DC voltage at a first predetermined voltage value, and in which the transferring energy from the energy storage device includes DC-to-DC converting a second voltage value provided by the energy storage device to the first predetermined voltage value of the DC voltage, and wherein the transferring energy from the energy storage device includes using the energy storage device having an energy storage capacity that is limited to approximately the energy storage needed to maintain the first DC voltage for a time from the turning on of the generator to the time at which the generator is supplying sufficient power to maintain the DC voltage at a first predetermined voltage value.