Wind turbine and method for detecting low-frequency oscillations in an electrical supply grid

Patent metadata

Field	Value
Publication number	US-12066474-B2
Application number	US-201917270818-A
Country	US
Kind code	B2
Filing date	Jul 31, 2019
Priority date	Aug 24, 2018
Publication date	Aug 20, 2024
Grant date	Aug 20, 2024

Abstract

A method for detecting low-frequency oscillations, in particular subsynchronous resonances, in an electrical supply grid is provided. The grid has a line voltage with a rated line frequency. The method comprises recording first and second series of measurements each for performing a frequency analysis (FFT). The method includes performing a lower frequency analysis for the first series for a lower frequency range and forming a lower amplitude spectrum. The method includes performing an upper frequency analysis for the second series for an upper frequency range and forming an upper amplitude spectrum. The method includes testing whether a low-frequency oscillation component can be identified in the lower amplitude spectrum, and testing whether a low-frequency oscillation component can be identified in the upper amplitude spectrum, where the presence of a low-frequency oscillation is assumed when a low-frequency oscillation component is identified in at least one of the lower and upper amplitude spectra.

First claim

The invention claimed is:

1. A method for detecting low-frequency oscillations in an electrical supply grid having a line voltage and a rated line frequency, comprising:
recording a first series of measurements and a second series of measurements;
performing a first frequency analysis on the first series of measurements for a lower frequency range and determining a first amplitude spectrum for the lower frequency range;
performing a second frequency analysis on the second series of measurements for an upper frequency range and determining a second amplitude spectrum for the upper frequency range;
determining whether the first amplitude spectrum has a first low-frequency oscillation component;
determining whether the second amplitude spectrum has a second low-frequency oscillation component; and
detecting a presence of a low-frequency oscillation in response to at least one of:
determining that the first amplitude spectrum has the first low-frequency oscillation component, and
determining that the second amplitude spectrum has the second low-frequency oscillation component,

wherein the low-frequency oscillation has a lower frequency than the rated line frequency, and
wherein:
the first and second series of measurements are recorded repeatedly and in self-repeating loops, and first and second frequency analyses are performed repeatedly,
a first loop includes recording the first series of measurements and performing the first frequency analysis,
a second loop includes recording the second series of measurements and performing the second frequency analysis, and
the second loop is run more frequently than the first loop.

2. The method as claimed in claim 1 , wherein:
the first series of measurements is recorded or evaluated by performing the first frequency analysis over a longer time period than the second series of measurements; and/or
the first series of measurements is recorded or evaluated by performing the first frequency analysis at a lower sampling rate than the second series of measurements.

3. The method as claimed in claim 1 , wherein:
the first series of measurements is recorded over a first time period in a range of 1 to 10 minutes; and/or
the second series of measurements is recorded over a second time period in a range of 1 to 10 seconds.

4. The method as claimed in claim 1 , comprising:
recording frequency measurements as the first series of measurements, wherein the first amplitude spectrum specifies frequency amplitudes in relation to frequency; and
recording voltage measurements as the second series of measurements, wherein the second amplitude spectrum specifies voltage amplitudes in relation to frequency.

5. The method as claimed in claim 4 , wherein performing the first frequency analysis includes determining a rate or frequency density of the frequency measurements or of a frequency gradient of the frequency measurements.

6. The method as claimed in claim 1 , wherein:
the electrical supply grid has a line frequency and a grid period; and
the second series of measurements is recorded for a second measurement time period which is dependent on the line frequency, wherein the second measurement time period is a multiple of the grid period.

7. The method as claimed in claim 1 , wherein:
the lower frequency range is from 0 to 5 Hz; and/or
the upper frequency range is from 0 Hz to the rated line frequency.

8. The method as claimed in claim 7 , wherein:
the lower frequency range is from 0 to 1 Hz; and/or
the upper frequency range is from 0.5 Hz to the rated line frequency.

9. The method as claimed in claim 1 , wherein:
the first and second series of measurements are recorded at a measurement point, and
the measurement point is arranged in a wind turbine connected to the electrical supply grid, the measurement point is arranged in a wind farm connected to the electrical supply grid, and/or recording of the first and second series of measurements is performed such that a voltage or a quantity representative of the voltage is detected at a grid connection point at which the wind turbine or the wind farm feeds into the electrical supply grid.

10. The method as claimed in claim 1 , comprising:
recording at least one further series of measurements;
performing, for each at least one further series of measurements, a respective further frequency analysis for a respective further frequency range and forming a respective further amplitude spectrum for the respective further frequency range;
determining whether the further amplitude spectrum has a respective low-frequency oscillation component; and
detecting the presence of the low-frequency oscillation in response to determining that the respective low-frequency oscillation component is detected in at least one of the further amplitude spectra.

11. The method as claimed in claim 1 , wherein the low-frequency oscillations are subsynchronous resonances.

12. The method as claimed in claim 1 , wherein the first frequency analysis and the second frequency analysis are fast Fourier transforms (FFTs).

13. The method as claimed in claim 1 , wherein the second loop is run at least 5 times as often as the first loop.

14. The method as claimed in claim 1 , wherein the second loop is run at least 10 times as often as the first loop.

15. The method as claimed in claim 1 , wherein the first low-frequency oscillation component in the first amplitude spectrum and the second low-frequency oscillation component in the second amplitude spectrum have a frequency of one hertz (Hz) or less.

16. A wind power system for detecting low-frequency oscillations in an electrical supply grid having a line voltage and a rated line frequency, the wind power system comprising:
a controller configured to:
record a first series of measurements and a second series of measurements;
perform a first frequency analysis on the first series of measurements for a lower frequency range and determine a first amplitude spectrum for the lower frequency range;
perform a second frequency analysis on the second series of measurements for an upper frequency range and determine a second amplitude spectrum for the upper frequency range;
determine whether the first amplitude spectrum has a first low-frequency oscillation component;
determine whether the second amplitude spectrum has a second low-frequency oscillation component; and
detect a presence of a low-frequency oscillation in response to at least one of:
determining that the first amplitude spectrum has the first low-frequency oscillation component, and
determining that the second amplitude spectrum has the second low-frequency oscillation component,

wherein the low-frequency oscillation has a lower frequency than the rated line frequency, and
wherein:
the controller is configured to repeatedly run a first process loop, wherein the first process loop includes recording the first series of measurements, performing the first frequency analysis, determining the first amplitude spectrum, and determining whether the first amplitude spectrum has the first low-frequency oscillation component,
the controller is configured to repeatedly run a second process loop, wherein the second process loop includes recording the second series of measurements, performing the second frequency analysis, determining the second amplitude spectrum, and determining whether the second amplitude spectrum has the second low-frequency oscillation component, and
the first and the second process loops are matched such that the second process loop is run more frequently than the first process loop.

Assignees

• Wobben Properties Gmbh

Inventors

• Brombach Johannes

Classifications

• H02J2101/28

  Wind energy · CPC title

• H02J3/00142

  Oscillations concerning frequency · CPC title

• H02J3/381

  Dispersed generators · CPC title

• G01R19/2513

  Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging · CPC title

• G01R19/2509 Primary

  Details concerning sampling, digitizing or waveform capturing · CPC title