Frequency and Sequence Couplings in Type 4 and Type 3 Wind Turbines

The multi-frequency (harmonic) interaction among converters is an increasing challenge in converter-dominated power grids. To study steady-state harmonics and transient harmonic stability, it is crucial to develop accurate multifrequency models for converters. However, the frequency and sequence couplings have not been addressed in the state-of-the-art analytical models as well as model validation tests for converters.

This paper overviews the impedance measurement test methods for converters and demonstrates the couplings in frequencydomain based on time-domain simulations using typical Type 4 and Type 3 wind turbine models. The analysis shows significant frequency and sequence couplings which are neglected in the simplified analytical models.