Combined Grid Inertia Contribution and Mechanical Active Damping Control for Variable Speed Wind Turbines

In the wind energy sector, economic interests for increasing the plant lifetime and the development of grid supporting control structures to comply with current and expected future grid codes are two main fields of interest. The virtual inertia control for an instantaneous grid frequency support excites torsional oscillations depending on the occurring ROCOF and the controller design. Hence the impact on the drive train is analyzed for varying controller parameters with experimental investigations considering a load step event in a low inertia grid. Moreover, a conventional control strategy for the active damping of torsional oscillations is implemented and tested. The analyses are focused on resulting mechanical loads but also on consequences for the grid frequency support. The results show that a reduction of torsional oscillations is recommended to reduce mechanical loads but also to prevent a grid power supply with power oscillations corresponding to drive train oscillations. Especially in low inertia grids, these power oscillations may deteriorate grid frequency behavior.