The integration into the grid of renewable energy poses a significant challenge regarding power quality. This thesis focuses on the analysis of the voltage fluctuations or flicker measurement procedure specified by the IEC 61400-21 standard to evaluate the power quality characteristics of grid-connected wind turbines.

The thesis revealed that the origin of the divergences lays on the first block of the procedure, named fictitious grid. Specifically, it is related to the two digital signal processing tasks involved: estimation of the instantaneous phase of the fundamental of the voltage, and the current differentiation. The thesis has required an extensive experimental work, involving both simulated waveforms and real records acquired in wind turbines. Additionally, a verification test protocol is suggested in order to limit the degrees of freedom of the digital implementation and narrow the divergences.

The conclusions derived from this thesis work have been translated to the IEC Maintenance Team TC88/MT21 of the IEC 61400-21 standard, and will be included in the third edition of the standard. In addition, the proposed recommendations regarding the implementation of the flicker measurement procedure could be used by developers of wind turbine power quality certification equipment, as a guide to optimize their implementations.