Research On The Mechanism Of Subsynchronous Harmonics And Inter Harmonic Induced By Doubly Fed Wind Turbine

With the increasingly serious environmental pollution and energy exhaustion,wind power has greatly improved its economy and the rapid development of the equipment industry because of its clean and renewable characteristics and technological progress.It has become an inevitable choice to solve the fossil energy problem in all countries of the world.The harmonics interharmonics are affected by the large-scale development of the wind power,which affects the stability of the power grid.In this paper,the harmonic mechanism caused by the doubly fed fan is studied in this paper.The main contents are as follows:(1)Considering the influence of the subsynchronous harmonic harmonic problem on the safe and stable operation of the power grid,a method of combining the synchronous phasor measurement device(PMU)with the synchronous extrusion wavelet transform(SWT)is proposed to analyze the sub synchronous harmonic harmonic problem.Firstly,the advantages and disadvantages of three harmonic extraction methods of Fourier transform,Hilbert yellow transform and synchronous extrusion wavelet transform are compared and analyzed.Secondly,the SWT algorithm is used to make continuous wavelet transform for the electric power signals with inter harmonics,to divide the frequency interval,and to extract the harmonics between the harmonic and the harmonics in the time frequency surface.And base wave component signals;then the transient voltage,connection line current and online active distribution recorded data are analyzed with the sub synchronous oscillation in the Hami wind collection area.Finally,some measures are provided based on the sub synchronous oscillation in this case.(2)First,a double fed wind turbine model is set up to derive the steady state voltage equation and magnetic chain equation of the doubly fed wind generator,and then the expression of the interharmonics induced by the rotor winding current on the stator side is constructed by considering the disturbance voltage component of the rotor side converter on the inverter side of the wind turbine.Finally,the theoretical calculation and the PSCAD are calculated.The simulation results are made to compare and analyze the harmonics of stator current caused by different wind speed and different frequency of rotor current in double fed wind turbine,and verify the correctness of the expression of the interharmonics induced by the rotor winding current on the stator side.(3)In view of the subsynchronous harmonic problem caused by the dynamic characteristics of the doubly fed wind turbine delivery system,the state space model of the double fed wind turbine grid connected system is established,and the related parameters of the components of the system are given,and then the oscillation of the single and multi machine grid connected systems is analyzed by the eigenvalue method.The influence of mode and oscillation frequency and participation factors on them is studied,and the influence of system strength and wind speed on the interaction between two typhoons is studied.