Voltage regulation of a utility power network

• US RE41,170 E1
• Filed: 01/19/2007
• Issued: 03/30/2010
• Est. Priority Date: 11/24/1999
• Status: Expired due to Term

• Current Assignee: American Superconductor Corporation
• Original Assignee: American Superconductor Corporation
• Inventors: Buckles, Warren Elliott, Hubert, Thomas Gregory, Folts, Douglas C.
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US11/655,817
• Time in Patent Office: 1,166 Days
• Field of Search: 323/205, 323/207, 323/208, 363/34, 363/35, 363/37, 363/39, 363/40
• US Class Current: 323/207
• CPC Class Codes: H02J 3/1842 wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
• CPC Class Codes: Y02E 40/22 Non-specified or voltage-fed active power filters

Abstract

Power compensation is provided from a power compensation device to a utility power network carrying a nominal voltage. The power compensation device has a steady-state power delivery characteristic. The power compensation is providing by detecting a change of a predetermined magnitude in the nominal voltage on the utility power network and controlling the power compensation device to deliver, for a first period of time and in response to the detected change in the nominal voltage, reactive power to the utility power network. The power compensation device is controlled to deliver, for a second period of time following the first period of time, reactive power to the utility power network at a level that is a factor N(N>1) greater than the steady-state power delivery characteristic of the power compensation device.

Claims

1. A system for use with a reactive power compensation device connected to a utility power network carrying a nominal voltage, the system comprising:

a controller which controls the reactive power compensation device to deliver, for a first period of time and in response to a detected change in the nominal voltage, reactive power, real power, or both real and reactive power to the utility power network;

wherein, in a second period of time following the first period of time, the controller controls the reactive power compensation device to provide reactive power to the utility power network at a level that is a factor N (N>

1) greater than a maximum power capability characteristic of the reactive power compensation device.

2. The system of claim 1, wherein, during the second period of time, the relative power compensation device provides real power to the utility power network.

3. The system of claim 2, wherein the controller controls the reactive power compensation device to non-discontinuously decrease the reactive power to a steady-state power delivery characteristic after the second period of time.

4. The system of claim 3, wherein a slope of the non-discontinuously decreasing reactive power is determined on the basis of a characteristic impedance of the utility power network.

5. The system of claim 1, wherein the factor N is determined on the basis of a transient thermal capacity characteristic of the reactive power compensation device.

6. The system of claim 5, wherein the transient thermal capacity characteristic is represented by an I²t rating of the reactive power compensation device.

7. The system of claim 1, wherein a sum of the first period of time and the second period of time is determined on the basis of the ability of the reactive power compensation device to absorb thermal energy.

8. A method of providing power compensation from a power compensation device to a utility power network carrying a nominal voltage, the power compensation device having a steady-state power delivery characteristic, the method comprising:

detecting a change of a predetermined magnitude in the nominal voltage on the utility power network;

controlling the power compensation device to deliver, for a first period of time and in response to the detected change in the nominal voltage, reactive power, real power, or both real and reactive power to the utility power network; and

controlling the power compensation device to deliver, for a second period of time following the first period of time, reactive power to the utility power network at a level that is a factor N (N>

1) greater than the steady-state power delivery characteristic of the power compensation device.

9. The method of claim 8, wherein, during the second period of time the power compensation device provides real power to the utility power network.

10. The method of claim 9, further comprising, after the second period of time, non-discontinuously decreasing the reactive power from the power compensation device to the steady-state power delivery characteristic.

11. The method of claim 10, further comprising determining a slope of the nondiscontinuously decreasing reactive power on the basis of a characteristic impedance of the utility power network.

12. The method of claim 11, wherein the characteristic impedance of the utility power network is determined on the basis of known characteristics of the utility power network.

13. The method of claim 11, further comprising determining the characteristic impedance of the utility power network by applying a stimulus to the network and measuring a response to the stimulus.

14. The method of claim 8, wherein the factor N is determined on the basis of a transient thermal capacity characteristic of the power compensation device.

15. The method of claim 14, wherein the transient thermal capacity characteristic is represented by an I²t rating of the power compensation device.

16. The method of claim 8, wherein the second period of time is determined on the basis of the ability of the power compensation device to absorb thermal energy.

17. A system for providing power to a utility power network, the system comprising:

a power compensation device having a maximum non-overload steady-state power capability characteristic; and

a controller which controls the power compensation device to deliver power to the utility power network at a first overload level greater than the maximum non-overload steady-state power capability characteristic and then to continuously decrease the power from the first overload level to a second level lower than the first overload level,

the controller determining a time period of the continuously decreasing power on the basis of a transient thermal capacity characteristic of the power compensation device.

18. The system of claim 17 wherein the second level is less than or approximately equal to the maximum non-overload steady-state power capability characteristic.

19. The system of claim 17 wherein the power compensation device has a maximum overload power delivery characteristic greater than the maximum non-overload steady-state power capability characteristic and the controller is configured to control the power compensation device to deliver power at the maximum overload power level to the utility power network prior to continuously decreasing the power to the second level.

20. The system of claim 19 wherein the controller determines the maximum overload power delivery characteristic using a transient thermal capacity characteristic of the power compensation device.

21. The system of claim 19 wherein the controller determines the maximum overload power delivery characteristic using the maximum current characteristic of the power compensation device.

22. The system of claim 17 wherein the controller is configured to determine an accumulation of energy dissipated in the power compensation device during a first period of time, and to determine a starting time for starting to decrease the delivery of power from the power compensation device based on the accumulation of energy dissipated in the power compensation device.

23. The system of claim 22 wherein the controller is configured to determine the starting time based on a transient thermal capacity characteristic of the power compensation device.

24. The system of claim 23 wherein the controller uses the accumulation of energy dissipated in the power compensation device to estimate when the transient thermal capacity characteristic of the power compensation device will be exhausted.

25. The system of claim 22 wherein the controller repeatedly calculates the accumulation of energy dissipated in the power compensation device.

26. The system of claim 25 wherein the controller calculates the accumulation of energy dissipated in the power compensation device once every line cycle.

27. The system of claim 17 wherein a rate of decrease of the continuously decreasing power is computed by the controller on the basis of a characteristic impedance of the utility power network.

28. The system of claim 17 wherein the controller is configured to decrease the power as a linear function of time.

29. The system of claim 23 wherein the transient thermal capacity characteristic is an I²t rating of the power compensation device.

30. The system of claim 17 wherein the controller determines a slope and a time period of the continuously decreasing power on the basis of the ability of the power compensation device to absorb thermal energy.

31. The system of claim 17 wherein the controller controls the power compensation device to deliver power to the utility power network at a level greater than the maximum non-overload steady-state power capability characteristic in response to a change in the condition of the utility power network.

32. The system of claim 31 wherein the change in the condition of the utility power network comprises a change in a nominal voltage carried on the utility power network.

33. The system of claim 17 wherein the power compensation device is configured to deliver reactive power, real power or a combination of reactive power and real power.

34. The system of claim 17 wherein the power compensation device comprises a reactive power compensation device and the controller is configured to control the reactive power compensation device to deliver reactive power to the utility power network.

35. The system of claim 34 wherein the power compensation device comprises a real power compensation device and the controller is configured to control the real power compensation device to deliver real power to the utility power network.

36. The system of claim 17 wherein the power compensation device comprises a real power compensation device and the controller is configured to control the real power compensation device.

37. The system of claim 36 wherein the controller is configured to control the real power compensation device to initially deliver a maximum level of real power to the utility power network.

38. The system of claim 36 wherein the real power compensation device comprises a superconducting magnetic energy storage device (SMES).

39. The system of claim 38 wherein the real power compensation device comprises a distributed SMES (D-SMES).

40. The system of claim 37 wherein the real power compensation device comprises a capacitor bank.

41. The system of claim 17 wherein the controller controls the power compensation device to deliver power to the utility power network at a level greater than the maximum non-overload steady-state power capability characteristic during a first time period, and to continuously decrease the power to the second level during a second time period.

42. The system of claim 41 wherein the second time period follows the first time period.

43. The system of claim 17 wherein power compensation device comprises one or more inverters.

44. The system of claim 17 wherein the controller controls the power compensation device to immediately deliver, in response to a detected change in the nominal voltage, power to the utility power network at a level greater than the maximum non-overload steady-state power capability characteristic.

45. A method for controlling a system connected to a utility power network, the method comprising:

controlling a power compensation device to deliver power to the utility power network at a first overload level greater than a maximum non-overload, steady-state power capability characteristic, and

controlling the power compensation device to continuously decrease from the first overload level the power to a second level less than the first overload level,

a time period of the continuously decreasing power being determined on the basis of a transient thermal capacity characteristic of the power compensation device.

46. The method of claim 45 wherein the second level is less than or approximately equal to the maximum non-overload steady-state power capability characteristic.

47. The method of claim 45 wherein the power compensation device has a maximum overload power delivery characteristic greater than the maximum non-overload steady-state power capability characteristic, the method further comprising controlling the power compensation device to deliver the power at the maximum overload power level to the utility power network prior to continuously decreasing the power to the second level.

48. The method of claim 47 further comprising determining the maximum overload power delivery characteristic as a function of a transient thermal capacity characteristic of the power compensation device.

49. The method of claim 47 further comprising determining the maximum overload power delivery characteristic as a function of a maximum current characteristic of the power compensation device.

50. The method of claim 45 further comprising determining an accumulation of energy dissipated in the power compensation device during a first period of time, and determining a starting time for decreasing the delivery of power from the power compensation device on the basis of the accumulation of energy dissipated by the power compensation device.

51. The method of claim 50 further comprising determining the starting time on the basis of a transient thermal capacity characteristic of the power compensation device.

52. The method of claim 45 further comprising determining the starting time based on an estimate of the accumulation of energy dissipated by the power compensation device.

53. The method of claim 50 further comprising using the accumulation of energy to estimate when the transient thermal capacity characteristic of the power compensation device will be exhausted.

54. The method of claim 50 further comprising repeatedly determining the accumulation of energy.

55. The method of claim 54 further comprising determining the accumulation of energy once every line cycle.

56. The method of claim 45 further comprising determining a rate of decrease of the continuously decreasing power on the basis of a characteristic impedance of the utility power network.

57. The method of claim 45 further comprising decreasing the power as a linear function of time.

58. The method of claim 51 wherein the transient thermal capacity characteristic is an I2t rating of the power compensation device.

59. The method of claim 45 further comprising determining a slope and a time period of the continuously decreasing power on the basis of the ability of the power compensation device to absorb thermal energy.

60. The method of claim 45 comprising controlling the system to deliver power to the utility power network at a level greater than the maximum non-overload steady-state power capability characteristic in response to a change in the condition of the utility power network.

61. The method of claim 60 wherein the change in the condition of the utility power network comprises a change in a nominal voltage carried on the utility power network.

62. The method of claim 46 wherein the power comprises reactive power, real power or a combination of real and reactive power.

63. The method of claim 45 wherein the system comprises a reactive power compensation device and the controller is configured to control the reactive power compensation device to deliver reactive power to the utility power network.

64. The method of claim 62 wherein the system comprises a real power compensation device and the controller is configured to control the real power compensation device to deliver real power to the utility power network.

65. The method of claim 45 wherein the system comprises a real power compensation device, the method further comprising controlling the real power compensation device to initially deliver a maximum level of real power to the utility power network.

66. The method of claim 65 wherein the real power compensation device comprises a superconducting magnetic energy storage device (SMES).

67. The method of claim 66 wherein the real power compensation device comprises a distributed SMES (D-SMES).

68. The method of claim 65 wherein the real power compensation device comprises a capacitor bank.

69. The method of claim 46 wherein the power compensation device comprises one or more inverters.

70. The method of claim 46 further comprising immediately delivering power to the utility power network at a level greater than the maximum non-overload steady-state power capability characteristic during the first time period.

71. The method of claim 46 comprising controlling the power compensation device to deliver power to the utility power networks at a level greater than the maximum non-overload steady-state power capability characteristic during a first time period, and to continuously decrease the power to the second level during a second time period.

72. The method of claim 71 wherein the second time period follows the first time period.

73. A system for providing power to a utility power network, the system comprising:

a power compensation device having a maximum non-overload steady-state power capability characteristic; and

a controller which controls the power compensation device to deliver power to the utility power network at a first overload level greater than the maximum non-overload steady-state power capability characteristic, calculates at least one rate of continuous decrease of power from the first overload level to a second level lower than the first overload level on the basis of a transient thermal capacity characteristic of the power compensation device, and then controls the power compensation device to continuously decrease power from the first overload level to the second level according to one of said calculated rates.

74. The system of claim 73 wherein the power compensation device comprises an inverter and the controller controls the inverter to continuously decrease the power from the first overload level to a second level lower than the first overload level according to the at least one of said calculated rates.

75. The system of claim 73 wherein the second level is lower than the maximum non-overload steady-state power capability characteristic.