The Study Of Two Mass Model Drive Train Torsional Oscillation Of Wind Turbine Generator System

Due to the conventional energy decreasing and the demand for energy increasing,wind power as a new development clean energy gradually gets more attention.Along with the rapid development pace of renewable energy,the application scale of wind power technology is also constantly expanding,wind power installed capacity is increasing every year,the problem of wind power generator during the process of parallel operation is increasingly apparent.Because the connecting part of wind turbine-the shaft stiffness is limited,when wind turbine is in the state of parallel operation,complex environment such as wind speed change,electrical disturbance and so on will arouse torsional oscillation,and lead to stability problems of wind system.So the further study of wind turbine stability problems has very important practical significance.Compare with the mathematical model of single mass,two mass and three mass,the two mass models are more suitable for the stability analysis of wind turbine.In order to meet the evaluation needs of wind turbine generator system resonance and the drive shaft torsional oscillation under voltage drop,the mechanical transient characteristics of transmission system under voltage drop are proposed.Based on the model of the transmission system,the state equation of the two mass model of the transmission system is established.the analytical formula of wind turbine speed and generator speed and the drive shaft torque are obtained through the state transition matrix of the transmission system.Then,on the basis of the physical expression which describes the natural frequency and the mechanical decay time constant,the influence of transmission parameters on natural frequency and decay time constant is analyzed,and the characteristic of the drive shaft torque under voltage drop is also analyzed.In order to study the transient characteristics of DFIG voltage drop,the dynamic mathematical model of DFIG is built based on the operating characteristics of wind turbine and DFIG Based on the superposition principle,the transient process of voltage drop is equivalent to the superposition of stable operation and reverse voltage operation.The transient characteristics of voltage drop are analyzed and the influence of voltage drop Transient characteristics of the main factors.On the basis of this,the state space equation is obtained.And according to the superposition principle,the transient process of voltage drop is equivalent to the superposition of stable operation and reverse voltage operation.The transient characteristics of voltage drop are analyzed and main factors affecting voltage drop transient characteristics are revealed.In order to comprehensively analyze the effect of drive shaft model and parameters on transient operation performance of DFIG wind turbine generator,Based on the equivalent mass method and the parameters of a practical transmission system,the two mass model considering the flexibility of the shaft between wind turbine and generator is built by MATLAB/Simulink(2013).According to the mathematical model of DFIG,the simulation model is established,combine with the model of wind turbine,DFIG and transmission system,the simulation model of two mass wind turbine generator is established.The transient operating characteristics are analyzed and the correctness and effectiveness of the analytical analysis are verified by the simulation results.