Sequence Domain Harmonic Modeling of Type-IV Wind Turbines

A sequence domain (SD) harmonic model of a grid-connected voltage-source converter is developed for decoupling converter generated voltage harmonics from voltage harmonics in the external grid. The modeling procedure includes a derivation of the baseband frequency response for regular-sampled pulse width modulation and an analysis of converter generated voltage harmonics due to compensated dead-time. The decoupling capabilities of the proposed the SD harmonic model are verified through a power quality (PQ) assessment of a 3 MW Type-IV wind turbine. The assessment shows that the magnitude and phase of low-order odd converter generated voltage harmonics are dependent on the converter operating point and the phase of the fundamental component of converter current, respectively. The SD harmonic model can be used to make PQ assessments of Type-IV wind turbines or incorporated into harmonic load flows for computation of PQ in wind power plants.