On The Harmonics Detection And Suppression Of The Grid-connected Photovoltaic System

With the gradual depletion of traditional energy,the renewable energy is got much attention,among which solar energy has been developed and applied for its inexhaustibility.In order to effectively eliminate the influence of harmonics on the grid connected photovoltaic power generation system,from the perspective of harmonic characteristics,harmonic detection and harmonic suppression in the system,harmonics are taken as the research object.This thesis is mainly focus on the harmonic detection and suppression in the system.According to the characteristics of photovoltaic cells,the simulation model of photovoltaic cells is established,where output characteristics of the voltage,current and power of the photovoltaic cells is simulated.The characteristics of electric energy in the system is also discussed.A harmonic detection method based on the wavelet transform and FFT(Fast Fourier Transformation)is applied in order to improve computing speed of harmonic detection by analyzing the traditional theory of harmonic detection algorithms.This method combines the advantages of both wavelet transform and FFT algorithms.The harmonic signal is decomposed into different frequency bands by the wavelet transform,and the reconstructed signal is used as the input of the harmonic detection algorithm,among which steady-state component is analyzed by the FFT algorithm and the transient component is analyzed by wavelet transform,the windowed function analysis of the reconstructed signal and the Fourier series expansion reduce the amount of the initial value brought in,so the calculation speed of the algorithm is improved.Then,with respect to harmonic suppression,the harmonic detection,suppression and reactive power compensation can be realized in a photovoltaic power generation system with active filter function that the tracking current is controlled with voltage and current as feedback signals,constructed according to the similarity analysis of the structure,function and control of the photovoltaic power generation system and the active filter.And based on the traditional PI algorithm,the anti saturation control algorithm is used to limit the PI parameters to solve the problem of too large instantaneous output deviation caused by frequency or amplitude fluctuation.The model simulation analysis of photovoltaic power grid signal under the influence of different factors is carried out.The algorithm can still detect the number,amplitude and phase of harmonic when there is interharmonics,frequency fluctuations and noise in the signal.According to the working state of photovoltaic system in different conditions,a new type of current tracking photovoltaic power grid system model is proposed to check the feasibility and correctness of the method.