Method and apparatus for detecting a short-circuit capacity at a grid connection point of a wind turbine

Patent metadata

Field	Value
Publication number	US-2021140407-A1
Application number	US-201816465792-A
Country	US
Kind code	A1
Filing date	Jul 13, 2018
Priority date	Mar 21, 2018
Publication date	May 13, 2021
Grant date	—

Abstract

The present disclosure discloses a method and apparatus for detecting a short-circuit capacity at a grid connection point of a wind turbine. The method includes: modulating, when a converter is in a grid-side no-load modulation state and a power grid is in a short-circuited state with respect to the converter, a reactive power reference value and a braking power reference value of the converter; collecting a modulated three-phase voltage signal and a modulated three-phase current signal at the grid connection point of the wind turbine; and obtaining, according to the modulated three-phase voltage signal and the modulated three-phase current signal at the grid connection point of the wind turbine as well as a rated line voltage at the grid connection point of the wind turbine, the short-circuit capacity at the grid connection point of the wind turbine.

First claim

1 . A method for detecting a short-circuit capacity at a grid connection point of a wind turbine, comprising:
modulating, when a converter is in a grid-side no-load modulation state and a power grid is in a short-circuited state with respect to the converter, a reactive power reference value and a braking power reference value of the converter, and collecting a modulated three-phase voltage signal and a modulated three-phase current signal at the grid connection point of the wind turbine; and obtaining, according to the modulated three-phase voltage signal and the modulated three-phase current signal at the grid connection point of the wind turbine as well as a rated line voltage at the grid connection point of the wind turbine, the short-circuit capacity at the grid connection point of the wind turbine.

2 . The method according to claim 1 , wherein when the power grid is in a short-circuited state with respect to the converter, a power system between the power grid and the converter is equivalent to a low-voltage side power supply, an internal resistance and a line impedance in series, and
said modulating the reactive power reference value and the braking power reference value of the converter comprise: performing, when a difference between the line impedance and the internal resistance is greater than a first predetermined threshold and a difference between an inductive reactance in the line impedance and a resistance in the line impedance is greater than a second predetermined threshold, a first no-load modulation operation on the converter in which the reactive power reference value is set to any power value between 0 and a rated apparent power of an inverter in the converter and the braking power reference value is set to zero.

3 . The method according to claim 2 , wherein said obtaining, according to the modulated three-phase voltage signal and the modulated three-phase current signal at the grid connection point of the wind turbine as well as the rated line voltage at the grid connection point of the wind turbine, the short-circuit capacity at the grid connection point of the wind turbine comprises:
obtaining, according to a three-phase voltage signal and a three-phase current signal at the grid connection point of the wind turbine after the first no-load modulation operation, a first short-circuit voltage effective value and a first reactive power feedback value; obtaining, according to a three-phase voltage signal at the grid connection point of the wind turbine when the power grid is disconnected with the converter, a first initial voltage effective value; and obtaining, according to the first initial voltage effective value, the first short-circuit voltage effective value, the first reactive power feedback value and the rated line voltage, the short-circuit capacity at the grid connection point of the wind turbine.

4 . The method according to claim 3 , wherein said obtaining, according to the first initial voltage effective value, the first short-circuit voltage effective value, the first reactive power feedback value and the rated line voltage, the short-circuit capacity at the grid connection point of the wind turbine comprises:
obtaining the inductive reactance in the line impedance according to the first initial voltage effective value, the first short-circuit voltage effective value and the first reactive power feedback value; and obtaining, according to the inductive reactance and the rated line voltage, the short-circuit capacity at the grid connection point of the wind turbine.

5 . The method according to claim 2 , wherein said modulating the reactive power reference value and the braking power reference value of the converter comprises:
performing, when a difference between the line impedance and the internal resistance is greater than the first predetermined threshold and the difference between the inductive reactance in the line impedance and the resistance in the line impedance is not greater than the second predetermined threshold, the first no-load modulation operation and a second no-load modulation operation on the converter, wherein in the second no-load modulation operation, the reactive power reference value is set to 0, and the braking power reference value is set to any power value between 0 and the rated apparent power.

6 . The method according to claim 5 , wherein said obtaining, according to the modulated three-phase voltage signal and the modulated three-phase current signal at the grid connection point of the wind turbine as well as the rated line voltage at the grid connection point of the wind turbine, the short-circuit capacity at the grid connection point of the wind turbine comprises:
obtaining a second short-circuit voltage effective value, a second reactive power feedback value and a first active power feedback value according to a three-phase voltage signal and a three-phase current signal after the first no-load modulation operation, and obtaining a third short-circuit voltage effective value, a third reactive power feedback value and a second active power feedback value according to a three-phase voltage signal and a three-phase current signal after the second no-load modulation; obtaining a second initial voltage effective value according to the three-phase voltage signal at the grid connection point of the wind turbine when the power grid is disconnected with the converter; obtaining, according to the second initial voltage effective value, the second short-circuit voltage effective value, the second reactive power feedback value, the first active power feedback value, the third short-circuit voltage effective value, the third reactive power feedback value and the second active power feedback value, the inductive reactance in the line impedance and the resistance in the line impedance; and obtaining, according to the inductive reactance, the resistance and the rated line voltage, the short-circuit capacity at the grid connection point of the wind turbine.

7 . The method according to claim 1 , wherein after said collecting the modulated three-phase voltage signal and the modulated three-phase current signal at the grid connection point of the wind turbine, the method further comprises:
obtaining, according to the modulated three-phase voltage signal and the modulated three-phase current signal at the grid connection point of the wind turbine when the power grid is short-circuited as well as the modulated reactive power reference value, a PWM (Pulse Width Modulation) signal for driving a switching device in the converter such that a reactive power output by the converter approaches the modulated reactive power reference value; or obtaining, according to the modulated reactive power reference value, a PWM signal for driving a switching device in the converter so as to adjust a reactive power outputted by the converter.

8 . The method according to claim 1 , wherein after said collecting the modulated three-phase voltage signal and the modulated three-phase current signal at the grid connection point of the wind turbine, the method further comprises:
obtaining, according to a voltage feedback signal and a current feedback signal of a braking unit in the converter after said modulating when the power grid is short-circuited as well as a modulated braking power reference value, a PWM (Pulse Width Modulation) signal for driving a switching device of a braking power module in the braking unit such that a braking power of the braking unit approaches the modulated braking power reference value; or obtaining, according to the modulated reactive power reference value, a PWM signal for driving a switching device in the braking unit so as to adjust a braking power of the braking unit.

9 . A

Assignees

• Beijing Goldwind Science & Creation Windpower Equipment Co Ltd

Inventors

• Gao Rui

Classifications

• H02J13/1323

  using optical fibres · CPC title

• H02J13/333

  the equipment forming part of substations · CPC title

• H02J13/12

  Monitoring network conditions, e.g. electrical magnitudes or operational status · CPC title

• Y02E10/76

  Power conversion electric or electronic aspects · CPC title

• G01R31/50 Primary

  Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections (testing of sparking plugs H01T13/58) · CPC title