System and method for islanding detection and prevention in distributed generation

Patent metadata

Field	Value
Publication number	US-10069304-B2
Application number	US-201514737468-A
Country	US
Kind code	B2
Filing date	Jun 11, 2015
Priority date	Jun 11, 2014
Publication date	Sep 4, 2018
Grant date	Sep 4, 2018

Abstract

A method for detecting and preventing islanding includes issuing a command to an inverter connected to a power source, where the inverter is coupled to a power grid and supplies power to the power grid, the command causes a frequency of a waveform output by the inverter to vary, and the frequency of the waveform output by the inverter is a command frequency, determining that a amount of change of the command frequency is a constant value for a predetermined amount of time, removing the power supplied by the inverter from the power grid, and determining whether the power grid is valid.

First claim

What is claimed is:

1. A method for preventing islanding comprising:
issuing a command to an inverter connected to a power source, wherein the inverter is coupled to a power grid and provides power from the power source to the power grid, wherein the command causes a frequency of a waveform output by the inverter to vary, and wherein the frequency of the waveform output by the inverter is a command frequency;
determining that a amount of change of the command frequency is a constant value for a predetermined amount of time;
removing the power supplied by the inverter from the power grid; and
determining whether the power grid is valid; and
wherein the predetermined amount of time is a first predetermined amount of time, and wherein removing the power supplied by the inverter from the power grid comprises removing the power supplied by the inverter from the power grid in a second predetermined amount of time following the determining that the amount of change of the command frequency is the constant value for the first predetermined amount of time.

2. The method of claim 1 , wherein determining that the amount of change of the command frequency is the constant value for the predetermined amount of time comprises determining that the amount of change of the command frequency is a positive value or negative value for the predetermined amount of time.

3. The method of claim 1 , wherein the waveform is a current waveform, a voltage waveform, or a waveform of a phase of a current waveform.

4. The method of claim 1 , further comprising determining whether the amount of change of the command frequency is within a first predetermined threshold.

5. The method of claim 1 , wherein determining that the amount of change of the command frequency is the constant value for the predetermined amount of time comprises sampling the frequency of the waveform output by the inverter at predetermined intervals.

6. The method of claim 1 , wherein removing the power supplied by the inverter from the power grid comprises disconnecting the inverter from the power grid.

7. The method of claim 1 , wherein determining whether the power grid is valid comprises determining whether a main power source is connected to the power grid.

8. The method of claim 7 , wherein the main power source is a power source provided by an electric utility.

9. The method of claim 1 , further comprising upon determining that the power grid is not valid, foregoing reconnecting the inverter to the power grid.

10. The method of claim 1 , further comprising upon determining that the power grid is valid, reconnecting the inverter to the power grid.

11. A method for preventing islanding comprising:
issuing a command to an inverter connected to a power source, wherein the inverter is coupled to a power grid and provides power from the power source to the power grid, wherein the command causes a frequency of a waveform output by the inverter to vary, and wherein the frequency of the waveform output by the inverter is a command frequency;
determining that a amount of change of the command frequency is a constant value for a predetermined amount of time;
removing the power supplied by the inverter from the power grid;
determining whether the power grid is valid;
determining whether the amount of change of the command frequency is within a first predetermined threshold; and
determining whether the amount of change of the command frequency is within a second predetermined threshold.

12. The method of claim 11 , further comprising upon determining that the power grid is not valid, foregoing reconnecting the inverter to the power grid.

13. The method of claim 11 , further comprising upon determining that the power grid is valid, reconnecting the inverter to the power grid.

14. The method of claim 11 , wherein determining that the amount of change of the command frequency is the constant value for the predetermined amount of time comprises determining that the amount of change of the command frequency is a positive value or negative value for the predetermined amount of time.

15. The method of claim 11 , wherein determining that the amount of change of the command frequency is the constant value for the predetermined amount of time comprises sampling the frequency of the waveform output by the inverter at predetermined intervals.

16. A method for preventing islanding comprising:
issuing a command to an inverter connected to a power source, wherein the inverter is coupled to a power grid and provides power from the power source to the power grid, wherein the command causes a frequency of a waveform output by the inverter to vary, and wherein the frequency of the waveform output by the inverter is a command frequency;
determining that a amount of change of the command frequency is a constant value for a predetermined amount of time;
removing the power supplied by the inverter from the power grid;
determining whether the power grid is valid;
determining whether the amount of change of the command frequency is within a first predetermined threshold;
determining whether the amount of change of the command frequency is within a second predetermined threshold; and
wherein the second predetermined threshold is a range of values that is within the first predetermined threshold.

17. The method of claim 16 , further comprising upon determining that the power grid is not valid, foregoing reconnecting the inverter to the power grid.

18. The method of claim 16 , further comprising upon determining that the power grid is valid, reconnecting the inverter to the power grid.

19. The method of claim 16 , wherein determining that the amount of change of the command frequency is the constant value for the predetermined amount of time comprises determining that the amount of change of the command frequency is a positive value or negative value for the predetermined amount of time.

20. The method of claim 16 , wherein determining that the amount of change of the command frequency is the constant value for the predetermined amount of time comprises sampling the frequency of the waveform output by the inverter at predetermined intervals.

Assignees

• Bhowmik Shibashis
• Mazhari Iman
• Parkhideh Babak
• Sinewatts Inc
• Univ North Carolina Charlotte

Inventors

• Bhowmik Shibashis
• Mazhari Iman
• Parkhideh Babak

Classifications

• H02J3/381 Primary

  Dispersed generators · CPC title

• H02J2101/20

  Dispersed power generation using renewable energy sources · CPC title

• H02J3/388

  Arrangements for the handling of islanding, e.g. for disconnection or for avoiding the disconnection of power · CPC title

• H02J2003/388

  Electricity · mapped topic

• H02J3/382 Primary

  Electricity · mapped topic