Study Of Characteristic And Propagation Of Supraharmonics In Low Voltage Distribution Grids

With the deepening of the power-electronized power system and the rapid development of power-line communication,the distortion of 2?150 kHz in the distribution grids is increasing and the resulting power quality events and their potential risks are gradually attracting much attention in the academic community and industry.Firstly,based on the principle of Pulse Width Modulation,the mechanism and frequency distribution characteristics of supraharmonics of high-frequency PWM inverters with different modulation methods are analyzed and a method of preferred aggregation band to reflect typical characteristics of supraharmonics is proposed.Then the effects of switching frequency,system voltage and DC side voltage,output power,system frequency and background power quality(harmonics)on the supraharmonics are studied by simulation.In order to study the propagation of supraharmonics in low voltage distribution,a general model of distribution which was suitable for describing high-frequency characteristics is built.Then the typical low voltage distribution system is established in Matlab/Simulink,and the influence of different power and line length on supraharmonics have been studied.At the same time,the influence of multi-inverters with rectifier load and the frequency conversion equipment on supraharmonics were emphatically analyzed.Based on the mechanism analysis,the supraharmonics emission levels of different equipments(i.e.the roof photovoltaic system,the double-fed induction generator and the permanent magnetic synchronous generator)in actual power system are measured and analyzed.The content and characteristics of supraharmonics of actual power system are grasped and the typical distribution characteristics of different equipments supraharmonics emission are obtained,which verify the correctness of the mechanism analysis and the superiority of the method of preferred aggregation band.The research results in this paper can provide theoretical basis for the detection and identification of supraharmonics,the characteristics of propagation.It provides a reference for the relevant standards and treatment of supraharmonics.