Method and system for island detection and anti-islanding protection in distributed power generation systems
AssigneeMichael Ropp
InventorMichael Ropp
Life of this patent
Estimating the term…
Abstract
An effective, yet relatively simple and inexpensive, method for detection of islanding in distributed power generation systems. Statistical analysis of the local line frequency, as measured at the distributed generator, is performed to detect when an island has been formed. The statistical characteristics of the local frequency are controlled by the grid when the distributed generator is not islanding. When an island is formed, however, frequency control switches to circuitry associated with the distributed generator. Because the statistical characteristics of the frequency control performed by the distributed generator are markedly different from those of the grid, the islanding condition can be detected and corrected.
Claims9
A method of detecting island formation in a distributed power system including at least one distributed generator interruptably coupled to a grid through a feeder, the method comprising:
- using a frequency measurement device to compile a plurality of values of frequency change in the power system, measured over a predetermined time window;
- using a processor to group the plurality of values of frequency change into a plurality of bins, a first one of the bins representing an expected behavior of power frequency change when the feeder is grid-tied, a second one of the bins representing an expected behavior of power frequency change when the feeder is islanded, and a third one of the bins representing another expected behavior of power frequency change when the feeder is grid-tied;
- computing a bimodality index for the grouped values of frequency change;
- using the processor to apply a predetermined decision criterion to the grouped values of frequency change to determine whether the feeder is islanded or grid-tied, wherein the decision criterion comprises determining whether a value of the bimodality index is in the range of between 0 and 10 over more than 75% of the time window;
- and
- automatically decoupling the distributed generator from the feeder if the feeder is determined to be islanded.
An anti-islanding control apparatus for use in a distributed power system including at least one distributed generator interruptably coupled to a grid through a feeder, the apparatus comprising a processor communicatively coupled with a control system of the at least one distributed generator and programmed with an algorithm for:
- grouping a plurality of values of frequency change in the power system, measured over a predetermined time window, into a plurality of bins, a first one of the bins representing an expected behavior of power frequency change when the feeder is grid-tied, a second one of the bins representing an expected behavior of power frequency change when the feeder is islanded, and a third one of the bins representing another expected behavior of power frequency change when the feeder is grid-tied;
- computing a bimodality index for the grouped values of frequency change;
- applying a predetermined decision criterion to the grouped values of frequency change to determine whether the feeder is islanded or grid-tied, wherein the decision criterion comprises determining whether a value of the bimodality index is in the range of between 0 and 10 over more than 75% of the time window;
- and
- decoupling the distributed generator from the feeder if the feeder is determined to be islanded.
An article comprising a machine-readable medium storing instructions operable to detect and correct island formation in a distributed power system, the power system including at least one distributed generator interruptably coupled to a grid through a feeder, the instructions for:
- grouping a plurality of values of frequency change in the power system, measured over a predetermined time window, into a plurality of bins, a first one of the bins representing an expected behavior of power frequency change when the feeder is grid-tied, a second one of the bins representing an expected behavior of power frequency change when the feeder is islanded, and a third one of the bins representing another expected behavior of power frequency change when the feeder is grid-tied;
- computing a bimodality index for the grouped values of frequency change;
- applying a predetermined decision criterion to the grouped values of frequency change to determine whether the feeder is islanded or grid-tied, wherein the decision criterion comprises determining whether a value of the bimodality index is in the range of between 0 and 10 over more than 75% of the time window;
- and
- decoupling the distributed generator from the feeder if the feeder is determined to be islanded.
Dependencies are inferred from the claim text.