A strategy for improving the accuracy of flicker emission measurement from wind turbines

• Voltage disturbances negatively affect the flicker measurement on wind turbines.
• Flicker measurement inaccuracy due to electrical angle estimation of the fundamental.
• Linear prefiltering guarantees convergent but inaccurate flicker results.
• Zero-phase prefiltering guarantees accurate flicker results.
• IEC 61400-21 could include a test protocol to ensure accurate flicker results.

The paper analyzes the flicker measurement procedure defined in the IEC 61400-21 standard to identify the sources of inaccuracy and divergence in the results. The analysis is focused on the estimation of the electrical angle of the fundamental frequency of the voltage measured in a wind turbine. The sensitivity to possible disturbances in the voltage signal was studied for different estimation methods. The harmonic and interharmonic pollution, as well as variations in the fundamental frequency, were demonstrated to be a source of error in flicker measurement. A narrow-band zero-phase filtering strategy is proposed to obtain accurate results with any of the estimation methods. The strategy has been validated using both simulated waveforms and an extensive set of recordings from a real wind turbine. The work highlights the need to define additional requirements in the IEC 61400-21 standard to guarantee accurate and convergent results of flicker emission from grid-connected wind turbines.