Fatigue Reliability Analysis On Shafts Torsional Vibration Of Doubly-Fed Wind Generator

Stability problem in the shafts of doubly-fed wind generator caused by electrical fault is critical, and the fatigue damage of the gears of wind turbine shafts caused by shafts torsional vibration start to receive more attention. Research on the reliability of the wind turbine shafts torsional vibration is still in its infancy at home and abroad nowadays. This paper adopts fatigue damage as the reliability index of the wind turbine shafts torsional vibration, mainly investigates the fatigue damage degree of gear during the shafts torsional vibration of doubly-fed wind generator caused by different types of electrical fault disturbance. This paper has got the support of large batch of new energy grid contact technology development.First, the doubly-fed wind generator transient model is established. According to the actual shafts mechanical structure of doubly-fed wind generator, the three-mass shaft model is established. On the basis, eigenvalue analysis method is put forward to analysis the torsional vibration modes of doubly-fed wind generator shafts. Thus, the natural frequency and vibration mode of the wind turbine shafts torsional vibration can be obtained.Secondly, unbalance excitation sources that cause doubly-fed wind generator shafting torsional vibration are put forward from the two aspects of wind disturbance and electrical fault disturbance. The mechanism of shafting torsional vibration of doubly-fed wind generator is studied caused by different types of electrical fault disturbance. The electromagnetic torque and mechanical torque of wind turbine when different types of electrical fault occur in power system is obtained by PSCAD simulation.Third, this paper put forward the fatigue damage mechanism of gears of doubly-fed wind generator during the shafts torsional vibration. And a polycrystal structure model of metal materials is put forward to analysis the fatigue failure process of DFIG gear model during the shafts torsional vibration. To analyze the fatigue characteristics of wind turbine gear material, this paper put forward the approximate fitting method via planetary gear material parameters to obtain the S-N curve of planetary gear model. The equivalent load spectrum is obtained via the rain flow counting method considering the memory characteristics and order effect. The multiaxial fatigue damage method and accumulated fatigue damage theory are introduced to analyze the fatigue damage of planetary gear model.At last, the finite element method is put forward to calculate the fatigue damage of planetary gear model during the shafts torsional vibration of doubly-fed wind generator caused by different types of electrical fault disturbance. The finite element model of planetary gear is set up by Solidworks software. And then it is meshed by ANSYS software and finally the equivalent von-Mises stress is achieved. The fatigue damage of transmission gear caused by different types of electrical fault disturbance could be accessed through Ncode software based on the S-N theory and Miner theory, and then it carries on the analysis of reliability.To sum up, the paper provided is a reliability analysis of the fatigue damage of doubly-fed wind generator shafts caused by different types of electrical fault disturbance. The results are helpful to predict the fatigue life of wind turbine gear, to better maintain wind turbine shafts in time and to improve the safety and reliability of wind power system.