Harmonic Analysis Of Distributed Photovoltaic Grid-Connected Power Generation System

The excessive use of traditional energy sources has led to a large degree of environmental pollution,and as people continue to explore,new energy sources have been discovered that can replace traditional energy sources.The traditional maximum power tracking algorithm cannot better track the maximum power point under shadow shading conditions.After the distributed PV grid-connected power generation meets the daily supply,the remaining power is integrated into the distribution grid load for power supply.Although distributed PV generation will reduce environmental pollution and generation and consumption can occur simultaneously,the presence of inverters generates a large number of harmonics.Harmonics can increase system losses,reduce equipment efficiency,interfere with communication networks causing network failure,and lead to defects such as spectrum leakage when using FFT for harmonic analysis,so it is important to analyze the harmonics of distributed photovoltaic power generation systems.The main research contents of this paper are as follows:(1)Analyze the characteristics and main components of distributed PV grid-connected power generation system,the working principle and equivalent circuit diagram of PV cell,the working principle of maximum power tracking and the basic theory of harmonic analysis,and get the problems such as spectral leakage when using FFT for harmonic analysis,so as to build the simulation model of distributed PV grid-connected power generation system and harmonic analysis.(2)Simulink is used to build a simulation model of the distributed PV power generation system when the fuzzy control algorithm is used to control the system alone,and two hybrid algorithm control systems combining the perturbation observation method and the conductance increment method with the fuzzy control algorithm are proposed for algorithm verification.The results show that the IC-FLC hybrid algorithm can achieve better tracking and higher power generation efficiency of distributed PV system,which proves the rationality of the proposed algorithm and lays the foundation for the subsequent harmonic analysis of harmonic parameter signals by using the simulation model of IC-FLC hybrid algorithm.(3)The simulation model of distributed PV grid-connected power generation system controlled by IC-FLC hybrid algorithm is used for harmonic analysis at different output powers of PV inverters,and the simulation results show that the total harmonic distortion rate is minimized at rated power.An improved FFT algorithm based on the dual spectral line interpolation of Kaiser and Nuttall hybrid convolutional windows is proposed,and the spectral characteristics of the hybrid convolutional windows are compared with those of other window functions to know that the hybrid convolutional windows algorithm have better partials and can better suppress the spectral leakage phenomenon.The harmonic analysis process is determined,and then the values of harmonic parameters are calculated by least-squares inverse fitting,and the algorithm has higher accuracy in detecting harmonics,interharmonics and weak harmonic components,and the harmonic parameters can be accurately obtained even under the influence of change of fundamental frequency and white noise,especially in the case of low noise.