With the gradual increase in the proportion of wind power generation in new energy generation

and the increase in the capacity of single wind turbine unit

the problem of subsynchronous oscillation caused by wind power output through series compensation lines has also become prominent. The torsional vibration characteristics of the shafting is analyzed in this paper to provide basis for solving the subsynchronous oscillation problem. On the basis of the torsional vibration model and motion differential equation of the shaft

planetary gear system and parallel gears

the transitive relation of state variables among the mass units of wind turbine transmission system is deduced. Moreover

the Riccati transfer matrix method is adopted to calculate the natural torsional vibration characteristics. Finally

a 1.5 MW doubly-fed wind turbine is taken as an example for calculating the natural frequencies of torsional vibration by the method proposed

and the result is compared with that calculated by the conventional method. The influence of gear meshing stiffness on major natural frequency is also analyzed. It shows that

the torsional vibration characteristics calculated by the model considering gear meshing stiffness are more accurate than that by the simple lumped mass model. This provides theoretical basis for revealing the mechanism of subsynchronous oscillation.