The Research On Detection Method Of Harmonics In Microgrid Based On Blind Source Separation Theory

The emergence of microgrids solves the problem of distributed power sources incorporating into traditional grids.However,because of the different nature of micropower sources,the control methods used are also different,which results in many power quality issues in the microgrids.In addition,the massive use of power electronic equipment and the large number of non-linear loads will generate a large amount of harmonics,causing pollution to the electrical energy of the grid and affecting the quality of electrical energy.Therefore,analyzing the power quality problems in microgrids and the causes of harmonic problems,and study harmonic detection techniques are of great significance to analyze power quality problems in the microgrid and develop power quality control devices and harmonic suppression devices.Firstly,the thesis studied the basic structure of the microgrid and the physical model and working principle of each micro power supply,established simulation models for photovoltaic grid-connected systems and fuel cell grid-connected systems,and then analyzed the causes of power quality problems in the microgrid and their impact.Finally,the in-depth study of the detection of harmonics has been focused.After comparing the advantages and disadvantages of each harmonic detection method,the harmonic detection method based on the blind source separation theory was introduced to detect the harmonics whose transmission channel characteristics are unknown.The thesis includes the following aspects:The basic structure of the microgrid,the physical models of photovoltaic cells and fuel cells,and their respective grid connection methods were systematically introduced.According to the physical model and control method of photovoltaic cells and fuel cells,the simulation model of photovoltaic grid-connected power generation system and fuel cell are built,which lays a theoretical foundation for the subsequent analysis of power quality problems in the microgrid.For the uncertainty problems of the harmonic transmission channel characteristics and harmonic times in the microgrid,blind source separation method is used to realize harmonic detection,find out the correlation between harmonic detection and blind source separation theory and establish a blind source separation model which is suitable for analyzing harmonics.When the number of harmonic signals is much larger than the number of observed signals,the separation of the fundamental and harmonic components cannot be achieved by blind source separation.In order to achieve harmonic detection,two reference signals are constructed by using prior knowledge of the fundamental frequency.For the problem of the uncertainty of waveform amplitude and order detected by the blind source separation algorithm based on the fundamental frequency,the matrix transformation is used to convert the model,and then the amplitude and phase of the harmonic components are obtained.Comparing and analyzing the simulation results of ip-iq,FFT and this article.The results show that the improved harmonic detection method based on the fundamental wave frequency blind source separation harmonic detection method has better harmonic detection accuracy.