Interface switch for distributed energy resources

• US 20070129110A1
• Filed: 11/04/2005
• Published: 06/07/2007
• Est. Priority Date: 11/04/2005
• Status: Active Grant

• Current Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Original Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Inventors: Piagi, Paolo, Lasseter, Robert
• Granted Patent: US 7,521,825 B2
• Time in Patent Office: Days
• US Class Current: 455/557
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers

Abstract

A method and apparatus for an interface switch having an external terminal electrically connected to an AC voltage E at a frequency ω₀ (for example a utility supply), and an internal terminal electrically connected to an AC voltage V at a selectable frequency ω (for example a microsource). In one embodiment, the interface switch is closed when the voltage difference between E and V and the relative phase angle δ_EV between E and V are both small, and when the higher frequency voltage (as between E and V) leads the lower frequency voltage. In another embodiment, the interface switch is closed when the envelope of the voltage difference between E and V reaches a local minimum at a point of inflection.

Claims

1. A method of operating an interface switch between a microgrid and a supply bus bearing an AC voltage E at a frequency ω

₀, the method comprising;

(a) providing a microgrid having a microsource bus and a microsource delivering an AC voltage V at a selectable frequency ω

to the microsource bus;

(b) providing an interface switch having an external terminal electrically connected to the supply bus and an internal terminal electrically connected to the microsource bus;

wherein the interface switch can be opened to electrically isolate the supply bus from the microsource bus and can be closed to electrically connect the supply bus with the microsource bus;

(c) opening the interface switch at a time when the interface switch is closed and the microgrid is importing power from the supply bus;

(d) measuring a voltage difference between E and V and measuring a relative phase angle δ

_EV between E and V while the interface switch is open; and

(e) closing the interface switch at a time when the voltage difference between E and V is relatively small, when the relative phase angle δ

_EV between E and V is relatively small, and when E leads V.

2. The method of claim 1 wherein the step of closing the interface switch is performed when the voltage difference between E and V is less than 10% of the average peak value of E.

3. The method of claim 1 wherein the step of closing the interface switch is performed when the voltage difference between E and V is less than 3% of the average peak value of E.

4. The method of claim 1 wherein the step of closing the interface switch is performed when the magnitude of δ

_EV is greater than or equal to about 0 degrees and less than or equal to about 10 degrees.

5. The method of claim 1 wherein the step of closing the interface switch is performed when the magnitude of δ

_EV is greater than or equal to about 0 degrees and less than or equal to about 3 degrees.

6. The method of claim 1 wherein the supply bus receives electrical power directly or indirectly from a utility grid.

7. A method of operating an interface switch between a microgrid and a supply bus bearing an AC voltage E at a frequency ω

₀, the method comprising;

(a) providing a microgrid having a microsource bus and a microsource delivering an AC voltage V at a selectable frequency ω

to the microsource bus;

(b) providing an interface switch having an external terminal electrically connected to the supply bus and an internal terminal electrically connected to the microsource bus;

wherein the interface switch can be opened to electrically isolate the supply bus from the microsource bus and can be closed to electrically connect the supply bus with the microsource bus;

(c) opening the interface switch at a time when the interface switch is closed and the microgrid is exporting power to the supply bus;

(d) measuring a voltage difference between E and V and measuring a relative phase angle δ

_EV between E and V while the interface switch is open; and

(e) closing the interface switch at a time when the voltage difference between E and V is relatively small, when the relative phase angle δ

_EV between E and V is relatively small, and when V leads E.

8. The method of claim 7 wherein the step of closing the interface switch is performed when the voltage difference between E and V is less than 10% of the average peak value of E.

9. The method of claim 7 wherein the step of closing the interface switch is performed when the voltage difference between E and V is less than 3% of the average peak value of E.

10. The method of claim 7 wherein the step of closing the interface switch is performed when the magnitude of δ

_EV is greater than or equal to about 0 degrees and less than or equal to about 10 degrees.

11. The method of claim 7 wherein the step of closing the interface switch is performed when the magnitude of δ

_EV is greater than or equal to about 0 degrees and less than or equal to about 3 degrees.

12. The method of claim 7 wherein the supply bus receives electrical power from a utility supply.

13. An interface switch comprising:

(a) an internal terminal electrically connectable to an internal power bus bearing an AC voltage V at a selectable frequency ω

;

(b) an external terminal electrically connectable to an external power bus bearing an AC voltage E at a frequency ω

₀;

(c) a controllable electrical switch between the internal terminal and the external terminal, the controllable electrical switch having an open condition wherein the internal terminal is electrically isolated from the external terminal and a closed condition wherein the internal terminal is electrically connected to the external terminal; and

(d) a switch controller adapted to control the electrical switch by placing the electrical switch into the open condition or the closed condition,

wherein the switch controller is adapted to monitor a voltage difference between E and V;

wherein the switch controller is adapted to monitor a relative phase angle δ

_EV between E and V;

wherein the switch controller is adapted to close the electrical switch at a time

when the voltage difference between E and V is small,

when the relative phase angle δ

_EV between E and V is small, and

when either E leads V if ω

≧

ω

₀ or V leads E with ω

≦

ω

₀,

whereby the interface switch is adapted for bidirectional power transfer between the internal power bus and the external power bus.

14. The interface switch of claim 13 wherein the switch controller is adapted to close the electrical switch when E leads V and ω

≧

ω

₀, whereby the interface switch is adapted for use with an internal power bus that imports power from, but does not export power to, the external power bus.

15. The interface switch of claim 14 wherein the switch controller is adapted to close the electrical switch when the voltage difference between E and V is less than 10% of the average peak value of E.

16. The interface switch of claim 14 wherein the switch controller is adapted to close the electrical switch when the magnitude of δ

_EV is greater than or equal to about 0 degrees and less than or equal to about 10 degrees.

17. The interface switch of claim 13 wherein the switch controller is adapted to close the electrical switch when V leads E and ω

≦

ω

₀, whereby the interface switch is adapted for use with an internal power bus that exports power to, but does not import power from, the external power bus.

18. The interface switch of claim 17 wherein the switch controller is adapted to close the electrical switch when the voltage difference between E and V is less than 10% of the average peak value of E.

19. The interface switch of claim 17 wherein the switch controller is adapted to close the electrical switch when the magnitude of δ

_EV is greater than or equal to about 0 degrees and less than or equal to about 10 degrees.

20. The interface switch of claim 13 wherein the voltage E is supplied by a utility supply, and wherein the voltage V is supplied by a microsource.

21. A method of operating an interface switch between an internal bus and an external bus bearing an AC voltage E at a frequency ω

₀, the method comprising;

(a) providing an internal bus bearing an AC voltage V at a selectable frequency ω

;

(b) providing an interface switch having an external terminal electrically connected to the external bus and an internal terminal electrically connected to the internal bus;

wherein the interface switch can be opened to electrically isolate the external bus from the internal bus and can be closed to electrically connect the external bus with the internal bus;

(c) opening the interface switch at a time when the interface switch is closed;

(d) measuring the envelope of the waveform of the voltage difference between E and V while the interface switch is open; and

(e) closing the interface switch at or just after a time when the envelope of the waveform of the voltage difference between E and V reaches a local minimum at a point of inflection.

22. The method of claim 21 wherein the external bus bears electrical power supplied directly or indirectly by a utility supply.

23. The method of claim 22 wherein the external bus bears electrical power at 60 Hz.

24. The method of claim 21 wherein the internal bus bears electrical power supplied directly or indirectly by a microsource.

25. The method of claim 24 wherein the external bus bears electrical power supplied directly or indirectly by a utility supply.

26. An interface switch comprising:

(a) an internal terminal electrically connectable to an internal power bus bearing an AC voltage V at a selectable frequency ω

;

(b) an external terminal electrically connectable to an external power bus bearing an AC voltage E at a frequency ω

₀;

(c) a controllable electrical switch between the internal terminal and the external terminal, the controllable electrical switch having an open condition wherein the internal terminal is electrically isolated from the external terminal and a closed condition wherein the internal terminal is electrically connected to the external terminal; and

(d) a switch controller adapted to control the electrical switch by placing the electrical switch into the open condition or the closed condition,

wherein the switch controller is adapted to monitor the envelope of the waveform of the voltage difference between E and V;

wherein the switch controller is adapted to close the electrical switch at or just after a time when the envelope of the waveform of the voltage difference between E and V reaches a local minimum at a point of inflection.

27. The interface switch of claim 26 wherein the external bus bears electrical power supplied directly or indirectly by a utility supply.

28. The interface switch of claim 27 wherein the external bus bears electrical power at 60 Hz.

29. The interface switch of claim 26 wherein the internal bus bears electrical power supplied directly or indirectly by a microsource.

30. The interface switch of claim 29 wherein the external bus bears electrical power supplied directly or indirectly by a utility supply.