Sequence Impedance Modeling and Analysis of Type-III Wind Turbines

Sequence impedance models are presented for type-III wind turbines that use doubly fed induction generators and back-to-back voltage source converters. The models, presented in analytical form for both positive- and negative-sequence impedances, include the effects of the induction machine, both the stator- and rotor-side converters as well as their controls, and the phase-locked loop used for synchronizing converter control with the grid voltage. The models are valid from subsynchronous frequency up to one-third of the switching frequency of the converter, making them useful for the analysis and mitigation of both subsynchronous and supersynchronous resonances and control interactions of type-III turbines with different types of grid.