Natural characteristic analysis of wind turbine drivetrain considering flexible supporting

The mechanical system of wind turbine is much complicated and can be divided into the drivetrain and supporting portions. The drivetrain consists of wheel, main shaft, gearbox, generator, etc. and the supporting portion mainly consists of a tower and a cabin. In order to reduce the unit cost of electricity, the capacity and size of wind turbine are increased gradually in the past years. Meanwhile, with the increase of the wind turbine height, the tower actually becomes more flexible as the supporting part. And the influence of the supporting tower flexibility becomes stronger due to the varying wind loads both in magnitude and direction. Using the rigid–flexible coupling multibody dynamic theory, the coupled dynamic model of the wind turbine drive train was developed considering the flexible supporting. Then the natural characteristics of the system were computed and investigated. For the dynamic modeling, the blades, the tower and main shaft were modeled as flexible bodies, while the other components, such as the hub and the gearbox, were modeled as rigid bodies. The potential resonance frequencies of the system were discussed through the Campbell diagram and the modal energy distribution analysis. The results show that the natural frequency of swing mode shapes for the tower was 0.399 Hz and 0.405 Hz. The first natural frequency of drivetrain, which represented a torsional vibration mode, was 1.64 Hz. From the Campbell diagram and the modal energy distribution analysis, resonances would not occur within the normal operating speed range for the drivetrain. And a comparison analysis indicated that the flexible supports would increase the bearing loads along axial direction and radial direction, especially in main shaft and torque arm, but that influence was not obvious at parallel stage. However, to some extent, the flexible supports can decrease the loads fluctuation of drivetrain. Finally, the online vibration experiments were carried out in the wind field. The vibration characteristics of the wind turbine drivetrain were analyzed and the experimental results also compared well with the theoretical dynamic results.