Method for supplying electric power into an electric supply network by means of a converter-controlled supply device

Patent metadata

Field	Value
Publication number	US-10862308-B2
Application number	US-201816622201-A
Country	US
Kind code	B2
Filing date	Jun 7, 2018
Priority date	Jun 13, 2017
Publication date	Dec 8, 2020
Grant date	Dec 8, 2020

Abstract

Provided is a method for feeding electric power into an electricity supply grid having a grid voltage at a grid frequency having a grid nominal frequency. Feeding the electric power is performed by a converter-controlled feeding-in device, which may be a wind farm or a wind turbine. The feeding-in device feeds in an infeed current as electric AC current having a frequency, a phase, an infeed voltage and a fed-in power. The infeed voltage may be set. The method includes estimating a converter proportion in a grid section of the electricity supply grid that represents a ratio of power fed in by way of converters to overall fed-in power and controlling the infeed of the electric power depending on the estimated converter proportion.

First claim

The invention claimed is:

1. A method for feeding electric power into an electricity supply grid having a grid voltage at a grid frequency having a grid nominal frequency using a converter-controlled feeding-in device, comprising:
feeding, by the feeding-in device, the electric power in an infeed current that is an AC current having a frequency, a phase and an infeed voltage, wherein at least one of the frequency of the infeed current, the phase of the infeed current, the fed-in electric power and the infeed voltage is configurable;
estimating a converter proportion in a grid section of the electricity supply grid, wherein the converter proportion represents a ratio of power fed in by way of converters to an overall fed-in power; and
controlling the feeding of the electric power depending on the estimated converter proportion.

2. The method as claimed in claim 1 , comprising:
recording a cyclic change in the grid frequency as an amplitude or cycle time; and
estimating the converter proportion based on the recorded amplitude or the recorded cycle time, wherein:
the converter proportion is estimated to be positively correlated with the amplitude of the cyclic change,
the converter proportion is estimated to be negatively correlated with the cycle time, or
the converter proportion is estimated based on a quotient of the amplitude of the cyclic change to the cycle time of the cyclic change.

3. The method as claimed in claim 2 , comprising:
classifying the estimated converter proportion as either a high converter proportion or a low converter proportion, wherein the estimated converter proportion is classified as the high converter proportion when the amplitude of the cyclic change is greater than a predefined amplitude limit or the estimated converter proportion is classified as the high converter proportion when the cycle time is shorter than a predefined cycle time limit.

4. The method as claimed in claim 1 , comprising:
recording a frequency of occurrence or a frequency of occurrence density of the frequency or a frequency gradient; and
estimating the converter proportion based on the recorded frequency of occurrence or the frequency of occurrence density.

5. The method as claimed in claim 4 , wherein:
the frequency of occurrence or the frequency of occurrence density is a frequency of occurrence function based on the frequency, and the frequency of occurrence function:
has a frequency of occurrence maximum value in a region of a main frequency or the grid nominal frequency;
increases from a starting frequency that is less than the main frequency to the region of the main frequency;
drops from the region of the main frequency to a predefined end frequency that is greater than the main frequency;
has a lower frequency of occurrence reference value at a first reference frequency that is greater than the starting frequency and less than the main frequency; and
has an upper frequency of occurrence reference value at a second reference frequency that is greater than the main frequency and less than the end frequency, and

the method comprises:
estimating the converter proportion based on the frequency of occurrence maximum value.

6. The method as claimed in claim 5 , wherein:
the converter proportion is estimated to be negatively correlated with the frequency of occurrence maximum value,
the converter proportion is estimated to be positively correlated with a distance between the first and second reference frequency, or
the converter proportion is estimated to be positively correlated with the greater the upper and lower frequency of occurrence reference value.

7. The method as claimed in claim 5 , comprising:
classifying the estimated converter proportion as either a high converter proportion or a low converter proportion, wherein the estimated converter proportion is classified as the high converter proportion when the frequency of occurrence maximum value lies below a predefined frequency of occurrence limit value, the estimated converter proportion is classified as the high converter proportion when a distance between the upper and lower reference frequency is greater than a predefined reference distance, or the estimated converter proportion is classified as the a high converter proportion when the upper or lower frequency of occurrence reference value lies above a predefined basic limit value.

8. The method as claimed in claim 5 , wherein a reference function is predefined for the frequency of occurrence or frequency of occurrence density and the converter proportion is estimated depending on a deviation of the frequency of occurrence function from the reference function.

9. The method as claimed in claim 8 , comprising:
selecting the frequency of occurrence function for a converter proportion of zero as the reference function;
obtaining a difference function as a difference between the frequency of occurrence function and the reference function, and integrating the difference function for frequency regions below the first reference frequency and above the second reference frequency to produce a deviation integral; and
estimating the converter proportion based on the deviation integral.

10. The method as claimed in claim 9 , wherein only positive regions of the difference function are integrated to produce the deviation integral.

11. The method as claimed in claim 5 , comprising:
estimating the converter proportion based on a deviation of the main frequency from the grid nominal frequency such that the converter proportion is estimated to be positively correlated with the deviation of the main frequency from the grid nominal frequency.

12. The method as claimed in claim 5 , comprising:
estimating the converter proportion based on a distance between the first and second reference frequencies, wherein the first and second reference frequencies are a predefined lower and upper frequency of occurrence reference values, respectively; or
estimating the converter proportion based on the lower or upper frequency of occurrence reference values that are predefined lower or upper reference frequencies, respectively.

13. The method as claimed in claim 12 , wherein the lower and upper frequency of occurrence reference values are the same.

14. The method as claimed in claim 1 , comprising:
recording a fluctuation spectrum representing fluctuations of the frequency over time as a frequency spectrum of the grid frequency; and
estimating the converter proportion based on the fluctuation spectrum.

15. The method as claimed in claim 14 , comprising:
estimating the converter proportion based on at least one fluctuation amplitude of a fluctuation frequency of the fluctuation spectrum, wherein the fluctuation frequency lies in a range from 0.1 Hz to 0.5 Hz, wherein the converter proportion is estimated to be negatively correlated with the fluctuation amplitude.

16. The method as claimed in claim 1 , comprising:
recording a voltage spectrum of the grid voltage using a fast Fourier transform of an FFT of the grid voltage; and
estimating the converter proportion based on the voltage spectrum.

17. The method as claimed in claim 16 , wherein the converter proportion is estimated to be negatively correlated with a maximum value, a sum of a plurality of maximum values, or an average of the plurality of maximum values.

18. The method as claimed in claim 17 , comprising:
classifying the estimated converter proportion as either a high converter proportion or a low converter proportion, wherein a distinction is drawn between a high an

Assignees

• Wobben Properties Gmbh

Inventors

• Brombach Johannes

Classifications

• H02J2101/28

  Wind energy · CPC title

• H02J3/38 Primary

  Arrangements for feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel · CPC title

• Y02E10/76

  Power conversion electric or electronic aspects · CPC title

• H02J3/381 Primary

  Dispersed generators · CPC title

• H02J3/46

  Controlling the sharing of generated power between the generators, sources or networks · CPC title