Torsional Vibration Control Of Doubly Fed Wind Turbine Drive Chain And Fatigue Life Prediction Of High Speed Side Gear Root

Due to the fast electrical control under grid disturbance,the drive chain of flexible structure of doubly fed wind turbine（DFIG）is easy to cause continuous torsional vibration,the long-term low amplitude and low frequency torsional vibration will cause the fatigue accumulation of the key components of the drive chain of the wind turbine.When the fatigue accumulation reaches a certain degree,the fatigue failure will occur.Therefore,it is of great significance to study the torsional vibration control and the fatigue life loss of the key components of the DFIG drive chain for the safety of the unit and the stable operation of the power grid.Firstly,introduced the research present situation at home and abroad and the basic composition of the DFIG.The models of wind speed,wind wheel,doubly fed generator and gear pair are established.The mechanical characteristics and electromagnetic torque characteristics of the drive chain of DFIG has been researched.The two mass drive chain mathematical model which can accurately reflect the torsional vibration of the drive chain of doubly fed wind turbine is established.On this basis,the natural frequency and natural vibration mode of the drive chain are studied,and the torsional stress distribution characteristics of the drive chain are analyzed,which lays the foundation for the active control strategy to suppress the torsional vibration of the drive chain of DFIG.Secondly,the torsional vibration characteristics of DFIG drive chain are analyzed,and a dual channel active control strategy is proposed to suppress the torsional vibration of DFIG drive chain during normal operation of power grid.The control strategy forms a new reference value of electromagnetic torque through two channels:one is the additional damping term formed by PID control channel,which is used to reduce the torsional vibration caused by frequency difference between drive chain shafting of doubly fed wind turbine;The other channel uses the torsion angle of the drive chain as the feedback signal,and an additional torque is formed by an additional damping controller composed of a band-pass filter（BPF）and a notch filter（BRF）.That is to say,two additional torques(T_damp1 and T_damp2)are formed near the natural frequency of the drive chain of the doubly fed wind turbine through two channels to achieve the purpose of suppressing the torsional vibration of the drive chain of the DFIG.For an evaluation of the proposed approach,under constant wind speed and turbulent wind speed,taking a 1.5 MW DFIG as an example,the method proposed in this paper is simulated and analyzed in MATLAB.The results show that the control method can well restrain the torsional vibration of the drive chain of the DFIG,and will not reduce the output active power of the DFIG,but the output active power of the unit of DFIG is slightly improved.Finally,the problem of the fatigue life loss of the tooth roots of the high-speed side gears of the drive chain gearbox caused by the long-term low-amplitude and low-frequency torsional vibration of the drive chain of the DFIG is addressed.Combined with the static stress analysis,a multi-body dynamics model of the high-speed side gear pair of the drive chain gearbox was established in the COMSOL multi physics simulation software,and the torsional stress distribution characteristics in the gear pair were studied,and the stress distribution cloud diagram of the gear pair was obtained.Based on the theory of stress-life and finite element modal analysis,the fatigue life prediction of the tooth roots of the high-speed side gears of the DFIG drive chain gearbox is carried out.By comparing the fatigue life loss of the tooth roots of the high-speed side gears of the DFIG drive chain gearbox when no control strategy is used and when the dual-channel active control strategy proposed in this paper is adopted.It is found that the dual-channel active control method proposed in this paper can reduce the fatigue life loss of the tooth roots of the high-speed side gears of the drive chain gearbox of the DFIG,and improve the life of the drive chain gearbox of the DFIG,it has important engineering practical significance.