Dynamic reactive compensation system and method

• US 20050194944A1
• Filed: 03/04/2004
• Published: 09/08/2005
• Est. Priority Date: 03/04/2004
• Status: Active Grant

• Current Assignee: American Superconductor Corporation
• Original Assignee: American Superconductor Corporation
• Inventors: Folts, Douglas C., Kehrli, Arnold P., Diaz De Leon, John A. II, Vareka, William A.
• Granted Patent: US 7,091,703 B2
• Time in Patent Office: Days
• US Class Current: 323/209
• CPC Class Codes: H02J 3/1828 with stepwise control, the possibility of switching in or out the entire compensating arrangement not being considered as stepwise control
• CPC Class Codes: Y02E 40/30 Reactive power compensation

Abstract

The invention features a system for connection to a utility power network. The system includes a reactive power compensation device coupled to the network and configured to transfer reactive power between the utility power network and the reactive power compensation device; a capacitor system configured to transfer capacitive reactive power between the utility power network and the capacitor system; an electro-mechanical switch for connecting and disconnecting the capacitor system to the utility power network; an interface associated with the electro-mechanical switch; a controller configured to provide control signals for controlling the electro-mechanical switch; and a communication channel for coupling the controller to the interface associated with the electro-mechanical switch. The electro-mechanical switch, interface, controller, and communication channel together are configured to connect or disconnect the capacitor system from the utility power network within about three line cycles or less of the nominal voltage frequency when a fault condition is detected on the utility power network.

Claims

1. A system for connection to a utility power network, the system comprising:

a reactive power compensation device coupled to the network and configured to transfer reactive power between the utility power network and the reactive power compensation device;

a capacitor system configured to transfer capacitive reactive power between the utility power network and the at least one capacitor system;

an electro-mechanical switch for connecting and disconnecting the capacitor system to the utility power network;

an interface associated with the electro-mechanical switch;

a controller configured to provide control signals for controlling the electro-mechanical switch; and

a communication channel for coupling the controller to the interface associated with the electro-mechanical switch; and

the electro-mechanical switch, interface, controller, and communication channel together configured to connect or disconnect the capacitor system from the utility power network within about three line cycles or less of the nominal voltage frequency when a fault condition is detected on the utility power network.

2. The system of claim 1 wherein the electro-mechanical switch, interface, controller, and communication channel together configured to connect or disconnect the capacitor system from the utility power network in less than 80 msecs from a fault condition being detected on the utility power network.

3. The system of claim 2 wherein the electro-mechanical switch, interface, controller, and communication channel together configured to connect or disconnect the capacitor system from the utility power network in less than 50 msecs from a fault condition being detected on the utility power network.

4. The system of claim 1 wherein the communication channel is a fiber optic channel.

5. The system of claim 1 wherein the interface is configured to receive digital control signals from the controller.

6. The system of claim 1 further comprising an inductive reactor configured to transfer inductive reactive power to the utility power network.

7. The system of claim 1 further comprising a plurality of capacitor systems, each configured to transfer capacitive power between the utility power network and a respective one of the plurality of capacitor systems.

8. The system of claim 7 wherein each of the plurality of capacitor systems is coupled to a corresponding electro-mechanical switch, the controller configured to operate each of the plurality of capacitor systems using a corresponding electro-mechanical switch.

9. The system of claim 7 wherein following a predetermined time period, the controller monitors whether to connect an additional one of the plurality of capacitor systems or disconnect one of the plurality of capacitor systems.

10. The system of claim 7 wherein the controller is system is configured to initially activate a predetermined subset of the capacitor systems.

11. The system of claim 1 wherein the reactive power compensation device is configured to provide voltage regulation.

12. The system of claim 1 wherein the reactive power compensation device is configured to provide reactive power to the utility power network to 0.90 P.U. of the nominal voltage within two seconds.

13. The system of claim 1 further comprising at least one mechanically-switched capacitor, each configured to transfer capacitive power to the utility power network in response to a signal from the controller.

14. The system of claim 1 wherein the reactive power compensation device comprises an inverter.

15. The system of claim 14 wherein the reactive power compensation device comprises an array of inverters.

16. The system of claim 1 wherein the controller is configured to, in response to the need to connect the capacitor system to the utility power network, activate the reactive power compensation device and, substantially simultaneously, cause the capacitor system to be connected to the utility power network.

17. A method for stabilizing a utility power network comprising:

electrically coupling to the utility power network;

a reactive power compensation device coupled to the network and configured to transfer reactive power between the utility power network and the reactive power compensation device;

at least one capacitor system configured to transfer capacitive power between the utility power network and the at least one capacitor system, the at least one capacitor system including an electro-mechanical switch;

detecting a fault condition on the utility power network; and

in response to detecting the fault condition, operating the at least one electro-mechanical switch within about three line cycles or less of the nominal voltage frequency.

18. The method of claim 17 further comprising coupling a controller to the at least one electro-mechanical switch with a fiber optic communication channel.

19. The method of claim 17 further comprising:

coupling a plurality of capacitor systems to the utility power network, each associated with a corresponding electro-mechanical switch and each configured to transfer capacitive power between the utility power network and a respective one of the plurality of capacitor systems; and

monitoring, with the controller, whether to activate an additional one of the plurality of capacitor systems or deactivate one of the plurality of capacitor systems.

20. The method of claim 19 further comprising initially activating a predetermined subset of the capacitor systems.

21. The method of claim 18 wherein the electro-mechanical switch includes an interface for receiving digital control signals from the controller.

22. The method of claim 17 further comprising controlling, by the controller, the reactive power compensation device to provide reactive power to the utility power network to 0.90 P.U. of the nominal voltage within 2 seconds.

23. The method of claim 17 further comprising coupling to the utility power network, at least one mechanically-switched capacitor, each configured to transfer capacitive power to the utility power network in response to a signal from the controller.

24. The method of claim 17 wherein the reactive power compensation device comprises at least one inverter.

25. The method of claim 17 further comprising, in response to the need to connect the at least one capacitor system to the utility power network, activating the reactive power compensation device and, substantially simultaneously, causing the at least one capacitor system to be connected to the utility power network.

26. The method of claim 17 further comprising, prior to detecting a fault condition on the utility power network, controlling the reactive power compensation device to provide voltage regulation of the utility power network.

27. The method of claim 26 wherein controlling the reactive power compensation to provide voltage regulation includes:

if the nominal voltage on the utility power network is greater than a predetermined upper threshold deactivating at least one of the plurality of capacitor systems; and

if the nominal voltage on the utility power network is less than a predetermined lower threshold activating at least one of the plurality of capacitor systems.

28. The method of claim 27 wherein the predetermined upper threshold is 1.04 P.U. and the predetermined lower threshold is 1.00 P.U.

29. The method of claim 27 wherein if bucking VARS are required and if a predetermined capacitor timing period has expired, deactivating the reactive power compensation device.

30. The method of claim 29 wherein the predetermined capacitor timing period is dependent on the reactive power output of reactive power compensation device.

31. The method of claim 28 wherein activating the reactive power compensation device if boosting VARS are required and if a predetermined capacitor timing period has expired.

32. The method of claim 31 wherein the predetermined capacitor timing period is dependent on the reactive power output of reactive power compensation device.

33. The method of claim 27 further comprising if the nominal voltage on the utility power network is less than a predetermined fast control threshold:

activating at least one of the plurality of capacitor systems; and

controlling the reactive power compensation device to increase VAR injection from the reactive power compensation device.

34. The method of claim 33 wherein the predetermined fast control threshold is greater than 10% of the nominal voltage.

35. The method of claim 34 further comprising:

controlling the reactive power compensation device to increase VAR injection from the reactive power compensation device if boosting VARs are required;

controlling the reactive power compensation device to decrease VAR injection from the reactive power compensation device if boosting VARs are not required and if the nominal voltage is less than a predetermined overvoltage threshold; and

controlling the reactive power compensation device to increase VAR injection from the reactive power compensation device if boosting VARs are not required and if the nominal voltage is greater than the predetermined overvoltage threshold.

36. The method of claim 35 wherein the predetermined overvoltage threshold is greater than 5% of the nominal voltage.

37. The method of claim 31 further comprising:

deactivating at least one of the capacitor systems if the nominal voltage is greater than a fast capacitor removal threshold; and

activating at least one of the capacitor systems if the nominal voltage is less than the predetermined fast control threshold.

38. The method of claim 37 wherein the fast capacitor removal threshold is greater than 5% of the nominal voltage.