Research on Transmission Characteristics and Torsional Vibration Control of Hybrid Transmission Wind Turbines

Abstract As wind turbines become larger and move into deeper sea, their operating environment is getting more and more harsh, which puts higher stability requirements of the transmission chain. The mechanical-hydraulic hybrid transmission (MHHT) combines mechanical and hydraulic systems to improve transmission stability. However, the related research is still in the stage of mechanism verification. In this paper, a 19-degree-of-freedom pure torsion model has been established to study the internal characteristics of the MHHT chain. The model contains parallel gearing, planetary gearing and closed hydraulic transmission simultaneously. The correctness of the modelling method was verified by a software model. The frequency characteristics of the hybrid transmission chain were summarized. The first two modes at different motor displacements were classified as "mechanical mode" and "hydraulic mode" based on the mode shapes. A hydraulic damping model was built based on the leakage of the hydraulic system. The influence of the hydraulic system on the MHHT damping characteristics has been discussed in detail with and without considering the mechanical damping. Finally, a damping compensation method by adjusting the hydraulic motor displacement was proposed. The control algorithm was derived by a simplified model and verified by the 19-degree-of-freedom pure torsion model. The simulation results under different working conditions show that this method can effectively reduce the first-mode torsional vibration and improve the life of the drivetrain.