On the Risk for Subsynchronous Control Interaction in Type 4 Based Wind Farms

The aim of this paper is to investigate the risk for subsynchronous control interaction (SSCI) in Type 4 based wind farms connected to series-compensated transmission lines. For this purpose, the frequency-dependent input admittance of the turbine is derived and the power-dissipation properties of the turbine are used to identify those control parameters and operating conditions that mainly impact the behavior of the wind turbine in the subsynchronous frequency range. It is shown that the Type 4 wind turbine presents a non-dissipative behavior in the subsynchronous frequency range, which is mainly dependent on the speed of response of the synchronization loop, the reactive power controller, and the active-power output. For a radial connection, a high series-compensation level also negatively impacts the risk for SSCI. The generalized Nyquist criterion is used to assess the stability of the system and the theoretical findings are verified using detailed time-domain simulations.