Torsional Damping Control of Gearless Full-Converter Large Wind Turbine Generators with Permanent Magnet Synchronous Machines

This study examines the torsional damping requirements for megawatt scale wind turbines having synchronous generators with full-wave ac/dc/ac inversion technology. The particular type has a low-speed permanent magnet synchronous generator with gearless drive train and a full power-frequency converter. The electrical connection via the full converter provides no torsional damping to reduce speed oscillations. With a large number of poles, this means that torsional oscillations in the mechanical drive train can be easily excited. The analysis investigates how control algorithms for the converters can help mitigate such torsional oscillations. The torsional oscillations, both during continuous operation in wind and during a voltage dip, are analysed. Improvements resulting from a controller are presented. A windfarm model is developed to analyse the possibility of interaction between individual controllers.