Anti-islanding techniques for distributed power generation

• US 20030080741A1
• Filed: 10/25/2002
• Published: 05/01/2003
• Est. Priority Date: 10/26/2001
• Status: Active Grant

• Current Assignee: The Switch Controls and Converters, Inc.
• Original Assignee: Youtility Incorporated
• Inventors: Welches, Richard Shaun, LeRow, Kevin E.
• Granted Patent: US 7,138,728 B2
• Time in Patent Office: Days
• US Class Current: 324/320
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers
• CPC Class Codes: H02J 3/388 Islanding, i.e. disconnection of local power supply from the network
• CPC Class Codes: H02J 3/40 Synchronising a generator for connection to a network or to another generator

Abstract

Techniques for detecting an island in a system including a node that is operatively coupled to a primary power source (e.g., grid) and one or more distributed power generation sources are disclosed. In one embodiment, a current pulse is included in the output of a distributed power source. The grid voltage is monitored at the node to determine if a pulse-related disturbance occurs. If the grid is present, no pulse-related disturbance will manifest. If grid is down, then a pulse-related disturbance will manifest. Detection of the pulse-related disturbance is used to signal island detection.

Claims

1. An anti-islanding system for distributed power on a grid, comprising:

a distributed power source operatively coupled to a grid and adapted with output current control, the distributed power source for providing power;

a voltage sensor connected to a node between the distributed power source and the grid, and adapted to monitor grid voltage; and

an anti-islanding protection controller operatively coupled to the distributed power source and the voltage sensor, the anti-islanding protection controller adapted to request the distributed power source to selectively output a current pulse in the power being provided so as to cause a voltage deflection in the grid voltage if an island condition exists, and to detect an island condition based on voltage deflection data provided by the voltage sensor.

2. The system of claim 1 wherein the distributed power source includes:

an inverter adapted to receive an input signal and provide output power from that signal in accordance with a pulse width modulation scheme; and

an inverter controller operatively coupled to the inverter, the inverter controller adapted to receive current pulse requests from the anti-islanding protection controller, and to sense and control the current output of the inverter.

3. The system of claim 2 wherein the inverter controller is further adapted to receive an island detect signal from the anti-islanding protection controller and to shutdown the inverter if an island is detected.

4. The system of claim 2 wherein the inverter controller is further adapted to receive grid voltage measurements from the voltage sensor.

5. The system of claim 1 further including:

a contactor operatively coupled between the distributed power source and the voltage sensor, and adapted for disconnecting the grid from the distributed power source; and

a second voltage sensor operatively coupled to a node between the distributed power source and the contactor, and adapted for monitoring local power.

6. The system of claim 1 wherein the distributed power source is adapted to be disabled in response to receiving an island detect signal from the anti-islanding protection controller.

7. The system of claim 1 wherein the system includes a plurality of distributed power sources connected in parallel.

8. The system of claim 1 wherein the distributed power source is a poly-phase source.

9. The system of claim 1 wherein distributed power source is adapted to provide an AC output, and current pulses requested by the anti-islanding protection controller are each applied at a zero-crossing of the AC output.

10. The system of claim 1 wherein distributed power source is adapted to provide an AC output that includes a number of half cycles including a current half cycle and an upcoming half cycle, with each half cycle associated with a direction, and each applied current pulse either opposes the direction of the upcoming half cycle, or coincides with the direction of the upcoming half cycle.

11. The system of claim 1 wherein the anti-islanding protection controller is further adapted to detect one or more zero-crossings of an AC signal output by the distributed power source, and to provide a distortion window about the zero-crossing, the distortion window allowing for a margin of error in zero-crossing detection.

12. The system of claim 1 wherein the distributed power source and other operatively coupled distributed power sources are synchronized using a zero-crossing associated with the grid.

13. The system of claim 1 wherein the anti-islanding protection controller is configured so that current pulses are applied at least one of periodically, randomly, or according to a pattern so as to maintain total harmonic distortion within agency standards.

14. The system of claim 1 wherein the current pulse is requested by the anti-islanding protection controller according to a pre-defined routine depending on the voltage deflection data provided by the voltage sensor.

15. The system of claim 1 wherein the anti-islanding protection controller is further adapted to request a current pulse at a pulse repetition frequency included in a first range when the system is operating in a normal mode, and a pulse repetition frequency included in a higher second range in response to an initial island detect threshold being exceeded.

16. The system of claim 1 wherein the anti-islanding protection controller is further adapted to change an interval at which the current pulse is applied based on quantity of island detections received in a given time period.

17. The system of claim 1 wherein the anti-islanding protection controller includes an island detect accumulator thereby enabling filtering and hysteresis of island detect indications.

18. The system of claim 1 wherein the system includes a plurality of distributed power sources connected in parallel, and a number of the sources are communicatively coupled with one another.

19. The system of claim 1 wherein the anti-islanding protection controller is further adapted to detect changes in line impedance based on data provided by the voltage sensor.

20. A method for detecting an island in a system including a node that is operatively coupled to a grid and one or more distributed power generation sources, the method comprising:

selectively applying a current pulse from at least one of the distributed power generation sources onto the node;

monitoring the node for a disturbance related to the applied current pulse; and

in response to detecting a disturbance, signaling an island detection.

21. The method of claim 20 wherein in response to detecting the disturbance, the method further includes at least one of disabling the at least one distributed power generation source and disconnecting the at least one distributed power generation source from the grid.

22. The method of claim 21 further including at least one of enabling the at least one distributed power generation source and re-connecting the at least one distributed power generation source to the grid in response to detecting grid voltage is re-established.

23. The method of claim 21 wherein the at least one distributed power generation source is adapted to provide an AC output, and selectively applying the current pulse includes:

detecting zero-crossings associated with the AC output; and

applying the current pulse at one or more zero-crossings of the AC output.

24. The method of claim 21 wherein the at least one distributed power generation source is adapted to provide an AC output that includes a number of half cycles including a current half cycle and an upcoming half cycle, with each half cycle associated with a direction, and selectively applying the current pulse includes applying the current pulse in a direction that either opposes the direction of the upcoming half cycle, or coincides with the direction of the upcoming half cycle.

25. The method of claim 21 further comprising:

synchronizing the one or more distributed power generation sources using a zero-crossing associated with the grid.

26. The method of claim 21 wherein selectively applying the current pulse includes applying current pulses at least one of periodically, randomly, or according to a pattern so as to maintain total harmonic distortion within agency standards.

27. The method of claim 21 wherein selectively applying the current pulse includes requesting the current pulse according to a pre-defined routine depending on the voltage deflection data measured at the node.

28. The method of claim 21 wherein selectively applying the current pulse includes applying the current pulse at a pulse repetition frequency included in a first range when operating in a normal mode, and a pulse repetition frequency included in a higher second range in response to an initial island detect threshold being exceeded.

29. The method of claim 21 wherein selectively applying the current pulse includes changing an interval at which the current pulse is applied based on quantity of island detections in a given time period.

30. The method of claim 21 further including performing filtering and hysteresis of signaled island detections so as to reduce nuisance trips.

31. The method of claim 21 wherein monitoring the node for a disturbance related to the applied current pulse includes:

measuring a voltage on the node at a time corresponding to application of the current pulse;

comparing the measured voltage to an expected voltage thereby generating a difference signal; and

in response to the difference signal exceeding a limit window, indicating the disturbance.

32. The method of claim 21 wherein monitoring the node for a disturbance related to the applied current pulse includes monitoring changes in line impedance based on data measured on the node.

33. An apparatus for detecting an island in a system including a node that is operatively coupled to a grid and one or more distributed power generation sources, the apparatus comprising:

a pulse request module adapted to generate a pulse request that causes a distributed power generation source to include a current pulse in its output signal so that a pulse-related disturbance will manifest on the node if an island is present; and

an island detection module adapted to generate an island detect signal in response to a pulse-related disturbance being detected on the node.

34. The apparatus of claim 33 wherein apparatus is included in an inverter controller associated with one of the distributed power generation sources.

35. The apparatus of claim 33 further including:

a zero-crossing detection module adapted to detect zero-crossings of the output signal and provide zero-crossing information to the pulse request module so that the current pulse can be applied at the zero-crossing.

36. The apparatus of claim 33 further including:

an island detect accumulator adapted to receive island detect signals from the island detection module, and to perform filtering and hysteresis of received island detect signals so as to reduce nuisance trips.

37. The apparatus of claim 33 wherein the system includes a sensor adapted to sense node data that characterizes the pulse-related disturbance, the apparatus further including:

a comparator module adapted to compare a sensed node data to expected node data so as to generate a difference signal; and

a limit window module adapted to receive the difference signal and to generate an island indication signal if the difference signal exceeds a limit associated with the limit window module.

38. The apparatus of claim 37 wherein the island detection module has a first input that receives the island indication signal from the limit window and a second input that receives a sync signal from the pulse request module that indicates when the current pulse is active, and an island detect signal is generated by the island detection module when both of its inputs are true.

39. The apparatus of claim 33 wherein the system includes a sensor adapted to sense node data, the apparatus further including:

a phase lock loop module that is adapted to receive node data, and to compute expected node data based on the received node data.

40. The apparatus of claim 33 wherein the pulse request module is configured so that current pulse are requested at least one of periodically, randomly, or according to a pattern so as to maintain total harmonic distortion within agency standards.

41. The apparatus of claim 33 wherein the pulse request module is configured to request current pulses according to a pre-defined routine depending on voltage deflection data provided by a voltage sensor that is operatively coupled to the node.

42. The apparatus of claim 33 wherein the pulse request module is configured to request a current pulse at a pulse repetition frequency included in a first range when operating in a normal mode, and a pulse repetition frequency included in a higher second range in response to an initial island detect threshold being exceeded.

43. The apparatus of claim 33 further including:

an island detect accumulator adapted to receive island detect signals from the island detection module, and to provide a threshold signal to the pulse request module, wherein the pulse request module is further configured to change an interval at which the current pulse is applied based on the threshold signal.

44. The apparatus of claim 33 wherein the pulse-related disturbance is a voltage deflection.

45. An apparatus for detecting an island in a system including a node that is operatively coupled to a primary power source and one or more distributed power generation sources, the apparatus comprising:

a disturbance request module adapted to cause a distributed power generation source to modify its output so that a disturbance-related to the modified output will manifest on the node if an island is present; and

an island detection module adapted to generate an island detect signal in response to a disturbance-related to the modified output being detected on the node.