Reduction of gearbox loads of a DFIG wind turbine during grid faults with optimized converter configurations

Abstract

Grid faults in wind turbines (WT) with doubly fed induction generator (DFIG) result in dynamic generator torque excitations, which can lead to dynamic load changes within the gearbox. Dynamic load changes in combination with changing rotational speeds can increase the risk of damage in the gearbox. WT gearbox damage occurs mainly on the high speed shaft (HSS) components. The torque excitations have the highest influence on the HSS since it is coupled to the generator. Therefore, an investigation of the correlation between grid faults and gearbox damage is necessary. The torque excitation in DFIG WTs due to grid faults is dependent on the converter and its fault ride through capabilities. The load analysis in this paper is done for a state of the art converter configuration and for one that is optimized in order to stabilize the performance during grid faults. It is shown via simulation with a WT drivetrain model that dynamic load changes of the HSS gear wheel are prevented for symmetrical grid faults with the optimized configuration. The analysis of a HSS bearing shows that the smearing damage risk can be significantly reduced (minus up to 56 percent) by using the optimized configuration. Therefore, the possibility to decrease the gearbox damage risk during grid faults via an optimization of the converter configuration is shown in this paper.