Behavior, Modeling and Damping of a New Type of Resonance Involving Type-III Wind Turbines

A new type of resonance has been identified involving DFIG type wind turbines and inductive grids. This is different from other resonance involving DFIG wind turbines as there is no series compensation, the frequency of resonance is close to the fundamental, and the resonance is accompanied by a second frequency that is mirrored to it with respect to the fundamental. This work explores this resonance through the use of impedance models of the wind turbine. The impedance models used in this work are improved version of previously reported models, the models used in this work consider the dc bus dynamics and the coupling that occurs across the converters due to the non ideal dc voltage. These new impedance models can also take into account the mirrored harmonic frequency currents that arise due to the nonlinear nature of the turbine. A representative case is studied using the new impedance models, and the resonance is found to be due to the interaction between the turbine and grid impedances at a single frequency. The additional current is present only due to the nonlinear nature of the turbine and its due to the coupling over frequency. Finally, an active damper was proposed to eliminate the resonance and shown through simulations to be effective.