Study On The Law Of Coupling And Propagation Of Harmonics/Inter-Harmonics Injected From Large-Scale Wind Farm In Power Grid

In response to the requirements of the 13 th Five-Year Plan,the new energy power generation rapidly develop in China,and more and more large-scale wind farms connected to the power grid,which has brought challenges to the stable operation of the power system.The abrupt change of wind speed in wind farm,the fault operation of power electronic equipment and the influence of grid fault operation on wind turbine may distort the output current and voltage waveforms of wind farm.In the process of wind farm connecting to power grid,harmonics/inter-harmonics from wind farms propagate and couple at each node of the power grid after they are injected into the grid at the point of common coupling(PCC),which seriously affects the power quality of the power system,and even threatens the safe and stable operation of the power system.Therefore,studying the dynamic change and trend of harmonics/inter-harmonics output of wind farm after grid-connected is the basis to ensure the safe and stable operation of power grid.In order to study harmonic/inter-harmonic characteristics of wind farms with the mutation wind speed,this paper firstly ensures the analysis accuracy of harmonics/inter-harmonics in simulation analysis.Therefore,it is proposed to use Black-man window and four third-order Nuttall windows for convolution,and derive the three-line interpolation Fourier transform(FFT)of the second-order hybrid convolution window(HCW),which is used to analyze the amplitude and frequency parameters of harmonic/inter-harmonic signals of wind farms.And the All-phase FFT(ap FFT)is used to analyze the phase parameters of harmonic/ inter-harmonic signals of wind farms.Secondly,based on MATLAB/Simulink simulation software,the grid-connected models of direct-drive and doubly-fed wind farms are established.The random noise wind is added to the wind farms to simulate,and then the harmonic/inter-harmonic characteristics of direct-drive wind farm and doubly-fed wind farm with the mutation wind speed are obtained.In order to study the influence of the coupling and propagation of harmonics/inter-harmonics injected into power grid by wind farms,this paper also study the coupling mechanism and propagation mechanism of harmonics/interharmonics in power grid.According to the transverse and longitudinal propagation characteristics of harmonics/inter-harmonics in power grid,it’s put forward that simulate and analyse the three factors that affect the propagation and coupling of harmonics/inter-harmonics in power grid,namely,the length of wind power feeder line,the length of transmission line and the voltage level of power grid.In order to study the law of coupling and propagation of harmonics/interharmonics injected from large-scale wind farm in power grid,finally,according to large-scale wind power grid-connected topological structures in Hami region of Xinjiang,a power grid simulation model with wind power nodes is established.By changing the types of wind farms connected by wind power nodes and carrying out simulation analysis,the coupling and propagation law of harmonics/inter-harmonics of the same and different types of wind farms in power grid are obtained.