Systems and methods for islanding detection

• US 9,142,968 B2
• Filed: 05/09/2011
• Issued: 09/22/2015
• Est. Priority Date: 05/07/2010
• Status: Active Grant

• Current Assignee: SMA Solar Technology AG
• Original Assignee: Advanced Energy Industries Incorporated
• Inventors: Ropp, Michael
• Primary Examiner(s): Lo, Kenneth M
• Assistant Examiner(s): Lopez Alvarez, Olvin
• Application Number:
  US13/103,721
• Publication Number:
  US 20110276192A1
• Time in Patent Office: 1,597 Days
• Field of Search: 700/293
• US Class Current: 1/1
• CPC Class Codes: H02J 13/00034 the elements or equipment being or involving an electric power substation
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 3/381 Dispersed generators
• 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
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y02E 40/70 Smart grids as climate change mitigation technology in the energy generation sector
• CPC Class Codes: Y02E 60/00 Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
• CPC Class Codes: Y02P 80/20 using renewable energy
• CPC Class Codes: Y04S 10/123 the energy generation units being or involving renewable energy sources
• CPC Class Codes: Y04S 10/16 Electric power substations
• CPC Class Codes: Y04S 10/30 State monitoring, e.g. fault, temperature monitoring, insulator monitoring, corona discharge

Abstract

A solar power inverter that detects islanding conditions includes a power generation component that generates alternating current (AC) from direct current produced by photovoltaic cells. The inverter generates AC for a load or an electrical power grid. The inverter also includes a component that generates synchrophasors from characteristics of electrically proximate AC. The inverter further includes a component that receives grid synchrophasors transmitted from a location on the electrical power grid (e.g., a transmission substation). The inverter further includes a controller that uses the inverter synchrophasors and the grid synchrophasors to calculate a degree of correlation between the electrical power grid AC frequency and the frequency of the electrically proximate AC. If the degree of correlation dips below a predefined value or exhibits certain patterns or behaviors that are indicative of a loss of mains (e.g., a loss of main power along the electrical power grid), the controller can cause the power generation component to stop generating AC or cause the inverter to intentionally island by electrically disconnecting from the electrical power grid.

Claims

1. A solar power inverter comprising:

a direct current (DC) input component configured to receive DC produced by one or more photovoltaic cells;

a power generation component configured to generate alternating current (AC) from the DC produced by one or more photovoltaic cells;

an AC output component configured to output generated AC, wherein the AC output component is electrically coupleable to an electrical power grid;

a data input/output component configured to receive signals indicating electrical power grid synchrophasors, wherein the electrical power grid synchrophasors describe characteristics of AC transmitted by the electrical power grid;

a phasor measurement unit configured to generate inverter synchrophasors, wherein the inverter synchrophasors describe characteristics of AC electrically proximate to the AC output component; and

a controller coupled to the data input/output component and the phasor measurement unit, wherein the controller is programmed to-receive the electrical power grid synchrophasors from the data input/output component;

receive the inverter synchrophasors from the phasor measurement unit;

based upon the electrical power grid synchrophasors, determine a first set of n frequency values for the AC transmitted by the electrical power grid;

based upon the inverter synchrophasors, determine a second set of n frequency values for the generated AC; and

determine a correlation coefficient representing a measure of a statistical correlation between the set of n frequency values for the AC transmitted by the electrical power grid and the set of n frequency values for the generated AC;

wherein the correlation coefficient is determined by

2. The solar power inverter of claim 1 wherein the controller is further programmed to:

cause the power generation component to stop generating AC upon determination that an islanding condition has occurred.

3. The solar power inverter of claim 1, wherein the AC output component is electrically coupleable to the electrical power grid through a switch positioned electrically between the AC output component and the electrical power grid, and wherein the controller is further programmed to:

detect that the correlation coefficient is below the pre-defined threshold; and

transmit a signal indicating that the switch is to be opened.

4. The solar power inverter of claim 1, wherein the data input/output component is further configured to receive signals indicating electrical power grid synchrophasors from a transmitter communicably coupled to a phasor measurement unit that generates the electrical power grid synchrophasors.

5. The solar power inverter of claim 1 wherein the signals received by the data input/output component include an identifier of at least one of a source of the signals and a source of the electrical power grid synchrophasors.

6. the solar power inverter of claim 1, wherein the electrical power grid synchrophasors are time stamped and contain information about the frequency of the electrical alternating current at a substation on the electrical grid.

7. The solar power inverter of claim 1, wherein the number of frequency values n in the first and second sets is greater than 5.

8. An apparatus that enables islanding detection, the apparatus comprising:

a processor; and

a computer-readable medium having instructions stored thereon that, if executed by the processor, cause the processor to perform operations comprising

receiving a first set of n frequency values, wherein each of the n frequency values in the first set indicates a frequency x of alternating current (AC) transmitted by an electrical power grid;

receiving a second set of n frequency values, wherein each of the n frequency values in the second set indicates a frequency y of AC electrically proximate to a power generation source electrically connected to the electrical power grid; and

calculating a correlation coefficient representing a measure of a statistical correlation between the first and second sets of n frequency values by

9. The apparatus of claim 8 wherein the computer readable medium further includes instructions that if executed, cause the processor to perform operations comprising:

receiving a first set of synchrophasors, wherein each of the synchrophasors in the first set includes characteristics of the AC transmitted by the electrical power grid;

receiving a second set of synchrophasors, wherein each of the synchrophasors in the second set includes characteristics of the AC electrically proximate to the power generation source;

determining the first set of n frequency values from the first set of synchrophasors; and

determining the second set of n frequency values from the second set of synchrophasors.

10. The apparatus of claim 8 wherein the computer readable medium includes instructions that when executed by the processor cause the processor to perform operations including disconnecting the power generation source from the electrical power grid if the correlation coefficient is below a pre-defined threshold value.

11. The apparatus of claim 8 wherein the computer readable medium further includes instructions that if executed, cause the processor to perform operations comprising:

detecting that the correlation coefficient is below a pre-defined threshold value; and

transmitting a signal indicating that the power generation source is to stop generating AC.

12. The apparatus of claim 8 wherein the computer readable medium further includes instructions that if executed, cause the processor to perform operations comprising:

detecting that the correlation coefficient is below a value that indicates a loss of main power along the electrical power grid; and

transmitting a signal indicating that the power generation source is to stop generating AC.

13. The apparatus of claim 8 wherein the computer readable medium further includes instructions that if executed, cause the processor to perform operations comprising:

detecting that the correlation coefficient is below a pre-defined threshold value; and

transmitting a signal indicating that an electrical connection between the power generation source and the electrical power grid is to be opened.

14. The apparatus of claim 8 wherein the computer readable medium further includes instructions that if executed, cause the processor to perform operations comprising:

detecting that the correlation coefficient is below a threshold which indicates a loss of main power along the electrical power grid; and

transmitting a signal indicating that an electrical connection between the power generation source and the electrical power grid is to be opened.

15. The apparatus of claim 8 wherein the computer readable medium further includes instructions that if executed, cause the processor to perform operations comprising:

receiving a first set of synchrophasors transmitted by a transceiver, wherein each of the synchrophasors in the first set indicates characteristics of the AC transmitted by the electrical power grid, and

determining the first set of n frequency values from the first set of synchrophasors.

16. The apparatus of claim 8, wherein the first set of frequency values are encoded as a time stamped synchrophasors and indicate the frequency of the electrical alternating current on the power grid at a substation on the electrical power grid.

17. The apparatus of claim 8, wherein the number of frequency values n in the first and second sets is greater than 5.

18. A method of operating a computing system having a processor and a memory, to disconnect a power generation source from an electrical power grid, the method comprising:

receiving a first set of n frequency values, wherein each frequency value x in the first set indicates a frequency of alternating current (AC) transmitted by an electrical power grid;

receiving a second set of n frequency values, wherein each frequency value y in the second set indicates a frequency of AC electrically proximate to a power generation source electrically connected to the electrical power grid;

calculating, by the computing system, correlation coefficient representing a measure of a statistical correlation between the first and second sets of frequency values by

19. The method of claim 18, further comprising:

receiving a first set of synchrophasors, wherein each of the synchrophasors in the first set includes characteristics of the AC transmitted by the electrical power grid;

receiving a second set of synchrophasors, wherein each of the synchrophasors in the second set includes characteristics of the AC electrically proximate to the power generation source;

determining the first set of n frequency values from the first set of synchrophasors; and

determining the second set of n frequency values from the second set of synchrophasors.

20. The method of claim 18 wherein the power generation source remains electrically connected to the electrical power grid as long as the correlation coefficient is above a pre-defined threshold number.

21. The method of claim 18, further comprising:

detecting that the correlation coefficient is below a pre-defined threshold value; and

transmitting a signal indicating that the power generation source is to stop generating alternating current.

22. The method of claim 18, further comprising:

detecting that the correlation coefficient is below a threshold that indicates a loss of main power along the electrical power grid; and

transmitting a signal indicating that the power generation source is to stop generating alternating current.

23. The method of claim 18, further comprising:

detecting that the correlation coefficient is below a threshold that indicates a loss of main power along the electrical power grid; and

transmitting a signal indicating that an electrical connection between the power generation source and the electrical power grid is to be opened.

24. A system for islanding detection, the system comprising:

means for receiving a first set of synchrophasors, each of the first set of synchrophasors describing characteristics of alternating current (AC) transmitted by an electrical power grid;

means for generating a second set of synchrophasors, each of the second set of synchrophasors describing characteristics of AC electrically proximate to a power generation source electrically connected to the electrical power grid; and

means for determining, based upon the first and second sets of synchrophasors, n samples of a frequency x of the AC transmitted by the electrical power grid and n samples of a frequency y of the AC generated by the power generation source; and

means for calculating a correlation coefficient {circumflex over (p)} representing a statistical correlation of the n samples of the frequency of the AC transmitted by the electrical power grid and the n samples of the frequency of the AC generated by the power generation source by;

25. The system of claim 24, further comprising means for transmitting a signal indicating that the power generation source is to stop generating alternating current in response to a determination that the correlation coefficient falls below a threshold that indicates a loss of main power along the electrical power grid.

26. The system of claim 24, further comprising means for transmitting a signal indicating that an electrical connection between the power generation source and the electrical power grid is to be opened in response to a determination that the correlation coefficient is below a pre-defined value.

27. The system of claim 24, wherein the means for receiving the first set of synchrophasors includes means for receiving a wireless signal indicating the first set of synchrophasors.