Prediction of Mechanical Stresses on Wind Turbine Drivetrain due to the Power Converters System

The wind turbine drivetrain is often subject to multiple early failures, which generate high maintenance costs and significant production losses. These failures may be due to the multiple stresses to which the mechanical components of the shaft are exposed. This paper shows that the power converters used for speed variation are one of the primary sources of these mechanical stresses. Furthermore, it highlights the method of reconstructing mechanical stresses of mechanical components from electrical quantities, mainly currents. The airgap torque components in a permanent magnet synchronous generator are analytically evaluated when it supplies power to the power electronic converters. The locations of the airgap torque components at different operating speeds are shown in the form of a Campbell diagram for an easy understanding of their interference with the shaft's natural frequencies. The induced torsional stresses have been evaluated analytically. The turbine shaft is a nodal interconnection of five moments of inertia linked with stiffness constants and damping factors. Numerical simulations are performed to support the accuracy of the theoretical developments. Finally, sampled simulation results are discussed.