DFIG Stator Active Filtering for Fast Harmonic Grid Compliance
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Solution Overview
Problem
Wind turbines with doubly-fed induction generators (DFIG) generate turbine harmonics that need to be controlled and reduced to comply with grid codes, particularly for fast and reliable harmonic control.
Innovation Solution
An active filter is connected to the stator bus of the DFIG system, controlled based on the rotor frequency to determine expected harmonic frequencies and amplitudes of the stator current, allowing for rapid and efficient harmonic reduction by actively filtering the stator current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If an active filter is used to reduce harmonics in DFIG systems, then harmonic attenuation is improved, but device complexity increases
Solution Approach 1:
The patent extracts the harmonic filtering function into a separate active filter component connected to the stator bus, independent from the rotor-side converter. This allows targeted harmonic mitigation without modifying the core DFIG operation, resolving the contradiction by isolating the harmful harmonic handling from the main power conversion system.
Solution Approach 2:
The control system determines expected harmonic frequencies based on rotor frequency before harmonics are generated, and pre-configures the active filter to attenuate these specific frequencies. This preliminary action enables efficient harmonic reduction without requiring complex real-time analysis of actual harmonic content.
2Reliability
If harmonic control is made fast and reliable, then compliance with grid codes is improved, but computational effort increases
Solution Approach 1:
The patent calculates expected harmonic frequencies in advance based on the rotor frequency, which is already known from normal DFIG operation. By determining harmonic frequencies before they are generated and preparing the filter response beforehand, the system achieves fast and reliable harmonic control without requiring complex real-time computational analysis of actual harmonic spectra.
Solution Approach 2:
The control system continuously monitors rotor frequency and uses this feedback to dynamically adjust the expected harmonic frequency determination. This feedback mechanism ensures reliable harmonic control adapts to changing operating conditions while maintaining computational efficiency through the established relationship between rotor frequency and harmonic frequencies.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The active filter effectively reduces harmonics supplied to the utility grid by quickly determining and controlling the stator current harmonics, achieving compliance with grid codes with minimal computational effort.
Implementation Method 1
An active filter is connected to the stator bus of the DFIG system, controlled based on the rotor frequency to determine expected harmonic frequencies and amplitudes of the stator current, allowing for rapid and efficient harmonic reduction by actively filtering the stator current.
Data Source
Figure 1
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Figure 3A~3B
AI summary
A method for operating a power supply system connected to a grid and including a rotor (106), a DFIG (118), a power conversion assembly (210), and an active filter (270) is disclosed. The DFIG (118) includes a generator rotor (122) mechanically connected with the rotor (106) and a generator stator (120). The power conversion assembly (210) includes a rotor-side power converter (220). The active filter (270) is electrically connected with the generator stator (120) via a stator bus (208). The rotor-side power converter (220) is electrically connected with the generator rotor (122) via a rotor bus (212). The method includes: determining (1100, 2100, 3100), based on a rotor frequency (fr) of the generator rotor (122), an expected harmonic frequency ({fh}) for a stator current (Is) flowing on the stator bus (208); determining (1200, 2200, 3200), in a data set comprising stator current values ({Is}), a current amplitude ({Ih}) of the stator current (Is) at the expected harmonic frequency ({fh}); and controlling (1300, 2300, 3300), based on the current amplitude ({Ih}) of the stator current (Is) at the expected harmonic frequency ({fh}), the active filter (270).